XPost: sci.electronics.design
From: cd@notformail.com
On Tue, 5 Mar 2024 20:58:49 +1100, Bill Sloman
wrote:
>On 5/03/2024 8:17 pm, Cursitor Doom wrote:
>> On Mon, 04 Mar 2024 16:41:40 -0800, john larkin wrote:
>>
>>> On Mon, 04 Mar 2024 23:03:05 +0000, Cursitor Doom
>>> wrote:
>>>
>>>> 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
cd@notformail.com>
>>>>>>>>>>>>> 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.
>>>
>>> Where in a circuit is a "smoothing" cap? Oops, sorry, there is no
>>> circuit.
>>
>> Yes, there's no circuit. Marconi/Aeroflex never published one and and
>> a lot of their designs are still under wraps. It's a real PITA.
>
>If you are repairing the units, you should be able to trace that bit of
>the circuit. It isn't going to be complicated.
Ordinarily it would be a piece of cake, but they seem to have gone out
of their way to make access as difficult as possible.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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