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Permanent Magnet Alternator Torque and volts?

Discussion in 'Electronic Basics' started by BobG, Jun 9, 2005.

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  1. BobG

    BobG Guest

    Is there a 'rule of thumb' for figuring out much torque it takes to put
    out xx volts and yy amps from a PMA given the gauss of the magnet and
    the N turns of the coils? Should spin free open circuit, and really
    stall out short circuit, and be somewhere in the middle during
    operation. I guess the 'max power' point is when the load drags the
    volts down to half the open circuit value? I guess the current here
    would be half the short circuit current too? I want to rig the pwm
    controller to not load down the pma too much under low power/low
    torque/ slow spinning conditions, like from a stirling or micro hydro.
    In general volts (and current) is proportional to rpm... someone got
    some formulas that are a little more specific?
     
  2. John - KD5YI

    John - KD5YI Guest

    Horsepower = Volts*Amps/746 = torque*RPM/5252 with torque in lb*ft.

    John
     
  3. Don Kelly

    Don Kelly Guest

    First of all. the torque to produce a voltage xx is 0. Torque is not related
    to voltage per se. Torque is related to current.
    If you can find the voltage -easiest done by spinning it and measuring it.
    then you will get a relationship E=Kw where E is in volts and w is in
    radians/ sec (2*Pi*60 rad/sec =1 rpm)
    Then a rough guide is Torque =KI torque in Newton meters and I in amps.
    same K as above.

    The relationship between E and I depens on the load.

    Finding the max power is another problem and it will not be at the half
    voltage level. Do you really want to be operating there? the alternator
    won't want to be operating there. It is a little different than what is
    implied by the maximum power theorem which implies matching load impedance
    to the alternator impedance., not the other way around (it also implies <50%
    efficiency)
     
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