how to make a current limiter ?

Discussion in 'The Projects Forum' started by mejlby, Apr 24, 2016.

  1. mejlby

    Thread Starter New Member

    Apr 26, 2013
    28
    1
    Hi All

    I have a 24 VDC motor that I want to turn off when the current exceeds approximately 500m amp
    and I want to be able to regulate the current limit from 300m amp to about 1 amp

    I want to protect the motor to be destroyed if it becomes overloaded

    I hope someone can help me with a circuit and explain how it works

    Best regard

    Mejlby
    Denmark
     
    Last edited: Apr 24, 2016
  2. Picbuster

    Member

    Dec 2, 2013
    374
    50
    use a 50milli Ohm resistor in series and measure the voltage as function of the current.
    feed this into an amplifier( opamp) 1amp does 50mV gain x 50 and feed into cheap 8 pin PIC use two ports analogue in one for current other for pot meter allowing to set cut-off current compare and use a fet to cut-off voltage.
    Advantage with Pic; you can easy omit switch off at temporally current peak( eq switch off when the current is for n milliseconds above, by pot, selected value).
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,783
    1,103
    What is (a) the motor current when free-running and (b) the stall (rotor-locked) current?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,979
    744
    What is it with you and these pics,
    Whats wrong with a simple voltage regulator like lm338 or lm317k???
     
  5. Picbuster

    Member

    Dec 2, 2013
    374
    50
    Nothing wrong with it but it's not as flexible as I like to see it.
    Like implementing hysteresis, slow start, rpm versus current used to calculate mechanical load.
    And as a real Picbuster I have to use pic's make them jump, swing and even make thee or coffee (smile).
    But again nothing wrong with lm series.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    How much voltage drop can you tolerate?
    Can you put a sense resistor in the return line?
    An LM317 used as a current-limiter will drop a minimum of about 2.5V.
     
  7. hp1729

    Well-Known Member

    Nov 23, 2015
    1,948
    219
    Can you deal with a microcontroller? Nothing special about PICs, any of them would work that have an analog port. Do you need to just limit the current at some point or shut power down and wait for a human to reset the overcurrent condition?
     
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