1995 Onan 7K NHM no output.

[RLS7201]

The 7K Onan NHM gas generator in my 95 Bounder runs but no output. I have reset the circuit breakers a couple of times. Normally a Onan will stop running with no output when the start button is released but mine keeps running. Go figure, I get the weird ones.
Any guesses where to start looking.

Richard

[johnhicks]

Mine was built in 1992.

[dougrainer]

I forgot about the slip rings, but as we thought the Genset should not have stayed running. How many hours on the Genset? Doug

[RLS7201]

My NHM had voltage regulator failure several years ago and would stop running when the start button was released. Still bugs me that it stayed running during this failure.

Richard

[johnhicks]

My elderly 6500LP did the same thing, ran fine but no output. A Cummins/Onan tech in Ocala cleaned the brushes and polished the slip rings and fixed it right up. Sitting in super-humid central Florida with no long runs during covid time was too much for it.

Apparently the NMH series will run with no output.

[RLS7201]

TA-DA! I wooped it! GRIN...........
Those tarnished slip rings were the problem.
But we'll probably never know why the engine kept running when the starter is released and no output.
Guess we know why Onan suggests running the generator once a month with with a load. Oh well, if my old Onan only fails once every 27 years, I guess I can live with it.
I'm now ready for the power & light company's black outs when the temperature goes over the top.


Richard

[RLS7201]

I finally found time to start trouble shooting my silly Onan.
Checked the fuse on the front of the control box. It is good.
Removed the brushes and they looked good. The slip rings look tarnished. Silly engine started and kept running while polishing the slip rings with a piece of scotch bright. Ohmed the the rotor and found 23.3 ohms. That should be good. Ohmed the 2 stator windings and found 1.3 ohms on each. That should also be good.

Next thing to do is install the brushes, start engine, and see what kind of DC voltage is being applied. If memory serves correctly, about 50 volts?

Stay tuned for more............

Richard

[RLS7201]

Thanks Doug. You always make me chuckle when you correct bad information from the unknowledgeable. I also suspect a loose wire from the 120 volt buss to the circuit breakers, in the control center box. Let ya know what I find. Now if I can only find the wiring print the I archived some place.

Richard

[dougrainer]

1. Brush problem---no stay running
2. Voltage regulator---no stay running
3. So, it stays running.
4. FIRST thing is to check the wire connections AT THE GENSET by the genset breakers. Verify you have 120 output and the connections are not burnt/open. Odds are they are OK. Since the Genset stays running you should have 120 output
5. Next is going to the 4 by 4 box that is usually within 4 feet of the Genset. You follow that flex cable from the genset and that will go to where the OEM attached the leads to the RV 120 going to the Transfer box.
6. IF you have power at step 5, then you go to the Transfer box. Now, 1995 does not guarantee you have a transfer box, but most do. Then check for 120 power on the INPUT leads for the Genset. IF you have power there and you have power on Shore Power, your Transfer box is bad.
7. IF no transfer box but a female receptacle you plug your Power cord in, check the receptacle, check the connections on it. Doug

[theoldwizard1]

If you want to DIY, watch some of James Condon's videos on YouTube.

It is not that difficult once you have access To the end opposite of the engine. You need a decent multimeter and patients. It could be bad brushes, dirty slip ring or a bad automatic voltage regulator.