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Wind Generoator Engineering Question.

Discussion in 'Home Power and Microgeneration' started by Drums, Jan 11, 2006.

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  1. Drums

    Drums Guest

    I notice many homebrew units are being built using Brake disks. I understand
    the lure as they are easily obtained
    and easy to maintain. I have one nagging question. What if the Magnet rotors
    disks were Aluminum?
    Not being an engineer I can't really answer that. Common sense tells me you
    would shaving
    off 50 pounds and that translates into a 20% increase in efficiency by
    reducing the inertia load,.
    however that gain is not real as would only apply to stop and start
    conditions. The actual loss
    once it was spinning at speed would be negligible I would think. So this
    leaves me thinking. Maybe you would get
    a much lower start up speed in lighter winds? I only bring this into
    question as I have the materials
    and tool to build any kind of rotor I want. If there is a reason the weight
    is there then obviously I would not want to use a lighter material.
    Intersted in your thoughts.
  2. daestrom

    daestrom Guest

    Well, saving weight is true. I'm not sure why you think you'll get an
    increase in efficiency though. To disk, being very close to the center of
    rotation doesn't contribute all that much to the inertia element. Those
    nice long blades represent most of the inertia in a wind turbine.

    Another thing to keep in mind is that the magnetic flux from the magnets has
    to have a nice low reluctance path. Mounting on steel automatically
    provides part of the path needed. But if they were mounted on aluminum,
    which has a higher reluctance to magnetic flux, you would probably reduce
    the generator output considerably. Unless you provide a relatively thick
    steel/iron plate for the magnetic flux, but then you're right back where you

  3. Drums

    Drums Guest

    Thanks. That's why I asked the question. Very good point.
  4. Drums

    Drums Guest

    Very usefull info. Thank you.

  5. daestrom

    daestrom Guest

    Aluminum can be used in a magnetic brake, but not because it provides a good
    path for magnetic flux. (ironic, I know) In many magnetic brake systems,
    the electromagnet is wound on a piece of iron shaped like an 'E' on one side
    of a rotor disk, and there is a flat 'I' piece of iron on the other. So the
    magnetic flux has a low reluctance path (high permiability) to focus the
    flux through the gap where the disk is. And yes, the rotating disk can be
    aluminum. But it works by induction and eddy currents generated in the
    disk. The moving disk has a voltage induced in it, and the 'circuit' is a
    circular path in the disk that is a short circuit so large currents
    circulate. These create counter magnetic fields that interact to produce a
    torque in the opposite direction to the direction of rotation.

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