A *VERY* good converter will run a 3 phase welder, though they don't like it a lot, lol. I have a 400 amp Union Carbide power supply that hums along fine, we get about 300 amps on .045 dual shield or metal core. Only lost one converter so far! Sad thing is we only have 100 amp 220 single phase in the shop we rent in a commercial yard. I have a 100KW three phase generator with a CAT 3208 for backup though!