K72P-6 ultra low DA, DF capacitors - Page 1
Forum section: electronics / general

author: shodan@micron
author_rank: Contributor
timestamp: June 12, 2021, 01:29:46 am
content: void

author: bsw_m
author_rank: Frequent Contributor
timestamp: June 12, 2021, 12:28:52 pm
content: Some time ago I measured the leakage current and the dielectric absorption coefficient of the K72P-6 22nF 200V capacitor.The leakage was about 8fA at a test voltage of 50V.Dielectric absorption was below 0.02%

author: bsw_m
author_rank: Frequent Contributor
timestamp: June 12, 2021, 12:38:37 pm
content: Now I decided to measure the leakage of a capacitor accidentally taken from the box at nominal voltage.It turned out to be K72P-6 56nF 200V.Since I am going to see a leakage <1E-12A, a 1TΩ KVM resistor was connected in series with the capacitor to avoid noise gain amplification. The capacitor body has been grounded to avoid leakage through the insulators. I will publish the results after the readings have been established. Please consider the time constant of this RC circuit. For shortening the experiment time, before measurement capacitor was charged to nominal voltage by shortening series resistor.

author: TimFox
author_rank: Super Contributor
timestamp: June 12, 2021, 03:37:05 pm
content: How would you measure the dielectric absorption (DA) on capacitors of this quality? In audio circles, they are highly regarded.

author: bsw_m
author_rank: Frequent Contributor
timestamp: June 12, 2021, 06:01:03 pm
content: Quote from: shodan@micron on June 12, 2021, 02:55:52 pmTook a random capacitor and measured it with my Tesla BM595.I also decided to publish preliminary data on the measurement of the leakage current. As you can see, the readings are still not established, but the leakage current is about 1pA.

author: bsw_m
author_rank: Frequent Contributor
timestamp: June 12, 2021, 09:31:25 pm
content: I ended up measuring the leakage current of the 56nF 200V K72P-6 capacitor at nominal voltage (200V).This test took approximately 9 hours.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 12, 2021, 10:44:36 pm
content: Quote from: shodan@micron on June 12, 2021, 09:08:15 pmSo the russian standard for measuring DA is slightly different from the US one. In the US they charge very long, discharge for some 10-15 seconds and measure after some 15 minutes. So the procedures are similar the numbers are not directly comparable. Expect a slightly larger DA number from the US test.To get more information out from the test, one can do a very short (e.g. 1 s) discharge phase and than contineously measure the voltage rise. subtracting the voltage at the beginning is the same as doing a longer discharge.This at least works with a good voltmeter that does not add much bias. In the old times one may had to disconnect the meter for the waiting time. If the capacitor is small it may help to repeat the test with reversed polarity.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 13, 2021, 08:29:03 am
content: The US test standard (MIL-PRF-19978) calls for 1 hour charge, 10 seconds discharge and than looking for the voltage after 15 min (or the maximum if reached earlier in a more leaky capacitor). The difference to the GOST is about a factor of 2-3 in the time scale and a longer charge time at the beginning.For many capacitors DA tends to go up with the longer time scale and the longer charge time at the start also gives slight higher DA numbers, though not much.The faster russian test procedure is slightly more convenient, as it does not need input impedance of the meter as high.With very low absorption it is a good idea to connect the voltmeter only after discharging the capacitor. Otherwise one would include also dielectric absorbtion of the input capacitance of the voltmeter. So there should ideally be a switch (relais) at the voltmeter input. With a slightly different configuration one can use a single switch to short the meters input and do the charging / discharging at the other side of the capacitor.One can see the effect of the length of the discharge phase, by using a short discharge and record the data from the start. Except for very high DA caps the recovered voltage just add up. So instead of a longer discharge, one can use the voltage at that time as the new "zero". So the information for a longer discharge time is already in the curve.In this repect the US way with a long charge time is more universal. With a long charge time a single measured curve could cover different time scales in a single test.