Onan generator shorted (110 side)

[vacuumbed]

Hello everyone.

My 1978 Pace Arrow developed an issue. When the shore cord is pugged in to power it will trip the residential house breaker immediately.

I traced it to the generator, which is an Onan 6.5 gas unit. The Hot and the Ground has full continuity! This can't be right. Has anyone heard of this issue?

I'm thinking the voltage regulator is blown or there is a problem in the generator itself.

[Generator_Jim]

That would probably be an ASCO 940 -- right

JimL

[TEXAS]

I am sorry Jim. I guess that would be a surprise. Kinda like the one I had at an old nursing home. Went into the transfer switch room. Found the switch marked USS Grayfish. Certified for service 1944.

[Generator_Jim]

TEXAS said -- What did I do Jim.

People today are use to 2 brushes not a possibility of 12, some ac and some dc.
Thanks for not telling him he might have a reconnectible unit or what those ceramic resistors are for.

JimL

[TEXAS]

What did I do Jim.

[DryCamper11]

Generator Jim wrote:
Last time I checked, Tampa Armature Works was charging well over two grand for the rotor.

Ouch! And if the stator is damaged, too .....

You can get a rotor rewound for less than half that price if it's not too badly damaged, but the best option is usually to find one with an engine that's shot and do a swap. Often, while looking for a donor, you find a donor in better shape, and just go with it as a replacement generator without doing any work on the damaged gen.

There are a lot of low time generators pulled from old RVs on Craigslist. I'm often tempted to buy them, put them into decent shape and wait for the next hurricane, snowstorm, or whatever when the gen prices seem to triple. I've got two right now, one on wheels that I can lend to the neighbors and one in the RV that I can switch to 120/240 to run my 240 VAC well pump.

[Generator_Jim]

TEXAS You are going to scare the******out of that guy when he pulls the wrapper off of the brushes. They don't make stuff like that any more for a reason. Last time I checked, Tampa Armature Works was charging well over two grand for the rotor.

JimL

[DryCamper11]

vacuumbed wrote:
Here is the model #
6.5 NH-3CR/16004K

I have a 6.5 NHD Onan. You said the hot and ground have continuity and " This can't be right". Actually, it is right. The hot and ground are connected together by a winding. The winding has relatively low resistance at DC (The manual has the DC resistance listed). On my gen the stator windings have 0.3 ohms resistance and the rotor winding has 22 ohms DC resistance.

When running, the winding generates AC and this low resistance doesn't act as a short.
If you need a service manual and can't find it with Google, post here, and I'll find one for you.
Edit (Somehow I didn't notice that there were 3 pages in this thread, and only read the first page. Sorry for any duplication)

[TEXAS]

Also pull the band off the back end. Make sure all the brushes have good contact with the slip rings.

[Kpackpackkelley]

You have two of the best here Jim and Texas . We are very lucky to have there knowledge. Thanks men.

[Handbasket]

You can buy a Kill-A-Watt meter for under $30 at Home Depot, I think. One of the readouts it's capable of is Hertz (Hz), as well as voltage.

Jim, "I drink coffee for _your_ protection."

[PaulJ2]

Your workaround would be, if you have a known accurate volt meter adjust it to 132 volts warmed up and no load. This would be very close to 62 hertz and is the maximum most 120 volt items are rated for.

[vacuumbed]

Generator Jim wrote:
134 vac is a little high. If you have a frequency (Hertz) meter, connect it across the 120 volts and adjust the governor speed spring on top of the cooling fan for 62 at no load and 58 at full load. Your voltage should be within tolerances at that point.

JimL

Scott and Sherrie -- where have you been, I missed you.

I don't have don't have one of these meters, is there a workaround? When I first fired it the voltage was at 124 and very slowly went up to 134 over 3-4 minutes time as the engine warmed up.

[ScottnSherrie]

TEXAS wrote:
Since you have voltage. No damage was done. If the engine is going up and down. That would cause your voltage swing most of the time. Do as Jim says and you will be ok.

Ditto, GeneratorJim is "The Man" when it comes to Onan generators.

[vacuumbed]

This is great news everyone, I would like to thank all of you for all of your help.