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Re: [TCML] Variac ballancing chokes re-visited
My first attempt at balancing 3 16 amp variacs resulted in very unbalanced loading. As i recall when I loaded the stack to about 15 amps one supplied over 11 amps and the second about 3 and the third less than one amp. I checked this with a clamp-on amp meter. I carefully aligned the wipers and checked the voltage at several points in the rotation and it was always less than 1 volt difference with the outputs separate. No matter how i tried it the balance was always way off. I had no balancing chokes at the time so I tried using all three legs of a 30 volt 40amp 3 phase transformer. The output terminal being the center of the Y connection and leaving the 240 volt primary unconnected. The result was all three variacs were within a quarter of an amp of eachother. If you don't have any ready made balancing chokes handy it may be worth a try.
Scott
--- On Thu, 5/10/12, bturner@xxxxxxxx <bturner@xxxxxxxx> wrote:
From: bturner@xxxxxxxx <bturner@xxxxxxxx>
Subject: Re: [TCML] Variac ballancing chokes re-visited
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Thursday, May 10, 2012, 8:03 PM
The balancing choke from what I remember acts as a common-mode rejection
ratio device. An increase in current draw on one side increases (boosts)
voltage to the other, thus re-equalizing. For two variac's, it's wired as
a 'center-tapped' transformer, so that the 'free' ends of each winding are
out of phase with each other. In fact, I've heard of folks using an old
variac core and winding their own. Usually 10-15 turns for each 'leg'. The
wiper's connect to the leg of each winding of the balance transformer, and
the combined output is via the 'center-tap'. (Factors in eddy-current
differences...) The classic diagram shows TWO transformers, however the
balancing winding is 'cross-connected' in order to place the current load
out of phase. A single center-tap design is a lot simpler!
- b
> I came across this web page after using goggle.
>
> http://bellsouthpwp.net/b/u/bunnykiller/parallel.html
>
> It refers to my "A)" scenario as I suspected was presented by
> "bunnykiller". "Connection 3" (on the right side of the page) seems like
> the best method because each 'choke' has a dedicated winding in
> correspondence to each variac. Therefore a 30A variac passes thru a #8
> wire
> winding (well within the current capacity of the wire). Can someone
> clarify
> the winding direction in relation to the H1,H2 winding and H3,H4 winding.
> I
> see it as if it were one center tapped winding H2 and H3 would be tied
> together and be the center tap, is this correct?The other scenario I
> presented used 2 chokes to feed a 3rd choke, which would see 90A max thru
> #8
> wire. Probably a bit too much stress.
> On a side note I'll look into 'IMGUR.com' Nicholas, thanks. Yes it's good
> to
> be coiling in Wisconsin and hear from a member I've met. Thanks to
> everyone
> who responded.
> ----- Original Message -----
> From: "MICHAEL HARDY" <mhardy4@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Sunday, May 06, 2012 9:59 PM
> Subject: [TCML] Variac ballancing chokes re-visited
>
>
> In my power control cabinet I have a 3 stack variac consisting of 3 X 520
> V,
> 30 A units. I was using one homemade balancing choke made from a 10 A, 240
> V
> variac core wound with 2 sets of 9 turns of #8 wire for balancing 2 of the
> 3
> stack variacs. I now wish to use all 3 in the stack. I have made 2 more
> similar balancing chokes from burned out
> 10 A, 240 V cores. I have seen 2 schemes for wiring these. Here's a shot
> at
> an asci drawing of each.
>
> A) ________________________
> I __ ___ I
> I I I I I I
> UUUU UUUU UUUU
> -------- -------- --------- The V1,V2,
> V3
> are the variac wipers (outputs)
> _ -------- _ -------- _ ---------` I think this
> was done by Matt D. (bunnykiller)
> V1 UUUU V2 UUUU V3 UUUU
> I_________I_________I
> I
> OUTPUT
>
>
> B)
>
>
> V2
> I
> -------------------- I -------------------
> V1_____ -------------------- __ I____ ------------------- _______ V3
> UUUU UUUU UUUU UUUU
> I I
> I I
> I -------------------------- I
> I -------------------------- I
> UUUU________UUUU
> I
> I
> OUTPUT
>
> Are both methods equally effective or is one preferred over the other?
>
> I would appreciate any comments,
>
> Thanks
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>
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