Why Do Electrolytic Capacitors Deteriorate When Not Used for Long Periods?

While some capacitors in standby power supplies may go bad if the equipment stays plugged in and unused, it is the environmental and operational conditions that contribute to the deterioration of electrolytic capacitors over time. If a device with an electrolytic capacitor is hardly ever used, unplugging it can help prevent wear and tear on the capacitors. This article explores the factors that cause electrolytic capacitors to deteriorate and how proper maintenance can mitigate these issues.

Key Factors Affecting Electrolytic Capacitors

Electrolytic capacitors are widely used in electronic circuits due to their high capacitance values. However, when left unused for extended periods, these capacitors can deteriorate. Several factors come into play, primarily the drying of the electrolyte, degradation of the oxide layer, corrosion, and temperature effects. Let's delve into each of these factors in detail.

Electrolyte Drying

Electrolytic capacitors contain a liquid electrolyte, which can gradually evaporate or dry out, especially under high-temperature conditions or during long-term inactivity. Once the electrolyte dries out, the capacitor's ability to store charge diminishes, leading to reduced capacitance and increased equivalent series resistance (ESR). This can significantly impact the overall performance of the electronic circuit.

Oxide Layer Degradation

The anode of an electrolytic capacitor is coated with a thin layer of aluminum oxide, which acts as the dielectric. Proper biasing during use is essential to maintain the integrity of this oxide layer. Over time, if the capacitor is not used correctly, the oxide layer may degrade. This results in increased leakage current and reduced voltage rating, further compromising the capacitor's performance.

Corrosion

The materials used in electrolytic capacitors can corrode over time, particularly in the presence of moisture or contaminants. This corrosion can affect internal connections and overall performance, leading to a deterioration in capacitor reliability and lifespan.

Temperature Effects

High temperatures can accelerate the deterioration of the electrolyte and the oxide layer. Even at room temperature, the aging process can lead to chemical changes that reduce the capacitors' effectiveness. These temperature-related changes can significantly impact the performance and longevity of the capacitor.

Voltage Stress

If an electrolytic capacitor is left charged for an extended period, it can experience voltage stress. This can further degrade the dielectric layer, leading to failure modes such as short circuits. Ensuring that capacitors are neither overcharged nor left uncharged for long periods is crucial.

Mechanical Stress

Physical factors such as vibrations or shocks can also affect the internal structure of electrolytic capacitors, leading to failures over time. This mechanical stress can cause structural changes within the capacitor, leading to potential breaches in the dielectric layer.

Mitigating the Effects of Deterioration

To prevent the deterioration of electrolytic capacitors, it is recommended to periodically apply a voltage within the rated limits to the capacitors. This helps maintain the integrity of the oxide layer and ensures that the electrolyte remains functional. Additionally, regular inspection and maintenance can prevent issues from arising, ensuring the optimal performance of the capacitors.

Conclusion

In summary, electrolytic capacitors can deteriorate over time due to several factors, including electrolyte drying, oxide layer degradation, corrosion, temperature effects, voltage stress, and mechanical stress. Proper maintenance and regular inspection can help mitigate these issues, ensuring the longevity and reliability of these critical components. It is always a good practice to unplug devices that are hardly ever used, as this can greatly reduce the wear and tear on their capacitors.