Re: [TCML] Salient Pole Query

[futuret@xxxxxxx]

Phil,

No.  Only a sync motor will run at 1500 rpm.   An async induction motor 
will
run at around 1425 rpm.  BUT there is another type of sync motor
(not salient pole)  This other type is called "hysteresis" sync motor.  
This
type will run at 1500 rpm, but will always start in a different 
position.
Oviously you want the salient type.  When you modify a 1425 induction
motor to make it salient, it will always give 1500 rpm, and will always
sync-lock to the same phase.

If you have an old fastioned flourescent fixture (not electronic) it's
pretty easy to verify sync lock.  Just slow the motor with a variac
and vary the speed and observe carefully, and you'll see the very
blurry rotating pattern.  then as you raise variac voltage, pattern
will stop rotating at some point.  Also you will hear the sound change.
When you're near (but below) sync lock voltage, you'll hear the motor
hunting (uneven pulsing sound), then as you raise voltage.  The sound
will become very steady roaring sound.   Some folks take awhile to 
"learn" how to
see this pattern.  But after you learn, it's very easy to see.  Also 
make sure
there isn't daylight or other indescent lights on in the room.  These 
motors
often sync lock at about 50 to 60% line voltage or so.  (without a 
electrode
rotor attached).

Some people prefer to build a circuit like a strobe to check sync-lock.

John
--

My understanding is that both a Synchronous and a Asynchronous can run 
at
1500 rpm, but the Synchronous (every time it runs) will always have its
rotor in the same angular position when the AC cycle reaches its peak. 
Yes
or no?

I have had no luck using a fluorescent tube and a marked cardboard disc
unfortunately. Nor any luck with a neon. 
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