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Single-phase AC motor - winding distribution

by Ergison
Tags: belt, coil, delco, single-phase, winding
Ergison is offline
Jul12-09, 05:24 PM
P: 3
Motor: Delco - 1/4 HP - 5.3A - 1735 RPM - single-phase AC; 32 slots - 4 poles

- I have run into conflicting terminology, so I apologize for any confusion -

Each of the four poles in this motor's stator core contains three coils with two empty slots at the center for a total of eight slots per pole. Is there a perfect distribution of windings between the three coils, or is it only a matter of widening the pole? I have read that distributing the coils in a belt like this creates a more sinusoidal pattern...but...I can't find any information on a proper distribution.

Also, is there a way for me to SAFELY increase the power of the motor without sacrificing RPM?

If you can at least point me toward a good explanation, I will be quite grateful.
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TurtleMeister is offline
Jul12-09, 08:53 PM
P: 734
I am not an engineer so you may need to wait for someone more knowledgeable to give you a better answer. However, I did work for a company that manufactured motors very similar to the one you're asking about. I can tell you that the distribution of turns between the three coils on each pole will vary depending on the model. If your motor has an auxiliary winding then the outer large coil will usually always have a greater number of turns than the inner two. As I've said, I'm not an engineer but I would suspect that the reason for the three coils per pole is to maximize the amount of copper in the field core. The engineers seemed to love to cram as much copper in there as they could. It was a real challenge for guys like me to keep the machines from scraping the wire as it was inserted into the field core.

I don't know of any way to safely increase the power. These motors are probably already engineered for maximum output. Trying to increase it would probably just saturate the field core and lead to increased heating which would cause the thermal overload to trip more often.
Ergison is offline
Jul13-09, 07:08 PM
P: 3
I was afraid I might not be able to increase the power...All I can think to do is remove the starter coils and add to the running coils, bringing the motor up to speed by hand or with another motor that I can disengage. But maybe that, too, would cause it to overheat..?

It makes sense for the outer coils to have more turns because the coils in the other circuit don't pass through those slots - at least, not in this 4-pole, 32-slot motor.
I do remember a greater number of turns in the outer coil, but my counts varied between coil belts (probably my fault). Tonight I'll measure the total length of each belt and try to recreate the distribution.

I just wish I knew if there were more to those numbers than maximizing the amount of copper! I read something about minimizing harmonics in the emf, but I couldn't begin to understand any of it. Maybe I'll study that again tonight.

berkeman is offline
Jul14-09, 01:09 PM
berkeman's Avatar
P: 39,612

Single-phase AC motor - winding distribution

Why is there an unrelated poll attached to this thread?
TurtleMeister is offline
Jul14-09, 04:52 PM
P: 734
I wondered about the poll also. I just assumed it was an error.

You are correct about the turns on the inner two coils. Since the aux winding (starter coils) do not occupy the same slot as the main outer coil, it allows for a greater number of turns on the main outer coil. If you're using the motor for intermittent duty and the motor is rated for continuous duty then you may be able to get away with boosting the power a little. But I'm curious to know why you would go to so much trouble. I know it's not easy inserting all that wire by hand. Why not just get a larger motor? Maybe the same type motor with a larger stack height?
Ergison is offline
Jul14-09, 05:39 PM
P: 3
I apologize for the poll; I can't seem to get rid of it. Perhaps a moderator can do that?

I'm rebuilding this motor because I found it in a pile of junk, started dissecting it, and my dad said 'Hey! That's mine! But don't bother - it's not worth it.' So...naturally, I'm trying very hard to resurrect this thing. That, and if it can be made to run it ought to - otherwise it's just another piece of junk, and we've got way too much of that around here.

How would I figure out whether the motor were rated for intermittent or continuous duty?
Continuous duty is what I'm after for the sake of efficiency.

If I can get enough power I'll put it on a wood lathe.

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