RE: 1256D Paralleling Choke

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Cameron,

What about following Finns suggestion but series your two cores and use the
Center connection as the tap? I believe they would need to be mutually
wound. (Inductors in series are additive). Please post your results as I
have the same senerio but haven't had the time to experiment with them. (the
previous owner just paralleled them.)

Regards,
Jim Mora

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, June 28, 2006 6:21 PM
To: tesla@xxxxxxxxxx
Subject: Re: 1256D Paralleling Choke

Original poster: Finn Hammer <f-h@xxxx>

Cameron,

When there is a difference in voltage output of a couple of paralled
transformers, the one with the lowest voltage will draw current from
the one with the highest voltage. This is called circulating current.
To minimize this current, a center tapped  parallelling choke is
used. This choke has an impedance at 50/60Hz which is high enough to
block current flow between the transformers at the low voltage
presented by the difference of the variacs, but low enough to be
neglegtible at higher voltages, so that it does not act as a ballast
into the load. The 2 sections of the choke are in series between the
variacs, but in paralell into the load.

What you have to do is sweep the variacs trough the full movement,
and record the voltage difference between them.
The maximum voltage between them has to appear across the
parallelling choke, without saturating it.
To test if the core is up to this task, wind as many turns on it as
you can, and connect it across a variac. turn up the voltage, while
you monitor the current draw. At a point, the curent increases
rapidly. This is the point where the core begins to saturate.
In the case that this happens at a point where the voltage across the
choke is higher than the maximum voltage difference of the variacs,
you are on safe grounds. Wind the choke center tapped with this
amount of turns, connect the ends of the turns to the wipers of the
variacs, and draw power from the center tap.


Hope this helps, Finn Hammer

Tesla list wrote:

>Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxx>
>
>Hey guys,
>
>I've got 2 1256's I've mechanically ganged together. I now need to build a
>paralleling choke for them. I've read some posts and websites on how this
is
>done, but they talk about using an old variac as the core. I have a ferrite
>torroid that measures 2.25 inches O.D. 1.50 inches I.D. and is .75 inches
>wide. I believe the core is physically large enough to get 16 turns of 8AWG
>around it, but I'm concerned if the core is magnetically large enough or
>not. Any thoughts about this would be appreciated. I do have two of these
>cores, so I could stack them and wind through both at once if need be.
>
>Thanks,
>Cameron
>
>
>