Re: Ganging 1256D's

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

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "Richard Wayne Wall by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <rwall-at-ix-dot-netcom-dot-com>
>
> 3/11/01
>
> I have recently added a second Powerstat 1256D variac to my power cabinet.
> They are identical 0-280vac, 28 amp, 7.8 kw single phase.  I have ganged
> them together and wish to increase the power to 15.6 kw at 56 amps.  I also
> wish the capability to just use one leg for occasional 0-140 vac output.
>
> My question is should I hook them up in parallel or in series with one hot
> leg going to each variac?  Seems if in series each will still be limited to
> 28 amps.
>
> RWW

Hi RWW...

I  have done the same thing you are wanting to do ...

but as you have seen, a paralleling choke is needed.  I made a paralleling
choke out of #10solid Cu. THHN
wire and an old core from a 7.5A 120V variac. You can easily nab one of
those ( 7.5A variac) from Ebay for
around 15$.  Remove the core assy from the case/base and remove the wire
that comes on it, all you want is
the core.

To make the choke, wind 10 turns of wire on one side of the core with wire
#1 and another 10 winds on the
other side of the core with wire number 2. Have the wires enter and exit
from the center hole of the small
variac core.


To wire up the variacs.   run one hot leg to both #1 terminals on the
variacs, the other hot leg to both of
the #2 terminals, the # 3 terminals attach to the wires on the choke. the
output leads of the choke are
attached to each other which go to the load ( inductor or load depending if
you are running a piggie). Use
leads #1 and the outputs of the choke for the full 280v -at- 56A.

While you are waiting for your small variac to arrive....   break down the
1256D's and add more insulation
between the core supports and the core. Either use some rubber sheeting
about 1/10" thick or use some of
the heavy rubber insulating tape ( not the thin vinyl stuff). This will
protect the cores from wanting to
arc to the mounting structure in case of a hi volt feed back ( believe me
it does happen... in fact it just
happened to me last week).

and BTW   2 1256D's tied together are HEAVY    :)~

hope this helped


Scot D