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Fake polypropylene capacitors from China?

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MasterT:

--- Quote from: Krampmeier on January 22, 2019, 09:18:02 pm ---///
EC/EN 60384-1 method
I charged each capacitor to 10.0 V for about 10 minutes (I am way too impatient to wait a full hour), and shorted the whole pack of them for 10 seconds directly after that. Then I disconnected the caps and let them sit without any connections. After 15 minutes, I measured the residual voltage using a Keithley 2010 DMM in 10 V range.

1 µ X7R: 0.138 V -> 1.38% (low, but still plausible)
1 µ Tantalum: 0.233 V -> 2.33% (plausible)
1 µ WIMA Polyester: 0.026 V -> 0.26% (plausible)
470 n Chinese PP: 0.076 V -> 0.76% (not plausible, should be 0.05 to 0.1% )

Conclusion

So it is very clear now, these capacitors are not what the seller advertises.
///

--- End quote ---

Some measurements I've done with my new project:
https://www.eevblog.com/forum/projects/absorption-insulation-capacitor-meter-arduino-based/msg2168257/#msg2168257

Capacitors tested at rated 100V, except HV ceramic (1kV) that I put in just for verification of the test gear, and CBB (630V).
My data for WIMA is different, (bought at Mouser) - well within spec. for polypropylene  0.05%.

Yellow-china is most likely polyester (Mylar) fake.


CBB also bought from China-ali, and do surprisingly well - same as WIMA MKP4. (Rated 630V - )


Ceramic - out of scale in 5 seconds.

Kleinstein:
One could check the dielectric from the torn open capacitor. PP film has a relatively low melting point. The likely alternative materials like polyester and polycarbonate are higher melting point. Usually PP caps are also physically larger than mylar ones. So the size will often tell.

There is a small chance that the caps could still be PP film, but just poor quality with way to much humidity inside or similar. If the production process is poor DA can be higher than the ideal film.

PS caps usually have better insulation than PP caps - one reason is that they are usually PS all the way to the leads, while PP caps are often encapsulated in some kind of epoxy and there may be some surface leakage there. Sill PP caps are usually good enough unless dealing with fAs.

Krampmeier:
I got a load of Wima MKP2 polypropylene last week, and also added a Panasonic ECWFA and some silver mica caps for comparison.

With the sourcemeter, I did not see any DA or leakage with neither of them. The 2461 is not as sensitive as MasterT's project, which I find realls awesome. A very simple design and great results!

The Wima MKP2-100 1,0µ polypropylene cap read 0.966 µF and Q=100 at 100 kHz, clearly better then the genuine MKP4 polyester or the fake PP from Amazon. The fake ones are much smaller than the genuine ones, so everything matches up.

I compared some 330 nF caps 10 100 kHz as well:
Wima MKP2-100 330N: C=326 nF, Q=265
Wima SMDID03330TB00KS00: C=342 nF, Q=420
Panasonic ECWFA 330N 250: C=333 nF, Q=340

The largest silver mica cap I got was 10 nF (CLEC brand), and it read Q=Overflow at 100 kHz and Q=1300 at 1 MHz. Even at 5 MHz, the old 4192A measured 11.5 nF and Q=235 for that one.

All the measurements were done with open and short compensation, but without a proper fixture and with an uncalibrated instrument. So the absolute values should be taken with a grain of salt.

floobydust:
Polystyrene are still in production, Xicon available from Mouser. Up to around 10nF and excellent for audio gear. I'd have to dig for the THD tests of various dielectrics, it was an Audio Precision rep that did the tests.

Doctorandus_P:
With what kind of a stupid meter are you measuring those things?
Is it able to put the axis on zero and have single digit numbers on the tick marks?  :box:

I'm jealous.

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