Measuring capacitor leakage current

How is capacitor leakage current measured?

Even after fully charging 2200uF cap to 3V, when I placed my
multimeter in series it displayed about 1uA current.

Is it the capacitor leakage current.

But after half an hour current surprisingly dropped to 0A.

Thanks to all

Animesh Maurya

e-mail address is invalid

 

Animesh Maurya wrote...

No, not leakage current. What you were observing is due to
dielectric absorption. This effect means that portions of
the capacitor remembered the previous voltage (discharged)
and were responding more slowly to the voltage change.

Thanks,
- Win

whill_at_picovolt-dot-com

 

I read in sci.electronics.design that Winfield Hill

While that is strictly correct, that 1 uA current has just the same
effects (if any) on your circuit as if it were leakage current. The only
difference is that after a while, it disappears, as you have observed.

 

2200uF at 3 volts sounds a lot like an electrolytic capacitor to me.
Most likely an aluminum electrolytic. In that case, the 1uA current may be
related to "forming" currents. If it is forming current, then it will likely
not be the same 1uA after one or more charge/discharge cycles.

Jim

 

A quote from the CDE Application Guide Aluminum Electrolytic Capacitors:

"DC Leakage Current (DCL)

DC Leakage Current is the DC current flowing through the
capacitor with the rated voltage applied. The value of leakage
current depends on the voltage applied, the charging
period and capacitor temperature.

DCL Method of measurement

Measure leakage current at 25 °C with the rated voltage
applied through a protective resistance of 1000 Ohm in series
with the capacitor in the measuring circuit. Five minutes
after the application of voltage, the leakage current is not to
exceed the maximum value indicated in the specification."

 

0.0000000 Amps is a very small current, requiring some very accurate
equipment to measure.

Your method is probably adequate, however.

RL

 

If this current is due to dielectric absorption then what is the cause
of leakage current.

Is there any specific term to define the above current, or we simply
call it dielectric absorption current.

Thanks again,

Animesh Maurya

 

Animesh Maurya wrote...

Right, here's a typical model, the trick is knowing
the R values. :>)

| C/2
| ----+--------||--------+-----
| | |
| +----||----/\/\----+ C/4
| | |
| +----||----/\/\----+ C/8
| | |
| +----||----/\/\----+ C/16
| | |
| +----||----/\/\----+ C/32
| | |
| +----||----/\/\----+ C/64
| | ... etc ... |
| | |
| '------/\/\--------'

The bottom element is leakage, and is not directly
related to the other values.

|

Thanks,
- Win

whill_at_picovolt-dot-com