Main Circuit Breaker Popping

The main alternator CB (50 amp) on our aircraft is popping intermittently. No other CBs popping. Checked the engine monitor. Volts steady at 14.4 but amps jumping very erratically between about 17 and 26 amps. Had the radios, strobes, and LED wig-wag lights on. Had a new 50 amp CB installed a little over a year ago. This problem just started recently. It's on a Husky Lycoming 0-360. Any thoughts?

What charging system? Is the ammeter located in the bus feed or in the alternator output lead? Is the noise in the headset when the ammeter moves between 17 and 26 amps? Also, 17 amps is a huge amount of current, is that a typical reading during normal ops? Is that reading during battery recharge such as right after startup?

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While the engine is running, watch for steady voltage and erratic amps, then pull one circuit breaker at a time (not the alternator output or field breaker) and watch for a change in the amp flow. Specifically you are looking for the erratic amp reading to steady down. When it does, the problem may lie with the circuit powered by the last breaker pulled.

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Turns out my question was premature since another problem has presented itself which will most likely require an engine teardown. So we'll have to wait until that problem is solved before chasing this one. Thanks for the replies though, Wireweinie. I'll revisit this one later...

Let us know.

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JWE said:

Turns out my question was premature since another problem has presented itself which will most likely require an engine teardown. So we'll have to wait until that problem is solved before chasing this one. Thanks for the replies though, Wireweinie. I'll revisit this one later...

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While you have the engine out-- look for an intermittent short in a line that would normally carry high amperage ie from the battery, starter etc. Wire going through/ around where it may have a chafe and an intermittent ground. Pulling that many amps you could look for scorching/ burning. A dead short wouldn't allow you to reset breaker. That's something that is a must find. Once had an internally shorted reverse current relay in a helicopter--- chased wires forever and finally figured that, "this is the only thing it could be"--and it was.

Thank, Seaworthy. We'll check for shorts and scorched lines.