Re: Variac as sync gap tuner?

To: tesla-at-pupman-dot-com
Subject: Re: Variac as sync gap tuner?
From: Bart Anderson <mopar-at-uswest-dot-net> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Sun, 07 Mar 1999 10:17:04 -0700
Approved: twf-at-verinet-dot-com

Hi Jim, Eddie, all,


> ><Eddie wrote>
> >  Has anyone ever used a variac as a variable inductor for the purpose of
> > tuning a synchronous rotary gap by varying the phase lag? The nice thing
> > about this is that it could be remotely tweaked. I realize the inductance
> > would probably be excessive after a point but I'm just wondering if it
might
> > be an alternative to a pivoting motor mount.

> <Jim wrote>Actually, you could probably even do it in a more clever
fashion by
> putting a capacitor across the winding of the variac, and perhaps some
> load to ground. The variac would be across two different phases, and you
> could fine adjust it quite nicely.  How much phase shift do you need for
> a sync rotary....?? If it is only 45 degrees, then this kind of strategy
> would have real promise.

Well, I put up such a circuit into PSpice last night. I placed an inductor in
series (variac) with the motor load and a 1k resistor and 100uF cap to
ground in
parallel with the motor load. I put voltage markers on each side of the
line and
load. Varying the inductor from 1mH to 100mH, I could get almost 45 degree
phase
shift. I'll try it today on my sync gap and report. Seems like it should
work. I
am more curious if the motor will stay in sync as a voltage drop will be placed
across the RC combo. I used these values because I have the components on hand.

Bart