Cessna-style GPU Plug Wiring?

[dannyb]

Hi,

My P2008 has an external Cessna-style GPU plug. I "thought" that plugging in a GPU unit would not only allow running the avionics (with master and avionics switch on) but also change the battery while it was just plugged in (without the switches on.) The GPU is a Schauer unit set for AGM battery and ground runs the avionics just fine. I'm beginning to suspect that the plug is not wired to the battery for charging though. Some documentation on the plug indicates that the 3rd smaller contact needs to be energized to activate the solenoid for the other 2 contacts to actually connect to the battery.

I can't seem to find an applicable wiring diagram in my documentation. I won't be at the airport to buzz things out until this weekend but was hoping to get the forum's feedback on this to help me sort things out.

From the earliest photos I could find, it looks like the GPU port was installed from the factory. If you have an external GPU connector, what have been your experiences with this?

Thanks!
Danny B.
N78AV

[ChiMike]

I have a P2008t; I cannot speak to your specific aircraft, however I use a trickle charger (the same Cessna plug as you described) without any issue. I have not attempted any type of higher amp connection, such as a ‘direct-to’ from a car battery. My setup —AC power source to trickle charger, charger connected to the ‘Cessna Plug-in’ has worked well for me to both provide power for software updates and to recharge the battery.

I hope this helps.

[dannyb]

Okay, I checked the connection from the contacts on the Cessna-stye plug to the battery terminals and yes, they do connect. What brought on my question is that I started occasionally getting Lane warning lights (912iS) illumination after starting especially when cold. I noticed that the Lane voltages would drop quite a bit at start likely causing the Lane warnings. A "Lane Check" would clear the warnings. I installed a new battery but had the same issue.

I noticed that the battery voltage was in the 12.1V range and thought that was low. The GPU I'm using is supposed to charge the battery (AGM setting) along with being able to run the avionics while on the ground. I replaced the GPU with a Powersport AGM Battery Minder. After a week on the Battery Minder I noticed that the volage was in the 13.6V range. The engine starts right up, and I've not had Lane warnings.

The GPU works great to keep things going when exercising the avionics on the ground, but it seems to under charge the battery. The Battery Minder seems to do a better job with charging (but not enough current to run the avionics.)

www.batteryminders.com/2012agm-12v-charger-maintainer-sealed-agm-lead-acid-batteries

Danny B.
N78AV