Ac series wound to DC permanent magnet ?

[flez1966]

Has anyone done any conversion of AC series wound to DC permanent magnet brushed motors?

I ask as I want to build my own motor in the 24-36v 750w area, and was finding it hard to come up with a stator, and then realised so many old electrical appliances like power drills or grinders etc are usually around 750w 100v or 240vAC range.

The grinder idea i find very interesting as we have seen from some other work on here of using the 90' drive of it to belt drive a bike.

Thinking a rewind of it and some hefty magnets and the jobs done?

But I have no idea how much wire to wind onto it, or how to get curved magnets....

 

[amberwolf]

Somewhere on my electricle blog in my signature, I have a post or two about converting a "universal" drill motor to a PM type, by replacing the field coils with teh magnets and case from some other small motor that would give a similar airgap (but not identical, which is what I'd've rather had).

I don't remember the results, exactly, but it still required high voltage to get similar results to it's original operation at 115VAC, kinda negating the usefulness, since I could have used it with DC instead of AC even with teh field coils instead of magnets, at those voltage.

I think you'd probably have to rewind the motor to change it's kV and such, to be able to run it on a lower voltage for DC, if that' why you want to use PMs instead of field coils. But I'm not sure how all that works, exactly. You'd have to look at motor winding posts or websites for the math and/or calculators to figure that part out. It's not hard, but I don't get along with math very well.

For the curved magnets, I'd recommend using the entire outer casing and magnets from a motor that is close enough to the right inside diameter to get the airgap right. Presumably the same airgap the field coils had. If you have a largish motor you're converting, the magnets off a treadmill motor or a powerchair motor may work. However, the powerchair motor probably already does everything you want it to, incluing running at the lower voltae with plenty of torque, plus a right-angle gearbox. Heavy-duty powerchairs with one motor per wheel can be 600-800W per motor, continous duty, with 24VDC.

 

[flez1966]

Thanks for the ideas, i do have a permanent magnet motor from a baggage puller, it had 2 of 200w each, but low geared for a top 5mph speed, infact they do about 1-2 rpm, which is similar to pedal speed......

however i was wanting about 500-600w, so thought the metalwork and commutator from an ac one would do, but now thinking about this some more, for the same wattage at lower voltage i would need more amps, and the original brushes would be designed for higher voltage and lower amps, so dont know how life would be affected in that area.

I have seen some car radiator fan motors that are a good diameter but fairly short on armature length, but the magnets would be curved, and if i took magnets from two motors and stacked them side by side, they should cover a longer armature, and they like $10 each so...

yes i need to read up on winding....

 

[REdiculous]

You might search for "Zubbly conversion" on google. He converted AC induction motors to PM....making them inrunners I guess.

 

[flez1966]

Thanks, had a look and found his 3 pages on converting to PM generator, but didnt for drive motors, but then a generator is built like a drive motor, main difference on the pages i found the magnets are in the middle and it generates power in a 3 phase way, still a good read.

I'm going the other way, replacing the outer field windings with magnets to make an old world standard motor, i'll also have to rewind the stator from lots of thin wire for the high voltage to thicker wire for the higher current, time consuming but needed.

 

[spinningmagnets]

One thing Zubbly showed was that many small button/cube magnets can act near the power of a properly shaped curved bar magnet. You may only get 80%-90% of the potential power of the best possible magnets, but it is doable to convert an inrunner or outrunner to a PM motor. Using lots of small magnets also allows you to add some skew, if that proves to be desireable in your build.

otherpower.com is a website thats mostly for DIY wind-gens, and they have sponsor ads for the best magnet suppliers.

 

[REdiculous]

I think the first time I read about "skewing" it was Zubbly explaining it..smart dude.