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Ammeter problem

  1. Feb 13, 2016 #1

    i bought this cheap ammeter/voltmeter off ebay. now, i bought 1 before but it was slightly different. the wires had blue red and black instead of blue yellow and green. this makes it confusing but still i never had the problem im having now.

    so, this one i simply TOUCH the yellow wire and it reads like 10-30 amps. i never had that problem with the other one. what might be causing this?

    i can get a volt reading fine, but the amp reading is definitely wrong. if i touch it to anything by itself it read like 30 amps. it doesnt do it with everything but anything like a negative or positive part of a battery or just my finger. it reads and jumps around with amps.

    what is causing this? are the wires mixed up? is it a defective one? cause my other one which was almost identical didnt do this.
  2. jcsd
  3. Feb 14, 2016 #2


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    Which means that you bought a sensitive voltmeter, not an amperemeter.
  4. Feb 14, 2016 #3

    jim hardy

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    my high school electronics teacher taught us boys

    "When all else fails
    read the instructions..."

    Here's instructions i snipped from that Ebay listing :

    Hmmmm... they must have lost something in translation.

    Svein is right - you have a voltmeter,

    are you familiar with use of meters and shunts?
  5. Feb 14, 2016 #4


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    After examining the ebay post I conclude that this means that the 5A and 10A models have an internal shunt. Higher current models will need an external shunt. So like Svein said you have a dual voltmeter calibrated so that a current shunt of the correct value (possibly 1mΩ?) will give you a voltage (100mV??) at 100A to put 100 in the line marked A.

    Was the other one 5A or 10A?

  6. Feb 14, 2016 #5
    100A. supposed to be 100v 100a. so i NEED a shunt to make it work right? my other one must have had an internal shunt, the highest amp i measured was under 30A and it worked fine with that. i used my other ammeter as a reference.

    so it should read amps with a shunt?
  7. Feb 15, 2016 #6


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    It should if you find the right shunt. Can you make a voltage divider to put 50mV on the current sense input? That will give you the information you need to source the proper shunt.

  8. Mar 8, 2016 #7
    I ended up buying another one for ~3$ and this one is just like the one I used to have. Wires are red black and blue instead othe the green and yellow plus it reads amps without a shunt.

    I still make sure I have it in series with the setup so it doesn't short out (unless I'm using it with my homemade broken solar cell panels, it seems to be unaffected by the short for the "short" term ;) ill deal with the long term damage later.

    Thanks for the help everyone, I hate that shunt ****! Pzzz
  9. Mar 8, 2016 #8


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    So you expected that meter to be able to carry 100 amps with those whimpy wires?
  10. Mar 8, 2016 #9


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    hahaha indeed

    The shunt MUST be external
  11. Mar 9, 2016 #10
    My old one did 30 amps. This one does I think 10 but could be more.

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