CAPACITOR Checking - Page 1
Forum section: electronics / beginners

author: vinlove
author_rank: Frequent Contributor
timestamp: July 24, 2019, 03:41:40 pm
content: Has this capacitor gone bad? In paper, it is supposed to be 100uF.But in checking out with the meters, it is 200 -230nF?And Vloss= 7.1%?

author: bob91343
author_rank: Super Contributor
timestamp: July 24, 2019, 05:05:56 pm
content: Yes it's bad. Throw it out.

author: vinlove
author_rank: Frequent Contributor
timestamp: July 24, 2019, 06:40:19 pm
content: Quote from: bob91343 on July 24, 2019, 05:05:56 pmThanks for advice. That cap is new, never been used. Just has been kept in the draw for 2-3 years. What could have made it gone bad?

author: Audioguru again
author_rank: Regular Contributor
timestamp: July 24, 2019, 07:26:06 pm
content: Quote from: vinlove on July 24, 2019, 06:40:19 pmIt is normal for cheap, poor quality parts bought from ebay, AliExpress or Amazon to be bad when new, not to go bad later. I never buy cheap junk so I do not know how long they last.

author: bob91343
author_rank: Super Contributor
timestamp: July 24, 2019, 07:57:33 pm
content: Failure of a component could be due to a number of causes. Sloppy manufacture, inadequate testing, deterioration on the shelf, exposure to hostile environments, and more.

author: vinlove
author_rank: Frequent Contributor
timestamp: July 25, 2019, 06:39:39 am
content: I was under impression those defects on capacitors are for vintage electrolycs made about 30-40 years ago, but quite shocked to see it can happen to recently manufactured caps.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: July 25, 2019, 06:45:37 am
content: Electrolytics have a poor shelf life and should not be stored. They need to be charged periodically to keep them healthy.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2019, 07:10:09 am
content: Shelf life of a proper elcap is more than two decades.2-3 years is absolutely nothing.They are just fake crap. Possibly from a reject bin, or something. The capacitance value is interesting: it isn't picofarads, so they are not empty cases. Maybe they are completely lacking the electrolyte, but have the foil structure, working like any film capacitor? That would explain a few hundred nF.I buy a lot of connectors, pin headers, etc. from Ebay and Ali. But never buy semiconductors, LEDs or electrolytic capacitors. Most are fakes and will waste a lot of your time. It's frustrating when you are a beginner, and learning things, because you tend to suspect you are doing something wrong.

author: vinlove
author_rank: Frequent Contributor
timestamp: July 25, 2019, 07:16:30 am
content: Interesting info. Thanks.What does Vloss = 7%, and ESR = 52ohms say about the cap?

author: Shock
author_rank: Super Contributor
timestamp: July 25, 2019, 09:40:50 am
content: Quote from: vinlove on July 25, 2019, 07:16:30 amIt's losing voltage due to a high internal series resistance (ESR). So rather than a capacitor it's behaving more like a small value resistor. It also has very limited storage capacity compared to it's rated capacitance. Google some ESR charts to use as a rough guide.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2019, 10:19:20 am
content: Electrolytic capacitors are supposed to have quite high ESR values; it has both positive and negative effects.Sounds a bit high, but not ridiculously excessive for such a tiny elcap. Maybe less than an order of magnitude too high. Would expect at least several ohms in any case.Vloss is a non-standard term and may mean anything, you need to refer to the manual of your meter, if such a thing exists.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2019, 10:32:10 am
content: Interesting readings, it's a useful 'bad capacitor' test case (you might want to keep it around,carefully marked). Fundamentally though, it's unfit for service in any circuit. There's no way a good cap should get that bad in storage, even after many years.P.S. Vloss is explained in the standard AVR based ESR meter writeup but I've never quite understood it. It's an arbitrary figure.

author: vinlove
author_rank: Frequent Contributor
timestamp: July 25, 2019, 11:15:21 am
content: Wow, thank you for all great info. Interesting.I was going to use the cap for the PIXIE 40m CW QRP kit radio, but it will have to be discarded, now it is confirmed as unfit for live circuit.Will have to search through parts draws to see if I have the same value capacitance cap.

author: Jwillis
author_rank: Super Contributor
timestamp: July 26, 2019, 11:50:45 pm
content: It's not unusual for electrolytic capacitors to go bad after 2 -3 years without reforming . Its depends on the manufacturer.For example Nichicon recommends no more than 2 years at 35C before forming is required.Storage temperature ,rate of dielectric dissolution ,electrolyte evaporation,volume of electrolyte,type of electrolyte are all factors ,but typically electrolytic capacitors should not be stored for longer than 3 years without reforming.Dielectric dissolution can almost always be reversed through reformation.For large capacitors, reforming may be an option because of the economics involved. For small ones like yours it would be much more economical just to replace it.As for the ESR.The smaller the rated capacitance the higher the ESR will be.For a 100uF it should be no more than 0.2 Ohms. 1uF caps can be as high as 20 Ohms.Best approach is not to store large volumes of electrolytic caps and only purchase as needed.

author: vinlove
author_rank: Frequent Contributor
timestamp: July 27, 2019, 08:05:14 am
content: I have searched my component draws, and found a couple of Electrolytic capacitors of the same value = 100uF, but the one gone bad is rated at 16V. The newly found ones are rated at 10V.Both of newly found caps were near the value of 100uF. This is strange, because these newly found ones are actually a lot older from the manufacturer. They are actually almost 10-20 years old, but never been used. ESR was about 1.9 ohms.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2019, 08:27:49 am
content: Quote from: Jwillis on July 26, 2019, 11:50:45 pmThis means they can't guarantee they are within specs, including leakage spec.It doesn't mean the caps are "bad". They just need reforming to be in spec again. Reforming happens in-situ, when power is applied.In practice, it means the leakage current is slightly more than specified for a few minutes to hours.For example, it's completely normal that an assembled unit sits for 2-3 years before power is applied for the first time. You would have a huge epidemic of warranty issues if this timeframe was a problem.If an elcap has gone bad enough to cause any issue (like excessive enough leakage current at first powerup to cause damage), after just 3 years, it's complete and total crap. No modern Nichicon or Panasonic cap does that.Never seen that.OTOH, in30(not 3) years old units, the result varies. Most of the time, they are fine, but the risk of caps blowing up or being severely out-of-spec (capacity and ESR), even after in-situ reforming, is considerable and varies a lot depending on manufacturers.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2019, 08:29:33 am
content: Quote from: vinlove on July 27, 2019, 08:05:14 amNot strange at all - usually "almost 10-20 years old" elcaps are just fine as is, and measure fine. (Although they may show higher leakage current when voltage is first applied.)The one that failed for you didn't fail because of time, but because it was crap from the beginning.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 27, 2019, 08:33:27 am
content: I got bags of electrolytics, all brand new, all originally packed, from a friend who closed a professional repair shop.By looking at them, I could already see that some of them had leaked badly. I ended up testing all of them and more than 80% were deteriorated, although the brand was not bad.

author: Shock
author_rank: Super Contributor
timestamp: July 27, 2019, 08:40:38 am
content: Quote from: vinlove on July 27, 2019, 08:05:14 amNo component is impervious to being defective, even it if it brand new. Sometimes it's a bad batch or series, unless it's a quality brand really you shouldn't dwell on it too much. Just buy from a reputable source and stick to superior brands if you want reliable components.Big difference with a marginal electrolytic capacitor and a bad one, don't waste time on dead ones. If you want to heal marginal caps, you can google reforming capacitors which should improve the capacitor you will need to monitor the ESR or leakage. Once done it will settle back after a period of time elapses if left out of circuit, it's one of those how long is a piece of string things. Not worth it for cheap capacitors.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 27, 2019, 09:40:39 am
content: If you haven't sledged it yetCharge it up to it's operating voltage and discharge, repeat a few times,then discharge it and run the tests again

author: Shock
author_rank: Super Contributor
timestamp: July 27, 2019, 11:06:36 am
content: Quote from: Electro Detective on July 27, 2019, 09:40:39 amEbay it as fully tested.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2019, 03:00:54 pm
content: Quote from: HighVoltage on July 27, 2019, 08:33:27 amEven high-brand manufacturers have had occasional epidemics of bad materials or processes. The most well-known is the "capacitor plague" in early 2000's, with the low-ESR models back then. But it wasn't the first time, and won't be the last time.I have seen and measureddozensof different unused new old stock electrolytic caps. One particular Nichicon type I had access to, had leaked without use, in about 15-20 years, you could both smell it and see it. And yes that particular type was 100% bad, every single unit more or less leaked. OTOH, all others (at least 20-30 different capacitor models) I have measured have been 100% OK despite age between about 10 to 20 years.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 28, 2019, 11:19:45 am
content: Surely there must be a purchase source in 2019 for decent capacitors that one canhoardhave in stock for few yearswithout worrying about leaks, dry outs, chemical contamination, online fakes,and everyones favorite > industrial thievery producing inferior knockoffs..or do the corporats plan this deliberately to sell new crappy cap filled gear and top up landfillsand make DIY electronics repair and design a living HELL for anyone daring to wield a soldering iron?It's bad enough one needs a freakin microscope just to see today'srats piss filledticking time bomm caps on PCBsHow much wishful thinking faradites can occupy such small spaces reliably anyway?Mini Rant over

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2019, 11:47:00 am
content: Quote from: Electro Detective on July 28, 2019, 11:19:45 amSurely there are:* Digikey* Mouser* Farnell / Element14* ... and many othersAnd good brands, such as:* Panasonic* Nichicon* Rubycon* Kemet* Cornell Dubilier* ... and many othersBut there's no need to stockpile them. They do have a shelf life, even if it's practically a lot more than just a few years. But time flies... Buy when needed. You could also expect the new high-tech aluminum polymer electrolytics to drop in price, hopefully.