Re: Microwave oven fan motors

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 8/30/00 8:17:01 AM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "Kelly & Phillipa Williams" <kellyw-at-ihug.co.nz> 
>  
>  
>  Thanks heaps for the help. I've read about synchronous, shaded-pole
>  induction motors, and all the rest.
>  I *think* that induction motors run at a speed determined by the frequency
>  of the AC source. Induction motors are nearly synchronous but run slightly
>  slow, 

Yes, the source freq and number of poles, and the amount of slip
which is load-dependent determines the speed.  So yes, you could
sort of say they are "almost" synchronous.  Of course that does you
no good at all if you want to build a sync gap.  You'd have to modify
it to make it truly synchronous by grinding flats on the armature
(squirrel cage rotor).

>  and synchronous motors run at an exact multiple of 60 hertz for the
>  U.S. and 50 hertz for New Zealand. Is this correct or another pipe dream?

That's correct.

>  Microwave oven motors are cheap, very inefficient, and slightly slower than
>  synchronous because of the starting system which slows it down when it is
>  running, after it has been started. Is this correct?

It's not the starting system that slows it, but rather the load which
causes slippage.  The more load, the more slippage, and the more
power available up to a point.

JOhn Freau
>  
>  My father brought home a tachometer from his timber mill and I am currently
>  conducting experiments on the reel-to-reel tape recorder motor. I am still
>  not confident on what that is.
>  
>  Alan.
>