Onan rotor resistance too low?

[jferre9570]

6.3NHEFA63753M SN J953443939 nice shiny slip rings, about 60VAC generated, good field flash, 16.6 ohms across terminals 9 and 10 of the regulator connector (with the regulator disconnected.) Time for a rewind?

[jferre9570]

Good point and, since it's not broken at the moment, I'll add that to my list of things to check the next time before it fixes itself!

[MEXICOWANDERER]

Big Katuna wrote:
I would submit you might get a high reading thru the brushes but not lower.

Carbon brush powder residue.

Coats brush holder and leads.

Direct path to brush holder steel chassis.

[jferre9570]

Today, after ignoring the genset for a week and a half, I checked the resistance one more time (just 'cause) and it was 24.5 ohms and the genset started and ran fine. I ran it for 4 hours with 2 ACs cycling (85 degrees) plus hot water heater, refrigerator, toaster, battery charger and the washing machine with no problems noted. So, do I have a "flying short?" Did it get wet and dry out? Did my fairy god-mother decide I'd been a good boy? BSOM.

[jferre9570]

If I had a borderline condition, I would certainly measure directly at the slip rings but when I'm already 20% low WITH the brushes......

[Big_Katuna]

I would submit you might get a high reading thru the brushes but not lower.

[MEXICOWANDERER]

You MUST measure right at the copper on the slip ring. Brush to copper contact cannot be ascertained with an ohm meter.

[mchero]

Keep us posted on your progress.

[Big_Katuna]

21 Ohms? There is a test where you ground or supply voltage and vary the output.
I'm guessing you have a shorted winding.

[jferre9570]

Regulator is new also. According to "the book" the rotor should be between 22 and 28 ohms; too high is normally bad or sticking brushes or bad slip ring film and too low is supposedly a shorted winding in the rotor. The $64,000 question is; What is too low?

[MrWizard]

Strange
60 volts, one half of what it should be, sounds like an open circuit some place
Or
A bad regulator board

[Big_Katuna]

When mine was putting out 60V I had to have the rotor replaced. $1200.
I looked into having it rewound but it wasn't guaranteed. And the new one ($900)
Wasn't guaranteed unless an authorized Onan shop installed it so I bit the bullet.

[jferre9570]

New brushes, block, and springs.

[Kpackpackkelley]

Forgot to post the thread. http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27730610.cfm

[Kpackpackkelley]

Here's a thread on a NHe with the service manual. Best I can do for you . Did you check the brushes when you cleaned the slip rings.
Has it been awhile since the gen ran ?