Testing Capacitors w/ ESR meter

Discussion in 'General Electronics Chat' started by johndoe45, Dec 10, 2010.

  1. johndoe45

    Thread Starter Member

    Jan 30, 2010
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    if capacitors are not showing a reading with an esr meter. does that mean they are shorted.
    i am testing small ceramic capacitors around 0.001 μF to about .0039μF
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    An ESR meter will show close to zero ohms when dealing with small and non-electrolytic caps.

    This is where you should use the capacitance range on your DMM, though most will measure down to 0.1uF at best.

    If you use your DMM on the same cap, it will show as an open. The ESR meter is like an "AC Ohmmeter", which gives the resistance ignoring the capacitance.
     
  3. johndoe45

    Thread Starter Member

    Jan 30, 2010
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    so on the cap it says 392K which is 3.92 nF.
    on my DMM it shows 4nF.
    When i check with resistance. It shows open.
    ESR shows no reading

    So is it good? :confused:
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Yes. The lower the ESR, the better (generally). When it reads 0.00, you may want to check for a shorted cap.

    ESR on caps smaller than 0.1uF is usually so small as not to impact the circuit anyway.

    For decoupling caps and small value caps, I look at the dissipation factor on an LCR meter, mostly out of interest is something is acting "hinky". Otherwise, ESR meters are mostly used to find bad Electrolytic caps in a quick fashion.

    I also use mine to check batteries, as the internal resistance goes up as they get discharged. Also a great way to "match" several NiMH cells. This is with a Blue ESR, I'm not sure about the capabilities of other types.
     
  5. johndoe45

    Thread Starter Member

    Jan 30, 2010
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    if i had an insulation tester to test for a short at the rated voltage of the capacitor, would that test it?
     
    Last edited: Dec 10, 2010
  6. gootee

    Senior Member

    Apr 24, 2007
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    If you just want to test a cap for a short, just measure Ohms with a multimeter set to Ohms or a DC ohmeter. After the cap charges, it should measure as an open circuit (infinite Ohms).
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If your DMM showed close to the rated value, and the ESR meter showed off scale on the low side resistance, then it is a good capacitor.

    Applying a single pulse to test for short would show true, as the leading edge pulse of DC is essentially high frequency AC, which capacitors do appear to meters as a short (ref: ESR meter).
     
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