Onan QD 7500 Rotor Failure

[Gt4rust]

I am in the process of rebuilding the stator and rotor on my 2004 Onan 7500qd generator. The epoxy on the magnets that are attached to the rotor are coming loose and exploding inside the stator. This appears to be an issue with many of these generators that are 20 years old.

I have talked with Cummins to get replacement parts and they are on national back order with no ETA. They told me of 3 other QD 7500 that just came in with the same issue, and that is just in Columbus, OH

This is just info for anyone else with a 20 year old Onan. My generator has 500 hours on it.

If anyone has a kit (stator & rotor) part #A053K355
Please let me know. Or a stator by itself.

[MrMark52]

Wow! Is there something that can be done now to prevent the failure on a 20 year old unit?

Ours is at 21 years, a 5.5kw HGJAB - would prefer to head off the grenading of our unit as opposed to waiting for it to happen when we need it most.

[donr103]

Did Cummings give you an idea where to send off for repair ? Cummings must use someone ? You tube shows different companies rewinding motors .. I guess engineers know the life spans of resins and glues used in these units.. and never expected they would be used past 20 to 30 yrs.. it's easy to make something last forever.. but hard to make the cheapest thing last just long enough to get out of warranty and make a fortune selling it..
Good luck and keep us posted

[USMCRET]

Originally Posted by MrMark52

Wow! Is there something that can be done now to prevent the failure on a 20 year old unit?

Ours is at 21 years, a 5.5kw HGJAB - would prefer to head off the grenading of our unit as opposed to waiting for it to happen when we need it most.

That issue is limited to the 7.5 kw models. You should be safe.

[MrMark52]

Originally Posted by USMCRET

That issue is limited to the 7.5 kw models. You should be safe.

Awesome - Thanks! Sorry for your plight. A couple of years ago when for whatever reason o was looking, I saw a lot of Onan/Cummins units For Sale cheap as pulls from old MoHo’s. That might be a resource if you can find one that someone has abused the engine.

[shootist]

I just had a stator off a Miller bobcat welder rewound on one end for the 220/120 output. It was 500$ in southern ca. I wouldn’t know where to source the magnets. I wonder if it’s extreme temperature swings that cause them to break loose?

https://www.partsfortechs.com/stator...an-p-2305.html
Not a bad price for new when they become available

[dons2346]

The problem is the glue used on the magnets. It absorbs moisture which weakens it and then the magnets let go. This one of the reasons Onan says to exercise the generator on a regular basis, to heat things up and dry the glue out. Got this from a certified Onan tech.

[shootist]

Originally Posted by dons2346

The problem is the glue used on the magnets. It absorbs moisture which weakens it and then the magnets let go. This one of the reasons Onan says to exercise the generator on a regular basis, to heat things up and dry the glue out. Got this from a certified Onan tech.

that is great information!

[2004Horizon]

Onan is covering their ass. Glue can cannot be "exercised" to prevent a failure.

Time and temperature variations are the killer. So, don't think this is your fault.
I.e., there is nothing you can do to extend the life of your glued on magnets. If it's your time, it's your time, and you will will need to A) Pay for a new stator; or B) Buy a used generator at a salvage yard, and spap-out your old generator for the best option you can find, which can be faster and cheaper since finding a Stator is not easy or cheap.

My Onan QD750 cost me $2,200 to replace the magnets that "spun-off" and I had only 700 hours on the genset.

Note: Another important fact is that these QD7500/QD800 generators support/require a 70A neutral, which is accomplished by running two 35A neutral lines per phase.

Why do you need 70A? Answer: Your Coleman Mach Basement AC can produce between 50A-62.5A of in-rush current every time you start the compressor.

What's you say? YES! This is why your QD-Generator has two 35A circuit breakers, which monitor and protect the "neutral line" ...So if you thought these 35A CBs wer for the hot black/red 120V line, you would be mistaken. (And now you know! ...Those breakers are for the NEUTRAL LINE!)

THIS RAISES THE SUBJECT OF YOUR ATS TOO

Your OEM Automatic Transfer Switch (ATS) supports 70A neutral. To do this your ATS has two neutral wires (35A times 2) which is not common.

Note: When you connect to shore power your ATS bonds to up to 100A- Neutral shore power. So you are okay there. However, when you start your Basement AC on generator power, your generator has the capability of returning 70A through the ATS.

Therefore, if you own a QD7500/QD8000 and you need to replace your ATS, you better opt for a 100A ATS in today's market, because they don't make the good old ATS boxes like they used to. I.e., don't think a 50A-Service ATS box will work. With today's contractor-type ATS boxes you will need to buy a 100A+ ATS box if you have a basement AC or you risk premature ATS failure and possibly even fire.

[MrMark52]

Good stuff 2004Horizon!

[Gt4rust]

The local Cummins dealer here in Columbus, OH was able to locate 2 of the matched sets of stators and rotors. I am just finishing the installation and hope to have it running tonight. It cost $1400.00 for the main part and about $400.00 for the other necessary pieces.
I was told by the Cummins dealer that they will do the work, 6 hours labor once the generator is out of the coach.

[MrMark52]

Good for you! Keep us posted. Sounds a lot cheaper than a new unit with likely better reliability than of a used unit.

[OldWEB]

Originally Posted by 2004Horizon

... Note: Another important fact is that these QD7500/QD800 generators support/require a 70A neutral, which is accomplished by running two 35A neutral lines per phase.

Why do you need 70A? Answer: Your Coleman Mach Basement AC can produce between 50A-62.5A of in-rush current every time you start the compressor.

What's you say? YES! This is why your QD-Generator has two 35A circuit breakers, which monitor and protect the "neutral line" ...So if you thought these 35A CBs wer for the hot black/red 120V line, you would be mistaken. (And now you know! ...Those breakers are for the NEUTRAL LINE!)

THIS RAISES THE SUBJECT OF YOUR ATS TOO

Your OEM Automatic Transfer Switch (ATS) supports 70A neutral. To do this your ATS has two neutral wires (35A times 2) which is not common.

Note: When you connect to shore power your ATS bonds to up to 100A- Neutral shore power. So you are okay there. However, when you start your Basement AC on generator power, your generator has the capability of returning 70A through the ATS.

Therefore, if you own a QD7500/QD8000 and you need to replace your ATS, you better opt for a 100A ATS in today's market, because they don't make the good old ATS boxes like they used to. I.e., don't think a 50A-Service ATS box will work. With today's contractor-type ATS boxes you will need to buy a 100A+ ATS box if you have a basement AC or you risk premature ATS failure and possibly even fire.

When you have two separate 120V 35A feeds and combine them, the neutral WILL need to be capable of handling 70A, not rocket science. You have two hot leads able to deliver 35A each, the neutral(s) will need to return that current.
Now, when you have (in this case) a 50A SP cable, it is ass-u-me-d it is 120/240V and then the two 50A hot leads are opposite polarity (still 1 phase), the most that can appear on the neutral is 50A, not 100A. This is where some get into trouble, if they wire both hot wires on their 50A SP outlet to the same 120V leg, you will then see all the current on the single neutral and tend to overheat things a bit.
Now, as for the ATS-5070, there is no "bond" for 100A neutral current... bonding is for the Dr. Phil show, they state in their brochure re: generator:
**Note: L1 and L2 rated 35 amperes per leg with 70 ampere neutral when L1 and L2 are in phase. (Optional jumpers must be installed).
You are using two contacts for the neutral.


You mention the 60A inrush current of the compressor... think about it, ALL that current is going through ONE 35A breaker on the generator (and its wiring).

[groveln]

The stator on my 7500 Onan in my '04 American Eagle let go on the road at 13 years old & was a very expensive fix at Cummins in Cedar Rapids Iowa. Lost 3 days waiting for parts. Wish it would've happened on my way home instead of on the way out 4 hrs. from home.