variable current limiter for dc motor

Discussion in 'General Electronics Chat' started by hozone, Dec 30, 2012.

  1. hozone

    Thread Starter New Member

    Dec 26, 2012
    i'm searching for a variable current limiter i would like to use with a dc motor.
    i would like to set a threshold for that limit the torque.

    my dc motor run at 12V, 0.1A, with a initial peak current of 0.15A

    i've read information here
    , but there are two missing thing for my project:
    1) i need to ignore the initial peak current
    2) i would like to set the threshold, let's say from 0.1A to 0.3A

    anyone can help me?

    p.s. i'm an hobbyst, so excuse me if made some basic mistakes.
  2. tindel

    Well-Known Member

    Sep 16, 2012
    Why are you trying to limit the current to the motor?

    If you're thinking safety (I'm guessing you are since the current limit is higher than the operation current) have you considered a slow-blow fuse?
  3. hozone

    Thread Starter New Member

    Dec 26, 2012
    it is a motor for a screwdriver project.
    i would like to limit electronically the torque, not using a mechanical torque limiter.
    i would like to stop it if the torque is more than a threshold.
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Use a simple constant current circuit on the National Semiconductor DATASHEET for a LM317. You will need a couple volts above your max output (12 at 300mA) as the input to the lm317.

    Alternatively, you can use a pass transistor with a current limiting transistor and a 2 ohm series resistor between the pass transistor's emitter and the current limiting transistor's base.

    Once 300 ma is reached, the current limiting transistors base is at +0.6V and the current limiting transistor starts turning off the base of the pass transistor.
  5. hozone

    Thread Starter New Member

    Dec 26, 2012
    thank you,

    LM317 and voltage question,
    my motor have to be also speed controlled, so i suppose i can not use a LM317, becuase if it run the motor with less current, the motor has less torque but it slow down, right?
    also, one thing i've not sayd before (my mistake), i use PWM at 12V to change the motor speed.

    i can not undestand the circuit, sorry :( something like this?
  6. bertus


    Apr 5, 2008
    SPQR likes this.
  7. hozone

    Thread Starter New Member

    Dec 26, 2012
    thanks for the link, i've look at educypedia link you post.
    unfortunately it does not contains any information about running a dc motor with speed setting and torque threshold. :(
    it contains speed setting by PWM, which is the method i'm actually using, but i also need a variable current limiter to add a threshold to torque.