Once more, capacitor leakage tester - Page 1
Forum section: electronics / testgear

author: Veketti
author_rank: Regular Contributor
timestamp: April 18, 2025, 06:18:49 am
content: Dear All,I've tried to find the answers to capacitor leakage questions. Hopefully someone can open these:1. I've read that capacitor leakage is capacitor parallel resistance. LCR meter like DER DE 5000 has in capacitance measurement secondary measurement of ESR and Rp. Is this Rp the same than capacitor leakage?2. Will leaky capacitor show signs in LCR meter capacitance, ESR, Q, D, Rp values as well?3. If not does it matter to most, if you're not working on Audio equipment (perhaps old tube amps etc)?Bit background. I've subscibed to Mr Carlsons Patreon and was about to build his leakage tester, but it seems some of the components were already obsolete without direct replacement. Then found this wonderful Canadian/Frenchman who had reiterate the design with modern components and a display. As he had shared the gerbers, BOM and firmware I built that. Now just need to start interpreting the results correctly.Thank you.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 18, 2025, 08:19:37 am
content: For truly accurate leakage testing you need to test at the intended operating voltage, which is why the more advanced capacitor test equipment can output some pretty high voltages. Also such equipment tends to be older, because it's not super critical in modern equipment generally (with the exception of some more sensitive TE I suppose), and capacitors are cheaper to replace shotgun style.It's a bit niche these days, and not too difficult to do with a decent PSU and DMM, so expensive dedicated capacitor testers just aren't worth making any more, it seems

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 18, 2025, 08:22:04 am
content: Nicekit

author: indman
author_rank: Super Contributor
timestamp: April 18, 2025, 09:52:16 am
content: Quote from: Veketti on April 18, 2025, 06:18:49 amThe most important difference that you must learn and remember first - is that the leakage test is conducted atDC currentand preferably at the operating voltage of the capacitor under test!LCR meters test capacitors using a low amplitudeAC signal!

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: April 20, 2025, 05:39:21 pm
content: At some point the mechanism for DC leakage current will affect AC measurements, but the measurement of EPR (effective parallel resistance) is related to the AC losses of the cap, just like ESR when you make a series measurement. Don't expect the EPR to agree with what you calculate from a DC leakage measurement. Also note that DC leakage measurements of electrolytics will change over time, typically starting out a bit high, then slowly dropping to some reasonable value. Decent small electrolytics will usually drop to <5 uA within 5-30 seconds. If they're old and nearing EOL, it might take several minutes and they might never drop as far, though they still work in the circuit.

author: TimFox
author_rank: Super Contributor
timestamp: April 20, 2025, 07:31:39 pm
content: At a given frequency, the loss of a capacitor can be expressed as either a series resistor (ESR) or a parallel resistance (or conductance, reciprocal of resistance).For a physical component, if one of these (e.g. ESR) is constant with respect to frequency, then the othercannotbe constant.Some capacitors are approximately a parasitic ESR in series with a lowish-loss capacitance, and the resulting calculated parallel resistance is inversely proportional to frequency, giving zero leakage at DC. However, the actual unit has further leakage in parallel with that model at DC.Other capacitors have a dielectric whoseQ=Rparallel/XCis roughly constant, and the parallel resistance again goes infinite at DC, whereXCis infinite.As stated above, LCR meters operate at reasonable frequencies, typically audio range for devices such as the DE-5000. They may be capable of a separate DC resistance measurement, depending on design.