DIY Arc Welder

March 2023

Picture of me using the arc welder

My school’s engineering class had us create some sort of “upcycled” product. I was looking for a use for two microwave transformers I accumulated and had seen some others build welders from a collection of transformers. I jumped at the chance to build one myself.

Design Inspiration

I based my design off of similar devices built by other people.

I based the sheet metal design and construction of my device somewhat heavily off of the device built by Murat. The electrical aspects were based off of Kurt’s Cottage’s, Mind To Machine’s and TKOR’s welders.


Inside of the welder


The electrical system is very simple, it is just two microwave oven transformers (MOT) with parallel primaries and series secondaries. The primaries are the stock coils built in to the MOTs. I cut out the high voltage secondaries and rewound them with between 20 and 30 wraps (I didn’t count because I don’t care) of 12 AWG wire. Before the transformers I wired in a 4000 watt light dimmer (which has to be one of the most non-Underwriter Laboratories-listed parts I have ever seen in my life, but seems to work alright. I also installed a volt meter that I am pretty sure is meant for model trains to show the voltage output of the welder. At max power it emits approximately 35 volts and can probably operate at about 70 amps (although I have no way to measure this). This is enough to weld 3/32 inch welding rods and maybe even 1/8 if you are willing to push it. All told I am rather happy with this, the schematic I made for the wiring is shown above.

Physical Construction

Outside of the welder

CAD Renderings

The main construction of my welder is made up of 1/32nd inch galvanized sheet metal scavenged from old computer chassis and ¾ inch fiber board that was scrap from something else. Prior to constructing it I modeled the whole thing in CAD to make sure everything would fit well (and because I was forced to by my instructor). Unfortunately my school requires use of OnShape as a CAD software, I am not particularly fond of it but I have publicly shared the OnShape project in case you would like to see the dimensions and other info.

You should be able to use the dimensions and sheet metal models on the CAD to create a copy of this if you would like to.

Welding & Photos

As mentioned above I have only welded with 3/32nd inch welding rods on this machine. The welds seem to penetrate rather well and are relatively strong. I think the steel will fail before weld. Below are a variety of photos of me welding and some examples of my welds.

Pipe thing

T Stock