Why do aluminum electrolytic capacitors explode when reversed?

The main reason for the explosion of aluminum electrolytic capacitors when reversed is due to their internal structure and working principle. ‌

There is a layer of aluminum oxide film inside the aluminum electrolytic capacitor as a dielectric, which gives the capacitor polarity. Under positive electrode voltage, the aluminum oxide film will gradually thicken, and the capacitance value of the capacitor will increase; Under reverse voltage, the aluminum oxide film will quickly rupture, causing a short circuit or explosion of the capacitor. In addition, hydrogen ions in the electrolyte will pass through the oxide layer under reverse voltage, forming gas and causing the oxide layer to detach, thereby causing the capacitor to fail.

The basic structure and working principle of aluminum electrolytic capacitors are as follows:

Aluminum electrolytic capacitors are composed of an anode, a cathode, and an electrolyte. The anode and cathode are respectively coated with aluminum oxide layers, and the electrolyte is immersed in the paper between the two aluminum layers. The aluminum oxide layer can withstand forward direct current voltage, but cannot withstand reverse direct current voltage, as reverse voltage can cause the oxide layer to rupture, resulting in capacitor failure.

The methods to avoid reverse connection of aluminum electrolytic capacitors include:

Correctly mark the positive and negative poles: When purchasing and using aluminum electrolytic capacitors, pay attention to the positive and negative pole markings on the capacitor to ensure correct connection and avoid reverse connection.

Adding a protection circuit: In some circuits that require protection against reverse voltage, a reverse voltage protection circuit can be added, such as using diodes.

Using bipolar capacitors: Bipolar capacitors can be used in both forward and reverse directions, and their internal structure is different from aluminum electrolytic capacitors, making them suitable for situations that require frequent reverse voltage.

By using the above methods, it is possible to effectively avoid the explosion problem caused by reverse connection of aluminum electrolytic capacitors and ensure the safe operation of the circuit.