The assembly process began with the same instructions as the 70 Amp unit. I modified the transformers up to the point of rewinding the secondaries. Instead of winding #10 AWG stranded, I used #10 solid copper insulated. I purchased 25 feet of #10 Romex, stripped the sheath, and wound the secondaries with that.
Rewinding the secondary was a bit more difficult with the solid wire but, I got 19 on the first tranny and 18 on the second. Using the wire/water test, I measured 37 vac and approximately 110 amps before the test assembly fried. Impressive is it not? Actually, extremely alarming is a better term. It just did'nt add up? The huge gain in power was just too great for such a small change in assembly proceedure, I had to dig deeper.
The math kept telling me that the primary turns had been reduced. Suspicious, I physically counted the primary turns as best I could and the number I came up with was approximately in range with standard mot configuration. So, why do the calculations claim fewer turns? Time to bring out the Magnifying glass!
Close examination revealed that the primary coil of one transformer had sustained a blow that did not deform the coil but was hard enough to rupture the insulation and allow the current to bypass some of the turns, effectively reducing the number of turns in the primary. Inductive reactance was also reduced as a consequence which significantly increased the output power. The solution to this mystery was elusive to me at first but, determination and math nailed it in the end.
This scenerio would be detrimental if this transformer were in a microwave oven, we're talking about the forth of July in a box but, as a welding power supply, it's perfect.
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