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  • DIY electric motor re-wind?

    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
    So many projects. So little time.

  • #2
    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...lant-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.

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    • #3
      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

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      • #4
        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

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        • #5
          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.

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          • #6
            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.
            Last edited by lakeside53; 03-18-2010, 11:06 PM.

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            • #7
              Craigslist. Baldor 3ph 5HP $75. Madison IN.

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

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              • #8
                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

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                • #9
                  Re-wind - yes!!

                  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.

                  Comment


                  • #10
                    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.







                    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.

                    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.
                    Last edited by Evan; 03-19-2010, 01:29 AM.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      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.

                      .
                      .

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                      Comment


                      • #12
                        Not here!!!

                        John,

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

                        Originally posted by John Stevenson
                        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!!

                        .

                        Comment


                        • #13
                          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.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            OK I'll do it in blue

                            Originally posted by oldtiffie
                            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.





                            .

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                            Comment


                            • #15
                              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.
                              I just need one more tool,just one!

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