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RE: synchronous motors

Original poster: "Ethersmith" <siveya@xxxxxxxxxxxxxx>

Thanks Bill,

So is the non-rotating-permanent-magnet type motor that you refer to below
called a hysteresis (which others are referring to in this thread)? Or is
that still something different? Because I have checked on the motors in
question and they are labeled hyst sync.

--Ethersmith

-----Original Message-----
Sent: Tuesday, August 09, 2005 7:32 PM
Subject: Re: synchronous motors

Original poster: William Beaty <billb@xxxxxxxxxx>

An "ideal" synch motor would have a rotating permanent magnet.  However,
the real-world synch motor I used for a rotary gap did not have an
absolute phase.  It would lock onto 60Hz, but with random phase relation.
I suspect that most synch motors are like this, since it's cheap to just
use steel in the squirrelcage rotor core rather than soft iron.  In such a
motor, at startup, the rotating magnetic field goes much faster than the
spinning steel rotor, so the rotor's permanent magnetization gets erased.
But then the rotor gets up to speed and "locks in," becoming magnetized
again.

The result is that the TC output is usually not max, and you have to
switch the sync gap motor on and off two or three times in order to "hit
the peak."  (From the sound and light of the TC output, it's pretty
obvious when you get it right.)  That, or instead you can leave it
running, but push something against the spinning gap electrode disk to
forcibly drag the rotor phase backwards until you hit one of the 60Hz
peaks.


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