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Forum Index : Windmills : Bike motor
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| ienciu Newbie  Joined: 08/07/2008 Location: HungaryPosts: 5 |
HI I'm new here I am from Hungary and i need help.I have a 24 volt electric bike motor with 2200 rpm 300 watt i want to use it to a wind mill to charge 12 volt battery the propeller have 4 blabe 52 cm long. It is posible at low wind speed to produce some energy?And also i need help how to make the conection to take down the cable from the motor to the connector.Thanks. |
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| KiwiJohn Guru  Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hi, welcome to our little community. You can judge if your motor is a potential for windmill use by shorting the leads and turning the shaft by hand. If the shaft is easy to turn the motor is either not suitable or it will only be any use at high RPM. However, if the shaft is hard to turn with the leads shorted and of course easy to turn with them not shorted then you have a potentially good generator! Most people on this site do not bother with complicated systems of slip rings for connecting the motor (i.e. generator), instead they just leave plenty of slack in the cable and allow it to twist around the mast a few times. Depending on how the wind is at your place the cable may never, or only occasionally, need to be untwisted from the mast and this is easy if you make a plug and connector at ground level. You should not in my opinion expect that motor to produce 300 watts, I would guess maybe 30 or 60 watts which is 2.5 to 5 amps charging your 12 volt battery in which case your 1 metre diameter turbine may be about right. In any case, my estimates are really only very rough guesses as there are so many unknowns and I suggest the best thing to do is to mount it on a pole to see what output you can get in your area using those blades. Please post your experiences here and I am sure there are several forum members who will be interested in your experiments and will be very helpful answering your questions and giving their advice. The only electronics you need for the initial experiments is a blocking diode to stop your battery trying to drive your motor and you need a meter to measure the current. |
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| ienciu Newbie Joined: 08/07/2008 Location: HungaryPosts: 5 |
Thanks KiwiJohn i try it. With hand turn give 2.4 volt hand turn not easy i measure the Amper go harder and give 1.1Amp.I make an other try with drill about 300-400 rpm i got 12 volt.Is this good? |
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| Dinges Senior Member  Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
Keep in mind that if you halve the voltage (24V -> 12V) that you will get much less power from it (I'm doubting as to whether it's 1/2 or 1/4, but probably depends on the motor characteristics too). Tried looking it up but haven't been able to quickly find it, though I by accident *did* find some info I was looking for earlier this week but couldn't find then. 
300-400 RPM is a bit fast but probably still usable for a windturbine of this size (75-150W). In the past I was advised to go for a cut-in of 250 RPM for a 1.3-1.5 m diameter blade on a 100W genny. Hmmm... on 2nd thought, maybe your 300-400 RPM is perfect for a 1 m blade. These motors have small bearings (608, if yours is the same as mine) and brushes which will wear out over time. Apart from that it may work, though I haven't seen any succesful windgennies built from such motors. I'm a bit surprized by the 300-400 RPM it takes to generate 12V, if it's a 2200 RPM (24V) motor I'd expect (very roughly) about 1100 RPM for 12V generation. You can 't really translate the numbers as simply/straightforward as I did above, but it gives a ballpark estimate. |
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| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
When voltage halves it looks like power from the motor decreases to a quarter. See the curves on page 18: http://www.soe.ucsc.edu/classes/cmpe118/Spring05/LectureNote s/ch19_DCMotors.pdf See also equation 19.19, that shows P= [constant] * V^2 |
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| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hmmmm...ienciu. The voltage is rather low but not so low that I could confidently say it will not work for you. Dinges has mentioned the bearing may be small which of course means it would soon fail supporting the weight of your blades. I had a motor once I used in a small wind generator and to protect the bearing I made a short shaft to mount the blades and put one bearing near the blades to take all the weight of the blades and I used a piece of thick reinforced rubber hose (like that used in car heater systems) to make a flexible coupling from the other end of the shaft to the motor. KiwiJohn |
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| ienciu Newbie Joined: 08/07/2008 Location: HungaryPosts: 5 |
http://i537.photobucket.com/albums/ff336/ienciu/Kp000.jpg This is my bike motor |
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| ienciu Newbie Joined: 08/07/2008 Location: HungaryPosts: 5 |
http://i537.photobucket.com/albums/ff336/ienciu/Kp000.jpg This is my bike motor.Yes the bearings are smals.I will try to check the rpm again.Thanks for help and i aspect more help i am a novice and if this motor is not good i thing to make a PMG but i need some help and some plans.Thx . |
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