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>

Dan, all,

A salient pole sync motor won't exibit any random rotor slip.
If it slips due to finger pressure on the disc, it will jump a full 
pole position or more, and will always relock in the correct
postion for our Tesla coil work.  This is 90 degree multiples for
an 1800 rpm motor and 180 degree multiples for a 3600 rpm motor.
The salient pole motor will start in the same position every time
you start it. 

It is only the hysteresis sync motors that can lock in any
random phase position, and are not convenient for Tesla coil
sync rotary gaps.  The hysteresis motor has no core rotor rods
at all, but uses a special one-piece magnetic material in the rotor.
It relies on the large hysteresis characteristic of the material to
operate properly.

I just saw your posting Dan that the motor says HYST on the
motor.  Those who bought these motors can probably return
them to DR Resonance for a refund.  

I'm not sure if my phase shifter circuit which uses a variac and 
capacitor will work well with a HYST motor.  My guess is that
it would work, but I've never tried that.
In any case, the phase shifter only gives 1/2 the needed phase
range.  You'd have to build a two stage shifter to get enough
range, and I've never tried that.  

Anyhow, my phase shifter circuit is shown at:

  http://hometown.aol-dot-com/futuret/page3.html

The phase shifter circuit is convenient to have, even for a
salient pole system, esp for research work, in which frequent
phase adjustments are needed.  For a portable coil, I just
set the phase and leave it, so I don't use the phase shifter.

John


>
> > 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
>
>
>
>
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