ZamF16 Posted April 8, 2015 Report Posted April 8, 2015 I have had my Bravo for 3.5 years now, and in that time I have learned my share about the various aircraft systems. My latest learning experience resulted from the failure of my left alternator. I thought I would pass on the symptoms of the failure so others may also learn from what I observed. It all began about 20 flight hours ago. As I was cruising along at 15k', the low voltage indicator light started to flash at me. However, the volt meter still showed 28 volts and I had even loads on both alternators (both around 15%). A few minutes later the light went out. This happened a few other times over the next 20 hours of flight sometimes during ground ops, sometimes in climb out, and other times at cruise. Each time it would last between couple minutes up to about 15 minutes. On my last flight, a cross country from Florida back to Texas, the alternator warning light illuminated, the left alternator field circuit breaker popped, and the left alternator gauge indicated no load (as expected with the popped circuit breaker). I shut off the left alternator, reset the field breaker and turned the left alternator switch back on. Everything returned to normal (light off and alternator carrying about half the load). About 15 minutes later I glanced at the left alternator gauge and saw that it was now at 0 load. I had no other indications (light off and circuit breaker remained set). I shut off the left alternator field and continued the flight to my location on the right alternator. As part of the trouble shooting, my A&P and I swapped the alternator inputs into the voltage regulator to isolate the problem. Upon engine start and power up, the problem now moved to the "right" side of the voltage regulator. Having now isolated the problem to the left alternator itself and not the voltage regulator, we swapped out the alternator. All ops checks are good and the intermittent low voltage indication has also ceased. Nothing eye-popping here, but I thought I would share to help others recognize the symptoms. -Zam 1
Guest Posted April 8, 2015 Report Posted April 8, 2015 How old was the alternator? Typically brushes are well worn at 500 hours and are completely worn out by 750, they should be replaced around 500 hours. We see this regularly in many airframe types. Clarence
Bravoman Posted April 8, 2015 Report Posted April 8, 2015 I just annualed my plane and decided to put in a new left alternator "prophylactically" since the old one was original to the aircraft. The old one was functioning properly but I figured all good things must come to an end since the aircraft is now 17 years old with a little over a thousand hours. Regards, Frank
N201MKTurbo Posted April 8, 2015 Report Posted April 8, 2015 Have you found out what was wrong with the alternator?
carqwik Posted April 8, 2015 Report Posted April 8, 2015 My left alternator (original unit) just failed in heavy rain....no warnings, no nothing...that was at about 800 hours or so. Got the idiot light but I don't think it tripped the circuit breaker when it failed. Never diagnosed the reason for failure. Replaced it with a PlanePower unit which has been going strong now for 300 or more hours. The right alternator still works just fine...hopefully will stay that way!
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