Since aluminum electrolytic capacitors are liquid electrolytes, gases are generated due to chemical and electrochemical reactions during product aging, storage, and operation, so that gas is continuously accumulated inside the capacitors. At the same time, the electrolyte itself has a higher vapor pressure, so that the inside of the capacitor maintains a certain pressure.
The aluminum electrolytic capacitor is a non-hermetic structure, and the electrolyte gas is slowly volatilized from the seal. As the evaporation of the electrolyte causes the amount of electrolyte in the capacitor to decrease, the capacitance of the aluminum electrolytic capacitor gradually decreases with the working time, and the loss tangent increases. The evaporation rate under normal conditions is very low, so the performance change of the aluminum electrolytic capacitor is very slow.
The design life of the capacitor is verified by the “durability test”: the product is applied with the specified rated voltage at the rated operating temperature, and the design life time is tested to determine the amount of change in the electrical parameters of the capacitor. The test methods and criteria are as follows:
Capacitance change rate: the change is ±20% of the initial measured value;
Loss tangent: no more than 200% of the initial required value;
DC leakage current: no more than the initial required value.
In general, the actual test life of a capacitor can be longer than the design life.
Of course, considering the voltage drop of the capacitor's environmental conditions (using 70% to 80% of the rated voltage), the ripple current is lower than the rated ripple current, the interstitial use, and the capacitor's heat dissipation conditions, so the actual life of the capacitor is also Greatly longer than the estimated life.