Hysteresis/Induction Motor

This is something I built a while ago, but I wanted to describe it in some more detail. It is a simple alternating current motor that spins a thin disk of metal balanced on a sharpened point of graphite.

The circuit applied roughly equal current to each of the coils, phase shifted by 90 degrees. The large AC capacitor provides both phase shift and current limiting to one coil while the other is simply fed through a high wattage resistor. I strung together 12 smaller resistors in series/parallel and even attached heat sinks with thermal grease to get a suitable dissipation power and reasonable resistance of 17.5 ohms.

The two coils act together to produce a rotating magnetic field, as one always precedes the other by 90 degrees. Four coils would produce a much more symmetrical field, but two will do the job. As the steel mason jar lid is magnetized by the increasing field from L1, that part of the steel becomes attracted to the simultaneously falling field from L2, and gets pulled around toward L2. Much the same way, when a rising field near L2 magnetizes the steel that same part of the steel is repelled by the falling field from L1, and pushes the disc from L1 toward L2. This might not be all that is going on, but it suffices for me as an explanation of why this simple induction motor functions at all.