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Author Topic: Worth Rewinding???  (Read 4126 times)

johnny williams

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Worth Rewinding???
« on: May 07, 2008, 09:59:48 PM »
Ok Guy's IthinkI already know the answer but I am going to ask anyway. I have a RMPS ST 7.5KW gen head that was oversped. Looks like the rotor expanded enough to rub the stator and built enough heat tomelt the insulation between the segments. Wires broken on the rotor also. Since I have no idea how to rewind one and really don't want to learn how I think this one is headed to the scrapyard. Right?

Johnny

Doug

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Re: Worth Rewinding???
« Reply #1 on: May 07, 2008, 11:53:13 PM »
Yes I would say its scrap.

Not sure how fast you oversped it, or what is considered safe ( I could look this up if I get a chance ), but I amagine that it not worth trying to salvage now. Once you starting rubbing rotor against stator and parts overheat and loosen its very hard to set things right again.

Sorry about your luck
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johnny williams

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Re: Worth Rewinding???
« Reply #2 on: May 08, 2008, 12:13:28 AM »
Thanks Doug, thats what I was thinking. Whe you play you gotta pay. We can't sit and watch these things all the time they are running, even if we want to. All we can do is make all is the best we can make it and go.

Thanks
Johnny

Doug

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Re: Worth Rewinding???
« Reply #3 on: May 08, 2008, 01:48:54 AM »
How fast did it over speed?

The fact that things spread and flung a part is kind of bothersome.

I have some tables that give the safe speed limits for armatures but they don't realy aply to to rotors. I would expect these shoudl safely survive 2500 to 3000 RPM over speeds before coming a part but honestly who knows its a a guess.

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mobile_bob

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Re: Worth Rewinding???
« Reply #4 on: May 08, 2008, 04:06:51 AM »
Doug could probably expand on this point as well

the laminations are insulated from each other to keep down eddy currents
when the lams get together and grind on one another you defeat some of this insulation
and i would expect come increase in eddy currents in this area, makes for more heat and
loss of efficiency.

probably never be the same after a rewind, and i wouldn't go to the trouble unless i was on a deserted island
and had no choice but to rewind it.

for the price of a new head it is hard to come out on a rewind unless you value your time pretty low.

after a rewind of the rotor it would need a rebalance anyway probably, adding to the cost or the time
to work that out as well.

if it were just the stator, i would go for it,
but given the fact the rotor took a beating too,, probably not worth the effort.

my .02

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

johnny williams

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Re: Worth Rewinding???
« Reply #5 on: May 08, 2008, 02:07:48 PM »
Doug, no idea how fast it was turning. A SWAG is >2500RPM.

Thats what I was thinking Bob. Just trying to figure out if I can travel and pick one up cheaper than having it shipped.
The house boss filled up the F-250 Monday- $99.00.
The closest dealert I can find is in Ga. close to Atlanta. Would be a nice day trip.

Johnny

Doug

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Re: Worth Rewinding???
« Reply #6 on: May 08, 2008, 09:03:45 PM »
We had a few tricks for spotting bad iron.....

A few loops of welding cable threw stator and feel around for hot spots.

We had a special rig for testing rotors that run current threw the shaft but that never realy told me much.

Sometimes you could save a stator that had rubbed out by beat the hell out of it with an oak block back and forth untill the the laminations shifted and moved back and forth to open them up a bit followed by a quick dip.

But as Bob said at this point its probably a lot more trouble than it worth.

Very few machines actulay have coated steel these days. The combination of oils burned onto surface and natural oxides after the heat treating process and then what ever wicks in from a vacuum dip is generaly good enough 
It's a Good Life, If You Don't Weaken