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average value of current pulses?

Discussion in 'Electronic Design' started by [email protected], Dec 15, 2006.

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  1. Guest

    i am trying to figure out the average current consumption of a pump. it
    draws 13ms pulses of about 500ma about 15 times per second at randomly
    spaced intervals.

    i put a 0.1ohm sense resistor in the positive lead of the battery which
    powers the pump, and i put an rc integrator across this resistor (10k
    and 1000uF capacitor).

    does this make sense as a way to average out these pulses and get a
    voltage which represents the long term (relative) average of the
    voltage across the sense resistor?
  2. Andrew Holme

    Andrew Holme Guest

    Yes, but the time constant doesn't need to be so long. With those values,
    it's going to take almost one minute to fully charge the capacitor. I would
    try 10k and 100uF.
  3. Bob Eld

    Bob Eld Guest

    This will work but it may give difficulty. The peak voltage is only 50mV
    across the .1 ohm resistor and the average voltage will be less than 10mV.
    That's a small number prone to errors with an electrolytic capacitor. I
    would use a film capacitor of several microfarads with hundreds of "k" in
    the resistor to get a time constant about one second. It is now 10 seconds,
    longer than necessary. You may want a little more sense voltage to work with
    by making the .1 ohm resistor .2 or even .5 ohms.

    What are you going to do with the average value for current? If it is going
    to feed any type of processor or controller for indication or control, you
    might consider doing A to D conversion and numerical averaging in the
    digital domain in that processor. It could be a single chip solution without
    any analog integration, large caps or other parts.
  4. Phil Allison

    Phil Allison Guest

    ** Groper alert !

    ** How ambiguous.

    What exactly are these " randomly spaced intervals " ??

    Every other Tuesday afternoon if it rains ??

    ....... Phil
  5. John  Larkin

    John Larkin Guest

    Random intervals can't be described exactly. That's because, I think
    the theory goes, they're random.

  6. redbelly

    redbelly Guest

    So, each pulse has a charge of 13x0.5 mC = 6.5 mC.
    There are about 15 of these pulses per second, so:
    15 x 6.5 mC/s = 98 mA.

    The average current is about 100 mA.

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