Why do electrolytic capacitors wear out?
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savatage1973
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All of the above, and then some more. Defects are certainly a factor. Underuse is is also a valid factor as caps have to "re-form" after sitting for a long time. Overuse (as in being constantly run at, near, or even above their rated voltages or temperature limitations), certainly is a factor. Electrolytic caps are "wet" caps--they have a wet electrolyte that can dry out with age and exposure to heat. Best way to "extend" cap life is to "exercise" them periodically--that's why (among other reasons) that I fire up gear periodically that is not currently in use, just to keep it working. Don't run everything "balls to the wall" all the time and make sure you have adequate cooling/ventilation. Nothing you can do about time--you can diminish the effects by not storing something in a hot attic, but time marches on. I do know people that store vintage NOS electrolytic caps in sealed containers in the refrigerator, but that is a little "out there" IMO--but who knows???--they may be onto something...
Great Thread. Now, would the same go for speaker caps as well? Have heard that some wear out and also heard that since there's really no heat then speaker caps last almost forever. Always wanted to know ....
Great Thread. Now, would the same go for speaker caps as well? Have heard that some wear out and also heard that since there's really no heat then speaker caps last almost forever. Always wanted to know ....
Depends. Some of them are electroytics, which are now rather disfavored for those applications. Others are film or paper-in-oil caps which may or may not be good. Film caps generally last a long time, but older ones can still degrade, just like any other old plastics. Depends on the stability of the substrate.
savatage1973
Addicted Member
Depends on the speaker--a lot of higher quality speakers use PIO (paper in oil) for the tweets and mids, but most use electrolytics for the woofer. More modern speakers use film caps for the mid and high frequencies--oftentimes the woofer caps are too large or too expensive to use anything other than electrolytics.
Retrovert
Addicted Member
This is a well-studied issue, with mountains of technical material on the subject trivially available on the interwebs. For example, see:
Physics Based Electrolytic Capacitor Degradation Models for Prognostic Studies under Thermal Overstress
Chetan S. Kulkarni, Jose R. Celaya, Kai Goebel, and Gautam Biswas
European Conference of the Prognostics and Health Management Society, 2012
https://ti.arc.nasa.gov/publications/5005/download/
2. ELECTROLYTIC CAPACITORS
Electrolytic capacitor performance is strongly affected by its operating conditions, such as voltage, current, frequency, and ambient temperatures. [...]
A primary reason for wear out in aluminum electrolytic capacitors is due to vaporization of electrolyte (Goodman et al., 2007) and degradation of electrolyte due to ion exchange during charging/discharging (Gomez-Aleixandre et al., 1986; Ikonopisov, 1977) , which, in turn leads to a drift in the two main electrical parameters of the capacitor: (1) the equivalent series resistance (ESR), and (2) the capacitance (C). The ESR of a capacitor is the sum of the resistance due to aluminum oxide, electrolyte, spacer, and electrodes (foil, tabbing, leads, and ohmic contacts) (Hayatee, 1975; Gasperi, 1996). The health of a capacitor is often indicated by the values of these two parameters. There are certain industry standard thresholds for these parameter values, upon crossing these threshold barrier the component is considered unhealthy to be used in a system, i.e., the component has reached its end of life, and should be immediately replaced before further operations (Lahyani et al., 1998; Eliasson, 2007; Imam et al., 2005).
[A]n aluminum electrolytic capacitor, consists of a cathode aluminum foil, electrolytic paper, electrolyte, and an aluminum oxide layer on the anode foil surface, which acts as the dielectric. When in contact with the electrolyte, the oxide layer possesses an excellent forward direction insulation property (Gasperi, 1996). Together with magnified effective surface area attained by etching the foil, a high capacitance value is obtained in a small volume (Fife, 2006). Since the oxide layer has rectifying properties, a capacitor has polarity. If both the anode and cathode foils have an oxide layer, the capacitors would be bipolar. In this work, we analyze “non-solid” aluminum electrolytic capacitors in which the electrolytic paper is impregnated with liquid electrolyte. [...]
2.1. Overview of Degradation Mechanisms
The flow of current during the charge/ discharge cycle of the capacitor causes the internal temperature to rise. The heat generated is transmitted from the core to the surface of the capacitor body, but not all the heat generated can escape. The excess heat results in a rise in the internal temperature of the capacitors which causes the electrolyte to evaporate, and gradually deplete (Kulkarni, Biswas, et al., 2011b; Kulkarni, Celaya, et al., 2011). Similarly in situations where the capacitor is operating under high temperature conditions, the capacitor body is at a higher temperature than its core, the heat travels in the opposite directions from the body surface to the core of the capacitor again increasing the internal temperature causing the electrolyte to evaporate. This is explained using a first principles thermal model of heat conduction (Kulkarni, Biswas, et al., 2011b; Kulkarni, Celaya, et al., 2011).
Degradation in the oxide layer can be attributed to crystal defects that occur because of the periodic heating and cooling during the capacitor’s duty cycle, as well as stress, cracks, and installation-related damage. High electrical stress is known to accentuate the degradation of the oxide layer due to localized dielectric breakdowns on the oxide layer (Ikonopisov, 1977; Wit & Crevecoeur, 1974). These breakdowns, which accelerate the degradation, have been attributed to the duty cycle, i.e., the charge/discharge cycle during operation (Ikonopisov, 1977). Further another simultaneous phenomenon is the increase in the internal pressure (Gomez-Aleixandre et al., 1986) due to an increased rate of chemical reactions, which can again be attributed to the internal temperature increase in the capacitor. This pressure increase can ultimately lead to the capacitor popping.
All the failure/degradation phenomenon mentioned may act simultaneously based on the operating conditions of the capacitors. We first study the phenomenon qualitatively, and then discuss the steps to derive the first principles analytic degradation models for the different thermal stress condition. Electrolyte evaporations is caused either due to increase in internal core temperature or external surrounding temperature. Both phenomenon lead to the same degradation mode,caused either by the high electrical stress or thermal stress, respectively.
Physics Based Electrolytic Capacitor Degradation Models for Prognostic Studies under Thermal Overstress
Chetan S. Kulkarni, Jose R. Celaya, Kai Goebel, and Gautam Biswas
European Conference of the Prognostics and Health Management Society, 2012
https://ti.arc.nasa.gov/publications/5005/download/
2. ELECTROLYTIC CAPACITORS
Electrolytic capacitor performance is strongly affected by its operating conditions, such as voltage, current, frequency, and ambient temperatures. [...]
A primary reason for wear out in aluminum electrolytic capacitors is due to vaporization of electrolyte (Goodman et al., 2007) and degradation of electrolyte due to ion exchange during charging/discharging (Gomez-Aleixandre et al., 1986; Ikonopisov, 1977) , which, in turn leads to a drift in the two main electrical parameters of the capacitor: (1) the equivalent series resistance (ESR), and (2) the capacitance (C). The ESR of a capacitor is the sum of the resistance due to aluminum oxide, electrolyte, spacer, and electrodes (foil, tabbing, leads, and ohmic contacts) (Hayatee, 1975; Gasperi, 1996). The health of a capacitor is often indicated by the values of these two parameters. There are certain industry standard thresholds for these parameter values, upon crossing these threshold barrier the component is considered unhealthy to be used in a system, i.e., the component has reached its end of life, and should be immediately replaced before further operations (Lahyani et al., 1998; Eliasson, 2007; Imam et al., 2005).
[A]n aluminum electrolytic capacitor, consists of a cathode aluminum foil, electrolytic paper, electrolyte, and an aluminum oxide layer on the anode foil surface, which acts as the dielectric. When in contact with the electrolyte, the oxide layer possesses an excellent forward direction insulation property (Gasperi, 1996). Together with magnified effective surface area attained by etching the foil, a high capacitance value is obtained in a small volume (Fife, 2006). Since the oxide layer has rectifying properties, a capacitor has polarity. If both the anode and cathode foils have an oxide layer, the capacitors would be bipolar. In this work, we analyze “non-solid” aluminum electrolytic capacitors in which the electrolytic paper is impregnated with liquid electrolyte. [...]
2.1. Overview of Degradation Mechanisms
The flow of current during the charge/ discharge cycle of the capacitor causes the internal temperature to rise. The heat generated is transmitted from the core to the surface of the capacitor body, but not all the heat generated can escape. The excess heat results in a rise in the internal temperature of the capacitors which causes the electrolyte to evaporate, and gradually deplete (Kulkarni, Biswas, et al., 2011b; Kulkarni, Celaya, et al., 2011). Similarly in situations where the capacitor is operating under high temperature conditions, the capacitor body is at a higher temperature than its core, the heat travels in the opposite directions from the body surface to the core of the capacitor again increasing the internal temperature causing the electrolyte to evaporate. This is explained using a first principles thermal model of heat conduction (Kulkarni, Biswas, et al., 2011b; Kulkarni, Celaya, et al., 2011).
Degradation in the oxide layer can be attributed to crystal defects that occur because of the periodic heating and cooling during the capacitor’s duty cycle, as well as stress, cracks, and installation-related damage. High electrical stress is known to accentuate the degradation of the oxide layer due to localized dielectric breakdowns on the oxide layer (Ikonopisov, 1977; Wit & Crevecoeur, 1974). These breakdowns, which accelerate the degradation, have been attributed to the duty cycle, i.e., the charge/discharge cycle during operation (Ikonopisov, 1977). Further another simultaneous phenomenon is the increase in the internal pressure (Gomez-Aleixandre et al., 1986) due to an increased rate of chemical reactions, which can again be attributed to the internal temperature increase in the capacitor. This pressure increase can ultimately lead to the capacitor popping.
All the failure/degradation phenomenon mentioned may act simultaneously based on the operating conditions of the capacitors. We first study the phenomenon qualitatively, and then discuss the steps to derive the first principles analytic degradation models for the different thermal stress condition. Electrolyte evaporations is caused either due to increase in internal core temperature or external surrounding temperature. Both phenomenon lead to the same degradation mode,caused either by the high electrical stress or thermal stress, respectively.
ferninando
Lunatic Member
finaly the truth.
I LIKE MUSIC
Super Member
Yes, thanks Retrovert.
savatage1973
Addicted Member
Excellent--never really looked, but technical data that backs up what I have been led to believe for decades!!!
hnash53
Super Member
FWIW... the term "electrolyte" refers to any substance (think NaCl... or ordinary table salt, as an example) that when you put it in water, it "ionizes." That means that the substance splits into a positive... Na+ and a negative... Cl- ion. An ion is an electrically charged particle. Na+ and Cl- are "ions." For ions to be ions, they need to be dissolved in water. Electrolytes can conduct electricity through water.
If you were to take a new capacitor, and open it up, you will find that it is wet inside. Wet = water. If it's still wet inside, the electrolyte will be present and in its ionic form. The capacitor will perform its function.
Capacitors, though, can dry out over time... this typically means "years." Once a capacitor dries out... the water has evaporated off over the years,... the capacitor's function will be diminished because the electrolyte's ions can no longer exist. The Na+ is attracted to the Cl- and a "salt" forms when the two oppositely charged particles form an ionic bond between them. At this point, there is no electrolyte left in the capacitor, and it no longer functions.
Please note: I am NOT saying that NaCl is THE electrolyte in capacitors. It isn't. I only use NaCl as an example of an electrolyte, since most readers are likely familiar with sodium chloride. But the principle is the same: A substance is an electrolyte because it dissolves or dissociates into its individual ions when placed in water.
Dried out caps will experience a loss of function... or at least some degree of loss of function.
If you were to take a new capacitor, and open it up, you will find that it is wet inside. Wet = water. If it's still wet inside, the electrolyte will be present and in its ionic form. The capacitor will perform its function.
Capacitors, though, can dry out over time... this typically means "years." Once a capacitor dries out... the water has evaporated off over the years,... the capacitor's function will be diminished because the electrolyte's ions can no longer exist. The Na+ is attracted to the Cl- and a "salt" forms when the two oppositely charged particles form an ionic bond between them. At this point, there is no electrolyte left in the capacitor, and it no longer functions.
Please note: I am NOT saying that NaCl is THE electrolyte in capacitors. It isn't. I only use NaCl as an example of an electrolyte, since most readers are likely familiar with sodium chloride. But the principle is the same: A substance is an electrolyte because it dissolves or dissociates into its individual ions when placed in water.
Dried out caps will experience a loss of function... or at least some degree of loss of function.
Retrovert
Addicted Member
Non-solid (wet or liquid electrolyte) electrolytic capacitors typically use boric acid.
Not all electrolytic capacitors are wet. Solid electrolytes exist, and conductive polymers are used for SMD applications.
It really doesn't matter if a wet electrolytic use water, a sulphuric acid solution, or unicorn blood. What really matters for longevity is that the liquid, as per the explanation I above posted, is lost over time, both through normal evaporation and being baked out by high temperatures. Electrolytics, by virtue of their design, are limited-lifespan devices. The seals are imperfect and the inherently higher ESR creates internal heat.
Poor-quality electrolytics can fail in a few years. Well-made ones can last a decade or two, sometimes longer if properly sealed. The issue is that the properties deteriorate with age, even if the capacitor does not fail. Old capacitors have no Magickal Mojo; what they have is a death sentence which will eventually be carried out. Electrolytics cans explode when they die, hurling metal around like an IED.
CIrca 2001 I had several expensive motherboards fail because of the famous capacitor plague, which arose because an incomplete electrolyte formula was stolen and used in production manufacturing:
This article is quite detailed and you might find it interesting.
The leaking electrolyte chewed up the boards and they were junk at that point. This is why I always tell people that buying cheap (as in shoddy) capacitors leads to misery.
View electrolytic capacitors with substantial suspicion, like a cat noticing their human removing the cat carrier from the closet. Nothing good comes of using them.
Not all electrolytic capacitors are wet. Solid electrolytes exist, and conductive polymers are used for SMD applications.
It really doesn't matter if a wet electrolytic use water, a sulphuric acid solution, or unicorn blood. What really matters for longevity is that the liquid, as per the explanation I above posted, is lost over time, both through normal evaporation and being baked out by high temperatures. Electrolytics, by virtue of their design, are limited-lifespan devices. The seals are imperfect and the inherently higher ESR creates internal heat.
Poor-quality electrolytics can fail in a few years. Well-made ones can last a decade or two, sometimes longer if properly sealed. The issue is that the properties deteriorate with age, even if the capacitor does not fail. Old capacitors have no Magickal Mojo; what they have is a death sentence which will eventually be carried out. Electrolytics cans explode when they die, hurling metal around like an IED.
CIrca 2001 I had several expensive motherboards fail because of the famous capacitor plague, which arose because an incomplete electrolyte formula was stolen and used in production manufacturing:
en.wikipedia.org/wiki/Capacitor_plague
Industrial espionage was implicated in the capacitor plague, in connection with the theft of an electrolyte formula. A materials scientist working for Rubycon in Japan left the company, taking the secret water-based electrolyte formula for Rubycon's ZA and ZL series capacitors, and began working for a Chinese company. The scientist then developed a copy of this electrolyte. Then, some staff members who defected from the Chinese company copied an incomplete version of the formula and began to market it to many of the aluminium electrolytic manufacturers in Taiwan, undercutting the prices of the Japanese manufacturers.[1][42] This incomplete electrolyte lacked important proprietary ingredients which were essential to the long-term stability of the capacitors[4][23] and was unstable when packaged in a finished aluminum capacitor. This faulty electrolyte allowed the unimpeded formation of hydroxide and produced hydrogen gas.[36]
There are no known public court proceedings related to alleged theft of electrolyte formulas. However, one independent laboratory analysis of defective capacitors has shown that many of the premature failures appear to be associated with high water content and missing inhibitors in the electrolyte, as described below.
Industrial espionage was implicated in the capacitor plague, in connection with the theft of an electrolyte formula. A materials scientist working for Rubycon in Japan left the company, taking the secret water-based electrolyte formula for Rubycon's ZA and ZL series capacitors, and began working for a Chinese company. The scientist then developed a copy of this electrolyte. Then, some staff members who defected from the Chinese company copied an incomplete version of the formula and began to market it to many of the aluminium electrolytic manufacturers in Taiwan, undercutting the prices of the Japanese manufacturers.[1][42] This incomplete electrolyte lacked important proprietary ingredients which were essential to the long-term stability of the capacitors[4][23] and was unstable when packaged in a finished aluminum capacitor. This faulty electrolyte allowed the unimpeded formation of hydroxide and produced hydrogen gas.[36]
There are no known public court proceedings related to alleged theft of electrolyte formulas. However, one independent laboratory analysis of defective capacitors has shown that many of the premature failures appear to be associated with high water content and missing inhibitors in the electrolyte, as described below.
This article is quite detailed and you might find it interesting.
The leaking electrolyte chewed up the boards and they were junk at that point. This is why I always tell people that buying cheap (as in shoddy) capacitors leads to misery.
View electrolytic capacitors with substantial suspicion, like a cat noticing their human removing the cat carrier from the closet. Nothing good comes of using them.
hnash53
Super Member
Great analogy!!! I like.
MikE
Color Me Gone
I have LCR 100uf+100uf 500v electrolytic that is at least 17 years old. At what point should it be replaced? I have a pair of Mundorf 100uf 550v polypropylene capacitors but looking more closely at what I was getting into not comfortable doing the conversion myself. Have to outsource.
Retrovert
Addicted Member
As per the paper, and other formulas, lifespan depends upon the rated voltage vs the operating voltage and temperature, and then the type of capacitor, which determines the electrolyte and foil, etc. You may read the capacitor plague article to better understand how poor manufacturing can doom an electrolytic to an early death. Adverse conditions, like higher temperature, derate the lifespan.
Yes, it's all complicated and you want a thumbs up or down. I would not push beyond twenty years for a modern capacitor, even though they are much better made and the seals are much better. Most tube amplifiers run hot and that bakes out the electrolyte.
MikE
Color Me Gone
^^ Thanks. LIke I said, I have a pair of polypropylene capacitors to switch out the dual section 'lytic, just need to find a reliable source to perform the upgrade.
The stock LCR cap is [now] out of production though I believe F&T are a direct replacement. I've yet to locate a dual section polypropylene capacitor.
The stock LCR cap is [now] out of production though I believe F&T are a direct replacement. I've yet to locate a dual section polypropylene capacitor.
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Retrovert
Addicted Member
Several AK members have posted wonderful guides to opening up cans, restuffing, and reconstructing the can so the upgrade is nearly invisible. Easiest way to do that upgrade.
MikE
Color Me Gone
Opening up, restuffing? No, I want to get away from the stock dual section electrolytic ps cap. I already have two polypropylene capacitors.
