One Man's DIY Creativity In This Wooden Alternator For Wind-Power Generation
After building the all wooden windmill I felt inspired to make a larger and sturdier version. The following page offers a brief description of building the alternator and testing it. I designed this alternator WHILE I was building it, using mostly intuition and working around supplies available. Undoubtedly many improvements could be made. If you have any ideas or thoughts about this, please share with us via email or our discussion board!
Initial test results--wired in series, reaches 12 volts for charging at 120 rpm, with 6 amps charging current at 300 rpm. Wired in parallel, reaches 12 volts at 240 rpm, with 12 amps charging current at 350 rpm. At 500 rpm it produces about 500 watts. Unfortunately this is the limit of our current testing rig--we need to build a bigger one. More tests and a chart to come!
Parts and supplies used
To build the alternator I used the following:
10" long piece of shaft, 1/2" diameter.
2 1/2" inner diameter ball bearings
18 surplus NdFeB rare earth magnets
5 Pounds 18 AWG magnet wire
1 1/2" drywall screws
3" deck screws
Fiberglass resin for final finishing
I cut out 5 plywood disks on a bandsaw, 9" diameter. In the center of each disc I drilled a 1/2" hole. These disks are laminated on the shaft to build up the armature. In order to hold the armature securely to the shaft, I drilled a hole about 4" from one end 1/8" diameter, and inserted the a pin, 4" long. On one disk I routed a slot, 4" long and 3/16" wide, 3/16" deep, to accept this pin so that it would be locked to the shaft. I generously coated the plywood discs with wood glue and clamped them together on the shaft, then screwed them together with 3" wood screws.
On the metal lathe (a wood lathe would work fine) I evened up the armature so that the diameter is approx 8.75". In the center of the armature I cut a slot 3/16" deep exactly wide enough to accept the magnets (1.74"). The magnets are laid in with alternating poles facing up. This particular magnet is available with either North or South on the outside. This alternator requires 9 of each variety. The diameter is such that the magnets stick out from the wooden surface of the armature, so the total diameter, magnets included of the armature is just short of 9.25". These magnets have an arc much more acute than that of the armature, so it looks kind of "lumpy"! I don't think this is a problem. Custom magnets simply cost too much, it often pays to work with that which is available. In order for 18 magnets to fit around the armature, there is a small space between each magnet (approx 0.10"). For spacers, I used 1" drywall screws, which were removed after the glue dried. Since they are tapered at the top, simply screwing them in deeper provides for a larger gap between the magnets, so...with a little patience, it is easy to adjust the screws and get the magnets evenly spaced around the armature.
Once all the magnets were pressed in place, properly spaced with screws, I glued them in with epoxy. As a clamp, I simply tied a rope around the magnets and tightened it with a stick through the knot. When the glue started to set up hard, I removed the screws and applied a new coat of glue over the entire surface of the alternator. This not only aids in holding down the magnets, but it will protect the alternator from moisture.
The stator (that part which will eventually hold the coils of wire) is built up of 3/4" plywood. The inner circle has radius of 5", which leaves room for coils between it, and the armature. The magnets protrude from the wooden alternator approx 1/8", so this allows for coils to be approx 3/8" thick and have close clearance with the magnets. A very small gap between coils and magnets is important, especially if the coils do not have a ferrous core. I cut pieces to build up the stator from the plywood and glued them together, clamped them tight and screwed them together with 1 1/2" drywall screws. Each piece is made up of 3 laminates, for a total thickness of 2 1/4".\
The shaft is supported by pillow blocks, also built up from 3/4" plywood pieces. I cut holes with a 1 1/2" hole saw to accept the bearings. Of course, the bearings have 1/2" inner diameter to accept the shaft. The outer diameter of the bearings is roughly 1.6" inches - a very tight press fit into the holes in the plywood. I coated the outside of the bearings with epoxy and pressed them in with an arbor press(a vice, or hammer should work fine too), as deep as possible so that I could still tighten the set screws. I was pleased with how well they fit the holes, and how straight they pressed in. I believe I got a little lucky here!