Alt Circuit Breaker Popped Twice Yesterday

[lrobichaux]

On flight yesterday, temps were 40 degrees F on the ground. My alternator circuit breaker popped twice during about two hours of flight. Once a couple of minutes after start-up while still on the ground, and again on approach at the end of the flight. There were no other unusual indications. I was not using pitot heat either time when the CB popped, although I turned it on during flight, let the alt load stabilize, and there were no problems. Any suggestions on where to start looking? Might it be related to the cold temps (although that would be troubling in and of itself if true)? I've got a 60 amp alt., plane is less than one year old.

 

[Neal]

You may want to review the logs and see what the amp draw pattern is. Feel free to attach the flight (csv) if you want or you could use FlySto if you haven't tried that yet.

 

[Neal]

I would also send the log off to Pete for review. Per our discussions of late any ALT issues are very concerning.

I would expect you'll be told to inspect wiring and areas around the alternator. I've heard of some grounding issues in the past from builders and having to grind off the painted surface. @Cactus Charlie may know more. Not sure if it's a faulty breaker but that could be a something to consider.

I've flown in crazy cold here in VA and no issues related.

 

[Cactus Charlie]

Events like this make me glad I added alternator current monitoring and recording to my FX-3. Battery current and Main bus volts may provide some clues. Plot both for the flight. Send me the CSV log if you need help with that.

I very much doubt you could have a normal 60 A load. A intermittent short after the alternator breaker seems more likely.

 

[Neal]

@lrobichaux if it were me I'd consider the plane grounded for now.

 

[lrobichaux]

You may want to review the logs and see what the amp draw pattern is. Feel free to attach the flight (csv) if you want or you could use FlySto if you haven't tried that yet.

Great suggestion ... will do. Will attach the data here and send to Pete.

Events like this make me glad I added alternator current monitoring and recording to my FX-3.

I seem to recall that you described this in a prior post. Can you remind me where this was discussed?

 

[Cactus Charlie]

C

Post in thread 'Carbon Cub EX-3 Engine Failure (N40DT)'

Oct 17, 2025

You don't need a shunt to add alternator current monitoring. Simply disconnect the alternator wire at the circuit breaker, slip a Hall effect sensor over the wire, re-connect the wire to the circuit breaker. That part is a 5 minute job.

What takes the time is fitting the sensor wires to the GEA 24 connector and configuring the custom GP input definition.

Some would argue that Battery Amps tells you if the alternator is working. Battery Amps will go negative immediately if the alternator fails. I prefer to have battery and alternator current displayed and recorded.

I used the Amploc...

• Cactus Charlie

• 

 

[lrobichaux]

Thank you!