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Is this motor synchronous?
From: Gary Lau 23-Dec-1997 1018[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Tuesday, December 23, 1997 8:29 AM
To: tesla-at-pupman-dot-com
Cc: lau-at-hdecad.ENET.dec-dot-com
Subject: Is this motor synchronous?
I'm attempting to build a synchronous RSG. I ordered a motor from the H&R
Surplus catalog for $7.50, a Fugi motor, 115VAC, .85A, 1800 RPM. To
verify that it was a synchronous motor, I attached a 9.5" load disk with
a small bar magnet in the center, and positioned a pickup coil as shown,
connected to a scope sync'ed to LINE.
pinch
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It spun right up to speed, the period of the waveform on the scope was
33.3 msec and was rock-solid in phase. If I pinch the disk to increase
the torque, the phase shifts slightly, but bounces right back to where it
was when released. However, if I pinch to apply above some critical
torque, the phase shifts and stays shifted. Same thing if I briefly
switch off power. At first I thought that the phase was shifting in some
even sub-multiple of one revolution, but find that I can shift any
arbitrary amount from 0-360 degrees. I have verified that the
disk/magnet cannot shift relative to the shaft, and cannot believe that
the shaft is shifting relative to the motor rotor.
Is it possible for a motor to be synchronous but at an arbitrary and
variable phase? Is this motor unsuitable for a sync RSG, or is my
analysis technique flawed?
Gary Lau
Waltham, MA USA