DC Motor Current Sensing

Discussion in 'The Projects Forum' started by ashish19183, Nov 9, 2010.

  1. ashish19183

    Thread Starter New Member

    Sep 16, 2009
    13
    0
    Hi all,

    i need to check DC current of following circuit . This is 24VDC , 5A DC motor
    with both direction movement.
    my query is this how can i measure current with this circuit for both
    direction of motor movement. in circuit i have put 24VDC on both side to
    show that which ever side get that voltage motor will run in that direction.
    means at a time only one path will get voltage. and i want to put resistor in
    one path only not in both paths. if my motor get voltage on path which
    having resistor then current sensing i can do by instrumentation amp, but
    how to measure current when voltage comes to other path ?????
     
  2. Artikbot

    Member

    Nov 7, 2010
    45
    1
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    Move current sensing resistor to ahead of V reversing ckt. SW or H bridge.
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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  5. ashish19183

    Thread Starter New Member

    Sep 16, 2009
    13
    0
    @ Artikbot - yaar i dont want to measure current by multimeter
    it is like to amplify that voltage drop across that resistor by op-amp or some thing, my problem is how i can measure bidirectional current with only one resistor in one line.

    Regarding hall effect sensor.... i didnt use earlier ..i will check but right now looking for some simle solution any op- amp circuit or some thing......
     
  6. Artikbot

    Member

    Nov 7, 2010
    45
    1
    Hall effect sensors are very precise, but hard to set up and not quite easy to find.

    Although if you want precision, it's the best option ;)
     
  7. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you are using an Opamp, just expand the circuit a little and make a precision full wave rectifier. Scroll down to that section here..... http://sound.westhost.com/appnotes/an001.htm

    No matter what polarity you see from your sense resistor, the output will always be the same polarity.
     
  8. ashish19183

    Thread Starter New Member

    Sep 16, 2009
    13
    0
    Thanks BillB3857

    But from that circuit i didnt get how can i feed voltage across resistor in to Op-Amp as in circuit of full wave precision rectifier it use only single i/p line, where in my case i have two voltage lines and wanna amplify that voltage diff.

    please if you have any suggestion provide me.......
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Most current sense resistors are between the ground lead of the motor (or reversing switch) and ground. The input to the op-amp would be taken from between ground and the ungrounded end of the sense resistor. Or you could use a differential amplifier as an input stage.
     
  10. ashish19183

    Thread Starter New Member

    Sep 16, 2009
    13
    0
    Ya i got your point but i have to sense bi-directional current and in one direction its fine but again for other direction it will be between motor and source,
    i just wanna make configuration which can solve these two problems.......
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you are stuck using the circuit shown in your first post, you need to use an isolator module. They allow transfer of low level signals with different base references. This an industrial version of what you are looking for. http://dynapowerstore.com/eug7100990006--dual-feedback-isolat7100990007.html

    Can you post a schematic of what comes before your original post. There is probably a much cheaper way around your problem.
     
    Last edited: Nov 13, 2010
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