Re: VARIAC's -> parallel??

To: tesla-at-pupman-dot-com
Subject: Re: VARIAC's -> parallel??
From: bob golding <yubba-at-clara-dot-net> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sun, 15 Nov 1998 19:54:26 -0700
Approved: terryf-at-verinet-dot-com

At 17:11 13/11/98 -0700, you wrote:
>>         My friend was talking to an engineer at a variac company the
>other day.
>> He warned against putting variacs in parallel.  Apparently, if the output
>> voltage of each variac is a little different, there will be heavy current
>> flow between the outputs due to the unbalanced voltage.  He had some
>> special choke or something for $100 that would fix this problem and allow
>> them to be put it parallel.  Anybody ever heard this before??
>> 
>>         We decided it was ok because we put the ballast resistors on each
>leg of
>> the three phase variac and then combined them.   So the resistors would
>> balance the voltages out before they were joined.  The engineer's concern
>> did seem very valid to us.

 Something else to ponder,

Is it possible, sensible even, to connect two variacs of difference rating
together in some way? I have one 8 amp and one 15 amp at the moment which
is fine for neons. I am getting a 8 kV 250 mA transformer and am worried
that the brushes on the 15 amp variac might not like it too much. 8 amp
variacs are more common than larger ones here in the UK so I could gang 3
of them together if I have to, but for now can I do anything with what I
have got?. Am I missing something really simple here?.

many thanks 

bob golding