Re: can this motor be made sync?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 10/6/05 5:34:48 PM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:


> What makes an induction motor a-synchronous, is the fact that the
> armature is not magnetized. Period. if the armature does not slip
> with regards to the rotating magnetic field, there would be no
> induced magnetic field in the armature. That is why induction motors
> run slower than synchrony. It's not because it has no flats.
> Manufacturers would have thought of that already, if it acutally
> worked. No amount of flats is going to fix that. I don't know where
> that idea came from, i've seen it before on some website. I just chuckled.
>
> The only way would be to somehow magnetize the armature, but since it
> is mostly aluminum, I don't see how you would do that.
>
> Dan


Dan,

A great many of us on this mailing list have modified induction
motors by grinding flats onto the armatures to make them
synchronous.  I've modified about 7 motors so far.  Works perfectly.
Some torque is lost however.  The armatures are mostly steel
in an induction motor.  These so-called salient pole type sync
motors always sync up to the same phase position.  This makes
them well suited for use in synchronous rotary spark gaps.

BTW manufacturers do sometimes use this method (flats) to build
synchronous motors

There is another type of synchronous motor called a hysteresis
synchronous motor which uses a different principle.  This hysteresis
type will always start up in a different phase position, so they
are generally not convenient for Tesla coil use.  There are
other types of synchronous motors also.

The poster who saw only failure in his modification attempts
was using a very small weak shaded pole type motor (or so it
appeared to me in the photo).  These motors tend not to work
well for the sync modification.  Suitable types of motors are
induction run- induction start, capacitor start, and capacitor run
types.

I made a circuit for controlling the phase of these motors remotely
while the Tesla coil is operating.  Many folks have built and are using
this circuit with their modified synchronous motors.  The circuit
works fine for commercial salient-pole synchronous motors too.

John