Capacitor plague
Encyclopedia
The capacitor plague was a problem with a large number of premature failures of aluminium electrolytic capacitors with non solid or liquid electrolyte of certain brands especially from Taiwan manufacturers . The first flawed capacitors were seen in 1999, but most of the affected capacitors failed in the early to mid 2000s. They failed in various electronics equipment, particularly motherboard
s, video cards, compact fluorescent lamp
ballasts, LCD monitors, and power supplies of personal computer
s. News of the failures (usually after a few years of use) forced most manufacturers to repair the defects. The problem seems to be ongoing; faults are still being reported as of 2010 .
(1996) and have affected equipment manufactured up to at least 2007. The motherboard companies assembled and sold boards with faulty caps sourced from other manufacturers (see below). Major vendors such as Intel, Dell
and HP were affected. Circa 2005, Dell spent some US $150 million replacing motherboards entirely and another $150 million on the logistics of determining whether a system is in need of replacement. HP reportedly purged its product line in 2004. The motherboards and power supplies in Apple iMac G5
s and some eMac
s were also affected.
While capacitor plague largely affects desktop computer hardware, this problem is by no means limited to that area. These capacitors can also be found in power supplies, network switches, audio equipment, flat panel display
s, and a range of other devices.
The most common method of identifying capacitors which have failed because of bad electrolyte is visual inspection. The capacitance may degrade to 4% of the original value, as opposed to an expected 50% capacity degradation over the lifetime. Such a capacitor will show one or more of these symptoms:
As the capacitor ages, its capacitance
decreases and its ESR increases. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current
voltage
s on the motherboard, and system instability results. Some common symptoms are:
Unlike the physical signs which are conclusive evidence the capacitors are failing, many of the operational signs may be caused by other factors, such as a failing power supply
, dust clogging a fan, bad RAM, or other hardware problems. Instability, once the operating system has loaded, may indicate a software problem (such as some types of malware
, poorly-written device driver
s or software), and not a hardware problem at all. If any of these symptoms are experienced, removing the system's case and inspecting the capacitors, especially those around the CPU
, may immediately identify capacitors as the cause. If there are no physical signs, an oscilloscope
may be used to examine the AC ripple voltage across capacitors during operation, or an ESR meter to measure ESR when powered down; excessive ripple or ESR is a sign that the capacitors are faulty.
The images of the failures were quite spectacular, bulged or burst cans, expressed sealing rubber and leaking electrolyte were found on countless circuit boards. Many well-known equipment manufacturers such as Dell
, Cisco
, Intel, Asus
and Abit
had to carry out recalls and repair costs to take account of these capacitors . Many repair instructions for self-help can be found on the Internet.
.
As a probable cause of the faulty capacitor-production industrial espionage in connection with the theft of an electrolyte formula is considered. An electrolyte
developer has probably taken with them, when moving from Japan
to Taiwan
, the chemical composition of a new low resistance, inexpensive, water
-containing electrolyte and tried to counterfeit these electrolytes in Taiwan, then to sell it cheaper than the Japanese could. But apparently the formula had been copied incompletely, and it lacked important substances to secure the long-term stability of the capacitors.
electrolytic capacitor with a liquid electrolyte, invented by Charles Pollak in January 1896. In principle, the electrolytic capacitors up to this day (2011) remained the same. On an aluminium anode
, the dielectric
out of very thin aluminium oxide
layer is raised by formation. The liquid electrolyte adapts the structure of the dielectric, forms the liquid cathode
of the capacitor and thus makes the thin layer thickness of the dielectric effective. A spacer made of paper prevents direct contact of the oxide layer with a second aluminium foil (cathode foil), the electrical connection to the liquid cathode and also saves him. Sealed and provided with connections this construction results in billions of inexpensive and within their lifetime reliable capacitors used for electronic devices.
The electrolyte as ionic conductor caused most of the ohmic losses in the capacitor. Great efforts have been made over the years to reduce these losses to increase the ripple current, because without such improvements the most important target of development - size reductions - cannot be realized.
In Japan, in the context of these developments, some manufacturers are busy to develop a new, low-ohmic water-based electrolyte. The conductivity of water-based electrolytes compared to electrolytes with organic solvents
like GBL
was significantly improved. Water, with its relatively high permittivity
of ε = 81, is a powerful solvent for electrolytes. As such, it dissolves salts in high concentration. The high concentration of dissolved salt ions
in the electrolyte increases the conductivity. But water will react quite aggressive and violently with unprotected aluminium. It converts aluminium (Al) with a highly exothermic reaction into aluminium hydroxide
(Al(OH)3). This is accompanied by a strong heat and gas development in the capacitor and may lead to the explosion of the capacitor. Therefore, the main problem in the development of new water-containing electrolytes, is to hinder the aggressiveness of the water against aluminium to get capacitors having a sufficiently good long-term stability.
The Japanese manufacturer Rubycon
was the late 1990s, a leader in the development of new water-based electrolyte systems with enhanced conductivity. Rubycon 1998 brought with two series, ZL and ZA, the first capacitors on the market that worked with an electrolyte with a water content of about 40 % and were suitable for a wide temperature range from -40 to +105 °C .
The improvement achieved the conductivity of the electrolyte can be seen by a comparison of two capacitors, both of which have a capacitance of 1000 µF at 16 V nominal voltage with the size DxL = 10x20 mm. The capacitors of the Rubycon YXG series, which are provided with an electrolyte based on an organic solvent can be at an impedance of 46 milliohms loaded with a ripple current of 1400 mA. ZL series capacitors with the new water-based electrolyte can be at an impedance of 23 mΩ charged with the ripple current of 1820 mA , an increase of 30 %. Other manufacturers, such as NCC , Nichicon , Elna , follows a short time later. The new series was called "Low ESR" or "Low-impedance", "Ultra-low-impedance" or "High-ripple Current” series in the data sheets. The highly competitive market in the digital data technology and the power supply handle this new development on fast, because by improving the conductivity of the electrolyte could capacitors not only withstand a higher ripple current rating, they were even cheaper, since water is very cheap. Better and even cheaper for high volume products like PCs, LCD screens and power supplies, the cost argument was decisive.
or lye
, which must be chemically inert, so that the capacitor, whose inner components are made of aluminium, remains stable over long time. But aluminium is a very reactive, easily oxidised metal. And aqueous acids behave quite aggressively against the aluminium. Only a stable aluminium oxide Al2O3 layer on the surface of the anode and protecting substances known as inhibitors or passivators in the electrolyte are able to protect aluminium from water-driven corrosive reactions. The problem of water-containing electrolyte systems lies in the control of aggressiveness of the water toward aluminium.
This problem runs through the development of electrolytic capacitors for over many decades.
For even the first technically used electrolytes mid 20th century were mixtures of ethylene glycol and boric acid. But even with these so-called glycol electrolytes do had an unwanted chemical water crystal reaction, according to the scheme:
From "acid + alcohol
" gets "ester
+ water"
In a first water-free electrolyte, as the result of esterification a generation of a water content of up to 20 % take place. These electrolytes were originally suitable only for a limited temperature range of -25 to +85 °C. They had a voltage-dependent lifetime, because at higher voltages the leakage current based on the aggressiveness of the water increases exponentially and the associated increased consumption of electrolyte leads to a faster drying out.
On the other hand water delivers the oxygen for the self-healing of electrolytic capacitors, the formation of the anode oxide, the dielectric layer of the capacitor. This normal process of formation or self-healing carried out in two reaction steps. First, it transforms with a strongly exothermic reaction aluminium (Al) into its hydroxide
Al(OH)3:
This reaction is accelerated by a high electric field and by high temperatures and is accompanied by a pressure build up in the capacitor by the released hydrogen gas. The gel-like aluminium hydroxide Al(OH)3, even called alumina trihydrate (ATH), aluminic hydroxide, aluminium(III) hydroxide, hydrated alumina converts, in the second reaction step usually slow in a few hours at room temperature, more rapidly in a few minutes at higher temperatures, in the crystalline form of aluminium oxide Al2O3:
Only the newly formed stable aluminium oxide heal the defects respectively the weak dielectric layer on the anode of the electrolytic capacitor, forms the stable dielectric of the capacitor. It also protects the capacitor from the aggressive reactions of aluminium in the presence of water. However, with the conversion process of the forming or self healing a small amount of water out of the electrolyte will be "consumed".
.
It is also known that the "normal" course of building the stable aluminium oxide by the formation of aluminium through the intermediate step of the aluminium hydroxide can be interrupted through an alkaline or basic electrolyte. Disruption to the chemistry of this reaction serves as an example the following:
In this case, it may happen that the hydroxide formed in the first step becomes detached from the aluminum surface and will be not transforms in the desired stable form of aluminium oxide. The cause of the healing process building new oxide layer, a defect or a weak dielectric point remains and the defect is not cured. Then there another additional formation of aluminium hydroxide at this point occurs without converting into the stable aluminium oxide. The self-healing inside the e-cap no longer takes place. The reactions do not come to a standstill, the hydroxide in the pores of the anode foil grow and caused by the first step reaction more and more hydrogen gas will be produced in the can increasing the pressure.
who analyzed the failed capacitors
).
These two scientists initially determined by ion chromatography and mass spectrometry
, that there really is hydrogen gas, which leads to bulging of the capacitor’s case or open the vent. Thus it was proved that the oxidation takes place according to the first step of the formation of alumina.
Because it has been customary in electrolytic capacitors to bind the hydrogen with the help of reducing or depolarizing
compounds to reduce the resulting pressure then they searched for compounds of this type. Usually aromatic nitro compounds or amines are used in this case. Although the above-mentioned methods are very sensitive to such pressure reducing compounds no traces of the agents was found within the failed capacitors.
With capacitors, the internal pressure build-up was just so great that the capacitor case was already bulging but the vent had not opened yet, then the pH value of the electrolyte could be identified. The electrolyte of the faulty capacitors was alkaline with pH (7
Since in the investigated Taiwanese electrolytes phosphate ions were missing and the electrolyte was also alkaline, so they lacked the protection against water and the more formation of stable alumina oxides was stopped. There only aluminum hydroxide was generated.
Underlined was the result of chemical analysis by measurement of the electrical capacitance and the leakage current in a long-term test for 56 days. Due to the chemical attack on the oxide layer of these capacitors has been weakened, so that after a short time, the capacitance and the leakage current increased, before both parameters rapidly after opening the vent fell off.
With the report of Hilmann and Helmond it was proofed that the cause of the failured capacitors actually was a faulty electrolyte used by the Taiwanese manufacturers. It lacked the necessary chemical ingredients to ensure the correct pH of the electrolyte over the time for a long-term stability of the electrolytic capacitors.
That the electrolyte with its alcaline pH value then had the fatal consequence of continual growth of hydroxide wíthout changing into the stable oxide can be detected on the surface of the anode foil either photographically or with an EDX-fingerprint analysis of the chemical components.
Even a microscopic image with only a 10-fold magnification, as shown in the pictures right, a significant change in the structure of the anode surface is visible. On the surface of the "fresh" anode from an unused e-cap the strias from the running direction of the anode, resulting in the production process, are clearly visible. The enlargement is however not sufficient to show the openings of the pores in the anode. At the anode, which comes from a failed capacitor out of the Taiwanese production, the surface is overgrown with a placke-like substance transverse to the running direction. An EDX-fingerprint analysis then showed the chemical difference in the surface oxide. The surface of the "fresh" Elko was covered with the stable aluminium oxide. The surface of the failed capacitor was covered with aluminum hydroxide this shows the significantly higher oxygen peak.
The dielectric voltage strength of the hydroxide only can reach the height of the operating voltage applied, which is usually lower than the rated voltage. This decreased dielectric voltage strength of the anode can be measured. Pictured right, such a measurement result is shown. The reduced dielectric voltage strength compared to the original anode voltage strength shows that a chemical process has sustained damaged the oxide layer of the anode.
Through this damage the thickness of the insulating dielectric layer gets smaller. That means, according to the formula of the plate capacitor,
with the permittivity “ε”, the electrode surface “A” and the distance between the electrodes to each other “d”, that with thinner dielectric the capacitance value increases. And indeed, electrolytic capacitors at the beginning of the fatal continual growth of hydroxide, shows a little bulging of the can but not yet open the vent an increased capacitance value can be measured, such as the red colored capacitance curve in a life test in the picture above right shows.
The final stage of this process is reached when the hydrogen gas generated by the constant continual growth of aluminium hydroxide is increased to so such high pressure that the vent gets open or the sealing rubber will be pressed out. Simply said, the capacitor bursts. If the capacitor then is open, it dries out very quickly loses its capacitance down to a minimum value and the ESR increases significantly up to the kΩ range. Because the ripple current still flows over the capacitors ESR, the heat losses grows on, increases the temperature of the winding up to an overheat situation and color the paper of the winding into clearly brown.
After this date actually no more incidents should occur. But even after the year 2007, the year in which the failure of Taiwan bad capacitors with the wrong electrolyte should really be over, the messages with failed capacitors are available on the Internet..
The problem of bursting electrolytic capacitors still exist, the images of failed capacitors described the identical effects with open vents and outpressed rubber. Affected by these failures are capacitor series for rated voltages from 6.3 V to 100 V, which have one thing in common, they have a water based electrolyte with a high water content of up to 75%. In the catalogs of the manufacturers, they are characterized by the catchword "Low-ESR" capacitors or “Low-impedance ", "Ulta-Low-impedance" or "High-ripple-current” capacitors. These capacitors must not be confused with aluminum-polymer capacitors, which are often called "low-ESR” electrolytic capacitors. The failures affects only aluminium electrolytic capacitors with non solid electrolyte.
If now failures occur in the above-described type of capacitors with a newer production date than 2007, so it can not be justified by the incomplete electrolyte of former Taiwanese production. If in an SEM and EDX analysis of the failed capacitors aluminium hydroxide is still detected, not necessarily the electrolyte is faulty because it also can be that the circuit have been wrong designed. Therefore, two questions must be answered first:
It should be noted that the commonly used 10-degree rule (Arrhenius rule, RGT-rule) to estimate the capacitors life time (10 °C reduction in temperature doubles the life time) for the electrolytic capacitors with water based electrolytes often is not valid. The 10-degree rule applies only when it is confirmed by the respective capacitor manufacturer, see .
Because some manufacturers specify different life calculation formulas, sometimes even different formulas for their various series
. Even though a graphical method is specified to estimate the lifetime of a capacitor by a manufacturer and it seems that the curves follows the 10-degree-law, one should not be fooled. The slope of the specified curve in this example is different than under the 10-degree rule
The following two examples of e-cap-life calculations show the difference in results between the 10-degree rule and the formula that the manufacturer Rubycon has specified for their water based electrolyte Series ZL..
For a PC power supply a capacitor with the lifetime specification of 1000 h/105 C ° is selected. The average operating temperature of the capacitor, measured in the metallic region near the vent is 45 °C. The ripple current load in the first example corresponds to the specified data sheet value (100%). This gives a lifetime of
For the second example the double data sheet value of the ripple current is obtained. This gives a lifetime of
The calculated lifetime at twice the value of the ripple current following the formula from Rubycon is significantly smaller than after the 10-degree rule. This reflects the fact that the operation of capacitors with water based electrolytes at ripple current overload can be problematic. This is also reflected in a disclaimer of many capacitor manufacturers, in which the operation is warned with a higher ripple current than the specified value:
The difference in shortening the lifetime of electrolytic capacitors at higher loads comparing e-caps with water based electrolytes with those with electrolytes based on organic solvents is to find in the aggressiveness of the water against the aluminum. Capacitors with solvent electrolytes such as GBL
have a significantly better leakage current behavior than those with water based electrolytes. .
Thus, in operation consumes lesser electrolyte which has a positive impact on the life time. Water-containing capacitors then because of the higher leakage current consume more electrolyte, whereby the life of the capacitors is reduced.
Measurement protocol of measuring the dielectric strength of a cathode out of a failed 10 V electrolytic capacitor, the specification was about 1.5 V, the measured voltage strength was 2.9 V.
On the other hand, a high ripple current load can also result in a consumption of electrolyte, especially during discharging the capacitor. This is based on a physical effect that can sometimes lead to a forming process of the cathode foil in the capacitor. Normally the cathode foil is covered with an oxide layer that is formed by contact with the air in a natural way on the aluminum surface. This oxide layer has a voltage strength at room temperature of about 1 up to 1.5 V. At 105 °C decreases the voltage strength down to about 0.7 to 1.2 V.
Now, if a charged capacitor will be discharged during the discharging parts of the ripple current, then the polarity of the capacitor reverses: The cathode becomes an anode, the current flows out of the capacitor. Than the voltage distribution over the internal resistances builds up a voltage of opposite polarity to the cathode foil. The natural voltage strength of the cathode oxide now can withstand the discharging loads up to the specified value in the relevant data sheet if the electrolytic capacitor has a correct design. The capacitor has a correct construction when the cathode capacitance CK is very large compared to the anode capacitance CA. This is usually given when the cathode capacitance is factor of 10 larger than the anode capacitance . Increasing the ripple current load over the specified value, especially when the temperature is high, however, may generate a reverse voltage to the cathode foil higher than the natural voltage strength and may be form up the oxide on the cathode foil. To form a thicker oxide layer on the cathode foil is associated with the loss of electrolyte which reduces the life time of the capacitor.
The lifetime of the electrolytic capacitors with high water content in the electrolyte is thus determined not only by the operating temperature and the aligned gradual evaporation of the electrolyte, but also by the leakage current and a possible forming process of the cathode foil at high ripple current load. All parameters, the evaporation of electrolytes, the higher leakage current for capacitors with water based electrolytes and, if it is applied, a high ripple current, are consuming fluid electrolytes. From a certain point the up to the saturation limit dissolved salts in the electrolyte will crystallize. The electrolyte changes, initially the conductivity of the electrolyte decreases, the ESR increases. The change of the electrolyte for some product lines also may have an influence to the pH, the pH may change as stronger as closer he gets to the end of the service life of electrolytic capacitors. Gets then the pH of the electrolyte at the end of life in the alkaline region, which is found often in capacitors with water based electrolytes, then stops, as described above, the regeneration of the defects and the fatal, unrestrained growth of aluminum hydroxide begins. If this behavior now comes together with the end of their calculated life and the electrolytic capacitors bursts, then it looks as if a new case of the "capacitor plague" occurred.
The failure pictures, burst e-cap, expressed sealing rubber, leaked electrolyte are identical to those of the production with the "wrong" electrolyte. If now with capacitors build after the year 2007, failures of this kind occur, it only can be determined by a careful recalculation of the entire circuit with all load conditions for the capacitor, such as temperature and ripple current load, whether it's a bug in the capacitor or an error in the design of the circuit.
Because only when the capacitor failed prematurely, before it reach the end of his life, may be assumed that it has a faulty electrolyte or another failure mode. That might be also the reason for the court between a well-known manufacturer of computer hardware with a capacitor manufacturer, as can be seen advertised in the "Techreport".
An incorrect calculation of the service life time and a faulty electrolyte results in the same failure pictures.
However, a burst of an electrolytic capacitor, even if it has reached its end of life, is an extraordinary process. Until now, could be assumed that electrolytic capacitors are drying out over the time, but also in the dry state showed no visible irregularities. It seems that water based electrolytes in e-caps of some manufacturers have a different behavior at the end of their life: they burst! Analysing the prematurely burst capacitor it not can be determined whether thermal or electrical overload has led to the opening of the vent or if the failure is based on a faulty electrolyte. For a correct assessment of new failures with e-caps, it is therefore absolutely necessary to determine the exact operating conditions and to calculate the service a life according to the manufacturer's specification.
Example: X8 = August 2009
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
s, video cards, compact fluorescent lamp
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...
ballasts, LCD monitors, and power supplies of personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s. News of the failures (usually after a few years of use) forced most manufacturers to repair the defects. The problem seems to be ongoing; faults are still being reported as of 2010 .
Prevalence
Faulty capacitors have been discovered in motherboards as old as Socket 7Socket 7
Socket 7 is a physical and electrical specification for an x86-style CPU socket on a personal computer motherboard. The socket supersedes the earlier Socket 5, and accepts P5 Pentium microprocessors manufactured by Intel, as well as compatibles made by Cyrix/IBM, AMD, IDT and others.Socket 7 was...
(1996) and have affected equipment manufactured up to at least 2007. The motherboard companies assembled and sold boards with faulty caps sourced from other manufacturers (see below). Major vendors such as Intel, Dell
Dell
Dell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
and HP were affected. Circa 2005, Dell spent some US $150 million replacing motherboards entirely and another $150 million on the logistics of determining whether a system is in need of replacement. HP reportedly purged its product line in 2004. The motherboards and power supplies in Apple iMac G5
IMac G5
The iMac G5 was a series of desktop Macintosh computers designed and built by Apple Inc. using the PowerPC chip architecture. It was the last line of iMac computers that used a PowerPC chip, making it the last of the iMacs that could run Mac OS 9 applications. In August 2004, the iMac design was...
s and some eMac
EMac
The eMac, short for education Mac, was a Macintosh desktop computer made by Apple Inc. It was originally aimed at the education market, but was later made available as a cheaper mass market alternative to Apple's second-generation LCD display iMac....
s were also affected.
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s, and a range of other devices.
Symptoms
- Bulging of the vent on the top of the capacitor. (The "vent" is the impression stamped in the top of the can. The impression forms the seams of the vent. It is designed so that if the capacitor becomes pressurized it will split at the vent's seams relieving the pressure rather than exploding.)
- Sitting crooked on the circuit board as the bottom rubber plug is pushed out
- Electrolyte (a crusty brown substance) leaked onto the motherboard from the base of the capacitor or vented from the top, visible as rust-like brown deposits, or a visible hole in the vent. The petroleum-based adhesive that is sometimes used to secure the capacitors to the board can be confused with leaked electrolyte; electrolyte is usually wet, adhesive dry. This glue is a thick elastic covering of a sandy yellow colour and darkens (towards black) with heat. A dark brown crust up the side of a capacitor is invariably glue, not electrolyte. The glue is itself sometimes harmful and can corrode leads and tracks covered by it, leading to leakage current or open-circuit; it is not required and can safely be removed. The presence of black glue is a sure sign that the capacitor has overheated due either to internal failure or inadequate ventilation.
- High equivalent series resistanceEquivalent series resistancePractical capacitors and inductors as used in electric circuits are not ideal components with only capacitance or inductance. However, they can be treated to a very good approximation as ideal capacitors and inductors in series with a resistance; this resistance is defined to be the equivalent...
(ESR) can be detected with an ESR meterESR meterAn ESR meter is a two-terminal electronic measuring instrument designed and used primarily to measure the equivalent series resistance of real capacitors—the ESR of an ideal capacitor is zero—usually without the need to disconnect the capacitor from the circuit it is connected to...
, but this test sometimes cannot be performed in-circuit without disconnecting the capacitor. Motherboard capacitors are typically in parallel with other capacitors, and cannot be measured individually while in-circuit. However, a high in-circuit ESR reading unequivocally indicates failure of the measured capacitor or capacitors.
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
decreases and its ESR increases. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
s on the motherboard, and system instability results. Some common symptoms are:
- Not turning on all the time; having to hit reset or try turning the computer on again
- Instabilities (hangs, BSODsBlue Screen of DeathTo forse a BSOD Open regedit.exe,Then search: HKLM\SYSTEM\CurrentControlSet\services\i8042prt\ParametersThen make a new DWORD called "CrashOnCtrlScroll" And set the value to 1....
, kernel panicKernel panicA kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover. The term is largely specific to Unix and Unix-like systems; for Microsoft Windows operating systems the equivalent term is "Bug check" .The kernel routines that...
s, etc.), especially when symptoms get progressively more frequent over time - Memory errors, especially ones that get more frequent with time
- Spontaneous reboots
- In case of on-board video cards, unstable image in some video modes
- Failing to complete the POST, or rebooting before it is completed
- Never starting the POST; fans spin but the system appears dead
- Capacitors with high ESR can make power supplies malfunction, sometimes causing further circuit damage. CPU core voltageCPU core voltageThe CPU core voltage is the power supply voltage supplied to the CPU , GPU, or other device containing a processing core...
or other system voltages may fluctuate or go out of range, possibly with an increase in CPU temperature as the core voltage rises.
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
, dust clogging a fan, bad RAM, or other hardware problems. Instability, once the operating system has loaded, may indicate a software problem (such as some types of malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...
, poorly-written device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s or software), and not a hardware problem at all. If any of these symptoms are experienced, removing the system's case and inspecting the capacitors, especially those around the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, may immediately identify capacitors as the cause. If there are no physical signs, an oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
may be used to examine the AC ripple voltage across capacitors during operation, or an ESR meter to measure ESR when powered down; excessive ripple or ESR is a sign that the capacitors are faulty.
Cause of the failing capacitors - Industrial espionage?
The massive numbers of failures of aluminium electrolytic capacitors with liquid electrolytes, also called “e-caps”, are based on millions of faulty capacitors in the years 1999 to 2007 produced from Taiwanese manufacturers and failing prematurely after only a few months of operation. Many of the used capacitors had the life time specification (load life) of 2000 h/105 °C. With an average internal temperature of 45 °C on a PC and a ripple current, which corresponds to the data sheet specification, these capacitors have a life expectancy of about 15 years of continuous operation. With respect to this life time expectation a failure after 1.5 to 2 years is really "premature".The images of the failures were quite spectacular, bulged or burst cans, expressed sealing rubber and leaking electrolyte were found on countless circuit boards. Many well-known equipment manufacturers such as Dell
Dell
Dell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
, Cisco
Cisco
Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...
, Intel, Asus
ASUS
ASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...
and Abit
Abit
Abit may refer to:*Universal abit, a Defunct Taiwanese computer firm*Abit, Burma, a village in Burma*Abit , an asphalt production company in Surenavan, Armenia...
had to carry out recalls and repair costs to take account of these capacitors . Many repair instructions for self-help can be found on the Internet.
.
As a probable cause of the faulty capacitor-production industrial espionage in connection with the theft of an electrolyte formula is considered. An electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
developer has probably taken with them, when moving from Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
to Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, the chemical composition of a new low resistance, inexpensive, water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
-containing electrolyte and tried to counterfeit these electrolytes in Taiwan, then to sell it cheaper than the Japanese could. But apparently the formula had been copied incompletely, and it lacked important substances to secure the long-term stability of the capacitors.
Development of electrolytic capacitors with water-based electrolytes
The first electrolytic capacitor ever was an aluminiumAluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
electrolytic capacitor with a liquid electrolyte, invented by Charles Pollak in January 1896. In principle, the electrolytic capacitors up to this day (2011) remained the same. On an aluminium anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
, the dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
out of very thin aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
layer is raised by formation. The liquid electrolyte adapts the structure of the dielectric, forms the liquid cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
of the capacitor and thus makes the thin layer thickness of the dielectric effective. A spacer made of paper prevents direct contact of the oxide layer with a second aluminium foil (cathode foil), the electrical connection to the liquid cathode and also saves him. Sealed and provided with connections this construction results in billions of inexpensive and within their lifetime reliable capacitors used for electronic devices.
The electrolyte as ionic conductor caused most of the ohmic losses in the capacitor. Great efforts have been made over the years to reduce these losses to increase the ripple current, because without such improvements the most important target of development - size reductions - cannot be realized.
In Japan, in the context of these developments, some manufacturers are busy to develop a new, low-ohmic water-based electrolyte. The conductivity of water-based electrolytes compared to electrolytes with organic solvents
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
like GBL
Gamma-Butyrolactone
gamma-Butyrolactone is a hygroscopic colorless oily liquid with a weak characteristic odor and is soluble in water. GBL is a common solvent and reagent in chemistry and is used as an aroma compound, as a stain remover, as a superglue remover, as a paint stripper, and as a solvent in some wet...
was significantly improved. Water, with its relatively high permittivity
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
of ε = 81, is a powerful solvent for electrolytes. As such, it dissolves salts in high concentration. The high concentration of dissolved salt ions
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
in the electrolyte increases the conductivity. But water will react quite aggressive and violently with unprotected aluminium. It converts aluminium (Al) with a highly exothermic reaction into aluminium hydroxide
Aluminium hydroxide
Aluminium hydroxide, Al3, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO, and aluminium oxide, Al2O3,...
(Al(OH)3). This is accompanied by a strong heat and gas development in the capacitor and may lead to the explosion of the capacitor. Therefore, the main problem in the development of new water-containing electrolytes, is to hinder the aggressiveness of the water against aluminium to get capacitors having a sufficiently good long-term stability.
The Japanese manufacturer Rubycon
Rubycon (company)
Rubycon Corporation was established in 1952 in Nagano, Japan.Rubycon specializes in the design and production of aluminum electrolytic capacitors , film capacitors and power supply units....
was the late 1990s, a leader in the development of new water-based electrolyte systems with enhanced conductivity. Rubycon 1998 brought with two series, ZL and ZA, the first capacitors on the market that worked with an electrolyte with a water content of about 40 % and were suitable for a wide temperature range from -40 to +105 °C .
The improvement achieved the conductivity of the electrolyte can be seen by a comparison of two capacitors, both of which have a capacitance of 1000 µF at 16 V nominal voltage with the size DxL = 10x20 mm. The capacitors of the Rubycon YXG series, which are provided with an electrolyte based on an organic solvent can be at an impedance of 46 milliohms loaded with a ripple current of 1400 mA. ZL series capacitors with the new water-based electrolyte can be at an impedance of 23 mΩ charged with the ripple current of 1820 mA , an increase of 30 %. Other manufacturers, such as NCC , Nichicon , Elna , follows a short time later. The new series was called "Low ESR" or "Low-impedance", "Ultra-low-impedance" or "High-ripple Current” series in the data sheets. The highly competitive market in the digital data technology and the power supply handle this new development on fast, because by improving the conductivity of the electrolyte could capacitors not only withstand a higher ripple current rating, they were even cheaper, since water is very cheap. Better and even cheaper for high volume products like PCs, LCD screens and power supplies, the cost argument was decisive.
Aluminum oxide - solid dielectric and corrosion protection
The electrolyte in an electrolytic capacitor is from an electrical point of view, the actual cathode of the capacitor. But it is on the other side also a chemical, an acidAcid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
or lye
Lye
Lye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...
, which must be chemically inert, so that the capacitor, whose inner components are made of aluminium, remains stable over long time. But aluminium is a very reactive, easily oxidised metal. And aqueous acids behave quite aggressively against the aluminium. Only a stable aluminium oxide Al2O3 layer on the surface of the anode and protecting substances known as inhibitors or passivators in the electrolyte are able to protect aluminium from water-driven corrosive reactions. The problem of water-containing electrolyte systems lies in the control of aggressiveness of the water toward aluminium.
This problem runs through the development of electrolytic capacitors for over many decades.
For even the first technically used electrolytes mid 20th century were mixtures of ethylene glycol and boric acid. But even with these so-called glycol electrolytes do had an unwanted chemical water crystal reaction, according to the scheme:
From "acid + alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
" gets "ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
+ water"
In a first water-free electrolyte, as the result of esterification a generation of a water content of up to 20 % take place. These electrolytes were originally suitable only for a limited temperature range of -25 to +85 °C. They had a voltage-dependent lifetime, because at higher voltages the leakage current based on the aggressiveness of the water increases exponentially and the associated increased consumption of electrolyte leads to a faster drying out.
On the other hand water delivers the oxygen for the self-healing of electrolytic capacitors, the formation of the anode oxide, the dielectric layer of the capacitor. This normal process of formation or self-healing carried out in two reaction steps. First, it transforms with a strongly exothermic reaction aluminium (Al) into its hydroxide
Aluminium hydroxide
Aluminium hydroxide, Al3, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO, and aluminium oxide, Al2O3,...
Al(OH)3:
- 2 Al + 6 H2O → 2 Al(OH)3 + 3 H2 ↑
This reaction is accelerated by a high electric field and by high temperatures and is accompanied by a pressure build up in the capacitor by the released hydrogen gas. The gel-like aluminium hydroxide Al(OH)3, even called alumina trihydrate (ATH), aluminic hydroxide, aluminium(III) hydroxide, hydrated alumina converts, in the second reaction step usually slow in a few hours at room temperature, more rapidly in a few minutes at higher temperatures, in the crystalline form of aluminium oxide Al2O3:
- 2 Al(OH)3 → 2 AlO(OH) + 2 H2O → Al2O3 + 3 H2O
Only the newly formed stable aluminium oxide heal the defects respectively the weak dielectric layer on the anode of the electrolytic capacitor, forms the stable dielectric of the capacitor. It also protects the capacitor from the aggressive reactions of aluminium in the presence of water. However, with the conversion process of the forming or self healing a small amount of water out of the electrolyte will be "consumed".
Aluminum hydroxide - loss of self-healing
The aluminium oxide layer in the electrolytic capacitor is resistant to chemical attacks, as long as the pH value of the electrolyte is in the range of pH 4.5 to 8.5. . However, it should be the pH value of the electrolyte ideally about 7 (neutral). Measurements of leakage current, which were carried out as early as the 1970s have shown that the leakage current was higher, thus chemically induced defects occurred when the pH value deviated from this ideal value.
It is also known that the "normal" course of building the stable aluminium oxide by the formation of aluminium through the intermediate step of the aluminium hydroxide can be interrupted through an alkaline or basic electrolyte. Disruption to the chemistry of this reaction serves as an example the following:
- 2 Al (s) + 2 NaOH (aq) + 6 H2O 2 Na+ (aq) + 2[Al(OH)4]− + 3 H2 (g)
In this case, it may happen that the hydroxide formed in the first step becomes detached from the aluminum surface and will be not transforms in the desired stable form of aluminium oxide. The cause of the healing process building new oxide layer, a defect or a weak dielectric point remains and the defect is not cured. Then there another additional formation of aluminium hydroxide at this point occurs without converting into the stable aluminium oxide. The self-healing inside the e-cap no longer takes place. The reactions do not come to a standstill, the hydroxide in the pores of the anode foil grow and caused by the first step reaction more and more hydrogen gas will be produced in the can increasing the pressure.
Evidence for wrong electrolyte
This situation of unbraked formation of hydroxide (hydration) and the associated hydrogen gas production was the case to as "capacitor plague" or even "bad caps" mentioned incident with the massive failures of aluminum electrolytic capacitors. It has been demonstrated with the analysis study by two researchers at the University of MarylandUniversity of Maryland
When the term "University of Maryland" is used without any qualification, it generally refers to the University of Maryland, College Park.University of Maryland may refer to the following:...
who analyzed the failed capacitors
).
These two scientists initially determined by ion chromatography and mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
, that there really is hydrogen gas, which leads to bulging of the capacitor’s case or open the vent. Thus it was proved that the oxidation takes place according to the first step of the formation of alumina.
Because it has been customary in electrolytic capacitors to bind the hydrogen with the help of reducing or depolarizing
Depolarizer
A depolarizer or depolariser, in electrochemistry, according to an IUPAC definition, is a synonym of electroactive substance, i.e., a substance which changes its oxidation state, or partakes in a formation or breaking of chemical bonds, in a charge-transfer step of an electrochemical reaction.In...
compounds to reduce the resulting pressure then they searched for compounds of this type. Usually aromatic nitro compounds or amines are used in this case. Although the above-mentioned methods are very sensitive to such pressure reducing compounds no traces of the agents was found within the failed capacitors.
With capacitors, the internal pressure build-up was just so great that the capacitor case was already bulging but the vent had not opened yet, then the pH value of the electrolyte could be identified. The electrolyte of the faulty capacitors was alkaline with pH (7
Since in the investigated Taiwanese electrolytes phosphate ions were missing and the electrolyte was also alkaline, so they lacked the protection against water and the more formation of stable alumina oxides was stopped. There only aluminum hydroxide was generated.
Underlined was the result of chemical analysis by measurement of the electrical capacitance and the leakage current in a long-term test for 56 days. Due to the chemical attack on the oxide layer of these capacitors has been weakened, so that after a short time, the capacitance and the leakage current increased, before both parameters rapidly after opening the vent fell off.
With the report of Hilmann and Helmond it was proofed that the cause of the failured capacitors actually was a faulty electrolyte used by the Taiwanese manufacturers. It lacked the necessary chemical ingredients to ensure the correct pH of the electrolyte over the time for a long-term stability of the electrolytic capacitors.
That the electrolyte with its alcaline pH value then had the fatal consequence of continual growth of hydroxide wíthout changing into the stable oxide can be detected on the surface of the anode foil either photographically or with an EDX-fingerprint analysis of the chemical components.
Even a microscopic image with only a 10-fold magnification, as shown in the pictures right, a significant change in the structure of the anode surface is visible. On the surface of the "fresh" anode from an unused e-cap the strias from the running direction of the anode, resulting in the production process, are clearly visible. The enlargement is however not sufficient to show the openings of the pores in the anode. At the anode, which comes from a failed capacitor out of the Taiwanese production, the surface is overgrown with a placke-like substance transverse to the running direction. An EDX-fingerprint analysis then showed the chemical difference in the surface oxide. The surface of the "fresh" Elko was covered with the stable aluminium oxide. The surface of the failed capacitor was covered with aluminum hydroxide this shows the significantly higher oxygen peak.
Electrical effects
A slightly different electrical behavior of almost all electrolytic capacitors with water based electrolytes can be measured against electrolytic capacitors with electrolyte systems based on organic solvents. The turn-on leakage current after storage times is at a higher level. However, if a water based electrolyte is still in stable condition, ie not yet fallen into the alkaline pH range, then the leakage current is adjusted after a few minutes on a low value. The defects that had been formed by the aggressive behavior of water on aluminum are healed quickly. But if the electrolyte during the operation time has drifted into the alkaline range, then the process of self-healing will end after the formation of aluminum hydroxide. The subsequent conversion into the stable aluminium oxide is prevented by the alkaline environment. The defects that cause the leakage current remains, covered only by hydroxide, and can get further be attacked from the water.The dielectric voltage strength of the hydroxide only can reach the height of the operating voltage applied, which is usually lower than the rated voltage. This decreased dielectric voltage strength of the anode can be measured. Pictured right, such a measurement result is shown. The reduced dielectric voltage strength compared to the original anode voltage strength shows that a chemical process has sustained damaged the oxide layer of the anode.
Through this damage the thickness of the insulating dielectric layer gets smaller. That means, according to the formula of the plate capacitor,
with the permittivity “ε”, the electrode surface “A” and the distance between the electrodes to each other “d”, that with thinner dielectric the capacitance value increases. And indeed, electrolytic capacitors at the beginning of the fatal continual growth of hydroxide, shows a little bulging of the can but not yet open the vent an increased capacitance value can be measured, such as the red colored capacitance curve in a life test in the picture above right shows.
The final stage of this process is reached when the hydrogen gas generated by the constant continual growth of aluminium hydroxide is increased to so such high pressure that the vent gets open or the sealing rubber will be pressed out. Simply said, the capacitor bursts. If the capacitor then is open, it dries out very quickly loses its capacitance down to a minimum value and the ESR increases significantly up to the kΩ range. Because the ripple current still flows over the capacitors ESR, the heat losses grows on, increases the temperature of the winding up to an overheat situation and color the paper of the winding into clearly brown.
E-cap failures after 2007
The first press releases about the massive problem with a large number of premature failures in Taiwanese electrolytic capacitors appeared in September 2002. It can be assumed that by mid-2003 the concerned producers have changed the production and used a "true" composite electrolyte. With a decreased life time of about 1.5 to 3 years for the failing capacitors from mid-2003 on therefore up to mid-2006, the last of the bad capacitors should be failed. The Internet often called the year 2007 as the end point of failures with bad capacitors.After this date actually no more incidents should occur. But even after the year 2007, the year in which the failure of Taiwan bad capacitors with the wrong electrolyte should really be over, the messages with failed capacitors are available on the Internet..
The problem of bursting electrolytic capacitors still exist, the images of failed capacitors described the identical effects with open vents and outpressed rubber. Affected by these failures are capacitor series for rated voltages from 6.3 V to 100 V, which have one thing in common, they have a water based electrolyte with a high water content of up to 75%. In the catalogs of the manufacturers, they are characterized by the catchword "Low-ESR" capacitors or “Low-impedance ", "Ulta-Low-impedance" or "High-ripple-current” capacitors. These capacitors must not be confused with aluminum-polymer capacitors, which are often called "low-ESR” electrolytic capacitors. The failures affects only aluminium electrolytic capacitors with non solid electrolyte.
If now failures occur in the above-described type of capacitors with a newer production date than 2007, so it can not be justified by the incomplete electrolyte of former Taiwanese production. If in an SEM and EDX analysis of the failed capacitors aluminium hydroxide is still detected, not necessarily the electrolyte is faulty because it also can be that the circuit have been wrong designed. Therefore, two questions must be answered first:
- 1) Was the ripple current and temperature stress on the capacitors correct?
- 2) Did the failure occur prematurely, before or after the end of life time?
It should be noted that the commonly used 10-degree rule (Arrhenius rule, RGT-rule) to estimate the capacitors life time (10 °C reduction in temperature doubles the life time) for the electrolytic capacitors with water based electrolytes often is not valid. The 10-degree rule applies only when it is confirmed by the respective capacitor manufacturer, see .
Because some manufacturers specify different life calculation formulas, sometimes even different formulas for their various series
. Even though a graphical method is specified to estimate the lifetime of a capacitor by a manufacturer and it seems that the curves follows the 10-degree-law, one should not be fooled. The slope of the specified curve in this example is different than under the 10-degree rule
The following two examples of e-cap-life calculations show the difference in results between the 10-degree rule and the formula that the manufacturer Rubycon has specified for their water based electrolyte Series ZL..
For a PC power supply a capacitor with the lifetime specification of 1000 h/105 C ° is selected. The average operating temperature of the capacitor, measured in the metallic region near the vent is 45 °C. The ripple current load in the first example corresponds to the specified data sheet value (100%). This gives a lifetime of
- 10-degree rule: 64,000 h, 7.3 years
- Rubycon formula: 64,000 h, 7.3 years
For the second example the double data sheet value of the ripple current is obtained. This gives a lifetime of
- 10-degree rule: 22.600 h, 2.6 years
- Rubycon formula: 6000 h, 0.7 years
The calculated lifetime at twice the value of the ripple current following the formula from Rubycon is significantly smaller than after the 10-degree rule. This reflects the fact that the operation of capacitors with water based electrolytes at ripple current overload can be problematic. This is also reflected in a disclaimer of many capacitor manufacturers, in which the operation is warned with a higher ripple current than the specified value:
- Do not apply a ripple current exceeding the rated maximum ripple current.
The difference in shortening the lifetime of electrolytic capacitors at higher loads comparing e-caps with water based electrolytes with those with electrolytes based on organic solvents is to find in the aggressiveness of the water against the aluminum. Capacitors with solvent electrolytes such as GBL
GBL
GBL could refer to:* Gainsborough Lea Road railway station National Rail station code* GAMCO Investors NYSE symbol* Game Based Learning otherwise known as Serious Games* Game Boy Light...
have a significantly better leakage current behavior than those with water based electrolytes. .
Thus, in operation consumes lesser electrolyte which has a positive impact on the life time. Water-containing capacitors then because of the higher leakage current consume more electrolyte, whereby the life of the capacitors is reduced.
Measurement protocol of measuring the dielectric strength of a cathode out of a failed 10 V electrolytic capacitor, the specification was about 1.5 V, the measured voltage strength was 2.9 V.
On the other hand, a high ripple current load can also result in a consumption of electrolyte, especially during discharging the capacitor. This is based on a physical effect that can sometimes lead to a forming process of the cathode foil in the capacitor. Normally the cathode foil is covered with an oxide layer that is formed by contact with the air in a natural way on the aluminum surface. This oxide layer has a voltage strength at room temperature of about 1 up to 1.5 V. At 105 °C decreases the voltage strength down to about 0.7 to 1.2 V.
Now, if a charged capacitor will be discharged during the discharging parts of the ripple current, then the polarity of the capacitor reverses: The cathode becomes an anode, the current flows out of the capacitor. Than the voltage distribution over the internal resistances builds up a voltage of opposite polarity to the cathode foil. The natural voltage strength of the cathode oxide now can withstand the discharging loads up to the specified value in the relevant data sheet if the electrolytic capacitor has a correct design. The capacitor has a correct construction when the cathode capacitance CK is very large compared to the anode capacitance CA. This is usually given when the cathode capacitance is factor of 10 larger than the anode capacitance . Increasing the ripple current load over the specified value, especially when the temperature is high, however, may generate a reverse voltage to the cathode foil higher than the natural voltage strength and may be form up the oxide on the cathode foil. To form a thicker oxide layer on the cathode foil is associated with the loss of electrolyte which reduces the life time of the capacitor.
The lifetime of the electrolytic capacitors with high water content in the electrolyte is thus determined not only by the operating temperature and the aligned gradual evaporation of the electrolyte, but also by the leakage current and a possible forming process of the cathode foil at high ripple current load. All parameters, the evaporation of electrolytes, the higher leakage current for capacitors with water based electrolytes and, if it is applied, a high ripple current, are consuming fluid electrolytes. From a certain point the up to the saturation limit dissolved salts in the electrolyte will crystallize. The electrolyte changes, initially the conductivity of the electrolyte decreases, the ESR increases. The change of the electrolyte for some product lines also may have an influence to the pH, the pH may change as stronger as closer he gets to the end of the service life of electrolytic capacitors. Gets then the pH of the electrolyte at the end of life in the alkaline region, which is found often in capacitors with water based electrolytes, then stops, as described above, the regeneration of the defects and the fatal, unrestrained growth of aluminum hydroxide begins. If this behavior now comes together with the end of their calculated life and the electrolytic capacitors bursts, then it looks as if a new case of the "capacitor plague" occurred.
The failure pictures, burst e-cap, expressed sealing rubber, leaked electrolyte are identical to those of the production with the "wrong" electrolyte. If now with capacitors build after the year 2007, failures of this kind occur, it only can be determined by a careful recalculation of the entire circuit with all load conditions for the capacitor, such as temperature and ripple current load, whether it's a bug in the capacitor or an error in the design of the circuit.
Because only when the capacitor failed prematurely, before it reach the end of his life, may be assumed that it has a faulty electrolyte or another failure mode. That might be also the reason for the court between a well-known manufacturer of computer hardware with a capacitor manufacturer, as can be seen advertised in the "Techreport".
An incorrect calculation of the service life time and a faulty electrolyte results in the same failure pictures.
However, a burst of an electrolytic capacitor, even if it has reached its end of life, is an extraordinary process. Until now, could be assumed that electrolytic capacitors are drying out over the time, but also in the dry state showed no visible irregularities. It seems that water based electrolytes in e-caps of some manufacturers have a different behavior at the end of their life: they burst! Analysing the prematurely burst capacitor it not can be determined whether thermal or electrical overload has led to the opening of the vent or if the failure is based on a faulty electrolyte. For a correct assessment of new failures with e-caps, it is therefore absolutely necessary to determine the exact operating conditions and to calculate the service a life according to the manufacturer's specification.
Date of manufacture code
Many manufacturers use an 2-digit abbreviation according to IEC 60062 standard to code the date of production (date code) of electrolytic capacitors- First digit: Year of production, S = 2004, T = 2005, U = 2006, V = 2007, W = 2008, X = 2009, A = 2010, B = 2011
- Second digit: Month of production, 1 to 9 = Jan. to Sept., O = Oct., N = Nov., D = Dec.
Example: X8 = August 2009
External links
- Capacitor Replacement Video Tutorial in HD - Explains the basics of replacement capacitor selection and how to replace capacitors
- Capacitor Lab - Repair and bad capacitor information site
- Motherboard Capacitor Problem Blows Up — An article about capacitor failures