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Checking ESR and Capacitance

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    #1

    Checking ESR and Capacitance

    Hey guys,

    I've just got the Peak ATLAS ESR 70 meter.

    Great Tool! just fixed a pentium 4 power supply with it, 1000uf 10v bad cap
    got high esr and half the capacitance it should be,
    the cap looked perfectly good, no buldge top etc...

    i've checked some more caps i have in my stash,
    i found that some have higher capacitane than should be
    for example 1000uf 10v showed 2000uf but good esr.

    what is the normal tolarance?

    is it safe to use caps with higher capacitance than should be?
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    #2
    Re: Checking ESR and Capacitance

    Originally posted by s_henya View Post
    i've checked some more caps i have in my stash,
    i found that some have higher capacitane than should be
    for example 1000uf 10v showed 2000uf but good esr.

    what is the normal tolarance?
    Most electrolytic caps are +/- 20% of their stated uF value.

    Here is an example of Panasonic FR 1000uF 25V cap.

    http://industrial.panasonic.com/www-...UFR1E102B+8+WW

    Note the tolerance on capacitance.
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    Comment

      #3
      Re: Checking ESR and Capacitance

      thanks for the quick reply,

      so more than 20% over to the + is bad?

      Comment

        #4
        Re: Checking ESR and Capacitance

        No, it's not bad.

        With power supplies, it's sometimes not recommended to go a lot over the capacitance value already used in the circuit.

        As capacitors are often +/- 20%, the manufacturer considered when they designed the power supply that the capacitor may be up to 1200uF (1000uF + 20%) so for example, I wouldn't worry about using 1200uF capacitor instead of that 1000uF if that's all I have.

        But 2000 uF is quite a lot over 1000uF - the power supply could work just fine or the higher capacitance could mess up a bit the filtering circuitry and cause higher ripple on the output...

        Comment

          #5
          Re: Checking ESR and Capacitance

          so the cap was made with that capacitance value?
          i thought it got that high from wear over time...
          (that's weird it should decrease, not increase)

          i would take your advice and won't use caps with tolarance above 20%
          maybe use the caps with higher capacitance as caps with that original value.

          for example a 1000uf cap that showed 2300uf, use it as 2200uf.

          im asking because i have a few caps like this,
          don't know if to throw them away or use as a different value.

          Comment

            #6
            Re: Checking ESR and Capacitance

            If you're sure of your readings, I would throw them away. How confident are you in your capacitance meters accuracy?

            If the manufacturer couldn't get within 20% of the labeled value or if for some reason it changed by such a massive amount, they will probably cause trouble sooner rather than later.
            The More You Learn The Less You Know!

            Comment

              #7
              Re: Checking ESR and Capacitance

              Originally posted by s_henya View Post
              for example a 1000uf cap that showed 2300uf, use it as 2200uf.
              Caps can fail with high uf readings (i.e. outside their +20%). Tom66 reported it in a thread here, but I can't find it right now.
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              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

              Please do not post inline and offsite as they slow down the loading of pages.

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              Comment

                #8
                Re: Checking ESR and Capacitance

                If they are leaky high capacitance will appear to result (meter error), but I don't think the capacitance actually increases. Someone else on here mentioned that capacitance can go up, but there's no such thing as a free lunch, so voltage rating decreases (due to thinning of the oxide layer or something similar.)
                Last edited by tom66; 04-12-2012, 01:31 PM.
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

                  #9
                  Re: Checking ESR and Capacitance

                  Badcaps.net: Capacitance can rise as cap begins to fail

                  There is no free lunch. If the capacitance goes up then the voltage must go down which means the capacitor is no longer suitable for purpose.
                  sig files are for morons

                  Comment

                    #10
                    Re: Checking ESR and Capacitance

                    Originally posted by s_henya View Post
                    i've checked some more caps i have in my stash,
                    i found that some have higher capacitane than should be
                    for example 1000uf 10v showed 2000uf but good esr.

                    what is the normal tolarance?

                    is it safe to use caps with higher capacitance than should be?
                    For electrolytics, there's no such thing as 'normal tolerance'. You need to consult the data sheet.

                    Back in the 80's, lots of electrolytics had a tolerance of -50% +100%, but due to advancements in technology, I don't see them much any more.

                    As for whether a higher value is safe or not, that depends a lot on the circuit. In many cases much higher values will be OK, other times they can cause problems.

                    Comment

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