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 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