Capacitor Leakage current

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Hi,
Whenever I check electrolytic leakage current and compare to the manufacturer's specification for leakage, I get results that are not similar.

What are the units used in the standard leakage formula?

Leakage = factor * V * C
usually I see spec quoting IL=0.02VC

using Amperes and Volts and Farads, I often get the factor coming out better than F<=0.00001. This seems so much less leakage that I always suspect I am doing something wrong.

Help !
 
Nippon Chemicon LXZ ALUMINUM ELECTROLYTIC CAPACITORS
Leakage Current
I=0.01CV or 3uA, whichever is greater.
Where, I : Max. leakage current (uA),
C : Nominal capacitance (uF),
V : Rated voltage (V)
(at 20C after 2 minutes)

Measuring temperature and voltage influence the leakage
current. The leakage current shows higher values as the
temperature and voltage increase.

In general, the leakage current is measured at 20C by applying
the rated voltage to capacitor through a resistor of 1000 Ohms
in series. The leakage current is the value several minutes later
after the capacitor has reached the rated voltage. The catalog
prescribes the measuring temperature and time.

The text above is from Nippon Chemicon publications.
The last thing capacitor manufacturers want is part
rejection based on leakage. Their parts typically
perform 100 times better for leakage than the
datasheet specifies.

Example 1000uF 16V LXZ Capacitor Leakage
I=0.01(1000)16=160uA
 
Since leakage is proportional to rated voltage, I have a question about leakage during actual use.

Take a capacitor rated at 50V. Lets assume that maximum leakage is specified as 0.01CV.

I understand that if this capacitor is used up to its rated voltage, leakage should not be greater than 0.01CV. But then, you have taken V to its maximum value.

So comes the question: does leakage depend on working voltage?

For example, take a 100uF, 50V capacitor rated for maximum leakage of 0.01CV. Then, it should be around 50uA. But if you use this cap under voltages that don't exceed 10V, would maximum leakage be 10uA, or still 50uA? :rolleyes:
 
I think it may depend on whether the cap has been reformed to full maximum voltage and how long since it was reformed.


I am pretty sure that a freshly reformed to 50V capacitor will have a leakage <<<<0.01CV @ 10V
Whereas a long time stored and not reformed since manufacture electrolytic will, maybe, eventually meet the <=0.01CV specification after many hours/days/weeks/months of in circuit use at it's very low operating voltage.
eg. the the DC blocking cap in the NFB may be rated for 16V, or 63Vdc, but in circuit it sees ~20mVdc. What is the leakage current? How long does it take for the leakage current to stabilise?
What is the equivalent resistance for that leakage current?
How much will the output offset vary during the "in circuit" reforming due to the NOT equal to unity, DC gain of the amplifier?
 
I think Andrew has it right. Leakage current in an electrolytic is a function both of current voltage, and the past history. It increases with current voltage, but reduces with past voltage. The oxide film is always slowly degrading, and the leakage current rebuilds it. Therefore it might be concluded that given a fixed voltage the current would eventually settle at about the same level whatever that voltage is. The current might depend more on temperature than voltage, as increased temperature will probably cause faster oxide degradation and so need more current to maintain it.
 
AX tech editor
Joined 2002
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Resurrecting an old thread (and yes, I know Andrew, sadly, is no longer among us).

Issue is whethger the leakage current of an electrolytic varies with applied voltage.

For instance, take a cap with this spec:

After 1 minute's (for case size 10 × 12.5 or smaller) or 2 minutes' (for case size 10 × 16 or larger) application of rated voltage at 20°C, leakage current is not more than 0.002CV or 0.2 (µA) whichever is greater.

If I use this cap at say 1/5 rated voltage, will the leakage be lower (albeit maybe not 1/5th)?

In the same capacitor series, there is one with 1/5th of the rated voltage but it has the same limiting 0.002CV rating. But if I look at these two caps side by side, they both have 0.002CV at rated voltage, then can I not expect a lower leakage when I dial the higher voltage one down to the rated voltage of the lower voltage one?

Jan
 
Hi,
Whenever I check electrolytic leakage current and compare to the manufacturer's specification for leakage, I get results that are not similar.

What are the units used in the standard leakage formula?

Leakage = factor * V * C
usually I see spec quoting IL=0.02VC

using Amperes and Volts and Farads, I often get the factor coming out better than F<=0.00001. This seems so much less leakage that I always suspect I am doing something wrong.

Help !


No, you are not realizing the leakage figure is for full voltage across the whole temperature range and age of capacitor - new caps will be much better, caps at room temperature much better than hot ones. When a cap has lost form (after storage, or if used near 0V), reforming it will cause much larger currents than leakage until the oxide layer has rebuilt, but that can be a minute or two so seldom an issue.


Pretty much any form of leakage current in any device rises precipitously with temperature.
 

PRR

Member
Joined 2003
Paid Member
jan> whethger the leakage current of an electrolytic varies with applied voltage.

https://tadiranbatteries.de/pdf/app...perties-of-modern-electrolytic-capacitors.pdf page 7

Altogether, leakage varies with time and temperature MUCH more than with voltage. If you are leak-sensitive, you need a long pre-charge and a cool room.

EDIT: interestingly, it appears current falls off faster than a pure resistor. Of course at some point above Vmax it rises real fast.
 

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