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Re: synchronous motors

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Your right Bill. When I built my SRSG, I used a rotating stationary setup. It easily honed in on the big sparks. As you said, it's obvious when you get it right (I use to just play with it to see the difference - and it's a major difference).

The stationary setup was rather unique, but did allow me to simply turn on the motor and use a toggle switch to set the stationary electrode alignment along the rotating path. I never had a problem with phasing the motor from that point on. Some may not like this approach, but I'd bet it is more of an arm-chair cowboy dislike.

These days, I'm not even using an SRSG. I've moved back to a variable speed gap with VFD controlled 3-phase motor. I just like that speed adjust at my finger tips. That "varoom" sound is simply too cool! ;-)

Take care,
Bart

Tesla list wrote:

Original poster: William Beaty <billb@xxxxxxxxxx>

On Mon, 8 Aug 2005, Tesla list wrote:

> Original poster: "Ethersmith" <siveya@xxxxxxxxxxxxxx>
>
> Well, on the advice of many, I am looking into building a synchronous rotary
> gap. Locally, there is a surplus house that has many motors. Often, some of
> these have "sync" stamped in the plate with the details. Can such a motor
> (given a good enough match in HP and RPM) be used for a snyc gap unmodified?
> Does it still require modification? Does it mean something entirely
> different?

An "ideal" synch motor would have a rotating permanent magnet.  However,
the real-world synch motor I used for a rotary gap did not have an
absolute phase.  It would lock onto 60Hz, but with random phase relation.
I suspect that most synch motors are like this, since it's cheap to just
use steel in the squirrelcage rotor core rather than soft iron.  In such a
motor, at startup, the rotating magnetic field goes much faster than the
spinning steel rotor, so the rotor's permanent magnetization gets erased.
But then the rotor gets up to speed and "locks in," becoming magnetized
again.

The result is that the TC output is usually not max, and you have to
switch the sync gap motor on and off two or three times in order to "hit
the peak."  (From the sound and light of the TC output, it's pretty
obvious when you get it right.)  That, or instead you can leave it
running, but push something against the spinning gap electrode disk to
forcibly drag the rotor phase backwards until you hit one of the 60Hz
peaks.


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