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Forum Index : Windmills : Simple questions to help the un-educated!
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| Marcus20VT Regular Member  Joined: 02/09/2008 Location: WalesPosts: 49 |
Hi, I have recently made 4 PVC blades as a quick experiment for my turbine. I made them from 4 inch waste pipe as shown on many internet sites, and they are about 50 cm long - I'm saving my 8 inch pipe for when I do it properly!! My generator is a 1.5 hp treadmeill motor like the one shown here http://cgi.ebay.co.uk/NEW-ROGER-BLACK-TREADMILL-MOTOR-GREENM ASTER-GMD118-1_W0QQitemZ330329068703QQcmdZViewItemQQimsxZ200 90510?IMSfp=TL090510118004r5239 http://i76.photobucket.com/albums/j19/Ajomssap/P1010223.jpg After fitting the blades, I was surprised that I could not get the motor to turn at all. The wind was fairly moderate yesterday here in north wales, but no matter how hi I lifted it, it was not turning. There is a blinking great flywheel attached to the motor - would this be making it more difficult to start? Should I( make a lower weight hub for the blades? Also, need to get turbine to at least 250 rpm before she will start to give me 12 volts for my battery. Would increasing the blade number to 8 increase the speed of the turbine, or will it just add more weight and not be that effective. Will post pics of prototype if able to later. Thanks for your help. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
Hi Marcus Sounds like the blades are the wrong shape, we would need a photo to help you out I think. The flywheel wont have much affect, dont worry about it. More blades will actually give a lower RPM, but more torque. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Marcus20VT Regular Member Joined: 02/09/2008 Location: WalesPosts: 49 |
Hi Glenn, The blades are like this - just about! http://www.yourgreendream.com/diy_pvc_blades.php Thanks |
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Bolty Regular Member Joined: 03/04/2008 Location: AustraliaPosts: 81 |
Sounds to me like there is too much friction with the motor. I agree with Glenn that it is not due to the heavy centre. This weight will just make the mill less responsive to wind gusts, missing the wind energy in the short gusts. It should not effect the ability of the mill to start. 2 things that you can do to improve the start is to increase the pitch of each blade, giving more torque, or increase the length of the blades. As mentioned more blades would also achieve this. However as you want your mill to spin to 250 rpm to generate, you are going to need to keep the number of blades down. All of the measures that I have listed will reduce your rpm under the same wind conditions. You mention that your motor is 1.5 HP or around 1100 watts. For a mill of diameter 1m, you would need a wind speed of approx over 20 m/s or 75 km/hr to produce this 1100 watts. (these figures are just ball park, in my head calcs) This is a fairly substantial wind which I would very rarely receive at my location. I suspect that your motor is too big for these smallish blades. My suggestion would be to try using bigger blades on the existing motor, or try to reduce the friction in the motor. |
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