There's no actual reason, but I'm curious, could you take a power supply, connect one end to a metal object, connect the other end to a piece of solder and use that to solder something. Also if it is possible how much current would be needed.
The current would melt the solder, all right, but you wouldn't get a good joint. For soldering, you need the work (wires, or metal) to melt the solder. Applying melted solder to cold metal gets you a failed joint.
> 6V -12 DC with > 25Amp Current Required with Graphite or Tungston +Ve Electrode is preferable Use Solder (Lead + alloys Stick ) & Flux required.(It is like a TIG Welding method).Weldment metal Should be very thick preferably Copper OR Brass (If so thin it will burn).
Power source needs about 2V to 4V depending on the wire length and thickness , current is between 5A to 10A.
It would not do the soldering because the whole solder is melting down in seconds.
As soon as the solder melts the circuit is open and it cools before it can bond with the work. And the voltage / current damages any attached electronic devices.