Why do I need a new Stator on a 750hr 10K Quiet Diesel?

[Mike Groves]

All,

Just got the bad news from Cummins/Onan in Coburg that our 10K Onan Quiet Diesel tests out to indicate the stator has been compromised and must be replaced.  That's an $1800 part plus typically is associated with a ruined control board which is another $900.  While it's out of the unit (we left it there and we're back at Pacific Shores lot 53), we were offered the "1000 mile service" so we've added that to the bill which in total with discounts for joining yet another "club" comes to around $5200.

The question I asked of Cummins/Onan Coburg is, "How does a generator with 750 hours develop such a catastrophic failure as to require a repair bill of 1/2 the cost of a new one, and what should I be doing differently in the future to limit to the degree possible that this doesn't happen again?

I'd like to ask this same question of the forum please.  I've had the coach since fall 2013 and the generator was serviced before I got it and I have continued to serviced it.  Never an issue during hours long drives in hot summer, etc.  As far as I know there is NO SERVICE for the electrical side of things which is the issue, so I guess servicing the engine has nothing to do with this.  Is it just a freak thing?

Thanks,
Mike

[harry kew]

Mike
I had a problem with a 7500 on Oman at around 350hrs, about 3 weeks after we bought the coach

The magnets let go taking out the rotor and stator, Cummings told me that some rotors had a smooth surface and the glue holding the magnets would let go. They roughed up the surface of the rotor so the glue would hold. I did the work my self and took a chance and used the same controller, three years later and everything is still working great

Cleaning up the shattered magnets after they flew everywhere was quite a job
Harry

[William Jordan]

I have been "told". turning the gen off while under heavy load like all the air running etc. can cause problems with the stators such as you described. Since being told this some years ago I've always reduced the load before Turning on or aff the generator. I too would be interested in the correct reason for a failure like this.
The  1000 "hour" service is  primarily a valve adjust as I've been told .. since it's already out on the "bench"  I can't imagine the cost being more than a couple hundred more ? Most of the cost when I asked was for removal of the generator.

[Mike Groves]

It took about 3 hours (8:30am to 11:15) to remove it, but they gave me a break on that at just 3 hours total to remove AND replace it.  The 1000 Hr includes all filters/fluids/thermostat/belt/injector service/valve adjustment.  They will use my air and fuel filter and I told them to skip the oil change/coolant change as I'd had those done.  The tech also told me the radiator was a mess and he'd clean that up.  I was told the cleanout of the spark arrestor would not be necessary as they will be running it on the bench at 90% power which should blow out the exhaust system.

The cooling down before shutting off does seem like a good way to ruin the stator windings as a sudden turn off after high voltage generation could burn them up.  I think I have been pretty good at doing that in the 3 years since I've had it, but can't say for certain I did it every single time.  I will now definitely adopt a procedure to turn loads off and let it cycle down before turning it off.

Mike

[Edward Buker]

"The cooling down before shutting off does seem like a good way to ruin the stator windings as a sudden turn off after high voltage generation could burn them up.  I think I have been pretty good at doing that in the 3 years since I've had it, but can't say for certain I did it every single time.  I will now definitely adopt a procedure to turn loads off and let it cycle down before turning it off."

Mike,

Not sure that was what you meant to say in first sentence but I got you meant...The varnish on the windings can just break down with age or misuse. Not cooling the windings down, before shutting down, can cause the stator to fail due to more extreme heat cycles. The stator, when generating electricity under load, gets hot due to losses in the windings consuming energy in the form of heating. There is resistance in the windings and that produces heat just like in a hair dryer. When you run the generator under no load before shutting down, it is actually eliminating the stator resistance losses, and therefor the heat generation within the stator by the windings is eliminated. When you start a no load cycle of the stator, that is when the cooling cycle begins with air flow from the cooling fan. The longer the running period and the higher the load the longer this cooling cycle should be run.

The adhesives holding components together in the stator can also fail just due to age, vibration, or poor construction. You did have an early fail, this component usually lasts longer.

Later Ed

[Mike Groves]

Ed,

Yes, that first sentence didn't come out right for sure.  Should have indicated that NOT COOLING it down before shutdown seems like a likely candidate to create the failures.  We did run it this past summer with significant loads while travelling.  I think the "book" recommends a 3 minute or so cool down time but doesn't say make it longer or shorter.  I will definitely establish a procedure for us to follow.

The only caution the shop has made is concerning the exercising of the unit and they recommend as full a load as you can get for 30 minutes.  I've heard 2 hours before.  How do the Beaver owners exercise their generators?

Mike

[LaMonte Monnell]

Mike, so sorry for your troubles.

I have the Onan 7500 Qd in my 2001 Contessa,

I have about 900 hrs on it so far. Since ownership from 4 years ago I try to run the generator with a good load at least every two weeks for a 1/2 hour.

I have it parked in my yard so it is an easy task. That may be overkill but that's what I decided to do at the time.

[john brunson]

http://www.utterpower.com/generator_realities.htm

[Mike Groves]

I suppose I should call onan (which one must assume is a factory authorized service center for onan) and ask that they hold onto any parts removed so they can show me what happened.  I think that's reasonable so as to encourage me to be "more careful" for whatever reason.  I think the primary thing to make sure of is that the generator cools down before stoppage and Margaret insists we always did that. 

Maybe the proper technique is to MAKE SURE that no load exists by turning off the breaker on the generator itself then letting it run an added 5 minutes or so to cool down.  Otherwise I can not assume NO LOAD was there while it is cooling down.

Mike