Bob Engelhardt wrote:
Also about the SSR: I've read that they should be derated 30-70% for
inductive loads. They were probably referring to motor loads, but the
spot welder is certainly inductive. As much as a motor, though? Did
you derate yours?
Bob

A transformer with a resistive load, which the weld is,is not very
inductive. Mostly only leakage inductance. So there shouldn't be
much of a spike regardless of what part of the cycle it isinterrupted on.
...lew...