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Do-It-Yourself Wind Turbine Project
4 Foot Wind Turbine - option for 6 Foot Sweep
There are 2 parts to this project:
Building the Wind Turbine
There are several DIY wind turbine science projects on the internet. This project is appropriate for high school level and was originally sourced from http://www.velacreations.com a very good site, maintained by a couple living off-grid. Their site is definitely worth a look. Another good website to visit for wind turbine projects is http://www.otherpower.com though these turbines can be fairly large.
We have included some modifications to the original instructions for a larger treadmill motor which weighs more, takes larger blades, requires better fastening for the blades and uses a bearing to attach to the tower.
Making a wind powered generator from scrap materials helps keep those materials out of the local dump. Most of the items you need, can be found in your local hardware store, your own garage or from one of the "Freecycle" groups in your area. . Try doing a search on Google for "freecycle" to see what parts you can pick up for free. For the wind turbine built in these pictures, we picked up the motor on eBay for $10 plus shipping and the PVC pipe for the blades from a junk pile. The tail is made from an old roller paint pan.
Safety should be your first priority. Your health is more important than a DIY project, so please follow all safety instructions you read, use common sense and get help if you are unsure about something. Wind turbines can be heavy, dangerous machines, with fast moving blades and the chance for electrical shocks.
This wind turbine is based on the Chispito Wind Generator with it's simple and efficient design and assembly. We have included several photos showing our changes, using the larger 20 amp motor.
I picked up a 90 VDC, 20A treadmill motor off eBay for $10 plus shipping. This motor requires an upgrade to most of the original instructions due to the increase in size and weight. It also produces a lower output voltage. The motor is better suited for a system with gearing to increase the RPM.
You may use any other simple permanent magnet DC motor that returns at least 1 V for every 25 rpm and can handle upwards of 10 amps. The Ametek 30 is one of the best motors but is hard to find and the price seems to be getting rather high.Try to find a motor that comes with a 6" hub to attach the blades too - a circular saw blade with a 5/8" shaft adaptor might work. For our larger motor we initially used a metal slow moving vehicle sign, bolted to a 3.5 inch pulley. The triangular shape was just what we were looking for. We reinforced the sign with a wooden ring. This hub ended up blocking much of the wind on the smaller blades and we eventually switched to a six inch wooden hub, reinforced with metal plating. When hurricane Ike went through, that hub was also damaged. Thus we'd recommend a metal hub such as the saw blade or a used thick metal frying pan bottom.
Mounting the Generator
Cutting Blades - makes 8 blades (or 2+ blade sets) and a thin waste strip.
I have created a separate page with more pictures and expanded on this process a bit. After you've done this once, it makes sense. These instructions could use a little help for the first time wind turbine blade maker.
Here's the link to the page: Making PVC Turbine Blades
Note: we also made a set of blades 38 inches long using the same measurement - only the length was changed - 24 inches to 38 inches.
Sanding the Blades
The angled (leading) edge wants to be rounded, while the straight (tailing) edge wants to be pointed.
Any sharp corners should be slightly rounded to cut down on noise.
Making The Tail
Drilling Holes in Blades - using the ¼" drill bit
Drilling Holes in Hub - using the 7/32" drill bit and ¼" tap
NOTE: You may want to modify these instructions. Try replacing the hub with an old, used 7 1/4 inch skill saw blade. The larger surface area will give you more space to screw or bolt the blades to. We also used 1/4 inch bolts rather than drilling and tapping holes. I've also see old aluminum frying pans used for this purpose. They are light and solid!
Note: the metal slow moving vehicle sign is not solid enough to stand-up in high winds. We screwed on a wooden ring to the back of the sign to give it the required strength. This blocked to much wind so we ended up replacing it with a 6 inch wooden hub, reinforced with a metal plate on the back. Even later, we ended up replacing this hub with a 6" metal hub for added strength.
Make a Protective Cover for the Motor
For a longer life span of your wind generator, you should paint the blades, motor sleeve, mount and tail.
On the larger 20A treadmill motor, we attached a dolly bearing directly to the bottom of the motor and then onto the top of the tower. Get a dolly wheel with a hole in the middle, which you thread the power wires through.
We also used the same PVC Blade Pattern to cut 3 foot blades. Just make the length 3 feet rather than 2 feet. The measurements at both ends stay the same - 145 cm wide sections that are next cut into 2 blades. This gives the same curve to the blades.
Depending on the size of your motor, you may want to experiment with different lengths of blades. Our larger blades were not balanced as well as the shorter blades initially and thus turned slower. We cut them down in length from 36 inches to 32 inches and balanced them. To balance the blades, we placed the blades and hub, onto a long pointed nail. We than slid a washer along the blades to find the balance point. Then epoxy the washer in place (try to account for the weight of the epoxy as well).
How much power can we get from the wind?
Power AVAILABLE in the wind = .5 x air density x swept area x (wind velocity cubed)
Example: air density = 1.23 kg per cubic meter at sea level. Swept area = pi x r squared. Our 2 foot blades = 0.609m, 4 ft = 1.219m. 10 mph = 4.4704 m/s, 20 mph = 8.9408 m/s.
How much power is in the wind: 2 ft blade, 10 mph winds = .5 x 1.23 x 3.14 x 0.609squared x 4.4704 cubed
= .5 x 1.23 x 1.159 x 89.338 = 63.7 watts
With 4 foot blades and 10 mph winds = .5 x 1.23 x 4.666 x 89.338 = 256 watts
With 4 foot blades and 20 mph winds = .5 x 1.23 x 4.666 x 714.708 = 2051 watts
That's the MAXIMUM power in the wind. However, it's impossible to harvest ALL the power. The Betz Limit tells us that the maximum percentage of power we can harvest from the wind is 59.26%.
Thus our maximum power from these turbines would be:
2 ft blades, 10 mph wind = 37.7 watts
4 ft blades, 10 mph wind = 152 watts
4 ft blades, 20 mph wind = 1,215 watts
These values are the maximum power achievable. Your results will be less, depending on how well you shape the blades, how well balanced the blade assembly is, drag going over the hub, copper losses, etc. A very well built DIY HAWT would not likely get more than 50% of the above numbers.
Gearing for a higher RPM motor
If you can't find a good, low RMP motor such as the Ametek 30 and need to gear-up the motor you have, here's a video of one possible layout:
Chances are, if you're making a science project, you'll need to vary a couple of parameters and measure the change. So what factors affect your power output? The power will vary with wind speed and with the size of the blades (swept area). Of course the power output will also vary as you change the height of the tower, but this is really just changing your wind speed. So what can you do?
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