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Alternator warning light on but alternator still working

Lars

Well Known Member
Sponsor
Yep, another Plane Power thread. Alternator has been in service for 8 years and about 1000 hours, it's an AL12-EI60/B from before PP was bought up by Hartzell.

Out flying around today trying to get above the smoke when the alternator warning light flickered, then came on steadily. I started watching the voltage, but it didn't drop. Ranged between 13.9 and 14.1 volts, as it has done since new. Not only that, but it appears to be charging still. The current was fluctuating from approximately +5 to -2, but it's been doing that since new as well, after the initial startup surge.

Gave up on getting above the smoke (9500' wasn't enough) and descended back to the airport. I noticed the light flickered a couple of times, but generally stayed on steadily. I have an AFS AOA system with the nice lady inside that reminds me through the audio panel that I'm getting too slow with "angle angle push!." This time when the message came through I noticed what I would describe as a classic alternator whine, but only while the warning was being transmitted. Otherwise there was no audio noise.

I don't mind replacing the alternator if it's warranted, but I'm curious as to what would cause this. For the record I haven't decowled the engine for a look yet. That's next.

Thoughts?
 
Really sounds like the alternator has a failed diode and is in need of replacement. Normally, I would have you chase down some connections, but the alternator whine is a dead giveaway.

Vic
 
following up...

The alternator was toast. No doubt a bad diode, though I haven't had it tested, and don't plan to since I won't be using that type anymore.

After the light came on I was seeing the charging current bouncing around negative to positive, with the buss voltage ranging from about 13.8 to 14.2 volts. Being no expert on alternators, I did not expect an alternator that was still producing current at least occasionally to sink the warning light input, but that's what happened. Adding to my confusion I swapped in a friend's spare PP alternator that had supposedly failed, but in which the regulator had been replaced. Got the same result. Turned out that alternator had a bad diode as well.

Swapped out the PP brand for one manufactured in Newton, KS. All well.
 
Swap

Swapped out the PP brand for one manufactured in Newton, KS. All well.

Just curious - how involved was the swap? (brackets, clearance to other items, regulator, etc). I also have a PP bought significantly pre-Hartzell. It has been bullet-proof for 640 hours - but I am just thinking ahead ;)
 
Just curious - how involved was the swap? (brackets, clearance to other items, regulator, etc). I also have a PP bought significantly pre-Hartzell. It has been bullet-proof for 640 hours - but I am just thinking ahead ;)

There wasn't much to the mechanical installation of the alternator itself + bracketry. Were it not for the non-stop parade of well-wishers (to be euphemistic) yesterday I could've done that in 20 minutes. No interference/clearance issues, the B-lead landed in the same place, existing alternator belt is fairly new and turned out to be the same one recommended by B&C (last two digits 55, don't remember the rest). Everything just lined up.

I had previously run the PP harness, which included wires for both field and warning light. I had hoped to reuse that, since it's the same connector. But the old one was beat up from multiple disconnects, and the wire in the B&C part was better strain-relieved. So I snipped that back near the firewall and grafted on the new connector plus several feet of wire (love me them solder sleeves).

Figuring out where to mount the regulator took some thinking, but the wiring was pretty easy. It found a home behind my EFIS. Had to run one new wire that required groveling, from fuse panel to regulator for buss voltage sense. The rest were easy.

It was smoky and hotter than the furnaces of Hades yesterday; between that and the visitors I wasn't running at 100% but I still managed in about 5 hours.

For what it's worth, my Plane Power alternator went about 985 hours. Given the online horror stories I wasn't sure it would last anywhere near that long. I have had a blast tube on it since the beginning. Can't say if it helped, since you can't prove a negative, but it's probably worth noting.
 
Thanks . . . .

. . . . for the response. I had to carefully modify the snorkle on my horizontal induction engine to clear the PP mounting brackets back when I built the plane. Was kind of wondering if the B&C alternator/brackets were enough like the PP's to still fit without having to hack on that again. Yours isn't horizontal injected by any chance is it?
 
I am experiencing something similar. My charging voltage is good (14.3 or so) and drops when the alternator breaker is pulled as I would expect but my battery won't hold a charge. My alternator light is dimly illuminated which is a new thing. I just figured that I was another Odyssey PC680 casualty but wonder if it is really an alternator problem.

Is it possible that my battery (Oct 2019) is fine but my charging system isn't? I was planning on going to the airport tomorrow to pull the battery but wonder if I should be looking a little forward of the firewall battery.

Thank you.
John
RV-7
 
If the charging voltage is 14.3 and the AC component is less than one volt, then the charging system is working fine.
 
I am experiencing something similar. My charging voltage is good (14.3 or so) and drops when the alternator breaker is pulled as I would expect but my battery won't hold a charge. My alternator light is dimly illuminated which is a new thing. I just figured that I was another Odyssey PC680 casualty but wonder if it is really an alternator problem.

Is it possible that my battery (Oct 2019) is fine but my charging system isn't? I was planning on going to the airport tomorrow to pull the battery but wonder if I should be looking a little forward of the firewall battery.

Thank you.
John
RV-7

Quick follow up. Short story....it was the Odyssey battery. I took it out and had Batteries Plus test it and it didn't pass. I didn't buy the battery since I recently bought the plane but the previous owner kept great records and receipts and it was covered under warranty. The sales clerk said that they had been getting a lot of the Odyssey batteries back recently. I had an Apex battery at the ready and would have installed it had I not found that receipt just before doing so.

I hope to fly it tonight and see if the ALT light still illuminates.

Thanks,
John
 
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