XPost: sci.electronics.design   
   From: bill.sloman@ieee.org   
      
   On 5/03/2024 2:50 am, Cursitor Doom wrote:   
   > On Mon, 4 Mar 2024 15:29:02 +1100, Bill Sloman    
   > wrote:   
   >   
   >> On 4/03/2024 5:03 am, Cursitor Doom wrote:   
   >>> Hi all,   
   >>>   
   >>> Using my Peak ESR/Capacitance meter, I was carrying out in-circuit   
   >>> checks on large electros in the linear PSU I've previously mentioned   
   >>> here. I was getting a lot of "in-circuit/leaky" warnings for two of   
   >>> them, so I pulled them out completely and am getting the same warning   
   >>> when they're checked out of circuit, which surprised me as it's   
   >>> unusual IME. Anyway, the leak would have to be very bad to result in   
   >>> ripple, would it not? AFAIK, the leading culprit for ripple is caps   
   >>> which have lost a significant amount of capacitance or else developed   
   >>> a very large ESR.  Do I have that right?   
   >>   
   >> What you have wrong is the imagined association between leakage and ripple.   
   >   
   > Eh? I did say leakage was probably about the least likely cause of   
   > ripple!   
      
   The error comes from imagining that the two were connected.   
      
   >> The "ripple" on the voltage across a capacitor reflects the charge that   
   >> is being taken out of and fed into the capacitor over the mains cycle.   
   >> More capacitance means smaller ripple.   
   >>   
   >> Leakage is just the current flowing through the oxide layer on top of   
   >> metal conductor surfaces inside the electrolytic capacitor. If the   
   >> capacitor has been un-used for a long time, some of the oxide layer may   
   >> have diffused away, making the capacitance and the leakage current   
   >> higher. Applying the working voltage will re-form the oxide layer by   
   >> making it a bit thicker.   
   >>   
   >>> I'd like a "second opinion" as it were on the leakiness of these caps.   
   >>> What's the best old-school method for testing for this? I just want to   
   >>> ensure the ESR meter isn't faulty (highly unlikely but the possibility   
   >>> must be eliminated to be sure).   
   >>   
   >> If an electrolytic capacitor hasn't been used for some time, it's going   
   >> to be  leaky. If you want to measure how leaky, measure the direct   
   >> current flowing through the capacitor as you increase the bias voltage   
   >> across it. It should drop as the oxide layer re-forms, perhaps over hours.   
      
   This might have been the information you needed, if you knew enough to   
   process it. The placement of your response suggests that you don't.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)