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Measuring DC current.

Discussion in 'Electronic Design' started by TheM, Jun 26, 2008.

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  1. TheM

    TheM Guest

    This is not the sort of thing I don't usually do so I'll ask here:

    What's the easiest and relatively cheap way of measuring
    high side DC current (0-30/50A, say 10% accuracy).

    Preferably without using any drop resistors. I found hall sensors,
    any advice from users of these?

    It has to be isolated (can't insert anything into ground loop)
    and the output would go to AVR so some processing can happen
    there, if needed.

  2. Phil Allison

    Phil Allison Guest


    ** Non contact, DC current sense with no resistive drop ?

    The ONLY way is to use a Hall effect transducer.

    LEM Heme and Honeywell make nice ones.

    I can vouch for them.

    ...... Phil
  3. TheM

    TheM Guest

    Ups, a typo, this is not the sort of thing "I usually do"

  4. neon


    Oct 21, 2006
    i don't know how cheap is? but harbor freight sell for $7.00 plus tax. that is for AC. for DC all you need is a very small resistor value inserted in the path and measure the IR drop. and to measure current there is no hi side low side or in between side . just anywhere that is the total I
  5. Tim Wescott wrote:

    Allegro Hall Effect sensors are pretty decent; I have used them. However
    they are intended for the currents minimum of 5A or so.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
  6. TheM

    TheM Guest

    I'm looking at those, 712 looks decent.
    They are cheaper than some of the rail-to-rail high voltage opamps that are designed for this
    same task and those require the added drop resistor which is usually big.

    The problem with the tiny allegro 712 is that they run 30A across 4 pins on a tiny so8
    package, kind of scary. I wonder what happens if the load shorts, would the fast fuse
    break fast enough?

  7. Phil Allison

    Phil Allison Guest


    ** The data sheet says it withstands 100 amps for 100 mS

    - see " Overcurrent Transient Tolerance".

    So, a fast acting 30 amp fuse should be OK.

    BTW Farnell in the USA have stock.

    ....... Phil
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