When the ripple current is constant (such as rated ripple current), the higher the ambient temperature, the shorter the service life of electrolytic capacitor. If the ambient temperature is too high and exceeds the maximum rated temperature of the electrolytic capacitor, the electrolyte boiling in the electrolytic capacitor will generate overpressure, and the pressure relief parts will produce irreversible pressure relief action, resulting in electrolyte leakage, which will cause permanent damage to the electrolytic capacitor. Therefore, the storage and use temperature of electrolytic capacitor must not exceed the rated temperature. On the contrary, if the working temperature is reduced, the service life of electrolytic capacitor can be greatly increased. For example, the service life of electrolytic capacitor with rated maximum temperature of 85 ℃ is 1000 hours at 85 ℃, while the life of electrolytic capacitor can be extended to about 10000 ℃ when the ambient temperature is reduced to 60 ℃. When the environmental temperature is reduced to 40 ℃, the service life of electrolytic capacitor can reach 80000 hours The actual life of the capacitor is much higher than the nominal value, which is the reason why the service temperature is lower than the maximum rated temperature. Therefore, if conditions permit, it is a good way to prolong the service life of electrolytic capacitor by reducing the ambient temperature as far as possible. Therefore, the electrolytic capacitor is required to be far away from the heat source in the design.
The service life of electrolytic capacitor is not only related to the ambient temperature, but also to the ripple current. As the thermal stress has a decisive influence on the service life of electrolytic capacitors, the thermal loss caused by ripple current is an important factor affecting the service life of electrolytic capacitors. Ripple current refers to the AC component current flowing through the electrolytic capacitor. It is affected by the ambient temperature and AC frequency. The maximum allowable value of ripple current varies with the ambient temperature. When the ambient temperature is constant, the larger the ripple current, the shorter the service life of electrolytic capacitor. The relationship between ripple current and life of electrolytic capacitor with rated temperature of 85 ℃ and life of 1000 hours is within the allowable range. The reason is: the heat dissipation of electrolytic capacitor is very poor. When the ripple current flows through the electrolytic capacitor, the equivalent series resistance (ESR) will convert the electric energy into heat energy. In the electrolytic capacitor with poor heat dissipation condition, the temperature rise will cause the effect of temperature rise, which will lead to the reduction of service life. The ripple current of electrolytic capacitor should be reduced as much as possible. Moreover, for ordinary electrolytic capacitors, the thermal effect of high-frequency ripple current will be greater than that of power frequency ripple current. Therefore, when the output filter or load of switching power supply has high-frequency ripple current, the application of ordinary electrolytic capacitor will feel obvious heat, which will lead to the decline of the life of electrolytic capacitor.
In general, the environmental temperature and ripple current should be considered when analyzing the service life of electrolytic capacitors. The service life of electrolytic capacitor is that the higher the ripple current and ambient temperature, the shorter the service life of electrolytic capacitor, and the higher the ambient temperature, the smaller the allowable ripple current.
In the application of electrolytic capacitors, it is necessary to select the appropriate maximum rated temperature and service life according to the needs. Generally, the price of electrolytic capacitors with high rated temperature and long rated life is correspondingly higher. However, if the ambient temperature is too high, even if the maximum rated temperature of the electrolytic capacitor used is not exceeded, the electrolytic capacitor will be premature damaged. Moreover, the thermal loss caused by ripple current has a great impact on the service life of electrolytic capacitors. Therefore, when selecting electrolytic capacitors, the electrolytic capacitors with rated values slightly higher than the required values should be selected. However, from an economic point of view, the higher the rated temperature, the longer the service life of the electrolytic capacitor, the higher the price. Therefore, in general, if there are no special requirements, the electrolytic capacitor with high rated voltage of + 85 ℃ and service life of 1000h can generally meet the design requirements.