XPost: sci.electronics.design   
   From: cd@notformail.com   
      
   On Sun, 03 Mar 2024 16:22:12 -0800, John Larkin    
   wrote:   
      
   >On Sun, 03 Mar 2024 23:50:08 +0000, Cursitor Doom    
   >wrote:   
   >   
   >>On Sun, 03 Mar 2024 15:16:12 -0800, John Larkin    
   >>wrote:   
   >>   
   >>>On Sun, 03 Mar 2024 22:41:09 +0000, Cursitor Doom    
   >>>wrote:   
   >>>   
   >>>>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 electrolytic is hardly a perfect cap. After the theoretical cap   
   >>>charge, you might see some mA of leakage, tapering off to uA's after   
   >>>some minutes or hours.   
   >>>   
   >>>If the current ever increases, as it will at some voltage above rated,   
   >>>it's probably on its way to destruction.   
   >>>   
   >>>Get a power supply and an ammeter and experiment. Your capmeter is   
   >>>obviously not telling you much.   
   >>>   
   >>   
   >>   
   >>Just spotted the meter only covers up to 22,000uF!   
   >>we   
   >   
   >I don't trust C or L meters, especially for large C or L values, or   
   >cheap meters.   
      
   How would you test for leakage, then? Those Peak meters aren't cheap   
   and they've never let me down before. I suppose technically this one   
   hasn't let me down either since I was attempting an out-of-range   
   measurement. Perhaps the later models have expanded ranges; I'll have   
   to check....   
      
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