Voltage Regulators

[macaman]

We have a 1968 T337C that has had problems with the Alt Field breaker popping. We've fixed a number of problems troubleshooting it but still haven't found the offending part.

For a little background, the '68 model has the alternator system where you select one of two voltage regulators (a switch on the dash) for the system as opposed to the standard where each alternator has its own regulator.

Here is the scenario, after running both alternators for just over 10 minutes, the alt field circuit breaker will pop. This happens only when both alternator switches are on with both or either engine running. If only one alternator is on, we cannot get the Alt Field breaker to pop.

We've checked both Alternators and both are fine.
All wiring is good.
Over Voltage Sensor (lights and all) is good.
We've checked every part on that breaker and all are well.

Here is what we think: We have the Zeftronics Voltage Regulators and have taken everything else off the circuit but the regulators and it still continues to trip the breaker. Could the problem be that these regulators are not meant to have 2 alternators feeding them?

[macaman]

Great News. The problem turned out to be the Voltage Regulators. We thought we had a related problem months ago when this all started when the High Voltage light would flash. Turns out that the maintenance manual says that this signals the need to put different voltage regulators in. I don't have the part numbers with me but the problem was that the original Cessna part number was listed as a possible replacement for the Zeftronic regulators we were using but not the other way around. I have yet to tell the A&P that made the mistake as I'm sure he'll feel awful we spent so long trying to figure this out. Just an expensive lesson learned I guess. So glad to finally have this finished. A couple days to finish the annual and we'll be back in the air. Hope this helps anyone out who may be having similar troubles.