XPost: sci.electronics.design
From: cd@notformail.com
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?
>
>>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....
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
|
