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in-rush current measurement.

Discussion in 'Electronic Design' started by Paul, Apr 6, 2006.

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  1. Paul

    Paul Guest

    How would I go about measuring the in-rush current on a DC feed of 30V. I
    have built a current limiting circuit which should limit current to 8mA and
    I need to how that the in-rush current does not exceed 10mA for 100ms.

    Currently I use a relay to switch the feed on and off, however this bounces
    so I am going to replace this with a mercury wetted 0 bounce relay is this
    the correct thing to do?

    Most sites I have seen discussing in-rush current seem to use a current
    probe but they are measuring Amps if not 100s of amps on motor feeds not a
    few milli amps are there current probes which can measure the mA range
    accurately enough for me.

    Currenly I am using a shunt resistor in lieu of the current probe and notice
    that I appear to exceed the in-rush just from powering the current limiter
    without a load although only for the firt 12uS. Is this likely to be noise
    from the relay or the response of the transistors limiting the current, I am
    using a Transistor VBE referenced current source circuit from AOE, is there
    anything I can do to remove this initial spike or do I need to allow that
    there will always be this inital rush.

    Any good web sites with this sort of info would also be appreciated

    Many Thanks for any help

  2. Ian Stirling

    Ian Stirling Guest

    Maybe, maybe not.
    The bouncing should not of itself cause problems.
    Might adding a smallish inductor to the power line work?

    Alternatively, a small resistor, in series with a capacitor may work, if
    you can connect it to the supply permenantly.
    The capacitor supplies the load when your supply is connected.

    A small capacitor on the base, with a time constant of a few
    microseconds may also work.
  3. mires

    mires Guest

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