RE: SRSG phase control? (and now also size of motor)

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

Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi Kent

>
> >  >Only a variac, capacitor, a fuse, and a resistor are needed.
> >  >In some cases where a cap-run motor is used, only a variac is
> >  >needed.
> >  >
> >  >John Freau
> >
> >    Wow, this is great help!  Perhaps a naive question, but will the
> >  "optimal" mechanical position of the sync gap change over time
> >  (ignoring mechanical drift, etc.) or can a sync gap be set once
> >  mechanically and forgotten?

On my coil, running a 5KVA pig with a 15/60 neon (two 120V primaries in
series) for ballast the sweet spot for the firing angle changes with
voltage. Up to breakout there is no phase shift, the timing is mechanical.
At higher power levels I need all of the phase shift I have available to get
into the sweet spot. I turn up the main variac a bit, then the phase shift a
bit, etc. till I get to the max power level the little 4" coil can handle.
Having the ability to adjust the phase of the firing of the gap is well
worth the trouble.

> >  Do you just try various caps and compare the voltage difference across
> >  the motor?
>
Basically yes. I am using 25uF for my 1/3HP A.O. Smith 3600 RPM (modified)
SRSG at 240V input. That means if I were using 120V to power the motor, I
would need 100uF. I have some pictures of the switch box I made to find the
right capacitance. I will post these tonight or tomorrow.

later

deano