Using Models to Predict Capacitor Leakage Current - Page 1
Forum section: electronics / testgear

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2018, 04:41:31 pm
content: Too bad the other thread was locked. Moderator's, if you feel this is an out of bounds thread, please feel free to close it.I had posted how I was a bit confused about how a test like this would be valid and assumed how such a design would assume the leakage current was linear. Reading through the comments, the following was from the designer:QuoteSo it does appear they have a simplistic view of what the model would be. I had linked a few papers the have some information on leakage currents and mentioned a case where some ceramic parts a friend of mine was having problems with were far from linear. Personally, I would like to continue the discussion to see if others have seen cases where the leakage currents are not linear.This paper talks about the effects of ESD on ceramics and their leakage current. I may try and look of some of the old capacitor catalogs and see if I can find some better information on this subject (assuming the thread stays active).https://cecas.clemson.edu/cvel/Reports/CVEL-14-065.pdf

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 24, 2018, 05:09:08 pm
content: I agree with you. If a capacitor is to be used at a certain Voltage, it can only be thoroughly tested at that Voltage. Resistors too.I do that on a daily basis, my instruments happen have that ability, up to 1000 V DC.For capacitors search "Forming Voltage" "Working Voltage"Here's a description of a LC-103 high end cap-inductor tester:Analyzes capacitors for all four failuresout-of-circuit:– Value from 1 pF to 20F– Equivalent series resistance– Leakage with up to 1,000 volts applied– Dielectric absorptionBEWARE, this is definitely not 1000V at 10 Amps. It must be current limited by design.Even the old Heathkit cap testers Magic Eye tube tested electrolytics at their working HV, otherwise they won't "form" properly.Geo>K0FF

author: PA4TIM
author_rank: Super Contributor
timestamp: May 24, 2018, 10:10:46 pm
content: Here an application note from Keithley about cap-leakage testing :http://www.scientific-devices.com.au/pdfs/WeTransfer-NZvJB6Cw/Sensitive%20&%20Semiconductor/Capacitor%20Leakage%20Measurement%20using%20Keithley%20Model%206517A.pdfThey use a sourcing electrometer, I have one from HP, the HP-4329A, that can measure down to 50 fA and 10-1000VI added 2 more documents

author: joeqsmith
author_rank: Super Contributor
timestamp: May 24, 2018, 10:11:22 pm
content: I wouldn't want to play with a 1000V at 10A, well er, maybe..I spent some more time with Google and turned up a few other articles that may be of interest on leakage.http://www.electronicdesign.com/analog/whats-all-capacitor-leakage-stuff-anyhowhttp://www.evanscap.com/pdf/Determination_of_Capacitor_Life_as_a_Function_of_Operating_Voltage_and_Temperature.pdfhttps://nepp.nasa.gov/files/24303/CARTS2013_Liu_FailureAnalysis.pdfhttp://www.opensourceinstruments.com/Electronics/A3028/HTML/Capacitor_Failure.pdfhttps://www.vishay.com/docs/49268/tn0003.pdf

author: PA4TIM
author_rank: Super Contributor
timestamp: May 25, 2018, 08:37:41 am
content: I was pretty sure this document was linked here but I must be wrong. Very interesting, it is about measuring partial discharge in dielectrics.https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940028538.pdfThey do some modelling too.It would be a good thing to have a model of a leaking cap and some leakage simulating device/fixture. This must be possible with the help os an opamp (adjustable current source triggered by the test voltage of the leakage tester), comparator (breakdown trigger) and/or maybe a sort of sparckgap/breakdown "device" maybe the avalanche behavior of semiconductor.If I understand well this is a form of leakage/breakdown due to imperfections in the material. One of the methods is a hiss test. That made me remember a cap in a Valhalla voltage/current calibrator. I found that by listening with a "stethoscope" (some flexible festo vaccuum tubing and a Y connector) I heard it ticking. Only above a certain voltage. After I knew where to look I did the leakage test again on my just finished 2nd leakage tester (I tested it before at my old one, that uses a max 750 uA current up to 365V, the new one can source upto 10mA at almost 600V) I then noticed smal meter reactions synchronous with the sound when charged to the max circuit voltage. The voltage on this cap was not fixed when in use. Only in current mode the max voltage was over it (if I remember well)This could be an interesting way to test leakage using an ultrasone detector.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2018, 11:20:41 am
content: Quote from: PA4TIM on May 25, 2018, 08:37:41 amAs I am reading this, I get to figure 2 and thought, no way I would hook into that. Then figure 5 shows the clamp. I wonder if any test equipment was damaged while putting this paper together. lolPage 16, #5 Yep, turn the thing off and ground it before you work on it! Words to live by! lol#6 is even better. I just get this feeling that the student learned a few lessons. Imagine, the TC connected and you not thinking about it and pick up the meter... One mistake like that, I too would make a note in my paper about it.Page 23, I am surprised 5 minutes was enough. Then again, considering the test, maybe they just didn't care and it is a fairly small chamber.Once they get into the results, things get a bit cloudy. If you are going to take the time to write about not connecting the TC to the high voltage, maybe they could have added more details to the results.Page 29, conclusion.. Wait, what.. You just showed cases where the PD went down with temp, not up.Page 30, OK, I give him a pass. At least he comes out and states it. Imagine trying to model this.Good read. Thanks for posting this paper.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 25, 2018, 11:22:57 am
content: Even IF the leakage current was linear (I don't think it is), wouldn't you need the rated voltage to judge if the leakage is too big?

author: David Hess
author_rank: Super Contributor
timestamp: May 25, 2018, 11:26:54 am
content: Even ignoring damaged parts which will suffer all kinds of weird breakdown effects, leakage tests need to be done at the capacitor's rated voltage or higher; low voltage tests will only reveal gross anomalies.The same applies to semiconductors and especially high voltage ones. A curve tracer is especially useful for detecting faulty transistors which operate at low voltages with mysterious behaviors that become readily apparent at high voltages.

author: GerryBags
author_rank: Frequent Contributor
timestamp: May 25, 2018, 11:44:52 am
content: Quote from: David Hess on May 25, 2018, 11:26:54 amHi David, wouldn't a curve tracer be useful for testing for cap leakage? you'd have control over how slowly the voltage was brought up and would get a clear indication of where the leakage current begins and how much there is, no?

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 12:15:47 pm
content: 1) How do you want to know if the leakage current measured at a low voltage is correct or not? On what basis do you base yourself? All manufacturers give the leakage current at the rated voltage in their technical specification.2) How can you know if the capacitor will support its working voltage if you do not test it with a voltage higher than its working voltage?What is the purpose of a low voltage test that does not guarantee the correct operation of the capacitor?3) And for electrolytic capacitors, how do you know if the capacitor needs to be reformed or not?An electrolytic must be reformed if its breakdown voltage is below its rated voltage. Without applying a sufficient voltage (with current limitation), it is impossible to know it...Results: when it is powered on, the surge current may be too high, the capacitor heats up and can even explode ....Doing tests that are useless is for those who have nothing to do with their lives, not for those who work.

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 12:40:07 pm
content: When we talk about HV tester, we often quote the Heathkit IT-11 and IT-28 ... It's a mistake because these devices1) do not measure the leakage current, they only give a very rough estimate per magic eye2) they are very dangerous because there is no limitation of current on the range 600V .... One can do much better with the safety level, (see the project of PA4TIM)An HV tester can also have other applications like testing high voltage zener diodes, gas tubes for regulating high voltage, reforming electrolytics, measuring the breakdown voltage of diodes and transistors ......

author: madires
author_rank: Super Contributor
timestamp: May 25, 2018, 01:42:55 pm
content: Quote from: joeqsmith on May 24, 2018, 04:41:31 pmOne could also argue that an amplifier stage would be able to deliver enough current for the magic eye in case of a sensitive leakage current detection. Tubes have a quite high input impedance. Maybe vendors chose the less sensitive approach to save a tube or two.

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 01:56:42 pm
content: QuoteThat's right, but not for this reason.According to my opinion, the true function of the Heathkit IT-11 and IT-28 testers was not to measure the leakage current per se, but the breakdown voltage.As the leakage current increases considerably when you reach the breakdown voltage, you should not have a device too sensitive ... when the magic eye closes, there is really a high leakage current and you can be sure that the capacitor is really defective if the closing of the magic eye occurs at a voltage below the nominal voltage.

author: madires
author_rank: Super Contributor
timestamp: May 25, 2018, 02:00:57 pm
content: Quote from: David Hess on May 25, 2018, 11:26:54 amTake a HV electrolytic with a degraded oxide layer for example. If the oxide layer is badly degraded a LV check works. But if it's mildly degraded the LV check might give you an ok while a breakdown would occur at voltage lower than the cap is rated for. This is something which happens with NOS. A LV leakage check is not 100% reliable, it will deliver a few false positives. So we should educate users of the limitations of LV leakage testers.

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 02:19:24 pm
content: QuoteThis type of problem does not only occur with NOS electrolytic capacitors but also with electrolytic capacitors which have been used for a long time at a voltage well below their nominal voltage. The breakdown voltage decreases, but remains above the operating voltage.For other capacitors, I have explained in the other thread why they may have a normal leakage current but a reduced breakdown voltage....I post it again !!!!

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 25, 2018, 02:21:28 pm
content: Oldway said: An HV tester can also have other applications like testing high voltage zener diodes, "My home made Zener tester uses a little over 1000V to test ALL Zeners, even he 5 and 10V ones, but the most use is for higher Voltage Zeners, up to 300V. Over the years of testing literally thousands of 100,200 and 300V Zeners both with leads and surface mount, rarely are any 2 the exact same V, so they must all get hand selected.You are correct that HV must be used to perform certain tests, and I add that capacitors vary by type radically. One type I test is vacuum capacitors. There is a special tester for this, it uses to 50kV high frequency AC. If the vacuum is intact, no sparks inside. If there is air inside there are sparks. CRTs tested same way.Leakage is not always "simply resistance" that can be measured with low Voltage."Meggers" have been around since the early days for this same reason.Capacitors that use liquid or paste dielectric are another can of worms.Geoedit-30 May 2018 Capacitor illustrations added for clarity.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 25, 2018, 02:23:30 pm
content: Oldway said "I post it again !!!!"Please do or link the locked posts, I am new here and missed themGeo

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 02:24:34 pm
content: I post it again, here we are:Here are some explanations about the need to do the leakage current testing at the rated voltage.1) For electrolytics, there is a fundamental problem since all electrolytics have a leakage current, this is normal.The problem is to know if this current is normal or not.For this, it is first necessary to measure this current, what the "invention" proposed does not and then compare the result of this measurement with the technical specifications of the manufacturer.These technical specifications for measuring the leakage current are made at rated voltage ...http://www.rubycon.co.jp/en/catalog/e_pdfs/aluminum/e_twl.pdfIt is therefore necessary to test the electrolytic capacitors at rated voltage.2) For other types of capacitors, it is essential to check if the breakdown voltage has not decreased.A capacitor may have a low leakage current at low voltage while having a greatly reduced breakdown voltage.This is due to a physical characteristic of the insulators: the dielectric strength.see here to understand what it is:https://en.wikipedia.org/wiki/Dielectric_strengthYou will find that the dielectric strength of polystyrene, for example, is 19.7 and that of air is only 3.What happens when a capacitor has been punctured by a surge?The insulation is pierced and some of the insulation has been replaced by air or gas from the spraying of the insulation.As a result, at this point, the polystyrene is replaced by air and the dielectric strength is then only 3 instead of 19.7.The breakdown voltage is then reduced by 6.56 times and this is not noticed during the leakage current test at low voltage because the leakage current of air and polystirene are substantially the same.Thus, testing a condensator at low voltage is dangerous because it let you think your capacitor is good when it is'nt.When you power on such a capacitor at rated voltage without current limitation, it will blow up and may injure you.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 25, 2018, 02:40:02 pm
content: Oldway said:When you power on such a capacitor at rated voltage without current limitation, it will blow up and may injure you."Amen. A short time ago I accidentally overVoltaged a LV surface mount high value cap, by no more than 6V and it exploded with shrapnel and smoke and a LOUD bang. Learned that lesson the hard way. Made me an instant convert to safety glasses.Geo

author: PA4TIM
author_rank: Super Contributor
timestamp: May 25, 2018, 02:58:14 pm
content: Maybe change the titel of the topic to "several ways to test capacitor leakage current" or "everything you wanted to know about leakage but were afraid to ask"I have a curve tracer (tek 576), they are able to test leakage but I never used it for caps.If I can find some time I shall try to do some linearity tests. I think first try a new cap and go in steps of 5 or 10V up to the WV. Ideal would be a programmable voltage source and a logging meter but I do not have those (that is with enough uA resolution) so I have to do it by hand.To do it according the datasheet I should apply the voltage, wait the stated minutes and then note the current, discharge and do the same but now to a higher voltage.Then test leakage by charging it, waiting a few minutes and measure the discharge current. and also step up the voltage.Maybe also between steps measure C and DIf this gives the expected results and both methods agree we can expand it to other types. So we know if the test set up is correctAnd then to bad caps. The problem with the latter is that this is unpredictable because it can be defect is many ways. Is it severe leaking or is it breaking down, is it short ? The problem is to find some usable caps that broke down because that is a very rare failure (in my line of work). And they vary from dead short to breaking down just under the WV.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 25, 2018, 03:07:08 pm
content: "The problem is to find some usable caps that broke down because that is a very rare failure (in my line of work). And they vary from dead short to breaking down just under the WV. "Seems like you just described the life cycle of a wet slug tantalum bypass. And it doesn't matter if they were powered up, never powered up, or new in a box, only age.Geo>K0FF

author: David Hess
author_rank: Super Contributor
timestamp: May 25, 2018, 04:39:36 pm
content: Quote from: GerryBags on May 25, 2018, 11:44:52 amA good curve tracer can be used that way. I only have a Tektronix 7CT1N but it has a "leakage test" mode which applies a continuously adjustable constant DC up to 300 volts to the device under test instead of a voltage sweep and measures down to 10 nanoamps/division. The only reason I would use it is because it is the highest DC voltage tester that I happen to have but 300 volts is not high enough for what I consider a "high voltage" part.With capacitors I do not think I could ramp the voltage up slowly enough to see a clean breakpoint because the charging current covers the leakage current. What might work is to control a constant but low charging current (higher currents for higher values of capacitance unless you like to watch grass grow) and display the voltage ramp. That might make for an interesting project for someone but I think a sourcemeter or a high voltage power supply and current meter is good enough.As far as a useful high voltage capacitor and diode tester, I have considered designing something dedicated to measuring leakage over a wide voltage range however when doing repairs, this is of questionable use because if you have to pull a part to test it, it is almost always better to just replace it. A tester which measures capacitance, leakage, ESR, and dissipation at different DC voltages and frequencies would be more interesting but is a lot more complicated than a standard LCR meter so I am not convinced there is any market for it except at the very high end. I only just recently had an inspiration about how to protect a standard LCR meter front end from high voltages; most of them are pretty fragile or at least all of the ones I know of are.

author: oldway
author_rank: Super Contributor
timestamp: May 25, 2018, 05:13:44 pm
content: QuoteI'm repairing audio amplifiers and receivers manufactured in the years 70's and I agree with PA4TIM.- a repairman usually does not keep the defective parts to avoid mixing them with the good ones.- a lot of defective capacitors can be identified by a simple visual inspection or a measure of capacity, no need of a leakage/breakdown tester.- contrary to what many people think, I have to replace more defective transistors than faulty capacitors.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2018, 05:28:07 pm
content: Quote from: PA4TIM on May 25, 2018, 02:58:14 pmKeeping in mind that the manufacture's procedures may be different for each device.I was thinking to try and make some different defective parts. Along the same lines, I am thinking to setup some sort of automated test to measure various leakages to the Joe Smith standard. Every part would be tested the same way. Then attempt to damage them and see how I effect the linearity. If they were perfectly linear we could easily make a model and predict how they would behave over the entire operating voltage.

author: Cliff Matthews
author_rank: Unknown
timestamp: May 25, 2018, 08:12:54 pm
content: Precise title Joe.Ok, I'm in for some reading/learning..

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 25, 2018, 08:26:29 pm
content: "- a repairman usually does not keep the defective parts to avoid mixing them with the good ones."Again I agree 100%. Most, nearly all, of the testing of components I do is to see if they are suitable to go into the spare parts inventory. These can be brand new or surplus. Like a dog chasing his tail, I learned that "new" parts can be bad.One time I bought a bunch of 7 segment LEDs from a local surplus electronics joint. Several were bad so next trip I returned them, which they gladly replaced. On the way out the door I noticed they threw the bad parts right back in the bin with the new ones!Geo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: May 25, 2018, 11:01:41 pm
content: I have picked out four low voltage (less than 100V) and two higher voltage caps. I plan to start with two each, just to get a feel for if I can get any meaningful data at all. Most of my test equipment is very old. My electrometer does not support GPIB or any other interface.Well, on the plus side it looks like placing the parts into a metal can and such, I can seem to get some sort of reading with the electrometer. I wonder if Keysight would donate that new electrometer.Now that would be the ticket.Here is another article that may be of interest. The low voltage knee caught my attention.https://www.avx.com/docs/techinfo/Low_Leakage_Current_Aspect_Designing_Tantalum_Niobium_Oxide_Capacitors.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2018, 03:32:43 am
content: First attempt at some sort of capacitor test fixture. I have been testing with a NOS polycarb. Using a single 9V transistor battery, it's no problem measure the current.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2018, 04:43:11 am
content: The part I am using is a 2uF 50V metallized polycarbonate. The datasheets for this part state the IR is 25,000Meg X uF at the rated voltage after two minutes. So basically it better be below 1nA at 50V. I wiped off the part with iso and let it dry. Was careful not to touch the body when installing it and then sealed the test fixture.I manually took three datapoints, allowing the part to settle for 5 minutes between each levels. At 0V I measure 90fA. At 25V, I measure 33.2pA. If it's linear at 50V I was expecting to see around 70pA. What I measured was 303.6pA. Sure it's a crude measurement but it's not even in the ballpark of what I would expect from the simple resistive linear model. Again, this is a new old stock part. I have not stressed the part in any way.Even at 2 minutes into the test, the part was well below the manufacture's number. It will be interesting to see what others come up with.

author: ChunkyPastaSauce
author_rank: Unknown
timestamp: May 26, 2018, 05:27:34 am
content: Lot of the charts I just checked have log-lin scale.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 26, 2018, 02:02:09 pm
content: That fixture looks great. Is that Teflon sheet? Who supplies Teflon sheet? ThanksIs that an MHV connector? does he cable have a BNC connector or did you modify the MHV connector to take both types with my hack? ThanksGeo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2018, 03:37:07 pm
content: Quote from: GEOelectronics on May 26, 2018, 02:02:09 pmYes, its Teflon. There was too much resistance to the case without it. I imagine there are many places to purchase Teflon. Google may be your best bet. I get most of my hardware like this from McMaster -Carr.https://www.mcmaster.com/#teflon-(made-with-ptfe)/=1d0dridThat is an SHV connector. It has not been modified in any way.Quote from: ChunkyPastaSauce on May 26, 2018, 05:27:34 amThere are several texts that talk about the leakage as a simple resistor. Many will show an electrical model with a simple resistor as well. It's easy to see how someone would come to the conclusion it is linear and that any problems (damage to a capacitor) with this part of the model would simply scale.

author: all_repair
author_rank: Frequent Contributor
timestamp: May 26, 2018, 03:52:24 pm
content: Quote from: David Hess on May 25, 2018, 11:26:54 amI have come across aged capacitors that the internal material has changed characteristics, i.e. insulating material is no more insulating, and vice versa. If the capacitors have experienced spike, the internal physical structure is deformed. I came across a capacitor that only started to short at 300V, and from the sound, it appeared that something inside started to bend at that voltage. Different voltage is like a differrent dimension when parts have failed. For new and unused parts, LV testing has its value I think.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 26, 2018, 04:26:03 pm
content: This is my box, the innerbox is double sided pcb with a layer of (i think) polystyrene.The copper is connected to a banana-bus. I use this for all kinda things.The leakage is 1x10¹¹ ohm with the switchoff and 4,5x10¹⁰ with everything set up for a leakage test.(I have not yet cleaned it) For the real tests I place a teflon disc inside as a platform.I did a quick test on a ceramic doorknob capacitor and 1000V mica cap. Also an old bumblebee (the biggest on the pcb) tested from 10 to 1000V. I measured the current with a benchmeter. from 10 to 50V the current was in the pA's. This meter has only 1nA resolution. The SMU is a HP-4329. Leakage was not lineair. Calculating current from the reading gave:10----25---50---100---250--500---1000V,0.5---1.5---3-------9-----33---79----200nA mica0.25-0.6---0.9-----3---- 17---44----117nA doorknob0.5--2.8--8.9--28.8-------------------this one in uA !!, Volt breakdown starts around 100V, current slowly rises and the meter jumps a bit so now and the,. at 250V the meter pegs in the lowest resistance range.I have not looked up the allowed leakage or max voltage of bumble bees. But it will cause real problems over 100V. Testing this at 25V only would not be a good idea. I think the 2.8 uA is not a bad value for 25V volt.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 26, 2018, 04:34:59 pm
content: Quote from: all_repair on May 26, 2018, 03:52:24 pmYou are right, The higher the voltage, the higher the mechanical force on the "plates" with probably more risk to breakdown.

author: bugi
author_rank: Regular Contributor
timestamp: May 26, 2018, 04:53:26 pm
content: Quote from: GEOelectronics on May 26, 2018, 02:02:09 pmI have bought thin teflon sheets from ebay/amazon searches, though what it really is, quality, and in what shape it appears, e.g. rolled vs. used as extra filling in the package might be pure luck, depending on the seller.For more exotic pieces, like thicker plates, sticks, cylinders, etc., I found a german seller (polyplaste) which apparently sells production leftovers on ebay.de. Took a while to find that one since I don't understand the language

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2018, 05:42:55 pm
content: Quote from: PA4TIM on May 26, 2018, 04:26:03 pmThat's what I was afraid of. I tried to look up your power supply but could not find any information on it. So far I am still testing at low voltages. I tried an AVX tant, TAP157K016 150uF 16V. These have a DCL or 19.2uA max.0v - 10fA2v - 39nA4v - 77nA8V - 188nA16v - 470nAI then tried an old ILL Cap. alum elec RLS series. These were a low leakage part. It's a 68uF 35V. Datasheet shows 0.002CV or 3uA, which ever is greater. So 4.76uA at 35V.2V - 17fA (I checked to make sure the thing was connected)4V - 50fA8V - 22nA16V - 32A35V - 124nAAgain, these are new old stock parts and have not been stressed. I have a few HV caps I plan to try next. These parts are all used pulls.

author: David Hess
author_rank: Super Contributor
timestamp: May 26, 2018, 06:41:44 pm
content: The photograph below shows eight NOS (new old stock) 25 volt 15 microfarad epoxy dipped solid tantalum capacitors of indeterminate heritage being burned in and tested for leakage. I just hack something together as required although I would not mind having a handheld capacitor tester which can make measurements and do the same thing as I described earlier.3.1 microamps divided eight ways is 388 nanoamps. Typical similar capacitors are rated to have a leakage of less than about 3 microamps.Note that the power supply is configured for a very low limit current to prevent damage to the current meter in the event that one of the capacitors shorts. This should be done externally with say a resistor if the power supply has excessive output capacitance.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 26, 2018, 06:45:29 pm
content: Joe, the SMU:http://www.pa4tim.nl/?p=2269

author: bugi
author_rank: Regular Contributor
timestamp: May 26, 2018, 10:30:28 pm
content: What would be interesting is that even if it is non-linear, would a change in the high voltage range (i.e. increased leakage at operating and/or rated voltage) also show as an increased leakage in the lower voltages, perhaps even proportionally increased? (Checking this would of course require deliberately worsening a previously measured good cap.)Also, would multiple caps of the same type but with slightly different leakages have curves of same shapes but proportionally different leakage levels over the voltage spans? (Or, the counter-point, could they e.g. have similar leakages at low voltages, but have proportionally larger variation at high voltages, or other way around, similar high voltage leakages but larger differences at low voltages.)If the curve shapes stay the same (with just proportional changes), it would allow some sort of testing at low voltage, _if_ the leakage "curve" for the component being checked is known. (Probably still not 100% certainty, but perhaps better than fixed good vs. bad threshold at low voltage. And of course, would not test breakdown.)

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2018, 12:32:49 am
content: I had recently repaired an old radio (link below) that is roughly 80 years old.https://www.eevblog.com/forum/repair/old-console-radio-repair/One of the caps was a 0.02uF 200V made by Cornell Dubilier. Because of the low voltage, I used used the bench meters to directly read both the voltage and current.

author: oldway
author_rank: Super Contributor
timestamp: May 27, 2018, 09:31:34 am
content: Topic very interesting but I think you make a fundamental mistake in the test procedure.You forget an important point.The curve that you take with your measurements is only valid if the breakdown voltage of the capacitor is higher than the rated voltage.Then, modelling is useless if you don't know the breakdown voltage of DUT.Breakdown voltage is an essential information in the modelling of the condensator under test.For this reason, to calculate the leakage current at rated voltage from a low voltage test is only valid with a good condensator with breakdown voltage higher than the rated voltage.You test the capacitors which have no problem of breakdown voltage too low and therefore you do not notice the phenomena that occur if the voltage applied exceeds the breakdown voltage.When the breakdown voltage is reached and exceeded, the leakage current increases exponentially and if there is no current limitation, there is an arc in the capacitor that causes a catastrophic failure.So you should do your tests until you reach the breakdown voltage even if it is higher than the rated voltage.This is one of the reasons why ALL manufacturers always specify the leakage current at rated voltage and not at low voltage because this test ensures that the breakdown voltage is higher than the rated voltage.A faulty capacitor is characterized by a low breakdown voltage lower than the nominal voltage and your tests on capacitors that are not defective can not measure the breakdown voltage since a good capacitor has a breakdown voltage greater than the rated voltage.It's obvious that a low voltage test does not let you mesure, nor even guess, what's the breakdown voltage an thus is not able to clearly and surely detect if a condensator is good or not.

author: BravoV
author_rank: Super Contributor
timestamp: May 27, 2018, 11:09:00 am
content: CMIIW, so the only valid test is the "destructive" one ? In order to know the exact breakdown voltage.Breakdown means once this condition reached, the CUT is no longer useable right ?

author: bugi
author_rank: Regular Contributor
timestamp: May 27, 2018, 11:09:42 am
content: Quote from: oldway on May 27, 2018, 09:31:34 amOne does not need to know or find out the breakdown to model a limited range, especially if the goal is not to decide whether the cap is good or not. Note the OP's / topic's limited goal to just find more measurement results on the non-linear leakage behavior vs. some ideas that leakage would be caused by a simple (ideal) resistor with linear response to voltage. (And there is no demand on the voltage range of the measurements, though the larger the better).Ignoring the breakdown will just result in a model that will not be as useful above the measured range (extrapolation of a model is always a risky thing). Even if the breakdown (or anything else for that matter) would start to affect leakage well below its voltage (or at any range), a simple model vs. measurements might reveal how the model starts to drift at higher voltages (or another range), leading naturally to limit models usable range. Just like every model should list the limitations. (E.g. "Note that this simple model is only valid upto 85% of breakdown voltage, whatever that voltage happens to be.")Of course, it would make the model better to also study the behavior near and up to breakdown, so as to know how it would affect the model, and especially, how far below the breakdown it has an effect on the leakage current. This is a sort of win-win possibility: if the breakdown affects leakage only near the breakdown voltage, then the bad side is that it can not be predicted beforehand, but the good side is that the simpler model is valid for larger range. On the other hand, if the breakdown affects leakage further below the breakdown voltage, the bad side is the simpler model has lesser useful range, but it may also become possible to predict the breakdown beforehand. It would then depend on how the breakdown affects the leakage, if or how well it could be predicted (with a better model that includes breakdown effects).EDIT: Personally I'd be happy just for a model that handles the non-linearity below breakdown effects better than the typical "parallel ideal resistor".

author: PA4TIM
author_rank: Super Contributor
timestamp: May 27, 2018, 04:27:31 pm
content: I agree with Bugi, breakdown is a failure and for most important to find but not predictable. They can go totally short or break down just under the VW. The only way to find one is measuring upto the WV. It is not part of the model. Like a transistor, stating max current at 100A during breakdown in the datasheet is not very useful.I cleaned the "farraday" box for these tests. (isolation was now 4x10¹⁰ ohm)Cap : 1000uF-250V, Nippon Chemicon SMH . replaced because it leaked 900uA after 5 minutes. This is within specs (max 3mA for this one) but 99% from the caps I test leak less as 100 uA so I replaced it. The tester was set at 7,5 mA and 250V, the cap was 250V around 2 minutes. C was 891.1 uF, D= 0.04 at 100Hz. Datasheet states a max D of 0.2 for a worn cap.I repeated the same test at 25V volt (and max 7.5mA) for 5 minutes. Leakage was less as 5 uA (the tester was in the 100 uA full scale setting),For more resolution and less noise I also used on my reformer/tester, set at 25V and max 750 uA, with a 6,5 digit Keithley 196 to measure the current. It was dancing around 100 nA. I did not timed it, just waited until it was stable.Line B, the same cap on the HP SMU from 10 to 100V, Leakage at 250V was to high for this meter. It can source only few hundered uA. Every measurement was exact 5 minutes. Here the meter worked in the charge position and the Keithley measured the current. Not usable because the charge current was to low to get it charged in 5 minutesLine C, also the HP + Keithly but now the HP in resistance measure mode and I waited until the current became constant. This results in much lower numbers under 100V but above the same problem, I did not liked the meter hammering in the corner so I did stopped at 100V.Line D, the cap on my leakage tester on 25V, 50V, 100V, 250V. And after excact 5 minutes. Also here around 100V some problems. I have no clue why the current had a peak there. The real values in uA are 10x lower (so it fitted in the same graph.)Line E is completely different, value is x100 in the graph. This is a 330 nF 400V Rifa miniprint tested from 0V to 350V on my Tek 576 in leakage mode, in 10V steps upto 100V, 20V steps upto 300V and then 350V.The graphs are only useful for the trend, not the absolute values because the small number of measurements. This 5 minute tests are as interesting as seeing the gras grow. This would be the perfect job for a Keithley 2450 SMU, if I ever win the lottery I buy one.Up to now all tests I did show a non lineair leakage.

author: oldway
author_rank: Super Contributor
timestamp: May 27, 2018, 04:36:30 pm
content: Quote from: BravoV on May 27, 2018, 11:09:00 amWhen you are testing new capacitors, you are only repeating the tests made by the quality control of the manufacturer...in this case the breakdown voltage should be above the rated voltage...It is not necessary to test the condensator above the rated voltage with the risk to damage it.For used capacitors, the caracteristic of the curve of the variation of leakage current with variation of voltage is only valid up to the breakdown voltage that can be lower than the rated voltage if the capacitor is bad /damaged.At breakdown voltage or above, the variation of leakage current varies much more than below.In my opinion, variation is more or less the same as a high value resistor (linear or not ?) in parallel with one or two zener diodes... The voltage of those zener diodes is the breakdown voltage.NB: Curve C (red) seems to show a breakdown voltage of 210V

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2018, 05:18:43 pm
content: QuoteThanks for your time none the less.I have yet to break out the gloves but cleaning everything is important at these low voltages. If you have a 1Tohm or so resistor, you could try and prove it's not something in your test setup. I am continuing to manually run my tests as well, also due to lack of better test equipment.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2018, 08:41:23 pm
content: 10 pcs all from the same lot. These are 0.01uF Z5U 1KV Cera-Mites. These all started out the day brand new. Using a 1V signal, the capacitance currently ranges from 8.9nF to 9.5. D is between 0.005 and 0.006. ESR from 88 to 108. However, 8 of the 10 pcs have been vary carefully and methodically damaged using various methods. 2 pcs remain as a control.I can't tell the the good from the bad with my RLC meter. Time to see if my old equipment can detect which ones are damaged using only a 24V DC source. I havn't tried it yet and plan to automate the test because as mentioned, this is like watching grass grow.

author: oldway
author_rank: Super Contributor
timestamp: May 27, 2018, 09:44:01 pm
content: And, if possible, could you test them with an old HV tester like the Heathkit to see if you can tell the good from the bad with it ?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 12:55:24 am
content: First attempt at automating the testing. I plan to sweep from 0.5 volts to 20 volts in 0.5 volt increments and will hold it at each level for 10 seconds. The software will collect the data every half second.BASELINE1: Showing the current through a 20 Meg, 40 Meg, 100 Meg and 1T ohm resistors. One of the test capacitors is also shown. The file format is the DUT#, capacitance,ESDESR and dissipation factor. So 20V/20M for example is 1uA which we can see is the green trace.BASELINE2: Showing the 1T ohm resistor only. So 20V/1T ohm is 20nA. I did not clean the parts and the effects can easily be seen. It gives us some idea of what we can expect from the test fixture.The datasheets for these parts state the insulation resistance is 1000ohmF or 20,000Mohm. There is no mention but I would assume the higher value, or 50nA at 1KV. At 20V that's only a nA assuming it is linear.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 04:36:55 am
content: Of the eight caps that were damaged, six exhibit very high leakages compared with the control. At 20V, we said 1nA was the max and these certainly fail. #2 (grn) and #4 (yel) are interesting.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 04:43:36 am
content: I decided to retest #4 to see if would behave the same and the leakage profile changed dramatically.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 04:45:37 am
content: Of course, I decided to see how it would continue to change so I ran a total of 13 sweeps on it.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 04:55:38 am
content: Zooming into the vertical axis we can get a better idea what this trend is looking like. And while it has greatly improved, keep in mind that the vertical axis is in uA. The fail point is 1nA or 0.001 and even after 13 sweeps the part has failed every time.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 05:02:12 am
content: If you are curious about if the 10 seconds is not long enough to settle.

author: oldway
author_rank: Super Contributor
timestamp: May 28, 2018, 09:41:28 am
content: Quote from: joeqsmith on May 28, 2018, 04:36:55 amIf only 6 of the 8 damaged capacitors have a leakage current much higher than the normal leakage current, it means that only 6 out of 8 faulty capacitors can be detected by an LV testIt's not acceptable.As Dave said:QuoteReply 213 page 9https://www.eevblog.com/forum/testgear/mr-carlsons-lv-capacitor-leakage-tester!-it's-finally-out!/200/It remains to be verified whether the test at rated voltage makes it possible identify 100% of the defective capacitors or not....That is why I asked to make the measurement of the leakage current on these 8 capacitors at the rated voltage (here 1000V) and to compare them with the leakage current of the capacitors which were not damaged.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 01:33:10 pm
content: The attached graph shows capacitor #4 with a one minute selling time (red) and a five minute settling time (green) when compared with the last sweep.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 01:47:04 pm
content: We are interested in if any parts fall below the manufacture's 1nA limit (again assuming linear which it is not). In the original plot showing the 10 samples, we can see something is going on in the sub 5nA range.

author: bugi
author_rank: Regular Contributor
timestamp: May 28, 2018, 01:48:48 pm
content: @OldwayI think it is a bit premature to say "not acceptable" already, when the testing has just begun, and plenty of things remains to be tested and learned. Also, he has not yet revealed how they have been damaged; perhaps those two are not damaged in a way that would also cause problems at high voltage. (I do assume they have issues, but the information revealed so far does not reveal it, thus any conclusion for "not acceptable" is premature.)Also, again, the interest of this topic is not, afaik, to find out if/how low voltage leakage allows detecting all possible higher voltage failures, but about studying the leakage model in general (and could include high voltage and/or breakdown, too, but not a necessity). For the leakage model point of view, those already shown results are quite awesome.That said, I am also interested in any higher voltage results, but I have patience... I understood those results were just the "First attempt at automating the testing", the latter ones some quick additions for exceptionally interesting results.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 02:01:13 pm
content: Deselecting all of the data sets except the five of interest, we can clearly see caps #7 & #8 deviate from the two control caps.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 02:13:58 pm
content: As we continue to push into the noise, we have three caps left that fall under 1nA.All the capacitors were stressed using various high voltage transients, DC, various current limiting resistors ranging from 250K to 60M.Cap #6 is a little special. In this case I had taken my old piezo ignitor that has damaged so many UNI-T meters and provided 50 pulses to the part.

author: oldway
author_rank: Super Contributor
timestamp: May 28, 2018, 04:24:20 pm
content: Quote from: bugi on May 27, 2018, 11:09:42 amA tester must give reliable and reputable results ...Otherwise, no need to waste time testing the capacitor, just check the circuit correctly, it is sufficient and more efficient than an unreliable test.The tester must give 100% certainty or at least one result equal to the old high voltage testers ...If we are not able in 2018, with all the technical means at our disposal, to do better than we did in 1950, we can eat our diploma and change our profession.That is why I asked to do the tests both at low voltage and at the rated voltage on the damaged (they have been stressed, but are they really damaged ? For exemple, a X2 capacitor is not damaged by surges) capacitors and to see if the results are concordant or not.Whether or not you can use a low voltage test to detect a faulty capacitor is well a Joeqsmith's goal in this topic, he wrote:"I can't tell the the good from the bad with my RLC meter. Time to see if my old equipment can detect which ones are damaged using only a 24V DC source."Can a faulty capacitor be detected using just a 24V power supply?If you want to use models to predict a capacitor leakage current:- It is necessary to know up to how much voltage this models can be used , it is an essential information .... Clearly, it is essential to know the breakdown voltage of the capacitor.In a faulty capacitor, there is no guarantee that the capacitor will be able to block the rated voltage.- the different types of capacitors certainly will not follow the same model, and there are hundreds of different types of dielectrics.If it is necessary to wait for the models of all types of capacitors, it will be too early for ever to draw conclusions.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 04:30:14 pm
content: I am in the process of setting up to collect some data at higher voltages. First I wanted to run a basic stability test. Using a 10Meg MOX, power supply was set to 1KV and I collected data for 5 minutes. The scale is mA now rather than uA. I ended up running a second sweep just to make sure the supply would not continue the downward trend.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 28, 2018, 05:08:29 pm
content: The visial recollection of "capacitors" to one group of technicians and to other groups of technicians can be vastly different.Lest anyone doubt that capacitors, ICs and transistors are not used that much with 1000+ High Voltage, I attach this picture of a precision 2400V DC generator (HVG) that uses state-of-the art regulators and multipliers and controls, all on one PCB. 6V goes in, 2400V DC regulated comes out (or any other up to 2500V) in a variation of KFC multiplier.Geo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 06:00:58 pm
content: Quote from: GEOelectronics on May 28, 2018, 05:08:29 pmI don't think anyone would doubt that we are using high voltages in consumer products, or in general. Did you build this supply for general hobby use or was it for a product?

author: oldway
author_rank: Super Contributor
timestamp: May 28, 2018, 06:35:05 pm
content: I just should like to remember that what was used in the old HV capacitors testers to detect a bad capacitor was not measuring the leakage current but well measuring the value of the breakdown voltage.My CR analyser Model TE-46 has two ranges of leakage current , 1mA full scale and 10ma full scale.....This has nothing to do with the leakage current of nA's you are measuring even with known bad capacitors.Trying to models capacitors is useless for detecting bad capacitors.From the breakdown voltage, model changes and leakage current increase rapidly and reach mA range.Such high leakage currents only occurs when the applied voltage is higher than the breakdown voltage.If the leakage current increase rapidly at a voltage lower than the rated voltage, that means that the condensator is bad.This is how these old testers worked.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 06:49:30 pm
content: Looking again at the low voltage data, CAPS1_10, we can see the highest currents are found with #3, #2, #5, #4 and #1.1KV_CAPS1_10_10MEG shows the current for all 10 capacitors being swept from 250 volts up to 1KV. The white flat line was our 10Meg MOX resistor with 1KV applied. Note how capacitors #7, #1 and #3 exhibit a very sharp edge up to the current limit.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 07:00:07 pm
content: Deselecting caps #7, #1 & #3 and zooming in on the remaining parts we can see #5, #2, #8 & #4 all deviate from the control.#4 continues to behave interesting compared with the others. If we wanted to detect this fault at high voltages, we better have a way to detect these events. #8 is a bit odd as well as the leakage drops with the higher voltages.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 07:06:26 pm
content: Looking closer into the noise floor we can see #4 actually has the lowest leakage at 1KV. It would be difficult to tell at 1KV if #4, #8 ard #6 are any different than the control caps #9 & #10.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 28, 2018, 07:12:55 pm
content: Hobby.Powers a photmultiplier tube form a 4 x D cells.Geo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 07:19:30 pm
content: Comparing cap #6 (tan) which again was exposed to 50 strikes from the piezo grill ignitor, it appears to have slightly better performance than our control parts.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 07:21:22 pm
content: Quote from: GEOelectronics on May 28, 2018, 07:12:55 pmWhat are you trying to detect with the PMT? What wavelength? Do you have a blog showing the entire project?

author: bugi
author_rank: Regular Contributor
timestamp: May 28, 2018, 07:42:01 pm
content: Soo, combining info from multiple images.Low voltage:#1 to #5 were noticed to have very clearly too high leakage within 20V. #4 playing really weird stuff..#6 was hanging happily around with the controls (#9 and #10).#7 and #8 were noticed after zooming in, #8 just barely above the limit at 20V.High voltage sweeps then seems to show that..#1 to #5 are still the highest leakers.#1, #3 and #7 apparently have a breakdown below the 1kV.#2, #4, #5, #8 all deviate from the control (in the zoomed view).#4 and #8 are especially interesting, having lower leakage (at high voltage or over measurements/time) after first having higher leakage.#6 still shows no signs of problems. (Is it really damaged after all?)#5 seems to have some up and down behavior, too.For me, the annoying result is the changes over time/measurements (i.e. the kinds of changes where the leakage gets less). Apparently, measure long enough and bad leakage can vanishEDIT: #8 started barely above the expected limit, had clearly more than control ones at higher voltages at first, but ended up with low leakage (and no breakdown).EDIT2: the control caps' (and couple others) seem to have quite constant leakage over the 250V-1kV range; I'd have expected an increase (at least linear if not even growing). The #4 of course being the joker and getting even lower (is it about to break open circuit?)

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 08:28:16 pm
content: Quote from: bugi on May 28, 2018, 07:42:01 pmWait, what? You didn't expect me to make sense of this did you??I still have at least one test I would like to run.Quote from: bugi on May 28, 2018, 07:42:01 pmYes, this seems correct. There is a reason I ran these low leakage ceramics. I assume detecting a fault with them would prove more difficult. Certainly with a good electrometer and test setup (which I don't have), every damaged device I tested could be detected at low voltages except for #6. I am not suggesting that you could use a simple threshold. Keep in mind, this was a very small and crude test of one type of capacitor all from one lot.Quote from: bugi on May 28, 2018, 07:42:01 pmLets ignore everything except #4, #6 and 8.#6 is a bit of a coin toss you may say. If I gave you that cap and you had no idea what it was, would you use it? If I told you I hit it with the grill starter 50 times, then would you?We know that grill starter's energy is very low compared with the IEC standard which is why I designed that gun I now use.#8 and 4, I am not too surprised after seeing a few other parts appear to improve as well.Quote from: bugi on May 28, 2018, 07:42:01 pmIt would be next to impossible to come up with a simple model (or even a complex one) based on these parts. They are not stable and would not make a good reference standard to evaluate other detectors.

author: bugi
author_rank: Regular Contributor
timestamp: May 28, 2018, 08:37:48 pm
content: Quote from: joeqsmith on May 28, 2018, 08:28:16 pmIt was more about me starting to lose track on which cap was doing what. Too many graphs etc. Combined it all into one message so I don't have to scroll back and forth the whole page.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 28, 2018, 10:05:48 pm
content: I think testing ceramic caps is not as easy as it looks.Many ceramics have a big voltco and piezo electric effect. Maybe the voltage pulls the plates together, that increases the leakage, that causes some reaction in the material, voltage drops, the plate distance increases and current drops, this goes on until the voltage becomes high enough to overcome the force and hold the plates and the current increases further.Besides that, the sudden "release" could cause a voltage by the piezo electric effect. Some ceramics have a rather big tempco.And referring to the pdf about partial discharge, maybe there are bubbles in the material .Maybe also some effect as mica's have on very low frequencies, as if they can not follow the change in polarity.This could also explain the non lineair behavior in tests.In electrolytic caps there is the chemical problem as an extra.I am curious what would happen if we make a big 2 plate cap and measure the movement, force and leakage. And then place several dielectrics between the plates (like a ceramic tile) And then look if they behave also "strange" But I do not have the gear to do those measurements.I made something like that years ago to test several materials behave as dielectric. (not with the sensors)http://www.pa4tim.nl/?p=2929the last picture on the page.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 11:12:50 pm
content: Quote from: PA4TIM on May 28, 2018, 10:05:48 pmI picked them for their low leakage and easy to source if someone wanted to try and replicate anything I had done. Alum elec may have been easier to measure but I was not sure they would repeat. Then again, these have done anything but be repeat.I wanted to know how running the HV test effected cap #4 and #8, so I set the system back up and ran a few parts including a 20Meg.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 11:18:53 pm
content: I repeated 5 sweeps for both #4 and #8 and compared them with the control. #8 is still a bit unstable but the high voltage has had a pretty dramatic impact on both parts.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 11:22:35 pm
content: Using a wet stone, I wanted to see where the device broke down.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 28, 2018, 11:37:33 pm
content: QuoteCool,now we see the bubbles. Very nice controlled sanding

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2018, 11:42:41 pm
content: And here is the problem:

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2018, 12:13:15 am
content: Very very cool Joe 'Sherlock' Smith.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2018, 12:51:59 am
content: Quote from: PA4TIM on May 28, 2018, 10:05:48 pmInteresting read on your fF project.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2018, 10:33:16 am
content: I tried to leave a post on the Carlson YT video to see if I could purchase a completed unit but I get this strange message that my comment failed to post. I looked around his channel and could not find where he has any type of store. Does anyone know if he offers to sell these as a final product? To try and review it, I want to start with one that the author has given his seal of approval on rather than something that was hand built by an amature with who knows what parts.Also, if you noticed that I had edited a few of my posts over the weekend. Lots of grammar and spelling made a few difficult to read was all.

author: BravoV
author_rank: Super Contributor
timestamp: May 29, 2018, 10:38:27 am
content: Quote from: joeqsmith on May 29, 2018, 10:33:16 amWonder what is that error message mean ?

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 10:50:14 am
content: Quote from: joeqsmith on May 29, 2018, 10:33:16 amI thought we were not going to talk about Mr Carlson's tester anymore ..... That's off topic for the new title.We will start again with the same problems as in the topic on the Mc Carlson tester.

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 11:11:26 am
content: You are topic starter, if yourself is speaking about capacitor tester, then I think that I can also post about testing capacitors:It is already obvious that the capacitors tested by PA4TIM and yourself have extremely different and even erratic behaviors and that it is therefore impossible to create a model that can predict the leakage current from a low-voltage measurement.Whatever the reasons for this abnormal behavior, it simply proves that a low-voltage test does not make it possible to verify whether a capacitor is good or not.Mr. Carlson's claims that the leakage current behaves like a resistance , that's not what you found .... As Dave would do, it's time to push the "fail" button.My point of view is not that of a theorist, nor of a researcher, but that of a practitioner who seeks practical results.I work in electronics repair (currently vintage audio with vacuum tubes and transistors) and:1) It is already extremely rare that I have to test a capacitor with regard to the leakage current because a simple measurement of the voltages of the circuit or of its functionality makes it generally possible to detect this kind of problem (only test needed: measure of capacity)2) If I have to measure the leakage current, I have to do it at the rated voltage to be sure that the capacitor is working properly when it is powered on.If the test does not guarantee it, this test is useless and is a waste of time.Cheaper and simpler to replace the capacitor.What is a capacitor good or bad? What are the criteria used to determine it?There are two possible points of view:1) to measure all the characteristics of the capacitor (measure and not predict!) And compare them with the technical data of the manufacturer.At the level of repair, it is inapplicable because it takes too much time.2) to be satisfied with a less rigorous test that detects the breakdown voltage ....If the breakdown voltage is lower than the nominal voltage, the capacitor is either defective or must be reformed (electrolytic)It should be noted that the circuits are not all equally sensitive to the leakage current.For example, in a leakage biased tube circuit with a 10M G1 resistor, the least leakage current of the capacitor coupling it to the preceding stage will prevent the circuit from operating.On the other hand, if it is a cathode resistance biased stage, where the resistance of g1 is generally of the order of 100K, a low leakage current is acceptable.There are hundreds of different types of capacitors and dielectrics.Each has a different behaviour and need his own model.It's obviously impossible to use hundred of models to predict leakage current from a low voltage test....The leakage current must be measured at rated voltage, this the only solution.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 29, 2018, 01:39:37 pm
content: Oldway said :The leakage current must be measured at rated voltage, this the only solution."A few pictures of my yesterday's test of a new-to-me 50(?) year old GR 1419-B Polystyrene Capacitance Decade. These are still made today by IET Labs and cost $3581 USD.Everything tested perfect at 50V and 2-Terminal mode (one side not grounded to case). Second set of tetsts with the common grounded to the case was a different story. One component failed at 200V. They are all rated for 500V continuous. Good thing I tested it thoroughly before using it in my shop.Pictures reduced in size to save bandwidth but full resolution originals will be linked in my upcoming topic "GR 1419-B Polystyrene Capacitance Decade Teardown"The last picture shows leakage test with the defective component removed and all the others in circuit at same time500V/ 0.00 uA />>500M Ohm leakageGeo>K0FF

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 02:31:22 pm
content: At $ 3581 USD the capacitor decade, I hope you did the tests with sufficient current limiting resistance to not exceed a few mA.With such current limitation, the test should not further damage the capacitor.As you know that the breakdown voltage is 200V, you can still use this capacitor at a voltage below 200V.However, the leakage current of this defective capacitor may be larger than the normal leakage current.

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2018, 02:33:33 pm
content: Quote from: oldway on May 29, 2018, 11:11:26 amSometimes even that is not enough. I have a Sprague series 30D aluminum electrolytic capacitor which was part of a decoupling network in a Tektronix 7904 oscilloscope and the capacitor meets all of its specifications when tested at 1000 Hz but fails for the high frequency decoupling that it was intended for. This leads to your next point:QuoteThe only test short of using a network analyser was to replace the capacitor which in combination with the typical low frequency tests revealed the issue.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 29, 2018, 03:04:32 pm
content: Quote from: oldway on May 29, 2018, 02:31:22 pmGood advice, a few microAmps limit even better, that's all it takes.Geo>K0FF

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 03:13:40 pm
content: Quote from: David Hess on May 29, 2018, 02:33:33 pmAn electrolytic capacitor test should include an ESR measurement at 100Khz ...If you had done this test, you would probably have noticed that this capacitor had an abnormally high ESR.Of course, you will answer that in the 70s and 80s, capacitor manufacturers did not give ESR values at 100Khz, that's right.

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 03:17:32 pm
content: Quote from: GEOelectronics on May 29, 2018, 03:04:32 pmSome current is usefull to reform the electrolytic capacitors you test...You see the breakdown voltage increasing and the leakage current decreasing.Current limited at 5 mA seems to be the best choice both for efficiency and safety.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 29, 2018, 03:42:42 pm
content: QuoteThe ESR is 99% of the time not given for 100 kHz. They state the impedance for 100 kHz. You measure that with an network analyser. (that is for normal electrolytics, for solid smd versions they often state the ESR) But for high enough capacitance the Xc part is so small that you can use it for ESR. (most ESR meters use a squarewave with a root frequency of 100 kHz. It contains odd harmonics probably upto 1MHz so it is a very crude test. The best way is often a scopeI often have to test caps, there is in those cases no other way. I then must be 100% sure I found the fault.I measure C, D, leakage at WV and almost always look up the datasheets.

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2018, 03:46:35 pm
content: Quote from: oldway on May 29, 2018, 03:13:40 pmIf that had been an option I would have used it but my impedance bridge is limited to 1000 Hz. Many of the modern multi-frequency LCR meters are essentially network analyzers and either would likely have revealed something.QuoteEven the modern datasheet for that part does not list specifications at 100kHz but I could have compared it to similar parts which do have such a specification. I was just using it as an example where the most common diagnostic tests are not sufficient and it is more economical to test it by replacing it which is likely whether the test reveals that it is bad or not.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 29, 2018, 04:02:40 pm
content: Quote from: oldway on May 29, 2018, 03:17:32 pmI've heard about reforming electrolytics (one of high $ value like those can type "computer grade" or high Voltage) but can't remember actually doing so before, except the old trick of bringing the AC supply up slowly on tube gear that has been in storage for a long time. Every service bench should have at least a small isolated Variac transformer with meters.K0FF's Proverb concerning 50 year old electrolytics: "Fixation by Replacation".Here's a trick for doing just that easily on old style leaded caps or other components wired to terminal strips:https://www.eham.net/articles/23125Geo>K0FF

author: PA4TIM
author_rank: Super Contributor
timestamp: May 29, 2018, 04:19:57 pm
content: I have done a lot of reforming and most times with succes. (only in my own gear but also just as measurement experiments)

author: oldway
author_rank: Super Contributor
timestamp: May 29, 2018, 04:21:00 pm
content: I just finished to repair a SANSUI AU-9900 of 1976....ALL the electrolytic capacitores are from 1976, none have been replace, and they are all good...The problems ? Bad contacts, four bad transistors, tests and adjusts....Whe should stop to have allergy of capacitores....they are not the culprit of all the failures....I have had far more failures with transistors than with capacitores.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2018, 11:31:59 pm
content: I am not too surprised that there were cases that the low voltage tester could detect faults that the old high voltage ones could not just based on the few parts I have looked at.Some searching, this person had a few pages dedicated to vintage capacitor test equipment. They to the time to measure the thresholds for the various capacitor types. Not too surprising that these old relics are not very sensitive and have no way to do a peak detect. I suspect none of these would catch #4 and #8. Possibly #2 and #5 as well. #6 is a lost cause. The variance is just too small.https://people.ohio.edu/postr/bapix/In the Carlson's Lab video, he mentions the threshold he used for the alum elec. I plan to run a few NOS alum elec 150V parts next to see how they behave at 20 and 150 volts and then again attempt to very carefully and methodically damage them.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2018, 04:27:23 am
content: This plot shows three different tests. All caps were swept to 20 volts. Current is in mA.Cap #1 (green) is tested without forming, while caps 2-4 have had a half hour form.I then formed cap #1 for an hour and repeated the test (white).I then formed all four caps an additional hour. As I mentioned, there was a time we were doing this in a fairly large scale.All capacitors are new old stock. The file names follow the same format, DUT#, capacitance, ESR in ohms and dissipation factor. At 20 volts, the only part that exceeded 5uA was the unformed part.

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 07:11:09 am
content: You consider that an abused capacitor is a damaged capacitor...I doe not think it is so easy....For example an abused X2 capacitor is not imediately damaged...It needs a lot of abuse to be damaged and the damage he suffered is only a reduction of it's capacitance.So, the first thing to determine is what is a damaged or bad capacitor ?For me, as user of capacitor tester, a bad capacitor is one who will not works correctly in the circuit it will be used...What do you consider as bad capacitor ?

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 07:47:04 am
content: What are the most important characteristics of a capacitor that we must check to be sure it will work correctly in circuit ?1) capacitance2) leakage current at rated voltage : this is in reality twodifferent characteristics: quality of dielectric + dielectric strength of isolation (ability to sustain the rated voltage without breakdown)3) ESR (not always important)A 20V tester does obviously not test the dielectric strenght of a capacitor with rated voltage higher than 20V.

author: bugi
author_rank: Regular Contributor
timestamp: May 30, 2018, 07:57:45 am
content: Quote from: oldway on May 30, 2018, 07:47:04 amI guess depending on the capacitor type, that should be "capacitance at the working voltage and frequency", since both parameters could affect the effective capacitance significantly.

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 08:39:48 am
content: Quote from: bugi on May 30, 2018, 07:57:45 amThe most important characteristics of a capacitor are those indicated on the capacitor, that's:- non electrolytic capacitors: capacitance (nothing more is specified), tolerance, rated voltage-electrolytics : capacitance, rated voltage, working temperature (85, 105C°)That are the first characteristics to be checked to know if the capacitor is bad or good.Without testing if a 400V capacitor is able to sustain 400V applied voltage, without breakdown, you miss one of the most important information you need to check to know if the capacitor is good or bad.Leakage current is only a secondary characteristic....that's why it is not specified on the marking of the capacitor.

author: bugi
author_rank: Regular Contributor
timestamp: May 30, 2018, 10:20:55 am
content: Quote from: oldway on May 30, 2018, 08:39:48 amThat would be quite an oversimplification.Afaik, the markings on a cap are mainly for identifying it, not for characterizing it, although in many cases the markings are conveniently obvious and enough for the latter, too. What really is important is defined by the circuit the cap is in (or schematics etc.).E.g. some caps have no markings on them at all, would that mean no parameter is important?I do not know of any electrolytic cap to have ESR marked on them, but in many circuits (especially in various power supply types) the ESR can be more important than the capacitance (as in, the allowable range of values can be tighter), even so that ESR must be within some range, instead of being less than some value, otherwise the circuit won't be stable. (Imho, a stupid design idea, but I guess the goal is to save 0.1 cents per device, ignoring any future costs of more difficult repairs or even full replacement of the device).Also, consider e.g. ceramic caps, where some types have a huge reduction in effective capacitance as one gets higher and higher in the voltage, and the nominal capacitance is stated at some low voltage (e.g. TDK rates capacitance of ceramics even down at 0.5+/-0.2Vrms, another at 0V+/-?), instead of at rated voltage. If one accidentally replaces C0G with a X5R or such types in a circuit that works at higher voltage, things can fail to work. (I'd have given an example for the reduction, but of course, now that I want to find such graph, I can not spot any in the datasheets, and just couple weeks ago I seemed to see them in every single one...)Of course, if the capacitance is out of spec already at a low voltage, it will be bad cap, but hey it was the same for the leakage current. According to you, test has to reveal all the issues, even the high voltage ones, or it is of 100% unusable. Right?

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 10:40:35 am
content: Oversimplification? You are kidding ?A 2 transistors LV tester is not even capable of making this oversimplificate and basic tests.....What are looking for ?There are Keysight testers to make the tests you want to do....but they cost an arm...Nothing to do with a condensator tester LV ou HV.If you need more tests than the oversimplificate and basic tests, simply replace the condensator by a new one, it is cheaper than to buy a 10K Keysight instrument.If you are speaking about measuring characteristics for new products development, nobody working as engineer will be satisfied withpredictingleakage current, he will measure it in the circuit.NB: capacitores with low ESR are identified by a marking on the capacitor.For exemple, here CJ = low ESR with specifications to -40°Chttp://www.nichicon.co.jp/english/products/pdfs/e-cj.pdf

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 30, 2018, 04:18:32 pm
content: Quote from: GEOelectronics on May 25, 2018, 02:21:28 pmWhen I think of capacitors it may be a very different mental picture of what the next person thinks of. Notice how the High Voltage, very ultra low leakage types are always handled and shipped with the leads shorted. These types can accumulate a really high charge from the air and hold it for a surprisingly long time.\edit-30 May 2018 Capacitor illustrations added for clarity.Geo>K0FF

author: oldway
author_rank: Super Contributor
timestamp: May 30, 2018, 04:47:33 pm
content: Any electrician knows that an insulation resistance measurement must be done in high voltage with a megger and that measuring the insulation resistance with a multimeter is useless because this gives a false (to high) value ....Similarly, to test a capacitor, it is necessary to measure its insulation resistance (or its leakage current) at its nominal voltage, not under low voltage.NB: At and up the breakdown voltage, model of the leakage current changes drastically and became highly non linear.That's why values of insulation resistances measured with a megger and with a multimeter are totally different IF THE INSULATION IS BAD AND DOES NOT SUSTAIN THE TEST VOLTAGE.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2018, 10:33:24 pm
content: Quote from: GEOelectronics on May 30, 2018, 04:18:32 pmI like the lamp.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 30, 2018, 11:48:30 pm
content: All for caps were then allowed to reform for a full 10 hours in addition to what had been done.

author: BravoV
author_rank: Super Contributor
timestamp: May 30, 2018, 11:51:01 pm
content: Quote from: joeqsmith on May 30, 2018, 11:48:30 pmJoe, with that cool logging there, is there possible to log the leakage during the reform ?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 12:05:20 am
content: Quote from: BravoV on May 30, 2018, 11:51:01 pmI don't see why not.

author: BravoV
author_rank: Super Contributor
timestamp: May 31, 2018, 12:09:35 am
content: Quote from: joeqsmith on May 31, 2018, 12:05:20 amGreat, really curious whether it will be linear or "else", which interest me, thanks and expecting to see the results.Also there are Japanese capacitor manufacturers app note that stated temperature also plays role in this reforming period, and most stated they did it at high temperature.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 12:44:26 am
content: We had always reformed them at room temp. I can tell you that the curve was not linear for these caps. I was watching them off and on during the first few cycles.

author: BravoV
author_rank: Super Contributor
timestamp: May 31, 2018, 01:17:39 am
content: Great, looking forward to see the "curve".

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 01:50:28 am
content: Quote from: BravoV on May 31, 2018, 01:17:39 amYou asked if it was possible to which I responded I didn't see why not. I think you are reading too much into my answer to your question.Don't you have a UT61E and power supply where you can run your own test? Join the fun. Let's see what you come up with!

author: BravoV
author_rank: Super Contributor
timestamp: May 31, 2018, 02:05:07 am
content: Quote from: joeqsmith on May 31, 2018, 01:50:28 amLOL .. my mistake.Actually I did , like this below for polymer cap, its new old stock Sanyo OSCON purple cap, leakage curve logged for about 1.5 hours below, the vertical axis 1 Volt = 0.01 uA, and its started to decrease at 30 minutes.Its just I don't HV DC psu, really interested at those mains rated electrolytic caps, like popular 350 or 400 V ones.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 04:01:09 am
content: Quote from: BravoV on May 31, 2018, 02:05:07 amAdded your link to that 2015 data:https://www.eevblog.com/forum/beginners/is-there-any-practical-or-quick-n-dirty-method-to-measure-capacitor-leakage/I take it you are not comfortable working with something like this. Let me see if I can locate some parts that have not been used for at least a couple of years.

author: BravoV
author_rank: Super Contributor
timestamp: May 31, 2018, 04:13:01 am
content: Quote from: joeqsmith on May 31, 2018, 04:01:09 amThanks.That thread started as question and ended with the test, the more accurate link at post #10 ->https://www.eevblog.com/forum/beginners/is-there-any-practical-or-quick-n-dirty-method-to-measure-capacitor-leakage/msg722332/#msg722332I'm not afraid of working with high voltage, its I'm just an enthusiast and I don't own any HV DC PSU with CC feature.Bit off topic if you don't mind, actually I'm looking at this circuit for quite sometimes now for candidate of simple DIY, its just it doesn't have the adjustable CC.Source ->EDN: Regulate a 0 to 500V, 10-mA power supply in a different way

author: PA4TIM
author_rank: Super Contributor
timestamp: May 31, 2018, 05:44:08 am
content: For leakage tests or reforming you do not need a psu with CC. Just use a resistor. That is needed for safety as a cap goes short. I never logged reforming. What I do with real old ones I want to survive is doing it in steps, for example first 10V, if the leakage then is under 50 uA, I go to 50V, wait until leakage is low enough and then I increase the voltage again etc. The charging is not interesting, you want to see the current decrease while the voltage stays the same.

author: BravoV
author_rank: Super Contributor
timestamp: May 31, 2018, 05:58:00 am
content: Quote from: PA4TIM on May 31, 2018, 05:44:08 amYou should try it as you have far better tools and also you show you're interested in capacitor all this time, its interesting at least for me.As my experience with polymer cap, 1st I thought it will be just boring with stable or at least predictable leakage, cause I was "assuming" that polymer type is well known to be better compared to common electrolytic ones, but the fact like my chart, its proven that its also has the "curve" as well, even at it's rated low voltage at 16 Volt.Not claiming an expert, especially with limited testings, but as my chart shows, even on polymer cap, especially the old one, it "needs time" to wake up, and there is no literature about this particular type of cap when old as far as I'm aware of.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 11:25:55 am
content: I would guess that most of the higher quality brands will provide a process for reforming, just like measuring leakage. Some will call out the resistor to use based on the voltage range (using CV). I've seen notes about an hour per year. So a cap that has sat unused for 5 years would require 5 hours to reform.For example, pages 15 & 18 may be of interest.https://de.tdk.eu/download/185386/5f33d2619fa73419e2a4af562122e90c/pdf-generaltechnicalinformation.pdfI've only ever been involved with alum elec reforming. Are there papers about reforming other types? I've never looked.

author: GEOelectronics
author_rank: Regular Contributor
timestamp: May 31, 2018, 05:32:20 pm
content: Quote from: joeqsmith on May 30, 2018, 10:33:24 pmYou might like the tube (Eimac 8171, also called 4CX10000D) we built a tube tester for that used components that were state of the art in 1975. No that was a HVDC power supply- 5kV @ 5A. \ Filament ran 75 Amps, HV was ramped up via a pair of 220V 28A ganged and inductor-balanced Variac a.k.a. "The Big Wheel".The transformer was a pole-pig backwards.Geo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: May 31, 2018, 11:13:53 pm
content: I would put both of those lamps in my office, no problem. The 5KV at 5A continuous, no thanks..... Well maybe...

author: joeqsmith
author_rank: Super Contributor
timestamp: June 01, 2018, 11:46:30 am
content: Quote from: BravoV on May 31, 2018, 02:05:07 amFor your reforming current curve, I found a United Chemi-Con part number EKMH451VQT221MB25T. This is NOS, 220uF, 450V, alum elec, sitting for at least five years.Datasheet can be found here:https://media.digikey.com/pdf/Data%20Sheets/United%20Chemi-Con%20PDFs/KMH%20Series.pdfThey spec 1.13 Ohm @ 120Hz, measured 0.266DF max is 0.15, measured 0.036C +/-20% @ 20C 120Hz, measured 206.9I=0.02CV (uA ) or 3mA, whichever is smaller, after 5 minutes at 20 deg C.Where I = Max. leakage current (uA), C = Nominal capacitance (uF) and V = Rated voltage (V)So that's 1.98mA after 5 minutes. This datasheet mentions a 30 minute reforming cycle at the rated voltage. Two pictures show the leakage after 15 seconds, 1 , 2 and 5 minutes. This part is already well below the specified leakage and could be put into service.

author: oldway
author_rank: Super Contributor
timestamp: June 01, 2018, 12:24:42 pm
content: Quote from: joeqsmith on May 31, 2018, 11:13:53 pmI have just been asked to repair a DIY vacuum tube amplifier with 1250V anode voltage and hand made cad provisional schematics ....No, thanks....http://www.diyparadiso.com/captainpp1.htm

author: Calambres
author_rank: Frequent Contributor
timestamp: June 01, 2018, 05:30:22 pm
content: Interesting thread!

author: joeqsmith
author_rank: Super Contributor
timestamp: June 02, 2018, 04:15:29 pm
content: I think I found a good alum elec HV cap for this reforming current curve test. Many years ago I gave my wife a USA made Mallory capacitor that she has kept all these years and as far as I know has never used it.This part is a CG (Computer Grade) series, 110uF 450V. I bought these at the Dayton ham fest some time in the early 80s for a linear power supply and would assume it was used when I bought it. I have attached a datasheet for it.Leakage is spec'ed at 6X10-6 CV, not to exceed 4mA after 30 minutes. So that's 2.97mA. The spec the ESR to 1.220 ohms at 120Hz.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 02, 2018, 10:51:57 pm
content: It's been running but will take some time.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 12:42:17 am
content: Well, you may make of this what you will. Basically, looked to see how it was leaking and it was pretty bad. So, I thought, no resistor and larger power supply right at the operating voltage and just see what happens. After about 40 minutes of pulling about 15mA or dissipating about 7 Watts it still hadn't out gassed. I decided to open the case and check it. Fairly hot as you may expect. The plot shown is in Amps, not ma.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 12:51:09 am
content: I turned off the supply and setup a fan to cool the part down. I then checked the capacitance, dissipation factor and ESR. There were no major changes.So I hook the part backup to the supply and was going to attempt round 2 with no changes to the setup other than allowing the part to cool. It seems that the hot cycling had some major effect and leakage had dropped from 15mA down below 1mA. I let it set a couple of minutes, then opened the box and shorted the cap. A pretty good bang. This is the spike seen in the data. I then turned down the supply and shut it down.I again retested the cap and it appears normal and there are no signs of any leaks.Also, this plot is in Amps, not mA.

author: GerryBags
author_rank: Frequent Contributor
timestamp: June 03, 2018, 02:28:22 am
content: Interesting results, Joe! I wonder whether we are seeing a faster rate of oxide growth with increased temperature or a higher maximum level of oxide growth. Given the fairly dramatic reduction in leakage to better than original spec, I rather suspect the latter. I reckon it may be something like: As the temp increases, the cap expands, allowing more room between the plate and separator for oxide to grow. Once the cap cools that oxide growth will stay even when everything shrinks back to normal. Possible?I bet the pressure in that cap was pretty close to the mechanical limit of its seals, which a manufacturer is not going to risk in their forming process, which could be why it's not done commercially. If you had an application, though, which calls for large capacitance and low-leakage currents maybe it would be an idea to get five times the amount you need and stress-form them at high temps, or at least do a few of the same brand/batch to beyond their limits to find out where they are and then do your forming?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 02:28:56 am
content: I changed the scale to mA and let it run another hour. About half way into the test, I installed a 250K series resistor. At 100uA its about a 25V drop off the 450VDC. After resistor was installed, I discharge the cap.I then retested the part and the ESR for some reason has improved after all of this abuse. It was 1.321 ohms @ 120Hz, which is out of spec. It's now down to 0.220 ohms.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 02:41:56 am
content: I was just surprised the thing stayed together. I should have had a temperature sensor on it. There are no signs where the seal deformed and no odors.

author: GerryBags
author_rank: Frequent Contributor
timestamp: June 03, 2018, 02:58:12 am
content: It may not work so well on the modern electros, with their blow-out tops, but I think that, because the pressure is spread out over the whole interior of the cap rather than a single point failure causing the over-heating, the cap is able to take the pressure, maybe?Really appreciate you doing these experiments, and yes, do it again with a temp sensor!

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 03:47:07 am
content: That was a one-shot deal. We can't order up 20-30 year old capacitors like scotch.I wonder what the Theta would be for this package, or in other words, what would be the core temperature based on the outside sleeve temp.

author: BravoV
author_rank: Super Contributor
timestamp: June 03, 2018, 06:16:13 am
content: Quote from: joeqsmith on June 03, 2018, 12:51:09 amQuote from: joeqsmith on June 03, 2018, 02:28:56 amJoe, thank you so much for the effort, time & energy to do this cap reforming, really interesting results.

author: GerryBags
author_rank: Frequent Contributor
timestamp: June 03, 2018, 06:40:05 am
content: Quote from: joeqsmith on June 03, 2018, 03:47:07 amAre you sure? Most of what is on offer on Ebay seems about that old.Saying that, I do have a big old Mallory CGS somewhere myself that I'll have to check the date code on, but you do see job lots of NOS (some of it really OS) caps come up now and again, usually with "Vintage!!" in the title, as if it's a good thing.Also, yours was an extreme example, but the effects of age start straight away and finding 5-10 year old caps should be much easier. If I'm near in what I think is going on it also means that even brand new caps could possibly see an improvement in both leakage and ESR, even if it's only small.

author: PA4TIM
author_rank: Super Contributor
timestamp: June 03, 2018, 11:47:45 am
content: Could it be you had the polarity wrong ? Probably not because it for sure would go with a bang, but you know, the thing with Murphy and I assume your are a humanI have tried that in the past to investigate the "zener" function of the oxide layer. (but with not more as 1mA current) I can not remember the "zener" voltage but it was less as 6V. The caps did survive this. It started as an experiment to see if it was possible to change the polarity.I think the layer was not short, I think the voltage caused a force that pulled the plates together thereby causing a short, maybe between the connections. While cooling down the short "moved" back and this time just far enough.Time for some surgery Dr Joe.. see if you can find some damage

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 02:15:17 pm
content: Quote from: BravoV on June 03, 2018, 06:16:13 amI see what you did there..

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 02:19:54 pm
content: Quote from: GerryBags on June 03, 2018, 06:40:05 amIf you look over the thread, I ran a NOS part just prior to this that I knew for a fact had sat at least 5 years unused and it still met spec. If you find yours and you have the ability to run it, give it a try and post the results.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 02:41:08 pm
content: Quote from: PA4TIM on June 03, 2018, 11:47:45 amI certainly make mistakes but you have a bit of evidence presented already. The first picture you can see the cap inside the containment box. First, it's not a really safe setup with those standard test cables and the color codes are a bit of a mix. However, the red clamp goes to the left of the text while the black clamp is attached to a small ground strap that I attached to the post. We can see the left Brymen is reading the voltage. The red and black leads are plugged into the V and Com respectively. You can see the red clip of this lead clipped to the backside of the gray, which goes to the large red clamp. The black is attached to the braid of the ground strap. Last, notice that you can't see the masking tape I have added to the cap as it is on the backside.Next look at Mallory5. This looks down on the top of the cap. We can clearly see the "+" or positive on the right and the tape with the marking below.There is a third bit of evidence that was presented as well. That's the very first graph where the part is pulling about 15mA as it settled. Note the supply was up to about 100mA before it started to drop. This is the same death trap I used to make that last video where I wanted to show YTer Voltlog what happens if you had a higher power 1KVDC supply attached to a cheap meter with the meter in the ohms setting. I lost a 440mA fuse in my Brymen that day.Anyway, any alum elec capacitor I have ran backwards pulled a lot of current and has frequently ended in a bang. This supply can certainly provide much more than 15mA. I suspect this cap would pull a lot more current even now if I tried to put 450V across it backwards.

author: PA4TIM
author_rank: Super Contributor
timestamp: June 03, 2018, 03:36:39 pm
content: Sorry, I have not studied the pictures. And if I did, it would not help much, on my small laptop I can not see the small details. I see in that box a red crock connected to a black wire and a black crock to a red wire. I can not see where they go.Have you cut it open to see if you can find the cause of the short ?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 05:39:32 pm
content: Please explain what short?

author: PA4TIM
author_rank: Super Contributor
timestamp: June 03, 2018, 06:13:23 pm
content: Turns out I'm not only blind, reading is also an art I do not always master.Quote

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 06:58:10 pm
content: Quote from: PA4TIM on June 03, 2018, 06:13:23 pmRight, so 0.015 Amps or 15mA, basically what is shown on the Brymen above. If the cap would have shorted, we would see some higher currents.I am currently attempting to carefully and methodically damage three of the alum elec that I had started to set on post 100. I finally got around to running them at their rated voltage. Shown is the current when sweeping from 15ish volts to 150ish volts. I have added a 1 and 2 meg resistor for comparison. I increased the hold time to 30 seconds to allow them more time to settle.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 07:43:47 pm
content: Attached are the two datasheets I could find on the net for the TVA ATOMs. I found a real early ad for them as well from the 60s or 70s. Non that I found show the leakage currents. Just that they are low. That's a technical term, low.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 08:03:00 pm
content: Cap#1 was subjected to 20 4KV positive pulses from my low energy transient generator.Cap#2 was reversed with a 800mA supply for several seconds allowing it to cook. It was hit enough you could smell the plastic jacket. Even after cooling for a minute, it was hot to the touch. Somehow it did not appear to out gas.Cap#3 was applied with an over voltage of about 2X for a few seconds. Again, drawing more than 100mA. Enough to make it warm.Cap#4 was left as a controlI allowed all the caps to cool. I then remeasured the C,DF and ESR but there was no major effects. I then repeated the same 150V sweep on the three capacitors I had stressed, expecting #2 to have major problems. However, that's not what happens. The largest changes were with caps #1 (purple) and #3.Note in the second plot, I only show the before and after for cap #2. Just a very slight change.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 03, 2018, 08:50:18 pm
content: And now that we have two caps that we can easily detect are defective at their rated voltage it's time to repeat the 20 volt sweep. As you can see, all three caps there were stressed have changed however even at 20V, the leakage is well below the 5uA limit. It seems to suggest that these would be difficult to detect when using a linear model with a fixed threshold.I think this answers my questions anyway that a simple model is out of the question let alone assuming one that is linear. I doubt anything too surprising but it's good sometimes to show some data. If anyone has some other test they would like to see ran, feel free to ask.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 04, 2018, 01:07:38 am
content: Short clip of the Sprague ATOM TVA1409, cap #1 being stressed to outgases. Brymen on left showing current in Amps, right, voltage across the cap through a series resistor. This part was rated for 150 volts. Hung in there fairly well I would say.https://youtu.be/KZ6jEW2VuW0

author: joeqsmith
author_rank: Super Contributor
timestamp: June 04, 2018, 11:43:57 am
content: The solution used in C1 smells like old tires. I checked it on the RLC meter after it had cooled. The ESR was higher and the capacitance was lower. I then ran another sweep at 20V (yellow). The leakage has a different profile than the virgin part had but at 20V, its a wash. With a 5uA threshold, both cases would fail. For fun I ran another half hour reform and repeated the 20V sweep (orange). We can see the leakage improved and is far below the 5uA, the ESR is still very high.

author: Shock
author_rank: Super Contributor
timestamp: June 04, 2018, 02:26:13 pm
content: Does anyone know if the "formulas" discussed in this video at about 32mins onward are documented in any book/whitepaper etc?

author: Shock
author_rank: Super Contributor
timestamp: June 04, 2018, 04:18:11 pm
content: Quote from: joeqsmith on June 02, 2018, 04:15:29 pmHope you gave it back before you destroyed it. If on a budget you could always gut it and insert a shiny new Capxon.Your video shows what happens if you don't have logging, you miss out on all that cool breakdown action. I think the best scenario when reforming electrolytics is to limit the current and step the voltage between plenty of soak periods. Check if the leakage at each voltage step has settled before moving up. This needs to be done before a high voltage is applied, which is not the case in most instances when discovering faults.Makes me think that using a LV tester directly after a HV tester could be characterizing a partial carbon short.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 05, 2018, 01:27:21 am
content: Obviously, I have the ability to log so I'm not understanding how the video shows what happens when you don't. Are you wanting to see the data and are not sure how to ask?

author: Shock
author_rank: Super Contributor
timestamp: June 05, 2018, 02:41:36 am
content: Quote from: joeqsmith on June 05, 2018, 01:27:21 amNo, I was fine with the videos.I mean in general, people characterizing caps without measurement and logging would miss out on all the swings in current that show the cap breaking down.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 05, 2018, 04:53:35 pm
content: Quote from: Shock on June 05, 2018, 02:41:36 amTrue. This is why I was wondering if some of the testers had some sort of peak detection. I have never owned a capacitor checker like the Carlson's lab shows. Looking through the documents I could find on these vintage systems, none appear to have such a feature. It would be fun to send all of these parts to him to have him run them across all of his testers and see what results he gets.I watched the video you linked from 32 minutes on. He was talking about clicks and ticks. I assume he had just not learned tau. That part was pretty basic. I'm guessing you did not have a problem with the part about ohms law and using the meters input resistance to measure the current. I am guessing what you are asking about is 41:44 into the video.https://youtu.be/xF15sv41AEY?t=2502I follow what ever the manufacture calls for. There is no constant rules. You could write them and ask. I am curious myself where these were first published. Let me check some of my old ARRL handbooks and see if they have some guidelines like these.

author: Shock
author_rank: Super Contributor
timestamp: June 06, 2018, 02:32:29 am
content: Quote from: joeqsmith on June 05, 2018, 04:53:35 pmYes about the 8 time constants for paper caps and the formulas he was using for electrolytic leakage. They do seem ballpark figures, but he seemed to have picked this up from somewhere so was wondering if they were hidden away in some book.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2018, 10:44:41 am
content: None of my old books have any estimates like what they show. Google time. This person show some of the same formulas. They give credit to a paper from Nichicon. The links they provide still work.https://www.nmr.mgh.harvard.edu/~reese/electrolytics/