Quote Originally Posted by Portable Welder View Post
Willie B.
They recommend AC because it creates more heat for the same amount of amps.
With DC, electrode positive heats the electrode, electrode negative heats the workpiece. I doubt this phenomenon carries over to pipe. Theoretically current would be equal throughout the complete circuit, voltage would vary with resistance. If you imagine a series circuit with four identical 100 watt bulbs connected to a 480 volt power source, each should receive 120 volts and work fine. Bump one or change it out with a 60 watt, the 60 gets most of the voltage, failure of the bulb is instantaneous, and catastrophic. The high resistance portion of a circuit ideally the pipe in the ground will uniformly heat spreading heat (3.4 BTU per watt) over the length of the pipe. If AC is better than DC it would be my guess it has to do with converting AC to DC in some welders.
Most of the pipe thawers I'm aware of use "pipeliner welders" that only produce DC using comutators.
By the way, when installing pipe underground, a #10 THHN conductor wrapped around a copper water pipe make it childs play later when it freezes, A layer of dirt in the ditch covered with sawdust or styrofoam will prevent freezing altogether.
Maybe global warming ain't all bad!