PDA

View Full Version : DIY electric motor re-wind?



Orrin
03-18-2010, 08:27 PM
Has anyone re-wound an electric motor successfully? Would you do it, again? I've done simple re-wind jobs, but one came up today that I'm not sure about.

The 5-h.p. 220 v. three phase idler motor on my rotary phase converter died, today. I've found a 3-h.p to use as a stop-gap, but it is barely adequate. I'd like to get the 5-horse back it operation if I could.

A professional re-wind would cost more than my hobbyist's budget should allow. I realize the materials, alone, would be very costly; but, I'd be willing to pay the money if I could do the job, myself.

Orrin

macona
03-18-2010, 08:36 PM
Done it, not successfully. Found out my laminations were shorted together so it was all moot in then end.

Here's the tread on PM where I rebuilt the motor:

http://www.practicalmachinist.com/vb/monarch-lathes/brady-penrod-coolant-ee-99260/

There is a book called "Electric Motor Repair" by Rosenberg. It is pretty much the bible when it comes to motor repair and rebuild. Kind of expensive. Turns out I had a copy sitting in my book case. Came in real handy.

doctor demo
03-18-2010, 08:43 PM
I guess I should stop dumping big old three phase motors for scrap prices and offer them to the needy for a small gratuity .

I would look around for a motor before rewinding one. Unless Colton is a motor desert there should be plenty around.

Steve

aboard_epsilon
03-18-2010, 08:53 PM
Used to watch my ex father inlaw do it ..
he was a pro rewind guy ..

it was quite involved

and he had to make plywood templates/ patterns to wind the wire around ..

and had to heat the motors in an old electric oven to soften the shellac

he also had counters on all his lathes to count the winds ..

for the larger motors ..he had to send them off after to have dynamically balanced .

hope this helps

all the best.markj

ADGO_Racing
03-18-2010, 09:27 PM
We used to do a lot of work for a couple motor shops....I wouldn't bother trying to rewind one yourself. Realistically, you can just about buy a new 5 HP motor for what you will have in a rewind. I would either find a good used 5 HP or just call up Baldor (Or who ever, I am not endorsing one over another, they just happen to have an ad in the magazine on my desk right now) and get a new one.

lakeside53
03-18-2010, 10:30 PM
Used 5hp 3ph motors go for close to free and up $100 around here.. Check the Seattle/Portland local Craigslist often. "Rebuilding" them (if required) is seldom more than just putting in new bearings and paint.

Tony Ennis
03-18-2010, 10:40 PM
Craigslist. Baldor 3ph 5HP $75. Madison IN.

http://louisville.craigslist.org/bfs/1638805705.html

Bob Ford
03-18-2010, 11:29 PM
I rewound motors for a living in the early 60s.
1. You have to get the proper size varnished wire.
2. You need milar or fish paper for the slots.
3. You need wooden wedges to tighten, but not smash the wires in the slots.
4. You need linen string to tie the winding together so they do not vibrate and short.
5. You need baking varnish or motor winding epoxy to stop vibration of the wires in the slots and spring vibration of the rest of the winding. If you use baking varnish you need a oven large enough to hold the stator while baking it at 350- 400 for about 6 hours.
6. It is probably easiest to burn the old wire out of the stator.

All things considered it is cheaper to just buy a motor.

Bob

oldtiffie
03-19-2010, 12:32 AM
I agree with Bob Ford.

I have had to have a couple of motors re-wound (and had them dynamically re-balanced as well). There were no replacements/spares for the motors which were then "specials".

The re-wind shop I used was in our industrial area and seems to get most of the work from the "Trade" - all of whom I spoke to held him in very high regard. I called in a few times to see what was involved and progress, and as a very definite non-electrical fitter, I can tell you that from what I saw I'd never attempt a re-wind.

I asked a couple of Electricians (Industrial) about it and they would not touch the job - just sent me off to the re-winder as being better, quicker and cheaper.

The re-winds lasted for years and were still going well when I disposed of the machines they were on.

I would not hesitate to get a motor re-wound if needs be. I'd never buy a "used" one unless I knew the owner and the motor history.

When I buy new I get a good 12-month warranty.

Its surprising just how expensive some of this "cheap" stuff can be - in many ways.

Evan
03-19-2010, 01:20 AM
I have rewound quite few small motors starting with slot car motors back in high school. Quite a bit more recently about 15 years ago I found a good deal on a 2000 watt under-hood mount alternator that is intended to produce 120vac at high idle. It had a cooked field so I rewound that and it still works. Very much more recently I rewound a 90VDC permanent magnet treadmill motor to run on 24VDC. I went down two wire gauges and managed to keep nearly the same number of windings as the original fill was only around 60 percent. By going very close to 100% fill and increasing the wire size two gauges the motor produces more torque and runs a lot cooler even though the voltage is lower.

There are more modern tricks that make it easier to do that it used to be. You can wrap the slots with Kapton tape instead of paper and use thin fiberglass shims instead of wood stick retainers. You don't need baking varnish if you use the rattle can equivalent and let it dry for a few days at a temperature near 150 F or so.

Any Varnish that meets ASTM-4228 will do. You can probably buy a can at your local motor rewinder which is what I do. If you talk nice to him he may also run off the coils for your job and sell them to you as a sort of a kit.

http://ixian.ca/pics6/varnish1.jpg

http://ixian.ca/pics6/varnish2.jpg

http://ixian.ca/pics6/armature.jpg

BTW, this evening I was ripping the copper out of an ancient 1/2 hp induction motor. It has a very lovely lamination stack and 36 generous poles with huge slots. It going to turn into a 4 or 5 hp 3 phase brushless DC motor. :D

Oh yeah, one other thing. I took apart a Maytag washing machine motor recently and started sawing off the copper on one side of the core. Damn thing is all aluminum wire with copper colored varnish.

John Stevenson
03-19-2010, 05:17 AM
Why do you have to have them dynamically rebalanced?

Orrin is talking about a 220v 5 Hp three phase motor which will have an alloy / iron rotor that you don't touch.

He'll be rewinding the stationary stator.

Different ball game from rewinding ARMATURES.

Mark has it correct, wind on plywood formers to get the coils, then fit into the slots.
Hard part is knowing how it was wound in the first place as regards what ends go where. Time for a sheet of paper and pencil, it's not hard, just tedious.

.

oldtiffie
03-19-2010, 07:47 AM
John,

I will answer by inter-lacing in red your post.


Why do you have to have them dynamically rebalanced?

I have any motor re-balanced that has any sizable rotating part/s. Doesn't cost much extra while it is in the re-wind shop.

Orrin is talking about a 220v 5 Hp three phase motor which will have an alloy / iron rotor that you don't touch.

He'll be rewinding the stationary stator.

Different ball game from rewinding ARMATURES.

Oops. You are right. I must have mis-read it as all of my motors are single-phase where the armatures are re-wound.

Mark has it correct, wind on plywood formers to get the coils, then fit into the slots.

I am no Electrician!!

Hard part is knowing how it was wound in the first place as regards what ends go where. Time for a sheet of paper and pencil, it's not hard, just tedious.

Too hard, too much to get wrong and with my luck and lack of the required skill-sets, it will wind up (sorry) in the re-wind shop anyway!!

.

J Tiers
03-19-2010, 08:03 AM
Re-winding is "simple".....

Just take off the bad stuff, and put on new insulation, wire, etc...... *nothing to it* just a little time and off you go........

However, the materials are not so easy to get. The process is a pain, there are details with 3 phase motors and other details with single-phase.

Motor manufacturers buy huge amounts of wire, and they can get odd-sizes that you can NOT get, if that is what is needed to fit. They have the facilities to dip and bake the varnish, etc, etc.

That varnish that Evan showed is "OK".... kind of. The right way to do it is to vacuum-fil the windings with the varnish, and then bake it. not all motors are done that way, they may be dipped and baked instead. But a spritz of varnish over the coil surface is NOT the same thing at all.

The thing to ask, about yourself OR a "rewind" shop, is "will the result be done better and more professionally than a chinese motor?". The answer to that determines what you should do, rewind it yourself, have it re-wound, or scrap it.

John Stevenson
03-19-2010, 08:55 AM
OK I'll do it in blue


John,

I will answer by inter-lacing in red your post.

Different ball game from rewinding ARMATURES.

Oops. You are right. I must have mis-read it as all of my motors are single-phase where the armatures are re-wound.

Single Phase AC motors still have a solid alloy / iron rotor.
It's only the stator windings, centrifugal switches and or capacitors that distinguish between a 3 phase and single phase.

wierdscience
03-19-2010, 09:02 AM
Done it before,probably will do it again,it's just tedious boring work,but we're used to that aren't we?

Problem is the current price of copper,new magnet wire floats with the copper market which is up right now.

Odds are you could get a new Chinese TEFC cast iron frame motor for what the two six pound spools of wire will cost.Last I bought was 4 years ago,two 6lb rolls of 18ga wire cost me $86/roll.That was when copper scrap was $.85/lb,now it's $3.15 do the math.

I priced a 10hp ,215t frame TEFC motor Monday,$310 including freight.

Lew Hartswick
03-19-2010, 09:04 AM
Who's for GREEN on the next post? :-)
...lew...

Circlip
03-19-2010, 09:10 AM
Once rewound a car alternator stator

What a pain in the rectum that was. Reason I did it was because the robbing main agent for the French car I had charged an arm and a leg for the previous one that only had a six month Guarantee.

Had access to the right wire, vacuum impreg etc. but it din't arf make yer fingies ache winding thick wire.

Regards Ian.

oldtiffie
03-19-2010, 09:13 AM
Not me Lew - yet.

Oops - I have.

So I have.

Silly me!!

Oops.

Sorry Ian.

You were too quick for me - I was buggerising around trying to find "Green" - I found evey shade of it first though.

Circlip
03-19-2010, 09:17 AM
Wuz it the Oz delay line?????:D

oldtiffie
03-19-2010, 09:25 AM
Nah Ian.

Its just that I am not the Wizard of OZ - maybe Tin Man - or a few others.

You will be pleased to know that I don't look half as good as Dorothy when I have my drag gear on.

So its not likely that I will have a career as a Drag Queen - or as a half-decent "machinist" - or bloody typist - either.

Evan
03-19-2010, 09:30 AM
But a spritz of varnish over the coil surface is NOT the same thing at all.




True. That wouldn't take three days at 150 to dry either, more like 15 minutes. The rattle can varnish MEETS ASTM-4228. It is the same standard as the vat dip type. I buy it from the Rewind shop in town. They don't stock it to sell to the public, they use it to rewind motors they can't dip in the 5000 gallon varnish vat.

The way to use it is to make sure it runs down into the coils completely. With modern coatings it isn't necessary for insulation purposes like it used to be. The main purpose is to immobilize the windings. Even then if you use high temperature nylon insulated magnet wire you can forget it completely and even get away with winding direct on the bare laminations. I don't recommend that but is done in competition situations where maximum fill and cooling are more important than anything else.

RWO
03-19-2010, 02:58 PM
Assuming you have the rewind materials, the biggest problem is removing the old windings. if you have a modern industrial duty motor, it will be epoxy or polyester impregnated. Motor shops use a 700 oven to burn out the stators leaving the winding wire fairly easy to remove by cutting. Very few industrial users rewind anything under 10 hp unless it is something special. It is much cheaper to buy new.

RWO

Evan
03-19-2010, 03:54 PM
There is another reason to burn out the stator. The silicon iron used in the laminations needs to absolutely dead soft annealed. Even the slightest amount of work hardenening will reduce the electrical efficiency. In some cases the alloys used are so sensitive that a single rap with a hammer to the entire core is enough to measurably reduce operating efficiency.

It also helps to reestablish the oxide coating between layers that will have worn away at contact points because of normal magnetostriction in operation.

Orrin
03-19-2010, 04:00 PM
Thank you, all, for your advice. I got lucky and found what I need on Spokane's Craigslist for a reasonable price. Seeing as how we'll be there tomorrow for a party, everything worked out perfectly.

Orrin

John Stevenson
03-19-2010, 06:50 PM
There is another reason to burn out the stator. The silicon iron used in the laminations needs to absolutely dead soft annealed. Even the slightest amount of work hardenening will reduce the electrical efficiency. In some cases the alloys used are so sensitive that a single rap with a hammer to the entire core is enough to measurably reduce operating efficiency.

It also helps to reestablish the oxide coating between layers that will have worn away at contact points because of normal magnetostriction in operation.

So how do you account for the fact they hammer the windings into place with bolsters.?

J Tiers
03-19-2010, 08:30 PM
So how do you account for the fact they hammer the windings into place with bolsters.?

They do tend to use wood mallets..... mostly to avoid damaging the wire.

wierdscience
03-19-2010, 08:41 PM
That brings up another point or two.

Slot liners and wedges,two more things you have to either buy or make.Liner material isn't so bad,it's just linen cloth impregnated with linseed oil and baked.Slot wedges,well it's a PITA to cut those little stips of bamboo or wood so they fit without spreading the slots.

Evan
03-19-2010, 08:46 PM
So how do you account for the fact they hammer the windings into place with bolsters.?


It entirely depends on the motor John. It depends specifically on the magnetic alloy used for the laminations. There are many fractional horsepower AC induction motors that may use ordinary low carbon steel rather than anything special. The Maytag motor had aluminum windings and that alone costs more in efficiency than any small extra losses in eddy currents.

Eddy current losses are frequency dependent and 50/60 hz is very low frequency. AC VFD rated and DC motors are a very different kettle of varnish and may have core switching requirements in the kilohertz. Very special lamination grades have been developed for these applications. They are laser cut, not stamped and nobody beats the windings in place.

Wierd, use FRP circuit board and etch off the copper. I have FRP as thin as .020".

wierdscience
03-19-2010, 09:01 PM
Wierd, use FRP circuit board and etch off the copper. I have FRP as thin as .020".

Slot wedges are fairly large even in a 1hp motor.Last ones were 1/4x9/32 cut in a dovetail shape.All this can be bought easily enough,it just isn't worth the effort unless the motor is super special.

Bill736
03-19-2010, 09:13 PM
I had the 1.5 hp. original "bullet" motor on my 1951 Delta Unisaw rewound by a motor shop. After the rewinding, it never ran well under load, and tended to overheat . I gave up on the rewind, and replaced it with a 2 hp. Dayton motor from Graingers designed to be a replacement for the Unisaw motor, and the replacement has performed well for the last 20 years or so. I keep planning on using the bullet motor for some lighter duty use, but I never have. I suppose my message is that even motor shops can have trouble with a rewind.

Evan
03-19-2010, 10:17 PM
Slot wedges are fairly large even in a 1hp motor.Last ones were 1/4x9/32 cut in a dovetail shape.All this can be bought easily enough,it just isn't worth the effort unless the motor is super special.


Yep, the motor I am stripping right now has bunches of them. My perspective is to build some very custom brushless DC motors. I need MORE POWER for this summer's continuance of the trike project so I am building a high power 3Ph BDCM that should be able to punch out at least several killowatts of power at 48 volts. It will be a special multipole design which will have minimal cogging and very low rpm as a natural consequence of the 36/38 pole relationship.

I have found the perfect N42SH magnets rated for a maximum of 302 degrees operating temp.

J Tiers
03-20-2010, 12:56 AM
Most motor laminations are the cheapest that will do the job. They are not disarranged by shocks or vibration.

You will not need to worry about metglas or the other similar brands, they don't come up for the usual motors. They are too expensive.

I have seen PM alternators made for 60,000 rpm operation, at 200 kW output. They did use a relative of metglas, and the laminations were only about a 6" stack, 8" or so diameter. For 200 kW, that is small...... the whole thing, case and all was maybe 10" diameter and 12" long. Quite efficient, and very expensive.

OldRedFord
03-25-2010, 06:57 AM
Done it before,probably will do it again,it's just tedious boring work,but we're used to that aren't we?

Problem is the current price of copper,new magnet wire floats with the copper market which is up right now.

Odds are you could get a new Chinese TEFC cast iron frame motor for what the two six pound spools of wire will cost.Last I bought was 4 years ago,two 6lb rolls of 18ga wire cost me $86/roll.That was when copper scrap was $.85/lb,now it's $3.15 do the math.

I priced a 10hp ,215t frame TEFC motor Monday,$310 including freight.

Looks to be about $100 a roll now.

http://www.magnet4less.com/product_info.php?products_id=188&osCsid=20259a5b8d1a560e859ad4c489ea71a7