Re: How are 240 VAC variacs made?

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

Original poster: Sean Taylor <sstaylor-at-uiuc.edu> 


>In a three phase variac, they are usually connected in Wye (star), with the
>low ends of the variacs tied together, even if the supply is delta fed. If
>you hook three variacs in delta, all moving the wiper(s) does is change the
>relative phase between the input and output, but the voltage remains the
>same. (draw a little picture/schematic, and this is obvious... three wires
>in and three wires out)

HEY!! There's an idea for a phase controller for a SRSG should one happen 
to be using a 3 phase system - one could also use a 3PDT relay to extend 
the range.  I suppose a similar thing could somehow be done on single 
phase, just a matter of figuring out exactly how - I'll have to think about 
it a bit.  Okay, thought about it while writing the email . . . if two 
variac are ganged, and wired opposite each other (so as the knob is turned, 
one wiper goes towards neutral, the other towards hot), the two wipers will 
change phase by (I think) 180 degrees across the entire range.  The benefit 
is you don't have to worry about having the right size capacitor - just 
plug in any motor and go, the obvious downside is a second variac!

Sean Taylor
Urbana, IL