DC motor circuit with automatic reverse

Discussion in 'General Electronics Chat' started by SteveInFlux, Aug 7, 2008.

  1. SteveInFlux

    Thread Starter New Member

    Aug 7, 2008
    2
    0
    Hi All, My first post!

    I need to reverse the direction of a small DC motor, 12vdc 500ma, when it (the load) comes to the end of it's travel. Think car windshield wiper, but solid state (OK it can use a DPDT relay).

    I don't think I need to apply a micro to this (not so good at them anyhow).

    I'm thinking some sort of current sensor (op amp?) that see's when the motor hits the end and senses the current rise, this could activate the relay and reverses the polarity so the cycle can repeat.....

    Being adjustable would be helpful, so that it can be tuned in.

    Any advice would be appreciated.

    Thanks,
    Steve
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Steve,
    See the attached.

    The first one is just using a single DPDT switch to automatically reverse the direction of the motor.

    The 2nd one uses two limit switches in conjunction with a DPDT switch. When a limit switch is struck, the motor stops - the switch must be manually flipped in order to reverse the motor.
     
  3. SteveInFlux

    Thread Starter New Member

    Aug 7, 2008
    2
    0
    SgtWookie,
    Thanks for the circuits, I really appreciate the effort.
    Unfortunately, because of the location of this motor, I was hoping to do this without any limit type switches attached (or near) the motor or the arm attached to it.

    Hence the idea of doing this with a current sensor.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It's going to be difficult to differentiate between the starting current and the stall current.

    It's also going to be pretty hard on the motor and equipment attached to it. Slamming a motor against a hard stop isn't a great thing to do to it. Once the current starts building due to the stall, the motor is already being stressed quite a bit, and motors generally don't "stop on a dime", so to speak.

    There must be SOME way to connect a limit switch on each end - even if you have to connect a rod and bring it outside the narrow confines of the current environment.

    Why don't you take some photos of the object you're trying to control, or if it's not built, post some conceptual drawings?
     
Loading...