Over the past few weeks I've been building a spot welder. A rather simple, brute force device that fuses couple thin sheets of metal together by pumping a tonne of current. We're talking 1,000 Amps of current. Now where does one find that much current lying around.... Well, conserving power, we can produce that much current if we step down the voltage from the mains. If we took 120V @ 15A (~1,800Watts) and stepped it down to 1.2V, we could in theory pull 1,500Amps! So where does one find a transformer with a primary capable of drawing 15A?
From a microwave! The first thing to do with the transformer, is to remove the high voltage secondary. The easiest way to do this, is to carefully chisel the exposed coil off, and then use a punch to push out the internal windings.
When done you should have a good primary coil and two holes to rewind the secondary coil.
Now wind some heavy (I used 6 gauge wire, but 4 or 2 would be better). This is not easy - that stuff is stiff. Finally add some heavy copper lugs and tips to press into the metal.
And you're done!
I have sort of weld 24 gauge tin and definitely blow a hole through soup can lids. It should be good enough for making small tin boxes.
