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Electrolytic capacitors need to experience their rated voltage during lifetime?

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treez

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We are using the 470uF , 25V electrolytic capacitor (UVR1E471), on a 5V rail (it is the output of a 5V, 1W SMPS).

Is it a problem that this capacitor will only ever see 20% of its rated voltage?…don’t electrolytics need to experience their rated voltage for at least a few minutes every year or so?

UVR1E471 470uF, 25V electrolytic capacitor:
http://nichicon-us.com/english/products/pdfs/e-vr.pdf
 

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Is it a problem that this capacitor will only ever see 20% of its rated voltage?…don’t electrolytics need to experience their rated voltage for at least a few minutes every year or so?
Where did you hear that? I've never heard anything of the sort.

What I have heard about and read about is that you never want to run an electrolytic cap at anywhere near it's maximum rated voltage for any reason to protect it against any inadvertent voltage spikes.

You might want to read over this.
 
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betwixt

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Showing my age... I remember many moons ago there were electrolytic capacitors with a MINIMUM voltage rating. Something like 10uF 50V-250V. I doubt it was anything to do with the value changing, more likely it had something to do with leakage current, perhaps needing a high voltage to keep them polarized. I've never come across any suggestion that a capacitor should be periodically taken to the limit though.

Brian.
 

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thanks, I think leakage current increases if they are not taken up near their rated voltage at least once in a while.
 

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thanks, I think leakage current increases if they are not taken up near their rated voltage at least once in a while.
Who told you this? Sounds more like some old wives's tale (or in this case old engineer's tale) probably someone, came up with that one because their XYZ design worked better when they periodically injected max rated voltage into a cap, not realizing or discovering it was something else that was causing the problem.

Whacking the cap with max rated voltage is more likely to breakdown the dielectric and increase the leakage.
 

SunnySkyguy

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Who told you this? Sounds more like some old wives's tale (or in this case old engineer's tale) probably someone, came up with that one because their XYZ design worked better when they periodically injected max rated voltage into a cap, not realizing or discovering it was something else that was causing the problem.

Whacking the cap with max rated voltage is more likely to breakdown the dielectric and increase the leakage.
This is very true for old high K large electrolytic caps. The ESR from lack of use could fuse inner kayers, so activation was required with a resistor slightly smaller than the EPR or parallel leakage or 100k.

Once the electrolyte chemistry was conditioned , the voltage would rise as leakage reduced. Any internal micro-corrosion would dissolve and an avalanche short circuit fould be prevented.


Why are you playing with 40yr old caps?
 

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Why are you playing with 40yr old caps?
This is even beyond my time, so I second the question, what are you doing with 40 yr old caps? Feeling nostalgic? :wink:
 
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I learnt that an electrolytic capacitor loses its "form" if it is not operated at near its rated voltage for a long time or is not powered for a long time (Vishay says 3 years or more). Then it will have a high leakage current (10 times the normal current) for about half an hour if it is given a voltage near its rating until it "re-forms".
 

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You are correct a.g.

It depends on chemistry

STORAGE
No pre-condition will be necessary for Vishay BCcomponents aluminum capacitors, when stored under standard atmospheric conditions (15 °C to 25 °C; 25 % to 75 % RH; 860 mbar to 1060 mbar) for the following periods of time:
• 1 year for DLC and polymer types
• 2 years for ENYCAPTM
• 3 years for non-solid 85 °C types
• 4 years for non-solid 105 °C types
• 10 years for non-solid 125 °C types and 150 °C types
• 20 years for solid types
After these periods, the leakage current for acceptance test shall not exceed twice the specified IL5 requirement.
A limited current can be applied to reduce the leakage current of long stored capacitors to normal values. The maximum allowed current when doing this at room temperature is given by the following formula:
x D2  Imax. = ----------- x --- + D x L
In this equation, Ur is the rated voltage, D the diameter of the capacitor can and L the length of the capacitor can. When Imax. is in mA, D in mm and L in mm, the value for  is 1 mW/mm2. During this reforming process, the rated voltage shall not be exceeded.The process has ended when the current drops below the specified leakage current.
To ensure good solderability and quality of taping, for all types and prior to mounting, the storage time shall not exceed 3 years. This means for example: 2 years storage time between manufacture and arrival at the customer, plus 1 year in customer storage.

However damage criteria is different than leakage spec criteria based on 5 minutes or 1hr burnoff of oxide molecular layer.

Damage criteria was not given, but well known in old wet types and also it seems hi K polymer types and dual layer supercaps.. Have short storage life for rated leakage....Tony

p.s. imagine large battery size caps with ultralow ESR and 1mA leakage at 50V initialy is only 50mW but if the zone of leakage is the size of a dot thermally insulated , it can conduct enough to heatup oxide slurry and short out foil and poof . Detonation.

most reliable caps are designed as self fusing plastic distributed fused in ultralow ESR types. See panasonic

this protects against contaminant particles <= 1ppm which the source of destructive flaws

which is also why cost, quality control, chemistry, ESR, leakage are critical cap selection criteria.
 

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"Detonation", hee, hee.
My first job was as a technician on the car radio production line. When the radio was built then it was housed in a solid metal can for the first time it was powered in case an electrolytic capacitor was connected backwards then detonated.
Some technicians (not me) connected the capacitor or power supply wires backwards on purpose in some radios for the fun of hearing the detonations.

In the '70ies I had most tantalum capacitors used as supply bypass capacitors "disappear". I never saw them or heard them detonate but all that remained was their wires.
 

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None of the manufacturer specifications about electrolytic capacitor reforming after elongated voltage free storage periods mentions a problem of not reaching a specific rated voltage. If a modern electrolytic capacitor is used at reduced voltage it will be well with it, I think. There many applications of this kind, and I never saw a capacitor failing in reduced voltage operation.

I'm not talking about pre world war II capacitors.
 

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I'm not talking about pre world war II capacitors.
FvM did you just suggest both treez & SunnySkyguy are pre-WW-II engineers, that still have boxes full of 75+ year old caps with datasheets! :thinker:

I applaud both treez and SunnySkyguy for having such long careers, they must have been "playing" around with electronics while still in diapers. ;-)
 

treez

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I wouldn't mind betting that the market is awash with ancient electrolytic capacitors, which have been stored under goodness knows what conditions for many years....they probably strip off the outer skin, and put a new skin on with today's date, and ship them to the distributors..........some distributors may be "in" on this.

I am convinced that this is happening...........and its a disaster for your production run of 100,000 SMPS's that will be using them.................this is why all electronics companies need very rich underwriters.
 

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I discovered the opposite, Brian.

... with a little excitation, they freely escaped orbit out of conductors to leap great lengths across insulators.

- - - Updated - - -

I wouldn't mind betting that the market is awash with ancient electrolytic capacitors,


I am convinced that this is happening...........and its a disaster for your production run of 100,000 SMPS's that will be using them.................this is why all electronics companies need very rich underwriters.
you must have experience buying off Ebay or Brokers via far east sources. Any competent distributor would get in deep doo doo for knowing doing this.

besides the reality is, great companies that I worked for, only hired competent QA and PRoduct Engineers for technical forensics and Design Engineers for qualifying components and suppliers for the AVL. QA looks after batch code expiry and moving SOH.

Escapes still occur tho, but are detected early in ICT.

ads-ee I think treez is still green but learning alot here, whereas I became senior design eng in '79 from 80hr weeks and numerous allniters.

my biggest booboo as a summer student doing assembly of 48 ch mixers designed in a recording studio and assuming all the plastic shelled Spanish Caps were non-polarized.
 
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SunnySkyguy said:
you must have experience buying off Ebay or Brokers via far east sources. Any competent distributor would get in deep doo doo for knowing doing this.
I was thinking the same thing. I've almost never seen a bad electrolytic cap from a reputable distributor, but on the other hand I've seen issues with parts that came from the gray market re-sellers. I'm pretty sure some (perhaps a lot) of those parts are fakes, clones, bad/marginal die, removed from circuit boards and "freshened up", or possibly even stolen.

SunnySkyguy said:
my biggest booboo as a summer student doing assembly of 48 ch mixers designed in a recording studio and assuming all the plastic shelled Spanish Caps were non-polarized.
Well I narrowly avoided getting some severe 1st/2nd degree burns from a tantalum, the factory installed backwards, that exploded <20 seconds after I started scope probing the back side of a board. Darn thing burnt a hole in the tile floor of the lab! :shock: I'm sure glad I had switched sides!
 
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SunnySkyguy

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Good as fire crackers, but more toxic.. Some carcinogenic

- - - Updated - - -

Date codes are usually reported now on broker market upon request.
 
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FvM

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FvM did you just suggest both treez & SunnySkyguy are pre-WW-II engineers, that still have boxes full of 75+ year old caps with datasheets!
Not particularly, but some electrolytic capacitor characterization presented in the discussion sounds like beeing preserved from those days. I checked electrolytic capacitors laying in a drawer for thirty or fourty years (they are already modern types related to this discussion) some time ago, and they performed well from the start.

I conclude from this experiment that the manufacturer specifications about need for capacitor reforming after two years of storage are more targetting to worst case than typical component behaviour.
 
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I learnt all about capacitors in my 1st job on my own in the 1st 6 months from the library for Mil-Std-Handbooks, Every type of capacitor and all other components were clearly documented for normal characteristics, abnormal features, physics, chemistry, and the factors which affect stress ratings for Failure rate that must be considered when doing a reliable design.

Since these may not be accessible to all, I suggest those who need to learn, search the better suppliers of parts for Technical Papers. Use a major distributor for documentation as well. Make them earn their salaries.

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