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Cant seem to measure mA using my multimeter

Discussion in 'General Electronics Discussion' started by simple295, Aug 3, 2011.

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  1. simple295

    simple295

    4
    0
    Jul 25, 2011
    I have a nice craftsman multimeter, and I'd like to measure the current draw of an electric motor I have.

    I have attached the negative lead to the motor, with a break in the positive connection where I insert my multimeter. The motor doesnt spin, although if I measure volts using that same set up, it measures the exact voltage of the battery.

    What gives?
     
  2. poor mystic

    poor mystic

    1,067
    31
    Apr 8, 2011
    :)
    So, current should be passing through the meter and powering the load? If that's not happening, check the fuse in the multimeter.
     
  3. daddles

    daddles

    443
    3
    Jun 10, 2011
    Make sure you don't have to change the jack that the lead is plugged into the multimeter to a different one to measure current (this is typical e.g. on Fluke multimeters and is, frankly, a better design than the types that let you measure voltage and current using the same jacks).

    Next, make sure you have the meter on a current range.

    If it still doesn't work, it's likely a meter's fuse is blown as poor mystic said. Read the manual, as you may be able to test this using the leads and the resistance mode.

    If a fuse is blown, replace it with a fuse with identical ratings. This is important because you can compromise your safety if you don't. Note that some fuses with high interrupt current ratings (in the 10 to 100 kA ranges) can go for $5 to $15 each. This is a great feedback tool to help you learn to make current measurements carefully. :p

    Some multimeters have more than one fuse, so make sure you replace the right one.
     
  4. simple295

    simple295

    4
    0
    Jul 25, 2011
    Thanks guys.

    My multimeter only has two spots the positive lead can go into, and i tried both of them. I will have to check the fuse.

    Btw, Im using a 1.5v alkaline cell, so theres no risk of electrocution
     
  5. shrtrnd

    shrtrnd

    3,773
    493
    Jan 15, 2010
    Yep, one jack is for volts, and the other is for mAmps.
    When you hooked-up to read volts with the mA jack, you blew it's fuse.
    mA meter reads in series with a circuit, it's a virtual short to the circuit under test, intended
    to read the current through the circuit.
    daddles pegged this one.
    When you replace the fuse for the ammeter, make SURE you don't use the meter
    to read in parallel across a voltage, or you'll just blow the ammeter fuse again.
    Read the manual, if you still have it.
     
  6. TBennettcc

    TBennettcc

    292
    2
    Dec 4, 2010
    Make sure the meter is rated to read past the possible max current draw of your motor...
     
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