Alt. Field Breaker tripping in warm weather

Looking for any ideas to what might be causing my alt. field breaker to trip. It only happens when engine is warm, ambients are above 60f or so, and only when on the ground during taxi. I can reset the breaker after only a short time in the air and it operates fine during flight regardless of OAT or OT ( 100f OAT yesterday, long taxi, 210f oil and I was still able to reset it after only a minute or so in the air)
I flew with the same configuration for 400 hours before this problem crept in.
I have done the following:
Changed alt. from Nippo to PP
Rewired alt. field from #18 to #16 awg
Isolated alt. field circuit directly to bus with new 10A breaker. (was on DC load Center)
Replaced alt. field switch.
Checked all ground wiring and engine ground.

The only item I changed that the timing corresponds with are adding an oil shutter to increase my oil temps. My alt. field wiring is bundled with my Alt. main line and other ff wiring with adle clamps off the sump. So, it is probably hotter in the lower cowl than before from higher oil temps but I am not buying that as the problem.
There is some low level crackling static in the headset usually right before the breaker trips.

Calling PP tomorrow. Looking for ideas here from the "experts".

How's the battery condition, how about voltage and current indications??

Walt said:

How's the battery condition, how about voltage and current indications??

Click to expand...

I have another symptom that started before this. I am unsure about the timing related to this issue. My ammeter is set up for charge indication and the ammeter fluctuates, bouncing around between +- 4 amps with the base amp when fully charged between -1 and 3 or 0 and 4. It always used to be solid.
I replaced the battery with no affect. I have systematically eliminated all loads except the dc load center. No change. Another trusted.sourced did not feel they where related.
Voltage is rock solid 14.2

The dc load center might be suspect but I removed the alt. field and ran it through its own 10a breaker directly off the buss to isolate it.
No luck.
I like the whole pizo idea but makes troubleshooting more hassle for sure.

I've had mine tripping as well but it wasn't related to OAT at all. It took it tripping a few times for the light bulb in my head to finally turn on. I've been flying for 5 years and 450 hours without issue and the only thing I had been doing differently was I had purchased a cigar lighter USB charger (2.1 amp) for my iPad. I realized that the only times it had tripped was when I had the adapter plugged in to the socket (not necessarily charging the iPad). I tried several times after this realization and sure enough it's the culprit.

Why does it do this? I have no idea. The PP will trip your field breaker in an over-voltage condition and I'm told that there are various devices that can erroneously trip the OV protection.

This is probably not the same issue you're having but it's at least something to chew on.

PP is baffled too. The suspect is the PP alternators overvoltage crowbar circuit seeing something that forces the alt. field to ground and purposefully trip the breaker.

Jamie - that is helpful.
My next step, the next time it trips, I will systematically shut off equipment and try resetting the circuit. Currently, it will not reset until I get in the air and air flowing again. It is tought to pin down the timing of the problem since it only does it when it is warm outside but I did install a Dynon EFIS and changed out my 296 to a 496. Both have charging circuits.

I am also going to run a dedicated ground from the alternator case to the firewall in the off chance that one of the crimps on the engine ground cable is developing some resistance when things get hot.
For now, it is a manageable problem.

Still open to ideas.

Perhaps the field wire is chafing on something that is grounded and causing the trip? Increased temperature might make it more likely to happen due to expansion or increased flexibility.

One thing to remember is that the resistance of wire will increase with an increase in temperature. Just a thought, maybe you are seeing higher amps and the cb is doing its job.

bird

Thanks Mark and Bird but already had those thoughts. Changed out the entire run from #18 to #16. Also verified with Plane Power that the max. amp draw on their unit is designed not to exceed 4.8 amps, ever, on the alt. field. I used a 10A breaker to isolate the circuit directly off the main buss and it was still tripping. It also never did this for the first 400+ hours of flight in similar conditions with #18 wire.
The only plausible explanation at this point is their crowbar circuit forcing the alt. field to ground. Now to figure out why.