A place I worked at a while back had a consumer product with an unrated contactor which was fine for a real 80 amps RMS continuous.

We never had to use it to switch the load because we used a transformer to generate the 80 amps from a 240 volt supply. The supply was not high power and it was controlled by standard 240V switchgear. If the unrated contactor had been used to switch the power directly I'm sure it would have died quite quickly.

I'm sure the high current contactor was as bulky as any knife switch I've seen. The use of such is no bad call. The thing you are going to be interested in is keeping the contacts clean. You ideally want a wiping action, perhaps silver or gold plate.

For a modern product, I would have to say that a Solid State Relay is the best way forward, but I don't think you'll get what you want off the shelf. I am equally certain that technology is up to the task, it's just that no-one much wants it, so it's hard to come by. If you were developing a product it would be worth developing a supplier for such a thing, because it would be more reliable than any mechanical solution.

I think the unrated contactor was a non-standard Crydom product. It was Bakelite/Phenolic with an open frame about the size of a playing card, perhaps an inch and a half thick.

Edited By Andy Ash on 18/12/2016 14:26:53

I completely get that.

If you were thinking about making something yourself, I would say that it is completely within the bounds of a normal ME workshop capability.

The one we used to use had a copper braid onto a rocking top. The solenoid was at one end and the contacts at the other. The pivot was across the middle looking down on top. The switch was double pole, single throw so it had one contact either side.

P.S. Because of the rocking action the contacts would wipe each time the switch was made.

IIRC the contacts were unplated copper, so one of the yearly service items was to dress the contacts with a diamond file.

You could make the body of the switch out of Paxolin on the mill.

P.P.S. Normally in a modern welder you can find a low voltage supply to pick off for control purposes. On my TIG welder I added a gas purge facility and the relay is powered from the welders own low voltage supply.

Edited By Andy Ash on 18/12/2016 15:07:14

As noted above, this is not technically a switch ie it will not be required to open or close under load. It would be more correctly referred to as a disconnector or isolator.

You could make something up easily with some Anderson connectors. You could put 2 double sockets side by side, wired straight and reverse polarity and choose which one to plug your ground and torch into. SB175 (175A) would work. These are widely used and well proven. And you hardly complain about the price.

Another solution would be to take 3 of the stackable single way PP180 (180A) connectors eg 2 red and 1 black (connected +ve, -ve, +ve) on the machine and a pair of them for the torch eg 1 red for the torch and 1 black for the ground clamp. Then you could choose which of 2 alternative ways to plug in to the welder.

Note that they also sell handles, boots etc to make a neat and tidy job, as well as a choice of crimp sizes to suit different cable gauges.

Murray

These plugs and sockets are available on eBay for under 10 quid for a pair, they are very quick to change as they are just turn to lock. Most industrial machines use these as they are very quick to change a torch and cable which is the bit that suffers most. If you fit the sockets on your machine life could be very easy.

Mike

Edited By Michael Poole on 18/12/2016 17:05:32

Edited By Michael Poole on 18/12/2016 17:09:36

That sounds like a better idea than the Andersons. Must admit I've seen these welder cable connectors but never used them myself. They sound ideal.