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Old Epson Printer Motor Questions

Discussion in 'Electronic Repair' started by hr(bob) [email protected], Aug 8, 2007.

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  1. hr(bob)

    hr(bob) Guest

    I just scrapped the two motors out of an old Epson printer. Markings
    on one are EM-289, 940906B, the second is marked EM-293, 940903B Each
    motor has 4 wires going to the motor. From the feel of the rotors,
    these may be stepping motors. Does anyone know the approximate
    voltage used to drive these motors?
    I can play around with them, but would feel better knowing about what
    they should be driven with.

    H. R. (Bob) Hofmann
     
  2. James Sweet

    James Sweet Guest

    They sound like bipolar stepper motors. What is the impedance of the
    windings? Most of these are 12V.
     
  3. hr(bob)

    hr(bob) Guest

    Jim:

    Thanx for the info, I'm on a vacation and don't have any of my stuff
    with me, so it will have to wait till I get back home. I didn't have
    any way to measure the power supply voltages before I scrapped the
    motors, but they look pretty substantial and I will play around with
    them when I get home. Based on the construction of the printer, I can
    see why Epsons cost more than Lexmarks.

    BOb Hofmann
     
  4. Chris Jones

    Chris Jones Guest

    It's better to think of the limitation being on the current in the winding,
    because the current determines how hot the motor will get and how much
    torque you will get. The current and voltage are not in a fixed
    relationship because of the inductance of the winding which causes a time -
    varying relationship. Higher performance stepper motor driver circuits
    normally work like some sort of current source.

    Too little current and the motor will lose step with relatively little
    torque, too much current and the motor will get hot. The amount of heat
    will depend on the current squared multiplied by the resistance (I^2 * R)
    of the winding. You can measure the resistance with an ordinary
    multimeter.

    To try out the motor you could try connecting the motor to a power supply,
    and increasing the voltage gently until you can't turn the shaft easily but
    there is a reasonable amount of torque required, then you could leave the
    motor on, checking the temperature every minute to begin with, then every
    few minutes, for an hour or so. If you're happy that the motor is not
    getting too hot then the current should be safe. Remember that sometimes
    two windings can be switched on which increases the heating effect, so that
    would be a good condition to test.

    High resolution (1.8 degree or 0.9 degree) motors intended to do high
    numbers of steps per second tend to have low resistance windings, maybe
    only an ohm. Low-resolution (7.5 degree) motors tend to have higher
    winding resistance and so need higher voltage and lower current.

    Chris
     
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