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Help with ESR

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  • Help with ESR

    I know I could measure it myself however I don’t have access to the capacitor at the moment…

    Could anybody give me an educated guess at the approximate ESR of a new 47uf Electrolytic capacitor? Bennic specifically.

    thanks

  • #2
    I measured a good number of 47uf electrolytics I have ranging from 16v to a 100v rating, both polar and non polar. I saw a range of 0.46 and 0.95.

    Dan

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    • #3
      Thank you very much! This is a dumb question but should I then use that esr number as the resistance of the component like the dcr of an inductor? I.e. is a npe, with it’s inherently high esr, the same concept of a poly cap damped with a half ohm or so resistor?

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      • #4
        Well esr isn’t stable. It changes with frequency I believe so I wouldn’t know the answer to that question, sorry.

        Dan

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        • #5
          That’s what always kind of confused me I guess..

          what frequency were the readings you provided taken at?

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          • #6
            ESRis the total in phase AC resistance of all parts and materials in the cap. ESR is not a constant with cap size.
            craigk

            " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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            • #7
              Originally posted by saabracer23 View Post
              Well esr isn’t stable. It changes with frequency I believe so I wouldn’t know the answer to that question, sorry.

              Dan
              That's correct. ESR is the Dissipation Factor divided by (2*Pi*F*C). Dissipation Factor isn't a constant, but it usually doesn't change more than a factor of 2 across audio frequencies, so it is often treated as a constant. So for a given capacitance, ESR is inversely proportional to the frequency. The ESR for electrolytic capacitors is usually specified at 120Hz. That means a capacitor specified as having a large ESR may have very low ESR at crossover frequencies..

              A lot of modern "audio grade" NPE capacitors have a dissipation factor in the 5% range, which will result in "negligible" ESR. If the DF is 10% or higher, you should probably use a modeling tool that takes ESR into account, especially for high-order crossovers. But the ESR isn't going to change the response much at all if you use 5% DF capacitors and typical crossover types.

              I just picked a NPE at random from the PE catalog: https://www.parts-express.com/33uf-1...citor--027-350 ..It's got a 5% DF, which I assume is typical of the NPE capacitors sold at PE. Don't worry about ESR with these caps.

              You can verify the effect of ESR on the response with PSD-Lite. Click on "Options" in the Passive Crossover Module and you can enable the ESR calculations. Just specify the DF and the program will add the ESR to all capacitors and recalculate the response. Spoiler: you won't see any significant change in the response unless the DF is 10% or higher.
              Free Passive Speaker Designer Lite (PSD-Lite) -- http://www.audiodevelopers.com/Softw...Lite/setup.exe

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              • #8
                Thanks guys, good info!

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