Rear alternator falls off line
 

have dual paralleling alternators and my rear alternator keeps getting kicked off line after airborne for 15 minutes or so. I have a digital installed front and rear voltage and amp meter and have noticed they start diverging in amperage and then The rear goes off line. It typically resets but will fall off line quicker after each reset. The front always stays on line. I turned the front off today to see if the aircraft would run on the rear. I was able to fly about 1 hour before the rear dropped off line. This is much different than than with the front is on line with it. I have already replaced both voltage regs to trouble shoot this: same problem with the new parallel regulators. Any ideas of where to go next? Could it be the circuit board or the 70 amp diodes and heat sinks mounted to the fire wall? I’m at a loss. If any ideas please help. Thank you
Any ideas out there
Weeby

If you turn off the front one after the rear drops, does the rear then come alive? If so, I suspect it's a voltage issue and can be fixed with an adjustment.

My 340 (similar setup to the parallel alternators in the 337s) will drop one alternator (usually the high one) if they differ by more than 0.5 volts. Both are working, but it won't parallel until the regulators are adjusted to have them match within 0.5 V. The good news is that it's a no-parts fix - just adjust the output voltage on each one to to match. I have to re-match them to compensate for drift about once a year.

Please reveal the vintage of your 337. There are many variations to these Skymasters and not knowing the model makes it hard to troubleshoot. There are a number of threads about your issue. If you use the SEARCH function above it may help you learn more of the system.

Rear alternator
 

Thanks guys; it is a 1979 P337H. I have not actually tried turning the front off while the rear has kicked off line. I will try that next time I get a chance to fly.
Maybe awhile as I also have a bad starter adapter on the front engine. I’ll search the threads as well
Brad “Weeby” Young

I sent you a pm with my cell if you would like to talk alternators, its easier than typing that much.

Brent