question about modifying alternator/generator

Discussion in 'The Projects Forum' started by mavava, Sep 26, 2006.

  1. mavava

    Thread Starter New Member

    Sep 26, 2006
    3
    0
    Hi there,
    I have been trying to get a question answered and am running into road blocks, could anyone possibly help in this area?
    Here's the scenario…

    Imagine a 3 phase induction turbine, similar to what's used for wind mills. Smaller ones (say a 4 - 10' for diameter blade configuration) are "geared" to operate at peak efficiency around 20 - 25 mphs about 10-12 m/s - (I think that's turning the shaft at 500 rpm up to about 1200 rpm). This is so because that's what average wind speeds usually are and they are designed to generate power at low wind speeds. What if you had a consistent high wind speed? Is it possible to "gear" or modify these turbines for peak efficiency at 45 to 65 mph? For example, instead of the typical configuration which is: begin working at 7 mph winds and peak (for efficiency) at 25 mph could it be modified to cut in at say 25 mph and peak at 45 mph? OR, Could an alternator be purchased separately (sort of "off the shelf") and then it's rotating shaft be "fit" for small wind blades.
    Put simply, I need a 3 phase alternator (or whatever is most efficient for generating and storing) that runs at higher rpms efficiently without 30 metre diameter blades - space is an issue in this project. I thank you kindly for your consideration and any help you could provide me. Thanks a million, Pete
     
  2. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Why not use gears to get down into the gennys max. efficiency range ? (Then you'd need smaller blades as well).
     
  3. mavava

    Thread Starter New Member

    Sep 26, 2006
    3
    0
    Thanks for replying, could you provide me a small example so i could visualize what you mean - i'm not completely sure that I understand fully the best approach to do this. I am however very excited about that prospect! Thanks again, Pete.
     
  4. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Well, say your generator needs to spin at 1200 RPM max. and the blades go 3000 RPM max. then you need a reduction of 30/12 (=2.5).

    If you couple the two shafts with eg. spur gears where the one from the blades has 10 cogs/teeth, you'd need 25 cogs/teeth on the one on the gennys shaft, so that the blades will have to go around 2.5 times for one revolution of the generators shaft. Any combination of cog-numbers that yeild a 2.5:1 erlationship will do.

    A timing belt (or V-belt) system could be used as well, as long as you get the appropriate gear ratio.
     
  5. mavava

    Thread Starter New Member

    Sep 26, 2006
    3
    0
    Thank you, that makes perfect sense. Would the efficiency of the power generation be reduced significantly by adding these steps in the process or is the effect marginal?
     
  6. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    If made well and with parts suitable for the power level, it won't be noticeable, but of course you'll allways have some loss due to generated heat.
    On the other hand, by gearing down, you get more torque.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    I think the big power generating types use a CVT to keep the alternator running in an efficient range. Belt-driven riding mowers have a variable pulley arrangement something like that. That lets them use drive belts, which are at least lubrication-free. Might be easier than gears, plus allowing for a governor to keep the output shaft closer o a constant speed over some range of winds.
     
  8. mavava

    Thread Starter New Member

    Sep 26, 2006
    3
    0
    Thanks for the CVT idea as well as Soren's gears, finally I have a starting point. I'm thinking of speaking to a mechanical engineer regarding the proper ratio's etc. Thanks so much and if any more ideas come through please do not hesitate - the more I wrap my head around this the better and probably cheaper it'll be! I really do appreciate this great forum and all of your help so far, I was striking out everywhere else. Pete
     
  9. Chris Wright

    Well-Known Member

    Jul 26, 2006
    62
    0
    Go to the library. I was leafing through two different books on this very subject just a few months ago. One was about "Living Off of the Grid", i.e. not hooked up to the electric company. The other was about reducing demand by supplimenting with wind, solar, water power among others. They both showed how to build wind generators out of car alternators as well as dedacated wind generators.
     
  10. windy

    Member

    Apr 19, 2007
    26
    0
    You might get your answers by going to the NREL site, you can do this with a google search for self excited induction generators, I am looking into building a wind turbine as well and found some good stuff there on the subject.
     
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