I. Application Scope of Aluminum Electrolytic Capacitors:

Electrolytic capacitors are widely used in various fields of power electronics circuits. They are mainly used for smoothing, energy storage, or filtering after the rectification of alternating voltages. In addition, they are also used in circuits such as non-precise timing delays. Therefore, it is very important to understand the factors that affect the lifespan of capacitors.

II. Factors Affecting the Lifespan of Aluminum Electrolytic Capacitors:

Both the design and application conditions of electrolytic capacitors can affect their lifespan. From a design perspective, the design method, materials, and processing technology of electrolytic capacitors determine the lifespan and stability of the capacitors. For users, factors such as operating voltage, ripple current, switching frequency, installation method, and heat dissipation method will all have an impact on the lifespan of electrolytic capacitors.

According to the formula for the hot spot temperature, the application environment temperature of aluminum electrolytic capacitors is also an important factor. During application, factors such as the environmental heat dissipation method, heat dissipation intensity, the distance between the electrolytic capacitor and the heat source, and the installation method of the electrolytic capacitor can be considered. The heat inside the capacitor always conducts from the "hot spot" with the highest temperature to the relatively cooler parts around. There are several ways of heat transfer: one is through the conduction of the aluminum foil and the electrolyte. If the capacitor is installed on a heat sink, part of the heat will also be transferred to the environment through the heat sink. Different installation methods, spacing, and heat dissipation methods will all affect the thermal resistance from the capacitor to the environment.

III. Factors Affecting the Lifespan of Capacitors in the Actual Usage Environment:

In actual use, some factors can cause the failure of electrolytic capacitors, such as extremely low temperatures, capacitor temperature rise (soldering temperature, ambient temperature, AC ripple), excessive voltage, instantaneous voltage, very high frequency, or reverse bias voltage. Among them, the temperature rise is a factor that has a relatively large impact on the working lifespan of electrolytic capacitors. The conductivity of the capacitor is determined by the ionization ability and viscosity of the electrolyte. When the temperature decreases, the viscosity of the electrolyte increases, so the mobility of ions and the conductivity decrease. When the electrolyte freezes, the mobility of ions is so low that the resistance is extremely high. Conversely, excessive heat will accelerate the evaporation of the electrolyte. When the amount of electrolyte decreases to a certain limit, the lifespan of the capacitor ends. When working in frigid regions (generally below -25°C), heating is required to ensure the normal operating temperature of the electrolytic capacitor. For example, outdoor UPS units are equipped with heating plates in the northeastern region of China.

Capacitors are easily broken down under overvoltage conditions, and surge voltages and instantaneous high voltages often occur in actual applications. Especially in China, which has a vast territory and complex power grids in various regions, the AC power grid is very complex, and the voltage often exceeds 30% of the normal voltage. Especially for single-phase input, phase deviation will aggravate the normal range of the AC input. Tests have shown that for a commonly used 450V/470uF 105℃ electrolytic capacitor with a lifespan of 2000 hours, when the voltage is 1.34 times the rated voltage, the capacitor will leak liquid, emit gas, and the top will burst open after 2 hours. According to statistics and analysis, the failure of electrolytic capacitors at the PFC output of communication switching power supplies close to the power grid is mainly caused by power grid surges and high voltage damage. Therefore, for the voltage selection of aluminum electrolytic capacitors, it is generally reasonable to perform a two-level derating and use them at 80% of the rated value.

IV. The Impact of Capacitor Installation on Lifespan:

Capacitors must be installed correctly to achieve their designed working lifespan. When the capacitors are arranged closely, at least a 5mm interval should be left between adjacent capacitors to ensure an appropriate amount of air flow. When installing capacitors, they should be kept as far away from heat-generating components as possible. Otherwise, the excessively high temperature will shorten the lifespan of the capacitors, making the capacitors the component with the shortest lifespan in the entire circuit. In an environment with a relatively high ambient temperature, forced air cooling should be used as much as possible, and the capacitors should be installed at the air inlet.

V. The Impact of Frequency on Lifespan:

If the current is composed of the fundamental frequency and multiple harmonics, the power loss value generated by each harmonic must be calculated, and the calculation results should be added together to obtain the total loss value. In high-frequency applications, the leads at both ends of the capacitor should be as short as possible to reduce the equivalent inductance. The resonance frequency of the capacitor varies depending on the type of capacitor. If the capacitor is used at a frequency higher than the resonance frequency, its external characteristics will be inductive.

VI. Conclusion:

In summary, by avoiding abnormal failures and selecting the correct application conditions and environment, the lifespan of electrolytic capacitors can be guaranteed.