CD drive disk brushless motor

Discussion in 'General Electronics Chat' started by hazim, Apr 18, 2010.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    13
    Hello,
    I have a CD drive disk brushless motor, and I want to build a simple anemometer using it. I detached the motor, it is built-on a small board containing 3 electronic components (H1, H2, H3) I think these are Hall-effect sensors... I don't know much about Hall-effect..etc and this is not the point of my question. I can see three wires come out from the coils of the motor. What I know about these motors is that they are BLDC (brushless dc motor), so they are DC. I want to know how to power it, if it needs a control circuit I'll be very thankful if someone provide me with a simple circuit, and notice that this motor have 9 coils and only 3 input lines to it. By the way this is not for the anemometer project. Back to the anemometer and the cd drive motor, I want to get out a DC voltage out of it, using a rectifier circuit (I don't know how to do it in this case -3 lines)

    Here is the project that I'm trying to build: http://www.instructables.com/id/Easter-Egg-Anemometer-Wind-Speed-Meter/
    In this one, the motor seems to be a normal brushed dc motor.

    Regards,
    Hazim
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    In optical drives and hard drives, the makers typically separate the electronics from the motor and put them on the main circuit board, rather than have an extra circuit board in the motor as with a stand-alone part like a brushless DC fan.

    The input to the control circuit may be DC, but there is a lot of interaction between the motor and it's controller.

    If you can trace the original connections back through the circuit board, you may be able to find the motor driver IC and then find a datasheet for it.

    Using it as a generator, the problem you will have is that at low speed the output voltage will not be enough to make a diode rectifier conduct.

    If you fed the AC output to a comparator instead, and counted the cycles with a microcontrloller, it woudl probably be quite effective - but to get DC out I think you would need a precision rectifier circuit using op-amps.

    Also have a look at the CD tray load motor - that's likely to be a conventional DC type.
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    I'll look for that.

    I will not use it as a generator, I'll connect it directly to a multimeter as in the link. I think it should work fine even without rectification, but the problem is which two lines I should use from the three?

    It's a conventional DC motor.. These motors which have brushes have nonlinear voltage-speed characteristics in contrast with brushless dc motors as I know.
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    The main motor is most likely wound as three phase from your descrption, so any two wires should have the same resistance and give the same (AC) voltage.

    For info, tachogenerators used for precision speed measurement in industry are near enough always DC/brush types, calibrated to eg. 20mV or 60mV per rpm.

    I've only seen AC ones on none-critical gear like washing machine motors.
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    Yes it is three face as you expected, the resistances are the same. Thank you for all the information :).
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    You can use a ripple counter (and a bit more) to use this as a tacho.
     
    hazim likes this.
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