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 gaussThe 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 aparalleling choke for them. I've read some posts and websites on how this isdone, 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