Old (but unused) electrolytic capacitors: Things I should know - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2017, 08:21:04 am
content: I have aquired a large amount of old electronic components from an auction (school that was moving, they got rid of most of their component-level stuff and equipment because they are now working with modular educational systems, from what I'm told). We are talking about a 3m tall, 2m wide, 1m deep storage cubbord/closet full of transistors, resistors, capacitors and diodes. I know a good part of it will be old and useless,but for the price I payed it seemed like a great deal to have as a "I quickly need this component" source.The main thing I'm curious about is the electrolytic capacitors. There are thousands of them in this thing, ranging from tiny ones (a few volts at a few uF) to 500V 10000uF capacitors. However, most of these are old, 15+ years, some going back to the late 80s. What I was wondering is if they are still any good, or if they will fail rapidly after using them. I also seem to remember reading a document from Kemet that you could "rejuvinate" old electrolytic capacitors (That haven't been used and just sat on the shelf for ages). It had something to do with applying a very, very small voltage (I think reverse biased) to rebuild the internal layers before using the capacitor.Anything to this? Other tips/things to keep in mind when dealing with electrolytic capacitors that have been stored for a very long time? Or perhaps components in general?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 20, 2017, 08:33:25 am
content: IME the only issue with electrolytics is if they've been run hot. I've certainly used ones that are 10+ yeard old. YMMV of course, so just test a random sample.

author: Vtile
author_rank: Super Contributor
timestamp: June 20, 2017, 09:41:47 am
content: They may come electrically leaky for an extented storage. Build yourself a unit or a semipermanent test setup for capacitor leakage testing from 0 to x00 volts dc. These can be found by googling and are many times an older electronics magazine projects. Usually they have also the revive process described.

author: LazyJack
author_rank: Frequent Contributor
timestamp: June 20, 2017, 09:56:27 am
content: There should not be any problem. If you are worried, charge the capacotors to their rated voltage via a couple of k value resistor. Monitor the current (or the voltage drop over the resistor). You may initially have large leakage, but as the oxide dielectric regenerates, it will go lower. If ot does not, only then discard the capacitor.Leave the voltage on for some minutes to complete regeneration.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2017, 10:59:37 am
content: Quote from: LazyJack on June 20, 2017, 09:56:27 amWould there be a benifit or downside of giong to a lower voltage than their rated voltage? I might look at building a standard test box that does this for a few fixed voltages (not to mention I don't yet feel confident buidling something that can put out a few hundred volts of DC to do this to some of the biggest ones).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2017, 11:15:51 am
content: Sure. I would take such a collection with skeptical optimism. They're probably fine, but just in case (especially for the larger values, and older looking parts), bring them up slowly (they may need reforming), and measure ESR and leakage if possible.Quote from: TheUnnamedNewbie on June 20, 2017, 10:59:37 amThe capacitance value may drift over time; running near rated voltage will probably keep it closer to nominal.Tim

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2017, 11:21:10 am
content: Unfortunatly I don't own a LRC/ESR meter, nor a multimeter capable of doing so. Buidling one could make an interesting project but I have a few projects lined up already... I'll see what I can do! Thanks alreay for the tips.

author: LazyJack
author_rank: Frequent Contributor
timestamp: June 20, 2017, 11:22:25 am
content: If you want to reform the dielectric, then you need to have voltages at the rated value or close. But since you do not need high current, you can for example use a set of zener diodes to clamp the voltage, so it is fairly simple to accommodate for different voltages.

author: LazyJack
author_rank: Frequent Contributor
timestamp: June 20, 2017, 11:26:17 am
content: To be honest, I don't think you'll have problems with 10 yrs old capacitors, even if you start using them right away without any formatiting. Maybe check for obvious things, like short or capacitance well below the nominal value.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2017, 02:35:57 pm
content: Simple ESR test: set function generator for 50 ohm output, square wave, modest frequency (10s to 100s kHz). Plug in to oscilloscope with a tee adapter. Attach BNC to binding posts connector to tee. Connect capacitor to binding posts. (Scope set for 1M input resistance.)The open circuit voltage, divided by generator Zo (50 ohms), gives the test current. If ESR << 50 ohm, then ESR ~= (measured voltage) / (test current). Bonus: you also get to see complex aspects of the impedance, like lead-edge overshoot (ESL), capacitance (the charging slope, if any; reduce frequency to see it better), and more subtle properties (like distributed ESR/ESL).This isn't very sensitive to mOhm ESR (even with the scope set to ~mV and the function generator set to ~V), but it's certainly effective enough to weed out any smaller ones that have gone bad!Tim

author: Paul Price
author_rank: Super Contributor
timestamp: June 20, 2017, 02:47:26 pm
content: Breadboard build your own ESR meter in minutes. Easy to find parts, you might even substitute your DVM for the readout meter.https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/

author: MosherIV
author_rank: Super Contributor
timestamp: June 20, 2017, 02:52:00 pm
content: QuoteBetter still ESR meter in 1 clickhttps://www.ebay.co.uk/i/322477147751?chn=ps&dispItem=1&adgroupid=41262231517&rlsatarget=aud-310271574880%3Apla-294967381109&abcId=1058846&adtype=pla&merchantid=101713788&poi=&googleloc=9046149&device=c&campaignid=796834294&crdt=0

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2017, 03:14:50 pm
content: Quote from: T3sl4co1l on June 20, 2017, 02:35:57 pmIf only I had all of that testequipment... I'm just getting started and still in uni. I have an old scope, and a multimeter. I might have a working function generator soon, but it's meant for audio and 600 ohm. Ofcourse, should still work under the same principle.Paul Price: Yeah, I've seen that in a few videos on youtube. However, as I said it's one of the things I could look at buildingMosherIV: I prefer not to get those cheapy ebay things. I never seem to be able to trust them and I much prefer making my own or just buying a reputable brand. An LCR meter that can measure ESR is one of the things on my ebay-watch list. After that keithley 2000.

author: MosherIV
author_rank: Super Contributor
timestamp: June 20, 2017, 03:42:43 pm
content: QuoteWhile this might be from some unknown vendor in China, the circuit and code is actually open sourceThere is an entire thread on it here :https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/I have one and it works as much as I expect it to (ie I take the results as an indication ONLY).If you read up on Equivalent Series Resistance - you will find that there is no absolute value to it, it depends on the measurement technique being performed.Most capacitor manufacturers do not even give a value for it in their specifications, they give a Q factor instead.ESR is only really useful for checking for bad electrolytic capacitors, and then you are just looking for abnormally high values eg >1

author: Omicron
author_rank: Regular Contributor
timestamp: June 20, 2017, 03:56:04 pm
content: Quote from: TheUnnamedNewbie on June 20, 2017, 03:14:50 pmSend me a PM, I might be able to donate you a starter set for your lab...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 20, 2017, 04:07:17 pm
content: Quote from: Omicron on June 20, 2017, 03:56:04 pmPm has been sent!