Category: Plasma Cutter


There are a few DIY plasma cutter plans floating around the Internet. Most of them are napkin-sketches that someone scanned and put on a forum for experienced welders to blanch at.

A rough schematic of a plasma cutter
Don't try this at home

This has a few issues. The main one is that it’s not properly isolated from the AC mains. An isolation transformer can provide that isolation, and can be improvised from two identical transformers back-to-back, with their secondaries connected. That will act as a 1:1 transformer, but instead of having a conductive path from the input to the output, the power is passed by induction.

I am making a plasma cutter with a pair of isolation transformers made from microwave oven transformers. I chose microwave oven transformers because I can get them for cheap or free, and they can handle a lot of power.

After I wire up my variac, I’m going to test the power supply. Assuming all goes well with the test, I’ll look into getting a plasma torch head off Ebay or from Harbor Freight, and finish the assembly with a borrowed or improvised air compressor.

Plasma cutter rectifier heatsinks

This evening, I added heat sinks to a couple of rectifiers that I’m planning to use in the power supply of a DIY plasma cutter. The rectifiers will each be handling half of the power load of the device, so I have beefy 35A/600V rectifiers. Each rectifier has a square metal case with a hole in the middle, so I drilled and tapped a hole in a the centers of a pair of CPU heat sinks and bolted the rectifiers to the heat sinks. This picture may help to make the assembly clear.

Rectifiers and heatsinks with fans

I had high hopes for the original fans that were on those heat sinks, but the lubricant that was in them had turned to gum, and so they didn’t spin. The new fans are from laptops, and run on 5V.

I’m planning to get the 5V from the low voltage filament windings of the microwave oven transformers that I’m using for the isolation transformer of the power supply. There are two sets of two transformers, wired “back-to-back” to act as isolation transformers. I’m going to post a complete schematic as soon as the power supply section of the cutter is fully assembled.