Confirming ground avionics power for 1977 182Q

[PBinPA]

Hello,

I just bought a 1977 182Q with a full glass garmin panel. I've read posts on using ground power to be able to play with the avionics without running the engine. My read of the POH is that when you use the ground power receptacle, a relay cuts off all power to the avionics bus. Is that accurate?

I saw another post (can't post links yet) that talked about using a 12V supply with a cessna ground power plug to power avionics - and all the reviews of that unit (on Aircraft Spruce, search for part 11-05084) talk about folks using it to power avionics.

Am I missing something? Appreciate any clarificaition!

 

[Mikey52]

Battery charger, 10 to 15 amps.

 

[bnt83]

Its possible that it works the way as described in the POH, and its possible that relay doesn't even exist anymore after several radio mods since it was built.

 

[Jesse Saint]

One of the main reasons of the ground power port is to power the panel. It should power the avionics.

 

[Bell206]

My read of the POH is that when you use the ground power receptacle, a relay cuts off all power to the avionics bus. Is that accurate?

Yes. Some Cessna's use a split main buss bar with one half powering the electrical equipment and the other half powering the avionics equipment. There is a relay connecting both sides that allows battery voltage to power all equipment. However, when external power in plugged in or the starter is activated, the buss relay will disconnect the avionics portion to protect the equipment during start loads. In these aircraft models the ext power receptacle is there for start assist only. You have several options for ground or aux power depending on how your mechanic looks at things.

One option is to add a separate switch to the buss relay which will allow you to power the avionics side with ext power as a minor alteration. Another option is to remove the buss relay but that is usually considered a major alteration. A 3rd option as mentioned above is to connect a properly sized battery charger to the main battery and use the existing system to power your avionics. However, I would ensure the charger is the correct one as recommended by the battery OEM.

 

[Ryan Klems]

As @bnt83 mentions, if may or may not work like that anymore. _If_ it is still wired per the factory, your avionics bus is connected to the main bus through a normally closed relay that is opened by ground power being connected, or when the starter is engaged. With a full Garmin glass panel, I'd be willing to bet it is _not_ wired like that anymore. Even prior to glass panel upgrades a lot of those were re-wired to add an avionics master switch which eliminated the interconnection with the GPU plug and starter circuit.