Re: Problem with Synchronous Motor and Timing Light

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

Original poster: "Daniel McCauley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

> >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
> >
> >
> >
> >
> >
> >
> Hi Dan...
>
> what you are seeing is the effects of "rotor slip". The rotor is made in
> such a way that the core ( rotor)  has rods running the length of the
> rotor, all or the rods are connected to each other via a ring on each
> end. ( kinda like the running wheel used for hamsters). This design
> allows a magnetic field to be created in the rotor when voltage is
> supplied to the field windings.
>
>
> Anyway...   the fields created by the motors stator ( field windings)
> "lock" onto these rod sets and "push/pull" the rotor around. When you
> slow the rotor (disc) the magnetic field looses its lock on the set of
> rods it originally "grabbed" hold of.  The field will then lock onto the
> next available set of rods in the rotor, thus shifting the grab point
> and giving you the results you are seeing.
>

Thanks.  So i guess i need to tune my SRSG everytime before i use my coil???
I thought a salient pole motor would start up in the same position every
time i powered it up.

Dan