Electrolytic Leakage Measurements and Discussion - Page 1
Forum section: electronics / projects

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 01:42:06 pm
content: This discussion started over here:https://www.eevblog.com/forum/metrology/lflna-80/and from here:https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg6016443/#msg6016443Our experience dates back in 70s when we were developing the MSP (MILES Signal Processor) which had an Integrating LNA requiring a large integrating capacitance. We tested numerous large value electrolytics for leakage current and ended up using the usual wet-slug tantalum types. Electrolytics have improved since then and they seem to last longer and also have much lower leakage, and lower cost!!Some folks have made leakage measurements on large valued electrolytics and the results are impressive, we've made measurements on a Rubycon 1500uF mentioned in the above link. EC8010, iMo, and a few others seem to have a good grasp of electrolytic capacitor behavior and maybe even construction.We're looking to collect information and measurements relative to large electrolytic construction and specific to leakage behavior for application in low frequency LNAs mentioned in the links above. How are different capacitor sources different in internal construction, processing and overall makeup, sure we can use Google and AI but prefer to hear from others.Measurements from others are encouraged, however please only comments about the scientific/chemistry behavior and construction of said capacitors should be left to thosecapacitor experts, not the usualself proclaimed Google/AI reading expert, trying to keep the "noise" downAnyway, this is to help with an understanding for use with low noise LNAs mentioned above and a little knowledge "gleaned" from thecapacitor expertsis welcomeOur Rubycon ZLH 1500uF 16V is now showing ~3na leakage SD of 600pa with 16V DC bias after ~ 70hrs and still following a very slow downward trend, other measurements welcome!!Best

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 23, 2025, 04:38:58 pm
content: I did some measurements on the electrolytics "leakage" v time about 17 years ago, and kept some of the results. With capacitors there are two components to the "leakage" current, one is a dielectric absorption (DA) which looks like an exponentially decaying current and at some point the current stops getting smaller and stabilizes at what can be considered the actual leakage current. The time for reaching this point could be tens and sometimes possibly hundreds of hours, if not more. Here are some of the graphs I've plotted all these years ago. Please excuse a rather crude presentation, the time scale is 2s/point on all graphs (i.e. 1800 points = 1h), the vertical scale is in Amps. At that time my measurement capabilities were not as advanced as today, so I might repeat this kind of experiment, perhaps with a number of various capacitors.CheersAlex

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2025, 04:52:10 pm
content: Can you provide the means for how you are conducting said measurement so others can reproduce the results, as well as test other capacitors and compare to the caps that have already been measured?

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 05:22:14 pm
content: Is this directed to us or Alex?Ours is just a Lab Power Supply (GPP4323) set to 16VDC and DUT in series with DMM (either KS34465A or DMM6500) set to lowest current range (1ua and 10ua respectively). KS34465A is set to 100NPLC, mx + b scaling, Slow Filter and Statistics. DMM6500 set to 10NPLC (doesn't go past 15), mx +b scaling, 10 Repeat Filter and Statistics.No shielding, just in open air on our test bench with banana leads.Best

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 05:25:54 pm
content: Alex,Those are interesting, thanks.We are "seeing" single digit na leakage levels now, likely due to the improved manufacturing process or maybe different/better chemistry?Best

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 23, 2025, 05:48:03 pm
content: Quote from: mawyatt on August 23, 2025, 05:25:54 pmAs far as I remember, I've used the HP3678A multimeter at 300mA DCI range and a bench DC supply, so the low current resolution was pretty bad, essentially 100nA was the limit. For really large caps, like 10000uF 63V BNC tested at 60V the results were good, but not so for smaller caps after the initial few hours. I will repeat the experiment using K34465AM to measure current (and if that is not enough I'll use the Keithley 617) and HP3245A as a 10V source. The main reason I've uploaded these graphs is to show the exponential part and how it depends on the state of the capacitor. There is also a temperature dependency, obviously, so to get useful results takes time and effort.CheersAlex

author: iMo
author_rank: Super Contributor
timestamp: August 23, 2025, 07:52:56 pm
content: Perhaps a simple "Elytcap Leakage Meter" or ELM should be designed such people may do their own measurements without a need for expensive meters.Like the simple "ESR" meters, or simple "Null Meters", etc.All you need is a "quiet" voltage source and a suitable opapm wired as a "nano-ammeter", like OPA145 or LMC662 and a like. With 10Meg in feedback you will get 10mV/nA at the output, what is a good resolution for an electrolytic caps measurement.So for example: a 12V battery, a 5V reference (any), an OPA145 (or similar), 10Meg resistor, a virtual ground (any cheapo opamp), perhaps a trimmer, 2-4 resistors, 3-4 capacitors, and that is all.And you will get 10mV/nA at the output..

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2025, 07:56:36 pm
content: Quote from: iMo on August 23, 2025, 07:52:56 pmProbably a good idea. Me personally, I have a collection of various decent opamps and passives (pulled from PCB's), but not any expensive equipment that would be able to easily measure + quantify the leakage current (in nA) of a capacitor. Or at least, not that I can immediately think of.

author: iMo
author_rank: Super Contributor
timestamp: August 23, 2025, 08:20:37 pm
content: This is the simplest stuff I've found in my ltspice archive - after trimming with the pot you will get 10mV/nA..If you have got 100Meg resistor handy you will get 100mV/nA with the same circuit.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 23, 2025, 09:53:23 pm
content: Quote from: iMo on August 23, 2025, 08:20:37 pmAnd now calculate the noise gain of these circuits. At the very least C1 should be connected between the output and the inverting input, and increased to something like 1uF... . A TIA circuit is not that good if your source is a large capacitor. Another way of taming it is to add a considerable resistance in series with the DUT, something like 1M. That would increase the charging time constants considerably though, even with a couple of protection diodes added to the input.CheersAlex

author: iMo
author_rank: Super Contributor
timestamp: August 23, 2025, 10:05:24 pm
content: So let us come with something different, but simple. Allocating expensive gear for watching the electrolytics bubbling and sparkling is not the best approach, imho..

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 23, 2025, 10:22:09 pm
content: Any cheap multimeter with 10M input resistance and 100mV range is a perfectly capable nanoampermeter. Any scope with 1M input will give you enough range to see a few nA... . A logging meter is good for the main DA time constant evaluation, so you may estimate where the current could be in a day after 10min or so...CheersAlex

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 23, 2025, 11:04:43 pm
content: It would make sense to build a fixture to run-in and measure the leakage on a number of capacitors, to select the best between various types/makes, and select the best devices of the best variety later...CheersAlex

author: 2N3055
author_rank: Super Contributor
timestamp: August 23, 2025, 11:08:31 pm
content: I agree with Alex.200mV range on DMM with 10MΩ input gives you 10mV/1nA ratio.Everybody has one, even better handhelds like BM869S is more than enough to measure reasonably well.Of course, bench multimeter is better because long measurements and logging might be battery killer.I used both Rigol DM3065 and new SDM4065A-SC and they do well.Both have stats and trend plot to see how it changed.SDM4000A is obviously better because better interface, but you can also log from meters on computer and do math there.I think that would be good common ground that many have.A voltage source also should be relatively stable and low noise. But not very critical.For source i use my AOIP calibrator. If I change voltage 10µV, obviously reading changes 10µV, i.e. 1pA.Even 1 mV will yield 100pA of change. So any decent linear PSU will do.That is short term stability, i.e. noise. Obviously absolute voltage value is not important, except to keep it in the vicinity of target voltage of interest. So 10V (or whatever) does not have to be very accurate.I was even thinking of making a small fixture that would have it's little voltage source, individual 10 MΩ shunts per capacitor and use DMM in high impedance mode together with switching unit (my 4065A is SC with scanner with 12 voltage channels) so I could measure 12 capacitors at the same time. Or even better, 10 capacitors and 2 channels for 1 temperature measurement and one voltage measurement of the source.....Voltage source could be just a 12 V battery and some decent low drop regulator. Power consumption would be negligible.. Mostly regulator quiescent current...Best,EDIT:While I was writing this, Alex wrote about fixture... hehehe...

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 11:47:07 pm
content: Quote from: Alex Nikitin on August 23, 2025, 10:22:09 pmWas getting ready to post about using an entry level DSO. Some have sweeps of 1000s/div, so as long as 10,000 second sweep (~2.8hrs), have 500uv/div (500pa/div) sensitivity, have statistics and even filters!!So one can watch the slow trend, get the leakage down in na regions with relevant statistics all from just a modern entry level DSOBest,

author: Hydron
author_rank: Super Contributor
timestamp: August 24, 2025, 05:08:15 pm
content: Got a couple caps cooking on my K236/237 SMUs right now, as I think it's time to build a LNA for Vref testing. 1k in series makes the SMUs stable into a big capacitor load, and both bias and measurement are obviously super easy.Got one cap (2200uF 50V, got hundreds of them) down to ~10nA in about a day but it's bouncing around a lot, already rejected a couple others when leakage didn't drop as quick.Not the quickest way to run through a bunch of caps, probably should recruit my electrometer as well for a third tester (DMMs are busy with other testing), and I will hopefully have another K238 SMU in a few weeks (got an irresistably cheap but faulty one from ebay waiting for me at the US office, so depends on being able to fix it). A scanner card is realistically probably the sensible answer though! Hopefully I find a good cap before needing to worry about testing capacity, though it would be a good reason to finally build my DMM6500 custom scanner.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 24, 2025, 07:58:43 pm
content: I use a General Radio 1617A. The lowest leakage scale is 60 uA. Most small electrolytics, say under 220 uF and under 63 VDC will come down to 5 uA in a couple minutes if they're any good. Maybe down to 2 or 3 after 10-15 minutes. Low leakage series will be "zero" and I've never bothered to set up to see how low they are. That's just a general average over probably hundreds of caps over many years.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 24, 2025, 10:39:24 pm
content: Here is the result for Panasonic FC 4700uF 25V 105C capacitor I had in storage for about 5-6 years. I've omitted the first 3 hours or so to make the graph easier to read (the initial current after charging was ~50uA and after an hour it dropped down to 1.3uA). It looks like I've just caught the start of the flat "leakage only" state in the last couple of hours, at about 50nA, I'll run the log overnight just to see if that is the case.10V sourced from HP3245AM, the current measured by Keysight 34465AM at 1s intervals, 10NPLC, the temperature of the capacitor was about 26C +/-2C.CheersAlex

author: TimFox
author_rank: Super Contributor
timestamp: August 24, 2025, 11:35:02 pm
content: Can you re-plot the data on a log-log graph (logIvs logt)?

author: mawyatt
author_rank: Super Contributor
timestamp: August 25, 2025, 12:21:36 am
content: Quote from: 2N3055 on August 23, 2025, 11:08:31 pmAgree, except one should check the PSU Voltage "noise & ripple" levels as this will couple thru the large valued DUT capacitor and show up as "leakage current noise". Those with SMUs are well setup for these measurements, we don't have any SMUs so must rely on what we have in house.The PSU we used is the GPP4323 but the SPD3303X would probably work just as well. The GPP4323 shows ~80uv SD "noise & ripple" and almost no drift after warmup at 16VDC unloaded output. So all our measurements show whatever contribution this PSU adds to the final measurements.Anyway, seems there are many options to gather the effective long term leakage currents from these modern large value electrolytics, and they seem to be quite low indeedBest

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 25, 2025, 02:23:59 am
content: Quote from: TimFox on August 24, 2025, 11:35:02 pmOKCheersAlex

author: TimFox
author_rank: Super Contributor
timestamp: August 25, 2025, 03:34:02 am
content: Thanks. One last request: semi-log graph, log(I) vs. lineart?

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2025, 06:08:26 am
content: Quote from: mawyatt on August 25, 2025, 12:21:36 amYes that is why I said (relatively) low noise. But capacitor leakage is very slow changing process so you can average the snot out of data as far as the leakage value is concerned.Super high precision is also not needed or possible because tempco introduces so much change.. Like I said, capacitors can easily detect me entering the room by change in temperature. It is clearly visible in trend plot in µV range.So I go for order of magnitude estimations as a decent result. Is it single digit nA, or 100s of nA, or few µA? Today I read 34mV on the same capacitor (that used to be anywhere from 45 to 65mV) which means 3.4 nA instead of 4,5 to 6.5 nA. Temp is 26,4 °C instead of ~ 27-28°C.Still, that is single digit nA for a general purpose elco from average manufacturer.Chemistry and manufacturing process sure has gone the long way in last 20-30 years..

author: iMo
author_rank: Super Contributor
timestamp: August 25, 2025, 06:51:09 am
content: Quote from: 2N3055 on August 25, 2025, 06:08:26 amFrankly, I doubt such a physically large part as the bulky capacitor would detect your entering the room. What you see most probably is the EMF created by the air draft (and temp change) when you entered the room on the various contacts/junctions you have got there..

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2025, 07:35:21 am
content: Quote from: iMo on August 25, 2025, 06:51:09 amSure air drafts will create thermoelectric effects in cabling.But not in time constants of 10s of minutes or longer....Air drafts are already visible on much faster scales.But I might not have explained well. I didn't mean detecting me in seconds.And also I sit less than a meter from the capacitor.As I sit next to it, in next few minutes it starts to rise up...It takes an hour, hour and a half to stabilize to new temperature.I exit the room, in next few minutes it starts to slowly go down.Capacitor is wrapped into paper towel together with thermocouple... Temperature tracks leakage current changes.Yesterday I connected DMM directly to calibrator. It stayed flat on 10,00018 V, without even flickering the last digit whole afternoon. I was entering and exiting the room and temperature changed as day progressed. I used the same cables that I use on capacitor. So I know at least it is not DMM or voltage source.Sure, everything is on the desk, unshielded.But as I said before, gain of measuring with DMM in voltage mode is such that 10mV is 1 nA. So even if I have 100µV errors (for thermoelectric effects, voltage source or DMM drift) that is just 10pA of error.We have decent error budget here.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 25, 2025, 01:05:01 pm
content: Quote from: TimFox on August 25, 2025, 03:34:02 amhereCheersAlexP.S.

author: mawyatt
author_rank: Super Contributor
timestamp: August 25, 2025, 01:25:04 pm
content: Quote from: mawyatt on August 23, 2025, 11:47:07 pmHere's an example of using a SDS800X HD and comparing to a KS34465A. Used a Rubycon 1500uF 16V that had been biased overnight by a GPP4323 at 16V. The DUT was sensed with DSO Probe set to 1X, thus 1MΩ effective impedance as seen in return to DC source. DSO voltage readings when scaled by DSO input impedance (1MΩ) and has a scale factor of 1ua/V.The SDS800X HD is showing a long term Mean of 41.24mV/1MΩ or 41.24na. Also added 3 Bit ERES result as shown. For comparison we used the KS34465A as shown, measuring the same DUT showing an Average of 41.85na.Edit: We could have used the DSO axis label and scale feature so the DSO shows results in na, maybe later. Results are a very slow downward trend as shown above. Added result (Img-11) 3 hours later, note the slight downward leakage trend.Best

author: Alex Nikitin
author_rank: Super Contributor
timestamp: August 27, 2025, 01:29:53 pm
content: Here is a small update, as I've left the meter running, so here is the leakage result for 60 hours after the initial 27 hours already shown. Plus a small illustration on the bias supply quality requirements, as I did +10ppm (100uV) step from 10V, and then -10ppm back to 10V, the result is shown on the second graph.CheersAlex

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 27, 2025, 04:45:42 pm
content: It's great that a cap will eventually reach such a low leakage value. One thing that I've noticed over the years is that a good/new cap will reach low leakage in a reasonable amount of time, and if you bring it to zero and repeat the test, it will reach that low leakage condition fairly quickly, faster than the first time. OTOH, an older cap (decade?), that by all tests is perfectly good, may eventually reach a low leakage state, but if you then bring it to zero for a while and repeat the test, it will take about as long as the first time for the leakage to come down.

author: Hydron
author_rank: Super Contributor
timestamp: August 27, 2025, 05:35:53 pm
content: Put my tests on hold for a few days as I came down with covid and had to sleep in the same room that the SMUs were running in. Just turned them back on set to source 0 current and measure voltage, and both caps I was testing were sitting at about 9.5V (down from 10V) a couple days later, which would work out to only about ~5nA of leakage over that time. I wonder if that is a reasonable (and easier) way to test? Just charge a bunch of caps up to 10V, leave them a while then use a high impedance meter to check how much they have dropped. I was struggling with noisy readings when trying to directly measure the leakage with either a SMU or DVM 10M input, which this also avoids.

author: mawyatt
author_rank: Super Contributor
timestamp: August 27, 2025, 05:44:01 pm
content: Quote from: Hydron on August 27, 2025, 05:35:53 pmThat seems as good an evaluation as any!!Hope you are feeling better!!Best

author: 2N3055
author_rank: Super Contributor
timestamp: August 27, 2025, 07:53:30 pm
content: Quote from: Hydron on August 27, 2025, 05:35:53 pmI agree with Mike that is good test indeed...Feel better soon!Sinisa

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 27, 2025, 08:04:00 pm
content: Has anyone done measurements on reverse leakage trend lines ?In a transistor monostable you get 600mV reverse, then a ramp to Vcc, which repeats, but a slow monostable may be in the reversed zone for some seconds.In a worst case the leakage could stall the oscillator. Above 1uA starts to limit resistor choices.

author: Hydron
author_rank: Super Contributor
timestamp: September 01, 2025, 09:34:58 am
content: 5 days later and the better of the two caps just hit 9V (down from 10V about a week ago). I'll try and do some other measurements on this one in a couple of weeks when I'm back from the US, but looks like a promising cap (WE 2200uF 16V WCAP-ATUL out of my parts box).

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 17, 2025, 06:41:28 pm
content: Quote from: Alex Nikitin on August 23, 2025, 10:22:09 pmThis is what been doing, but people need to keep in mind that some multimeters when auto-ranging will actually change their input impedance (therefore changing the actual leakage current value). For example, my HoldPeak HP-770D was giving me wildly different input impedance, from 20Mohm+, to 10Mohm. Instead, I've swapped to a crappy DT9205A (cheap Chinese manual-ranging multimeter), which has a 10M ohm resistor on the Volts range, and 1Mohm on the mV range. On the mV range, it can go down to 0.1mV, which is good enough for most capacitors. Most electrolytic caps that I've measureed thus far have 500mV of leakage or greater @ 10V, after being measured for 8+ hours.Interestingly, I have some Nippon Chemicon (450v 180uF) + Nichicon (450v 680uF) caps that I salvaged and have leakage below 100mV which surprised me considering they're likely 10+ years old and used.I'm considering building a simple op-amp circuit dedicated to testing capacitor leakage, using a 10M ohm resistor (that I managed to salvage) + LDO.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 19, 2025, 07:02:17 pm
content: Quote from: iMo on August 23, 2025, 08:20:37 pmI've been doing some research & simulation testing for making a discrete op-amp circuit (paired with a voltage panel meter for a readout, instead of a multimeter), and it seems like some people have used the EEVblog uCurrent formeasuring nanoamps/picoampsfairly reliably. Creating a circuit in a dead-bug style will additionally decrease leakage currents and problems with the measurements, as discussed inthis EEVBlog discussion.Many cheap multimeter can fairly-accurately measure millivolts and do utilize 1M or 10M input resistors (as discussed by Alex Nikitin, earlier in the thread), so a focus on measurements below 10nA-pA is likely more important for such a design.For the circuit I plan to build, I'm thinking of using some ofGyro's designelements, as many people have reported success, such asthis poster, except that I'll need to find a replacement for Gyro's 1G ohm resistor, as that's quite a niche part. I plan to setup the circuit to have a gain of 1nA = 1v (0.1nA/100pA = 100mV), as for higher leakage currents, I can simply use my multimeter. I'll likely use an Microchip MCP6v86u chopper op-amp (because I have a lot of them, they're cheap, low noise, low bias currents).