Onan QD7500 Inverter

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
Daleg1970

Daleg1970

Well-known member
Joined
May 2, 2013
Posts
89
Location
Palm Beach Gardens FL
I have an Onan QD7500 -- model 7.5HDKAJ11451D

According to the parts manual a model D uses Inverter 300-4800-96

Does anyone know if the inverter from the Model F, (300-5925-96 or equivalent)-- can be used in the earlier model Onan QD7500 ???

When I search for Onan 300-4800-96 I return nothing.

thx Dale
 
Have you tried Cummins Power Tech Support?  1-800-888-6626
 
Dale , if yours is bad, do you know why//>>>Dan  ( I found the hard way that the QD is VERY sensitive about removing loads BEFORE shutting down the generator, it was a $1400 lesson)
 
I have no real idea why.

I tested the generator the day before we left for a week -- worked fine (though I did hear a clicking somewhere in the front area, but could not isolate that to the diesel-- and things were just airing up etc.)
Tried to fire up in Key West last week -- nothing

No lights -- nothing -- No fault codes either  (I have since pulled that switch and it is good and the light works on the bench)

I have now used the service book to do everything suggested and am to the line that says -- replace the controller board.
I have jumped the starter and there is good power to turn the diesel over -- just no start circuits.

If I understand correctly you are saying -- "Do not shut down under load" --like with an AC running.

thx -- Dale


 
Dale-

Yes, I believe that's what he is saying.  That is something I was taught as well, going both directions.  i.e., when starting the generator up, make sure you don't have things switched on that will immediately put it under load.  Wait a few minutes after the genny is started before switching on loads and shut off electrical items and let the genny idle for a few minutes before shutting the genny off. 

Good luck in diagnosing your troubles.

 
Hello Scott == long time since we emailed ===


I have not done that and I hear the generator start and run briefly (maybe 20 -30 seconds) before it fully kicks in and accepts a load.

How do you ensure no load when starting then shed load prior to shutdown?
Do you use the AC output breaker on the Generator????

thx Dale

 
Good talking to you, Dale.  Nice to see you are "living the dream".  With RV ownership comes RV repair.  :)

I don't worry about shedding ALL load, so no I don't shut off any breakers.  I just make sure there is nothing major turned on when either starting or stopping the generator.  By "major", I mean battery charger/inverter, air conditioning and electric water heater.  Those are the big consumers of AC power.  I might be missing something, but I think that about covers it. 

Perhaps others more knowledgeable will chime in.
 
I don't worry about anything smaller than the a/c units, which combine for about 25A and have a start surge double that. Even a large inverter/cahrger won't pull more than about 10A, and that only with near-dead batteries. Water heater is 12A, if the thermostat is calling for heat.

Fleetwood RVs usually have a delay time built into the transfer switch to allow the power system to "settle down". Mine is almost a full minute.

It is good practice to avoid switching power under load, regardless of whether it is genset, shore power or inverter. Big power surges are hard on both the power source and the appliances involved, and mechanical switches can arc.  The systems are designed to withstand that, but each time takes a small toll, the electrical equivalent of wear & tear.
 
Whenever I state in a post, "others more knowledgeable will chime in," I'm generally thinking of Gary.  ;)  Good information to know from Gary.  I just shut off everything I listed because they are all within arms reach of each other in the coach.
 
Nothing wrong with that, and the more things that are off, the better it is.  However, 10 amps is not considered a large load in this sort of system.

Note that for any really serious load, the genset's own breakers will trip before serious damage occurs. We are talking about reducing wear & year, not avoiding disaster.
 
  DISASTER meaning an inverter that requires removal, teardown ,replacement and re installing, all expensive.  ( I did all my own removal, and replacement,  still got knicked for the inverter install by Onan.>>>Dan
 
thanks all -- the comments make sense and is what I have been doing -- no large loads on either shutdown or startup --- such as AC/waterheater/propane heaters -- and such.

Am still deciding what to do about the controller/inverter ---currently talking to someone on EBAY about a used one -- but looking for a bit more security before going that way.

thx again --- Dale


 
Sounds like a trip to a shop that knows Onan generators might be in order. Get them to troubleshoot and provide a quote and description of what is needed. I would hate to pay big bucks for a part and that not be the problem.
 
Does your QD7500 have two inverters?  Or is it just one? I'm under the impression mine has two, but maybe it's one physical unit. The Service Manual refers to it as the "controller/inverter assembly", and everything electronically important seems to be package in that one module.
 
Hello Gary --

it appears to be one large unit -- the parts manual calls it an "Inverter" with one part number --- but in the troubleshooting area when you get to where I am it says -- replace the controller.
Neither in the parts diagrams, nor in the parts index, is anything called a controller.

I am negotating on a used one now -- the question is how much risk and headache do I want to go through to potentially save a thousand dollars.'

The Generator has been disassembled to the point I am ready to take out the inverter.

I really see nothing more to test.

thx Dale

 
I have debated going ahead and removing that Inverter "assembly" as you call it, and open it and see what is inside.
I doubt anything is serviceable or repairable but you never know.  I might find a board number and google it and get lucky.

thx --- Dale
 
The main reason for turning off the large loads before stopping the generator is to avoid stressing the voltage regulator in the controller board.

The voltage regulator varies the amount of drive current sent to the generator's field coil to control the output voltage.  Powering a load requires more drive current than when the generator is idle.

When you stop the generator, it's output voltage falls as the generator slows to a stop.  The voltage regulator sees the decrease in voltage and sends the maximum current to the field in an attempt to keep the voltage within spec.  This is stresses the regulator to it's limit and if the generator is powering a load the regulator spends more time at maximum stress compared to shutting down the generator down without a load on it.

The other reason not to shut down a generator while it's under load is the same as not shutting down the main engine immediately after pulling a hill.  When the engine is working hard all of it's parts are hotter than when it's not under a load.  The cooling system shuts down when the engine stops, and you want to give it a chance to remove the excess heat from the engine before shutting it off.
 
You must log in or register to reply here.

Latest posts

Members online

Total: 1,171 (members: 24, guests: 1,147)

Forum statistics

Threads
131,932
Posts
1,387,726
Members
137,682
Latest member
duckyw7528
Back
Top Bottom