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Differences in Voltage rates with same capacitance

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    Differences in Voltage rates with same capacitance

    Good evening,

    Given a cap value of, say, 100uF/10V (but can be any other), I'd like to know if there's much difference in (worse, better or no variation) performance comparing it to a, say 100uF/50V.

    I know it's (way!) safer to use the 50V rated version. But will it do a "better" job as it "should"? How the plates and dielectric are made and how they behave in different voltages?

    I'm curious about this, since 'modern' electrolytics are much smaller than their older (and vintage) counterparts, which some still do a really good job. Example, I replaced a labeled 1991 Matsushita cap with a modern (2017) Nichicon, same capacitance but rated 50V. Results were pretty disappointing with no significant improvement in terms of sound (or video) quality.

    Thank you.

    P.S.: the newer 100uF/50V had some 3 days of the "burn-in" process, the amp was always on during this time.
    Last edited by Cap_search; 11-08-2018, 01:03 PM.

    #2
    Re: Differences in Voltage rates with same capacitance

    Taking modern series parts from just one series, a 470uF, 10V part is likely to be lower in impedance and larger in size than a 470uF, 50V part. The size difference would be due to a thicker aluminum oxide dielectric layer, forcing the use of more foil (= longer strips) to get the same capacitance. The longer foils also affect the ESR and ESL, and therefore the impedance.

    OTOH, if you pick the parts from different series it becomes less predictable as to impedance, since the electrolyte is conductive, and the conductivity of different electrolytes varies.

    Then there's the 1991 vs. 2017 parts. The foil with the aluminum oxide layer formed on it is the anode (+) foil. The cathode foil is simply a conductor that "connects" to the conductive electrolyte. Anode foils are not perfectly smooth. They are etched so that there are hills and valleys that the oxide layer can follow, increasing the effective surface area or the foil ("gain"). Lower voltage foils are higher gain, since the thicker higher voltage oxide layer would just fill in tightly packed "valleys". Foil etching has been going on for decades, but etching techniques have improved over that time, so that, for example, the anode foil in a modern 470uF 10V low impedance part will be higher gain than that of a 30 year old low impedance part of the same value, allowing shorter anode foils and smaller parts.

    If you're terminally curious, I think there are guys here who could fill in details where I used a very broad brush. In school profs usually start off with, "Assume an ideal capacitor." Real world parts are much more complex and have evolved over time.
    PeteS in CA

    Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
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      #3
      Re: Differences in Voltage rates with same capacitance

      Originally posted by PeteS in CA View Post

      Taking modern series parts from just one series, a 470uF, 10V part is likely to be lower in impedance and larger in size than a 470uF, 50V part. The size difference would be due to a thicker aluminum oxide dielectric layer, forcing the use of more foil (= longer strips) to get the same capacitance. The longer foils also affect the ESR and ESL, and therefore the impedance.

      OTOH, if you pick the parts from different series it becomes less predictable as to impedance, since the electrolyte is conductive, and the conductivity of different electrolytes varies.

      Then there's the 1991 vs. 2017 parts. The foil with the aluminum oxide layer formed on it is the anode (+) foil. The cathode foil is simply a conductor that "connects" to the conductive electrolyte. Anode foils are not perfectly smooth. They are etched so that there are hills and valleys that the oxide layer can follow, increasing the effective surface area or the foil ("gain"). Lower voltage foils are higher gain, since the thicker higher voltage oxide layer would just fill in tightly packed "valleys". Foil etching has been going on for decades, but etching techniques have improved over that time, so that, for example, the anode foil in a modern 470uF 10V low impedance part will be higher gain than that of a 30 year old low impedance part of the same value, allowing shorter anode foils and smaller parts.

      If you're terminally curious, I think there are guys here who could fill in details where I used a very broad brush. In school profs usually start off with, "Assume an ideal capacitor." Real world parts are much more complex and have evolved over time.
      Thank you so much, PeteS in CA!!

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