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Erratic charging alternator

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scott airshows

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I?ve had a B&C 14V alternator and regulator on my plane for nearly 8 years. The battery voltage has started fluctuating as if the batt was being charged sometimes and not other times leading to a gradual voltage drop. There?s enough charging going on to start the engine when it?s not hot, but the alternator isn?t keeping the voltage high enough to hot-start the engine after a flight. Can anyone advise me of the likely causes and/or things to look for?
 
Hard to say if it is the alt or voltage regulator, but the later is far more likely given the description of the problem. Would be wise to first check that all connections to the VR and alternator are in good shape, including the VR and alternator's ground connections. Also check the engine ground strap for fraying.

Larry
 
Field wire and connector. Even if it "looks" ok, it is probably a 30min operation to run a new one just to rule it out.
 
Check any Rectifier Diodes. I had one that went bad. Figured it out after replacing alternator. $$. Fun to work on the plane though!
 
scott airshows said:
I?ve had a B&C 14V alternator and regulator on my plane for nearly 8 years. The battery voltage has started fluctuating as if the batt was being charged sometimes and not other times leading to a gradual voltage drop. There?s enough charging going on to start the engine when it?s not hot, but the alternator isn?t keeping the voltage high enough to hot-start the engine after a flight. Can anyone advise me of the likely causes and/or things to look for?
Click to expand...

I am curious of two things, are you looking at the battery voltage or the Alternator voltage when you say fluctuating?

Also, during the hot start, the voltage drops too quickly due to the need for cranking more or any other reason/cause?

It looks like the battery might be on its last leg. Have you tested your battery?
 
What is electrical system voltage during cruise?
If it fluctuates, what is the minimum and maximum?
 
Don?t overlook the obvious...

All connections nice and snug-torqued to proper value.

I had a similar issue on my aircraft, and started at the alternator and worked backwards.

The rubber boot covering the main power takeoff lug had hidden the fact that the hold-down bolt had backed off to the last thread on the lug, allowing the connector to bounce around during acro/turbulence, giving me an erratic reading on the ammeter. Torqued it up and the problem disappeared.

Something I check now (along with other stuff) every time the cowl comes off.
 
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