Common problem
Common electrolytic capacitor failure phenomenon
Source：本站 | Time：2021-12-13 | Read：444
There are times when electrolytic capacitors fail, and the failure mechanism varies due to the different materials, structures, manufacturing processes, performance and use environments of various types of capacitors. Common failure modes: leakage, explosion, open circuit, breakdown, deterioration of electrical parameters, etc.
??1、Liquid leakage
??Liquid leakage is one of the causes of capacitor failure, and aluminum electrolytic capacitors are no exception. The working electrolyte of aluminum electrolytic capacitor is acidic, if it overflows, it will seriously pollute and corrode other components and printed circuit boards around the capacitor. Meanwhile, inside the electrolytic capacitor, the working electrolyte gradually dries up due to the leakage and loses the ability to repair the anodic oxide film medium, leading to the failure of the capacitor by breakdown or deterioration of electrical parameters. There are various reasons for liquid leakage.
??① Poor sealing of aluminum electrolytic capacitors.
??②The use of rubber plugs to seal aluminum electrolytic capacitors may cause liquid leakage due to aging and cracking of the rubber as a result of using it for too long.
??③ Problems with mechanical sealing process.
??④ Installation problem, generally manufacturers will consider the leakage problem, they will specify in the enterprise standard to vertical installation, while some companies adopt horizontal installation, etc.
??2、Explosion
??Aluminum electrolytic capacitors have too much AC component in the working voltage, or the oxide film medium has more defects, or there are harmful anions such as chlorine and sulfate, so that the rate of gas generated by electrolysis is faster when the leakage current is higher, and the longer the working time is, the higher the leakage current is, the more gas is in the shell, and the temperature is higher. The difference of air pressure inside and outside the capacitor metal shell will increase with the working voltage and working time. If it is well sealed, and there is no explosion-proof measures, then the air pressure will increase to a certain degree and cause the capacitor to explode.
??Nowadays, the capacitors on the market generally adopt the explosion-proof case structure, adding a crease in the upper part of the metal case, which will open the crease when the air pressure is high and increase the inner volume of the case, thus reducing the air pressure and the risk of explosion. In use, such as adding overload voltage, rapid charging and discharging of capacitors, applying reverse voltage, etc. may make the capacitor explode.
??3、Breakdown
??Breakdown of aluminum electrolytic capacitor is caused by the rupture of anodic aluminum oxide dielectric film, resulting in direct contact between electrolyte and anode. Aluminum oxide film may be damaged locally due to various materials, processes or environmental conditions. The oxygen ions provided by the working electrolyte under the action of an applied electric field can re-form the oxide film at the damaged area, allowing the anodic oxide film to be filled and repaired. However, if there are impurity ions or other defects in the damaged area that prevent the filling and repair work from being perfected, the anodic oxide film will be left with microscopic holes, which may even become penetration holes, causing the aluminum electrolytic capacitor to break down.
??In addition, with the growth of use and storage time, the solvent in the electrolytic solution is gradually consumed and volatilized, which makes the solution acid value rise and has a corrosive effect on the oxide film layer in the storage process.
??4、Burning
??Aluminum electrolytic capacitor burns out, generally caused by the following reasons.
??①The positive and negative poles are reversed The aluminum electrolytic capacitor is a kind of capacitor with positive and negative poles, if the positive and negative poles are connected wrongly when installing the aluminum electrolytic capacitor, the capacitor will be burned.
??② Insufficient voltage resistance When the voltage exceeds the voltage resistance value of aluminum electrolytic capacitors, the capacitor will be burnt.
??③ Unqualified quality Some manufacturers produce unqualified aluminum electrolytic capacitors, which may also lead to the burning of capacitors.
??5、Open circuit
??When the aluminum electrolytic capacitors work in high temperature or hot and humid environment for a long time, the open circuit failure may occur, which is due to the breakage of the anode lead foil due to electrochemical corrosion. For high-voltage large-capacity capacitors, this failure mode is more frequent.
??In addition, if the anode lead-in foil and the anode foil are riveted together without sufficient flatness, poor contact can cause intermittent open circuit in the capacitor. In use, over mechanical stress may make the capacitor open-circuit.
??6、Deterioration of electrical parameters
??1. Decrease of electric capacity and increase of loss; 2. Increase of leakage current
??1、Liquid leakage
??Liquid leakage is one of the causes of capacitor failure, and aluminum electrolytic capacitors are no exception. The working electrolyte of aluminum electrolytic capacitor is acidic, if it overflows, it will seriously pollute and corrode other components and printed circuit boards around the capacitor. Meanwhile, inside the electrolytic capacitor, the working electrolyte gradually dries up due to the leakage and loses the ability to repair the anodic oxide film medium, leading to the failure of the capacitor by breakdown or deterioration of electrical parameters. There are various reasons for liquid leakage.
??① Poor sealing of aluminum electrolytic capacitors.
??②The use of rubber plugs to seal aluminum electrolytic capacitors may cause liquid leakage due to aging and cracking of the rubber as a result of using it for too long.
??③ Problems with mechanical sealing process.
??④ Installation problem, generally manufacturers will consider the leakage problem, they will specify in the enterprise standard to vertical installation, while some companies adopt horizontal installation, etc.
??2、Explosion
??Aluminum electrolytic capacitors have too much AC component in the working voltage, or the oxide film medium has more defects, or there are harmful anions such as chlorine and sulfate, so that the rate of gas generated by electrolysis is faster when the leakage current is higher, and the longer the working time is, the higher the leakage current is, the more gas is in the shell, and the temperature is higher. The difference of air pressure inside and outside the capacitor metal shell will increase with the working voltage and working time. If it is well sealed, and there is no explosion-proof measures, then the air pressure will increase to a certain degree and cause the capacitor to explode.
??Nowadays, the capacitors on the market generally adopt the explosion-proof case structure, adding a crease in the upper part of the metal case, which will open the crease when the air pressure is high and increase the inner volume of the case, thus reducing the air pressure and the risk of explosion. In use, such as adding overload voltage, rapid charging and discharging of capacitors, applying reverse voltage, etc. may make the capacitor explode.
??3、Breakdown
??Breakdown of aluminum electrolytic capacitor is caused by the rupture of anodic aluminum oxide dielectric film, resulting in direct contact between electrolyte and anode. Aluminum oxide film may be damaged locally due to various materials, processes or environmental conditions. The oxygen ions provided by the working electrolyte under the action of an applied electric field can re-form the oxide film at the damaged area, allowing the anodic oxide film to be filled and repaired. However, if there are impurity ions or other defects in the damaged area that prevent the filling and repair work from being perfected, the anodic oxide film will be left with microscopic holes, which may even become penetration holes, causing the aluminum electrolytic capacitor to break down.
??In addition, with the growth of use and storage time, the solvent in the electrolytic solution is gradually consumed and volatilized, which makes the solution acid value rise and has a corrosive effect on the oxide film layer in the storage process.
??4、Burning
??Aluminum electrolytic capacitor burns out, generally caused by the following reasons.
??①The positive and negative poles are reversed The aluminum electrolytic capacitor is a kind of capacitor with positive and negative poles, if the positive and negative poles are connected wrongly when installing the aluminum electrolytic capacitor, the capacitor will be burned.
??② Insufficient voltage resistance When the voltage exceeds the voltage resistance value of aluminum electrolytic capacitors, the capacitor will be burnt.
??③ Unqualified quality Some manufacturers produce unqualified aluminum electrolytic capacitors, which may also lead to the burning of capacitors.
??5、Open circuit
??When the aluminum electrolytic capacitors work in high temperature or hot and humid environment for a long time, the open circuit failure may occur, which is due to the breakage of the anode lead foil due to electrochemical corrosion. For high-voltage large-capacity capacitors, this failure mode is more frequent.
??In addition, if the anode lead-in foil and the anode foil are riveted together without sufficient flatness, poor contact can cause intermittent open circuit in the capacitor. In use, over mechanical stress may make the capacitor open-circuit.
??6、Deterioration of electrical parameters
??1. Decrease of electric capacity and increase of loss; 2. Increase of leakage current
