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*analog* brushless DC motor control?

Discussion in 'Electronic Basics' started by [email protected], Mar 5, 2013.

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  1. Guest

    My son and I took apart a dead hard drive, and salvaged the motor. Apparently it's a brushless DC motor that needs a dedicated controller.

    Any way it can be powered by analog, discrete circuitry?

    If I understand it correctly, each of the three power wires needs to be energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?


  2. Guest

    Oh, nice! Still have a controller chip in there though, huh.

    Wiring... I'm not sure; I'll have to check it more thoroughly when I get home. There were three very obvious wires, but from some YouTube vids I saw there is sometimes a fourth wire...

    I did see a very clever way to turn the hard disk platter itself into a commutator, using electrical tape, and turn the whole motor into a brushed DC motor, but that kind of defeats the purpose of a brushless DC motor.

  3. ehsjr

    ehsjr Guest

    Yes, but it's not worth the effort, unless the goal
    is the experimentation.

    There's a relatively cheap (< $20) controller available on
    Ebay that will work well to control the motor. I'd post the
    details if I could remember, but ... Grumble.

  4. Guest

    Right, that's the goal. =) I know there are cheap R/C motor controllers that control 3-phase DC motors, but... yeah.

    Seems like some sort of modified Astable Multivibrator should do the trick...?
  5. ehsjr

    ehsjr Guest

    I did a search and found this for ~ $10.00

    Regarding the experiment - I did that a while back and found
    that it was touchy as all get out, very critical adjustment
    of the speed control pot to get it to run. As I recall, I
    _very_ rarely could get it to self start - I had to manually
    spin it to start it, and even that was difficult.

    Read up on brush-less motor control, it's interesting. :)

  6. Guest

    On Tuesday, March 5, 2013 10:53:50 AM UTC-8, ehsjr wrote:


    Good price! Then again, I just took apart a 9-amp, 110v electric weed eater that could never hold the weed-eating spool properly, on a hunch put it on 24 VDC, and it WORKED! That is going to be fun.

    And of course I horrified my 10-year-old son by plugging in a C-frame fan motor directly into the outlet... wires only, no plug... ahahaha...

    Will do, that sounds like fun!

  7. Guest

  8. Guest

    On Wednesday, March 6, 2013 8:36:22 AM UTC-8, Tim Wescott wrote:


    Oh yeah, PC fans!

    Researching them now... found this after a brief search.


  9. Jasen Betts

    Jasen Betts Guest

    last time I pulled one apart it had a single coil with shaded poles and a
    hall-effect chip to detect the rotor position,

    the ones used on CPUs seem to be more complex, the go in to a
    different mode when forcibly stopped and then short time later start
    Y 4-wire Y-connected motors seem fairly common on hard drives.
  10. whit3rd

    whit3rd Guest

    As others have said, it's a four-wire Y (wye) wired motor; this makes it
    a synchronous (permanent magnet) AC motor. It's certainly
    brushless (but for an AC motor, that's not noteworthy).
    The easiest way to generate three out-of-phase drive signals is
    with some kind of digital logic, but you can make an analog phase-shift
    oscillator with taps to get all three phases.

    Simple speed control can be had by controlling a VCO (CD4046 works well)
    that drives a three-flipflop twisted tail counter (to generate three phases)
    which drives three transistors (I'd use discrete NPNs, but MOS and monolithic
    transistor arrays are also good). Attach the center of the wye to +12V through a
    suitable limit resistor, and each branch to a switch-to-ground transistor.

    Because this IS an AC motor, you can get better efficiency by driving the windings
    with AC (without the DC bias). Modulating the DC produces a mix of DC and AC
    currents, and only the AC part of the drive is actually torque-producing.
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