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Reasons Influencing the Life of Electrolytic Capacitors (2)
Author：本站Release time：2018-12-17 10:54:15Browsing：
1. Design considerations
In the capacitance of non-solid electrolyte, the dielectric is anodic aluminium foil oxide layer. The electrolyte acts as the electrical contact between cathode aluminium foil and anode aluminium foil oxide layer. The paper layer absorbing the electrolyte becomes the isolation layer between the cathode aluminium foil and the anode aluminium foil. The aluminium foil is connected to the terminal of the capacitor through the electrode lead sheet.
By reducing ESR value, the internal temperature rise caused by ripple current in capacitor can be reduced. This can be achieved by using multiple electrode leads and laser welding electrodes.
ESR value and ripple current determine the temperature rise of capacitor. One of the main measures to make the capacitance have satisfactory ESR value is to connect the external electrode and the core pack with one or more metal electrode leads to reduce the impedance between the core pack and the pin. The more electrode leads on the core, the lower the ESR value of the capacitor. With the help of laser welding technology, more electrode leads can be added to the core package, so that the capacitance can reach a lower ESR value. This also means that capacitors can withstand higher ripple currents and have lower internal temperature rise, which means longer service life. This is also conducive to improving the ability of capacitors to resist vibration, otherwise it may lead to internal short circuit, high leakage current, capacitance loss, ESR value rise and circuit opening.
Through good mechanical contact between the capacitor core and the bottom of the aluminium shell and heat sink in the middle of the core, the internal heat of the capacitor can be effectively released from the bottom of the aluminium shell to the bottom plate connected with it.
Internal heat conduction design is very important for the stability and working life of capacitors. In EvoxRifa's design, the negative aluminum foil is extended to the bottom of the shell thickness of the direct contact capacitor. This bottom becomes the heat sink of the core package so that the heat of the hot spot can be released. If the installation method with bolts is selected and the capacitor is installed safely on the floor (usually aluminum), a more comprehensive heat conduction solution with low thermal resistance (Rth.) can be obtained.
The loss of electrolyte can be greatly reduced by using a phenolic plastic cover with electrodes and double special gaskets to closely occlude the aluminium shell.
The evaporation of the electrolyte through the gasket determines the working time of the long-life electrolytic capacitor. When the electrolyte of the capacitor evaporates to a certain extent, the capacitor will eventually fail (this result will be accelerated by the internal temperature rise). EvoxRifa's double-layer sealing system can slow down the evaporation rate of electrolyte and make the capacitor reach its longest working life.
These characteristics ensure that the capacitor has a long working life in the required field.
3.2. Application Factors Affecting Life
According to the lifetime formula, the application factors affecting the lifetime are: ripple current (IRMS), environmental temperature (Ta), and total thermal resistance (Rth) transferred from hot spot to surrounding environment.
1. ripple current
The ripple current directly affects the hot spot temperature inside the electrolytic capacitor. The permissible range of ripple current can be obtained by inquiring the manual for the use of electrolytic capacitors. If it goes beyond the scope, it can be solved by parallel connection.
2. Environmental temperature (Ta) and thermal resistance (Rth)
According to the formula of hot spot temperature, the applied ambient temperature of aluminium electrolytic capacitor is also an important factor. In application, environmental heat dissipation mode, heat dissipation intensity, distance between electrolytic capacitor and heat source and installation mode of electrolytic capacitor can be considered.
The heat inside the capacitor is always transferred from the "hot spot" with the highest temperature to the part with relatively low temperature around it. There are several ways of heat transfer: one is through aluminium foil and electrolyte conduction. If the capacitor is mounted on the radiator, part of the heat will be transferred to the environment through the radiator. Different installation methods and spacing and heat dissipation methods will affect the thermal resistance of capacitors to the environment. The total thermal resistance transferred from the "hot spot" to the surrounding environment is expressed in Rth. The capacitor is mounted on the heat sink with a thermal resistance of 2 C/W, and the thermal resistance value of the capacitor is Rth=3.6 C/W. When the capacitor is mounted on the heat sink with a thermal resistance of 2 C/W and a forced air cooling rate of 2 m/s, the thermal resistance value of the capacitor is Rth=2.1 C/W. Take PEH200OO427AM capacitor as an example, the ambient temperature is 85 C.
In the capacitance of non-solid electrolyte, the dielectric is anodic aluminium foil oxide layer. The electrolyte acts as the electrical contact between cathode aluminium foil and anode aluminium foil oxide layer. The paper layer absorbing the electrolyte becomes the isolation layer between the cathode aluminium foil and the anode aluminium foil. The aluminium foil is connected to the terminal of the capacitor through the electrode lead sheet.
By reducing ESR value, the internal temperature rise caused by ripple current in capacitor can be reduced. This can be achieved by using multiple electrode leads and laser welding electrodes.
ESR value and ripple current determine the temperature rise of capacitor. One of the main measures to make the capacitance have satisfactory ESR value is to connect the external electrode and the core pack with one or more metal electrode leads to reduce the impedance between the core pack and the pin. The more electrode leads on the core, the lower the ESR value of the capacitor. With the help of laser welding technology, more electrode leads can be added to the core package, so that the capacitance can reach a lower ESR value. This also means that capacitors can withstand higher ripple currents and have lower internal temperature rise, which means longer service life. This is also conducive to improving the ability of capacitors to resist vibration, otherwise it may lead to internal short circuit, high leakage current, capacitance loss, ESR value rise and circuit opening.
Through good mechanical contact between the capacitor core and the bottom of the aluminium shell and heat sink in the middle of the core, the internal heat of the capacitor can be effectively released from the bottom of the aluminium shell to the bottom plate connected with it.
Internal heat conduction design is very important for the stability and working life of capacitors. In EvoxRifa's design, the negative aluminum foil is extended to the bottom of the shell thickness of the direct contact capacitor. This bottom becomes the heat sink of the core package so that the heat of the hot spot can be released. If the installation method with bolts is selected and the capacitor is installed safely on the floor (usually aluminum), a more comprehensive heat conduction solution with low thermal resistance (Rth.) can be obtained.
The loss of electrolyte can be greatly reduced by using a phenolic plastic cover with electrodes and double special gaskets to closely occlude the aluminium shell.
The evaporation of the electrolyte through the gasket determines the working time of the long-life electrolytic capacitor. When the electrolyte of the capacitor evaporates to a certain extent, the capacitor will eventually fail (this result will be accelerated by the internal temperature rise). EvoxRifa's double-layer sealing system can slow down the evaporation rate of electrolyte and make the capacitor reach its longest working life.
These characteristics ensure that the capacitor has a long working life in the required field.
3.2. Application Factors Affecting Life
According to the lifetime formula, the application factors affecting the lifetime are: ripple current (IRMS), environmental temperature (Ta), and total thermal resistance (Rth) transferred from hot spot to surrounding environment.
1. ripple current
The ripple current directly affects the hot spot temperature inside the electrolytic capacitor. The permissible range of ripple current can be obtained by inquiring the manual for the use of electrolytic capacitors. If it goes beyond the scope, it can be solved by parallel connection.
2. Environmental temperature (Ta) and thermal resistance (Rth)
According to the formula of hot spot temperature, the applied ambient temperature of aluminium electrolytic capacitor is also an important factor. In application, environmental heat dissipation mode, heat dissipation intensity, distance between electrolytic capacitor and heat source and installation mode of electrolytic capacitor can be considered.
The heat inside the capacitor is always transferred from the "hot spot" with the highest temperature to the part with relatively low temperature around it. There are several ways of heat transfer: one is through aluminium foil and electrolyte conduction. If the capacitor is mounted on the radiator, part of the heat will be transferred to the environment through the radiator. Different installation methods and spacing and heat dissipation methods will affect the thermal resistance of capacitors to the environment. The total thermal resistance transferred from the "hot spot" to the surrounding environment is expressed in Rth. The capacitor is mounted on the heat sink with a thermal resistance of 2 C/W, and the thermal resistance value of the capacitor is Rth=3.6 C/W. When the capacitor is mounted on the heat sink with a thermal resistance of 2 C/W and a forced air cooling rate of 2 m/s, the thermal resistance value of the capacitor is Rth=2.1 C/W. Take PEH200OO427AM capacitor as an example, the ambient temperature is 85 C.