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Ladies and Gents,
Been running into a problem lately that has me scratching my head. After getting back to flying after a top overhaul (lengthy aircraft downtime), my alternator has been randomly dropping off (negative ammeter charge) about 10-20 minutes into flight. All circuit breakers are in and there’s no other abnormal indication – the ammeter just subtly goes negative. Cycling the alternator half of the master switch reengages it, but the problem usually worsens quickly thereafter (shorter time between resetting the alternator and it dropping off again).
Initially thought it was the voltage regulator, so I replaced the ’90s-era VR with a Zeftronics 12V regulator. The ammeter needle was much more stable, but the alternator still cuts out 10-20 mins into flight and worsens over time.
An A&P friend suspects that my sealed concorde battery is bad, resulting in excessive demand from the alternator and the alternator field kicking off. We were seeing ~13.7V when the alternator was charging and ~12.6 V for a few minutes after the alternator field kicked itself off. I suspect he’s right, because the battery couldn’t even start the engine today after a brief stop for fuel (the alternator had kicked off for only a minute or two in a 1-hr flight before the fuel stop). The battery had been completely discharged once before (interior light left on), so the battery is already suspect.
The interesting part is that the alternator seems to stay in a charging state longer if I give it more demand (more lights, pitot heat, etc.). I think this corroborates my friend’s theory since a crappy battery won’t give the alternator much demand, resulting in it kicking off without some other electrical system demand. It ultimately still gives up though, even with everything on.
I’m just guessing at what to replace next, so I figured I’d open this to the forum in case anyone has seen these tell-tale signs before. Thanks for any and all help!
-Doug
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AA-1 / 1A or later? Is the over-voltage diode kicking in if it has it? Seams like that is not the case as this would pop the 5 Amp field breaker unless this is an AA-1 or -1A (which did not have it). Does this have an aftermarket over-voltage circuit? My Cessna occasionally will do that requiring me to reset the master, and I have not been able to trace the issue. But that has several different components then a Grumman. More diagnostics would be needed to determine if the battery is bad or maybe the alternator.
Rich Harrison
AA-1B
AA-1 Project
C-182
Dog is my Co-Pilot
Wife is my A&P-
Sorry, forgot to mention – it’s a ’79 AA-5B. Update on the issue:
We replaced the voltage regulator with a Zeftronics R15v00, replaced the battery, and bypassed the separate overvoltage relay (the Zeftronics has its own internal overvoltage protection). We’re still seeing the ammeter go negative occasionally, although with much lower frequency (and it usually seems to self-recover if the load is reduced). Still no popped circuit breakers.
Now we’re thinking that the alternator brushes (or something else in the alternator) are bad…
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An update (in case anyone was following this):
Finally figured it out: loose alternator field wire – DUH. The field wire was poorly crimped in a butt splice near the alternator, and a little dab of oil had worked its way into the splice – as the engine heated up, the butt splice was loosening enough (or the resistance was rising enough) to basically kill the field connection and force the alternator offline (hence why the alternator usually worked at first then died after the engine warmed up). Luckily I don’t think replacement of the battery or voltage regulator was wasted – they were both bad and trending worse anyway, but they simply weren’t the problem.
Replaced all of the wires between the alternator and the voltage regulator and everything works great now. I think this was a pretty rare circumstance, but hopefully this helps anyone who runs into a similar issue.
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Hi Doug:
Just read this thread and want to thank you for detailing your issue, very informative.
I also had an issue with my charging system. Battery was discharging and I lost full electrical in flight a couple of times. I replaced the battery and flew fine for some time. Always saw a charge at run-up, but would later have electrical issues in flight. Turned out to be a loose alternator bracket that allowed the belt to slip. After tightening this I started to notice the Ammeter light remaining lit. The shop that had just performed my annual said everything was fine. Turned out to be a faulty relay in the voltage regulator. After replacing that, I have had no electrical issues since – replaced the engine, full glass in the canopy, repaired a leak in the ram pressure line…
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