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.
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.
Because amps (ampre) is a measurement of how much electricity passes through a specific point in a unit of time its 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.