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Onan 25EC-4R8/302D Stator rewind questions


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  #1  
Old 12-17-2010, 04:00:09 PM
Old Style Old Style is offline
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Default Onan 25EC-4R8/302D Stator rewind questions

25EC-4R8/302D 17B556724 3phase 208Volt 25Kw built Feb 1955 less than 2000hrs.

Stator is fried and the owner is considering rewinding. Questions are:

1) Is it worth it? 2) Can we change/upgrade the voltage to 240v?

The rewind shop owner is a friend of mine so cost will be less.

Haven't broke it down yet hoping the rotor is good.

Thanks Glenn
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Old 12-17-2010, 04:40:31 PM
Isaac-1 Isaac-1 is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

If it were mine I would strongly consider replacing the entire generator end with one off a somewhat newer Onan model (assuming it would bolt up), perhaps you can find a 1980's vintage UR series 30EK with a bad engine, they seem to be everywhere, or similar (either 12 lead reconnectable, or 120/240 single phase end), this would not only fix your stator issue, but would give you electronic voltage regulation, better safeties, and easier parts availability.

Ike
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Old 12-17-2010, 06:26:30 PM
K D Redd K D Redd is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

If you rewind it and the slots in the stator are correct, I would have it rewound as a 12 lead head. Then you can get any voltage, with the correct regulator, from it.

Kent
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Old 12-17-2010, 11:34:00 PM
Jim Rankin Jim Rankin is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

or just wind it for whatever you want it to be, single phase, 3 phase like it is, etc. Should be possible for the shop to do it.

What kind of regulation/exciter does it have? Magneciter? or DC generator on the back end with a mechanical regulator?

That serial number is January of 1957 (1=Jan, 7= the 7th year, B = the '50s)
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Old 12-18-2010, 08:44:32 AM
Old Style Old Style is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

Quote:
perhaps you can find a 1980's vintage UR series 30EK with a bad engine, they seem to be everywhere
Ike Simple upgrade but I'm on the wrong coast, I see more on the East coast. Will keep looking till the day we start wrapping wire... Thanks!

Quote:
If you rewind it and the slots in the stator are correct, I would have it rewound as a 12 lead head.
Kent Haven't torn it down yet but that was my first thought.

Quote:
just wind it for whatever you want it to be // Jan 1957
Jim The new location is now wired 3ph to the transfer sw. But the new coolers on the roof (liquor store) are 240 single ph. Haven't been able to get the electrician to say if they are 240 only.... Rain projected for 5 more days.

Not a Magneciter but is regulated by a Powertronics A-50. Here is a pic of the brush pac. One of the brush spring clips came off and shorted the stator, I think, letting out the magic smoke.... '57 was a good yr! My Favorite Chevy

The rewind shop here doesn't do generators or DC motors and we are a small town so mostly water pump rebuilding and standard rewinds.

Any insight or link to helpful info as to rewinding to change to 240v or 12 lead head would be great! They can do the job but a few good pointers will go a long way to get it done right!

If the rotor isn't damaged. Is there any concern or change needed?


Thanks guys! Great as always!!



Last edited by Old Style; 12-18-2010 at 08:47:38 AM. Reason: add rotor info
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  #6  
Old 12-25-2010, 06:02:37 AM
Old Style Old Style is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

Merry Christmas!

The tear down is done! 7hrs later (including lunch) here are the pics: Click here

No visible signs of a root cause. I thought it was a brush spring clip that was missing. The unit had been hooked up to the building before I had a chance to run it independently of any connections.

Transfer switch isolated everything but neutral but smoke erupted upon start-up. Looks like just the stator but it was late so no testing and no spring clip!

More next week! Nappy New Year to All!!!
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  #7  
Old 12-25-2010, 09:54:14 AM
Gunny Gunny is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

Looked at your photos and do not see where the smoke came from, you might get lucky and be able to repair, not have to do a rewind.

Somewhere, I have Onan rewind data, not sure if it goes back that far, will look for it today when the Christmas uproar calms down and if I do find it, I'll be glad to share.

To answer the original question, yes, it can be rewound to whatever voltage configuration you want it to be, including stuff you probably never heard of or have any use for. And yes, usually costs about half of a new to rewind.

Good luck with it and thanks for sharing the photos.

Merry Christmas.
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Old 12-25-2010, 03:25:46 PM
Jim Rankin Jim Rankin is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

The motor shop should have 3 phase available to run up their rewinds for testing. Even 208 or 240 should be enough to connect to the stator and see if it will rotate a ball bearing around the inside of the stator. They should be able to confirm it's good or bad since that's pretty standard stuff in that business. There's nothing really different about that stator and a 4 pole 3 phase induction motor. If you want to go to another phase arrangement, winding data would be nice. A 12 lead reconnectable stator is wound exactly the same as common 9 lead dual voltage Y wound 3 phase motors which are convertable between 460 and 208/230 volt, only the 10,11,12 terminals are not spliced into a Y buried inside the motor, instead they are brought out into the terminal box like the other leads.

If your load is primarily single phase with the 240 volt condensors on the roof, but you do need some 3phase for somthing, a good connection would be the 120/240 3 phase delta 4 wire connection. BUT, you need to match the utility service unless you will always operate off grid. Utilities do not often install the 120/240 open delta service which uses 2 transformers (2 phases and the powerline neutral) where they have 3 phases available. They will almost always use a 120/208 Y 3phase 3 transformer bank.
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Old 12-25-2010, 05:08:49 PM
mrmegoo mrmegoo is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

I am not real blessed with knowledge on the big gen sets, but looking at the pictures I did not see too much indication of a burnt up stator. However the rotor sure looked like a crispy critter. Just my $.02 worth.
Have a Merry CHRISTmas & may all your power outages be short lived.
Mel
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Old 12-25-2010, 08:11:24 PM
Old Style Old Style is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

Nothing new till Monday. Then I will know more about condition of the stator. Also I will take closer pics of both the rotor and stator as they are now.

Since the location is now wired for 3phase I might as well stay that way; other wise it might get complicated both at the control box (genset) and at the transfer switch (3 pole). Right now there are four leads: neutral, plus 3 hot. If I go single phase I guess we just drop one wire to the transfer switch.

As I understand it the stator is 4 wire 120/208. If I rewind it I should upgrade it to 120/240 3phase. Since it is dedicated to this location I don't see a reason to go 12 wire unless that is the best/only way to get 120/240. I will check to see if there is any reason 3phase is needed now.

My friends rewind shop does small to large rewinds (biggest I saw was 3 x 4ft) but doesn't do generators. Liability? Refresher instruction might be needed.

More pics Monday but when I first looked at the rotor I thought it looked fried also. I think it is just the coating but I haven't tested it for shorts. I can see what looks like burnt insulation on the end of the stator but again no testing. What simple tests can I take?

Stator: Slip ring to ground. Slip ring to slip ring. Rotor: commutator to ground. My books don't cover this topic.

Thanks for the ideas so far! If I get this corrected Mike's buying! ( This gen's powering a "Liquor" store ya know )
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  #11  
Old 12-25-2010, 11:10:26 PM
Jim Rankin Jim Rankin is offline
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Default Re: 25EC-4R8/302D Stator rewind questions

If everything in the store functions properly on utility power, match that. The overloads and circuits should be set up for the 208 single and 3 phase. If you are having trouble with some of the "220" motors which are probably the ones that aren't dual voltage rated 208/230 volts, then you could use the 120/240 3phase connection of the 12 lead 3phase stator, but that would only help when running on generator power.

While it wouldn't be a problem for the shop to connect the rewind for the 120/240 3 phase delta, it would be simpler and less chance of difficulties to have them connect it as a 12 lead and then make the connection afterwards. Then you have the option of 120/208 3phase Y, 120/240 3phase delta and 277/480 3phase Y, whatever you need. All for the cost of attaching 3 leads to the ends of 3 coils in the stator instead of splicing them in a Y.

The Powertronics probably can handle any of the voltage combinations as long as you feed it from the correct connections to the stator.
http://www.power-tronics.com/archive...ts/a50/a50.htm
I'm not familiar with that one, does it regulate the DC exciter field or the main field on the rotor directly? Another question, is this an exciter crank set, or is there a regular gear drive starter on the engine?

On the tests, an ohmeter from lead to lead on the stator should show continuity when any combinations of leads are tested A-B, B-C, A-C should be equal and higher than A-N, B-N, C-N by about 2X. None of the leads should show any continuity to the iron of the laminations. The same goes for the rotor. Slipring to slipring should show continuity, and ??? ohms (if you can get the spec you can compare). Also no continuity to the shaft.

Same thing for the DC exciter field if it is being used, F1(F+) and F2(F-) should show continuity/resistance of ????, but no continuity to the iron laminations. On the commutator of the DC exciter, every bar should show nearly equal continuity to the ones next to it, all the way around the commutator. Any ones that do not show continuity or higher resistance, inspect carefully where the wires are connected to the backside of the bar. Again, no continuity to the iron.

Most likely you just have a bad stator, but some of the other components might be the problem and be cheaper to fix or expensive enough to change your plans on fixing it. It's worth checking it all out even if the stator is bad.
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  #12  
Old 12-27-2010, 06:55:51 PM
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

Update Monday

More Pics: Click here I tried to get all 4 sides and edges of the rotor.

Well it doesn't look good. I am located in a canyon in the redwoods everything metal sweats here. I tried to get him to take it back to the original location after the motor service & trailer removal but it was easier for him to leave it here. Only had one rain event but.... even covered the damage was done. (guessing) ... Right now I don't know when it was run under a balanced load last. It's possible one phase was loaded heavy, I just don't know.

Old varnish and moisture don't mix... The AC stator is burnt, the rotor shows it needs to be baked and re-varnished.
The DC stator shows it needs baking also; the rotor is good but it could use baking too.

As it stands we spend 800.00 and still have 1957 vintage with no guarantee there isn't other problems. The Powertronics regulator could have taken a hit
also. But it's not my decision. I can't guarantee smooth sailing

If we decide to do all the above I have a question about the voltage change.

Is there any issue with the rotor; originally being for 208v now running in a 240v stator?

The stator would be rewound: 120/240 3 phase delta internal.

I need a beer.....
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  #13  
Old 12-27-2010, 07:23:28 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

You are past the point where I would probably be looking for another generator or a replacement end. As much as I dislike imported stuff , buying a new SAE single bearing 24kw end with VR for about $1K compares favorably to paying $800 for a rewind with "no guarantee".
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Old 12-27-2010, 09:18:35 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

I have to agree with Wayne. It has not been too long ago there was a 30 KW unit in the Redwood City area in the $3,000 range. There is a nice looking 1993, 35EK in Denver now http://ebay.com/ONAN-GENSET-35EK-35-EK-GENERATOR-35KW-44KVA-/290515377273 $4,000 buy it now, surely it would ship for under a grand.
Unless I need the generator next week I think I would look a little more. When you get into the 30KW range there is less competition from “home owners” wanting back up units.
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Old 12-28-2010, 01:39:06 PM
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Smile Re: Onan 25EC-4R8/302D Stator rewind questions

If the use of this generator is really "important" (a compared to the one at my house, which makes life easier in the event of a power failure), I would think a new or newer unit, like the one listed above on ebay, would be in order (That one appears to be extended-stack, since it delivers 35 KW in single-phase or 3-phase operation).
There is a BIG difference between those of us who keep and work on generators as a sort-of "hobby", and those who absolutely depend upon them to avert disasters or large monetary losses. My son is the IT manager for a food-service organization - they called him yesterday (he was off for the Christmas holidays) because the main UPS for their IT equipment had only 12 minutes remaining as the result of a power failure. He reminded them that they had a natural-gas manual-transfer generator installed for that equipment, and to go outside and start it up! Battery was dead (no one had run it recently), but it jump-started OK, and solved the problem. That use (and many like it) doesn't need a 50+ year-old generator to rely on. Just my thoughts.
Dave Edmonds
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Old 12-28-2010, 04:12:54 PM
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

I completely agree that a newer unit would be best! I saw that one listed on ebay. But the decision has been made; almost.

What I need to know is if anyone has knowledge as to the relationship between the rotor and stator.

Rotor stays the same 120/208v 3phase (just baked and dipped) ; stator changes to 120/240v 3phase windings. Any issues there?

Thanks for all the suggestions so far. I have read and considered each one.

If it were mine I would wait till the right unit at the right price came along.
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Old 12-28-2010, 04:54:22 PM
Isaac-1 Isaac-1 is offline
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

If you are ever going to consider selling this generator you would be better off having the stator rewired as a 12 lead reconnectable, 120/240 3 phase Delta is a rather unusual voltage (I know we have it here). A 12 lead could somewhat easily be reconnected for any of the common output voltages, and doe snot cost much more to do.
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Old 12-28-2010, 06:40:10 PM
Jack Hottel Jack Hottel is offline
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

Quote:
Originally Posted by Old Style View Post
What I need to know is if anyone has knowledge as to the relationship between the rotor and stator.

Rotor stays the same 120/208v 3phase (just baked and dipped) ; stator changes to 120/240v 3phase windings. Any issues there?
I believe that no changes are required to the rotor no matter how the stator is wound.
Jack Hottel
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Old 12-29-2010, 09:20:32 AM
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

Thanks Jack the rotor was a unknown issue! Ike I don't understand the problems with 120/240 3ph delta but adding a wiring box where the gas tank used to be will solve (without good access) that! So 12 lead it is!

Gunny if you find time and your re-wind data goes back that far Thanks!

Dave , Max & Wayne I am just doing this for a friend. I set this gen-set up for him 5 yrs. ago and it has been ok up till now. He has a $$$ investment in this unit and I just went thru the motor and relocation. (Moved to new building next door to him) Pulled it off a trailer and onto a new pad. I tried for 2ft risers but only got 1ft.

That '93 unit would have been ideal but cost plus shipping is a no-go. The rewind is guaranteed but after reassembly there is no guarantee other problems won't arrive! After all it is still a 50yr old unit!

Jim Thanks for the testing procedures! I am still going to allow the shop make sure of the results I found. Especially the rotor as it shows moisture grounding but not a direct short. At first glance the dip they used sure looked burnt...

Pulling the rotor this morning and giving the owner one last chance to cut his looses and upgrade to something NEWER like that '93 unit. He can afford it ; he's getting my labor for next to nothing. But... It gives me something to do and you know how it is to be so close to finished when disaster strikes. All that work and nothing to show for it.

.
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Old 12-29-2010, 11:40:38 AM
Jim Rankin Jim Rankin is offline
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Default Re: Onan 25EC-4R8/302D Stator rewind questions

Nothing wrong with 120/240 3phase, except it's uncommon. We also have it here in the country.

The connection is/was commonly used by a utility where there is only 2 phases run to a location or they want to keep motor starting surge loads off the 3rd phase for some reason. They can take 2 high voltage phases and the neutral and connect 2 standard single phase 120/240 transformers in an open delta which produces 120/240 3phase. It works out ok for combinations of single and 3 phase loads especially when either one is a small part of the total. So if someone needs 3phase for a single piece of equipment, it's simple and cheaper to add one transformer and bring it in.

The thing to watch out for is one of the phases will measure ~208 Volts to the neutral instead of all 3 phases being 120 like with 120/208 Y 3 phase. The other 2 phases are 120 to the neutral and they are used for all the single phase 120 circuits. If you snap in a breaker on the "stinger" by mistake, you will damage something. Some jurisdictions will only approve an installation like this with all the single phase circuits run into a sub panel which feeds out of the main 3phase panel.

Most utilities will install a 120/208 3phase 3 transformer bank wherever they can and may not even quote the option of an open delta bank where they do not already have all 3 phases. Out here in the country, we only recently had a 3rd high voltage phase conductor run through. Our REA cooperative is not replacing the open delta banks, and it is not a good option to "close the deltas" on these 120/240 3 phase services since the loss of a phase or even a blown fuse will lead to a full delta bank backfeeding the dead phase, usually at reduced voltage with overloading of the transformers involved. The open delta bank does not behave this way.
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