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Onan 7.5JB - Wiring


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  #61  
Old 02-01-2017, 02:15:36 PM
len k len k is offline
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Default Re: Onan 7.5JB - Wiring

Agreed, likely need a new main stator or a rewind. Think a few people here have a genhead available.

There is slight hope mice chewed T leads inside the genhead and shorted them. When I started my JB mice nesting blew out the bat charge resistor vent (my stator was good). But at 7.5 kw won't take many seconds to cook the windings, guessing it's gone within 15 sec (maybe 5 sec). Still I'ld open it up and take a look, nothing to lose. At least you get to see what went wrong.

Last edited by len k; 02-01-2017 at 02:47:26 PM.
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Old 02-01-2017, 03:01:30 PM
Kevin K Kevin K is offline
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Default Re: Onan 7.5JB - Wiring

Maybe Joe (Yellowlister) has a genhead available. It wouldn't hurt to go to the parting out thread and ask. Otherwise the unit is BER. Having it professionally rewound will cost more than it is worth, and prices of parts on eBay are just crazy.

If it were mine, I would pull the stator and see if it could be repaired.

What is the backstory on the generator? What did the previous owner say? Once again this serves as a warning: If you don't actually SEE it running and generating, it's really not worth much more than scrap value.
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  #63  
Old 02-01-2017, 04:59:23 PM
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Default Re: Onan 7.5JB - Wiring

I think before condemning the stator I would want to physically examine it carefully. I would suggest taking it to a local motor rewinding shop to have them check it. It is a bit of work to get the stator off but it will give a definitive answer to whether it is good or not. I have at least one stator - rotor pair in 120/240V but someone else closer might have one too. Pm me if you want to discuss troubleshooting over the phone in more detail. Cheers Dan
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  #64  
Old 02-04-2017, 04:02:00 PM
kiteoregon kiteoregon is offline
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Default Re: Onan 7.5JB - Wiring

Ok, so after some bad weather and some power outages i had a chance to remove the cover and get a look at the stator. Attached are a couple pictures of the windings.
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  #65  
Old 02-04-2017, 04:04:43 PM
kiteoregon kiteoregon is offline
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Default Re: Onan 7.5JB - Wiring

Here are some pictures, i am not sure if you can see it but it looks like the wire wrap in the back right side is a bit melted?

How do i remove the assembly, i have the outer bolts / nuts removed, looks like i need to remove the center nut on the shaft, however the unit turn when any pressure is applied. What is the best way to keep the shaft still while cranking on the bolt? Impact gun?

Thanks.
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  #66  
Old 02-04-2017, 04:49:32 PM
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Default Re: Onan 7.5JB - Wiring

The first four photos are the exciter, which looks good. In the last two you can see the main generator armature windings *stator* which look mighty dark to me.

Yeah, an impact wrench ought to do the job nicely. Even tapping on the end of the wrench with a hammer will likely break loose the bolt.
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  #67  
Old 02-04-2017, 05:02:45 PM
kiteoregon kiteoregon is offline
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Default Re: Onan 7.5JB - Wiring

Once i fee the bolt, do i need to use a puller, or should the assembly pull out as a unit?
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  #68  
Old 02-04-2017, 05:37:13 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB - Wiring

Quote:
Originally Posted by kiteoregon View Post
Once i fee the bolt, do i need to use a puller, or should the assembly pull out as a unit?
No.

Generator disassembly is covered in the YD service manual pretty thoroughly.

Remove the F-1 & 2 Wires. pull the end bell containing the bearing. Disconnect the wire from the charge resistor and feed it back as you remove the stator, then the rotor will be exposed.

This is the short version, it is all pretty straight forward until you need to remove the rotor. Rotor removal usually involves a BFH and a block of wood and sometimes much patients and a few bad words.

There are many threads on this subject.
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  #69  
Old 02-04-2017, 06:52:42 PM
len k len k is offline
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Default Re: Onan 7.5JB - Wiring

The front 1-st stage windings look good.
Those rear windings in the 2nd stage (main stator) look questionable. You'll see them better as you take it apart.
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  #70  
Old 02-04-2017, 11:18:41 PM
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Default Re: Onan 7.5JB - Wiring

If you can get a puller to bear on the end of the rotor it will pull the end bell off and if you are lucky the stator will crack loose from the engine side housing as well. then just wiggle it forward over the rotor. You can remove the rotor then but it may not be necessary. Cheers Dan
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Old 02-09-2017, 11:17:37 PM
kiteoregon kiteoregon is offline
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Default Re: Onan 7.5JB - Wiring

So far, I have removed the rotor through stud bolt, the bolts on the stator through stud as well as the cover. I can't however move the end bell at all. I have been following the YD major service manual page 16, i think i am stuck on step 5. Can anybody provide some pro tips to get this thing removed?

Also 3/4 of the stator through studs un-threaded with the bolts on them, should i get the bolts off and thread them back in, or does it make any difference?

Here is the doc i have been using:
http://www.twinslan.net/~n0nas/manua...0(10-1975).pdf

Thanks.
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  #72  
Old 02-09-2017, 11:30:35 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 7.5JB - Wiring

If memory serves me correctly, put the thru stud back in, just leave the nut off.

Getting the end bell off, try using a flat bar of some sort and smacking the raised ridge on the bell where it meets the stator, do it all around the bell and see if that does not break it loose.

For pulling the stator, I would leave the two top thru studs screwed in to help support the stator as you gently slide it out once you break it loose. I believe there are small screw driver size slots between it and the bell housing. Also do not forget to unplug F1 and F2 from the end bell.

Rotor, take a solid block of wood, aluminum or something and smack at least 4 places around the rotor on the bare steel area. Not on the windings or the poles!!! It is a taper fit on the crankshaft. I like to put the nut back on the thru stud so as to not have it slide back and fall off when it breaks loose, once loose remove nut and carefully slide it off. I hope this helps.

Last edited by nothingbutdarts; 02-10-2017 at 12:20:46 AM. Reason: spelling
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  #73  
Old 02-09-2017, 11:45:52 PM
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Default Re: Onan 7.5JB - Wiring

Try to get a biggish 2 jaw puller on to the end bell. If you reinsert the rotor center through bolt and install a second nut for the puller to bear on make sure to get the correct thread size as it is not a coarse thread or you can use a small socket to push on. The 4 stator bolts have to be removed but then you can tighten the puller and either the stator and end bell will come off the rear bearing together or the end bell will come by itself then you can pull the endbell free as it comes off the rear bearing. If the stator stays put it can be loosened by whacking it with a 2x4, usually it wont take much. This leaves the rotor in place. In your case you may not have to remove the rotor to check the stator. If you do need to remove the rotor you can loosen the rotor through bolt a couple of turns to give it some slack. Then whack the side of the rotor with a hammer cushioned by a piece of hardwood or a big brass hammer so as not to damage the laminations of the rotor. The through bolt will prevent the rotor from falling off and getting damaged. You will be able to see the rotor move when it breaks loose but check to see after every time after you hit it. Then you can remove the through bolt while supporting the rotor with a big block of wood or something, the rotor is heavy!!. Don't remove the rotor if you don't have to!! Cheers Dan
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  #74  
Old 10-12-2017, 12:11:55 PM
kiteoregon kiteoregon is offline
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Default Re: Onan 7.5JB - Wiring

Bringing an old thread back to life, this generator sat un-touched since my last posts. The weather has changed and we had our first power outage. Now i am back on getting this thing working.

Model: 7.5JB
Serial: A960597423
Spec: 68774E

I have pulled the stater / winding, they look very crispy. What is the best course of action, try to find somebody to rebuild this or purchase a working gen head? Attached are the pictures of the gen side of the problem.

Thanks.
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  #75  
Old 10-12-2017, 06:42:55 PM
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Default Re: Onan 7.5JB - Wiring

Looks like the "Magic Smoke" has left the generator.

Yes, it is time to look for another JB. You now know a little more about what to look for. You might get lucky and find one that has a seized motor with a good gen section.

You now have a bunch of spare engine parts though.
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  #76  
Old 10-12-2017, 08:36:43 PM
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Default Re: Onan 7.5JB - Wiring

As it happens I have couple of 7.5 JB genheads attached to partly functional MDJE generators which I could be pursuaded to part with for reasonable money. But you would have to come get one of them. I bought 8 7.5 MDJEs in the last year and am never going to get to all of them. I actually drove down to Portland to get a few. These would be 120/240V genends so you would get full output. PM me if you are interested. Cheers Dan
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