Dual MOT Spot Welder


Introduction

The heart of this spot welder is made out of the two microwave oven transformers mounted inside the two ATX power supply cases. The price of this project was cca 15€ however you can find most of the needed parts on the electro-junkyard for free.

Construction

The transformer itself can be used for projects like MOT Resonant Arcs. However, for a spot welder, we need much more current at lower voltage.

Therefore, the secondary coil needs to be replaced with a thick wire.

The terminal lugs were hammered to match the 90° angle of the handle and attached to a copper tube.

My MCBs didn't really like the current that two coils have drawn while magnetizing their cores (when starting), so I have added a softstart circuit made out of a delay relay and a power resistor.

Warning

MOTs are extremely dangerous transformers capable of outputing more than 2000VAC at a current that is lethal. Do not try to replicate anything you see, unless you know exactly what you are doing. Be sure to read disclaimer before proceeding.

Summary

  • Dual MOT
  • Soft start
  • 12V fan regulator
  • Handle trigger