Multiple Battery Setup

Andy wrote:
On Feb 6, 12:10 pm, jcarlyle wrote:
I bet there isn't a glider pilot out there who
doesn't look at his battery voltage at least several times during each
flight, and who doesn't understand switches...


I'll take your bet on understanding switches. How many glider pilots
do you think understand the difference between the AC and DC rating of
a switch and select one with an approprate DC rating? How many know
why the ratings are very different? How many glider pilots know the
inrush current of their installed avionics? How many know if the the
load has a significant inductive component?

It's only a switch after all.

Andy

Andy,

Mea culpa - in my attempt to tread a fine line between brevity and
excruciating detail I omitted the phrase "how to use" between the
words "understand" and "switches" in the last sentence of my post. I
also omitted giving precise instructions on how to switch over from
the supplying battery to the unused battery, and I didn't explain the
need to size the batteries to avionics current draw, expected
temperatures, battery age, etc.

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'm not going to provide answers the questions you raised, even though
I could. I'll just say that for those who are interested in this
topic, if you don't understand the questions Andy raised, then don't
attempt to select components and wire your glider yourself. Rather,
use this thread as a rough guide, get professional advice (Radio Shack
doesn't count, spend a few bucks at an avionics firm), and avoid the
horror of fire in the air.

-John

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

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, 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

On Thursday, February 9, 2012 5:37:29 PM UTC-5, JohnDeRosa wrote:
... A FLARM transmitts and anything that
Transmitts (transceiver, transponder) is THE variable and can be
massive power hogs...

Please, FLARM takes very little power !
For PowerFLARM, keep the backlight turned down to minimize draw...

Thanks,
Best Regards, Dave "YO electric"

On Feb 9, 8:37*pm, Dave Nadler wrote:
On Thursday, February 9, 2012 5:37:29 PM UTC-5, JohnDeRosa wrote:
... A FLARM transmitts and anything that
Transmitts (transceiver, transponder) is THE variable and can be
massive power hogs...

Please, FLARM takes very little power !
For PowerFLARM, keep the backlight turned down to minimize draw...

Thanks,
Best Regards, Dave "YO electric"

Please excuse anything demeaning to the FLARM. The only power
requirement specifications I have found are in the PowerFLARM manual
which says, "Supplied power must be 12 V DC nominal at 500mA". 0.5A
is nothing to sneeze at but is probably the instantaneous maximum.
Does someone have some real world power requirement information for
the various (US) FLARMS? I have not found an online FLARM or
PowerFLARM Brick manual (sources?). Thanks.

On Thu, 9 Feb 2012 14:37:29 -0800 (PST), JohnDeRosa
wrote:

. 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

A Flarm transmits at only 50mW power. The power consumption is
negligible, always less than 100mA, and it includes a GPS engine
capable of NMEA communication.
A radio in receive-only mode, will use more power than a Flarm.

And, if I were low on battery, Flarm is still the latest "switch-off"
option, considering the benefits for safety.

aldo cernezzi
www.voloavela.it

On Thu, 09 Feb 2012 04:33:04 +0000, RAS56 wrote:

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.

I just did the same: bought a pair of Yuasa 12v 7Ah SLAs, call them D and
E, because A, B and C dropped off their charge curves when tested during
the week before last. A and B had also been bought together in 2008 and
had both been measured at a bit over 6500 mAh then, but both were under
4000 mAh this time.

I put them both the new batteries on my three phase mains charger to top
them off as soon as they arrived. E took over an hour longer to top off.
Then I measured them with a Pro Peak Prodigy II charger/cycler. E ran the
device while I measured D. Then both went back on the mains charger and
this time D ran the device while it measured E.

Results: D was measured at 7003 mAh and E at 7510 mAh

I was a little surprised at the difference since, with both batteries
being the same model there's every change they're from the same batch.

The Prodigy II isn't what you'd call a heavy duty discharger and self
limited itself to 0.4A despite me being optimistic and asking for a 0.7A
rate. IIRC it has a 5 watt discharge limit. I As this somewhat less
current than we'd expect to use during a flight and all batteries show
lower capacity the faster you discharge them and the colder they are. IOW
this over-estimated the in-flight capacity due to the lower current and
higher temperature during my test, but thats fine: I do the same tests at
about the same time of year and am only interested in the relative drop
in capacity from one year to the next.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |