XPost: sci.electronics.design   
   From: cd@notformail.com   
      
   On Mon, 04 Mar 2024 09:16:53 -0800, John Larkin    
   wrote:   
      
   >On Mon, 04 Mar 2024 15:55:53 +0000, Cursitor Doom    
   >wrote:   
   >   
   >>On Sun, 03 Mar 2024 18:28:46 -0800, John Larkin    
   >>wrote:   
   >>   
   >>>On Mon, 04 Mar 2024 00:31:27 +0000, Cursitor Doom    
   >>>wrote:   
   >>>   
   >>>>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?   
   >>>   
   >>>Power supply and DVM.   
   >>   
   >>But then how do you determine - given that electrolytics come in all   
   >>sorts of votlage and temperature ratings, capacitance values etc - how   
   >>much leakage current in each case is "too much" leakage current   
   >>rendering the cap unsuitable for use?   
   >   
   >That's for you to decide. No instrument is going to have red and green   
   >LEDs to tell you if a cap is suitable for your circuit.   
      
   That's not how cap testers work, though. They take virtually none of   
   the following into account:-   
      
   >Gross capacitance   
   >C vs voltage   
   >C vs temperature   
   >Leakage vs temperature and voltage, both polarities   
   >Dielectric absorption   
   >Failure voltage or current   
   >ESR vs temperature   
   >ESL   
   >Lifetime   
   >Power dissipation/cooling   
   >Solderability/washability   
   >   
   >One should measure or calculate whichever of those might matter in   
   >your circuit.   
   >   
   >Post your circuit and we can talk about it.   
      
   No circuit involved. The question relates to generic smoothing caps of   
   linear power supplies.   
      
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