Feds Want to Equipe Gliders With Transponders and Radios

Alan wrote:

Other factors include the output voltage under load at discharge -- a
lead acid battery is rated to 10.2 to 10.5 volts for a "12 volt" battery
at discharge.

Powersonic uses 10.5 volts for 5 to 20 hour discharge rates.

Unfortunately, most 12 volt radios and devices are designed
for a charging electrical system, with a voltage of about 14 volts.

Most panel mounted radios (definitely for Dittel and Becker radios)
bought new in the last 20 years (and even some older ones) meet the
current requirements to function properly to 10.5 volts, and at even
lower voltages, but with reduced power output. "Very old" radios likely
will have problems at 10.5 volts. I have no idea what the percentage of
"old" and "new" are.

When
the battery is down to 75% of the expected voltage for the radio, not all
of them work. I have had aircraft radios that would not transmit below
about 11.5 volts, at which point the battery would be still above 50% charged.

Powersonic shows it's batteries have only 25% capacity left at 11.5
volts. I haven't checked other brands, but believe they are the same for
the batteries we use in our gliders.

Lead acid batteries are normally rated for capacity at a 20 hour rate of
discharge. A 7 AH battery would deliver 7000 / 20 = 350 mA for 20 hours.
Faster discharge rates result in less capacity being available (look up
Peukerts exponent for more details). Discharging faster than that, reduces
the amp-hour capacity of the battery.

At a current drain of 700 ma (10 hour rate) that you might have with
transponder, radio, etc, Powersonic shows a capacity of 90% of the 20
hour rate. That's not a show-stopper, but worth taking into account.

Lead acid batteries have less capacity when cold. One guide suggests that
for every 10 degrees centigrade below room temperature, you should add 10%
to the battery capacity needed. High altitude flight tends to get up into
cold places.

This corresponds with the Powersonic chart, so at -10C (15F), you have a
30% loss of capacity. For winter flying, and spring or fall flying in
places where you can climb to, say, 10,000' agl, it's an important
factor. Especially so, when you know your encoder will likely be using
it's heater, adding 50-150 milliamps to your current drain.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

"Eric Greenwell" wrote
This corresponds with the Powersonic chart, so at -10C (15F), you have a 30%
loss of capacity. For winter flying, and spring or fall flying in places where
you can climb to, say, 10,000' agl, it's an important factor. Especially so,
when you know your encoder will likely be using it's heater, adding 50-150
milliamps to your current drain.

Put a insulated cover around the battery, and the heat of discharge will keep
it warm and the capacity up, unless it is seriously freakin' cold.
--
Jim in NC

Morgans wrote:

"Eric Greenwell" wrote
This corresponds with the Powersonic chart, so at -10C (15F), you have
a 30% loss of capacity. For winter flying, and spring or fall flying
in places where you can climb to, say, 10,000' agl, it's an important
factor. Especially so, when you know your encoder will likely be using
it's heater, adding 50-150 milliamps to your current drain.

Put a insulated cover around the battery, and the heat of discharge will
keep it warm and the capacity up, unless it is seriously freakin' cold.

Insulating it will keep if from cooling off as quickly, but I'm
skeptical about the amount of self-heating. Do you know how much it is,
or where I can find a reference to it that applies to the batteries we
us? Insulating my battery is difficult due to it's location, so I'd like
to know it's worth the effort before attempting it.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

In article "Morgans" writes:

"Eric Greenwell" wrote
This corresponds with the Powersonic chart, so at -10C (15F), you have a 30%
loss of capacity. For winter flying, and spring or fall flying in places where
you can climb to, say, 10,000' agl, it's an important factor. Especially so,
when you know your encoder will likely be using it's heater, adding 50-150
milliamps to your current drain.

Put a insulated cover around the battery, and the heat of discharge will keep
it warm and the capacity up, unless it is seriously freakin' cold.

With a resistance of a few milliohms, a 1 amp discharge will only give a
few milliwatts of heat. I really doubt the battery will keep itself warm.
(After all warming the battery would consume energy from its stored capacity.)

Alan

"Alan" wrote in message
...
In article "Morgans"
writes:

"Eric Greenwell" wrote
This corresponds with the Powersonic chart, so at -10C (15F), you have a
30%
loss of capacity. For winter flying, and spring or fall flying in places
where
you can climb to, say, 10,000' agl, it's an important factor. Especially
so,
when you know your encoder will likely be using it's heater, adding
50-150
milliamps to your current drain.

Put a insulated cover around the battery, and the heat of discharge will
keep
it warm and the capacity up, unless it is seriously freakin' cold.

With a resistance of a few milliohms, a 1 amp discharge will only give a
few milliwatts of heat. I really doubt the battery will keep itself warm.
(After all warming the battery would consume energy from its stored
capacity.)

Alan

The greater problem might be a need to remove the problem during charging,
when a lot more heat is likely to be generated.

Peter

On Sun, 04 May 2008 09:37:13 -0400, Peter Dohm wrote:


The greater problem might be a need to remove the problem during charging,
when a lot more heat is likely to be generated.

I use an automatic charger with bulk charge and float modes.
This unit is designed for 12v batteries in the 6-15Ah capacity range.
It outputs 14.7v at 1.5 amps in bulk mode. My batteries never even get
warm to the touch when on charge.

I'd suggest that if your batteries get hot on charge then there are only
three possibilities:

- you're using a fixed-rate charger with far too high a rate for
the battery.
- you're overcharging with a fixed-rate changer.
- your automatic charger is faulty.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

(After all warming the battery would consume energy from its stored capacity.)

Sure, but a warm battery can deliver more power than a really cold battery.

Tony V.