When an alternator is installed in a vehicle, the engine's power spins it, creating DC (direct current) electricity. An alternator is also ideal for use in a wind generator, since it will produce power regardless of what force is being used to turn it. When combined with a windmill, very little modification is required to begin creating wind power. That power can be used for a number of purposes, such as directly powering devices or charging a battery for later use.
Determine the ideal alternator size for your application. A typical vehicle alternator will produce up to around 100 amps of power. Larger or smaller alternators can be selected based upon your individual needs.
Select a suitable windmill. An ornamental backyard windmill will suffice, although a windmill designed to actually perform work (such as an aeration windmill) will usually be constructed in a sturdier fashion and will be easier to work with.
Attach an automotive accessory-drive pulley to the output shaft of the windmill using a liberal amount of metal-to-metal epoxy, such as J-B Weld. If an output shaft is not available, simply connect the pulley to the back of the rotating assembly behind the propellers. Allow the epoxy to fully cure before continuing.
Place one end of a serpentine belt around the pulley, and the other end around the alternator's shaft. Use the belt length to determine where to mount the alternator on the windmill's frame. Place an automotive belt tensioner between the alternator and the newly installed pulley. With the belt pulled tight, use a marker to indicate where the bolts used to hold the alternator and tensioner in place should go.
Drill through the frame of the windmill at each of the points marked in the last step. Use an appropriate sized bolt, washer and nut to mount the alternator and tensioner to the frame. Push the tensioner in to allow the belt to slide on, then test the slack in the belt to make sure it is tight enough.
Connect the power leads of the alternator to the device you wish to power, such as a DC-to-AC inverter or a car battery. When the windmill blades spin, the alternator will produce power just as it would when installed in a vehicle.