How to Build a Microwave Transformer Spot Welder


DIY: Microwave Spot Welder Part 1 - Salvage

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Rewiring Microwave Oven Transformers (MOT) for building things is a common hacker trick. We are doing this to build a Microwave Oven Spot Welder, but it can be used to do much more.

I have seen these be used to make small scale transformers for off grid power transmission, tesla coils, power supplies, induction furnaces, and many other things that take low voltage high amperage power.

In the video above I salvage a microwave

Specifically for the microwave oven transformer (commonly called a MOT).  I also got all sorts of other parts.

The reason I tore this microwave apart for the MOT is that I want to make a microwave spot welder.

First thing be careful as their are some high voltage items inside the microwave.

The capacitor inside holds high voltage and can kill you if it is charged and you make contact with the ends.  Be sure you short the capacitor out to be safe

There is also some motors, light bulbs, switches, wire, and a magneto.

There are instructions online to modify a microwave magneto and a wave guide (antenna) and send a charge that can short out small electronics from about 20 feet away.

Now that I have the microwave oven transformer and the power cord I can make my microwave spot welder.

In video below  I will show you how to rewire your MOT.

This is to change the transformer from low amps and high voltage to make the low voltage high amperage current needed to heat metal to the melting point.



I am staying simple for my first attempt at rewiring transformers since a microwave over transformer can easily kill you. Building a Microwave Oven Spot Welder is a good first project.

In the video we show how easy it is to dissemble a MOT and then rewire it so that instead of taking 115VAC power and stepping up to thousands of volts it steps the power down to 3 volts at several amps.

Amps (ampre) is a measurement of how much electricity passes through a specific point in a unit of time.  It is like measuring how much water flows. Water flows easier through a large large pipe than it does a small pipe – large amps is similar to a large amount of water flowing in large pipe.

When the large flow is reduced pressure is increased – if a large amount of amps is funneled into poor connecter or a small wire that pressure turns to heat.

This is a very basic (VERY BASIC) explanation of how a Microwave Oven Transformer can be rewired to create the heat necessary to melt and weld metal.

Below is a Test of the Rewired MOT Spot Welder


Just a quick test before I weld it up. I needed more hands to hold the camera and plug it in


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