Battery Connected - “Reverse Polarity” 1981 M20J

[Frank B.]

My friend, who is an older gent and doesn’t participate in any of the online forums, called me last night in a panic. He had the battery out of his 1981 M20J just to do a little PM on his battery box and when he went to put the battery back in his aircraft one of his much younger hangar neighbors stopped by and offered to lend him a hand with setting the battery back in the aircraft. From what I understand it all went down hill from there. Somehow ….. someway the hangar neighbor connected the battery backwards. How he got the lid on etc is all a mystery to me but none the less they did power the aircraft and they did throw the avionics master ON. I have minimal details after this except when nothing worked Jim looked at the battery installation and immediately identified the problem but after reversing the battery leads he has at minimum ZERO avionics function. He said that there is no blown / tripped breakers in the circuit panel. I don’t know if anything else illuminates, works, or not. It was late, he was highly discouraged so I advised him to disconnect the hot lead on the battery and told him that I would come by this evening and check it out for him. Based on the limited info that I have provided, any ideas? If there isn’t power on the hot lead I guess it couldn’t trip any breakers or blow any fuses. How did the solenoid energize, will it energize with reverse polarity on the solenoid coil? Is there anything simple that I should go straight to before starting a potentially lengthy diagnostics process? Knowing Jim as I know him he didn’t sleep at all last night and will more than likely be back out at the airport first thing this morning visually checking things and impatiently waiting my arrival which more than likely isn’t going to be until late evening. If he put power on the ground side how did it find a ground through the hot side?

I haven’t worked on a Mooney electrician system in a few years and I don’t have a service manual for the plane here at my office.

Any knowledgeable speculation is appreciated !

 

Thanks, Frank

[N201MKTurbo]

Wow, that's bad.

I would start by seeing what works on the plane. DONT TURN ON THE AVIONICS! I would pull all the avionics breakers. See if the engine starts, runs and the alternator charges. I would put it on jacks and cycle the gear. Try all the lighting and see if they work. Check all other airframe electrical systems.

As for avionics, the first thing I would do is make sure the avionics buss is powering up. You could have fried the reverse current diodes on all the relays. I don't know any easy way to check the avionics buss except with a meter on the buss itself. If the avionics buss does power up and none of the avionics power up, you might want to talk to your insurance company.

[Fly Boomer]

9 minutes ago, N201MKTurbo said:

If the avionics buss does power up and none of the avionics power up, you might want to talk to your insurance company.

Ouch.

[thinwing]

modern avionc boxes are generally diode reverse polarity protected.This however is bound to have some consequence to older APs and other equip.Reverse polarity to alt field and regulators are prob affected...i agree..this is an insurance issue...sorry

[kortopates]

definitely the Mooney annunciator box will have about 8 fried diodes if it saw the reversed polarity voltage


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