Re: Paralleling Chokes

["Tesla list" <tesla@xxxxxxxxxx>]

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

Curt,

This was covered only 4 months ago:
-------------------------
Original poster: "Paul Benham" <paulb@xxxxxxxxxxxxxxxxxxxx>

Hi Cameron,

I used a 225VA toroid transformer core with 16 turns from the center tap to
each variac output and it worked really well.  My variacs were 15A each.  I
did check for saturation as Finn mentions.

Only the winding resistance is seen in series with each variac output as the
flux from each winding cancels in the core and thus the inductance is zero.
Any circulating current between the variacs will see the full inductance of
the two windings.

Cheers,

Paul.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, June 29, 2006 2:20 AM
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 skrev:
> Original poster: "C. Sibley" <a37chevy@xxxxxxxxx>
> In the process of builing my "dream" power control console I am 
> planning on connecting two 1256D variacs in parallel.  To do that I 
> understand I need a paralleling choke.  Does anyone have such a 
> device for sale? Or as a second choice, does anyonbe have any 
> suggestion how I could build one?
> Thanks,
> Curt.