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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 side then the volts per turn will be halved and the
> flux density will be halved.
>
> Cameron, if you could measure the actual voltage difference and
> confirm the total number of turns on your existing toroid, I will
> crunch the numbers for you.
>
> Gerry R.
>
>
> >Original poster: BunnyKiller <bunnikillr@xxxxxxx>
> >
> >hmmmm doesnt look good and besides I must have been thinking in
> >a wrong direction anyway if Cameron is using the variacs with
> >240VAC he should attach each hot leg to each variac
> >respectively... one leg per variac no parralelling
> >needed.... but if he is trying to parallel the 2 variacs for 120VAC
> >at 50amps then the choke is needed.... and a rather healthy sized
> >one at that a 15 Amp variac core should fill the bill.... shouldnt
> >saturate even at 60 Amps...
> >
> >
> >
> >Scot D
> >
> >
> >
> >Tesla list wrote:
> >
> >>Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> >>
> >>Hi Scot and Cameron,
> >>
> >>I ran the toroid dimensions thru my toroid ballast design program
> >>assuming 5Vrms difference between variacs, 16 turns on the toroid,
> >>and a permeability of 20000 and then 10000, and I think that core
> >>will saturate badly. Following are the computed results:
> >>
> >>permeability = 20000:
> >>
> >>******************** BALLAST DATA ********************
> >>
> >>Ballast Voltage = 5 Volts rms
> >>Ballast Current = 1.6 Amps rms
> >>Line Frequency = 60 Hz
> >>Outside Toroid Diameter = 2.3 inches
> >>Inside Toroid Diameter = 1.5 inches
> >>Toroid Core Area = 0.3 square inches
> >>Relative Permeability = 20000
> >>
> >>GAP Size = 0.00 inches
> >>
> >>********************** RESULTS **********************
> >>
> >>Required Inductance = 8.3 mh
> >>Required Number of Turns = 16
> >>Volts per Turn = 0.3 volts
> >>Peak Flux Density = 62700 gauss
> >>
> >>
> >>permeability = 10000:
> >>
> >>******************** BALLAST DATA ********************
> >>
> >>Ballast Voltage = 5 Volts rms
> >>Ballast Current = 3.2 Amps rms
> >>Line Frequency = 60 Hz
> >>Outside Toroid Diameter = 2.3 inches
> >>Inside Toroid Diameter = 1.5 inches
> >>Toroid Core Area = 0.3 square inches
> >>Relative Permeability = 10000
> >>
> >>GAP Size = 0.00 inches
> >>
> >>********************** RESULTS **********************
> >>
> >>Required Inductance = 4.1 mh
> >>Required Number of Turns = 16
> >>Volts per Turn = 0.3 volts
> >>Peak Flux Density = 62700 gauss
> >>
> >>The conditions for the computations are no load on the toroid
> >>center tap so the current is what passes thru the choke from one
> >>variac to the other. Didn't know what the permeability is but it
> >>doesnt seem to affect the flux density (and it shouldn't since the
> >>volts per turn and cross sectional area remain the same).
> >>
> >>Gerry R.
> >>
> >>
> >>
> >>
> >>>Original poster: BunnyKiller <bunnikillr@xxxxxxx>
> >>>
> >>>Hey Cameron...
> >>>
> >>>I would go ahead and use both stacked together to make it " 2.5 X
> >>>??thick" and carefully watch the voltage differences between each
> >>>output.... if there is much more than 5 volts between each leg
> >>>you will need to go to a larger core ( a small variac core minus
> >>>its original wire)
> >>>
> >>>to test voltage between legs, VOM the neutral and one leg (
> >>>approx 120 - 140 V depending on how you have the varaic set up)
> >>>and repeat for the other leg. If voltage difference is same/equal
> >>>or less than 5 V difference, then you are ok if not, start
> >>>looking for a 7.5 amp variac on Ebay ;)
> >>>
> >>>next step is to load the variacs with something that can pull a
> >>>decient amount of power ( approx 20A) and retest the voltage
> >>>differences between legs...
> >>>
> >>>I am assuming that you are running 240VAC opposed phase ( single
> >>>phase in more common terms)....
> >>>
> >>>
> >>>Scot D
> >>>
> >>>
> >>>
> >>>
> >>>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
> >>>
> >>>
> >>
> >>
> >>
> >
> >
> >
> >
>