# Question regarding AC Induction motor rotors



## Tesseract (Sep 27, 2008)

iti_uk said:


> Hi, I posed this question on the Endless-Sphere board with one reply which didn't seem to answer my question, then nothing more. Could anyone here shed some light on this?


The number of rotor "bars" (shorted turns, actually) is related to the number of stator poles. I don't remember the exact formula... Google turned up this forum post which goes into it some. I know of electricpete from other forums and he is very knowledgeable. 




iti_uk said:


> ...
> A further thought on the idea, if I may. I have seen videos of AC motor stators spinning coke cans and the like. What I am suggesting here would effectively be a thick-walled, radially laminated can. Mad? Pointless?


That sounds like a hysteresis motor. Typically spin at synchronous speed but with very low torque output. Used almost exclusively for "mechanical timers" and clocks and such. Not something I'd want to use for an EV as the rotor losses are extremely high.


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## JimDanielson (Oct 19, 2008)

starting at page 265 this book starts to describe how number of bars are determined-
http://books.google.com/books?id=4-...irrel cage rotor&pg=PA265#v=onepage&q&f=false


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## iti_uk (Oct 24, 2011)

Thanks for the responses. Plenty of reading to do


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## steven4601 (Nov 11, 2010)

Good intentions, but Oh ooh, you are not too serious with this or are you?


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## iti_uk (Oct 24, 2011)

steven4601 said:


> Good intentions, but Oh ooh, you are not too serious with this or are you?


 What are you saying? (that read very camp-ly btw ) I have a lot of time on my hands at the moment and I'm just throwing out ideas for solutions which I haven't seen before. Maybe one day, if I find something that works I can spend some proper time developing and making prototypes.

Chris


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## PStechPaul (May 1, 2012)

I had researched this some time ago and discovered that it is (to me) insanely complicated, and somewhat of an "art". There are ways to use FEA but ultimately it requires experience and building prototypes and doing lots of testing. Here is a PPT from a seminar that goes into some of what is involved:
http://ceme.ece.illinois.edu/seminars/CEME1109HarleyGeorgiaTech.ppt

There's probably not much that has not already been tried and tested. But it is interesting and valuable to conceive of novel ideas and knock them around. As for the number of rotor induction bars, and the skew angle, it seems to be related to smoothness of operation, cogging, and physical noise. I have seen some charts of optimal and problematical numbers of rotor poles for various numbers of stator slots.


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