Capacitor explosion

When the voltage applied by the capacitor exceeds its withstand voltage, or when the voltage polarity of a polarized electrolytic capacitor is reversed, the leakage current of the capacitor will rise sharply, causing the internal heat of the capacitor to increase, and the electrolyte will generate a lot of gas.

In order to prevent the capacitor from exploding, three grooves are pressed on the top of the capacitor shell, so that the top of the capacitor can rupture first under high pressure and release the internal pressure.

(Blasting tank on top of electrolytic capacitor)

However, during the manufacturing process of some capacitor, the groove on the top is not qualified, and the pressure inside the capacitor will cause the sealing rubber at the bottom of the capacitor to be ejected. At this time, the pressure inside the capacitor is suddenly released and an explosion will occur.

1. Explosion of non-polar electrolytic capacitor

The figure below shows a non-polar electrolytic capacitor on hand, which has a capacity of 1000uF and a withstand voltage of 16V. After the applied voltage exceeds 18V, the leakage current suddenly increases, and the temperature and pressure inside the capacitor increase. Eventually, the rubber sealing ring at the bottom of the capacitor exploded, and the internal electrodes were smashed and loosened like popcorn.

(Overvoltage explosion of non-polar electrolytic capacitor)

By bundling a thermocouple on the capacitor, the temperature of the capacitor can be measured as the applied voltage increases. The following figure shows the process in which the voltage of a non-polar capacitor increases, when the applied voltage exceeds the withstand voltage value, the internal temperature continues to increase.

(Relationship between voltage and temperature)

The figure below shows the change in the current flowing through the capacitor in the same process. It can be seen that the increase in current is the main reason for the increase in internal temperature. In this process, the voltage increases linearly, and as the current rises sharply, the internal group of the power supply causes the voltage to drop. Finally, when the current exceeds 6A, with a loud noise, the capacitor explodes.

(Relationship between voltage and current)

Due to the large internal volume of the non-polar electrolytic capacitor and the large amount of electrolyte, the pressure generated after the overcurrent is huge, resulting in the pressure relief groove on the top of the shell not rupturing, and the sealing rubber at the bottom of the capacitor is exploded.

2. Explosion of polar electrolytic capacitor

For electrolytic capacitor with polarity, apply voltage. When the voltage exceeds the withstand voltage of the capacitor, the leakage current will also rise sharply, causing the capacitor to overheat and explode.

The figure below shows a limit electrolytic capacitor, its capacity is 1000uF, withstand voltage of 16V. After the overpressure, the internal air pressure process is released through the top pressure relief groove, so the capacitor explosion process is avoided.

(Polar electrolytic capacitor overvoltage blasting)

The following figure shows how the temperature of the capacitor changes with the increase of the applied voltage. When the voltage gradually approaches the withstand voltage of the capacitor, the remaining current of the capacitor increases, and the internal temperature continues to rise.

(Relationship between voltage and temperature)

The following figure shows the change of the leakage current of the capacitor, which is called a 16V withstand voltage electrolytic capacitor. During the test, when the voltage exceeds 15V, the leakage current of the capacitor begins to rise sharply.

(Relationship between voltage and current)

Through the experimental process of the previous two electrolytic capacitor, we can also see the withstand voltage limitation of such 1000uF ordinary electrolytic capacitor. In order to avoid capacitor breakdown by high voltage, when using electrolytic capacitor, it is necessary to leave enough margin according to the actual voltage fluctuations.