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DC motor current spike

Discussion in 'Electronic Design' started by [email protected], Apr 10, 2006.

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  1. Guest

    i'm running a .5 hp 12v dc motor. it works fine until i put a load on
    it. with the load i am using, the initial current spike exceeds the
    rating of my power supply so the power supply shorts. my power supply
    is rated for 52a surge, 40a constant. is there a device or some sort
    of circuit that i could utilize to solve this problem?
     
  2. It would depend on the characteristics of the load and load application.
    Also, what kind of DC motor is it (series, shunt, etc.). What is the
    time duration for that power supply 52A surge rating?

    Typically, the worst case inrush current will be the locked rotor level
    experienced when the motor starts. However, if it starts unloaded, the
    motor will accelerate rapidly and the current will decrease with
    increasing motor speed. It seems that your power supply is capable of
    providing this current-time envelope successfully. However, the load
    inertia is such that it exceeds this, which the power supply treats as
    an overload.
     
  3. Tim Wescott

    Tim Wescott Guest

    The best thing to do is to use a power supply or amplifier that will
    current limit gracefully. This may make the motor take longer to
    recover from a load change, but it'll keep your power supply happy.

    Are you driving the motor with an amplifier, or just a switch? If
    you're using an amplifier, you should be able to find one that'll
    current limit.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/
     
  4. Ban

    Ban Guest

    It doesn't short, it shuts down
    With full load yor motor will probably draw already more than your
    continuous 40A rating, when stalled maybe 120A. just measure the DC
    resistance and you will know. :) To supply such a current, your power
    supply is not sufficient. The only possbility would be to connect a car
    battery across the output and set your supply to 13.8V, to recharge the
    battery.
     
  5. Boris Mohar

    Boris Mohar Guest

    Flywheel and or one of those Farad capacitors that they use in car audio.
    Make sure that you power supply can charge such cap.



    Regards,

    Boris Mohar

    Got Knock? - see:
    Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

    void _-void-_ in the obvious place
     
  6. w_tom

    w_tom Guest

    An additional point to supplement your other good responses. The
    "initial current spike exceeds the rating of my power supply" will
    create problems if power supply is a foldback current limit type. With
    excessive current, load must be removed so that foldback current
    limited supply can recover.
     
  7. ehsjr

    ehsjr Guest

    I don't think it's a spike. I think what you have
    is a simple overload - at start up, the motor draws more
    current than the supply can provide. I'll bet the LRA
    exceeds the power supply capability.

    So it seems your first step has to be to determine the
    LRA rating of your motor. If it exceeds the supply
    rating, you'll need to increase the supply or decrease
    the load on the motor at startup. Or maybe "kick start"
    the motor with a battery, then switch in the supply
    to handle the continuous run and to recharge the battery.

    Ed
     
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