I've just designed and built a practical, portable 12 Volt 17 Watt wind generator that is ideal (and appropriate) for setting up in campgrounds, parks, Earth Day exhibitions, research stations, and third world homesteads.
On "light breeze" days (5mph = 2.2m/s) when most wind generators are becalmed, this light-and-nimble unit reliably generates power, at charging levels, fully taking advantage of the erratic, gusting winds that are so common in near-ground conditions.
A 48VDC, 1,600 rpm brushed permanent magnet motor (#370-350-00 / PE24113G -from a medical centrifuge), with a standard keyed 5/16 inch diameter steel shaft, was used to serve as the generator. A shaft arbor, 3/8-24 right hand (Grainger Item# 3ZN05 / Dayton Item# 3ZN05) was fitted on the shaft, to use as a 12 Volt generator, @ 550 rpm, when turned clockwise. The motor, weighing in at just under 3 pounds, has permanently lubricated bearings, but is not weatherproof.
Note: If you plan to use a counter-clockwise set of blades, the timing of the "generator" brushes (2 carbon brushes) and internal commutator is such that the same amount of power (Amps and Volts) is also generated when turned counter-clockwise, but be aware that the shaft arbor manufacturer's suggestion as to "right-hand" and left-hand" thread pertains to motors only, and not wind generators, where the just the opposite thread is required.
Note that the Grainger Shaft Arbor requires a thin, soft metal shim inserted against the flat face of the standard keyed generator shaft, for the allen set screw (which has a knurled cup point) to bite into and firmly hold the arbor in place. I used 2 layers, fashioned from an aluminum beer can. Or, use a replacement allen set screw with a soft brass core. Also, two, 1-1/4" thin neoprene washers are needed to pad (and grip) the 1-1/4" steel washers that come with the shaft arbor. The original shaft arbor nut was also replaced, with a nut with a thicker profile, with a nylon locking core.
This portable wind generator is ideally suited for one 12 Volt, 21 Amp Hour sealed lead acid battery.
Granted, that's not much power, when compared to typical permanent, stationary wind generators. But this lean-and-mean device was designed to fill in the void, to reliably provide 12VDC power to remote, inaccessible locations.
Step 1: Stock High-Speed Blades for the Wind Generator:
After running the "generator" through a series of bench tests, it became obvious that my simple homemade PVC blades (300 max. rpm) would require a gear-up to properly turn the generator, an inefficient scheme that I was not wild about. And I was also reluctant to commit myself to a number of weekends designing, developing and refineing a set of small, lightweight blades that would achieve the necessary direct-drive speeds (550+ rpm), so I purchased a matched set of three Air-X Airfoil blades.
22-3/16 inches long, and designed for a clockwise rotation, when viewed from the front (shaft end), each with two .25" holes spaced at 23mm (25/32") on center. Having only about 1/4 the torque of the much larger Air-X generator, the 17 watt generator spins very easily, in the slightest of breezes.
The blades were mounted on a 5-3/4" diameter, 3/16" thick, ABS faceplate (blade hub), and carefully drilled out to handle either a 3-blade arrangement (as well as a 2-blade arrangement option). The blades were mounted to the backside of the faceplate (hub), to position the mass of the blades as close as possible to the shaft bearings. After bolting the three blades to the ABS faceplate, the tip-to-tip distances of the blades were measured and the blades adjusted with light hand pressure until all three of the tip-to-tip distances were equal, then the blade bolts snugged down.
2 blades are more portable, being easier to stow, protect from damage, and transport, but tend to teeter on the generator shaft, in actual practice. But, after a series of tests, I decided on the 3-blade arrangement, as it provided better performance in low wind conditions (actually typical for many locations).
I fashioned a discarded (actually I'm a hopeless pack rat) thick-walled plastic easter egg ornament into an aerodynamic parabolic plastic nose for the hub, and outline-cut the hub to 4-7/8" diameter, flush with the parabolic nose. The arrangement allows for a smooth flow of air through the blades and greatly enhances the performance of the generator, in low wind speeds.
The Air-X blades, in a portable environment, are much more exposed to rough handling and damage, than they would experience in a permanent installation. A triangle shaped box will soon be built, to carry the blades, hub, shaft arbor and nose, together as one unit, in order to protect the sharp, thin blades from dings and damage, and ease installation onto the generator shaft, in the field.