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Onan 7500w Quiet Diesel Generator


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I have a Onan 7500w Quiet Diesel Generator in my 02 Diplomat pbdd.  The coach has 133k and genset has 3800hrs.  On my current trip twice the genset breaker has tripped.  The second time I was watching the numbers on the EMS panel hover close to 38amps.  I was making coffee, using microwave and charging batteries.  A normal load in the past.  I was NOT the winner of the 650million Powerball so not really interested in going to Cummins Coach Care.  We will be at our Arizona City home in 7-8 days and the coach will be parked for 3-4 months before heading to Quartszite.  My genset is not on sliding tray and must be removed to work to be done.  Does anybody know a genset mechanic that doesn't have solid gold tools like Coach Care?  The  engine is still humming even when the breaker is tripped.  Not being knowledgeable on gensets my guess something is wearing out.  Any thoughts?  Ken Parsons 72707 541 963 8990

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I would check the the screws at those breakers if you can access them, then go to the transfer switch and check them where they come into the transfer switch. Work your way back to the panel inside the coach doing the same thing. Try to recreate the scenario when you had the problem see if it is still happening. Are you running both rooftop ac’s? Try bringing on some loads one at a time maybe while monitoring your amp draw. Think your way thru it and observe.

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Onan recommends preventative maintenance on their generators. Your text on not removing the genset tells me that you have not kept up the required PM recommended in your manual.  Those PM's are there for a reason.  Some of them require removing side, back, and top panels to perform the work.  If not, you are running on borrowed time with the 3800 running hours you posted. Good luck on not having to spend a lot of money to bring it up to par. 

Chuck B 2004 Windsor

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A cheaper possibility is that the breaker itself may be worn out. After a few times of tripping a breaker can start tripping at less and less amps. May not be the cause but it is a simple replacement and cheap. Also like Chuck said that is a lot of hours without PM.

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13 minutes ago, Tony G. said:

A cheaper possibility is that the breaker itself may be worn out. After a few times of tripping a breaker can start tripping at less and less amps. May not be the cause but it is a simple replacement and cheap. Also like Chuck said that is a lot of hours without PM.

Not real sure which breaker he is tripping.  Sounds like the one on the gen itself, and I have heard of those getting weak.  That's where I would look first.

I don't see where he says it hasn't been serviced though.  Just not as easy to do.

 

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The front cap opening for the generator has to come off.  Then the generator has to be removed using a fork lift in order to have access to all the panels on the generator to service it.  That is probably why he has not performed any PM on it.  Been there and experienced that on my 1998 Dip.  Chuck B 2004 Windsor

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34 minutes ago, Chuck B said:

The front cap opening for the generator has to come off.  Then the generator has to be removed using a fork lift in order to have access to all the panels on the generator to service it.  That is probably why he has not performed any PM on it.  Been there and experienced that on my 1998 Dip.  Chuck B 2004 Windsor

Our Endeavor was the same, difficult to access the generator.

However, none of that is necessary to replace or check the breaker,  and where does he say no PM has ever been done.

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The last 4 items on the Onan Periodic Maintenance schedule are 1000 hours items.  His generator is almost at 4,000 hours of run time.  Flush coolant system, replace coolant pressure cap, replace engine V belt, and replace coolant hoses and thermostat.  One has to gain access to those items.  One has to have access to them in order to perform them.  Top, side, and rear panel has to be removed to gain access to them.  Chuck B 2004 Windsor

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 Ok granted,  so how do you know that hasn't been done?  All Ken said in that regard was he knows that if it has to come out it is expensive especially at Cummins.           It really doesn't matter anyway,  none of that is even remotely likely to cause the breaker to trip.  IMHO

 

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On 10/10/2021 at 4:23 PM, kenandjoanne2002 said:

I have a Onan 7500w Quiet Diesel Generator in my 02 Diplomat pbdd.  The coach has 133k and genset has 3800hrs.  On my current trip twice the genset breaker has tripped.  The second time I was watching the numbers on the EMS panel hover close to 38amps.  I was making coffee, using microwave and charging batteries.  A normal load in the past.  I was NOT the winner of the 650million Powerball so not really interested in going to Cummins Coach Care.  We will be at our Arizona City home in 7-8 days and the coach will be parked for 3-4 months before heading to Quartszite.  My genset is not on sliding tray and must be removed to work to be done.  Does anybody know a genset mechanic that doesn't have solid gold tools like Coach Care?  The  engine is still humming even when the breaker is tripped.  Not being knowledgeable on gensets my guess something is wearing out.  Any thoughts?  Ken Parsons 72707 541 963 8990

Ken I am with TonyG7RayDavis,I would start with breaker on genny itself first. I have an 04 40'Diplomat PDQ and a few years ago my breaker kept tripping randomly on genny,I did amazon trick and put new one on .As I remember it was somewhat of a PIA even though mine is on a pullout tray not rocket science but time consuming to get all covers off to access mounts of breaker. Solved problem never tripped again,I think breaker was somewhere around $30-$40.Cheap fix! Good Luck! My Dip currently has 62k miles I did this repair at probably 15k miles ago...so you did well to get 133miles! Whatever your doing keep it up!

Bruce E Crocker

2004 40'Diplomat PDQ

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Ken - please disregard any unfounded assumptions in this thread and focus on the helpful suggestions.  I would be very interested in knowing what the findings are on your genset breaker issue.   Maybe the folks in Tucson can help.  I find myself in possession of a coach with an 8k Onan with 1400 hours, and I have limited info on prior owner maintenance.  If I develop similar problems in spite of my attempts to get up to snuff with the maintenance and still hold down a full time job, your outcome could give me a place to start. Good luck in the days ahead.  Please circle back here to post progress and results! 

Thanks, 

Steve

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The most likely problem is the breaker on the generator is weak and tripping.  The other thing related to this is the way the generator is wired and the current reading you see.  There are two 120 circuits on the 7500 and 8000KW units with a common ground.  Set up such that the voltage between the hots is zero or some would say in-phase. The amp reading is the total amps being supplied by both circuits because the sensor is on the ground wire in the 120 volt distribution panel.  What you don't know is the current draw on a individual circuit.  It's possible nearly all of the 38 amps is being drawn on one circuit.  The inverter/charge circuit supplies power to the charger, microwave, and all the outlets in the front of the coach including the TV.  So if you have the charger going at full bulk charging and then turn on the microwave, a coffee pot, toaster and maybe a hair dryer, all the amperage is going through one of the breakers on the generator and can exceed the 30/32 amp breaker capacity.  In addition the front or rear A/C will be on the same 120 volt circuit in the distribution box.   You can determine what is on each side of the distribution box by looking at it.  The main breakers are in the center, everything to the left is on one circuit and everything to the right is on the other.  Thus, you need to careful to balance your loads.  The 02 Dip probably doesn't have an EMS but that doesn't help either because it is disabled when on generator.  

The circuit breaker can be changed out without removing the generator from the coach.  It is panel and has to removed by opening the access panel.  Not easy to get it in (based on personal experience) but do able.

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