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Alternator and poles

Discussion in 'Automotive Electronics' started by martino, Oct 26, 2016.

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  1. shortbus=

    shortbus= Well-Known Member

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    After thinking about what I said about the BLDC, while it would/could be considered AC it definitely wouldn't be sine wave AC, it would be square wave AC. This is due to the way the stator poles react with the magnets. In a car alternator it is sine wave because of the winding pattern of the stator and the "V" shape of the rotor poles.
     
  2. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Look at the PDF again on post #32. Done this many times when confirming the hall effect associated with a particular stator phase on a BLDC motor.
    I back feed the motor at around 100rpm, then scope the hall and the generated output on a D.B. 'scope.
    The out put is as shown, I use the resistor set up as described to provide a virtual zero or neutral.
    If you have a BLDC motor and a 'scope, you can confirm it
    Max.
     
  3. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    martino I did a few tests on the one I have dismantled on the bench, it is a GM-Delco older style alternator, it has 12 rotor poles and a Delta connected armature (stator) consisting of 3 sets of 12 coils between each phase with a total of 36 poles faces.
    Each field pole sits under 3 armature faces.
    The field is ~2 Ω and the new brushes are ~1Ω ea.
    With 2.5 amps to the field I was surprised on the apparent pole strength.
    Once I get it reassembled I am going to try and get it to self excite using field residual, so that no external power is needed.
    Max.
     
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  4. dave

    Dave New Member

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  5. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Max, after you get it assembled, if you could look at the stator voltage waveform before it's rectified, that would be of interest. :)
     
  6. martino

    martino Member

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    Thank You Max, also the waveform after the full rectifier should be interesting, to evaluate the amplitude of the ripple and its frequency.
     
  7. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Yes, I intend to, the stator has to be unsoldered from the bridge anyway, in order to dismantle.

    Can do, although the frequency and % of ripple on a 3ph full wave bridge is fairly predictable.
    Max.
     
  8. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Here is the results of the alternator output when 2 amps is fed to the field, both monitor of two phases and the resultant rectified DC at approx 1880rpm.
    Max.
     

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  9. MaxHeadRoom78

    MaxHeadRoom78 Active Member

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    Incidentally, The attempt at self excitation did not work.
    Max.
     

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