Master Switches

[K]

Just finished a panel upgrade on a Normal category (Not Experimental). One change made was to use PowerFlarm for GPS logging and glide computer. My master switch is a 3 position switch (Bat 1, Off, Batt 2). My old Volkslogger had no problem with swtching batteries as long as I flipped the switch fast, If I was slow it would reboot. Can I expect the same from the PF? I was thinking of wiring both batteries to one master or having two battery switches. I see no reason to use one battery at a time.
I bought the ship recently and it has much of the original electrical wiring and hardware (looks straight out of a German Home Depot). I initially purchased factory replacement electrical parts but they are expensive and not of very high quality. I wish to switch to Mil-Spec or higher quality for the master switch(S). Any recommendations? Discussed this with my IA and he has no problem with non factory stuff as long as it is aircraft grade (Which my sentiment also).
Thanks in advance.
Kirk

[[email protected]]

Craggy Aero and others have the wire (Tefzel), switches & breakers you'll need. Call Richard there for help. There are a couple of schools of thought on how to configure batteries. A-off-B versus separate switches as you suggested. The experts will clarify more.

[JJ Sinclair[_2_]]

On Saturday, April 20, 2013 1:22:49 PM UTC-7, K wrote:
> Just finished a panel upgrade on a Normal category (Not Experimental). One change made was to use PowerFlarm for GPS logging and glide computer. My master switch is a 3 position switch (Bat 1, Off, Batt 2). My old Volkslogger had no problem with swtching batteries as long as I flipped the switch fast, If I was slow it would reboot. Can I expect the same from the PF? I was thinking of wiring both batteries to one master or having two battery switches. I see no reason to use one battery at a time.
>
> I bought the ship recently and it has much of the original electrical wiring and hardware (looks straight out of a German Home Depot). I initially purchased factory replacement electrical parts but they are expensive and not of very high quality. I wish to switch to Mil-Spec or higher quality for the master switch(S). Any recommendations? Discussed this with my IA and he has no problem with non factory stuff as long as it is aircraft grade (Which my sentiment also).
> , now
> Thanks in advance.
>
> Kirk

I have used 2 separate master switches (one for each battery)for years. If you hook both batteries together in parallel, you will need to charge both batteries after each flight. I use my primary (12a/h) until I get a low voltage warning on my SN-10, then switch to my backup 7a/h. This happens at about the 3 hour mark. I turn on the second battery and then turn off the first battery to prevent even a slight voltage gap. Please, no posts talking about voltage spikes, I have tested that and got something like 120 m/a flow as the new battery briefly tried to 'charge' the old battery and no voltage spike!
JJ

[[email protected]]

We recently put a re-paneled Duo Discus into service with a Clear Nav and CN vario (which I like a lot). We discovered the type of switch you have (ON-OFF-ON) would re-start the ClearNav no matter how quickly it was flipped. We have gone to a switch for each battery and the protocol is to turn on the subsequent switch before turning off the first one. No problems.

[Peter von Tresckow]

> wrote:
> We recently put a re-paneled Duo Discus into service with a Clear Nav and
> CN vario (which I like a lot). We discovered the type of switch you have
> (ON-OFF-ON) would re-start the ClearNav no matter how quickly it was
> flipped. We have gone to a switch for each battery and the protocol is
> to turn on the subsequent switch before turning off the first one. No problems.

Now keep in mind that I am a software guy and know just enough about
electronics to be dangerous, but couldn't you just wire in a sufficiently
large capacitor to bridge the temporary loss of power? I seem to remember
something like that in the wiring instructions for my Volkslogger.

Pete

[Craig Funston[_2_]]

On Monday, April 22, 2013 4:32:03 PM UTC-7, vontresc wrote:
> <> wrote:
>
> > We recently put a re-paneled Duo Discus into service with a Clear Nav and
>
> > CN vario (which I like a lot). We discovered the type of switch you have
>
> > (ON-OFF-ON) would re-start the ClearNav no matter how quickly it was
>
> > flipped. We have gone to a switch for each battery and the protocol is
>
> > to turn on the subsequent switch before turning off the first one. No problems.
>
>
>
> Now keep in mind that I am a software guy and know just enough about
>
> electronics to be dangerous, but couldn't you just wire in a sufficiently
>
> large capacitor to bridge the temporary loss of power? I seem to remember
>
> something like that in the wiring instructions for my Volkslogger.
>
>
>
> Pete

Not sure why folks want to make this complicated. I've been doing it JJ's way and it's rock simple and works flawlessly. Time spent with both batteries in parallel is minimal.

Cheers,
Craig

[JS]

Agree, two switches and parallel the batteries for as long as you need. It really doesn't matter much.
The NKK toggle switches which require pulling out to unlock before you can change position seem the best. I've bought them from Mouser.com.
The SPST is Mouser part# 633-M2011LL3W03
NKK part# M2011LL3W03
(hopefully that's correct, I'm on Mouser's antipodal site at the moment)
Or search locking toggle switch spst
They make them in SPDT, DP, On/Off/On, etc.
Jim

[Alan[_6_]]

In article > K > writes:
>Just finished a panel upgrade on a Normal category (Not Experimental). One =
>change made was to use PowerFlarm for GPS logging and glide computer. My ma=
>ster switch is a 3 position switch (Bat 1, Off, Batt 2). My old Volkslogger=
> had no problem with swtching batteries as long as I flipped the switch fas=
>t, If I was slow it would reboot. Can I expect the same from the PF? I was =
>thinking of wiring both batteries to one master or having two battery switc=
>hes. I see no reason to use one battery at a time.

I would suggest that there is an advantage to using both batteries together,
all the time.

If you buy a pair new from a good source, they should have the same capacity
and discharge curve. Connect them both together (with a fuse at the positive
terminal of each battery, just in case), then run that to your single master
switch.

This will give you a longer total run time than using them individually,
as the lower discharge rate will provide more energy before the battery is
discharged. (Or, it will discharge them by a lower percentage of charge
for a given flight time resulting in a longer lifetime for the batteries.)

For example, the common 7 AH battery used in many gliders will provide
..35 amps for 20 hours, or .7 amps for a bit over 8 hours.

If you run them one at a time, you get .7 amps for about 17 hours.

If you parallel two of these, they each provide .35 amps for 20 hours, so
you get a total of .7 amps for 20 hours.

When the charge does start to get lower, your current peaks will be split
between the two batteries, so you should get less voltage drop (such as when
you transmit).

To do this, use a good low resistance connection between the batteries,
on both positive and negative terminals. You want the current to come from
both equally, so it would be best to connect your lead to the master to a
midpoint of that connection (as well as the lead to airframe ground).

Notes:

Safety: Some caution needed if connecting in the aircraft that the second
positive doesn't touch the airframe while not yet connected. For this reason,
connect both positives first, then both negatives; disconnect negative (ground)
first, then the positives. That way, a positive touching airframe metal won't
short things.

Charge the batteries together. Ideally, you can avoid the above safety note
and have the harness between them be permanent, so they charge as a pair, again
with lead lengths balanced.

Alan

[Jim White[_3_]]

If your batteries are dissimilarly discharged during flight (which is
possibly the reason you want to switch batteries) then the instantaneous
current flowing through your circuit when you join them could be quite high
and cause you more problems.

There are two better ways to solve this problem:

1) Insert a capacitor across the power as has been suggested. A further
enhancement would be a choke across the switch.

2) Power your loggers etc off a separate bus which is connected through a
rectifier bridge to both batteries. The logger will draw power from the
higher voltage battery and neither battery can charge the other. There will
be a voltage drop of between 0.5 and 1 volt but most loggers will work down
to 9v so no problem.

Jim

ps: avoid thermal trips if voltage loss is an issue.

[[email protected]]

I'm setting up a way to switch between each battery independently versus two or three batteries slaved together via the use of a simple circuit of diodes (rectifiers) and capacitors. The switches we all use are break before make so you don't want to lose power to instruments when switching between batteries. I found a suitable rotary mini-switch with up to 6 positions so you can do any combination of batteries you like (individually or slaved together). I realize the diodes cost about 0.15 volts on the output side so being able to get a little extra juice might be better but I also discovered that batteries last longer if you don't regularly deep discharge them. Since I have two main batteries in the baggage area plus one in the tail I figure my main scenario will be to slave the two mains together via diodes so theres no cross-charging and each draws down at half the rate. On a typical day they only get halfway drained and keep the tail battery as a fallback. I don't want to take the tail off to recharge the tail battery every day. This means I need a switch to go between Batt 1, Batt 2, Batt 1+2 and Batt 3. A position for Batt 1+2+3 is an option, but not super attractive if you wan an emergency reserve.

I've been using around 2500 micro farads of capacitor with a 1 ohm power resistor across the leads for several years. Works great.In v2 I'm upping the capacitance.

9B

On Tuesday, April 23, 2013 1:06:58 AM UTC-7, Jim White wrote:
> If your batteries are dissimilarly discharged during flight (which is
>
> possibly the reason you want to switch batteries) then the instantaneous
>
> current flowing through your circuit when you join them could be quite high
>
> and cause you more problems.
>
>
>
> There are two better ways to solve this problem:
>
>
>
> 1) Insert a capacitor across the power as has been suggested. A further
>
> enhancement would be a choke across the switch.
>
>
>
> 2) Power your loggers etc off a separate bus which is connected through a
>
> rectifier bridge to both batteries. The logger will draw power from the
>
> higher voltage battery and neither battery can charge the other. There will
>
> be a voltage drop of between 0.5 and 1 volt but most loggers will work down
>
> to 9v so no problem.
>
>
>
> Jim
>
>
>
> ps: avoid thermal trips if voltage loss is an issue.

[John Godfrey (QT)[_2_]]

On Tuesday, April 23, 2013 7:39:54 AM UTC-4, wrote:
> I'm setting up a way to switch between each battery independently versus two or three batteries slaved together via the use of a simple circuit of diodes (rectifiers) and capacitors. The switches we all use are break before make so you don't want to lose power to instruments when switching between batteries. I found a suitable rotary mini-switch with up to 6 positions so you can do any combination of batteries you like (individually or slaved together). I realize the diodes cost about 0.15 volts on the output side so being able to get a little extra juice might be better but I also discovered that batteries last longer if you don't regularly deep discharge them. Since I have two main batteries in the baggage area plus one in the tail I figure my main scenario will be to slave the two mains together via diodes so theres no cross-charging and each draws down at half the rate. On a typical day they only get halfway drained and keep the tail battery as a fallback. I don't want to take the tail off to recharge the tail battery every day.. This means I need a switch to go between Batt 1, Batt 2, Batt 1+2 and Batt 3. A position for Batt 1+2+3 is an option, but not super attractive if you wan an emergency reserve.
>
>
>
> I've been using around 2500 micro farads of capacitor with a 1 ohm power resistor across the leads for several years. Works great.In v2 I'm upping the capacitance.
>
>
>
> 9B
>
>
>
> On Tuesday, April 23, 2013 1:06:58 AM UTC-7, Jim White wrote:
>
> > If your batteries are dissimilarly discharged during flight (which is
>
> >
>
> > possibly the reason you want to switch batteries) then the instantaneous
>
> >
>
> > current flowing through your circuit when you join them could be quite high
>
> >
>
> > and cause you more problems.
>
> >
>
> >
>
> >
>
> > There are two better ways to solve this problem:
>
> >
>
> >
>
> >
>
> > 1) Insert a capacitor across the power as has been suggested. A further
>
> >
>
> > enhancement would be a choke across the switch.
>
> >
>
> >
>
> >
>
> > 2) Power your loggers etc off a separate bus which is connected through a
>
> >
>
> > rectifier bridge to both batteries. The logger will draw power from the
>
> >
>
> > higher voltage battery and neither battery can charge the other. There will
>
> >
>
> > be a voltage drop of between 0.5 and 1 volt but most loggers will work down
>
> >
>
> > to 9v so no problem.
>
> >
>
> >
>
> >
>
> > Jim
>
> >
>
> >
>
> >
>
> > ps: avoid thermal trips if voltage loss is an issue.

Using a single rotary switch to control all your power sources creates a single point of failure.
FWIW

[kirk.stant]

I guess I'm not as worried about switching batteries as you guys. I have 2 batteries powering 2 separate busses with the instruments split onto each bus about equally, with some consideration for redundancy: Bus 1 has SN10 and PFB/Oudie. Bus 2 has radio, backup vario, and Themi backup logger.

Each bus can be powered by either battery 1 or battery 2 (or turned off). With 8AH batteries I rarely run low on either battery (I recharge both each night, rotating 3 batteries through the system.

If one battery gets low, I can power all the panel off the other battery if needed. In that situation I would probably shut down unneeded systems.

Works fine so far (> 12 years since I put it in the glider).

Kirk
66

[JohnDeRosa]

On Apr 23, 6:39*am, wrote:

> via the use of a simple circuit of diodes (rectifiers)...I realize the diodes cost about 0.15 volts on the output side

A couple of points on the use of diodes.

1) For those that don't understand their use, diodes only allow
current to flow one direction (i.e. from the battery to your
electronics) sort of like your sump pump's check valve. If you
connect two batteries in parallel without diodes then one battery
could charge the other (I don't think this is as bad a thing as it is
made out to be). However, if you have a diode on each battery, then
each battery can still power your electronics but cannot charge each
other.

2) 9B mentions that the "diodes cost about 0.15 volts" (called the
forward voltage drop). But this all depends on the type of diode.
The most common silicon diodes have significantly higher voltage
drops. Take for example the Radio Shack 1N4001 "rectifier" diode
(276-1101) which is good for 1 amp. According to the Motorola spec
sheet (http://www.futurlec.com/Diodes/1N4001.shtml) the voltage drop
is between 0.93-1.1 volts! That is a lot of voltage to loose in our
glider's closed power systems and could cause older electronics to
drop out due to low voltage on long flights.

There are other technologies that can handle the current flow we need
and prevent cross-charging of the batteries. One is a pair of
Schottky diodes which have very low forward voltage (http://
en.wikipedia.org/wiki/Schottky_diode). Another interesting item is
the MOSFET "Ideal Diode" which basically has zero forward voltage drop
- see http://www.linear.com/product/LTC4358 - which is made for just
our situation and good to 5 amps!

FWIW - I run my batteries in parallel and have Bat A and Bat B
switches (both on all the time) and no diodes. No issues. YMMV.

My $0.02.

- John

[bumper[_4_]]

On Tuesday, April 23, 2013 1:06:58 AM UTC-7, Jim White wrote:
> If your batteries are dissimilarly discharged during flight (which is
>
> possibly the reason you want to switch batteries) then the instantaneous
>
> current flowing through your circuit when you join them could be quite high
>
> and cause you more problems.
>
>
> Jim
>

Jim,

I have often connected dissimilarly charged batteries with no ill effects. My ASH26E has a miniature 5 amp rated "shorting switch" to connect the avionic bat to the engine bat (both 18AH) for charging. No problems.

This is maybe due to the more deeply the battery is discharged, the higher it's initial internal resistance. That, and the fact that the voltage delta between evan a 50% discharged and a fully charged battery is not that great.

bumper

[BobW]

Snipped from another thread...

>> via the use of a simple circuit of diodes (rectifiers)...I realize the
>> diodes cost about 0.15 volts on the output side
>
> A couple of points on the use of diodes.
>
> 1) For those that don't understand their use, diodes only allow current to
> flow one direction (i.e. from the battery to your electronics) sort of like
> your sump pump's check valve. If you connect two batteries in parallel
> without diodes then one battery could charge the other (I don't think this
> is as bad a thing as it is made out to be).

The engineer in me - N.B. I am not an electrical engineer, nor have I ever
played one on TV - has long wondered about the validity of, but never bothered
to research, the widely held caution I'll state as: "Connect two batteries
together in parallel at your own risk because THE STRONGER WILL CHARGE THE
WEAKER!!!"

Being curious, but still too lazy to do real research on the matter, I'll ask
RAS readers instead. :-)

So what? If the starting place is nominally identically sized/charged dual
batteries (e.g. in a sailplane), why should the weaker battery care whether it
gets charging current from another battery or a regulated power supply? Why
should the stronger one care where it's sending its current?

As to the last question, I realize internal resistance of the "being charged"
battery matters, at least theoretically, but in the real world are the risks
(given the underlying starting assumptions) genuinely problematical...or
purely theoretical...or somewhere in-between?

Wouldn't two "nearly identical batteries" directly wired "otherwise
electrically sensibly" together in parallel pretty quickly self-equalize their
charges?

Hoping to receive more factually-based replies than "theoretically-based
handwaving" I am...just curious.

Bob W.

[[email protected]]

On Tuesday, April 23, 2013 4:45:50 AM UTC-7, John Godfrey (QT) wrote:

> Using a single rotary switch to control all your power sources creates a single point of failure.
>
> FWIW

Oh snap! Now I need two independent switches?!?

9B

[JJ Sinclair[_2_]]

Bob,
I did the 'test' the last time this came up on RAS. I hooked a fully charged battery (13v) to discharged battery (10v), in parallel and my multi-meter read
120 m/a as the fully charged battery started 'charging' the dead battery. 120m/a is nothing ,,,,,,,,,,, just over a tenth of an amp and that is only for the brief second that both batteries are connected to the buss as I switch from battery one to battery 2.
Can't we finally put this to rest?
JJ

[Bart[_4_]]

On Apr 24, 9:56*am, BobW > wrote:
> The engineer in me - N.B. I am not an electrical engineer, nor have I ever
> played one on TV - has long wondered about the validity of, but never bothered
> to research, the widely held caution I'll state as: "Connect two batteries
> together in parallel at your own risk because THE STRONGER WILL CHARGE THE
> WEAKER!!!"

Two (or more) batteries wired in parallel will basically act as a
single battery. Basically, the voltages will track, during both
charging and discharging. Moreover, types and capacities do NOT have
to be identical.

Now, if we have a common bus and separate switch for each battery, the
situation changes. The "the stronger will charge the weaker" scenario
occurs when you parallel two batteries at different states of
discharge. There are two things to worry about here: (a) wasting the
"stronger" battery charge and (b) current spike, potentially blowing
fuses, damaging wiring and switches.

Let's start with (b). I tested this scenario a year or so ago so my
memory is a bit fuzzy, but here is what I can recall. I had two 9 Ah
batteries, one fully charged and one discharged. I put a current clamp
on a wire, connected the clamp to a scope and flipped the switch.
Result - peak current of two amps or so, decaying *very* quickly. One
could not possibly see those two amps using a standard meter, which
probably explains JJ's results. Anyway, those two amps should not
damage anything.

Now, let's have a look at (a). For the sake of the discussion I am
going to assume that the "charging" current does not decay, but stays
at 2 A - basically, a worst-case scenario. Our pilot notices that his
first battery is dying and flips a switch, bringing a fresh battery
online. He then looks up, scans for traffic, maybe answers a radio
call. Ten seconds later he flips another switch, disconnecting the
first battery. How much of the "good" battery charge did he loose? Two
amps times ten seconds, or 0.002777 hours equals 0.00555 AH or 5.55
mAh. Really, nothing to worry about.

As I wrote, I tested it a while ago and do not remember all the
details. Should someone express interest, I can redo the experiment
and post the waveforms.

I do not understand where would the "voltage spike," mentioned earlier
in this thread, come from. Maybe if one had really long wires with a
bunch of distributed inductance...

Bart

[Tom Gardner[_2_]]

Bart wrote:
> On Apr 24, 9:56 am, BobW > wrote:
>> The engineer in me - N.B. I am not an electrical engineer, nor have I ever
>> played one on TV - has long wondered about the validity of, but never bothered
>> to research, the widely held caution I'll state as: "Connect two batteries
>> together in parallel at your own risk because THE STRONGER WILL CHARGE THE
>> WEAKER!!!"
>
> Two (or more) batteries wired in parallel will basically act as a
> single battery.

Maybe, maybe not, depending on what you mean by "act as a
single battery".


> Basically, the voltages will track, during both
> charging and discharging. Moreover, types and capacities do NOT have
> to be identical.

The voltages will indeed track, but that does not mean the currents,
temperatures, pressures, and chemical reactions will track. And
it is those aspects that cause concern.

No two cells in a battery are identical, and they each form a
link in a chain. And we know which link breaks.

Two batteries in parallel are like two chains in parallel.
I think you can see where the analogy is heading.


> Now, if we have a common bus and separate switch for each battery, the
> situation changes. The "the stronger will charge the weaker" scenario
> occurs when you parallel two batteries at different states of
> discharge.

Which will /always/ be the case, even with nominally identical
batteries.


> There are two things to worry about here: (a) wasting the
> "stronger" battery charge and (b) current spike, potentially blowing
> fuses, damaging wiring and switches.

"Spike" implies short duration; that may not be the case,
particularly when you consider "short compared with what".


> Let's start with (b). I tested this scenario a year or so ago so my
> memory is a bit fuzzy, but here is what I can recall. I had two 9 Ah
> batteries, one fully charged and one discharged. I put a current clamp
> on a wire, connected the clamp to a scope and flipped the switch.
> Result - peak current of two amps or so, decaying *very* quickly. One
> could not possibly see those two amps using a standard meter, which
> probably explains JJ's results. Anyway, those two amps should not
> damage anything.

It is unwise to base "good practice" on a "single anecdote"


> Now, let's have a look at (a). For the sake of the discussion I am
> going to assume that the "charging" current does not decay, but stays
> at 2 A - basically, a worst-case scenario.

Why do you presume 2A is worst case? Why not 4A or 8A etc? It
would be unwise to base a recommendation on a single test
under one set of conditions.


> Our pilot notices that his
> first battery is dying and flips a switch, bringing a fresh battery
> online. He then looks up, scans for traffic, maybe answers a radio
> call. Ten seconds later he flips another switch, disconnecting the
> first battery. How much of the "good" battery charge did he loose? Two
> amps times ten seconds, or 0.002777 hours equals 0.00555 AH or 5.55
> mAh. Really, nothing to worry about.

I agree such loss of charge is not a serious concern.
But there are other causes for concern.


> As I wrote, I tested it a while ago and do not remember all the
> details. Should someone express interest, I can redo the experiment
> and post the waveforms.

If you do, please state *all* the conditions of *all* the
equipment in the test -- which is not a trivial exercise
and will clarify the limitations of the test.


> I do not understand where would the "voltage spike," mentioned earlier
> in this thread, come from. Maybe if one had really long wires with a
> bunch of distributed inductance...

I'm not sure what that "voltage spike" was, but you can
indeed get "interesting" voltages associated with large/fast
current changes, due to a variety of mechanisms. Whether or
not those spikes are significant will depend on the protection
and margins built into the other equipment attached to the power
supply.

If you go against the battery manufacturers recommendations
and/or generally recognised "good practice", then if push
comes to shove, what would be the attitude of insurance
companies and courts of law?

[Evan Ludeman[_4_]]

On Wednesday, April 24, 2013 4:34:01 PM UTC-4, Bart wrote:
> On Apr 24, 9:56*am, BobW > wrote:
>
> > The engineer in me - N.B. I am not an electrical engineer, nor have I ever
>
> > played one on TV - has long wondered about the validity of, but never bothered
>
> > to research, the widely held caution I'll state as: "Connect two batteries
>
> > together in parallel at your own risk because THE STRONGER WILL CHARGE THE
>
> > WEAKER!!!"
>
>
>
> Two (or more) batteries wired in parallel will basically act as a
>
> single battery. Basically, the voltages will track, during both
>
> charging and discharging. Moreover, types and capacities do NOT have
>
> to be identical.
>
>
>
> Now, if we have a common bus and separate switch for each battery, the
>
> situation changes. The "the stronger will charge the weaker" scenario
>
> occurs when you parallel two batteries at different states of
>
> discharge. There are two things to worry about here: (a) wasting the
>
> "stronger" battery charge and (b) current spike, potentially blowing
>
> fuses, damaging wiring and switches.
>
>
>
> Let's start with (b). I tested this scenario a year or so ago so my
>
> memory is a bit fuzzy, but here is what I can recall. I had two 9 Ah
>
> batteries, one fully charged and one discharged. I put a current clamp
>
> on a wire, connected the clamp to a scope and flipped the switch.
>
> Result - peak current of two amps or so, decaying *very* quickly. One
>
> could not possibly see those two amps using a standard meter, which
>
> probably explains JJ's results. Anyway, those two amps should not
>
> damage anything.
>
>
>
> Now, let's have a look at (a). For the sake of the discussion I am
>
> going to assume that the "charging" current does not decay, but stays
>
> at 2 A - basically, a worst-case scenario. Our pilot notices that his
>
> first battery is dying and flips a switch, bringing a fresh battery
>
> online. He then looks up, scans for traffic, maybe answers a radio
>
> call. Ten seconds later he flips another switch, disconnecting the
>
> first battery. How much of the "good" battery charge did he loose? Two
>
> amps times ten seconds, or 0.002777 hours equals 0.00555 AH or 5.55
>
> mAh. Really, nothing to worry about.
>
>
>
> As I wrote, I tested it a while ago and do not remember all the
>
> details. Should someone express interest, I can redo the experiment
>
> and post the waveforms.
>
>
>
> I do not understand where would the "voltage spike," mentioned earlier
>
> in this thread, come from. Maybe if one had really long wires with a
>
> bunch of distributed inductance...
>
>
>
> Bart

It's perhaps worth mentioning that the LFP batteries becoming popular now have much lower internal resistance than SLA batteries. They also have a flatter voltage versus state of charge characteristic *but* if you connect in parallel an LFP battery than is fully discharged (< 10 V) with one at full charge (> 13.9 V) I wouldn't be a bit surprised to see blown fuses, and boy, that would suck on a long ridge/wave mission.

Diodes would be cheap insurance here. Agreed that they are overkill for SLA batteries.

T8

[Bart[_4_]]

On Apr 24, 2:04*pm, Tom Gardner > wrote:
> The voltages will indeed track, but that does not mean the currents,
> temperatures, pressures, and chemical reactions will track. And
> it is those aspects that cause concern.

"Currents, temperatures, pressures, and chemical reactions" will
almost certainly NOT track. We cannot even exclude the worst case,
which is all current being sourced by one battery, or - during
charging - going to just one battery. I would not assume that if, say,
one battery can be charged at 3A the two batteries in parallel can be
charged at 6A.

> No two cells in a battery are identical, and they each form a
> link in a chain. And we know which link breaks.
> Two batteries in parallel are like two chains in parallel.
> I think you can see where the analogy is heading.

Quite honestly, I am not sure. You may be suggesting that, should one
cell fail, we will have a 6-cell battery charging a 5-cell battery. Of
course, if a cell gets shorted, our hypothetical pilot is in trouble
anyway.

Or are you saying that connecting two batteries in parallel makes a
cell failure more likely? Please explain. One never stops learning.

> Why do you presume 2A is worst case? Why not 4A or 8A etc? It
> would be unwise to base a recommendation on a single test
> under one set of conditions.

I assume 2A because this is the maximum value I measured. Bob asked
for "factually-based replies" and I provided a single data point.

By the way, I was greatly surprised by the reading. I thought it would
be more.

> If you do, please state *all* the conditions of *all* the
> equipment in the test -- which is not a trivial exercise
> and will clarify the limitations of the test.

You seem to have certain conditions of certain parts of equipment in
mind. Please, do not keep me guessing. What is it that you would like
to know?

> If you go against the battery manufacturers recommendations and/or generally recognised "good practice"

I am not entirely sure if it is "against the battery manufacturers
recommendations" or a "generally recognised good practice". As a
matter of fact, even a quick google search reveals a lot of
information to the contrary. Can you have a look at the following
examples?

http://www.cdtechno.com/pdf/ref/41_7952_0112.pdf
http://www.batteryweb.com/manuals/techman.pdf
http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf


Now, there is one thing I would like to make clear: I make no
recommendations. Personally, if I was setting up my own glider with
multiple batteries, I would not connect them in parallel, for reasons
unrelated to anything discussed in this thread.

Bart

[Tom Gardner[_2_]]

Bart wrote:
> On Apr 24, 2:04 pm, Tom Gardner > wrote:
>> The voltages will indeed track, but that does not mean the currents,
>> temperatures, pressures, and chemical reactions will track. And
>> it is those aspects that cause concern.
>
> "Currents, temperatures, pressures, and chemical reactions" will
> almost certainly NOT track. We cannot even exclude the worst case,
> which is all current being sourced by one battery, or - during
> charging - going to just one battery. I would not assume that if, say,
> one battery can be charged at 3A the two batteries in parallel can be
> charged at 6A.

Precisely.


>> No two cells in a battery are identical, and they each form a
>> link in a chain. And we know which link breaks.
>> Two batteries in parallel are like two chains in parallel.
>> I think you can see where the analogy is heading.
>
> Quite honestly, I am not sure.

If you put two chains with a breaking strain of X in
parallel, the breaking strain isn't going to be 2X!
There will still be a single weakest link, that will
go first and then all the 2X strain will go onto the
remaining chain. The consequences will be predictable.


> You may be suggesting that, should one
> cell fail, we will have a 6-cell battery charging a 5-cell battery. Of
> course, if a cell gets shorted, our hypothetical pilot is in trouble
> anyway.

It would depend on the way in which the cell fails, and that
may well be dependent on the fundamental chemistry and
manufacturing details.

Even in a single battery, when one cell runs out of charge,
continuing to draw current from the other cells will "reverse
charge" the exhausted cell - and that's usually not good news.


> Or are you saying that connecting two batteries in parallel makes a
> cell failure more likely? Please explain. One never stops learning.

I suspect it might make it more likely, because
the currents are less constrained. But a manufacturer
may have designed and manufactured the batteries so
that there isn't a problem.


>> Why do you presume 2A is worst case? Why not 4A or 8A etc? It
>> would be unwise to base a recommendation on a single test
>> under one set of conditions.
>
> I assume 2A because this is the maximum value I measured. Bob asked
> for "factually-based replies" and I provided a single data point.
>
> By the way, I was greatly surprised by the reading. I thought it would
> be more.
>
>> If you do, please state *all* the conditions of *all* the
>> equipment in the test -- which is not a trivial exercise
>> and will clarify the limitations of the test.
>
> You seem to have certain conditions of certain parts of equipment in
> mind. Please, do not keep me guessing. What is it that you would like
> to know?

To start off...
Type of battery, how they've been treated during their life, wire
gauge and insulation, length of wire, to what extent it is coiled,
how it is supported and mounted, airflow, temperature, switch
characteristics, test equipment characteristics, etc etc etc.


>> If you go against the battery manufacturers recommendations and/or generally recognised "good practice"

That was a question, not a statement of my position.


> I am not entirely sure if it is "against the battery manufacturers
> recommendations" or a "generally recognised good practice". As a
> matter of fact, even a quick google search reveals a lot of
> information to the contrary. Can you have a look at the following
> examples?
>
> http://www.cdtechno.com/pdf/ref/41_7952_0112.pdf
> http://www.batteryweb.com/manuals/techman.pdf
> http://www.battcon.com/PapersFinal2002/McDowallPaper2002.pdf

With anything like this, the devil is in the details.
If the manufacturers of a particular battery say it is
OK to do X, then you are in a position that can be
defended. And that's important w.r.t. insurance claims
and courts of law.


> Now, there is one thing I would like to make clear: I make no
> recommendations. Personally, if I was setting up my own glider with
> multiple batteries, I would not connect them in parallel, for reasons
> unrelated to anything discussed in this thread.

Fair enough.

[GC[_2_]]

On 25/04/2013 07:04, Tom Gardner wrote:
> ...
> No two cells in a battery are identical, and they each form a
> link in a chain. And we know which link breaks.
>
> Two batteries in parallel are like two chains in parallel.
> I think you can see where the analogy is heading.

> ...
> It is unwise to base "good practice" on a "single anecdote"

> ...
> If you go against the battery manufacturers recommendations
> and/or generally recognised "good practice", then if push
> comes to shove, what would be the attitude of insurance
> companies and courts of law?

Boy! That was a good dose of FUD.

Here's a bunch of data points on paralleled batteries which might be
helpful. My DG-800 series glider is one of 400 or so which have been
built (and certified by the LBA and FAA) with 4 permanently fitted 6V
12AH SLA batteries screwed in under my legs. They are connected in
series and parallel to produce 12V 24AH of power - fed to the glider
through a single master switch. I've never heard of a battery based
problem with the 800's power supply. My glider was built in 1994 and I
bought it in 2005 with the original batteries still fitted. I replaced
them in 2008, mainly as a precaution.

Mind, it's a bloody big master switch and a serious battery fuse!

I'm with those who say: install the capacity you need using as many
cells as you need. Use all of them all the time.

GC

[Eric Greenwell[_4_]]

On 4/23/2013 5:44 AM, kirk.stant wrote:
> Each bus can be powered by either battery 1 or battery 2 (or turned
> off). With 8AH batteries I rarely run low on either battery (I
> recharge both each night, rotating 3 batteries through the system.

Why not just connect them in parallel and leave them that way? It would
be simpler.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Tom Gardner[_2_]]

GC wrote:
> On 25/04/2013 07:04, Tom Gardner wrote:
> Boy! That was a good dose of FUD.

Fear uncertainty and doubt? Certainly!
Good old FUD has preserved my health on several occasions unrelated to this topic!

And the "FUD" w.r.t. batteries has a definite foundation in reality. For example I
recently had to clean out a battery compartment (fortunately not in a glider) in
which an SLA's gel had come out of the battery; the cause was not apparent, either
to myself or to the technicians that dealt with those batteries on a daily basis.

Note that I never said it was categorically dangerous under all circumstances:
I always added the caveat about specific battery chemistry, construction,
(ab)usage, and manufacturers' recommendation.

[kirk.stant]

On Thursday, April 25, 2013 6:43:03 AM UTC+2, Eric Greenwell wrote:

> Why not just connect them in parallel and leave them that way? It would
>
> be simpler.

Honestly, it just evolved that way. Batteries are widely separated in the cockpit and wiring is a bit "odd" so it's what my partner and I came up with.

If I had to do it again, parallel seems to make more sense...;^)

Anyway, I've had no problems with it so far - so if it isn't broken...!

Cheers,

Kirk
66

[Vaughn]

On 4/25/2013 5:19 AM, Tom Gardner wrote:

> And the "FUD" w.r.t. batteries has a definite foundation in reality. For
> example I
> recently had to clean out a battery compartment (fortunately not in a
> glider) in
> which an SLA's gel had come out of the battery; the cause was not
> apparent, either
> to myself or to the technicians that dealt with those batteries on a
> daily basis.

None of which has anything obvious to do with battery switches or
paralleled batteries. I have had to do the same cleanup job to
countless UPSs and the cause was no mystery, although the manufacturers
were unlikely to make any incriminating admissions.

Why? Because cheap UPSs almost universally have crappy chargers built
into them that habitually overcharge the batteries. In my experience,
more SLA batteries are ruined by improper charging than any other single
cause.

[K]

On Saturday, April 20, 2013 2:22:49 PM UTC-6, K wrote:
> Just finished a panel upgrade on a Normal category (Not Experimental). One change made was to use PowerFlarm for GPS logging and glide computer. My master switch is a 3 position switch (Bat 1, Off, Batt 2). My old Volkslogger had no problem with swtching batteries as long as I flipped the switch fast, If I was slow it would reboot. Can I expect the same from the PF? I was thinking of wiring both batteries to one master or having two battery switches. I see no reason to use one battery at a time.
>
> I bought the ship recently and it has much of the original electrical wiring and hardware (looks straight out of a German Home Depot). I initially purchased factory replacement electrical parts but they are expensive and not of very high quality. I wish to switch to Mil-Spec or higher quality for the master switch(S). Any recommendations? Discussed this with my IA and he has no problem with non factory stuff as long as it is aircraft grade (Which my sentiment also).
>
> Thanks in advance.
>
> Kirk

Thanks for all the input and to those who sent private emails. I keep finding AC rated switches in the online catalogs. I have read that it is best to use DC switches but most of these tend to be of the automotive variety. I have found some aviation style master switches on AS&S, Is there a specific switch anyone would recommend?

[Tom Gardner[_2_]]

Vaughn wrote:
> On 4/25/2013 5:19 AM, Tom Gardner wrote:
>
>> And the "FUD" w.r.t. batteries has a definite foundation in reality. For
>> example I
>> recently had to clean out a battery compartment (fortunately not in a
>> glider) in
>> which an SLA's gel had come out of the battery; the cause was not
>> apparent, either
>> to myself or to the technicians that dealt with those batteries on a
>> daily basis.
>
> None of which has anything obvious to do with battery switches or paralleled batteries.

Strawman argument; I didn't claim that.

What it does illustrate is that batteries can have "interesting"
failure modes that the (hopefully professional) designers didn't
believe could happen. And that's particularly true in the field
as opposed to the relatively controlled conditions in the lab.

Now the people on this forum might be "gifted amateurs" that can
beat "professional designers" in this area. However, that's not
the way to bet, unless there is specific evidence to indicate it.

As I said, follow the manufacturer's recommendations as to
what is safe. Not my recommendations, not what anybody else
on this newsgroup says.


> I have had to do the same cleanup job to countless UPSs and the cause was no mystery, although the
> manufacturers were unlikely to make any incriminating admissions.
>
> Why? Because cheap UPSs almost universally have crappy chargers built into them that habitually overcharge the batteries. In my experience, more SLA batteries are ruined by improper charging than
> any other single cause.

I've no reason to doubt that. But it doesn't have any relevance
to crudely paralleled batteries.

[rk]

I had two parallel batteries years ago. On one flight, other battery suddenly died. It took less than 15 minutes to drain the other one completely flat. All the time I could just watch the voltage indication and plan my way back home using uncontrolled airspace. I use now simple selector switch to choose between 2 or 3 batteries. I run one empty and then switch to other one. Please never connect batteries parallel, it's just asking for trouble.

[Don Johnstone[_4_]]

At 14:16 25 April 2013, rk wrote:
>I had two parallel batteries years ago. On one flight, other battery
>sudden=
>ly died. It took less than 15 minutes to drain the other one completely
>fla=
>t. All the time I could just watch the voltage indication and plan my way
>b=
>ack home using uncontrolled airspace. I use now simple selector switch to
>c=
>hoose between 2 or 3 batteries. I run one empty and then switch to other
>on=
>e. Please never connect batteries parallel, it's just asking for trouble.
>

Absolutely, if you are not convinced ask yourself why aircraft
manufacturers go to the added expense of designing and fitting expensive
and complicated fuel crossfeeds. The simple solution would be to connect
all tanks so they all feed, the problem with this approach is that if one
tank has a leak it will drain the fuel from all the other tanks. Same thing
applies to batteries.

[Alan[_6_]]

In article > writes:

>What it does illustrate is that batteries can have "interesting"
>failure modes that the (hopefully professional) designers didn't
>believe could happen. And that's particularly true in the field
>as opposed to the relatively controlled conditions in the lab.
>
>Now the people on this forum might be "gifted amateurs" that can
>beat "professional designers" in this area. However, that's not
>the way to bet, unless there is specific evidence to indicate it.
>
>As I said, follow the manufacturer's recommendations as to
>what is safe. Not my recommendations, not what anybody else
>on this newsgroup says.

Power Sonic seems ok with it:

http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/1256780054_Connecting_in_Series_or_Parallel.pdf

Alan

[Tom Gardner[_2_]]

Alan wrote:
> In article > writes:
>
>> What it does illustrate is that batteries can have "interesting"
>> failure modes that the (hopefully professional) designers didn't
>> believe could happen. And that's particularly true in the field
>> as opposed to the relatively controlled conditions in the lab.
>>
>> Now the people on this forum might be "gifted amateurs" that can
>> beat "professional designers" in this area. However, that's not
>> the way to bet, unless there is specific evidence to indicate it.
>>
>> As I said, follow the manufacturer's recommendations as to
>> what is safe. Not my recommendations, not what anybody else
>> on this newsgroup says.
>
> Power Sonic seems ok with it:
>
> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/1256780054_Connecting_in_Series_or_Parallel.pdf

Fair enough.

However, it is worth keeping this class of experiences in mind:

Subject: Re: Master Switches
From: rk >
Injection-Date: Thu, 25 Apr 2013 14:16:43 +0000
I had two parallel batteries years ago. On one flight, other
battery suddenly died. It took less than 15 minutes to drain
the other one completely flat. All the time I could just watch
the voltage indication and plan my way back home using uncontrolled
airspace. I use now simple selector switch to choose between
2 or 3 batteries. I run one empty and then switch to other one.
Please never connect batteries parallel, it's just asking for trouble.

I wonder how much energy was dissipated, and where, and consequently
whether any temperature rises were noticed.

[Bart[_4_]]

On Apr 24, 4:51*pm, Tom Gardner > wrote:
> If you put two chains with a breaking strain of X in
> parallel, the breaking strain isn't going to be 2X!

This is debatable. But I see your point. I am also going to argue that
it is not relevant for a glider pilot.

We do not consider running batteries in parallel to get more power out
of them. We want more capacity, that's it. We are typically drawing
currents that can easily be supplied by a single battery. It's just
that we want it to run for, say, six hours instead of three.

Back to your chain analogy. We have two chains with a breaking strain
of X each. Someone put them in parallel. That someone did not know
what he was doing and, due to tiny difference in length of the two
chains, just one chain carries all the load. Fortunately, the load is
still less than X and our chain combination happily carries it. Should
the first chain fail for whatever reason (fatigue? Manufacturing
defect?), the other one will take over with no problems. It's a bit
like a primary/reserve Tost weak link combination.

> I suspect it might make it more likely, because
> the currents are less constrained. But a manufacturer
> may have designed and manufactured the batteries so
> that there isn't a problem.

I have to ask: do you have anything more than a "suspicion"?

> To start off...
> Type of battery, how they've been treated during their life,

This information I do not have. Should I re-run the experiment, I will
be sure to record it for you.

> wire gauge

Probably something between 12 and 16.

> and insulation,

PVC. But, you have my full and undivided attention here. Pray tell,
how is it relevant?

> length of wire, to what extent it is coiled,

Some 10 inches total, no coiling.

> how it is supported and mounted,

Self-supported.

> airflow,

No forced airflow.

> temperature,

Room temperature.

> switch characteristics,

Actually, the "switch" was just a Faston connector I put on the
terminal.

> test equipment characteristics,

I would be happy to provide the relevant characteristics if you
indicated what exactly it is that you wanted to know. You did not. So,
here are the models - look it up yourself.
Scope: LeCroy WaveRunner 6050. Current clamp: Fluke 80i-110s.

> etc etc etc.

Here we go again...

> >> If you go against the battery manufacturers recommendations and/or generally recognised "good practice"
> That was a question, not a statement of my position.

Looked a lot as an implied statement of a position. But I have
misunderstood things before. ESL.

So, to clarify things: are you or are you not claiming that it is
"generally recognised good practice" not to run batteries in parallel?
Are you aware of any manufacturers that prohibit or recommend against
connecting their batteries in parallel?

> With anything like this, the devil is in the details.
> If the manufacturers of a particular battery say it is
> OK to do X, then you are in a position that can be
> defended. And that's important w.r.t. insurance claims
> and courts of law.

Yeah, no. Should a manufacturer expressly forbid paralleling their
batteries for whatever reason, I would not do it. I would probably not
buy from them at all. But absence of recommendation is not a
prohibition. I do not seek manufacturer's approval to parallel
resistors, diodes or FETs. You either know how to do it, or you do
not.
Oh, and try finding a battery manufacturer that says it is OK to use
their products in a glider.

Bart

[Tom Gardner[_2_]]

Bart wrote:
> On Apr 24, 4:51 pm, Tom Gardner > wrote:
>> If you put two chains with a breaking strain of X in
>> parallel, the breaking strain isn't going to be 2X!
>
> This is debatable. But I see your point. I am also going to argue that
> it is not relevant for a glider pilot.

Analogies are always dangerous! You are analysing the analogy
in more depth than can be justified.


>> I suspect it might make it more likely, because
>> the currents are less constrained. But a manufacturer
>> may have designed and manufactured the batteries so
>> that there isn't a problem.
>
> I have to ask: do you have anything more than a "suspicion"?

Yes and no.

Yes... A few decades ago I designed rechargeable
batteries into equipment, and the manufacturer and
general engineering lore said it was A Bad Idea.

No... I have not looked in detail at modern SLAs.

And that is the reason I have always added caveats
about specific chemistries and manufacturers.


>>>> If you go against the battery manufacturers recommendations and/or generally recognised "good practice"
>> That was a question, not a statement of my position.
>
> Looked a lot as an implied statement of a position. But I have
> misunderstood things before. ESL.
>
> So, to clarify things: are you or are you not claiming that it is
> "generally recognised good practice" not to run batteries in parallel?
> Are you aware of any manufacturers that prohibit or recommend against
> connecting their batteries in parallel?

I have not made any claims in that area for SLA batteries.
All I'm saying is "It is generally recognised that Here There
Be Dragons", and giving a few pointers to why it would be
prudent to investigate and understand the topic thoroughly
before making claims.

OTOH, *you* are the one making specific claims which it
would be prudent to be able to justify, e.g. your post starting
Two (or more) batteries wired in parallel will basically act as a
single battery. Basically, the voltages will track, during both
charging and discharging. Moreover, types and capacities do NOT have
to be identical.


>> With anything like this, the devil is in the details.
>> If the manufacturers of a particular battery say it is
>> OK to do X, then you are in a position that can be
>> defended. And that's important w.r.t. insurance claims
>> and courts of law.
>
> Yeah, no. Should a manufacturer expressly forbid paralleling their
> batteries for whatever reason, I would not do it. I would probably not
> buy from them at all. But absence of recommendation is not a
> prohibition.

Actually often the *effect* is exactly that of a prohibition!
I spent too much of my life understanding what data sheets,
patents, application notes, and fundamental theory did *not*
say. Why? Because understanding the limits of what they weren't
saying often illuminated the limitations of how a component
will behave in a system.

In practice, if you put a battery in a system and the system
behaves in such a way that the battery is operated outside
the envelope specified by the manufacturer, then the
manufacturer is perfectly justified in saying "Pfft; I told
you not to do that. Go away and shutup".

Hence it is prudent to understand components' and systems'
normal operating modes and failure modes. The latter don't
seem to be well described in most components' data sheets.



> I do not seek manufacturer's approval to parallel
> resistors, diodes or FETs. You either know how to do it, or you do
> not.

And, of course, some people think they know when actually they
do not! We've all come across such dangerous people.


> Oh, and try finding a battery manufacturer that says it is OK to use
> their products in a glider.

That's a red herring, of course.

[Alan[_6_]]

In article > writes:
>Alan wrote:

>> Power Sonic seems ok with it:
>>
>> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/1256780054_Connecting_in_Series_or_Parallel.pdf
>
>Fair enough.
>
>However, it is worth keeping this class of experiences in mind:
>
> Subject: Re: Master Switches
> From: rk >
> Injection-Date: Thu, 25 Apr 2013 14:16:43 +0000
> I had two parallel batteries years ago. On one flight, other
> battery suddenly died. It took less than 15 minutes to drain
> the other one completely flat. All the time I could just watch
> the voltage indication and plan my way back home using uncontrolled
> airspace. I use now simple selector switch to choose between
> 2 or 3 batteries. I run one empty and then switch to other one.
> Please never connect batteries parallel, it's just asking for trouble.

Were the batteries used parallel from the time they were new?

Don't forget the class of experiences where no trouble was encountered.

>I wonder how much energy was dissipated, and where, and consequently
>whether any temperature rises were noticed.

Years ago, those batteries common in gliders were 6 AH. The discharge
curve plots available from providers show that it would take about 10
amps to discharge one from full charge in 15 minutes. ( Less if it was
already partly discharged. ) 10 amps at 11 - 12 volts would give 110 -
120 watts.

If this really worries you, run a matched pair of power leads from the
batteries to a pair of master switches, and turn them both on, then turn
off the failing one if it ever fails. You need to be careful to balance
the drain, but you can get the lower current draw for more capacity from
the battery.

If you don't like using two batteries in parallel, you could simply buy
a larger battery. The Power Sonic 12140 gives 14 AH capacity ( the same
as two of the 7 AH batteries that are in common use ) and shouldn't scare
you as much.

Alan

[GC[_2_]]

Tom, advice so wrapped in caveats that it's never wrong is also usually
useless. You sound like a product liability disclaimer. Are you a lawyer?

I'll still quote the example of the DG-800 which leaves the factory with
4 cells wired in series/parallel providing power through a single master
switch. The batteries are in the extreme nose for CG reasons and the
space limitations there are probably why a single large one wasn't used.
The LBA (EASA) and the FAA certify it that way and the battery system
is certainly one of the least troublesome systems on those aircraft. It
would be great if the alternator were as reliable.

I think most of your qualms are at the nit-picking level and I'd be
perfectly happy to use parallel SLA batteries in a glider - if I
couldn't use one big one. I'd wire each to be switchable individually
and use them all together until something went wrong. I'd also charge
them together. I wouldn't go looking for the data sheets and I wouldn't
be too worried if I couldn't sue anyone. ...And I'd read all I could
find on r.a.s.

Cheers,
GC

On 26/04/2013 10:36, Tom Gardner wrote:
......

[rk]

On Friday, April 26, 2013 10:27:20 AM UTC+3, Alan wrote:
> In article > writes:
>
> >Alan wrote:
>
>
>
> >> Power Sonic seems ok with it:
>
> >>
>
> >> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/1256780054_Connecting_in_Series_or_Parallel.pdf
>
> >
>
> >Fair enough.
>
> >
>
> >However, it is worth keeping this class of experiences in mind:
>
> >
>
> > Subject: Re: Master Switches
>
> > From: rk
>
> > Injection-Date: Thu, 25 Apr 2013 14:16:43 +0000
>
> > I had two parallel batteries years ago. On one flight, other
>
> > battery suddenly died. It took less than 15 minutes to drain
>
> > the other one completely flat. All the time I could just watch
>
> > the voltage indication and plan my way back home using uncontrolled
>
> > airspace. I use now simple selector switch to choose between
>
> > 2 or 3 batteries. I run one empty and then switch to other one.
>
> > Please never connect batteries parallel, it's just asking for trouble..
>
>
>
> Were the batteries used parallel from the time they were new?
>
>
>
> Don't forget the class of experiences where no trouble was encountered.
>
>
>
> >I wonder how much energy was dissipated, and where, and consequently
>
> >whether any temperature rises were noticed.
>
>
>
> Years ago, those batteries common in gliders were 6 AH. The discharge
>
> curve plots available from providers show that it would take about 10
>
> amps to discharge one from full charge in 15 minutes. ( Less if it was
>
> already partly discharged. ) 10 amps at 11 - 12 volts would give 110 -
>
> 120 watts.
>
>
>
> If this really worries you, run a matched pair of power leads from the
>
> batteries to a pair of master switches, and turn them both on, then turn
>
> off the failing one if it ever fails. You need to be careful to balance
>
> the drain, but you can get the lower current draw for more capacity from
>
> the battery.
>
>
>
> If you don't like using two batteries in parallel, you could simply buy
>
> a larger battery. The Power Sonic 12140 gives 14 AH capacity ( the same
>
> as two of the 7 AH batteries that are in common use ) and shouldn't scare
>
> you as much.
>
>
>
> Alan

Yes batteries were used as parallel since new. I doubt that there wasn't any big currents, as my 5 amp battery fuses were not blown.

The most important point with this experience, at least for me, was that using one battery at a time, and using it until empty, gets you a pretty good idea about the condition of individual batteries during flying season. One year they go for 6-7 hrs until flat, other year 4-5 hrs -> time for a new battery. And all this before batteries lose all capacity.

In my case quoted earlier, the other battery was probably close to dead before flight, and drained the better battery slowly during the flight. When the bad battery died, good one was probably close to empty. All this happened without any indication. You just get one low voltage warning and 15 min later you are done.

Let me repeat: there is no good reason for parallel connection, do not use it.

[Tom Gardner[_2_]]

GC wrote:
> Tom, advice so wrapped in caveats that it's never wrong is also usually useless.

But safer than advice which omits to mention the envelope outside which
the advice is invalid.

My "advice" has been to tread carefully and RTFM.


> You sound like a product liability disclaimer. Are you a lawyer?

Well spotted, but nope :)

I'm a chartered electronic and software engineer. It has several times
struck me that there are significant similarities between some aspects
of the two professions!

Old electronics aphorism: there are lies, damned lies, statistics,
and adc/dac/rf data sheets. (The latter omit _many_ things which
do _significantly_ affect their operation)

Old software learning experience: "I said 'I wouldn't give you a
cheese sandwich before you gave me £100'. I didn't say anything
about what I would do after you gave £100. So, no cheese :)".
(Anybody that has used software developed by another company
will be aware of that kind of phenomenon).

And then there's technical patents. 'Nuff said.


> I'll still quote the example of the DG-800 which leaves the factory with 4 cells wired in series/parallel providing power through a single master switch. The batteries are in the extreme nose for CG
> reasons and the space limitations there are probably why a single large one wasn't used. The LBA (EASA) and the FAA certify it that way and the battery system is certainly one of the least
> troublesome systems on those aircraft. It would be great if the alternator were as reliable.

As I said, if TFM says it is OK, then fine!

Other people can and have quoted anecdotes to the contrary.


> I think most of your qualms are at the nit-picking level and I'd be perfectly happy to use parallel SLA batteries in a glider - if I couldn't use one big one. I'd wire each to be switchable
> individually and use them all together until something went wrong. I'd also charge them together. I wouldn't go looking for the data sheets and I wouldn't be too worried if I couldn't sue anyone.
> ...And I'd read all I could find on r.a.s.

There certainly /are/ reasons for caution, and there are multiple
ways to avoid possible problems. If there are easy ways to avoid
possible problems then it is worth avoiding those possible problems.

W.r.t. suing: I'd be more concerned about someone sueing me if
there was an accident and an ambulance chaser got wind of it.

Ignorance is not always bliss.

[Tom Gardner[_2_]]

rk wrote:

> Let me repeat: there is no good reason for parallel connection, do not use it.

Precisely.

I haven't yet seen anybody articulate any significant advantages of
direct parallel connection, let alone why they overwhelm the
disadvantages.

[[email protected]]

On Friday, April 26, 2013 9:09:48 AM UTC-5, Tom Gardner wrote:
> rk wrote:
>
>
>
> > Let me repeat: there is no good reason for parallel connection, do not use it.
>
>
>
> Precisely.
>
>
>
> I haven't yet seen anybody articulate any significant advantages of
>
> direct parallel connection, let alone why they overwhelm the
>
> disadvantages.

Tom, let me be the first to 'articulate significant advantages of parallel':
http://www.amazon.com/dp/B005KLOYO2/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1
http://www.amazon.com/BALLISTIC-PERFORMANCE-LITHIUM-EVO2-MOTORCYCLE/dp/B005KLOYYC/ref=pd_sim_auto_1
These are both Lifepo4 batteries that would be well suited for glider usage.. Note that the higher capacity battery has 8 cells but still 13.2V nominal voltage. Obviously, inside are two of the first kind batteries connected in parallel. This has to do with the standard cell (3.3V, 7,000mah) they are using, makes sense to me.

Herb

[Evan Ludeman[_4_]]

On Friday, April 26, 2013 11:28:31 AM UTC-4, wrote:
> On Friday, April 26, 2013 9:09:48 AM UTC-5, Tom Gardner wrote:
>
> > rk wrote:
>
> >
>
> >
>
> >
>
> > > Let me repeat: there is no good reason for parallel connection, do not use it.
>
> >
>
> >
>
> >
>
> > Precisely.
>
> >
>
> >
>
> >
>
> > I haven't yet seen anybody articulate any significant advantages of
>
> >
>
> > direct parallel connection, let alone why they overwhelm the
>
> >
>
> > disadvantages.
>
>
>
> Tom, let me be the first to 'articulate significant advantages of parallel':
>
> http://www.amazon.com/dp/B005KLOYO2/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1
>
> http://www.amazon.com/BALLISTIC-PERFORMANCE-LITHIUM-EVO2-MOTORCYCLE/dp/B005KLOYYC/ref=pd_sim_auto_1
>
> These are both Lifepo4 batteries that would be well suited for glider usage. Note that the higher capacity battery has 8 cells but still 13.2V nominal voltage. Obviously, inside are two of the first kind batteries connected in parallel. This has to do with the standard cell (3.3V, 7,000mah) they are using, makes sense to me.
>
>
>
> Herb

Herb: No! Much better off with a battery pack that includes current limiting protection. These are starting batteries. There are several good looking 9 - 12 AH LFP battery packs available now that include in-the-pack battery management. Over charge protection, under charge protection, cell balancing and over current protection (all somewhere between "really good ideas" and "essential" for safe LFP use). It remains to be seen how well these systems work over the long haul. Technology is still a little young to say for certain imo. Vendors include K2, Bioenno, Starck. If you choose to go any of these routes, get the spec sheets, ask questions, do some diligence..

best,

Evan Ludeman / T8

[Tom Gardner[_2_]]

wrote:
> On Friday, April 26, 2013 9:09:48 AM UTC-5, Tom Gardner wrote:
>> rk wrote:
>>
>>
>>
>>> Let me repeat: there is no good reason for parallel connection, do not use it.
>>
>>
>>
>> Precisely.
>>
>>
>>
>> I haven't yet seen anybody articulate any significant advantages of
>>
>> direct parallel connection, let alone why they overwhelm the
>>
>> disadvantages.
>
> Tom, let me be the first to 'articulate significant advantages of parallel':
> http://www.amazon.com/dp/B005KLOYO2/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1
> http://www.amazon.com/BALLISTIC-PERFORMANCE-LITHIUM-EVO2-MOTORCYCLE/dp/B005KLOYYC/ref=pd_sim_auto_1
> These are both Lifepo4 batteries that would be well suited for glider usage. Note that the higher capacity battery has 8 cells but still 13.2V nominal voltage. Obviously, inside are two of the first kind batteries connected in parallel. This has to do with the standard cell (3.3V, 7,000mah) they are using, makes sense to me.

It appears that, with that specific chemistry, design, and
manufacturer, parallel operation is possible. Presumably the
manufacturer did RTFM, so that's fine!

But, what is the *significant* *advantage* of such direct parallel
connection over indirect parallel connection?

Whether or not they are suitable for glider operation I don't
know since I haven't seen any assessment of the technology.

[Bart[_4_]]

On Apr 25, 5:36*pm, Tom Gardner > wrote:
> Analogies are always dangerous! You are analysing the analogy
> in more depth than can be justified.

I have to agree that the chain analogy is not particularly applicable
to the subject at hand. I would also like to point out that it is not
my analogy.

> Yes... A few decades ago I designed rechargeable
> batteries

Out of curiosity. Were they NiCd/NiMH batteries, by any chance?

> into equipment, and the manufacturer and
> general engineering lore said it was A Bad Idea.

If they were lead-acid, I would really appreciate more data. Both
about the manufacturer and the source of the "engineering lore." Even
if it is "guy in the next cubicle said so." I like learning new
things.

> > So, to clarify things: are you or are you not claiming that it is
> > "generally recognised good practice" [....]
> I have not made any claims in that area for SLA batteries.
> All I'm saying is "It is generally recognised that Here There
> Be Dragons",

"...generally recognised good practice..."
"It is generally recognised..."
"...general engineering lore..."

> OTOH, *you* are the one making specific claims which it
> would be prudent to be able to justify, e.g. your post starting
> * *Two (or more) batteries wired in parallel will basically act as a
> * *single battery. Basically, the voltages will track, during both
> * *charging and discharging. Moreover, types and capacities do NOT have
> * *to be identical.

This was an answer to a specific question. Also, I happen to stand by
*this* claim. If someone happens to read from it more than I actually
wrote - well, I can't help it.

In particular, I did not state that the current rating of this
combination will be a sum of individual ratings, either during
charging or discharging. I also did not recommend such a connection or
stated that it offers any advantages compared to alternatives. As a
matter of fact, I can think of reasons *not* to connect batteries in
parallel, but they have nothing to do with the question I was
answering.

> > But absence of recommendation is not a prohibition.
> Actually often the *effect* is exactly that of a prohibition!
> > Oh, and try finding a battery manufacturer that says it is OK to use
> > their products in a glider.
> That's a red herring, of course.

Reductio ad absurdum. Quotes above rearranged to make it obvious.

Bart

[Alan[_6_]]

In article > writes:
>rk wrote:
>
>> Let me repeat: there is no good reason for parallel connection, do not use it.
>
>Precisely.
>
>I haven't yet seen anybody articulate any significant advantages of
>direct parallel connection, let alone why they overwhelm the
>disadvantages.


Perhaps you didn't read my posting >, where
I articulated the 25% greater capacity obtained by the slower discharge rate.

I recall that folks wanted longer operating time from their batteries for
cross-country or contest flights. 25 percent more seems worthwhile.

Alan

[Jim[_31_]]

On Thursday, April 25, 2013 12:43:03 AM UTC-4, Eric Greenwell wrote:
> On 4/23/2013 5:44 AM, kirk.stant wrote:
>
> > Each bus can be powered by either battery 1 or battery 2 (or turned
>
> > off). With 8AH batteries I rarely run low on either battery (I
>
> > recharge both each night, rotating 3 batteries through the system.
>
>
>
> Why not just connect them in parallel and leave them that way? It would
>
> be simpler.
>
>
>
> --
>
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
>
> email me)

Me? I would just buy good automotive ones. These are gliders not space ships. Real glider pilots don't need no stinkin electronics anyway!

-PC

[Dan Marotta]

From the web page:

These batteries are manufactured for Motorcycles, ATVs and Jet-Skis, any
other manner of use voids the warranty.

Some people care about warranties...


> wrote in message
...
On Friday, April 26, 2013 9:09:48 AM UTC-5, Tom Gardner wrote:
> rk wrote:
>
>
>
> > Let me repeat: there is no good reason for parallel connection, do not
> > use it.
>
>
>
> Precisely.
>
>
>
> I haven't yet seen anybody articulate any significant advantages of
>
> direct parallel connection, let alone why they overwhelm the
>
> disadvantages.

Tom, let me be the first to 'articulate significant advantages of parallel':
http://www.amazon.com/dp/B005KLOYO2/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1
http://www.amazon.com/BALLISTIC-PERFORMANCE-LITHIUM-EVO2-MOTORCYCLE/dp/B005KLOYYC/ref=pd_sim_auto_1
These are both Lifepo4 batteries that would be well suited for glider usage.
Note that the higher capacity battery has 8 cells but still 13.2V nominal
voltage. Obviously, inside are two of the first kind batteries connected in
parallel. This has to do with the standard cell (3.3V, 7,000mah) they are
using, makes sense to me.

Herb

[Tom Gardner[_2_]]

Bart wrote:
> On Apr 25, 5:36 pm, Tom Gardner > wrote:
>> Analogies are always dangerous! You are analysing the analogy
>> in more depth than can be justified.
>
> I have to agree that the chain analogy is not particularly applicable
> to the subject at hand. I would also like to point out that it is not
> my analogy.
>
>> Yes... A few decades ago I designed rechargeable
>> batteries
>
> Out of curiosity. Were they NiCd/NiMH batteries, by any chance?

NiCd. Hence my caveats about the chemistry.

>> OTOH, *you* are the one making specific claims which it
>> would be prudent to be able to justify, e.g. your post starting
>> Two (or more) batteries wired in parallel will basically act as a
>> single battery. Basically, the voltages will track, during both
>> charging and discharging. Moreover, types and capacities do NOT have
>> to be identical.
>
> This was an answer to a specific question. Also, I happen to stand by
> *this* claim. If someone happens to read from it more than I actually
> wrote - well, I can't help it.
>
> In particular, I did not state that the current rating of this
> combination will be a sum of individual ratings, either during
> charging or discharging. I also did not recommend such a connection or
> stated that it offers any advantages compared to alternatives. As a
> matter of fact, I can think of reasons *not* to connect batteries in
> parallel, but they have nothing to do with the question I was
> answering.

Fair enough. It sounds like we probably agree with each other.

[Eric Greenwell[_4_]]

On 4/25/2013 3:13 PM, Tom Gardner wrote:
> Alan wrote:

>>
>> Power Sonic seems ok with it:
>>
>> http://www.power-sonic.com/images/powersonic/literature/SLA_Batteries/1256780054_Connecting_in_Series_or_Parallel.pdf
>>
>
> Fair enough.
>
> However, it is worth keeping this class of experiences in mind:
>
> Subject: Re: Master Switches
> From: rk >
> Injection-Date: Thu, 25 Apr 2013 14:16:43 +0000
> I had two parallel batteries years ago. On one flight, other
> battery suddenly died. It took less than 15 minutes to drain
> the other one completely flat. All the time I could just watch
> the voltage indication and plan my way back home using uncontrolled
> airspace. I use now simple selector switch to choose between
> 2 or 3 batteries. I run one empty and then switch to other one.
> Please never connect batteries parallel, it's just asking for trouble.
>
> I wonder how much energy was dissipated, and where, and consequently
> whether any temperature rises were noticed.

I don't see what we learn from that experience, without any indication
of what happened. You can always protect against any particular
situation, but the solution might add other ways for things to go bad.
Maybe you forget to charge both batteries, the extra wiring isn't done
well and shorts out, and so on.

If you read the SLA datasheets and technical manuals, you'll see
paralleling isn't a problem. As one poster pointed out, many hundreds of
DG 400 and 800 motorgliders were manufactured (and still are, I believe)
with four 6 volt SLA batteries in series-parallel configuration, so it's
a common glider technique.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Eric Greenwell[_4_]]

On 4/25/2013 11:56 AM, Don Johnstone wrote:
>> Please never connect batteries parallel, it's just asking for trouble.
>> >
> Absolutely, if you are not convinced ask yourself why aircraft
> manufacturers go to the added expense of designing and fitting expensive
> and complicated fuel crossfeeds. The simple solution would be to connect
> all tanks so they all feed, the problem with this approach is that if one
> tank has a leak it will drain the fuel from all the other tanks. Same thing
> applies to batteries.

The two tank solution solves one problem and introduces at least one
other: many pilots have mismanaged the switching between tanks, causing
big problems they would not have had with a single tank.

Losing instrument battery power isn't nearly as dangerous as running out
of fuel. My preference is to install a single battery that can easily
operate the glider for at least two very long flights; second choice is
paralleling two identical batteries to obtain that duration.

I have considered my options for a dead battery in flight. Because it is
such a rare occurrence for me - never in 35 years of soaring - I'm only
concerned with how it would affect my safety, and not convenience or
running a flight recorder (eg, during a contest or record attempt):

* Where I normally fly (Pacific NW), I'll land at an airport.
* At more challenging areas I fly at infrequently, like out of Ely, I
carry a handheld GPS, or soon, use something like the ClearNav vario
with a primary battery good for an hour or two, so I can actually find
that airport to land on.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

[Eric Greenwell[_4_]]

On 4/26/2013 8:38 AM, Evan Ludeman wrote:
> On Friday, April 26, 2013 11:28:31 AM UTC-4,

>>
>> http://www.amazon.com/dp/B005KLOYO2/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1
>>
>>
>>
http://www.amazon.com/BALLISTIC-PERFORMANCE-LITHIUM-EVO2-MOTORCYCLE/dp/B005KLOYYC/ref=pd_sim_auto_1
>>
>> These are both Lifepo4 batteries that would be well suited for
>> glider usage. Note that the higher capacity battery has 8 cells
>> but still 13.2V nominal voltage. Obviously, inside are two of the
>> first kind batteries connected in parallel. This has to do with
>> the standard cell (3.3V, 7,000mah) they are using, makes sense to
>> me.
>>
>>
>>
>> Herb
>
> Herb: No! Much better off with a battery pack that includes current
> limiting protection. These are starting batteries. There are
> several good looking 9 - 12 AH LFP battery packs available now that
> include in-the-pack battery management. Over charge protection,
> under charge protection, cell balancing and over current protection
> (all somewhere between "really good ideas" and "essential" for safe
> LFP use). It remains to be seen how well these systems work over the
> long haul. Technology is still a little young to say for certain
> imo. Vendors include K2, Bioenno, Starck. If you choose to go any
> of these routes, get the spec sheets, ask questions, do some
> diligence.

I agree with Evan: these are totally unsuited for glider use. In
addition to the concerns he noted, also note that this particular 4-cell
unit has only 2.3 Amp hours! Beware of Li batteries offered for
"powersports" use: they often are rated by _equivalent_ lead-acid
numbers batteries, but they are ration only the cranking amps ability,
no the actual low current amp hour capacity.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

[Eric Greenwell[_4_]]

On 4/26/2013 7:09 AM, Tom Gardner wrote:
> rk wrote:
>
>> Let me repeat: there is no good reason for parallel connection, do not
>> use it.
>
> Precisely.
>
> I haven't yet seen anybody articulate any significant advantages of
> direct parallel connection, let alone why they overwhelm the
> disadvantages.

I parallel the two 12 volt, 18 AH batteries in my ASH 26 E. The
advantages for me:

* Triple the effective starting capacity of a single battery, especially
useful in cold conditions.
* Simplicity when charging, whether by solar on the trailer or at the
tiedowns, with an AC charger, or a DC/DC charger.
* Wiring simplicity - just two 8" cables from the front battery to the
rear battery.
* Simplicity when using: glance at the volt meter ocasionally.

I've been doing this for 12 years, and haven't had any reason to change.

There are other methods used by ASH 26 E pilots that keep the batteries
separate: one for the engine starter, charged by the alternator; one for
the instruments, charged by the on-board solar panels. I think most of
these can switch the instruments to use the engine battery, but not the
reverse.

Disadvantages: the only one that is significant to me is the potential
to inadvertently leave an instrument (such as the radio) AND the master
switch on. The trailer/tiedown solar panel charging overcomes that drain
easily.

I do capacity tests on the batteries once a year, and replace them as
needed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

[Eric Greenwell[_4_]]

On 4/27/2013 3:42 PM, Eric Greenwell wrote:

> I agree with Evan: these are totally unsuited for glider use. In
> addition to the concerns he noted, also note that this particular 4-cell
> unit has only 2.3 Amp hours! Beware of Li batteries offered for
> "powersports" use: they often are rated by _equivalent_ lead-acid
> numbers batteries, but they are ration only the cranking amps ability,
> no the actual low current amp hour capacity.

That should be "they are _rating_ only the..."

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)