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Unipolar stepper, bipolar driver

  1. Nov 21, 2009 #1
    I got an unidentified 6-wires stepper motor, which i suppose is unipolar.
    But, the motor drivers i have is for bipolar ones.
    As i understand, a bipolar driver can drive a unipolar motor, by plugging in the ends of the coils and leaving the middle wires hanging.
    Is it that simple or are there some caveats?

    Second problem, how can i identify which wires do what?
    There are two trios of interconducting wires, in each one there is a pair that gives the most resistance on rotor when shorted, but when i plugged these two pairs, the motor does not work in a consistent way - either vibrate in place or starts moving back and forth. i tried swapping one pair and different step rates to no avail.
    What can be wrong?
  2. jcsd
  3. Nov 21, 2009 #2
    Yes, an H-bridge usually can be used to drive a unipolar motor by driving the two ends and leaving the center-tap wires hanging. Read about various types of steppers in above URL. Based on stepper motor voltage and current ratings, set up the two H-bridge drivers, with series resistors if necessary, and drive the stepper at 1 or 2 Hz with the two H-bridges in phase quadrature. My experience is that many H-bridge drivers are not full-rated below ~ 6 or 8 volts, which may be too high for some steppers.
    See the schematic on page 2 of:
    for two 5-50 volt H-bridge drivers using P-type and N-type mosfets.
    Two popular integrated H-bridges are the L298N and the LMD18200.
    Bob S
    Last edited: Nov 21, 2009
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