A complicated question about LiFePO4 batteries, - and switching.

[[email protected]]

Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.

Thanks ahead, Mark

[[email protected]]

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark

There shouldn't be an issue, as long as both batteries have diodes to ensure that current can only come out of the batteries, not into them. The BMS will still serve as a second line of defense to limit the current (in either direction) if needed.

The only downside of the diodes is that you lose a bit of the battery voltage, since the diode has some voltage drop between its terminals. You can use Schottkey type diodes to minimize that voltage drop, about 0.3V as compared with 0.7V with a standard silicon diode. This is less of a problem with LiFe batteries, since their voltage is somewhat higher than that of SLAs, especially after they're partially discharged.

An arrangement that can be used to eliminate the voltage drop, especially if using SLAs, is to have both the two diodes and also an SPDT or on/off/on switch, from the junction of the two diodes to the other end of either diode. (Or you can think of it as the normal switch arrangement, with the diodes added in parallel with the two arms of the switch.) That way you get the full voltage of whichever battery is chosen by the switch at the time, but if you forget to switch over, or if the switch fails, you still get the other battery to kick in if the first one gets weak. E.g., with normal silicon diodes, if the first battery is down to 12.0V and the second one is sitting at 12.7V then the diode in series with the second one will start conducting, keeping the voltage supplied to your gizmos from falling lower than 12.0V at first, decreasing slowly from there as both batteries work effectively in parallel albeit at different voltage levels. If you then remember and flip the switch you'd get the full voltage of the second battery. Moreover, with this arrangement, if the switch momentarily disconnects both batteries while you flip it, there is no supply gap to your gizmos since the current can keep flowing through the diode. More precisely, the momentary dip in voltage is limited to the small voltage drop in the diode.

[kinsell]

On 06/18/2018 07:22 PM, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark
>

Do you not have the space required to install one big battery, instead
of multiple small ones? Never understood the fascination with switching
batteries, it just a distraction during flying. I think there's some
airline captain wannabees who just want more switches to flip.

-Dave

[Emir Sherbi]

Redundancy, that's the answer.

[Martin Gregorie[_6_]]

On Mon, 18 Jun 2018 21:24:27 -0600, kinsell wrote:

> Do you not have the space required to install one big battery, instead
> of multiple small ones? Never understood the fascination with switching
> batteries, it just a distraction during flying. I think there's some
> airline captain wannabees who just want more switches to flip.
>
He's talking about a Libelle, which has a battery compartment that was
apparently designed to hold one larger, flattish battery which now seems
to be an obsolete form factor. However, it will hold a pair or 7.2 AH 12v
SLAs if they are stood on one end and the top of the battery compartment
is raised 50mm by extending the hold-down bolts.

FWIW, My Std Libelle is set up that way, though with the hold-down bolts
running through brass tubes to keep them aligned with the screw holes
they fit into. I mount my EW Microrecorder on the battery lid with two
diodes so it always draws from the highest voltage battery and run power
to the panel separately from each battery via an XLR socket on the lid,
which also holds the fuses: one battery powers the radio and T&B while
the other runs both varios (SDI C4 and Borgelt B.40 with 9v backup
battery), PNA (running LK8000) and FLARM. This more or less balances the
load on both batteries - their recharge times after a day's flying are
fairly similar.

--
Martin | martin at
Gregorie | gregorie dot org

[[email protected]]

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark

I use good quality switches(DPST with both contacts wired in parallel fot added reliability). Each is wired from the battery to my main bus. To change over I switch the new one on and other off a second or two later. I have had no issues with doing this. The LiFePo4 batteries are pretty much out of power at 12.3 volts or so. Fully charged they show about 13.7 or so. The resulting voltage differential doesn't generate enough current to cause a problem in my experience. I do not suggest leaving both on in parallel.
FWIW
UH

[OHM Ω http://aviation.derosaweb.net]

A beginning comment: With modern avionics drawing less power than their predecessors and LiFePo4 with greatly increased energy capacity, maybe only one battery is needed these days for most glider pilots. Just sayin'.

I agree that our batteries should not be run in parallel (without diodes). If one is of a significantly different voltage than the other, then the higher one will charge the lower one possible at a high rate (current) that you don't want. This can potentially blow one or both battery fuses (you do have a fuse on each battery, right???), or might cause one battery to fail in a bad way, either of which can leave you in a poor situation especially during flight.

I have a presentation on my thoughts on the subject of two battery systems at http://aviation.derosaweb.net/presentations#wiring.

Here is my setup on my current glider.

- Two batteries (lithium)
- Each battery has a fuse.
- Two separate power buses with one battery powering each.
- One bus is for "communications" (radio, transponder, FLARM) and the other bus is for "navigation" (GPS, Vario, etc.).
- Each bus has a separate breaker (5A) which is also a master switch (a true breaker/switch by Tyco http://www.aircraftspruce.com/catalog/elpages/pbcircuitbrkr2.php?clickkey=5950).
- But I do have Schottkey diodes in each bus. Why, you might ask, do I have diodes if I have two separate electrical buses? Because I can bridge the two buses with another switch for that "just in case situation" (belts and braces engineering over design). I have never have to use this switch but then again you never know ...

Thanks, John OHM Ω

[[email protected]]

We just turn them on and leave them on...or tell the first officer to do it.

[JS[_5_]]

On Monday, June 18, 2018 at 8:28:44 PM UTC-7, Emir Sherbi wrote:
> Redundancy, that's the answer.

As with SLAs, prefer switches for each battery. The locking toggle switches made by Alcoswitch are great, for example their SPDT part # MTL106D.
Switch battery 2 on before switching battery 1 off. There is no need for capacitors or diodes.
Believe two standard 10Ah LiFePo4 will fit in the Libelle's battery compartment.
Jim

[Andy Blackburn[_3_]]

John,

Have you tried any of these?

https://www.ebay.com/itm/15A-Solar-Panel-Anti-Reverse-Irrigation-Ideal-Diode-Battery-Charging-Board-US/372313986807?hash=item56afa496f7:g:aKsAAOSw-0RbApaz

They claim almost zero voltage drop compared to Schottkey diodes. Of course with the rapid voltage fallow of LiFePO4 batteries, it may only make a tiny difference in effective capacity.

Andy Blackburn
9B


On Tuesday, June 19, 2018 at 6:23:07 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:

> - But I do have Schottkey diodes in each bus. Why, you might ask, do I have diodes if I have two separate electrical buses? Because I can bridge the two buses with another switch for that "just in case situation" (belts and braces engineering over design). I have never have to use this switch but then again you never know ...
>
> Thanks, John OHM Ω

[jfitch]

On Tuesday, June 19, 2018 at 9:30:32 AM UTC-7, Andy Blackburn wrote:
> John,
>
> Have you tried any of these?
>
> https://www.ebay.com/itm/15A-Solar-Panel-Anti-Reverse-Irrigation-Ideal-Diode-Battery-Charging-Board-US/372313986807?hash=item56afa496f7:g:aKsAAOSw-0RbApaz
>
> They claim almost zero voltage drop compared to Schottkey diodes. Of course with the rapid voltage fallow of LiFePO4 batteries, it may only make a tiny difference in effective capacity.
>
> Andy Blackburn
> 9B
>
>
> On Tuesday, June 19, 2018 at 6:23:07 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>
> > - But I do have Schottkey diodes in each bus. Why, you might ask, do I have diodes if I have two separate electrical buses? Because I can bridge the two buses with another switch for that "just in case situation" (belts and braces engineering over design). I have never have to use this switch but then again you never know ...
> >
> > Thanks, John OHM Ω

Being pedantic for a moment, the diode drop is proportional to the endurance reduction, and has little to do with the battery voltage characteristic. If you drop 0.7V on a 13V battery, you're going to be drawing 5% more power and have 5% less endurance. 0.3 across a Schottky is starting to look pretty small and across those virtual diodes not much at all.

The explanation is that almost all modern electronics are using switching power supplies to produce the required amount of power at 5 or 3.3V. Less input voltage to the power supply just means it draws more current to get the same output. On that basis alone a 13.5V LFP will last 10% longer than a 12.5V SLA, at the same AH.

If it weren't windy, I'd be flying instead of pedantic :).

[[email protected]]

>If you drop 0.7V on a 13V battery, you're going to be drawing 5% more power and have 5% less endurance.

I have slightly different numbers. I use low drop (0.4 v) diodes and per battery switches with K2's. Operating rules are when bus gets below 11 volts, it's time to turn on another battery. (about 4-5 hours with glide computers and transponder, and not too talky on the vhf.)

Most of the electronics have switching power supplies, so as the volts go down they adapt and the amps go up. The K2's have a fairly flat discharge curve up until they fall off the cliff. All the diodes do is slightly adjust where on the cliff edge we stop and go to another battery.

So at the worst case switchover point the batteries are at 11.4 and I'm loosing 3.5% in the diodes. Costing perhaps a few minutes out of 4 hours. Seems simple and cheap to prevent bus glitches and prevent circulating currents between the batteries.

The old plan was pairs of SLA's as friends. They got bought each year at the same time, charged in parallel, and discharged in parallel. This also worked, but the K2's seem to last for years and provide more run time.

[jfitch]

On Tuesday, June 19, 2018 at 5:47:17 PM UTC-7, wrote:
> >If you drop 0.7V on a 13V battery, you're going to be drawing 5% more power and have 5% less endurance.
>
> I have slightly different numbers. I use low drop (0.4 v) diodes and per battery switches with K2's. Operating rules are when bus gets below 11 volts, it's time to turn on another battery. (about 4-5 hours with glide computers and transponder, and not too talky on the vhf.)
>
> Most of the electronics have switching power supplies, so as the volts go down they adapt and the amps go up. The K2's have a fairly flat discharge curve up until they fall off the cliff. All the diodes do is slightly adjust where on the cliff edge we stop and go to another battery.
>
> So at the worst case switchover point the batteries are at 11.4 and I'm loosing 3.5% in the diodes. Costing perhaps a few minutes out of 4 hours. Seems simple and cheap to prevent bus glitches and prevent circulating currents between the batteries.
>
> The old plan was pairs of SLA's as friends. They got bought each year at the same time, charged in parallel, and discharged in parallel. This also worked, but the K2's seem to last for years and provide more run time.

But you are also losing and additional 3% in the higher current draw, 6.5% total, 15 minutes out of the 4 hours. Those of you running two batteries should consider simply running them in parallel. Just make sure you charge them in parallel too. This is actually better for battery life (particularly true for SLAs) because the average depth of discharge is less. Might want to check with the battery manufacturer and see of the BMS will like that - some do, some don't.

[[email protected]]

https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/VS-12TQ045PBF/12TQ045PBF-ND/812018

Even with a 0.4V drop forward, you're still ahead of SLA on voltage to the electronics and no switching required in flight.

[[email protected]]

On Tuesday, June 19, 2018 at 5:55:05 PM UTC-7, jfitch wrote:
> On Tuesday, June 19, 2018 at 5:47:17 PM UTC-7, wrote:
> > >If you drop 0.7V on a 13V battery, you're going to be drawing 5% more power and have 5% less endurance.
> >
> > I have slightly different numbers. I use low drop (0.4 v) diodes and per battery switches with K2's. Operating rules are when bus gets below 11 volts, it's time to turn on another battery. (about 4-5 hours with glide computers and transponder, and not too talky on the vhf.)
> >
> > Most of the electronics have switching power supplies, so as the volts go down they adapt and the amps go up. The K2's have a fairly flat discharge curve up until they fall off the cliff. All the diodes do is slightly adjust where on the cliff edge we stop and go to another battery.
> >
> > So at the worst case switchover point the batteries are at 11.4 and I'm loosing 3.5% in the diodes. Costing perhaps a few minutes out of 4 hours. Seems simple and cheap to prevent bus glitches and prevent circulating currents between the batteries.
> >
> > The old plan was pairs of SLA's as friends. They got bought each year at the same time, charged in parallel, and discharged in parallel. This also worked, but the K2's seem to last for years and provide more run time.
>
> But you are also losing and additional 3% in the higher current draw, 6.5% total, 15 minutes out of the 4 hours. Those of you running two batteries should consider simply running them in parallel. Just make sure you charge them in parallel too. This is actually better for battery life (particularly true for SLAs) because the average depth of discharge is less. Might want to check with the battery manufacturer and see of the BMS will like that - some do, some don't.

I've used two K2 LifePo and one K2 charger. They are used and charged in parallel as per K2 advice. No problems in several years of use.

[Shaun McLaughlin[_2_]]

I have re-wired 2 glider panels in the last year or so and used John's
presentation as the starting point.

Fuse on each battery -> a battery master switch for each battery (ON/OFF)
-> IDEAL DIODES -> +12V power bus -> TYCO breaker for each device -> DEVICE
-> GND -> DIODE -> BATTERIES

I can recommend the Ideal Diodes and Tyco breakers (although they are not
cheap). I liked the idea of reducing the number of connections (separate
fuse and switch) by having a combined fuse/switch. Since first installing
the Ideal Diodes I know they have been used on a number of other gliders at
my club and everyone seems happy so far.

http://re-voltage.eu/

I installed the Diodes behind the panel rather than on each battery as I
didn't want to damage them while handling the batteries. However they can
be used to connect both batteries to the same charger safely.

This setup means I only need to switch a battery off if there is an issue.
It allows me to combine battery types (SLA/LiFePO4) if the need arises.

I went down this path of having both batteries always on and sharing the
load after having issues switching batteries in flight. If I wasn't quick
enough I would find my FLARM rebooting, then having to wait to download the
last 'trace' onto the SD card. I found this quite frustrating while running
ridges in the Alps! My stop gap fix to this was to add a capacitor and a
rotary make before break switch to select the batteries, but this was still
less than ideal and lacked redundancy.

Shaun

At 13:23 19 June 2018, T0hNIOKEpiBodHRwOi8vYXZpYXRpb24uZGVyb3Nhd2ViLm5ldA ==
wrote:
>A beginning comment: With modern avionics drawing less power than their
>pre=
>decessors and LiFePo4 with greatly increased energy capacity, maybe only
>on=
>e battery is needed these days for most glider pilots. Just sayin'.=20
>
>I agree that our batteries should not be run in parallel (without
diodes).
>=
> If one is of a significantly different voltage than the other, then the
>hi=
>gher one will charge the lower one possible at a high rate (current) that
>y=
>ou don't want. This can potentially blow one or both battery fuses (you
>do=
> have a fuse on each battery, right???), or might cause one battery to
>fail=
> in a bad way, either of which can leave you in a poor situation
>especially=
> during flight.
>
>I have a presentation on my thoughts on the subject of two battery
systems
>=
>at http://aviation.derosaweb.net/presentations#wiring. =20
>
>Here is my setup on my current glider.
>
>- Two batteries (lithium)
>- Each battery has a fuse.
>- Two separate power buses with one battery powering each.
>- One bus is for "communications" (radio, transponder, FLARM) and the
>other=
> bus is for "navigation" (GPS, Vario, etc.). =20
>- Each bus has a separate breaker (5A) which is also a master switch (a
>tru=
>e breaker/switch by Tyco
>http://www.aircraftspruce.com/catalog/elpages/pbci=
>rcuitbrkr2.php?clickkey=3D5950).=20
>- But I do have Schottkey diodes in each bus. Why, you might ask, do I
>hav=
>e diodes if I have two separate electrical buses? Because I can bridge
>the=
> two buses with another switch for that "just in case situation" (belts
>and=
> braces engineering over design). I have never have to use this switch
but
>=
>then again you never know ...
>
>Thanks, John OHM =E2=84=A6
>

[OHM Ω http://aviation.derosaweb.net]

Andy,

I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.

That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.

One other comment: If you use diodes* (of any type) you can run two batteries in parallel safely. The danger was always been that without diodes, and with two batteries at different voltage output levels, that one battery could cross-charge the other. This could potentially happen without any current limit (!) until they equalize voltages. On a single bus with two batteries and diodes, the battery with the greatest voltage level would power the bus by itself until the separate battery's voltages equalized.

- John OHM Ω

* Teaching Moment - A diode only allows current to flow in one direction. In our case current will be limited to flowing from the battery to our avionics. As current flows through a diode there is a small voltage drop across the input to the output. We want to avoid, or limit, this voltage drop in our glider based power systems as we have no generating power source as found in airplanes.

[John Godfrey (QT)[_2_]]

On Wednesday, June 20, 2018 at 9:27:33 AM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
> Andy,
>
> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount..
>
> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>
> One other comment: If you use diodes* (of any type) you can run two batteries in parallel safely. The danger was always been that without diodes, and with two batteries at different voltage output levels, that one battery could cross-charge the other. This could potentially happen without any current limit (!) until they equalize voltages. On a single bus with two batteries and diodes, the battery with the greatest voltage level would power the bus by itself until the separate battery's voltages equalized.
>
> - John OHM Ω
>
> * Teaching Moment - A diode only allows current to flow in one direction. In our case current will be limited to flowing from the battery to our avionics. As current flows through a diode there is a small voltage drop across the input to the output. We want to avoid, or limit, this voltage drop in our glider based power systems as we have no generating power source as found in airplanes.

I like the ideal diodes, dislike the 0.3v drop across the Tyco breakers, run my batteries to one bus through low loss Schottky diodes.

I also believe that the number of angels on the head of the pin should be represented in Roman, not Arabic numbers in base 8.

[OHM Ω http://aviation.derosaweb.net]

QT,

All breakers suffer a voltage drop of some amount (see more below). Therefore some pilots like fuses as they have no voltage drop at all. I went away from fuses as they don't give me a positive indication of a trip, are difficult to fix in (soaring) flight, and are fragile.

Breaker voltage drop - As you probably know current is passed inside of breakers through a tiny "heater" (for want of a better phrase). The more current, the hotter the "heater" gets, until finally things get too hot and the heat trips a bi-metallic strip, and the current flow is interrupted. This "heater" can be thought of as a resistor. Small value breakers have a high value resistance and thus they drop a high voltage across them. For a 1A Tyco W31 breaker this is 0.6v! Ouch! A 5A breaker only drops 0.15v, 10A = 0.1v, 15A = 0.09v, etc. That is why I only recommend 5A breakers and above to be used. These are maximum voltage drop values so I am still holding with choosing breakers over fuses. See the specs at See https://www.alliedelec.com/m/d/6526f8dfd0bf2b27f14db672ec951f9f.pdf.

PS - I had stated before that ONLY switch/breakers like the Tyco W31 may be used as a switch. I said that pull-type breakers should NEVER be used as a switch. I just found out that the pull-type Tyco W23 breaker is rated to be used as a switch! Huzzah! But I digress.

- John OHM Ω

[Charlie M. (UH & 002 owner/pilot)]

To add to a good post, part of the reason to NOT use most breakers as a switch is you derate (drop the ampacity) of the breaker over time due to wear. Add in a hot ambient (low save, sitting on the ramp on a sunny day, battery voltage drop, etc.) and the breaker can trip early/lower amperage.

Digression, but related.
Industrial environment, the company added a building with lots of lights. I suggested breaking up the light rows and putting them on lighting contactors but that added quite a bit of money.
The old plant manager stated, "We'll just use the breakers!".
A few years later (breakers switched twice a day, 5-6 days a week) we lost lights in the middle of summer as the building got hot.
Great money saver.......:-(

[[email protected]]

On Wednesday, June 20, 2018 at 9:27:33 AM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
> Andy,
>
> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount..
>
> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>
> One other comment: If you use diodes* (of any type) you can run two batteries in parallel safely. The danger was always been that without diodes, and with two batteries at different voltage output levels, that one battery could cross-charge the other. This could potentially happen without any current limit (!) until they equalize voltages. On a single bus with two batteries and diodes, the battery with the greatest voltage level would power the bus by itself until the separate battery's voltages equalized.
>
> - John OHM Ω
>
> * Teaching Moment - A diode only allows current to flow in one direction. In our case current will be limited to flowing from the battery to our avionics. As current flows through a diode there is a small voltage drop across the input to the output. We want to avoid, or limit, this voltage drop in our glider based power systems as we have no generating power source as found in airplanes.

I wonder about those "ideal diodes". They are presumably similar to what's in the batteries' BMS, I would guess power FETs that are switched on or off - and when "on" they conduct well with minimal (but not quite zero?) voltage drop. The "ideal diodes" must also have a sensing circuit that responds to the small voltage drop, amplify it and feed it to the gates of the FETs. (Seems like a Schottkey diode would be a good enough substitute.) The ones in the BMS can conduct in both directions (for charge and discharge), perhaps there are separate FETs for each direction.

[jfitch]

On Wednesday, June 20, 2018 at 7:56:31 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> QT,
>
> All breakers suffer a voltage drop of some amount (see more below). Therefore some pilots like fuses as they have no voltage drop at all. I went away from fuses as they don't give me a positive indication of a trip, are difficult to fix in (soaring) flight, and are fragile.
>
> Breaker voltage drop - As you probably know current is passed inside of breakers through a tiny "heater" (for want of a better phrase). The more current, the hotter the "heater" gets, until finally things get too hot and the heat trips a bi-metallic strip, and the current flow is interrupted. This "heater" can be thought of as a resistor. Small value breakers have a high value resistance and thus they drop a high voltage across them. For a 1A Tyco W31 breaker this is 0.6v! Ouch! A 5A breaker only drops 0.15v, 10A = 0.1v, 15A = 0.09v, etc. That is why I only recommend 5A breakers and above to be used. These are maximum voltage drop values so I am still holding with choosing breakers over fuses. See the specs at See https://www.alliedelec.com/m/d/6526f8dfd0bf2b27f14db672ec951f9f.pdf.
>
> PS - I had stated before that ONLY switch/breakers like the Tyco W31 may be used as a switch. I said that pull-type breakers should NEVER be used as a switch. I just found out that the pull-type Tyco W23 breaker is rated to be used as a switch! Huzzah! But I digress.
>
> - John OHM Ω

Glass fuses also suffer a voltage drop - how do you think they work? They are simply a resistive element that heats beyond the melting point above the label current. In fact a Bussman 1A AGX fuse has a resistance as much as 0..15 ohms, or a 1.5V drop. See http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/product-datasheets-b/Bus_Ele_DS_2041_AGX_Series.pdf

In addition, fuses are mounted in holders, and the ones used by many German glider manufacturers have at least 5 extra sliding connections in them: Faston to holder, holder to fuse, fuse to holder cap, holder cap to holder, Faston back to circuit - 5 more opportunities for voltage drop or failure. I've found them to age poorly and become quite unreliable. If you are going to breakers, I'd pick the Klixon 7277/7274 series, these are more compact and made for aircraft use.

[OHM Ω http://aviation.derosaweb.net]

Joe - Damn. There goes my electrical merit badge. Mea Culpa. Revamping my presentation as we speak. The Bussman AGC spec sheet tells the tale and seems to ping to a 1A fuse having a typical drop of 0.31Vdc. http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/product-datasheets/Bus_Elx_DS_OC-2543_AGC_Series.pdf

About Klixon 7277/7274 breakers. I read the specs and don't see it mentioned that it can be used as a switch like the Tyco. Only a mention of an option for an "auxiliary switch". Also, the maximum voltage drop for the 5A Klixon model is 0.25Vdc versus that of the Tyco which is 0.15Vdc. https://www.sensata.com/sites/default/files/media/documents/ourproducts_AircraftCircuitBreaker_7277Series_data sheet.pdf and https://www.alliedelec.com/m/d/6526f8dfd0bf2b27f14db672ec951f9f.pdf.

My $0.01 (de-rated).

- John

[Benedict Smith]

At 14:56 20 June 2018,
T0hNIOKEpiBodHRwOi8vYXZpYXRpb24uZGVyb3Nhd2ViLm5ldA ==
wrote:
>QT,
>
>All breakers suffer a voltage drop of some amount (see more
below).
>Theref=
>ore some pilots like fuses as they have no voltage drop at all. I
went
>awa=
>y from fuses as they don't give me a positive indication of a trip,
are
>dif=
>ficult to fix in (soaring) flight, and are fragile.=20
>
>
>- John OHM =E2=84=A6
>
John,
You can connect a 12v led indicator in parallel with the fuse, it will
light up if the fuse blows, regarding fixing them in flight, I would
want to know why it had blown before replacing it, not easy to
diagnose electrical faults and fly safely at the same time!
Ben.

[jfitch]

On Wednesday, June 20, 2018 at 10:03:22 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> Joe - Damn. There goes my electrical merit badge. Mea Culpa. Revamping my presentation as we speak. The Bussman AGC spec sheet tells the tale and seems to ping to a 1A fuse having a typical drop of 0.31Vdc. http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/product-datasheets/Bus_Elx_DS_OC-2543_AGC_Series.pdf
>
> About Klixon 7277/7274 breakers. I read the specs and don't see it mentioned that it can be used as a switch like the Tyco. Only a mention of an option for an "auxiliary switch". Also, the maximum voltage drop for the 5A Klixon model is 0.25Vdc versus that of the Tyco which is 0.15Vdc. https://www.sensata.com/sites/default/files/media/documents/ourproducts_AircraftCircuitBreaker_7277Series_data sheet.pdf and https://www.alliedelec.com/m/d/6526f8dfd0bf2b27f14db672ec951f9f.pdf.
>
> My $0.01 (de-rated).
>
> - John

Similar to Tyco, rated at 5000 cycles loaded, 10,000 unloaded. Also, the Tyco voltage drop is actually 0.195V, so they're pretty close. Tyco specs resistance as 0.03 ohms +/- 30% so max is 0.195, Klixon specs 0.25V drop max at max current. That Bussmann spec is typ, they don't spec max.

[John Godfrey (QT)[_2_]]

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark

Are the angels on the pin all the same size?

[[email protected]]

Are the angels on the pin all the same size?

Scholars have spent considerable time debating this question, but likely not as much time as some of the arguments and discussions on the R.A.S. !

But seriously, Angels are pure intelligence and don't occupy space. And for a more thoughtful answer one would really need to know if it is the head of the pin you are referring, or the sharp point, it could make a difference.

John - my Libelle still has the original contest letters on it - QT

Mark Guay

[krasw]

On Wednesday, 20 June 2018 20:15:06 UTC+3, Benedict Smith wrote:
> At 14:56 20 June 2018,
> T0hNIOKEpiBodHRwOi8vYXZpYXRpb24uZGVyb3Nhd2ViLm5ldA ==
> wrote:
> >QT,
> >
> >All breakers suffer a voltage drop of some amount (see more
> below).
> >Theref=
> >ore some pilots like fuses as they have no voltage drop at all. I
> went
> >awa=
> >y from fuses as they don't give me a positive indication of a trip,
> are
> >dif=
> >ficult to fix in (soaring) flight, and are fragile.=20
> >
> >
> >- John OHM =E2=84=A6
> >
> John,
> You can connect a 12v led indicator in parallel with the fuse, it will
> light up if the fuse blows, regarding fixing them in flight, I would
> want to know why it had blown before replacing it, not easy to
> diagnose electrical faults and fly safely at the same time!
> Ben.

Fuse blows it there is a short in wiring. You would like to continue supplying current via LED to shorted wires, so you can see that fuse was blown?

[Charlie Quebec]

A 1K resistor in series will fix that.

[John Godfrey (QT)[_2_]]

On Wednesday, June 20, 2018 at 10:23:41 PM UTC-4, wrote:
> Are the angels on the pin all the same size?
>
> Scholars have spent considerable time debating this question, but likely not as much time as some of the arguments and discussions on the R.A.S. !
>
> But seriously, Angels are pure intelligence and don't occupy space. And for a more thoughtful answer one would really need to know if it is the head of the pin you are referring, or the sharp point, it could make a difference.
>
> John - my Libelle still has the original contest letters on it - QT
>
> Mark Guay

I still think the core issue is whether the count is represented in Arabic or Roman, and in what base. The "head" of the pin is generally agreed to be the "not pointy" end, but I will defer to St. Thomas and the Talmudic scholars for final guidance. Angels can change state as proven by the Large Haydron Collider experiments.

I loved that Libelle, if you ever want to sell it please let me know.

QT

[Benedict Smith]

At 08:16 21 June 2018, krasw wrote:
>On Wednesday, 20 June 2018 20:15:06 UTC+3, Benedict Smith
wrote:
>> >
>> John,
>> You can connect a 12v led indicator in parallel with the fuse, it
will
>> light up if the fuse blows, regarding fixing them in flight, I
would
>> want to know why it had blown before replacing it, not easy to
>> diagnose electrical faults and fly safely at the same time!
>> Ben.
>
>Fuse blows it there is a short in wiring. You would like to
continue
>supplying current via LED to shorted wires, so you can see that
fuse was
>blown?
>
Yes, 3-5ma through an LED and it’s dropper resistor is not going
to cause any problems, it’s not like I suggested using a car
headlamp bulb!!
I would be interested to know why you think that it would be a
problem.
Ben.

[SF]

I started off with two K2'S I charged RIPthem in parallel, discharged them in parallel. No issues. Then one of the cells died in one of the batteries. Ran them in parallel on the test rig current meters on both. The good battery ran the load until the voltage dropped and then the battery with the bad cell started sharing the load until I stopped the test when the voltage dropped under 11V. There was never current flow from one battery to the other. It was all 0 current or current supplied to the load.

Now running two starks in parallel, discharge and charge. No issues in 2 years now.

Fuses on each battery, separate switches for each, each battery's connection to the bus is also fused.

Don't need to make this complicated. But you can if you want to.

SF

[jfitch]

On Thursday, June 21, 2018 at 4:12:09 PM UTC-7, SF wrote:
> I started off with two K2'S I charged RIPthem in parallel, discharged them in parallel. No issues. Then one of the cells died in one of the batteries. Ran them in parallel on the test rig current meters on both. The good battery ran the load until the voltage dropped and then the battery with the bad cell started sharing the load until I stopped the test when the voltage dropped under 11V. There was never current flow from one battery to the other. It was all 0 current or current supplied to the load.
>
> Now running two starks in parallel, discharge and charge. No issues in 2 years now.
>
> Fuses on each battery, separate switches for each, each battery's connection to the bus is also fused.
>
> Don't need to make this complicated. But you can if you want to.
>
> SF

The way you would have a problem is if the batteries are in a very different state of charge when they are paralleled. If always charged and discharged in parallel, this can't happen under normal use. If one suddenly developed an internal short, then the other would dump current into it.

[krasw]

On Thursday, 21 June 2018 22:30:06 UTC+3, Benedict Smith wrote:
> At 08:16 21 June 2018, krasw wrote:
> >On Wednesday, 20 June 2018 20:15:06 UTC+3, Benedict Smith
> wrote:
> >> >
> >> John,
> >> You can connect a 12v led indicator in parallel with the fuse, it
> will
> >> light up if the fuse blows, regarding fixing them in flight, I
> would
> >> want to know why it had blown before replacing it, not easy to
> >> diagnose electrical faults and fly safely at the same time!
> >> Ben.
> >
> >Fuse blows it there is a short in wiring. You would like to
> continue
> >supplying current via LED to shorted wires, so you can see that
> fuse was
> >blown?
> >
> Yes, 3-5ma through an LED and it’s dropper resistor is not going
> to cause any problems, it’s not like I suggested using a car
> headlamp bulb!!
> I would be interested to know why you think that it would be a
> problem.
> Ben.

I would be very interested to know why this excellent feature cannot be found in any airplane.

[Martin Gregorie[_6_]]

On Fri, 22 Jun 2018 00:18:42 -0700, krasw wrote:

> I would be very interested to know why this excellent feature cannot be
> found in any airplane.

Because there are very few panel mount fuse holders available with built-
in LED indicators?



--
Martin | martin at
Gregorie | gregorie dot org

[[email protected]]

> Because there are very few panel mount fuse holders available with built-
> in LED indicators?

How many do you want?

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=fuse+holder+with+LED&_sacat=0

[[email protected]]

> Because there are very few panel mount fuse holders available with built-
> in LED indicators?

How many do you want?

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=fuse+holder+with+LED&_sacat=0

[Martin Gregorie[_6_]]

On Fri, 22 Jun 2018 06:22:27 -0700, markmocho53 wrote:

>> Because there are very few panel mount fuse holders available with
>> built-
>> in LED indicators?
>
> How many do you want?
>
:-)

I was curious, never having seen any, if indicator fuse holders were
available> So I did a bit of searching on the local electronics suppliers
(RS, Farnell and Rapid Electronics) websites for individual LED indicator
equipped 5 x 20mm fuse holders and didn't find any. I looked for that
type because those would be direct replacements for the in-flight
accessible fuse holders in my glider.

I did see indicator fuse blocks and individual indicator holders for auto-
type fuses and rather more with neon indicators, but none of the latter
worked at 12v - they're all for 90-240v circuits.

I'm somewhat surprised that LED indicator holders for 5x20mm fuses aren't
available - it wouldn't be hard to fit an LED in the cap of these
holders.


--
Martin | martin at
Gregorie | gregorie dot org

[jfitch]

Glass fuse holders are kind of 20th century aren't they? If you were replacing them, going to a circuit breaker which is both resettable and indicates that it has been tripped, might be the direction to go?

[2G]

On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> Andy,
>
> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount..
>
> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>
> One other comment: If you use diodes* (of any type) you can run two batteries in parallel safely. The danger was always been that without diodes, and with two batteries at different voltage output levels, that one battery could cross-charge the other. This could potentially happen without any current limit (!) until they equalize voltages. On a single bus with two batteries and diodes, the battery with the greatest voltage level would power the bus by itself until the separate battery's voltages equalized.
>
> - John OHM Ω
>
> * Teaching Moment - A diode only allows current to flow in one direction. In our case current will be limited to flowing from the battery to our avionics. As current flows through a diode there is a small voltage drop across the input to the output. We want to avoid, or limit, this voltage drop in our glider based power systems as we have no generating power source as found in airplanes.

I drew up a zero-loss battery switching circuit in a few minutes. It is based on 2 power p-channel mosfets. A dual opamp compares two battery inputs and selects the higher voltage by turning on its mosfet. Transient suppressors protect the circuit from voltage spikes. The total component count is 12 (16 if you want LED indicators). Send me a private email if you want a copy of the circuit.

Tom

[Andy Blackburn[_3_]]

On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> Andy,
>
> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount..
>
> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B

[Chris]

Thanks John OHM for putting this presentation together and for keeping it current!

[Dan Marotta]

In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>> Andy,
>>
>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
>>
>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>>
> John (OHM),
>
> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
>
> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
>
> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
>
> Andy Blackburn
>
> 9B

--
Dan, 5J

[2G]

On Tuesday, July 24, 2018 at 7:31:44 AM UTC-7, Dan Marotta wrote:
> In my last experimental glider I used two rather stout SPST toggle
> switches to control my two LiFePO4 batteries.Â* At some point of the
> flight I would switch the second battery on and then switch the first
> battery off.Â* I don't think it was really necessary given the longevity
> of these batteries compared with the SLAs that I used previously, I
> simply switched about half way through the flight so that both batteries
> would get some use.Â* I like John's idea with the MOSFETs.
>
> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> >> Andy,
> >>
> >> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> >>
> >> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> >>
> > John (OHM),
> >
> > Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> >
> > My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> >
> > If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> >
> > Andy Blackburn
> >
> > 9B
>
> --
> Dan, 5J

Here is a demo circuit board you can buy that does pretty much everything:

http://www.analog.com/en/products/monitor-control-protection/powerpath-ideal-diodes-load-switches/ltc4370.html#product-evaluationkit

Tom

[OHM Ω http://aviation.derosaweb.net]

On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> In my last experimental glider I used two rather stout SPST toggle
> switches to control my two LiFePO4 batteries.Â* At some point of the
> flight I would switch the second battery on and then switch the first
> battery off.Â* I don't think it was really necessary given the longevity
> of these batteries compared with the SLAs that I used previously, I
> simply switched about half way through the flight so that both batteries
> would get some use.Â* I like John's idea with the MOSFETs.
>
> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> >> Andy,
> >>
> >> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> >>
> >> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> >>
> > John (OHM),
> >
> > Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> >
> > My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> >
> > If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> >
> > Andy Blackburn
> >
> > 9B
>
> --
> Dan, 5J

Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?

I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).

On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".

YMMV. Be careful out there.

- John OHM Ω

[[email protected]]

On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> > In my last experimental glider I used two rather stout SPST toggle
> > switches to control my two LiFePO4 batteries.Â* At some point of the
> > flight I would switch the second battery on and then switch the first
> > battery off.Â* I don't think it was really necessary given the longevity
> > of these batteries compared with the SLAs that I used previously, I
> > simply switched about half way through the flight so that both batteries
> > would get some use.Â* I like John's idea with the MOSFETs.
> >
> > On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > > On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> > >> Andy,
> > >>
> > >> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> > >>
> > >> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> > >>
> > > John (OHM),
> > >
> > > Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> > >
> > > My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> > >
> > > If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester).. I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> > >
> > > Andy Blackburn
> > >
> > > 9B
> >
> > --
> > Dan, 5J
>
> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>
> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>
> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>
> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>
> YMMV. Be careful out there.
>
> - John OHM Ω

With two SLA batteries that are in good shape it probably won't blow any fuses. The danger is if one battery goes bad, e.g., one of its six cells shorts out, so it effectively becomes a 10 volt battery. This happens fairly often in SLA batteries that are quite old. Then the good battery will keep sending current into the bad one, wasting its energy, and potentially causing the bad one to burst. You can minimize the chances of problems by only using fairly new batteries (say under 4 years old) and only as a matched pair of the same size/brand/age. LFP batteries typically have protection circuits built in that would prevent major issues like that, but why take chances? Schottky diodes are cheap enough.

[John Godfrey (QT)[_2_]]

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark

Just to add an angel to the pin, a rotary switch is a single point of failure...

[John Godfrey (QT)[_2_]]

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
> Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
> The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
> While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.
>
> Thanks ahead, Mark

Just to add an angel to the pin, a rotary switch is a single point of failure...

[kinsell]

On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
>> In my last experimental glider I used two rather stout SPST toggle
>> switches to control my two LiFePO4 batteries.Â* At some point of the
>> flight I would switch the second battery on and then switch the first
>> battery off.Â* I don't think it was really necessary given the longevity
>> of these batteries compared with the SLAs that I used previously, I
>> simply switched about half way through the flight so that both batteries
>> would get some use.Â* I like John's idea with the MOSFETs.
>>
>> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
>>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>>>> Andy,
>>>>
>>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
>>>>
>>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>>>>
>>> John (OHM),
>>>
>>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
>>>
>>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
>>>
>>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
>>>
>>> Andy Blackburn
>>>
>>> 9B
>>
>> --
>> Dan, 5J
>
> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>
> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>
> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>
> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>
> YMMV. Be careful out there.
>
> - John OHM Ω
>

In one of the many previous incantations of this discussion, the same
claim was made about huge currents flowing between a charged and
discharged SLA. At my urging, the claimant actually tried doing that
with an ammeter. Didn't see even a flicker of the needle.

You know how you have to apply 14 volts to charge up a 12 volt battery?
A charged battery sitting at probably 12.6V has basically no capability
of charging a moderately discharged battery.

Switching to lithiums, maybe they have current limiting, maybe they
don't. RIchard P shorted one out, the terminals got hot enough to melt
the case in that area. Doesn't sound like much current limiting going
on to me.

Talking to a pilot who just switched to lithiums, he was touting how
great the current limiting feature was. I asked if he ever shorted the
terminals on purpose to test it? Well no. Would he be willing to try
that? Again no. If you really believe you have limiting, then go ahead
and put the wrench across the terminals just to satisfy yourself. Film
it for use on YouTube, just in case.

-Dave

[Dan Marotta]

Thanks John,

These were lithium batteries and, yes, they were fused at the battery.Â*
As I recall, I used 5 amp fuses, no diodes, and never blew a fuse.Â* Read
these words out loud:Â* On, Off.Â* That's how long it took to switch
batteries.Â* I know that's not best practice, but it worked...Â* That was
on my previous glider which was experimental. My current glider has
Standard certification and it has a factory installed toggle switch
which is labeled:Â* Main and Aux.Â* I don't know if it's a make before
break switch but I've never had any electronics waver during switching.

On 7/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
>> In my last experimental glider I used two rather stout SPST toggle
>> switches to control my two LiFePO4 batteries.Â* At some point of the
>> flight I would switch the second battery on and then switch the first
>> battery off.Â* I don't think it was really necessary given the longevity
>> of these batteries compared with the SLAs that I used previously, I
>> simply switched about half way through the flight so that both batteries
>> would get some use.Â* I like John's idea with the MOSFETs.
>>
>> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
>>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>>>> Andy,
>>>>
>>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
>>>>
>>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>>>>
>>> John (OHM),
>>>
>>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
>>>
>>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
>>>
>>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
>>>
>>> Andy Blackburn
>>>
>>> 9B
>> --
>> Dan, 5J
> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>
> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>
> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>
> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>
> YMMV. Be careful out there.
>
> - John OHM Ω

--
Dan, 5J

[[email protected]]

On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> > In my last experimental glider I used two rather stout SPST toggle
> > switches to control my two LiFePO4 batteries.Â* At some point of the
> > flight I would switch the second battery on and then switch the first
> > battery off.Â* I don't think it was really necessary given the longevity
> > of these batteries compared with the SLAs that I used previously, I
> > simply switched about half way through the flight so that both batteries
> > would get some use.Â* I like John's idea with the MOSFETs.
> >
> > On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > > On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> > >> Andy,
> > >>
> > >> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> > >>
> > >> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> > >>
> > > John (OHM),
> > >
> > > Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> > >
> > > My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> > >
> > > If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester).. I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> > >
> > > Andy Blackburn
> > >
> > > 9B
> >
> > --
> > Dan, 5J
>
> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>
> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>
> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>
> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>
> YMMV. Be careful out there.
>
> - John OHM Ω

How much current do you project when switching from a low LiFe at 12.4 volts(pretty much done) to high at 13.7? I have been doing this switching with SLA batteries for 25 years. Switch new one on- switch old off a second or two later. Have not blown up anything yet.
UH

[2G]

On Tuesday, July 24, 2018 at 10:30:11 AM UTC-7, kinsell wrote:
> On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
> > On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> >> In my last experimental glider I used two rather stout SPST toggle
> >> switches to control my two LiFePO4 batteries.Â* At some point of the
> >> flight I would switch the second battery on and then switch the first
> >> battery off.Â* I don't think it was really necessary given the longevity
> >> of these batteries compared with the SLAs that I used previously, I
> >> simply switched about half way through the flight so that both batteries
> >> would get some use.Â* I like John's idea with the MOSFETs.
> >>
> >> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> >>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> >>>> Andy,
> >>>>
> >>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> >>>>
> >>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> >>>>
> >>> John (OHM),
> >>>
> >>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> >>>
> >>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> >>>
> >>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester).. I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> >>>
> >>> Andy Blackburn
> >>>
> >>> 9B
> >>
> >> --
> >> Dan, 5J
> >
> > Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
> >
> > I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
> >
> > For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
> >
> > On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
> >
> > YMMV. Be careful out there.
> >
> > - John OHM Ω
> >
>
> In one of the many previous incantations of this discussion, the same
> claim was made about huge currents flowing between a charged and
> discharged SLA. At my urging, the claimant actually tried doing that
> with an ammeter. Didn't see even a flicker of the needle.
>
> You know how you have to apply 14 volts to charge up a 12 volt battery?
> A charged battery sitting at probably 12.6V has basically no capability
> of charging a moderately discharged battery.
>
> Switching to lithiums, maybe they have current limiting, maybe they
> don't. RIchard P shorted one out, the terminals got hot enough to melt
> the case in that area. Doesn't sound like much current limiting going
> on to me.
>
> Talking to a pilot who just switched to lithiums, he was touting how
> great the current limiting feature was. I asked if he ever shorted the
> terminals on purpose to test it? Well no. Would he be willing to try
> that? Again no. If you really believe you have limiting, then go ahead
> and put the wrench across the terminals just to satisfy yourself. Film
> it for use on YouTube, just in case.
>
> -Dave

That happens because the internal resistance of the battery performs a balancing function: when the higher voltage donor battery supplies current, its voltage drops due to the IR voltage drop across its internal resistance. The discharged battery voltage, likewise, rises, again due to its internal resistance. These two voltages equalize to some intermediate voltage. If the bad battery has high internal resistance, which is very likely, the actual current flow between the two is correspondingly low.

Most lay people I talk to are unaware of battery internal resistance, and don't know how to analyze a simple dc circuit if they are. This series of lectures will start to get you up to speed on doing this (you will need to watch the whole series):
https://www.khanacademy.org/science/ap-physics-1/ap-circuits-topic/current-ap/v/circuits-part-1
I consider this time well spent in that it will aid you in troubleshooting elementary electrical problems. Hey we are not talking differential equations here!

Tom

[2G]

On Tuesday, July 24, 2018 at 10:30:11 AM UTC-7, kinsell wrote:
> On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
> > On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> >> In my last experimental glider I used two rather stout SPST toggle
> >> switches to control my two LiFePO4 batteries.Â* At some point of the
> >> flight I would switch the second battery on and then switch the first
> >> battery off.Â* I don't think it was really necessary given the longevity
> >> of these batteries compared with the SLAs that I used previously, I
> >> simply switched about half way through the flight so that both batteries
> >> would get some use.Â* I like John's idea with the MOSFETs.
> >>
> >> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> >>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> >>>> Andy,
> >>>>
> >>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> >>>>
> >>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> >>>>
> >>> John (OHM),
> >>>
> >>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> >>>
> >>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> >>>
> >>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester).. I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> >>>
> >>> Andy Blackburn
> >>>
> >>> 9B
> >>
> >> --
> >> Dan, 5J
> >
> > Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
> >
> > I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
> >
> > For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
> >
> > On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
> >
> > YMMV. Be careful out there.
> >
> > - John OHM Ω
> >
>
> In one of the many previous incantations of this discussion, the same
> claim was made about huge currents flowing between a charged and
> discharged SLA. At my urging, the claimant actually tried doing that
> with an ammeter. Didn't see even a flicker of the needle.
>
> You know how you have to apply 14 volts to charge up a 12 volt battery?
> A charged battery sitting at probably 12.6V has basically no capability
> of charging a moderately discharged battery.
>
> Switching to lithiums, maybe they have current limiting, maybe they
> don't. RIchard P shorted one out, the terminals got hot enough to melt
> the case in that area. Doesn't sound like much current limiting going
> on to me.
>
> Talking to a pilot who just switched to lithiums, he was touting how
> great the current limiting feature was. I asked if he ever shorted the
> terminals on purpose to test it? Well no. Would he be willing to try
> that? Again no. If you really believe you have limiting, then go ahead
> and put the wrench across the terminals just to satisfy yourself. Film
> it for use on YouTube, just in case.
>
> -Dave

All batteries will current limit: that is what their internal resistance does. Again, it is Ohm's law:
I = V / R
where R is the internal resistance. R is about 0.01 ohm on a typical glider SLA battery, so I = 120 amp. Now, you are going to get heating as a result of that energy dissipation, in watts:
W = I^2 * R = 120^2 * .01
or 144 W. This will cause the battery to warm considerably. Given that batteries are poor at radiating heat, the battery can get quite hot, to the point of exploding. This is why batteries should have fuses.

Tom

[[email protected]]

On Tuesday, July 24, 2018 at 8:56:37 PM UTC-4, 2G wrote:
> On Tuesday, July 24, 2018 at 10:30:11 AM UTC-7, kinsell wrote:
> > On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
> > > On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> > >> In my last experimental glider I used two rather stout SPST toggle
> > >> switches to control my two LiFePO4 batteries.Â* At some point of the
> > >> flight I would switch the second battery on and then switch the first
> > >> battery off.Â* I don't think it was really necessary given the longevity
> > >> of these batteries compared with the SLAs that I used previously, I
> > >> simply switched about half way through the flight so that both batteries
> > >> would get some use.Â* I like John's idea with the MOSFETs.
> > >>
> > >> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > >>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> > >>>> Andy,
> > >>>>
> > >>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> > >>>>
> > >>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays.. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> > >>>>
> > >>> John (OHM),
> > >>>
> > >>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> > >>>
> > >>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> > >>>
> > >>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> > >>>
> > >>> Andy Blackburn
> > >>>
> > >>> 9B
> > >>
> > >> --
> > >> Dan, 5J
> > >
> > > Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
> > >
> > > I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other..
> > >
> > > For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
> > >
> > > On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
> > >
> > > YMMV. Be careful out there.
> > >
> > > - John OHM Ω
> > >
> >
> > In one of the many previous incantations of this discussion, the same
> > claim was made about huge currents flowing between a charged and
> > discharged SLA. At my urging, the claimant actually tried doing that
> > with an ammeter. Didn't see even a flicker of the needle.
> >
> > You know how you have to apply 14 volts to charge up a 12 volt battery?
> > A charged battery sitting at probably 12.6V has basically no capability
> > of charging a moderately discharged battery.
> >
> > Switching to lithiums, maybe they have current limiting, maybe they
> > don't. RIchard P shorted one out, the terminals got hot enough to melt
> > the case in that area. Doesn't sound like much current limiting going
> > on to me.
> >
> > Talking to a pilot who just switched to lithiums, he was touting how
> > great the current limiting feature was. I asked if he ever shorted the
> > terminals on purpose to test it? Well no. Would he be willing to try
> > that? Again no. If you really believe you have limiting, then go ahead
> > and put the wrench across the terminals just to satisfy yourself. Film
> > it for use on YouTube, just in case.
> >
> > -Dave
>
> All batteries will current limit: that is what their internal resistance does. Again, it is Ohm's law:
> I = V / R
> where R is the internal resistance. R is about 0.01 ohm on a typical glider SLA battery, so I = 120 amp. Now, you are going to get heating as a result of that energy dissipation, in watts:
> W = I^2 * R = 120^2 * .01
> or 144 W. This will cause the battery to warm considerably. Given that batteries are poor at radiating heat, the battery can get quite hot, to the point of exploding. This is why batteries should have fuses.
>
> Tom

For the example 0.01 ohm, make that 1200 amps and 14,400 watts!

[RR]

There is no issue switching batteries with overlapping on states. I charge my batteries with a smart charger designed for multi chemistry. This shows me everytime I charge, how much current is required by the battery when the supply side is 14.4v. It requires a nearly fully discharged battery to demand over 3 amps, and that is for a voltage differential far greater that you will get from a fully charged battery, as you would get from going from batt A to B. And just to fan the fire so to speak, I did not mention chemistry. As I see similar charge currents regardless of chemistry.

This is simply not a practical matter, as UH reports from years of experience. It is a fiction from the lack of understanding of charge dynamics. These devices are not superconcuctors...

RR

[Craig Funston[_3_]]

On Tuesday, July 24, 2018 at 2:22:09 PM UTC-7, wrote:
> On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
> > On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
> > > In my last experimental glider I used two rather stout SPST toggle
> > > switches to control my two LiFePO4 batteries.Â* At some point of the
> > > flight I would switch the second battery on and then switch the first
> > > battery off.Â* I don't think it was really necessary given the longevity
> > > of these batteries compared with the SLAs that I used previously, I
> > > simply switched about half way through the flight so that both batteries
> > > would get some use.Â* I like John's idea with the MOSFETs.
> > >
> > > On 7/23/2018 10:43 PM, Andy Blackburn wrote:
> > > > On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
> > > >> Andy,
> > > >>
> > > >> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
> > > >>
> > > >> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays.. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
> > > >>
> > > > John (OHM),
> > > >
> > > > Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
> > > >
> > > > My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
> > > >
> > > > If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
> > > >
> > > > Andy Blackburn
> > > >
> > > > 9B
> > >
> > > --
> > > Dan, 5J
> >
> > Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
> >
> > I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
> >
> > For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
> >
> > On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
> >
> > YMMV. Be careful out there.
> >
> > - John OHM Ω
>
> How much current do you project when switching from a low LiFe at 12.4 volts(pretty much done) to high at 13.7? I have been doing this switching with SLA batteries for 25 years. Switch new one on- switch old off a second or two later. Have not blown up anything yet.
> UH

Plus one. KISS principle.

[Dan Marotta]

On 7/24/2018 7:22 PM, wrote:
> On Tuesday, July 24, 2018 at 8:56:37 PM UTC-4, 2G wrote:
>> On Tuesday, July 24, 2018 at 10:30:11 AM UTC-7, kinsell wrote:
>>> On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
>>>> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
>>>>> In my last experimental glider I used two rather stout SPST toggle
>>>>> switches to control my two LiFePO4 batteries.Â* At some point of the
>>>>> flight I would switch the second battery on and then switch the first
>>>>> battery off.Â* I don't think it was really necessary given the longevity
>>>>> of these batteries compared with the SLAs that I used previously, I
>>>>> simply switched about half way through the flight so that both batteries
>>>>> would get some use.Â* I like John's idea with the MOSFETs.
>>>>>
>>>>> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
>>>>>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>>>>>>> Andy,
>>>>>>>
>>>>>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
>>>>>>>
>>>>>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>>>>>>>
>>>>>> John (OHM),
>>>>>>
>>>>>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
>>>>>>
>>>>>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
>>>>>>
>>>>>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
>>>>>>
>>>>>> Andy Blackburn
>>>>>>
>>>>>> 9B
>>>>> --
>>>>> Dan, 5J
>>>> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>>>>
>>>> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>>>>
>>>> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>>>>
>>>> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>>>>
>>>> YMMV. Be careful out there.
>>>>
>>>> - John OHM Ω
>>>>
>>> In one of the many previous incantations of this discussion, the same
>>> claim was made about huge currents flowing between a charged and
>>> discharged SLA. At my urging, the claimant actually tried doing that
>>> with an ammeter. Didn't see even a flicker of the needle.
>>>
>>> You know how you have to apply 14 volts to charge up a 12 volt battery?
>>> A charged battery sitting at probably 12.6V has basically no capability
>>> of charging a moderately discharged battery.
>>>
>>> Switching to lithiums, maybe they have current limiting, maybe they
>>> don't. RIchard P shorted one out, the terminals got hot enough to melt
>>> the case in that area. Doesn't sound like much current limiting going
>>> on to me.
>>>
>>> Talking to a pilot who just switched to lithiums, he was touting how
>>> great the current limiting feature was. I asked if he ever shorted the
>>> terminals on purpose to test it? Well no. Would he be willing to try
>>> that? Again no. If you really believe you have limiting, then go ahead
>>> and put the wrench across the terminals just to satisfy yourself. Film
>>> it for use on YouTube, just in case.
>>>
>>> -Dave
>> All batteries will current limit: that is what their internal resistance does. Again, it is Ohm's law:
>> I = V / R
>> where R is the internal resistance. R is about 0.01 ohm on a typical glider SLA battery, so I = 120 amp. Now, you are going to get heating as a result of that energy dissipation, in watts:
>> W = I^2 * R = 120^2 * .01
>> or 144 W. This will cause the battery to warm considerably. Given that batteries are poor at radiating heat, the battery can get quite hot, to the point of exploding. This is why batteries should have fuses.
>>
>> Tom
> For the example 0.01 ohm, make that 1200 amps and 14,400 watts!
Wow!Â* That's a lot!Â* Let's see, now...Â* 14,400 watts / 3,600
seconds/hour * 1/4 sec (as in 1 quarter second to switch one on and then
the other off) =Â* 1 watt hour or 0.001 KWH.

I won't be losing any sleep over it.Â* 2G's math is correct but, in the
absence of a dead short, I see no problems with doing without diodes.Â*
Still, I keep both batteries fused very close to the positive terminals.
--
Dan, 5J

[kinsell]

On 07/24/2018 08:16 PM, Craig Funston wrote:
> On Tuesday, July 24, 2018 at 2:22:09 PM UTC-7, wrote:
>> On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
>>> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
>>>> In my last experimental glider I used two rather stout SPST toggle
>>>> switches to control my two LiFePO4 batteries.Â* At some point of the
>>>> flight I would switch the second battery on and then switch the first
>>>> battery off.Â* I don't think it was really necessary given the longevity
>>>> of these batteries compared with the SLAs that I used previously, I
>>>> simply switched about half way through the flight so that both batteries
>>>> would get some use.Â* I like John's idea with the MOSFETs.
>>>>
>>>> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
>>>>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
>>>>>> Andy,
>>>>>>
>>>>>> I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount.
>>>>>>
>>>>>> That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.
>>>>>>
>>>>> John (OHM),
>>>>>
>>>>> Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.
>>>>>
>>>>> My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.
>>>>>
>>>>> If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.
>>>>>
>>>>> Andy Blackburn
>>>>>
>>>>> 9B
>>>>
>>>> --
>>>> Dan, 5J
>>>
>>> Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?
>>>
>>> I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.
>>>
>>> For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).
>>>
>>> On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".
>>>
>>> YMMV. Be careful out there.
>>>
>>> - John OHM Ω
>>
>> How much current do you project when switching from a low LiFe at 12.4 volts(pretty much done) to high at 13.7? I have been doing this switching with SLA batteries for 25 years. Switch new one on- switch old off a second or two later. Have not blown up anything yet.
>> UH
>
> Plus one. KISS principle.
>

Two switches and two fuses should work fine, certainly an improvement
over some of the Rube Goldberg solutions proposed here.

But two batteries, two fuses, and two Schottky diodes would be an
improvement. Perfect for everyone except jet jockeys who want more
switches to flip.

Finally, one properly sized battery with a fuse is probably the best
solution, half the number of BMS boards to blow up. Can't get much
simpler than that. There's a lot to be said for reducing component count.

[[email protected]]

There's a lot to be said for reducing component count.

Yes, there is a definite charm to single point-of-failure systems.

But charm don't count when the failure occurs and you are out of backups and ideas.

[Dan Marotta]

Right on, Mark.

As a former jet jockey, myself, I prefer simplicity and fewer switches.Â*
And, whereas one big battery would be nice (forgetting single point
failures), space quickly becomes an issue.Â* It's much easier to locate
two or more smaller batteries around the ship than finding a place for a
big one.Â* One of my friends removed the nose ballast from his glider and
replaced it with an SLA battery.Â* A much better use of lead, don'tcha think?

....And if you want more switches, go to an air museum and take a look in
the cockpit of a MiG-21
<https://www.google.com/search?q=mig-21+cockpit&rlz=1C1CHBF_enUS697US697&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjjsanSoL3cAhUF-6wKHfHSA_EQ_AUICigB&biw=1365&bih=662#imgrc=kTdKHIULN9Ro9M:>...

On 7/25/2018 8:55 PM, wrote:
> There's a lot to be said for reducing component count.
>
> Yes, there is a definite charm to single point-of-failure systems.
>
> But charm don't count when the failure occurs and you are out of backups and ideas.
>

--
Dan, 5J

[Jonathan St. Cloud]

On Thursday, July 26, 2018 at 10:10:25 AM UTC-7, Dan Marotta wrote:
> Right on, Mark.
>
>
>
> As a former jet jockey, myself, I prefer simplicity and fewer
> switches.Â* And, whereas one big battery would be nice (forgetting
> single point failures), space quickly becomes an issue.Â* It's much
> easier to locate two or more smaller batteries around the ship than
> finding a place for a big one.Â* One of my friends removed the nose
> ballast from his glider and replaced it with an SLA battery.Â* A much
> better use of lead, don'tcha think?
>
>
>
> ...And if you want more switches, go to an air museum and take a
> look in the cockpit
> of a MiG-21...
>
>
>
>
> On 7/25/2018 8:55 PM,
> wrote:
>
>
>
> There's a lot to be said for reducing component count.
>
> Yes, there is a definite charm to single point-of-failure systems.
>
> But charm don't count when the failure occurs and you are out of backups and ideas.
>
>
>
>
>
>
> --
>
> Dan, 5J

I always thought the Migs looked best while on fire!

[kinsell]

On 07/26/2018 12:34 PM, Jonathan St. Cloud wrote:
> On Thursday, July 26, 2018 at 10:10:25 AM UTC-7, Dan Marotta wrote:
>> Right on, Mark.
>>
>>
>>
>> As a former jet jockey, myself, I prefer simplicity and fewer
>> switches.Â* And, whereas one big battery would be nice (forgetting
>> single point failures), space quickly becomes an issue.Â* It's much
>> easier to locate two or more smaller batteries around the ship than
>> finding a place for a big one.Â* One of my friends removed the nose
>> ballast from his glider and replaced it with an SLA battery.Â* A much
>> better use of lead, don'tcha think?
>>
>>
>>
>> ...And if you want more switches, go to an air museum and take a
>> look in the cockpit
>> of a MiG-21...
>>
>>
>>
>>
>> On 7/25/2018 8:55 PM,
>> wrote:
>>
>>
>>
>> There's a lot to be said for reducing component count.
>>
>> Yes, there is a definite charm to single point-of-failure systems.
>>
>> But charm don't count when the failure occurs and you are out of backups and ideas.
>>
>>
>>

I got an idea! How about you keep flying the A/C? Do you fly a glider
that crashes if you lose the panel? In 40 years of flying with a
single battery for the avionics, I've never lost the panel. Absolutely
could happen. Not catastrophic if it does.

The reality is all the solutions proposed have single points of failure.
If you can't handle an occasional failure, maybe find a different hobby?

[2G]

On Thursday, July 26, 2018 at 3:42:56 PM UTC-7, kinsell wrote:
> On 07/26/2018 12:34 PM, Jonathan St. Cloud wrote:
> > On Thursday, July 26, 2018 at 10:10:25 AM UTC-7, Dan Marotta wrote:
> >> Right on, Mark.
> >>
> >>
> >>
> >> As a former jet jockey, myself, I prefer simplicity and fewer
> >> switches.Â* And, whereas one big battery would be nice (forgetting
> >> single point failures), space quickly becomes an issue.Â* It's much
> >> easier to locate two or more smaller batteries around the ship than
> >> finding a place for a big one.Â* One of my friends removed the nose
> >> ballast from his glider and replaced it with an SLA battery.Â* A much
> >> better use of lead, don'tcha think?
> >>
> >>
> >>
> >> ...And if you want more switches, go to an air museum and take a
> >> look in the cockpit
> >> of a MiG-21...
> >>
> >>
> >>
> >>
> >> On 7/25/2018 8:55 PM,
> >> wrote:
> >>
> >>
> >>
> >> There's a lot to be said for reducing component count.
> >>
> >> Yes, there is a definite charm to single point-of-failure systems.
> >>
> >> But charm don't count when the failure occurs and you are out of backups and ideas.
> >>
> >>
> >>
>
> I got an idea! How about you keep flying the A/C? Do you fly a glider
> that crashes if you lose the panel? In 40 years of flying with a
> single battery for the avionics, I've never lost the panel. Absolutely
> could happen. Not catastrophic if it does.
>
> The reality is all the solutions proposed have single points of failure.
> If you can't handle an occasional failure, maybe find a different hobby?

Early on when I was more careless about checking on the health of my battery, I have had electrical failures while flying. Since then I have only been inconvenienced a few times on the ground when my batteries were incapable of starting the engine. That said, having a backup is not a bad idea. Especially for my new glider where the primary flight display is electronic. Even then, I could still fly the glider by visual reference only.

Tom

[[email protected]]

Let's get something straight. I am NOT going to bail out if I lose the battery, OK? But IF the panel goes out when I am 100 miles away from the home 'drome, and it's getting late in the day, I don't necessarily need the added hassle of not having my moving map, electronic vario and instruments, my transponder, radio and all those helpful little devices.

We enjoy the benefits of many technologies on cross-country flights. It's not to say that we HAVE to depend on them, but we use them to our advantage much of the time.

When I am way out of simple glide ratio of the field, I like to have some information about the wind, along with things like communication and traffic avoidance.


If I was a "twirly bird," screwing around the airport no farther away than a 20:1 glide, I wouldn't care. But with the sort of flying I prefer, I will not depend on a single power source. And, yes, I had a failure earlier this year due to a poor ground connection on one battery. But I switched to number two, flew two more hours and tightened the screw on the ring terminal when I got back. My own fault for not securing the connection in the first place, BUT!...

I had a backup. And another after that.

[[email protected]]

Talking about backup batteries, I sometimes carry a portable USB "power bank" as a backup power source for my flight computer (Nook), in case of problems with the main glider battery, 12v-5V converter, or the associated cabling. I found one of the rare models with a real (slide) on-off switch - the far more common ones with a pushbutton seem to turn themselves off whenever the Nook isn't drawing enough current.

So, unlike the LiFePO4 batteries discussed in this thread, this is a lithium-polymer battery, a less stable chemistry, albeit a lot smaller (about 2-3AH at 5V). Is it safe enough to carry in the cockpit? Before you reflexively say "no", remember that you are (probably) carrying at least one such battery, in your cellphone. There's also one inside the Nook, and any other tablets people use in the cockpit. And inside some varios, Portable powerFlarm, who knows what else - almost anything that is rechargeable these days.

[Charlie Quebec]

I use a cheap android phone with xcsoar, kept in the side pocket, fully charged. Powered off it can be going in a minute, and using its own GPS.
I have a mechanical Winter as vario backup. You dont get to go solo here without the ability to do a circuit and land with all instruments covered.
Losing power would little to no inconvenience.
A truly independent backup that costs less than $100.

[[email protected]]

On Friday, July 27, 2018 at 4:21:41 AM UTC-4, Charlie Quebec wrote:
> I use a cheap android phone with xcsoar, kept in the side pocket, fully charged. Powered off it can be going in a minute, and using its own GPS.
> I have a mechanical Winter as vario backup. You dont get to go solo here without the ability to do a circuit and land with all instruments covered.
> Losing power would little to no inconvenience.
> A truly independent backup that costs less than $100.

I have a mechanical variometer and a chart. They have gotten me home when needed for more than 40 years. I expect they would again albeit without a flight log.
That said the only power issue I've had was due to a very low primary battery and a backup that wasn't charged as I thought. I turned everything off except the ClearNav and got around OK.
FWIW
UH

[Jonathan St. Cloud]

On Friday, July 27, 2018 at 1:21:41 AM UTC-7, Charlie Quebec wrote:
> I use a cheap android phone with xcsoar, kept in the side pocket, fully charged. Powered off it can be going in a minute, and using its own GPS.
> I have a mechanical Winter as vario backup. You dont get to go solo here without the ability to do a circuit and land with all instruments covered.
> Losing power would little to no inconvenience.
> A truly independent backup that costs less than $100.

I have a LxNav S3 with the UPS battery pack, which according to specs should give me 8 hours of vario with audio should I lose ship's main bus, and all those pretty glass instruments. Coupled with a JSW, Super Class, wiz wheel it is just like my first 300 hours of xc flying before I purchased the most modern flight computer made, at the time, the B100. I also have a real sectional(s) for the area I fly, and iGlide loaded on a phone zipped into my pants on flight mode.

[kinsell]

On 07/25/2018 08:44 PM, kinsell wrote:
> On 07/24/2018 08:16 PM, Craig Funston wrote:
>> On Tuesday, July 24, 2018 at 2:22:09 PM UTC-7,
>> wrote:
>>> On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω
>>> http://aviation.derosaweb.net wrote:
>>>> On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
>>>>> In my last experimental glider I used two rather stout SPST toggle
>>>>> switches to control my two LiFePO4 batteries.Â* At some point of the
>>>>> flight I would switch the second battery on and then switch the first
>>>>> battery off.Â* I don't think it was really necessary given the
>>>>> longevity
>>>>> of these batteries compared with the SLAs that I used previously, I
>>>>> simply switched about half way through the flight so that both
>>>>> batteries
>>>>> would get some use.Â* I like John's idea with the MOSFETs.
>>>>>
>>>>> On 7/23/2018 10:43 PM, Andy Blackburn wrote:
>>>>>> On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω
>>>>>> http://aviation.derosaweb.net wrote:
>>>>>>> Andy,
>>>>>>>
>>>>>>> I have used the ideal diodes mentioned by Shaun McLaughlin
>>>>>>> (http://re-voltage.eu/ US$27 each) as I was given a pair to test
>>>>>>> with.Â* They do what they say with minuscule voltage drops across
>>>>>>> them.Â*Â* Full disclosure, I am currently using two 1N5821 Schottky
>>>>>>> diodes in my panel right now (page 74 of my presentation) -
>>>>>>> small, simple, cheap, plentiful, robust, and easy to mount.
>>>>>>>
>>>>>>> That being said - the availability of inexpensive ideal diodes
>>>>>>> has exploded in recent years mainly for use in systems like solar
>>>>>>> panel arrays.Â* See
>>>>>>> https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=ideal+%28diode%2C+diodes%29&_sacat=0.
>>>>>>> I also like the increasing range of mounting styles available
>>>>>>> allowing for placement options behind our increasingly cramped
>>>>>>> panels.
>>>>>>>
>>>>>> John (OHM),
>>>>>>
>>>>>> Yup, I have one of Shaun's (on your recommendation) and some of
>>>>>> the anti-revere-irrigation ones. I haven't installed either.
>>>>>>
>>>>>> My current install uses the Schleicher rotary switch to select:
>>>>>> Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3
>>>>>> (tail). I use a bank of capacitors connected through a power
>>>>>> resistor to energize the circuit when the switch is between
>>>>>> batteries.
>>>>>>
>>>>>> If I had to do it again I would use ideal diodes (though as others
>>>>>> have mentioned this is really not nearly a necessary with LiFePO4
>>>>>> batteries since they go through voltages below 11v quite quickly
>>>>>> on my battery tester). I would also separate the batteries to
>>>>>> individual switches to eliminate the switch as a single point of
>>>>>> failure.
>>>>>>
>>>>>> Andy Blackburn
>>>>>>
>>>>>> 9B
>>>>>
>>>>> --
>>>>> Dan, 5J
>>>>
>>>> Dan - Do you have diodes in this circuit to prevent cross-charging
>>>> of the batteries?
>>>>
>>>> I will repeat something I said above that (without diodes) putting
>>>> the batteries in parallel can cause a large current to flow from the
>>>> "high" battery to the "low" battery.Â* Effectively one battery is
>>>> charging the other.
>>>>
>>>> For dumb SLA batteries this will almost certainly blow the fuse on
>>>> your batteries (you do have a fuse right at your battery's positive
>>>> terminal, right??).
>>>>
>>>> On lithium batteries, which probably have intelligent current
>>>> limiting electronics inside, this should not be an issue.Â* But
>>>> notice the words "probably" and "should".
>>>>
>>>> YMMV.Â* Be careful out there.
>>>>
>>>> - John OHM Ω
>>>
>>> How much current do you project when switching from a low LiFe at
>>> 12.4 volts(pretty much done) to high at 13.7? I have been doing this
>>> switching with SLA batteries for 25 years. Switch new one on- switch
>>> old off a second or two later. Have not blown up anything yet.
>>> UH
>>
>> Plus one. KISS principle.
>>
>
> Two switches and two fuses should work fine, certainly an improvement
> over some of the Rube Goldberg solutions proposed here.
>
> But two batteries, two fuses, and two Schottky diodes would be an
> improvement.Â* Perfect for everyone except jet jockeys who want more
> switches to flip.
>
> Finally, one properly sized battery with a fuse is probably the best
> solution, half the number of BMS boards to blow up.Â* Can't get much
> simpler than that.Â* There's a lot to be said for reducing component count.
>
>

Speaking of losing the panel, Garret Willat just posted a video on FB of
flying in the Czech Republic with no avionics power, which also took out
his engine controller. Did have a paper map and mechanical vario.

[jfitch]

On Friday, July 27, 2018 at 8:24:30 AM UTC-7, Jonathan St. Cloud wrote:
> On Friday, July 27, 2018 at 1:21:41 AM UTC-7, Charlie Quebec wrote:
> > I use a cheap android phone with xcsoar, kept in the side pocket, fully charged. Powered off it can be going in a minute, and using its own GPS.
> > I have a mechanical Winter as vario backup. You dont get to go solo here without the ability to do a circuit and land with all instruments covered..
> > Losing power would little to no inconvenience.
> > A truly independent backup that costs less than $100.
>
> I have a LxNav S3 with the UPS battery pack, which according to specs should give me 8 hours of vario with audio should I lose ship's main bus, and all those pretty glass instruments. Coupled with a JSW, Super Class, wiz wheel it is just like my first 300 hours of xc flying before I purchased the most modern flight computer made, at the time, the B100. I also have a real sectional(s) for the area I fly, and iGlide loaded on a phone zipped into my pants on flight mode.

I'm using an iPhone X with iGlide as the primary tactical display. If the avionics battery and everything connected to it fries, iGlide simply switches to internal GPS, barometer and battery. It will give a warning about the charge power going out, if you miss that it is seamless enough that you may fly the rest of the day without noticing. The main thing I notice is no more Flarm targets to leech from.

On the other hand, with a well done installation the chances of the whole panel failing should be quite remote. I'v got two independent batteries with two independent supply paths to the power bus - which is the single point of failure but being a solid piece of copper fairly reliable.