Re: Stacking Variacs, paralleling

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

Original poster: Esondrmn-at-aol-dot-com 

In a message dated 4/2/04 10:37:58 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>I have three 240V/28amps (ea.) variacs on the way (225Lbs ouch!).  They do
>not have the paralleling chocks.  Can I make my own?  Are these really
>necessary to connect the variacs in parallel?  I have seen on commercial
>units that they are actually just transformers, I've got enough MOT cores
>to make transformers, but what am I after?
>
>Randy


Randy,

You will probably get more educated answers, but here's mine.

I have used 10A 120V variacs connected in parallel on a common shaft with 
no choke and not had any problems.  You can get it all set up, apply power 
and measure the voltage from wiper to wiper and see if it is zero.  If it 
is even a volt or two, large currents will want to flow to balance things 
out.  For large variacs like yours, I would wind some chokes with say # 8 
insulated wire around some unused transformer core material or steel 
welding rods that have been varnished.  I would think 20 or 30 turns would 
be enough.  You would have three of these with one lead going to the wiper 
of each variac and the other three leads tied together as the variac output.

Ed Sonderman