Onan voltage spikes

Hi all! I have an Onan Emerald 1 BGE spec F genset. The unit starts and runs fine without hunting or surging. With no load the unit runs at 130 volts at 62Hz for about 10 minutes. Then, with still no load, (all breakers turned off) the voltage will spike to 160 and the Hz will remain at 62. The unit runs steady at this voltage for 2 to 3 minutes, then the voltage drops back to 130 at 62Hz. The unit does this the whole time its running. I have checked all of the electrical connections and wires on the control board and voltage regulator, everything "looks" fine. I have done the diode check on the voltage reg. as per the Onan service manual. All the readings were within spec. exept the 5-9 terminals which were about double(0.945) as compared to the other diodes(0.495 to 0.515). I am thinking the voltage reg. is the problem, but just wondering if anybody has had a similar problem. Any ideas on what could causing the voltage spikes would be greatly appreciated!


Senior Member
Re: Onan voltage spikes

It sounds like you are on the right track, but to be honest I think that you seem to know more about this than I do! Please do let us know what it is when you solve the problem.

DL Rupper

Senior Member
Re: Onan voltage spikes

From all I have read about generators it is best to only run with a load on it. Without a load it is like idling a car for long periods of time. Just a thought. Sounds like it's fixed so it doesn't matter.