Dynon's Transponder power connection

[B.Blenden]

I have read the read the installation manual regarding the transponder hookup and note that the power is to be supplied by a dedicated circuit protected with a 3 or 5 amp breaker. Do I need to install a switch for power on/off to the transponder or is it controlled from the EFIS display. I will use a circuit on the Avionics Bus so the power lead will not be hot until the Av Master is switched on.

 

[dynonsupport]

Whenever the transponder is receiving power, it's powered up. However, the spec'd power consumption is only applicable when the transponder is actually broadcasting in ALT or GND mode. When in standby, the power consumption is consideraably less. We'd suggest that you use a dedicated breaker, as suggested (this really protects the wiring from lighting up, realize) , but have it switched with the master or avionics bus, so that it powers up with SkyView. It sounds like this is what you're thinking, so you're good.

 

[dabear]

So it is ok to have the transponder on during engine start?  I was going to have it hooked up to the radio switch for after start.  Is there a reason to have it powered when the SV comes up?

Bear

 

[mmarien]

IMHO there is no reason to power the xponder (or any avionics) with the master switch. Two things. You don't need all that equipment drawing power when you're trying to start and the power surge after start can't be healthy for the electronic equipment unless it's made to take that abuse.

Take note of the radio in your car the next time you start it and you'll notice that it shuts off when the key is turned to start and comes back on when you let go. I think you have it right to power it with the Avionics switch.

 

[jlbpropilot]

How do you know if you have oil pressure after startup if you don't have your avionics on?

 

[dabear]

You raise a good question. I would agree for the radio systems if you have major power fluctuations or major power draw for the start system. However, my plane uses an air start system so there is little power changes during start. My avionics (SV EFIS) is on during start because that is how I'm monitoring fuel/oil/etc.

My question was if there was any danger to the transponder due to normal plane starts. If not, then there is little danger on mine. Was I clearer than the last post? Sorry if not.

 

[jlbpropilot]

Good thing you are asking the question now because I would ask the same one in a few weeks when my transponder finally shows up :-[

 

[mmarien]

The transponder is just another radio so I suspect it would need to be protected by a second electrical bus powered up after start. The SV is made to be on during engine starts.

As far as communication to the transponder, it's just a serial connection so in that case it no different then a nav or gps communicating with the SV - other than it's a two way communication.

On my system, the comm/xponder/gps etc are on the second avionics bus. When I switch that bus on, the SV sends altitude to the xponder and the gps sends vector information to the SV. They don't need to be switched on at the same time as the SV.

 

[dynonsupport]

It is fine for the Trig transponder to be on at any time the SkyView is - so on during start is fine. The transponder and SkyView system are designed to the same specs.