XPost: sci.electronics.design   
   From: cd@notformail.com   
      
   On Sun, 03 Mar 2024 13:28:05 -0800, John Larkin    
   wrote:   
      
   >On Sun, 03 Mar 2024 18:03:51 +0000, 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?   
   >>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).   
   >>   
   >>CD.   
   >>   
   >>PS: the aforementioned caps are 47000uF 16V Vishay ones - and I have a   
   >>brand new spare that's also testing as "leaky"!   
   >   
   >How leaky? You could apply 16 volts and measure current for a while.   
   >It will typically taper off over some minutes or hours.   
      
   Well, the 'perfect cap' in series with an ammeter will cause an   
   initial surge of current which will taper off over time and eventually   
   settle at zero. But a leaky cap will continue to pass a small amount   
   of current, I would assume, indefinitely? Again, I would guess that a   
   real-world cap in good condition would continue to pass a tiny amount   
   of current - a negligible amount?   
      
   >An electro that hasn't been used for some time will be leaky at first.   
   >That's normal.   
      
   Good point.   
      
   >   
   >Expect a 47m cap to leak more than a 47u. Your capmeter may not know   
   >the value.   
      
   It wasn't able to measure the capacity at all. It did report a very   
   low ESR commensurate with a large value electrolytic. But that was all   
   it was able to measure.   
   >   
   >It's interesting to test elec and polymer caps, current vs voltage   
   >over time, forward and reverse.   
      
   Indeed.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)