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X-Ray Jacob's Ladder - Was 1256D Paralleling Choke

Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxx>

Hey guys,

I did some more testing with those dual 1256 variacs tonight and can't
really find any problems with them running without the paralleling choke
other than one getting just slightly warmer than the other. I've ran them up
to about 75% for several minutes until the 60A breaker trips and the setup
seems solid.

I took some pictures tonight you can see here:


Comments or suggestions welcomed.


> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Friday, June 30, 2006 12:59 PM
> To: tesla@xxxxxxxxxx
> Subject: RE: 1256D Paralleling Choke
> Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxx>
> Hey guys,
> Yes, I am trying to get 56 amps by ganging these 1256's in parallel on a
> 240V 60 amp circuit. This setup is to drive my x-ray transformer for a
> massive Jacobs ladder. I do have a factory dual-ganged set of 1256's in my
> coil control panel and it came with the choke in a box mounted to the side
> of the front variac. It has the outputs of both 1256's tied to it and the
> output to the ballast and pig come from it. It's wired as shown on Scot's
> page. I was basically wiring these other two 1256's like the factory dual
> ganged set I have now.
> Tonight my son wanted to see the Jacobs ladder so I just paralleled all
> the
> connections to both variacs and tried it. I popped the fuse out of one of
> them and compared the output voltages at different positions. The 1256B
> had
> typically between 1 and 2 volts higher output than the 1256D. I went ahead
> and ran the Jacobs ladder at about 70% for almost 10 minutes. My 1.2 ohm
> 5000W ballast resistors showed 380 degrees on my Raytech and were pretty
> toasty. I monitored the temps of the windings in both variacs closely and
> one was running around 82 degrees and the other was at 86 degrees.
> Certainly
> nothing to worry about there.
> I'm thinking I'll just run them in straight parallel as they are now and
> just keep an eye on things. The output of the Jacobs ladder is very strong
> at about 16 inches point to point and probably closer to 20 inches if you
> count the bow of the arc.
> Are there other symptoms of problems caused by running without the choke
> besides heat I should be looking for?
> Thanks,
> Cameron
>  > Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>  >
>  > Hi Scot and Cameron,.
>  >
>  > Since both variacs have the 220V (240V) input,  I'm thinking Cameron
>  > really wants to parallel them for 220V  operation to get the current
>  > up to 56 amps. Of course he could always put 120V into the 220 volt
>  > tap to run them in series for 280V output, but he would still have a
>  > 28 amp variac (determined by the wire guage and brush design) - same
>  > capability as one 1256.  His toroid only has 0.28 sq inchs of cross
>  > sectional area.  If he could find one with 1.5 to 2.0 sq inchs of
>  > area, things would probably work.  Of course things could scale down
>  > if the voltage difference was less than 5 volts or more than 16 total
>  > turns could be put on the toroid.  If Cameron meant 16 turns from
>  > center tap to one msnip...