Lowering ESR can be bad?

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  • Koda
    Badcaps Veteran
    • Aug 2011
    • 317
    • Macedonia

    #1

    Lowering ESR can be bad?

    Hey guys in one of the posts here someone (can't remember who) mentioned that in some cases lowering ESR can be a bad thing so I'm wondering in which cases that might be since everyone here suggests low ESR caps for replacements.
    Guns don't solve problems. I'll take 12
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: Lowering ESR can be bad?

    Originally posted by Koda
    Hey guys in one of the posts here someone (can't remember who) mentioned that in some cases lowering ESR can be a bad thing so I'm wondering in which cases that might be since everyone here suggests low ESR caps for replacements.
    Probably PCBONEZ.
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    Comment

    • momaka
      master hoarder
      • May 2008
      • 12170
      • Bulgaria

      #3
      Re: Lowering ESR can be bad?

      It depends on the circuit.

      With switching PSUs, you DON'T want to change the ESR too much. Reason being is that the output filters in these power supplies are tuned circuits built to filter certain frequencies that the PSU produces. Change the ESR too much, and that tuned circuit may become unstable or pass much more ripple and noise than it should.
      Of course, some PSUs are more tolerant than others. LCD monitors and PSUs with very small or no inductors in the filtering circuit are usually more tolerant when you use caps with lower ESR that the original ones. In contrast, PC PSUs almost always are not. They will still likely work, but they will be passing more ripple.

      With motherboards, it depends where the caps are located. Caps in CPU VRM can safely be replaced with ones with much lower ESR without side effects. In fact, this is one place where very low ESR is beneficial.
      Outside of VRM, it can be hit-and-miss. In most cases, caps with lower than the original ESR will likely work fine too.

      Comment

      • Longbow
        Badcaps Veteran
        • Jun 2011
        • 623
        • USA

        #4
        Re: Lowering ESR can be bad?

        I disagree. Lowering ESR won't necessarily change Xc, capacitative reactance. Of concern to designers is the inductive reactance of the secondary which is reflected back into the primary, and is important for proper selection of the switching device. I do agree that arbitrarily changing part values in a complex smps is not a good idea.
        Is it plugged in?

        Comment

        • KeriJane
          Mac Enthusiast
          • Sep 2008
          • 681
          • USA

          #5
          Re: Lowering ESR can be bad?

          I noticed once that replacing cheap caps like Teapo and CapXon with NCC and Nichicon low ESR caps increased ripple.

          It was in the output of a PC PSU and is probably somewhere in the forum.
          This seems to support the argument that these circuits are tuned to parts that have specific characteristics, even if they are of poor quality.

          So the burden is on us to find stable, reliable caps that operate very similarly to the cheapies. Except for the short lifespan that is.
          The More You Learn The Less You Know!

          Comment

          • japlytic
            Badcaps Legend
            • Oct 2005
            • 2086
            • Australia

            #6
            Re: Lowering ESR can be bad?

            I've seen an application circuit for an LT1184F CCFL controller which recommended an electrolytic capactior with an ESR of 0.5 ohms or greater at the Royer pin (pin 13) to prevent damage to the high side sense resistor in the controller due to surge currents at turn-on.

            Basicially, this depends on the application.
            My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

            Comment

            • Koda
              Badcaps Veteran
              • Aug 2011
              • 317
              • Macedonia

              #7
              Re: Lowering ESR can be bad?

              Well I need to change 2 caps on a KTC 19" LCD power supply. The caps are located near the ribbon cables that go to the logic board. The originals (Capxcon) have ESR of 0.6 and I want to replace them with Panasonic M equivalents but those have ESR of 0.2. Would it be ok??
              Guns don't solve problems. I'll take 12

              Comment

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