Re: Microwave oven fan motors

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Alan,

On 30 Aug 00, at 8:27, Tesla list wrote:

> 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, 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?
> 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?

Induction motors do suffer slip and their speed is roughly 
proportional to Fmains and inversely proportional to the 
number of poles.
    Shaded pole motors are non-synchronous right frmo the word 
go. The shorting copper bands are a cheap way of simulating a 
start/run winding. They are terribly inefficient compared with 
a good induction motor.
 
> 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.

It might well be - it has to transport the tape at a constant 
speed regardless of line voltage.

Whereabouts in NZ are you? Please let me know (offlist).

Regards,
malcolm