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Dragonfly Wind Generator
Wind Generator plans and kits by Bill Cornelius
Note: This design is developed from plans published by the USDA in 1939. Typical use supplies 12 v. fluorescent or LED light, radio, and laptop for a cabin. Please let me know what you think!
The Dragonfly is designed for people who operate and maintain their own system, it will last as long as the user has interest (rather than the manufacturer). Dragonfly opposes planned obsolescence. For example: spare parts are available from a variety of local sources, it has few critical tolerances, maintenance is uncomplicated. Components are adaptable to the supply: off the shelf hardware, lumber, and almost any make of alternator or generator. A lot of innovation has taken place since 1980, the demographic has developed like race car or computer tech, where it's bad form to be represented by anything but the newest and best. Dragonfly opposes this marketing because it is a competitive fad, where shiny new today looses half it's value in 3 months. Ultimately the buyer's stuck with finding specialty replacement parts which definitely will go out of production given fad marketing.
- Included with plans are directions for construction, wiring,
troubleshooting, towers, battery maintenance, site selection (wind
appraisal without an anemometer), some sources of inexpensive materials, and instructions for blade making and balancing (though I also sell blades and kit blades).
- Watts per dollar, Dragonflies are one of the most "efficient" wind
generators on the market, though one could expect that initial low cost might be offset by higher maintenance, this is not necessarily true, and depends on the local environment. This Dragonfly was erected near the Pacific coast in N. California, it was still working fine after
2 years without any maintenance, or even inspection.
- There's been a lot of advancement in wind generator design since 1939, and so that Dragonfly isn't misrepresented as the pinnacle of technology (an understandable mistake), these are some improvements that can be incorporated into this flexible design:
- The most common problem with small wind generators is location, it really helps to have a lot of wind, and it's easy to overestimate. This link describes testing your site for potential without hiring a pro, or investing in expensive equipment.
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The feathering mechanism consists of a horizontal hinge which allows the blade, axle, and alternator to tip back as a unit to spill high winds over the top. It is held in operating position by its own weight and a coil pull-spring. Units that I sometimes make are guaranteed to survive winds to 80 mph, when the blade is properly balanced, and the field is loaded. Manual shutdown for stronger wind can be accomplished from the ground. The blade, bearings and drive pulley rotate as one unit about a fixed axle. The v-belt drive pulley is available in several sizes from heating and air-conditioning stores, and may be easily interchanged to obtain the best power ratio.
Frame Material: Wood, Metal brackets.
Net Weight: 50 lbs.
Blade Diameter: 9 feet.
Blade Material: wood, stainless steel.
Blade Weight: 10 lbs.
Minimum windspeed: 10 mph.
Maximum output: 700 watts at 45 mph with Chrysler alternator and a 10 inch drive pulley.
Power Chart in Watts for 40 amp
Chrysler Alternator model 7000 on a Dragonfly frame
Using your own Alternator or Generator
Any alternator will work, but those with higher rated output means more wind is necessary to overcome the draw of larger electromagnetic fields, so big alternators don't produce at all in milder winds. Generators and lower rated alternators loose the power advantage of storms, (which occur to a greater or lesser extent about every 2 weeks worldwide), but take better advantage of wind below 10 MPH. Some desirable characteristics are:
Rated Power Output: 400 to 800 watts.
RPM Output Range: between 200 and 1,000. Alternators starting around 450 rpm.
The Charge Controller for a car alternator is that same cars' Voltage Regulator. They're designed to go together. Some are built into the alternator, and some are separate units. They turn the field off when the battery voltage reaches about 14 Volts.
The alternators exposure to the elements is not a problem unless the unit is used in a marine environment. Otherwise there is nothing at the top of the tower that won't be found under the hood of a car, except sunlight which may affect the wiring insulation.
Units used in a marine or other harsh environment may require marine alternators, available with enclosed brushes, bearings and a corrosion resistant finish. Electrical terminals can be coated with protective caulking or shellac.
There are two kinds of automatic field switches shown in the Dragonfly plans, either will do: one is a momentary switch that requires occasional cleaning, this switch is normally on and is turned off by the weight of the feathering mechanism at rest in still air. The other is an enclosed mercury switch (good to 32 degrees below zero, needs no cleaning or attention after initial adjustment) which is clamped to the side of the feathering mechanism. The blade is designed to have a high RPM which will create a vacuum behind it to instigate feathering. When the RPMs are sufficient to produce electricity, the blade has already begun to feather slightly. As it tips back, the mercury switch tilts, or the momentary switch closes, to turn the field on.
Check list in order of probability, depending on climate, 2 to 4 times a year:
- loose nuts, or fatigue at wire terminals. Too much loose stuff means the
blade's out of balance. See manual for balancing.
- belt tension.
- check for wear or dirty turntable brushes.
- loose or dry blade bearings (grit in bearings or unbalanced blade). Zerks
require grease gun, should be greased regularly.
- tight feathering hinge (need oil?)
- check wood parts for rot, warp, or splitting.
Maintenance plan B: Wait till it stops working, then fix it. This actually is practical, but risks complications like:
- parts falling off
- drained battery
- working in the rain w/ perhaps a testy woman on the porch
- (so plan ahead)
The following customer responses testify to the simplicity of design and
construction of the Dragonfly wind generator as well as its durability and the ease with which it can be modified to local materials and conditions.
... I really like your design and feathering mechanism. Around Thanksgiving the mill went through an 8 hour storm with winds 50 to 60 mph with one
recorded gust of 78 mph and held together.
N.S., Ferndale, WA
...also the other (Dragonfly) worked very well with a permanent magnet
generator which I borrowed from a friend...
P.A.W., Kingman, AZ
..We would like to try another machine at a second location...
B.B., Glendora, N.J.
...instead of the mercury switch, I have a centrifugal switch from a Coleman furnace that turns it (a Chrysler alternator) on at about the time it is going fast enough to charge...
J.C., Kingman AZ
We presently (1982) have 20 wind students on-site on our Energy Education Center working with a Dragonfly wind generator that is on campus...
P.E., Red Wing, MN
... the prop blades were very nice and the plans were good... the Dragonfly has proven to be very practical and has been through the worst weather here in more than 100 years. I just had to write you to tell you I am very satisfied with the whole project. Thru rain snow, sleet, hail, sub-zero and winds to 60 MPH plus. It turned 2 days and nights thru a snowstorm and in the morning the prop hub looked like a giant sunflower made of ice and snow...
R. H., Hampton Bays, NY
Plans:   $10. Size = 9.6 mb.
Available only in HTML format (like this page), as a download link, or e-mail attachment (Please provide currant email address). Can be read and printed from any internet browser.
Approximately 27 pages (without padding, spam, or wide margins).
Blade Balance Kit: 1lb   $15.00
A piece of copper pipe, 2 washers, and string. weights not included. Works only for Dragonfly design, easy to make, get plans & make your own.
Kit blade set: 14 lbs.   $100.00
pitch and foil are rough cut, centers not located. holes not drilled. Needs
sanding, painting, and sometimes light planning. Does not include bearings, pulley, or hub.
Finished Blade Set: 14 lbs   $200.00
centers not located. holes not drilled. Does not include paint, bearings, pulley, or hub.
Individual blades: 5 lbs   cost = 1/3 set, kit or finished
All blades sold unbalanced and unpainted. A stainless foil strip comes
attached to the leading edge in finished blades, and included unattached with
kits. Does not include bearings, pulley, or hub.
Shipping: Blades delivered within 3 weeks. Inside US & Canada: by United Parcel Service. COD (Cash On Delivery) accepted for postage inside US & Canada. Elsewhere: please specify carrier and include correct postage.
Contacts, E-mail, Questions:
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