XPost: sci.electronics.design   
   From: cd@notformail.com   
      
   On Tue, 5 Mar 2024 12:52:04 +1100, Bill Sloman    
   wrote:   
      
   >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.   
      
   How's the weather on Planet Sloman today, Bill?   
   >   
   >>> 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.   
      
   Your remarks were so trite they didn't bear a response. Everyone here   
   knows electrolytic caps need to be re-formed if they've been unsused   
   for any significant length of time. It's vintage scope repair 101 and   
   even you must be aware restoring vintage scopes is my prime interest   
   in the subject. God knows I've posted enough about it over the years!   
      
   --- SoupGate-Win32 v1.05   
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