Need help with voltage issues in a motor control application

Discussion in 'General Electronics Chat' started by jumanji, Dec 10, 2012.

  1. jumanji

    Thread Starter New Member

    Nov 4, 2011
    I am creating a motor controller board using a micro and the ST VNH2SP30 motor controller IC. I have a potentiomter that allows you to vary the speed and direction of the motor. I have the circuit all working and I am using a 12V automotive wiper motor as a test. The motor draws between 1A and 5A depending on the load. The issue I am having is that I when I turn the pot quickly and the motor changes direction sometimes the controller goes in a 'fault' condition and stops. I assume that this is happening because of a current spike. So my question is should I be using some kind of EMF protection (ie diodes) to reduce this problem like you do in a circuit with a relay? I don't know how you would do this in this application where the motor is changing directions.
  2. Audioguru


    Dec 20, 2007
    When a motor is running and you change its direction quickly then the motor draws a HUGE current. Normally a motor is slowed until it stops before its direction is changed.
  3. tshuck

    Well-Known Member

    Oct 18, 2012
    Do you have appropriately sized supply capacitors?
  4. tubeguy

    Well-Known Member

    Nov 3, 2012
    If I understand the datasheet correctly, you are controlling the speed with PWM and direction signals from the MCU.
    If that's correct you could write the software to respond more slowly to abrupt speed potentiometer changes.

    As pointed out by Audioguru it's a good idea to bring the motor to a stop before abruptly reversing it. Easier on the motor and whatever is attached to it.
  5. #12


    Nov 30, 2010
    Experience has told me that shorting the motor will make it stop quickly.
    AFTER it stops, you can change direction.
    Tubeguy offered a very good idea; write the code to refuse to reverse a running motor.