Re: Ganging 1256D's

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

Original poster: "Chuck Curran by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ccurran-at-execpc-dot-com>

Hello Richard:

It sounds like you have arrived at a similar point that I did when I built
my power cabinet several years ago.  I built my power using a pair of the
1256D Powerstats as you are about to use.  I would highly recommend placing
these two units in a parallel input/output connection.  As you already
pointed out, the result is 0-280 VAC output at 56 amps continuous.  There is
however a catch.  I wanted a high level of reliability, so I chose to spend
the money and install a Powerstat T5587 current balancing choke on the
output legs of the two autotransformers.  This simply balance the output
load 50/50.  If you skip this item, manufacturing variations could provide
an opportunity for a large cloud of smoke.  That's fun to watch, but not if
it's your stuff!

If you connect it like this, you can always provide yourself with the 140
VAC too that you mentioned you also needed -- just don't go over 50 % on the
dial.  That last comment labels me as having a gift for the obvious :^)

I have used this set up to pull as much as 85 amps for significant periods,
3-4 minutes, with no problems to realized (so far).  I do have a bank of
four whisper fans blowing directly across the stack of autotransformers to
help out.

Just so you are forewarned, that little current balancing choke from
Powerstat is expensive, I paid $147.00 several years ago through Newark
Electronics.  I do have the Powerstat catalog, which has the connection
diagrams for many combinations of product types.  If you need any of this
I'd be happy to scan it and send it to you.  Photographs of this package can
be seen at:

                                    http://www.execpc-dot-com/~ccurran
just pick on the link to "Power Cabinet".

The second photo from the top on the Power Cabinet page has a view of the
choke.  It is the black rectangular item, hanging on a bracket, directly
beneath the two Powerstat 1256D's.  It is about 6" x 6" x 2"

Good Luck with your project.

Chuck Curran
Cedarburg, WI





----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, March 13, 2001 12:43 PM
Subject: Ganging 1256D's


> 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
>
>
>