WindTura 750 Overdrive

Discussion in 'Windtura Generators' started by WindyFAQ, Jun 18, 2012.

  1. WindyFAQ

    WindyFAQ WindyNation FAQ Staff Member

    I am looking for a pma to power my windmill project. My blades are 10.6ft dia 3 blade and I am looking to overdrive with lightweight chain and sprocket sets. TSR for my blades is ideal for 300 to 400 rpm. My avg wind speed over the last year is 12 mph. I believe i can consistently turn a pma around 600 rpm if 2to1 overdrive and 900 if 3to1. I am hoping to make 1 to 1.4kw.
    Is this a good fit for the windtura 750?
    Will it hold up?
  2. timber

    timber WindyNation Engineer

    There have been varying degrees of success in doing this, your relatively large blade diameter may make this a good candidate.
    From a mechanical standpoint, I would highly recommend using synchronous belt and pulleys over chain and sprockets. Pulley manufacturers have charts available for proper sizing.
    As for PMA output potential, others here are more qualified to give you an answer.

    Here's a link to a similar setup made by a 19 year old engineering student from Belgium
  3. Thanks for the reply.
    I read that post yesterday. Good stuff. I will use a timing belt if 2to1 ratio works OK.
    Otherwise I may try bicycle chain and sprockets to save rotating mass.
    I hope to make heat and not usable electricity. Hot water and heated air in the winter. I am hoping this eliminates the issues others have had when gearing. Bluejay had loading issues. Couldn't get any usable rpm when charging 12v because of the massive load. Did much better at 24. I want to see if 48v works even better. It may allow enough inertia to build so that when the load does build the blades power thru.
    My goal is 700 Watts with a 15mph wind.
  4. windyguru

    windyguru WindyNation Expert

    You should be able to achieve some increase in power performance by using the larger blades but keep in mind that building a geared turbine is not simple. Direct drive wind turbines are hard enough to build!

    Using a 10.6 ft diameter rotor (5.3 ft blades), it is not going to be realistically possible to produce 700 Watts in a 15 mph wind.

    Assuming a 25% coefficient of power and that the wind turbine is mounted on a tall tower in clean non-turbulent wind, here is what you can expect to produce:

    103 Watts in a 10 mph wind

    178 Watts in a 12 mph wind

    349 Watts in a 15 mph wind

    826 Watts in a 20 mph wind

    A 35% coefficient of power for a small wind turbine is considered excellent. This would involve a lot of research and field testing to properly match the generator design with the blade design. A 20-25% coefficient of power is fairly realistic for a well designed DIY wind turbine.
  5. timber

    timber WindyNation Engineer

    I think you will find that bicycle chain is prone to stretching and wear and will wear out in no time. If you do use chain, I would use at least #40 chain (It's often used on go-carts).
    I went through various setups using belts and chain when building an electric bike. The bicycle chain would not stand up to the torque and V-belts had way too much friction.
    I finally used a combination of synchronous belt (first reduction) and #40 chain (second reduction) and this ended up working well. (In this case I had a 12:1 reduction since the motor RPM's were quite high to obtain maximum torque).

    I agree that a 24 or 48 V system would be much more efficient and likely work best in this scenario. I'm not sure how many RPM's you would need to obtain using the Windtura 750 to see the 48 Volts, I think it's designed more for the 12-24V range.
  6. I have read that with rpm you can do 48 or higher with the 750. Josh even eluded to a new higher voltage model coming out soon. I'm just not sure when. If I use the current 750, I will probably do a 2.5 to 1 or even 3 to 1 to get around 1000 rpm or more.
  7. Are these figures based on the extraction capabilities of the blades alone or what the blades can generate with the wn750?
    I ask because the blades i have are off a 2kw turbine rated at 18 mph. i have seen 2.4 kw at 25mph, at least in video on a tall tower. I plan to have it pretty far up.

    I also can acquire some 13ft blades as well if they will yield better results. I was worried about tower requirements with that kind of force.
  8. windyguru

    windyguru WindyNation Expert

    These figures are based on (1) the amount of power available in the wind at a given wind speed taking into account the swept area of the blades and (2) What percent of that power the wind turbine can harvest.

    A fair number to use is 25% of (1) above. Remember Betz proved that only 59% of the power can be extracted from the wind. Then there is blade inefficiency, generator inefficiency, bearing inefficiency, wind turbine vibration, and, in your case, gearing inefficiencies... etc.

    Assuming you dialed in your wind turbine to perfection and reached a 35% coefficient of power, at 18 mph a 10.6 blade diameter will make:

    about 840 Watts (if I did my math correctly)

    To make 2000 Watts at a wind speed of 18 mph the wind turbine with a 10.6 blade diameter would have to operate at a coefficient of power of 83%. This is impossible.

    The 13 foot blades will definitely make more power if you dialed in the gearing properly to match the optimal torque and rpm's for the generator.
  9. This is why I want to build the turbine!

    Measured at 10 foot above ground. Much higher at 40 to 50 ft. I have a 50 ft pecan tree 300yds south and its top is always zinging around even when the wind is measuring 10 or 12mph.

Share This Page