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Single PM DC motor

I took apart a DC motor of questionable quality and I noticed that it uses only one permanent magnet. Basically a round cylinder covering the whole circumference of the steel can that it sits in. How can this work? I thought you'll need two permanents, one with the polarity N and another S to produce a consistent magnetic field. Can anybody tell me if these motors were designed badly or maybe somebody can educate me on how it can work. Thank you.

Reply to
aircorr
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Thanks John. Is there any drawback to use such magnets? Any correlation with electrical noise generated by motors equipped with such magnets?

Corey

John Woodgate wrote:

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Reply to
aircorr

I read in sci.electronics.design that snipped-for-privacy@yahoo.com wrote (in ) about 'Single PM DC motor', on Thu, 16 Dec 2004:

It's magnetised across a diameter, so that one spot on the surface is N and the opposite spot is S. You can even get quadrupole magnets, which have N-S-N-S at 90 degrees around the circumference. This is especially so with ferrite magnets, because they have a very high coercivity. Without that, the magnet would gradually weaken.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

wrote

Please don't top-post. :-) Any rf noise you're getting is most likely from the brushes, assuming of course that there are brushes.

Reply to
Anthony Fremont

I read in sci.electronics.design that snipped-for-privacy@yahoo.com wrote (in ) about 'Single PM DC motor', on Thu, 16 Dec 2004:

No. Electrical noise comes form commutation, whether by a mechanical commutator or semiconductors.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

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