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3 pole DC motor failure mode?

Discussion in 'Electronic Repair' started by N_Cook, Apr 28, 2012.

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  1. N_Cook

    N_Cook Guest

    Or internalised self destruction of one pair of drivers and nothing to do
    with motor playing up?
    Motor supply is 33V and 3 amp fuse , main drive motor for a photocopier, 3
    poles and magnets. I have a parts mule for this copier but do not want to
    take all the frame apart to change the motor unnecessarily, the driver board
    is easy to get to.
    Other than lubricate the motor bearings and change the
    driver+speed/direction processing board over , anything else to check?
    Both motors measure 1.5 ohms all 3 ways between coils , also inside is 3 off
    4 pin, presumably hall effect devices, can only see the pins. The
    electronics is for speed control, direction and braking. One pair of NPN+PNP
    TO220 drivers , 3 pairs in all, is all-pin shorted , well 1 to 3 ohm. Failed
    at switch on , knocking out fuses , no overheating or odd noises/smoke etc,
    Of course may have failed at final braking of the motor at last useage but
    as presumably braking is once per sheet cycle as not used for batch copying,
    seems unlikely it would happen to fail on the last of dozens of sheets
  2. Phil Allison

    Phil Allison Guest

    "Nutcase Kook"

    ** There is no way a 3 pole DC motor can handle 33V and survive.

    6V is normal, 9V at most.

    All got to do with arcing across the contacts on the comm.

    .... Phil
  3. N_Cook

    N_Cook Guest

    Maybe something to do with lack of lubrication, seems to run quiter now,
    perhaps a bearing stuck enough for overload. Seems to turn, by finger
    ,easier than before.
    Decided to solder 3 tell-tale small 28V bulbs to each coil and ground and
    power up with changed board. Overdriven by 33V at power up and half
    brightness but balanced in operation.
    3 coil ,36 degree stepper motor rather than DC motor to be more exact. Will
    power up a few more times and then remove the telltales
    The hall-effect presumably for phase monitoring and an external 12 vane
    interupted slotted opto for speed and a PTO solenoid clutch to transfer
    power presumably at the right operational speed. Must vary that speed for
    different size paper and magnification. Anyone know where the braking
    fusnction comes in? perhaps the PTO system will not disengage reliably at
    speed and operational torque.
  4. N_Cook

    N_Cook Guest

    If there is no binding of bearings etc there should be no load to speak of.
    It just turns the OPC drum and some rollers that feed paper through the
    system. The main load is probably the fuser roller as it is pushed against a
    backing roller to fuse the toner into the paper. Worst normal situation
    would be scrunched up paper jamming in the fuser section
  5. N_Cook

    N_Cook Guest

    I could not divide 360 by 12, it is 30 degree steps and turning by hand it
    has a stepper motor feel against the magnets and 12 magnetic steps. Ground
    is mechanical to the frame if any ground. 11 wires 3 are related to the
    coils, 1.5R between each to the other leaving 8 ,
    the 3 hall effect have one common I could detect by probing with a needle,
    probably one other in common leaving 2 for each sensing part of the Halls.
    Separately there is a slotted opto.
    Without scoping or strobing or something I cannot tell whether PTO is
    coincident with starting or stopping. When I had the tell-tales in there
    (from common collector of each driver pair to ground)
    bright at startup, half bright for motor run , then off or too low a voltage
    to light the lamps for half a second then a second of half bright. Perhaps
    the bulbs off is the braking stage.
    In normal operation you see the axial fan which is directly coupled to this
    motor , ie not via PTO, kicks back before stopping.
    The motor control chippery is TC9192P, TA75358, NEC uPC494C, TA7712 and a
  6. Jamie

    Jamie Guest

    That is a 3 phase servo/synchronous DC brushless motor.

    Made pretty much the same way as your basic cooling fans with extra
    feed back to be able to lock rotor and slowly turn either direction to
    keep a lock.

    These motors work very nicely in regards to holding things in position.

    It's possible you have a 12 pole motor which would make it not the
    fastest motor but give you some torque and tight tracking.

    That first chip in the list is a Phase lock Loop controller that can
    handle 2 motors.

    The nice thing about these motors is due to the integrated feed back
    which has to be mechanically position correctly so the controller knows
    exactly where the rotor is in relation to the poles.

  7. N_Cook

    N_Cook Guest

    Are you saying there could be microstepping involved, not perhaps with a
    copier but if that sort of motor was used in a plotter say
  8. Jamie

    Jamie Guest

    There are different types of feed back systems and you must have the
    correct drive electronics per motor.

    One of the most common ones I can think of that we use at work is
    that using a A+B and Z channel.
    The A+B can be used for both, direction detection and position. The Z
    is a index pulse and in the case of that motor, it could be at the
    corner of each pole. Or, it could be just one rotation and the driver
    just knows the number of poles there are and the PPR count and does the
    count after initial rotation.

    Some systems simply generate a gray code which works very nicely too!
    In your case, it could be a 3 bit code which gives you an absolute
    position of rotor per pole. The 3 bit code should yield a combination of
    8 places. Put that together with a 12 pole motor and you can have 96
    positions for holding index. That's strange, that almost looks like the
    Font size per inch in windows by default! :)

    You see the problem with using a 3 phase system like that for
    positioning and hold, the torque changes on the rotor are depending on
    what position of the pole you're in. So, it is common for a drive
    electronics to bias the drive to over come jitters between the poles and
    to do this, it needs to know exactly where the poles with relation to
    the PM is.

    You said you had R's in the coils? that tells me the Q has been
    lowered so less ringing will develop, maybe.

  9. N_Cook

    N_Cook Guest

    With this copier there is paper size selection from A5 to A3 nut more
    interestingly reduction or magnification from 64 percent to 154 percent by 1
    percent steps, so need some pretty precise control of speed. I always
    thought it was feather action microswitches that set other parts of the
    operation as paper goes through the machine but they may be for timeout
    error determination and the real sequence process timing done via the
    hall-effects and slotted opto/vane system around the motor
    The motor is this, from the stock number, but no technical info known about
    the internals/specs
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