Electronics > Metrology

Film and Ceramic Capacitor Leakage Current

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chuckb:
I have been using my Keithley 617 Electrometer to measure the leakage current of large Electrolytic capacitors for several years. It has an internal +-102VDC source for biasing the Capacitor Under Test.
I was working on an error budget and I needed to know the actual leakage current of some small filter capacitors. I ran into some surprises with C0G ceramic caps and PE film caps.

The AVX and TDK C0G caps are very low leakage. Other brands of C0G have 20x more leakage and a large Dielectric Absorption. To be fair the leakage of the other caps is within their specifications. However, if you want some very good caps, see the attached pdf.

I do not have the time or budget to test all available brands and configurations. This is just what I have measured.
NOTE: This article is just to caution you to check all your components before you use them in critical applications. I just did a sample from one batch of parts. I may have a bad batch or a great batch of parts.

I looked into some WIMA film capacitors and was surprised at the rated leakage currents. I simply had not researched them before.
The WIMA MKS2 data sheet states >1000 Megohm-uF for the 6.8uF 50V part. I take that to mean over 147 Megohm or less than 68na of leakage at 20 deg C at 10V. Well, that’s a lot more than I assumed.

When I checked the WIMA MKS2B046801M00JS, 50V 6.8ufd small red film (Polyester film, PE) cap they 30 minutes it has 1500pa of leakage with just 10V applied at 27 deg C. After 12 hours the current had settled to 650pa of leakage. With 50V it had 22,000pa after I let it settle for 30 minutes.

I spent the next week checking a wide selection of new small capacitors. Then of course, I had to expand the testing to two temperatures.
When I warmed the MKS2 cap to 60 deg C (the temp in circuit) the leakage was 5.5na at 10V. With 50V it was 259na, wow.

A physically larger Panasonic 100V 10uF ECQ cap (PE) had 50pa a 10V. This settled to 10pa overnight at room temp. At 60 deg C the leakage current was 150pa at 10V.

What are your experiences with small (<100uF) capacitor leakage current?

bsw_m:
Time ago I'm measured leakage of elcap Epcos B41859 100uF 35V. After 1 hour this cap has leakage 180nA at rated voltage and 11nA at 10V.
I can add measurement results as they are carried out.
To measure I'm using V7-49 electrometer.

Kleinstein:
It is really difficult to tell apart true leakage and dielectric absorption. The settling over time is a characteristic of dielectric absorption current.  When testing with an applied external voltage source, one also has to care about drift of the voltage source - this would look like additional current.
A way to separate leakage from DA would look like first recording the apparent leakage with voltage applied to the capacitor, keep the capacitor charged for a longer time (e.g. 10 x the initial test, e.g. over night) and than discharge the capacitor and measure the apparent current from charge recovery after the same time. The 2 nd current would be a approximately (lower limit) to the DA contribution in the first test.

I have tested few small (2.2 nF)  C0G and PP , PS caps and found about comparable DA. The TDK brand C0G was considerable (e.g. 5-10x) lower DA.  Over the time scale tested (100 µs to 40 ms) the DA is dominating over leakage.

Polyester film is way higher DA than PP or C0G. So it can take considerably long time (e.g. more like days) to really see leakage.

bsw_m:
Murata RPER71H104K2S1A03A after 5 hours settling time: 29pA at rated voltage. But this cap have big DA.

bsdphk:
When I did something similar, I found that a lot of the actual leakage was crepage across the exterior plastic surface of the capacitors.

Wash the capacitors in isopropanol and distilled water and measure again, without touching them with your fingers.

The lowest leakage I found were high voltage (>=500V) wide lead-spacing (37.5mm) film capacitors.

Art of Electronics has useful wisdom on this topic.

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