EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: vinlove on July 24, 2019, 03:41:40 pm
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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%?
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Yes it's bad. Throw it out.
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Yes it's bad. Throw it out.
Thanks 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?
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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?
It 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.
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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.
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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.
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Electrolytics have a poor shelf life and should not be stored. They need to be charged periodically to keep them healthy.
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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.
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Interesting info. Thanks.
What does Vloss = 7%, and ESR = 52ohms say about the cap?
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Interesting info. Thanks.
What does Vloss = 7%, and ESR = 52ohms say about the cap?
It'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.
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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.
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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.
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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. :(
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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.
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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.
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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.
This 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, in 30 (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.
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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.
Not 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.
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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.
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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.
No 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.
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If you haven't sledged it yet :horse:
Charge it up to it's operating voltage and discharge, repeat a few times,
then discharge it and run the tests again
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If you haven't sledged it yet :horse:
Charge it up to it's operating voltage and discharge, repeat a few times, then discharge it and run the tests again
Ebay it as fully tested.
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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.
Even 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 measured dozens of 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.
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Surely there must be a purchase source in 2019 for decent capacitors that one can hoard have in stock for few years ::)
without 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 landfills :--
and 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's rats piss filled ticking time bomm caps on PCBs |O
How much wishful thinking faradites can occupy such small spaces reliably anyway? :popcorn:
Mini Rant over :D
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Surely there must be a purchase source in 2019 for decent capacitors that one can hoard have in stock for few years ::)
without worrying about leaks, dry outs, chemical contamination, online fakes,
Surely there are:
* Digikey
* Mouser
* Farnell / Element14
* ... and many others
And good brands, such as:
* Panasonic
* Nichicon
* Rubycon
* Kemet
* Cornell Dubilier
* ... and many others
But 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.