That didn't last long. The relay shorted out again, on the same place, only much more violently this time (there's a sutt spot on the metal casing of the welder) The relay is beyond all repair and the PCB is pretty messed up at the relay solder spots too: pretty much charred from front to back. The good news is that it doesn't look like I fried anything else. When I get a new relay, I'll have to bypass the messed-up part of the board and sorder it to some different solder points.