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Old 05-13-2018, 05:40 PM   #1
Senior Member
Join Date: Dec 1969
Posts: 1,827
Onan generator stops producing 120 vac

Here is a problem with an Onan generator that I have not found discussions with similar intermittent symptoms. It started last summer.

The Onan generator installed in our 1998 motorhome stopped producing 120 vac after a short period of time. The generator starts normally. After a short time delay, 120 vac circuits transfer from the inverter and then after another time delay batteries start being charged at about 1500 watts. This the normal loading sequence.

After 5 to 10 minutes, 120 vac drops out but the generator continues to run unloaded until manually stopped.

This problem appears to be temperature related and getting progressively worse. When it first started, the generator ran 30 minutes on cool mornings and for a shorter time in the afternoon. I cleaned the slip rings but this did not seem to make a difference. Then if it was above 60 degrees F, the generator starts but 120 vac does not kick in.

Next I unbolted the voltage regulator and put it in an ice bath. Starting the generator, the normal loading occurred and then more load was added until approximately 4000 watts. Voltage was controlled within 2 v of 120 vac and maybe 1 v of droop as load was added. It ran for 40 minutes.

After a discussion with the folks at flight systems who confirmed that the symptoms indicated a failing voltage regulator. I replaced it with their aftermarket Model 305.

Now we have run the generator enough times to be satisfied that was the problem and the problem is fixed.
Additional information: Model number: 6.5NHMFA/26116G, runs on propane, approximately 600 hours run time.
Kit & Rita (in memory)
37 foot Ď98 HolidayRambler Endeavor diesel pusher
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Old 05-13-2018, 05:51 PM   #2
Junior Member
Join Date: Dec 2009
Posts: 26
I also have a 4000 watt Onan. I have replaced the voltage regulator twice since I bought the Bounder new in 1994. Last time was just last winter. The symptoms then were, it would run while pushing start button, but stop running when released.
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