Making an ARC Welder

J5 Tactical Flashlight

Making an ARC Welder

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I run the system on 240 VAC, which is metered by a power controller I built called the “Scariac”. It’s similar to the idea of a Variac (variable auto-controller), with a few more hazards to be aware of. The Micro-Welder itself does not have an on-off switch, and can pose a fire hazard if plugged directly into a mains power socket. I made this to be used exclusively with the Scariac. (Look for how to build that in another project.) Stick welding, and/or the modification of a Microwave Oven Transformer (M.O.T), can be very dangerous and presents risk of UV radiation, shock hazards, burns, fires, fumes and a multitude of other risks. This project should not be attempted without adult supervision and adequate training. Misuse, or careless use, of tools or projects may result in serious injury. Use of this video content is at your own risk.

Project History & More Info:

Did you know you can make an AC arc welder using parts from your microwave?

I used 2 transformers from 2 different microwaves, and about 50′ of 8 AWG stranded copper cable from a local hardware store. You could probably save some money by scavenging for free wire, but I decided to look at the “end of coil” section at the hardware store, and was able to negotiate a deal for half price on the cable, so the 50′ only cost me about $17.

The modified MOTs will have a new secondary that is 18 turns of the 8 AWG cable, and both MOTs are tied together in series. I also found I needed to run the system on 240 volts AC to get the power output for good welding. My goal was 30+ volts AC with a variable amperage from 0-120+ Amps.

There are a few videos on the internet that show various people who have tried making a stick welder from a Microwave Oven Transformer. There are even a couple of tutorials suggesting how to do it. However, in my experience of trying to duplicate these projects, my MOT welder either got so hot that the insulation on the wires melted and shorted it out, and/or it didn’t provide enough power to strike and maintain an arc.

The idea of the Microwave Welder isn’t new, but to date, I personally haven’t come across a video or project where anyone actually welded anything with one of these “so-called” microwave welders. The most that’s been shown is to lay a bead on a piece of metal, which I didn’t feel was very credible because this doesn’t prove it can weld. My earlier experiments with 1 MOT could also lay a bead, but it didn’t have enough heat or penetration to make anything stick. A welder also needs a way to reliably control the amperage (which no other project does). I saw one project where dimmer switches were used on the primary coils, however dimmer switches are only able to handle around 600 watts, and these stick welders require upwards of 2,000-3,000 watts. In my experience, the dimmer switches fail very quickly and within a couple minutes of trying to weld.

I’m happy to say that the welder in my project does work for me. It welds 1/16″ AC rods very well, and I believe the transformer temperatures are very reasonable and sustainable for the amount of welding I plan to do as a simple hobbiest welder.