Battery life when running a transponder

On Jul 2, 12:21*pm, Chris Nicholas wrote:
Can anybody tell me what battery life you get in practice, when
running a transponder from a dedicated lead-acid battery, and what
size battery that is? And what model of transponder is it?

Has anybody measured the actual current drawn during operation, if so
what is it?

I am particularly interested in flights which include some high
altitude, cold ambient operation such as in parts of North America.

I am only interested in modern, solid state transponder operation, not
the older Mode C with a heater for the height encoder.

I have been given figures which suggest that a 7-amp-hour battery
would run one for 12 hours at surface ambient conditions, and I wonder
if anything like that is achievable in practice.

Thansk - Chris N.

Chris N. (In UK, but collecting data from anywhere that has it!)

I run the following:

- Becker 4401 175W
- Becker 4201 Radio
- Cambridge GPS-Nav
- Cambridge L-Nav
- EDW Micro-recorder
- Compaq 1550 PDA

I operate just outside the New York Class B airspace, so
interrogation is essentially constant. All of this runs for a typical
5 hour flight off one 12V/12AH battery with voltage down to around
10.9-11V at time of landing. I have two of these batteries, so
plenty of reserve for long flights. Operations include winter ridge
runs at ambient temps of around 20F, but those are limited not by
battery but by cold soaking of the pilot.

P3

Thanks for all the answers so far. It is not specifically for me to
fit in my glider, though I am considering it for when the European
system will allow me to, but in connection with a paper I am writing,
so I wanted a rough idea for the benefit of anyone with limited
battery capability. Some UK potential users would be mainly lowish
level thermal soaring, but there would be times when visiting wave
sites and climbing to FL 195 or higher, sometimes for extended
periods.

Also, as more flying things get TCAS, there will be more
interrogations. I thought gliders around Reno and similar high fliers
might have some useful experience.

Chris N. (In UK, but collecting data from anywhere that has it!)