I also got time to try my polystyrene cutter. 20 cm of 13.77Ohm/meter nichrome wire will cut polystyrene slowly with 3V across it. So that's about 1A, so heating is 3W. If you compare that to a low powered soldering iron of 10 or 15W I suppose it sounds about right, but I might try different voltages and see if I can get a faster cut.

Well that went ok. I got two capacitors and put a diode in series with each, reversed one and put them across the wires that were showing a 44Ohm resistance (they're electrolytic and I don't want them to pop in my face). That should keep some energy around in the coils. It does look as if it'll have to be spinning quite fast to generate any useful voltage... but best of all, I didn't electrocute myself.

I'm guessing that the voltage produced against rpm looks like a nice smooth curve, and that the frequency of the AC generated goes up with increasing rpm. Anyway, if it's an 1800 rpm motor, we'd need somewhere around 30 revolutions a second. That sounds a bit fast to me. I don't really want to have to do any gearing, but maybe I'll have to. I suppose I should try and plot some graphs before I start worrying about all that.

Nothing is happening with 12V AC ... I might have to try mains. If anything goes wrong, I just want you to know that I love you.

This is a common or garden single phase induction motor. I bought it from Supashed for $10NZD.

These operate in a different way to the little DC motors or the kind you get in electric drills. There's no commutator (the split ring that allows transfer of power to the coils on the rotor). Instead, the rotor is basically a cunningly-shaped piece of metal - the squirrel cage. The turning force comes from the interaction between the magnetic field in the coils on the stator and the induced magnetism of the bars of the squirrel cage.



Here are the stator coils. I've got three wires left, with resistances of 22Ohms, 22Ohms and 44Ohms between them respectively. I'm not totally sure why that is - I assume there's either an option to have full speed/half speed, or they are wound in a way that allows you to do something clever, like start it.

I was initially confused by the fact that there were five wires, but when I took it apart the two thicker ones seemed to attach to some sort of safety device (pfft!), probably a thermal fuse? I suppose consumer goods tend to err on the side of safety, but we won't be needing it so I carefully removed it from it's position on the coils.


And here it is.

There's some good stuff on the internet about making your own generator, but much is quite technical (equations and stuff) and some just doesn't apply to me (permanent magnet motor). So I thought it might be worth documenting my efforts. Next step will be to run the motor to see which way it goes round, and what connecting to the different coils will do. I'll use 12V AC for that.


This man makes his own generators, using a petrol engine and an induction motor.
This is a straight-forward set of instructions for using an induction motor as a generator.