Onan 5500 with only 70 Volts. Why?

johnandcaren · 04-05-2010, 08:58 AM

We have a gas, Onan genarator, 5500 watt model. We have only had the MH for 6 mos and just now trying to use gen power. It has 46 hours on it.

The gas engine runs great. When de-winterizing I tried to run the AC's with no luck. Checked and no 110 volt power. Shore power works fine. After checking I found the isolator box, popped the top and found that the leads from the generator to the box showed 66 - 70 volts, with the voltage moving constantly. Both leads (phases) ahd the same voltage. I assume this is not enough to energize the coils as there was no output voltage. There is also a big B+ terminal on the front that was in the 7 Volt DC range.

I do not have experience with AC generators, their internals, and don't want to dive into disassembling the thing.

Any ideas before I take it in to a repair facility? Just wanted to check in case it is something simple.

I did search the Onan site and this site with no luck regarding this particular type of problem. THANKS Anyone.

**RJay** · 04-05-2010, 12:26 PM

If the generator hasn't been run for sometime the slip rings may be corroded. The slip rings are located where the brushes are. After cleaning the slip rings make sure the brushes are making full contact. From there I would check the voltage regulator and then the control board. Get yourself a user manual, it should have all the troubleshooting you need to check the above but your first check should be the slip rings.

**Gary RVRoamer** · 04-07-2010, 08:09 AM

You will also have low voltage if the generator does not get up to its proper speed (RPMs).

Luv2go · 04-07-2010, 08:25 AM

The fact that the B+ terminal reads 7VDC and you're only getting 66-70VAC out are probably related. Maybe the low voltage at the output is caused by too low DC voltage. I believe the B+ terminal should have 12V from the battery on it.

Stewart

wa8yxm · 04-07-2010, 09:28 AM

Try running a electric space heater for an hour or so with it.. Nothing else, just the space heater on HIGH.. This resistive load could care less what the voltage is (It will work on 50 volts, it will work, briefly on 250 volts but that's dangerous) unlike a motor.... This may "Clean up" the generator a bit.

And if it does.. then 1/2 hour under 1/2 load every 1/2 month for this summer, switch to every month after that.

johnandcaren · 04-07-2010, 10:42 AM

All good advise and makes sense.

I found some good reading also and will check speed (Hz) first, then battery voltage before moving to the voltage regulator. Also found a wiring diagram associated with checking which PC board terminal for which test I hope will help.

As with most of the coach, its new to me but not terribly difficult and a learning process - which is sort of fun and mentally healthy.

Take care all.

johnandcaren · 09-22-2010, 01:38 PM

Just in case anyone checks back, I found the problem. This generator started and ran fine but the voltage was low and the Hz a mess. Turns out, after checking all the wrong things, one of the two spark plug wires was loose. It was a two cylinder engine running on one, thus it could not keep the Hz correct.

Remember the simple things first. Never know what a problem may be.