Quote Originally Posted by rspears View Post
Are you thinking of a flyback diode - Flyback diode - Wikipedia, the free encyclopedia From what I see the diode is there to protect the contacts in the relay from arcing, not from pushing power into the system vs being driven. I'm a gearhead vs a spark chaser, and that generator thing just doesn't make sense to me. Then again, on big power generators (electric utility size) one of the most important pieces in the generation controls is the backfeed prevention to keep from motoring the generator with grid power if the turbine trips..... I think you've got some other gremlin to chase, and good luck with it!! Keep us in the loop as you try/find things. Interesting, interesting......
Yes, the diode acts as a one way valve to stop the backfeed. I also realized that I had changed the wires when I re-installed everything. Before the dual fans were wired in series. I became concerned that a single failure would take out both fans so I changed the connections so each fan is independent but share a common power supply. (As an aside, when running dual emergency generator sets, a synchronizor on the motor govenors must be used as one generator will become dominant and force the other generator to become a motor and drive the prime mover.. so you end up with a electric motor driving the engine! The synchro keeps the generator output matched and in phase.)

Quote Originally Posted by firebird77clone View Post
Disconnect components until it goes away.
Just run for short periods with the components isolated.
I'd start with the alternator.
A capacitor to ground might be the ticket for your fans, maybe an in-line diode as well.
I think a diode would be the way to go if I can prove the fans can become a generator. I know it is potentially possible depending on the motor. I just don't know these fan motors. Since it only happens above 70, I don't see me "testing" many things on the highway. But thanks for the thought~~