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Re: variac



Subject: 
            Re: variac
       Date: 
            Sat, 22 Mar 1997 00:46:59 -0800
       From: 
            Open Minded <"unknown-at-apc-dot-net (No spamming! Try
\"70314.1744"-at-compuserve-dot-com~but_remove_this_part!~.pupman-dot-com>
Organization: 
            I'm NOT organized!
         To: 
            Tesla List <tesla-at-pupman-dot-com>
 References: 
            1


Tesla List wrote:
> 
> Subject:
>         Re: variac
>   Date:
>         Tue, 18 Mar 1997 15:12:23 -0600 (CST)
>   From:
>         c604313-at-showme.missouri.edu
>     To:
>         Tesla List <tesla-at-pupman-dot-com>
>     CC:
>         tesla-at-poodle.pupman-dot-com
> 
> > Bert,
> >
> > I have sucessfully ganged two 10 amp variacs in parallel for heavy neon
> > sign
> > transformer use.  Using power factor correction caps on the transformer
> > primaries will help lower the current.
> >
> > Ed Sonderman
> >
> >
> Yeah Ed, I had thought of a paralleling variacs also, but then thought
> simultanious adgustment of the variacs would be to tricky. Are your
> variacs mechanically linked together or do you adjust them with both
> hands?
> 
> Also, out of interest, what are the values of your PFC caps?
> 
> Thanks,
> -Bert S.


Gentlemen -

 Thought I'd jump in here and give my 2 cents worth....

 When you parallel 2 or more variacs together, you really ought
to use a paralleling choke. Even though you might get the brushes
aligned on the exact same turn, there will still be slight variation
in inductance and such.

 A paralleling choke works as a common-mode current choke. A current
imbalance in one variac is coupled to the other so that each variac
actually 'sees' it's share of the current. (The choke will create
a slight voltage imbalance on the input though - this is how it
keeps the currents split equally.

 I use two 20-amp 120-volt variacs paralleled with a choke to drive
my 3.6KVa coil system. Each variac sees it's share and runs nice and
cold.

- Brent