Multiple Battery Setup

The 'split services' approach is much better than running
everything off 1 battery, and then switching to another. The
standard 7AH gel cell is rated at the 20hour discharge current -
about 300mA. Any higher current and the total energy available
decreases. (and that 7AH is a new battery at room temperature,
not a 2 year old one freezing at 18,000ft).

If you have room, paralleling batteries works well, so long as
you have another independent battery to run essential services
if the main one drops below 11V (for me vario/flight director
only, and radio when 5 minutes out on final glide).

At 16:27 05 February 2012, kirk.stant wrote:
On Feb 5, 7:43=A0am, rk wrote:
On 3 helmi, 18:10, JohnDeRosa wrote:

At the panel I use three switches to run the batteries in
parallel.
Battery 1 on/off, battery 2 on/off and then the output of
both to a
master switch and then to the avionics. =A0The thinking of
separate
battery switches is that you can disconnect a "bad"
battery. =A0I
alway=
s
have all three switches turned on during flight - the need
to be able
to turn off a bad battery hasn't arisen for me and I am
unsure how I
would even know (everything dies? =A0smoke?).

You would know that by total power loss of all your batteries.
You
have essentially parallel connection with all your batteries
during
flight. When one fails, it drains your good batteries empty.
When your
radio or computer starts blinking it's too late. Best option is
to use
simple selector switch to choose one battery at time, and
keep other
batteries disconnected.

rk

I've been using a somewhat different approach. Two batteries,
each
powering half the avionics. So batt 1 has the radio and nav
computer
bus; batt 2 has the logger/PDA and backup vario bus.
Instrument
"busses" hooked up via individual 3 position switches so that
either
buss can be powered by either battery or disconnected.
Normally, run
the batts/busses independent, but have had occasions when
one batt
went low early, and just switched the bus it was on to the other
battery for all instruments for rest of flight.

I also use the built-in voltmeters in various instruments (AR-
4201,
SN10) to monitor the health of the batteries during flight.

Seems to work OK for the past 12 years...

Kirk
66

On 7 helmi, 09:45, Peter Purdie wrote:
* The 'split services' approach is much better than running
everything off 1 battery, and then switching to another. *The
standard 7AH gel cell is rated at the 20hour discharge current -
about 300mA. *Any higher current and the total energy available
decreases. (and that 7AH is a new battery at room temperature,
not a 2 year old one freezing at 18,000ft).

If you have room, paralleling batteries works well, so long as
you have another independent battery to run essential services
if the main one drops below 11V (for me vario/flight director
only, and radio when 5 minutes out on final glide).

I see the point of using parallel batteries to achieve lower current
draw per battery, though you have basically no way to know or control
the current draw from each battery.

The main benefit of using one battery at time is that you allways know
exactly how good your batteries are. I use two batteries, usually one
battery is just enough for day's flying, if it's cold I might have to
use second one for an hour or two. After flight I charge it overnight
and next day use the second battery as my primary. This way cycles are
evenly split between batteries and running them empty on regular basis
gives me pretty good idea how healthy they are (bad batteries develop
symptoms long before they actual fail). Only failure I have had during
flight was parallel connected batteries with one of them failing and
draining the other one empty in two minutes. After that I have flown
no 5 years with three way selector switch, without a single glitch.
This is the way they do electrical systems in Schempp, Schleicher etc.
No need to invent wheel again, IMO.

Of course running batteries empty might shorten their life a bit, but
replacement cost is next to nothing (for 7 Ah lead gel). One more
thing, switching batteries doesn't power off my acionics. They have
some capacitors built into them too.

On Feb 6, 3:45*pm, jcarlyle wrote:


Others kindly added some of the information I omitted regarding the
last two points, thus furthering the conversation. It would have been
nice if you'd done the same, rather than attempt to pick a fight. But,
I guess you're not one of those people who share.


I never considered taking a bet to be the same as picking a fight.
Each to his own I suppose.

To further the conversation - When selecting a glider main battery
switch please ensure that the DC rating is appropriate for the current
being switched. Some switches may not even be marked with a DC
rating. Why does it matter? The AC rating relies on the fact that
any arc induced as the contacts are opened will be quenched as the
alternating current passes through zero. No such quenching can happen
in a DC circuit and the arcing may reduce contact life or even sustain
long enough for the switch to burn.

Andy

On Monday, February 6, 2012 11:10:18 PM UTC-5, Bart wrote:
I get the "reverse polarity" part. But how is it supposed to help with
connecting batteries in parallel? The weaker battery will still pull
the strong one down - at least SPICE says so.

Right, as noted in the "PS" above.

On an unrelated note, I enjoyed your presentation in Reno.

Thanks ! Which one ?

See ya, Dave "YO electric"

On Feb 7, 5:41*am, Dave Nadler wrote:
On an unrelated note, I enjoyed your presentation in Reno.
Thanks ! Which one ?

Actually, both. But I was thinking of the "electric flight" one when I
made the comment above. Speaking of which - in Antares, is it possible
to use all those batteries to power avionics? I would imagine that
long after they are depleted as far as powered flight is concerned,
there should be enough juice for radios, varios, transponder etc.

Bart

On Feb 7, 8:32*pm, Bart wrote:
On Feb 7, 5:41*am, Dave Nadler wrote:

On an unrelated note, I enjoyed your presentation in Reno.
Thanks ! Which one ?

Actually, both. But I was thinking of the "electric flight" one when I
made the comment above. Speaking of which - in Antares, is it possible
to use all those batteries to power avionics? I would imagine that
long after they are depleted as far as powered flight is concerned,
there should be enough juice for radios, varios, transponder etc.

Bart

This is the route the Front Electric Sustainer guys have gone - using
the large high-voltage LiPo pack with a DC/DC converter with just a
small 12 V battery for stabilization. A neat solution.

Mike

On Tuesday, February 7, 2012 10:32:02 PM UTC-5, Bart wrote:
Thanks ! Which one ?
Actually, both.

I guess you missed the third one ;-)

... Speaking of which - in Antares, is it possible
to use all those batteries to power avionics? I would imagine that
long after they are depleted as far as powered flight is concerned,
there should be enough juice for radios, varios, transponder etc.

Antares has no separate battery for avionics,
just the big battery in the wings (which also
powers the hydraulic system).

See ya, Dave "YO electric"

Originally Posted by JohnDeRosa

This came from a separate thread "Typo in Battery Article in Soaring"

My $0.02. Let me know how your testing turns out.

- John DeRosa
http://aviation.derosaweb.net

Hi John,

I enjoyed your article and just completed 2 test runs using the rig you detailed..I was mildly surprised to find 2 identical batteries with identical manufacture dates vary significantly on the results.

Battery #1 took 4:13 to run down to 11.5 volts, at about 5:45 it hit the "knee" at 10.5V described in the article and started dropping rapidly.

Battery #2 lasted almost an hour longer...5:10 to hit 11.5, then longer than 6:30 to get below 10.5V.

Both batteries were 12V 7.5 AH SLA.

Now I have a limited exposure to longer duration flights, heck I've not got my Silver duration yet, but I'm concluding from this test that, as long I stay off the XMIT button, I've got enough juice to keep electrons flowing as long as needed. My panel consists now of a Borgelt B-400 (soon to be Lx7) and an Oudie which I power off the ship. I've got a PowerFLARM brick on order and use a Lx Nano which I don't connect to the glider's electrical system. Hopefully, I have enough battery to power my expansion plans...your thoughts appreciated here.

A few questions? I've got an older Dittel radio (ship is an ASW 19b) that may be as old as the glider. The manual for the radio says it needs 13.5V to operate...obviously, it's getting nowhere near that. Last season, I had comm issues with other gliders or ATC facilities having trouble hearing my transmissions. Receive works fine for me. I was going to put the ship in a radio shop to test the transceiver, but now this whole electrical discussion has me wondering if the older radio is just needing more juice than a 12V battery can provide? Especially as I get 2, 3, 4 hours into a flight. Could that be a cause of the transmission difficulties? If so, do the newer radios work better on lower voltages?

Also, any anecdotal experience with battery manufacturers? I have a couple of "generic" SLA batteries that I picked up cheap...but now after my testing am wondering if brands like "Powersonic" or others might push my curves further to the right till hitting 11.5V...does price=quality in the battery world?

As to wiring, I jerked all the hardware/auto supply junk out and did the Tefzel wire as you suggested. Every component is fused, including the batteries. I decided to put in an A/B battery switch and a separate Master. Switching between batteries has never been a problem for the Oudie...probably b/c of its internal battery.

The one electrical failure I've had so far was not hardware related but human...I had flung the drinking tube to my Camelback back over my shoulder to get it out of the way one flight...when I retrieved it, it took some
tugging to get it back. I figured it had hung up on the parachute harness or seat back...Actually, it had snagged on the wiring leading to TQD connector on the battery. Tugging it (unknown to me at the time) disco'ed the TQD and killed everything. At the time I was 45 miles from home and my mechanical vario was inop...it would not have been fun for a newbie to struggle back home with no vario! Fortunately, flipping the A/B over to "B" got me onto #2 and home to a happy ending! The lesson I learned on this was...now I put a couple of winds of electrical tape around each of the TQD connections after assembly before securing them behind the seatback. Murphy struck, glad I had a backup!

Thanks again for the article, good off season project info!

Regards,

Rob S.
ZAP

On Feb 8, 6:47*am, Dave Nadler wrote:
Thanks ! Which one ?
Actually, both.
I guess you missed the third one ;-)

Electric flight and POWER Flarm. What was the third one?

B.

On Feb 8, 10:33*pm, RAS56 wrote:

I enjoyed your article and just completed 2 test runs using the rig you
detailed..

Glad you enjoyed the article, I've gotten lots of positive feedback.

I was mildly surprised to find 2 identical batteries with
identical manufacture dates vary significantly on the results.

The good news is that both batteries each lasted a "long" time. If
older batteries then you might put this down to one battery has been
used more often than the other as based on your recovery story you
don't run them in parallel.

Hopefully, I have enough battery to power my
expansion plans...your thoughts appreciated here.

I will evasively say, "time will tell". Obviously, adding more
devices to your bus is going to run down your batteries faster. How
long? Sorry too many variables. A FLARM transmitts and anything that
Transmitts (transceiver, transponder) is THE variable and can be
massive power hogs so keep those on a separate battery (my thinking is
changing in this regard) from the other stuff like GPS, PDA, vario and
recorder...those really important things for soaring pilots (which
don't transmit)! If you loose the "T" (transmit) battery, you can
still get home on the other "S" (soaring) battery. Think about
getting a bigger T battery next round.

I've got an older Dittel radio (ship is an ASW 19b)
that may be as old as the glider. The manual for the radio says it needs
13.5V to operate...Could that be a cause of the transmission
difficulties? If so, do the newer radios work better on lower voltages?

Certainly old radios (meant for airplanes with generators) did want a
nice warm 13.5VDC. I have seen these frankenstein combinations of a
12V and 1.5V battery to get that much voltage. Newer radios like the
Microaire work down to 10.7VDC. Older radios are also more power
hungry so when you transmit the voltage might droop (nice to have a
voltmeter on board to test with). Have you always had transmit
problems or just recently? If always then voltage could be your
problem. Have someone drive to the other end of the runway and test
with a handheld (anything works when you are 5 feet away from each
other). As radios are expensive, send it in for a bench test before
replacing. I recommend http://www.erieaviation.com.

does price=quality in the battery world?

You would think so wouldn't you. But I really don't know. Not
enough data points. Sorry.

As to wiring, I jerked all the hardware/auto supply junk out and did the
Tefzel wire as you suggested. Every component is fused, including the
batteries.

Tefzel! Fuses! You are my hero! Send me before/after pictures.

Thanks again for the article, good off season project info!

You are very welcome!

- John