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Are MOSFETS best for this?

Greetings All, I have a small Lincoln wirefeed welder. Depending on the wire and the process the welding wire will be either + or - polarity. To switch polarity two thumb nuts must be removed and swapped. This sounds easier than it is. Partly because of the way the welder is made. I swap polarity on a pretty regular basis so I would like to do this with just a switch. The max voltage is 30 volts and the max amperage is 140 amps. That 140 amps is very brief, maybe just a few seconds. Continuous current is 100 amps and 30 volts. I thought an H bridge would work but I can't find and MOSFETS that are rated this high for positive current. Can the MOSFETS be paralleled easily? Is there a better choice? The polarity would never be changed with power applied. I thought about using a relay with contacts rated at 150 amps or a double pole contactor or even a big toggle switch. All these options are too expensive. I'm cheap. I don't wanna spend more than $75 US on this project. Anybody here have some guidance? Thanks, Eric

Reply to
etpm
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Just put a pair of Tweco MPC cam-type quick disconnects either on the output terminals, or in-line in the leads. Or add a loop of leads that comes out where you can get to them if the thing gives you no room for that inside (small wirefeed, probably true.)

Might cost you $28-60 altogether, or more if you are supporting a local supplier who's not in competition with the internet/does not give you a nice fat discount.

I color code the ground clamp green, the stinger yellow, so it's easy to see at a glance how it's connected to the normally-coded terminals (Red+/Black-)

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Reply to
Ecnerwal

Check out some winch reversing switches, they handle the current you want, reasonably priced, compact. Only downside is that you need 12 for some of the solenoid coils.

Reply to
default

I didn't even think about winch reversing switches and I have a winch on my Jeep. Thanks, I'll look at them. Eric

Reply to
etpm

Greetings Lawrence, I looked at those some time ago and there is really no room for them inside the wire spool enclosure. But thanks for the suggestion. It's important to me to have the switching inside the enclosure, one reason being that I have already added some knobs and switches to the welder that take up the available space. I added a purge button and a pulse timer to the welder. So now I can purge the welding lead of air before I start welding without feeding the wire out and I can do stitch welding. Cheers, Eric

Reply to
etpm

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