With the wide variety of wire sizes available, I haven't been able to settle on the right gauge to use for my experiments.
Lighter wire will allow more turns, capturing more voltage. On the other hand, heavier wire will carry higher currents.
Choices, choices.
To figure out what to do, I'm winding some test coils to get some "preliminary results", and will base a final decision upon that. To help with the work, I've built a coil winder out of some spare parts. If I were to go with fine wire, I could be facing 12 coils of 200 turns each. Some people are willing to hand-crank something 2400 times, but I'm not!
The coil winder pulls wire from the original spool, over a pulley, and onto the bobbin. It will slowly wind a round alternator coil, and I hardly have to supervise it at all.
From left to right: Microwave turn-table motor, bobbin with wire winding on, and cam for counter.
The counter on top tells me how many turns have been placed on the bobbin.
Electrical wiring is simple. Obviously not something to leave unattended around kids. The switch makes it a (little) bit safer. The motor is rated at 120 volts (not all microwave motors are the same), and it turns at 6 rpm. Not very fast, but since I can do other things while the machine winds, who cares? This is a 4 Watt motor. Seems like a minimum. Using a lower-power motor might cause problems (see warning below).
This pulley was taken out of a plotter, but it could be just about anything. Make sure to choose something that won't scrape the enamel off of the wire. It must be set back far enough from the bobbin that the spooling wire doesn't wander all over the place. If the angle is small enough, it will pack into tight coils. Tension in the wire is also critical!
The cam is a drilled penny-washer with another screw in it. It pulls down on the counter's arm once per turn.
Most microwave motors come with a plug with a triangular or square shape that makes the plate turn. I used this plug to mount the spool.
The spool can be completely disassembled. The core comes from a dowel, though any round hollow object would do. The sides of the spool came from the remains of hole-saw cuttings. The pieces all tighten up on a long 1/4" bolt.
If you take apart a microwave and all you find is a low-voltage motor, you'll need to pull out the little transformer (not the big one) to step-down the volts. The motor currently being used (120V, 6RPM), probably won't have enough torque to wind heavier gauge wire. 18-gauge, and 20-gauge seem to be fine. There are a wide variety of microwave motors out there, so you may find a slower one, which may have more torque. The larger the micro you get it from, probably the better.
Microwave motors are "synchronous motors". That may not sound important, but there's something to bear in mind: microwave motors can turn in EITHER direction. All you have to do is give it a twist as it's turning, and off it goes the other way!
If it gets blocked in one direction, it will just turn the other way. That means that if something gets stuck in your winder, you will suddenly find your bobbin UNWINDING, and wire coiling down on the floor!
