Permanent magnet sync motor

To: tesla-at-pupman-dot-com
Subject: Permanent magnet sync motor
From: Gary Lau 14-Apr-1999 1312 <lau-at-hdecad.ENET.dec-dot-com> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Wed, 14 Apr 1999 19:06:01 -0600
Approved: twf-at-verinet-dot-com

>Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>=20
>
>SNIP
>
>I guess I`d better start gluing PCB sheets together for a rotary disk.
>Already got a nice Siemens 3-phase permanent magnet sync. motor for that
>gap......
>
>SNIP
>
>Cheers, Finn


I once bought a 1800RPM motor (-at-60Hz) that had a 4 pole permanent magnet
for its rotor.  With a disk with a cross drawn on it under florescent
lights, it was clear that the motor's phase was rock-steady in sync with
the mains.  However, if I applied a sufficient amount of torque above a
well defined threshold to the spinning disk, the phase would shift.  The
phase would also vary each time I spun the motor up.  Not just in 1/4
turn increments, but in any arbitrary angular increments.  And I'm sure
there was no slippage between the disk and the rotor.  I never did figure
out how this was possible with a permanent magnet rotor, but it was clear
that this motor was not suitable for use in a sync RSG.  You might want
to check this before proceeding too far with it.

Did you say 3 phase?  Be a shame if your motor drew more power than the
rest of the coil!

Gary Lau
Waltham, MA USA