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We let the smoke get out

Dugaru

Well Known Member
So at the conclusion of my condition inspection, my A&P discovered my battery (PC680) was dead and would not take a charge. That was weird because the battery was only a few months old. Anyway, after cursing Odyssey, I flew down to pick up the plane with a new PC680 in hand. We hooked that up (top and bottom cowlings were off), turned on the master, and… got visible smoke from the battery contactor (!). It was found to have at some point made a burn mark on the firewall, and was welded open. Meanwhile, the old battery was found to have a negative voltage.

There were no issues or warnings on my original flight down to the shop. We currently theorize it went south at some point after landing, and apparently took the battery with it.

So it looks like I need a new battery contactor. Everything I read, however, suggests a contactor failure like this is extremely rare. Are there any other problems/issues I should be looking for?

Thanks!
 
Contactor

It sounds like the contactor failed internal short to ground.
Just curious...
Does the airplane have an ANL between the battery and contactor?
 
We hooked that up (top and bottom cowlings were off), turned on the master, and… got visible smoke from the battery contactor (!). It was found to have at some point made a burn mark on the firewall, and was welded open.

Sounds like an internal coil winding short, lowering resistance, which would explain the heat. However, to kill the battery with the panel master switch open, the short had to have also created a high resistance connection to ground, perhaps via melted insulation. Subsequently closing the master switch after installing a new battery again allowed lots of amps due to less resistance.

I would replace the master switch, as it may have seen more amps than its rating allows, and take a good look at the contactor->master switch->ground block wire.

Interesting failure.
 
Dropped wrench?

This component begs for an autopsy. Hope you could measure resistances on bench and grind off the cap.

Weird/odd failure.
 
This component begs for an autopsy. Hope you could measure resistances on bench and grind off the cap.

Weird/odd failure.

I agree - this is a strange and interesting one. It will be great to see what you find. If you don't feel up to it, I'm sure if you send it to Bob Nuckolls he'd be happy to do the autopsy.
 
Update

Okay, additional findings:

1. Engine monitor data uploaded to savvy shows that bus voltage was too low and was falling over time. My dead battery (and the short life of the one before it) appear to have been caused by a failing alternator. My guess is that I was keeping the batteries on life support by hooking them to a tender at the end of each flight.

2. My inability to recognize (1) as it was happening is weird. I may have set the voltage warning level too low, or otherwise configured the avionics incorrectly. An additional confounding factor is that my flashing red light (attached to an EIS 4000) appears to be recently inop.

3. None of this, however, would seem to explain the smoking battery contactor when we installed the new battery and turned on the master.

4. Now for the really weird part: various diodes are fried, and my A&P is seeing reverse polarity at the alternator.
 
This brings up a question. My electrical system indication (D180) is hooked up to show amps to and from battery. Usually on zero or 1to 2 amps. What will be best indication the alternator is going bad and do they usually give you clues before they die completely? Usually shows 14 to 13.9 volts.
 
I can tell you what mine did

I looked at my voltage data from my engine monitor, and it basically shows less voltage than that. I was under 12.75 much of the time. Bus voltage appears to have declined over time as the alternator did a poor job recharging the battery.

This brings up a question. My electrical system indication (D180) is hooked up to show amps to and from battery. Usually on zero or 1to 2 amps. What will be best indication the alternator is going bad and do they usually give you clues before they die completely? Usually shows 14 to 13.9 volts.
 
Still more info

The alternator is kaput. It appears to be the model used in a Kubota tractor, which I gather is a typical install in an RV. On the bench it's grounding positive.

Thinking I'll go with a PlanePower alternator and regulator at this point. Any downsides to that?
 
The alternator is kaput. It appears to be the model used in a Kubota tractor, which I gather is a typical install in an RV. On the bench it's grounding positive.

Thinking I'll go with a PlanePower alternator and regulator at this point. Any downsides to that?

PlanePower alternators have a well-deserved reputation for dying at about the 500-600 hour mark. B&C alternators are generally regarded as the best, but will dent your budget somewhat.
 
Good to know

I think I may try to source a replacement for the current one then (saves on surgery as well). I *think* this will do; the model number on the old one is.... burned off. But it's definitely 3 pin.

https://www.amazon.com/Electrical-A...DB+Electrical+400-52244&qid=1630348079&sr=8-2

PlanePower alternators have a well-deserved reputation for dying at about the 500-600 hour mark. B&C alternators are generally regarded as the best, but will dent your budget somewhat.
 
My denso has 850 hrs on it and still going strong. It does have a scat tube cooling it.
 
This brings up a question. My electrical system indication (D180) is hooked up to show amps to and from battery. Usually on zero or 1to 2 amps. What will be best indication the alternator is going bad and do they usually give you clues before they die completely? Usually shows 14 to 13.9 volts.

Okay, additional findings:

1. Engine monitor data uploaded to savvy shows that bus voltage was too low and was falling over time. My dead battery (and the short life of the one before it) appear to have been caused by a failing alternator. My guess is that I was keeping the batteries on life support by hooking them to a tender at the end of each flight.

2. My inability to recognize (1) as it was happening is weird. I may have set the voltage warning level too low, or otherwise configured the avionics incorrectly. An additional confounding factor is that my flashing red light (attached to an EIS 4000) appears to be recently inop.

3. None of this, however, would seem to explain the smoking battery contactor when we installed the new battery and turned on the master.

4. Now for the really weird part: various diodes are fried, and my A&P is seeing reverse polarity at the alternator.
One does not need warning alarms or warning lights to inform you of alternator problems. Yes, those are good to use. However, if there is a voltmeter in the panel monitor it. 13.9 volts? Time to examine the alternator. 15.0 volts? Check the alternator. Amps don’t help. Volts will tell you the story.
 
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