I’ve been needing a low voltage, high current power supply lately for a couple of projects I’m working on (I can’t post about all my projects because some of them are proprietary for paying customers). I was looking for not just a few amps but hundreds of amps. This can be done with a transformer taken out of an old microwave with a little modification. Cayta found a heavy duty one at the thrift store for cheap so the fun could begin.
Word of warning: these are very dangerous and I’m not recommending that anyone try this. If so it is at your own risk and you should know that hundreds of amps is easily lethal.
I took apart the microwave (with the help of my godson) and pulled out the transformer. There are two coils of wire around an iron core, a primary coil and a secondary. By replacing the many wrappings of thin gauge wire with a single turn of heavy gauge wire, the higher voltage, lower current can be traded for a lower voltage with much higher current.
Transformer operation is explained by Faraday’s law of induction: basically when you have a varying electrical current (AC power) around a conductor it creates a varying magnetic field. A varying magnetic field with then induce an emf (electromotive force) or voltage in another coil that is in this field. It is remarkable that the other coil, the secondary, is not physically connected in any way to the primary, it is simply a single turn of wire, yet an amazing amount of current is “induced” in the wire by the magnetic field. This is something I “knew” but did not fully grasp until trying it myself (not that you should :).
Video of the device heating up a nail until its pulled apart:
and then fusing two nails:
So that was all fun and games but I took the nail melter apart because I needed to incorporate it into a power supply that outputs DC voltage. For this I added a bridge rectifier to convert from AC to DC, a capacitor for smoothing the output, and also incorporated a fuse in case things get out of hand. For example, these things get very hot when operating for any amount of time and can cause the wire windings to burn through their insulation and short out. This would usually just throw a breaker but I don’t want to create a fire situation. I’ll be using forced air to keep it cool and heavy duty heat sinking.