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AC current measuring

Discussion in 'General Electronics Discussion' started by docb, Sep 28, 2014.

  1. docb

    docb

    131
    2
    Feb 11, 2010
    I'm trying to check current on an AC LED driver. Output is 12vac

    I have a current shunt inline with the LEDs, and measuring AC volts across it.

    The current values I get are a bit far from what I get when driving this same circuit with a transformer.

    I have a feeling the drivers complex, changing waveform, makes the AC voltage value across the shunt jump all over, so the meter is doing it's best to average it, possibly not very well.

    Does it make sense I'd not be able to measure AC current very accurately this way?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    All you need is a meter that can read true RMS values.
     
  3. docb

    docb

    131
    2
    Feb 11, 2010
    It's a Fluke with True RMS, but current seems different compared to transformer.

    Perhaps I should look at numbers again. With a .1 shunt, I should see 10mv AC across the shunt for 100mA, correct?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    Assuming it's 100mA RMS.

    Can you not do RMS current measurements with that Fluke (what model is it)?

    Different ways of measuring may introduce their own individual types of inaccuracy. Why not tell us the different methods you've used and how much the results differ?
     
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