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Old 26th Dec 2020, 11:14 pm   #1
Andrew B
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Default DC motor rewind help ?

Good Evening.

How difficult is it to figure how to rewind a DC permnant magnet motor?

This isn't a giant, it's off a treadmill, rated at 180v DC and 1.25 Hp. The windings are pretty burnt up but intact. I have tried to find out around the 'net but it doesn't yielded the right information, so I am looking for advice from someone who has done it before.
Thanks
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Old 27th Dec 2020, 12:02 am   #2
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Default Re: DC motor rewind help ?

You may find that the armature windings are welded, not soldered to the com segs. This is for heat rather than cost.

David
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Old 27th Dec 2020, 4:03 pm   #3
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Default Re: DC motor rewind help ?

I suppose I was lucky with my "skip find" treadmill, I was sure I was going to have to replace the seized-up motor and I had priced up a replacement at 50 including postage, but when I dismantled it I found that although the windings had overheated, they were undamaged and some resin had leached out into the gap and needed carefully dressing away with a file.
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Old 27th Dec 2020, 5:29 pm   #4
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Default Re: DC motor rewind help ?

I might be a bit OT but why a treadmill, I have a perfectly good pavement outside my house and it has changing scenery. "Green" too, no electric needed.
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Old 27th Dec 2020, 5:32 pm   #5
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Default Re: DC motor rewind help ?

Quote:
a replacement at 50
Thanks David and Graham.
An absolute giveaway price. This one starts at 140 + (on eBay). It actually looks like the same armature, certainly seems wound the same. Mine has that crispy blackened look with shiny bare copper shining through. Bad news the comm segs appear to be welded, so crimp and solder are out of the question I suppose?
I would like this thread to run a little longer, longer the the treadmill anyway and see if anyone has tackled one before.
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Old 27th Dec 2020, 5:35 pm   #6
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Default Re: DC motor rewind help ?

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I might be a bit OT but why a treadmill, I have a perfectly good pavement outside my house and it has changing scenery. "Green" too, no electric needed.
It's for a rather agile and athletic young lady and she rather dislikes displaying her >>assets<< in the street
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Old 27th Dec 2020, 6:32 pm   #7
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Default Re: DC motor rewind help ?

Quote:
and she rather dislikes displaying her >>assets<< in the street
I see, sometimes when I wake in the early hours and can't get back to sleep I go for a night walk. SHMBO likes it because when I get back I have a lovely quiet sleep.
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Old 27th Dec 2020, 8:47 pm   #8
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Default Re: DC motor rewind help ?

It strikes me as fundamentally wrong that these treadmills require energy input from the mains. Shouldn't a good exercise machine be doing something useful like charging batteries?

David.
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Old 27th Dec 2020, 9:37 pm   #9
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Default Re: DC motor rewind help ?

Quote:
Originally Posted by merlinmaxwell View Post
I see, sometimes when I wake in the early hours and can't get back to sleep I go for a night walk.
For one frightening moment I thought we were still going with the 'displaying one's assets in the street' angle

I bought a dead treadmill from ebay for the motor (small machine tool project). If you're lucky you may find the same model listed cheap with a scruffy case or dead control board. Also like bread machines and juicers, they seem to be the kind of thing folks buy and then sell on, not having used them that much!
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Old 27th Dec 2020, 11:29 pm   #10
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Default Re: DC motor rewind help ?

dont these normally have to be dynamically balanced after a rewind? They tend to run rather fast.
You also need to take precautions when dismantling a PM motor as far as weakening the field magnets is concerned. You need to make a keeper.

I'd be tempted to look for new one, these chinese treadmill parts are usually pretty cheap.
For example someone sent me in a speed controller blown up and the new board (I think it was a Reebok branded chinese machine) was about 18
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Old 27th Dec 2020, 11:49 pm   #11
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Default Re: DC motor rewind help ?

It's not particularly difficult but slow and error-prone until you have had some practice. I don't think rewinding a small armature that is available off the shelf is worthwhile unless you are doing it mainly for your own interest. I've done various motor and generator repairs and have never been tempted despite being at least reasonably well equipped to do it. OTOH this size and rating of motor should be fairly forgiving as the wire is robust and easy to handle, and the turns few in number, so it's as good a place to start as any. The only thing you won't be able to do is to dynamically balance the finished job. As Kevin says that might be a noticeable problem given the running speed and the domestic application. In locales where wages are low and goods are relatively more expensive, you can get power tools rewound in roadside shacks by guys working with little more than a hammer and a screwdriver. They don't seem to worry about balancing, but then the aim is simply to get a working tool rather than one working to original spec.

You might be able to change the comm for one with hook-type risers for a couple of quid, in which case you have more options for termination. HMP solder might do as there's more heat dissipation surface and it's further from the bars. Riserless comms are cheaper and ideal for automated winding and assembly, hence used in original production.
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Old 28th Dec 2020, 9:37 am   #12
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Default Re: DC motor rewind help ?

I am one for having a stab at fixing something, but I would definitely not bother even attempting a rewind on a motor like that. For the reasons stated, reliable termination of the windings, and final balancing of the armature for rotation at high speed.

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Old 28th Dec 2020, 3:04 pm   #13
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Default Re: DC motor rewind help ?

It appears to me now that treadmill motors are a rather hard-done-to item, from the dead one in front of me it appears that cooling has been almost overlooked. This motor does have a small fan on the end of it to draw air through the motor,, the air inlet holes being rather small and clogged up with dust. Bad design all around.

This particular treadmill is a "Re***k" high ender, over 1000, any reason why they didn't use an AC/DC motor and Triac speed control ?
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Old 28th Dec 2020, 3:22 pm   #14
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Default Re: DC motor rewind help ?

I've had a look at a couple of dead treadmills and both were problems with the microcontroller. One of them used a thyristor bridge as a rectifier to power a DC motor.

Maybe they want the low speed torque because of the stiction of the belt? The motor will have its worst cooling problem at low speeds, so a fan on its own shaft is useless. A small blower unit as a separately powered unit is needed.

I guess a brushed DC motor is cheaper than a three phase motor with an inverter.

So, it takes 1.5 horsepower to overcome the belt friction to allow the runner to get some exercise... Words like 'inefficient' don't do it justice. I prefer a definitive 1 horsepower exerciser that doesn't need fossil fuels. You can even get a decent bicycle for less than 1000, but it won't be branded R**b*k.

To get a reliable machine will be much more expensive, and would have to be from a specialist manufacturer where the extra money goes to extra engineering, not extra brand marketing. An engineering high-ender.

David
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Old 20th Jan 2021, 1:02 pm   #15
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Default Re: DC motor rewind help ?

Refreshing this thread. I have the armature in front of me, the commutator segments are just bent over. Using domestic oven I have picked off some of the >glue< and can see a lot better now.

The windings would be easy to get off IF they weren't glued together with the wire enamel? So far I have tried MEK, Benzl alcohol based paint stripper, acetone, meths and isopropl to try and remove the ?enamel?.

Italian made motor , I want to rewind it for my own interest now. Any suggestions would be welcome.
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Old 20th Jan 2021, 1:28 pm   #16
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Default Re: DC motor rewind help ?

One of the problems with DIY rewinds, is finding a supplier of new copper wire in small quantities. So, keep all wire and weigh it, then add 10/25% as your bound to waste some. Try and remove the windings such, as to obtain the stepping of the slots and spacing of the com connections. Also, modern machine wound armtures don't use slotting, which as a hand winder you would need to protect the wire as you insert it into the slots, so space is a problem. Then there is varnish and stoveing before and after then balance. I notice that modern armature windings are not soldered to the com any more sort of crimp. Not so easy as it looks, I hope I haven't put you off. Ted
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Old 20th Jan 2021, 1:52 pm   #17
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Default Re: DC motor rewind help ?

Not at all Ted, I have studied up a bit in the last week. My problem is removing the old windings, modern paint strippers don't cut mustard, Nitromors USED to be good but the 'elf n safety killjoys took out the active ingredient (methylene chloride) and strippers containing it are unavailable :-(
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Old 20th Jan 2021, 2:01 pm   #18
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Default Re: DC motor rewind help ?

Ted and everyone, this is the enamel? I wish gone.
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Old 20th Jan 2021, 4:36 pm   #19
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Default Re: DC motor rewind help ?

Quote:
Originally Posted by Andrew B View Post
Not at all Ted, I have studied up a bit in the last week. My problem is removing the old windings, modern paint strippers don't cut mustard, Nitromors USED to be good but the 'elf n safety killjoys took out the active ingredient (methylene chloride) and strippers containing it are unavailable :-(

Dichloromethane (methylene chloride) based strippers are still available (for industrial/professional use only). They're offered for sale on Ebay with various disclaimers and declaration requirements. Rather like full fat solder!
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Old 20th Jan 2021, 5:23 pm   #20
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Default Re: DC motor rewind help ?

The quick method, once you are completely happy that you have all the information other than the number of turns per coil, is to saw the coils off (or turn off in a lathe) close to the lams. The coil sides within the slots can be driven out from one end, possibly after cooking to loosen them. Then you can dissect a sample to count the turns.
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