Chinese electronic for spot welder need a little fix. "Get MOT, rewind secondary winding, add chinese PCB with triac" - sound easy, but I was upset that it wasn't working. One of chinese genius add LED diode in serial connection to the driving optotriac with 1Kohm resistor (on 5V). The result was that weldet did not work at startup fewtimes. When it "worked", then worked bad (can't make proper weld) and blew the 16A circuit breaker. There is easy "FIX". Replace resistor 1K near LED for 200Ohm and add varistor S20K275 to the triac (for better protection). Happy welding!
