DIY induction motor rewind

[Martin of WickParticipant @martinofwick]

I have a small 0.375 kW 3 phase induction motor where one of the coils is in continuity with the case, not obvious where, probably deep in one of the coils.

Clearly not worth paying for a commercial rewind (circa £300) but thought could try a rewind myself.

so has anyone attempted this? was it successful?

Does anyone have a ballpark figure for the weight of copper in the windings? only asking as the enamelled wire is about £20 per kilo and was hoping that would be enough, any more ad it probably isn't worth it.

Are there any UK sources for the material for coil shrouds and separators? I guess rustins shellac will be ok to stick it all together.

Thanks for anyone willing to share advice.

[Martin of WickParticipant @martinofwick]

anybody attempted? availability of materials

[DC31kParticipant @dc31k]

Brocott UK. Have everything you need, including the proper varnish which is probably better.

Lots of Youtube videos on rewinding, mainly in Urdu but with enough English to understand.

Pay very good attention to the arrangement and winding direction of the coils.

Just about to try to rewind my coolant pump motor.

If the motor is not working, you will have to strip the windings so just weigh the old ones.

[old martParticipant @oldmart]

The cost of one this rating is less than £60 all in, brand new.

**LINK**

[Robert Atkinson 2Participant @robertatkinson2]

Only really worthwhile for two reasons:

1/ Learning how to do it for self satisfaction

2/ To keep the motor for reasons of originality or rareity

Otherwise just get a replacement motor.

Robert G8RPI.

[Martin of WickParticipant @martinofwick]

DC3,

thanks for that, hadn't come across the name before so very useful.

OM and G8R Hmm… hardly seems worth the effort as you say. I suppose I could remove the flange.

Anyway, I think I will price up how much the materials for a rewind are and see if it outweighs my thirst for knowledge and satisfaction.

Thanks to those that responded.

[DC31kParticipant @dc31k]

This is speculation, so view it critically: if you know the resistance of one of the good coils and the diameter of the wire, you can calculate the length of the winding and hence the weight. Wire manufacturers usually publish resistance per kilometre for their products. If not, you might have to go back to first principles and use resistivity of copper and cross-sectional area.

[Speedy Builder5Participant @speedybuilder5]

Don't forget the insulating 'card' that the coils sit in and the closing card that keeps the winding in place when you dip it into the the insulating resin.

Ps and the Elastoplast for your knuckles.

Edited By Speedy Builder5 on 24/03/2020 07:18:51

[Mike PooleParticipant @mikepoole82104]

If you go ahead then make sure you flash the wire coating off in a flame before measuring the wire. When you wind the coils be careful to wind neatly and avoid untidy crisis crossing which will make the coil hard to insert in the slot,a neatly wound coil will slide easily into the slot and it will be easy to squash with your fingers. An untidy coil will be hard to squash and feed through the narrow slot. Getting the former for the coils right makes the job easier. If the coil is too small then it will be hard to dress the coils back to leave a clear entrance for the rotor, too big and it will be difficult to lose the excess coil in the casing. It will have a small effect on the resistance of the coil. After you have connected the coils together and before you lace it all up and shellac or resin it, give it a trial assembly and run it to check it works properly. You will have lots of ends to connect and it’s very easy to get one wrong and the motor will sound awful and not run properly, if it runs properly and the phase currents are balanced then lace it up and seal it. Getting the exact same performance as the factory build may not be achieved but may not matter. I remember being told by SEW Eurodrive not to use rewound motors in a low profile scissor lift drive that used two motors driving a common shaft paralleled from one inverter, the reason was the motors needed to be a balanced pair and a rewound motor could vary as much as 10% from a factory built item. In industry small motors are regarded as disposable, automated manufacturing has driven the cost so low that repair is not economical unless the motor is a special. I found motor winding very enjoyable for a few months when there was loads to learn but it could get a bit routine as we had a never ending pile of fan motors from steam space heaters, the heat just cooked the lube out of the bearings and bye bye motor. With most motors being squirrel cage type then winding is straightforward. I watched the proper winding guys rebuild a 600hp synchronous motor in our compressor house, lots of copper bar wrapped in empire tape in that job, very clever chaps.

Mike

[Martin of WickParticipant @martinofwick]

DC3, Thanks

excellent – hadn't managed to get that far in the thought process – approx. 20 ohms per phase comes out at approx. 240m x 3 worked out at about 1.3 to 1.4 Kg Cu.

Back checked to turns per stator slot coil is about 150 t, which looks about the right order (24 slots so 3×4 coils).

Will count the true turns from the original when I figure out a way to cut out the old coils (whatever it takes I suppose).

The tip about Elastoplast looks to be pretty helpful too!

[not done it yetParticipant @notdoneityet]

1.3 – 1.4 kg of scrap copper is worth a bob or two. Every little helps…

[Martin of WickParticipant @martinofwick]

Thanks mike, hadn't thought about how the suppliers specify their wire – I guess you are saying that it is on conductor size nett.

The wire measures at 0.5mm D gross. so will re-measure with the insulation removed as it could be 0.45mm.

If I procede, I will use one of those expandable staged former thingies available from Ali. They permit winding of all four stator coils in the phase at once, each staged in length so they all come out with about the same projection from the stator when installed (about a fiver delivered).

Looking as if the materials will cost about £40 so very much a learning exercise than a money saving scheme.

[Mike PooleParticipant @mikepoole82104]

To remove the windings I sharpened a cold chisel so it was very sharp and at an angle that would lay flat on the end of the stator laminations, cut all the ends of the coils of at one end of the stator then lever the coils out from the other end, they will often slide out fairly easily. Take a coil and use a hammer gently to spread the end you have cut and fan out the wires to make counting the turns easier. Make sure you know how the coils are installed before you destroy the windings. If you can find the connections for the coils before you take it apart it could be useful unless you know how to connect it up. it’s a long time since I wound a motor and I expect I have forgotten more than I remember.

The wire size does not include the coating so hence the need to remove it, even a candle flame will suffice.

Mike

 

Edited By Mike Poole on 24/03/2020 10:26:47

[John HaineParticipant @johnhaine32865]

Posted by not done it yet on 24/03/2020 09:41:14:

1.3 – 1.4 kg of scrap copper is worth a bob or two. Every little helps…

Actually about $5. **LINK**

An old friend of mine was once a junior manager in BT City Area, in charge of Faraday House a huge pre-WW2 repeater station. Floors of it were filled with unused old equipment which had been superceded by new technology, and they would remove it only when more space was needed. My friend was walking through one of the floors and there was a guy with a hacksaw cutting large sections out of thick bundles of cotton-covered copper wire, then wheeling them out in a barrow to his van. Graham asked how much he was paying and what he'd get for the scrap. Paying he said? They're paying me to take them away!

[old martParticipant @oldmart]

That link I posted was for a supplier who sells all types of motor, you don't have to buy one with a flange.

There are You tube videos of motors being manufactured, it might be useful to see what you are up against.

https://www.youtube.com/watch?v=dDH_bsS0j_c

Edited By old mart on 24/03/2020 20:05:09

Edited By old mart on 24/03/2020 20:10:32

[SparksParticipant @sparks]

Would it be an idea to measure the wire SWG or AWG first and then count the number of turns, the number of turns will be the same on all the sections, thought I'd just mention.

And as said always use the start and finish of the winding in the same direction…. there are motor rewind firms, how much they charge I wouldn't like to guess, better to sit down and then ask.

Should you get stuck for 'magnet wire' I get mine from UK wires

Dave

Edited By Sparks on 26/03/2020 17:12:17

[Martin of WickParticipant @martinofwick]

Thanks to all those that helped, I will post here as a sort of build thread in future and put some photos in the album as I progress. Might be helpful for anyone else contemplating such madness.

The material for the job was approx. £30 as only about 800g copper was required when using vendors wire data and correct stripped diameter. Decided to have a go as a learning experience.

Quite difficult to determine the original winding pattern from the old motor, as not quite what I expected. Eventually worked out it was : 2 No. phase groups, each with 3No. concentrically arranged pairs of coils (1 pair coils per phase). So need to wind a nested coil pair x 6, arranged and connected appropriately to generate the 4 alternating poles.

This is where the 3d printer comes in – to produce a demountable double former to generate the concentric coil pair. Haven't got as far thinking about the winder yet – probably on the lathe faceplate with some Heath Robinson arrangement using the small cheap mechanical counters commonly available .

[Mike PooleParticipant @mikepoole82104]

Our motor winding workshop utilised an old milling machine as a coil winder, a large collection of formers hung on the wall with the details of the motor they were made for. The formers were mostly fashioned from plywood and wood and as the works engineering carpenters being next door they often obliged with making the former, another style was to use two plywood cheek plates and a spacer for the coil width and steel pins drilled through the cheeks to make the shape of the coil required, these were often just rectangular or a squashed hexagon shape, a resettable mechanical counter operated by a cam logged the turns and a foot pedal started and stopped the machine. The wire drum was behind you and the wire was fed manually onto the coil by letting it run through your fingers, you soon developed the feel to apply the right amount of tension with your fingers and wind a neat coil With a smooth side to side motion, be careful to not feed side to side too quickly or coil will a hard uncooperative bundle, if you get it right then the coil will squash between your fingers and feed into the stator slot easily. The wire gauges for small motors are easy to work with but things get a lot more physical with heavy gauge wire in large motors. If you succeed in this project it will be very satisfying.

Mike

[SparksParticipant @sparks]

Wonder if we need be careful about the insulation…. the enamel type? I've rewound 'radio coils' never a motor, I do know there are different types of coating, I should have mention this in my post.

Dave

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