Onan low voltage

UltraKen · 06-28-2010, 09:26 AM

I have a 6.3kw NHE in my coach. Ran well until just recently. I exercise it monthly over the winter, at half load, for about an hour each month.

Started it the other day. Voltage was just at red line (about 108V). Turned on air conditioner and voltage dropped into the red.

I tried it again today. Voltage was about 115V. After it stabilized I turned on a/c for a load (and it was hot). Voltage dropped to about 108V and stayed there for a while and then slowly came up to about 112V. Turned on the rear a/c to add load and cooling and it dropped to into red zone - about 106V.

I turned off the 2nd a/c and ran the generator and the first a/c for over an hour. It ran about 108 to 110V with one a/c and about 115 to 116V after the turning off the a/c (at the end of the hour+).

I checked the plug-in voltmeter against my RMS digital plugged into a wall socket and the voltages were within 1V of each other.

In the past the generator ran at around 125V, and dropped with the a/c to about 120V. It easily handled both a/cs.

Would this be caused by a problem with the voltage regulator or are there other possible causes? I'd like a range of possible problems before I take it in for servicing.

Summary - initial voltage low-normal, with a/c barely acceptable, and with two a/c voltage too low. Voltage drops when compressor comes on and doesn't rise back.

Theberrys · 06-28-2010, 12:21 PM

My Voltage Regulator has a Trim Pot adjustment for the Voltage. It could yours has moved or become dirty. You may want to try adjusting the voltage up and see if it goes down again on it's own. If so you may need a new regulator. These folks have the best prices I could find and give real good service. https://www.partsfortechs.com/asapcart/

Dick

**Gary RVRoamer** · 06-28-2010, 03:45 PM

'm not familiar with the NHE model, but I can't think of anything but the regulator for those symptoms.
Is this a gas genset or diesel? Inverter type or direct generation? Engine RPMs are be critical. If the genset cannot supply enough engine RPMs in response to the regulator, the voltage will go low. So will the frequency.

UltraKen · 06-28-2010, 04:06 PM

Quote:

Originally Posted by RV Roamer [Gary]

'm not familiar with the NHE model, but I can't think of anything but the regulator for those symptoms.
Is this a gas genset or diesel? Inverter type or direct generation? Engine RPMs are be critical. If the genset cannot supply enough engine RPMs in response to the regulator, the voltage will go low. So will the frequency.

It's an LP generator. 6.3KW.

What's confusing is that the voltage is low, but close. It's not as though there is no AC output, it's just lower than it should be.

If I had about 10V more with the second A/C, I'd be happy.

inspectorudy · 06-28-2010, 04:17 PM

I would say it sounds like a voltage regulator or an rpm problem. Either one will cause the same issue.

**RV Wizard** · 06-29-2010, 03:24 AM

Be sure you do not have any loose connections that are causing some resistance in the feeders from generator. There are many things that can cause your symptoms; brushes, rings, connections in power conductors, voltage regulator, engine performance (dirty air filter, plugs, etc.). You may have to check them all, and that would not be a bad thing to do anyway.

UltraKen · 07-09-2010, 06:17 PM

I took it to a Cummins-Onan shop today (Bridgeway-Cummins, Maumee, Oh).

What I learned.

First, the NHE model used a mechanical governor so, voltage regulation is not perfect as load increases.

Second, there was nothing seriously wrong with the generator.

It turns out that the governor linkage was sticking and the governor spring was weak. RR the spring and free up the linkage, and some tweaking brought the no-load to 128V, one A/C to 126V, and two A/Cs to 123V.

Frequency varied from 60hz no-load to about 64hz with both A/Cs.

I happily drove the 60 miles home with the generator humming and the front A/C cooling things down. The new higher load range tires running at lower pressure than formerly gave a really nice, smoother, and more stable ride. The high-speed on the wipers dealt with the "Noah-get-your-Ark" torrential downpours I hit once each way at the same stretch of road.

It would have been perfect if the Onan warranty covered a 1996 generator....