Alternator (V2)

Alternator Requirements:

• “Front-and-Center” roller, 3.5 inches in diameter, 1 inch wide
• 20 watts output power @ 15-20 MPH, withstand up to 50 MPH

After a few weeks of playing around in Adobe Illustrator and DAZ Bryce, I settled on the design for my alternator. It’s an axial flux design similar to those used in wind-driven alternators. In fact, my design is the result of studying wind alternator designs on the internet.

Stator: I wound 6 coils around triangular wooden cores, each with 244 turns of #26 magnet wire. They each have about 2 ohms DC resistance, for a total of 12 ohms across the stator. I connected the coils in a three-phase “Y” pattern – two coils per phase – and potted them, the axle and all the wire connections into a 2.5″ diameter by approx 5/16″ thick mold. Near the axle, the mold is an additional 1/8″ thick on either side for strength. For additional strength, I sandwiched the coils between two sheets of fiberglass. Also, the axle has a pin driven through it to prevent the axle from breaking free and allowing the coils to rotate relative to the axle.

Rotor: I fashioned two 16ga steel disks and mounted the magnets directly to them. Eight standoffs secure the two steel disks around the outer edge and set the air gap between the magnets. Washers between the stator and rotor bearings provide centering and positioning of the magnets relative to the stator. I removed the hub from a Razor scooter wheel and cut eight notches in it for it to fit around the standoffs and provide a suitable “tire” surface to ride on.

Rectifier: It is a three-phase alternator, so the rectifier circuit uses 6 diodes. I put all that onto a pad-per-hole board and mounted it on top of the alternator mount in an aluminum box. The box is big enough to hold additional circuitry and backup batteries.

Wind alternator design references:

• Windstuffnow.com
• Hugh Piggot

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