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.

 

[Anthony Fremont]

<aircorr@yahoo.com> wrote

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

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

 

[John Woodgate]

I read in sci.electronics.design that aircorr@yahoo.com wrote (in
<1103234210.517608.323890@f14g2000cwb.googlegroups.com&gt about 'Single
PM DC motor', on Thu, 16 Dec 2004:

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

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