Re: Problem with Synchronous Motor and Timing Light

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 8/16/02 10:20:06 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:

Dan,

You unfortunately may have a hysteresis sync motor.  This type
locks into a different position every time it starts, and everytime
it loses lock.  You need a salient pole sync motor.  These can
be bought, or made, by modifying a normal induction motor, by
grinding flats onto the armature.....  2 flats for a 3600rpm motor,
4 flats for an 1800 rpm motor.  The width of the flats should be about 1/4
the armature diameter.  If you have an 1800 rpm motor, and it shifts
90 degrees when loses lock and re-locks, that would be normal.
If it locks to any a spot at any random number of degrees shifted,
then it's a hysteresis motor.  You can use a hysteresis motor,
but you have to adjust the phase every time you use the tesla coil.
This is usually inconvenient, so folks usually avoid the use of those motors.
One fellow flips the motor switch on/off a few times until it happens
to phase up good enough for the coil to run.  I don't favor that 
technique however.

John


>
> 1.  The timing light worked great.  Basically froze the rotor to free time
> so you could see the position of the rotor in respect to the 60Hz input
> power.  However, the problem is that if I briefly touched the side of the
> rotor to slow it down just for an instant (yes, it does burn my finger), the
> rotor locks in speed again, but in a slightly rotated position and will
> continue to move about everytime i slow it down for an instant.  Is this
> normal for a synchronous motor???  I was under the impression that once
> attached securely to the shaft that it would maintain its relative position
> forever unless you rotated the rotor about the motor axel.  What are your
> thoughts??
>
> Thanks
>
> Dan
>
>
>