Does shorted electrolytic cap will shorten it's shelf life ? - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: August 01, 2018, 09:10:55 am
content: I googled and seems can't find any good information on this subject.Reason for shorting the cap's terminal is to reduce possibility of accident, caused by the capacitor's dielectric absorption while its in storage, especially for high voltage or big capacitance cap.

author: Thewafflication
author_rank: Contributor
timestamp: August 01, 2018, 09:43:34 am
content: This might be an ESD thing? I am not sure. I have attached an image of an electrolytic caps equivalent circuit. I did not find an answer in this but it is pretty awesome.http://www.cde.com/resources/catalogs/AEappGUIDE.pdf

author: BravoV
author_rank: Super Contributor
timestamp: August 01, 2018, 10:16:29 am
content: Quote from: Thewafflication on August 01, 2018, 09:43:34 amThanks for the appnote, but no, its not the ESD I worry about, its just I collect quite numbers of high voltage and big capacitance caps (in Farads), yes, I'm a hoarder.Just worry if stored without strapping both terminals with a piece of conductor, someday, I mean probably months or years away from now, all it needs is a simple stupid bare wire touched accidentally at both charged terminals will create fire hazard, or a long enough piece of metal say like a bolt or screw driver and etc.Btw, your app note there mentions about it too (quote attached below), its just not clear if stored shorted will have affect long term bad side effect compared to stored not shorted.

author: Gyro
author_rank: Super Contributor
timestamp: August 02, 2018, 12:03:40 pm
content: It's hard to think that a shorted capacitor would age any faster than an open one. With most electrolytics in storage their voltage will eventually decay to zero over time due to internal leakage current. If they're in a stored piece of equipment then there will probably be a resistive discharge path anyway.Dielectric absorption can be a real pain in high voltage caps. I've experienced it with film caps and it hurts!@Thewafflication: A useful document link. Thanks.

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2018, 06:20:43 pm
content: Shorted or unshorted will have no effect on life. High voltage capacitors are sometimes shorted as a safety issue because they can regain considerable charge from dielectric absorption.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 02, 2018, 06:28:35 pm
content: Shorting a charged cap may damage it, due to mechanical or electrical stresses.As a storage method, it has no effect. As mentioned, it's typically used as a safety feature.Tim

author: AndyC_772
author_rank: Super Contributor
timestamp: August 02, 2018, 06:44:57 pm
content: How could shorting have an effect on the storage life of a capacitor?If it's discharged, the two terminals are at the same potential, so the current through the shorting link is zero. Just like it would be if the shorting link weren't there at all.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 02, 2018, 09:53:01 pm
content: I'll say itmightshorten the shelf life, and here is why:1. The oxide layer (for Al electrolytics) tend to thin out when the capacitor was unpowered for years or decades, and thus lowering the admitted voltage so much that the capacitor can short-circuit itself when re-powered at normal voltages (to recover capacitors unpowered for many years or decades, the oxide layer can be grown back by "reforming" the capacitor with a very small current for many hours).2. Disconnected electrolytic capacitors (with open terminals, stored in boxes, not on the PCB) usually does not have zero volts. When measured, even after years or decades, they still have tens or hundred of millivolts (not very sure why this is happening, but it's true, if you don't believe it, measure yourself a few big electrolytics desoldered years ago), so at least in theory this will help with keeping the oxide layer thickness. If this is relevant or not for the shelf life, I have no idea.Anyway, AFAIK the dielectric absorption will not auto-charge a capacitor from nothing, dielectric absorption happens only when achargedcapacitor isshortedfor ashorttime and then re-open the terminals. If they are properly discharged (in tens of seconds, with a resistor) the voltage will not came back like in a discharge with a short-circuit.I heard only once about a guy saying his electrolytics charge themselves from open air upto many volts or tens of volts, but I could never found more than a few hundred millivolts on uncharged stored capacitors.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 03, 2018, 12:54:42 am
content: A few hundred millivolts is well within the scope of dielectric absorption and electrochemical potentials; it's nowhere near enough to activate the reforming process, even for, say, bare aluminum that's been exposed to air (thus having a ~nm layer of oxide on its surface), let alone a capacitor of notable rating (up to 500V).Tim

author: amyk
author_rank: Super Contributor
timestamp: August 03, 2018, 01:20:46 am
content: Quote from: RoGeorge on August 02, 2018, 09:53:01 pmThat could be due to a high EMF environment. Interestingly, an electrolytic capacitor makes a very poor diode so it's plausible that it could charge itself given a high enough environmental field strength...

author: BravoV
author_rank: Super Contributor
timestamp: August 03, 2018, 02:28:28 am
content: Quote from: RoGeorge on August 02, 2018, 09:53:01 pmAbout the decaying oxide film layer overtime when not in used, as this is well known that it will reduce capacitance and increase leakage, I think my question is more like does shorted cap will speed up the deterioration process ?May be we need a chemist here on the oxide deterioration mechanism ? Or anything else ?Guess this becoming more academical rather than practical, cmiiw.Another info at the net ->http://www.tuks.nl/Mirror/faradnet_com/deeley/chapt_06.htm#shelf

author: BravoV
author_rank: Super Contributor
timestamp: August 03, 2018, 02:29:35 am
content: Quote from: T3sl4co1l on August 03, 2018, 12:54:42 amTim, why up to 500V ? Something different in this region ?

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2018, 08:17:07 pm
content: Quote from: amyk on August 03, 2018, 01:20:46 amNicely dead-pan.EDIT: Sorry, I couldn't resist, but a quick thought experiment (yes the 'diode' effectively exists):- According to the document that Thewafflication linked, the 'diode' Vf is about 1.5V- Think of how high the junction capacitance of the 'diode' is- Think how high an impedance the capacitor leads (normally closely spaced) present to any external EMF- Imagine the RC filter formed by the above impedance and the junction capacitance and guess at the maximum frequency that might be effectively rectified and stored - it's as close to DC as makes no difference.You would need a considerable DC voltage gradient presented at a right angle and in line with the capacitor leads to be able to inject any charge of even a few hundred millivolts into it. Not the sort of thing that happens with randomly arranged capacitors in a box or draw.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 03, 2018, 11:56:58 pm
content: QuoteUnfortunately I couldn't find the original topic (it was a much older and detailed topic). The message translated above is more recent, but contains more or less the same story, and was written by the same person.All I can say is thatzalwas never a liar. He is an experienced retiree electrician/electronist with a lot of practice under his belt, so I'm also sure those 20V were not because of a faulty measurement, or something like that.

author: JS
author_rank: Frequent Contributor
timestamp: August 04, 2018, 01:44:24 am
content: Big caps usually have big leakage, so years from stored they are not only not likely to build up any charge but get discharged in the way. Problems with big caps is when somebody left a charged one in the bin, either by accident or for fun, and someone come back short after and gets zapped. From there to spontaneous fire hazard there's a long long way. Properly and slowly discharging them before storage is good practice but I don't see need to leave them shorted while stored.JS

author: ocset
author_rank: Super Contributor
timestamp: August 04, 2018, 10:20:19 am
content: Shorting it wont affect shelf life.The voltage measured on a cap after years in storage could just be the DMM charging the cap up a little....i dont think the full capaciutance is there till the vin goes above a certain amount...say above 5% of nominal voltage....so if its only got say 100mv on it, then its only a small cap then...say if its a 100v rated cap.The thing as you know with EL caps is that they have high leakage after being stored for a long time...and in theory, if they then get used...they can overheat and blow up...due to the high leakage current that flows through them till they "cure"....i used to work in a xenon flasher place.....and when we had an order,.......we had to time it so we ordered freshly manufactured EL caps for the production run...no way would we produce an order with big el caps that had been in storage....for a start...if a el cap has been in storage...then for how long has it been there?....some store keeper may have an error in the storage record...........your caps might have been there for 10 years and they thought they were there for only 2 days."Fresh off the line" el caps or "forgot it" was our motto.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 04, 2018, 10:40:48 am
content: Quote from: BravoV on August 03, 2018, 02:29:35 amYes, aluminum is not capable of / practical to anodize higher. You see electrolytics up to "630V" but they're internally series pairs, AFAIK. Almost all regular serieses go up to 450-550V.I don't know what the controlling or limiting factors are for this, just that it happens.Tim

author: BravoV
author_rank: Super Contributor
timestamp: August 07, 2018, 04:15:58 am
content: These are what I'm talking about, just bought recently on impulse.Even aged > a decade, when arrived, some have residual voltage about 0.6 volt.Even shorted (with resistor) for few hours until zero volt, once opened, after about an hour it keeps bounce back to about 0.5 volt, guess I need to keep them shorted longer to suppress further.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 07, 2018, 12:16:05 pm
content: Yes, the absorption time constant can be very long indeed, days or weeks. I suppose it's an ionic diffusion thing (in which case it won't have a time constant as such, but a diffusion response instead).Tim