I have an old, transformer-based welding machine, which is rated to draw about 70A at 240V, at full output. It uses an electro-mechanical relay (contactor) to energize the main power transformer, and depending on the point in the AC cycle that the contacts close, it may have a high inrush current, well in excess of the rating of the circuit breaker that feeds it. When it was built, in 1960, fuses were the norm, and one would simply use a time-delay fuse, to tolerate the spike. Since it's in my garage at home, and not in a commercial environment, I don't have the ability to use a breaker with a D trip curve, without replacing my entire breaker panel, at the cost of hundreds of dollars US. I'm looking for a more elegant solution.
Ideally, I'd like to find an off-the-shelf solid-state relay, which is designed specifically to power inductive (single-phase) loads, by switching on and off only at peak voltage, where the current is at a minimum. Does such a device exist, or would it be realistic to design an analog circuit that would accomplish this?
A resistive (NTC) inrush current limiter isn't really suitable for this application, because sufficiently high current devices would cost as much as replacing the circuit breaker panel, or more, and I need the ability to rapidly turn off and on the main power transformer primary as many as 20-30 times per minute, and NTC resistors at that power level tend to have cool-down times in the range of minutes.
Best Answer
There are many Soft Starter available in very reasonable price. You can search the Term "Single Phase soft starter". or "Three Phase Soft Starter" according to your welder specifications.