I have seen several 4 pole induction motors that have coils wound like this:


Both the main winding and the auxiliary winding have 2 pairs of these coils.

This is concentric winding and I've only found some information about this on the internet, but nothing about why is this made and how this works.

I see the current also has an radial orientation (going inwards or outwards) besides the axial orientation (rotating cw or ccw).

Should this cause any difference?

For instance, imagine I take two overlapping coils (like one from main and one from auxiliary) to make the same pole. Then I have two options, like in this figure below:

enter image description here

In option 1 the current has the same radial and axial orientation in both coils, while in option 2 the radial orientation is he opposite.

Should they produce different fields?

And, disregard of being different or not: How should be the field produced by them?

Will it have a single maximum in the middle of the overlap? Or will it split in two maximums?

Cause I have tested some configurations using those to try to make a 2 pole motor (out of a 4 pole motor) and I have the impression that somehow I always have weaker extra poles, because it works, but it's strange.

I may explain it better here if you want, but I tested several possible configurations and even the best one I got to make a 2 pole motor still have the strange behavior of not accelerating to 3600 rpm by itself, even using only the main winding and giving an initial impulse.

It will always accelerate to 400 rpm or so and then keep that speed. And it doesn't stop there by simple lack of torque, if I try to accelerate it further it brakes down to that speed again quite fast.

Only if I give it quite a speed (like 2000 rpm) before energizing it will then accelerate to 3600 rpm and keep at 3600 rpm.

All of that sounds like it's producing a field with more poles than what I was expecting.

  • \$\begingroup\$ Sorry, what? Your answer looks seems to be about the structure of the metal core (laminated cores), but my question has nothing to do with that, I'm asking about the winding style. \$\endgroup\$ Aug 27, 2020 at 2:30
  • \$\begingroup\$ I think that maybe I didn't meant to use the word "core" here, I was looking for a word to describe these units that compose the winding \$\endgroup\$ Aug 27, 2020 at 2:32
  • \$\begingroup\$ It was supposed to be "coil", now that I got it. I used "core" following someone in an answer in a previous post of mine but it was supposed to be "coil". \$\endgroup\$ Aug 27, 2020 at 2:35
  • \$\begingroup\$ I have deleted my comment as it no longer applies. \$\endgroup\$
    – user105652
    Aug 27, 2020 at 3:31
  • \$\begingroup\$ @İbrahimİpek LOL, you know absolutely nothing about distributed windings nor induction machines and you're trying to sound smart. "A coil spins around 2 slots, nothing happens in between", NO. Just NO. You can do that but that's way less optimal (in an induction machine) than having a distributed winding. The goal in distributed windings is to produce a sinusoidally distributed MMF. The stators are made with many slots exactly so you can make a distributed winding to begin with. You're the prime example of the Dunning-Kruger Effect. Go study distributed windings before talking shit. \$\endgroup\$ Jul 4, 2023 at 14:05

1 Answer 1


The concentric winding produces a stronger filed in the center and weaker field by steps in the outer zones

This approximates the shape of a sine wave and reduces harmonic currents in the rotor. (harmonic currents don't produce torque, only heat)

this winding scheme also puts two windings in each slot of the stator, (but elsewhere you say that some of the windings have more copper than others so there will be somewasted space.)

With a single the strength goes

 1  2  3  3  3  2  1  

The double option 1 goes like

 1  2  3  3  3  2  1  
            -1 -2 -3 -3 -3 -2 -1  

Which makes

 1  2  3  3  2  0 -2 -3 -3 -2 -1 

The double option 2 (1 red + 1 green) goes

 1  2  3  3  3  2  1  
             1  2  3  3  3  2  1  

which makes

 1  2  3  3  4  4  4  3  3  2  1  

I'm just counting ups and downs of the current

  • \$\begingroup\$ So, if I use two overlapping coils to produce the same pole, would it end up having two maxima (at the middle of each coil) instead of a single maximum in the middle of the overlap? \$\endgroup\$ Aug 27, 2020 at 18:21
  • \$\begingroup\$ i'm just counting ups and downs of the current, see edit \$\endgroup\$ Aug 27, 2020 at 19:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.