So, what exactly is the service life of an electrolytic capacitor? What happens when this lifespan is exceeded? Some might think that exceeding the lifespan means the capacitor will open circuit, short circuit, or even explode. That's overthinking it. During normal operation, the capacitance value, dissipation factor, and leakage current of an electrolytic capacitor change over time. The service life is defined as the duration the capacitor has been operating under specified conditions while these parameters (capacitance, dissipation factor, leakage current) remain within certain allowable deviations from their initial rated values .

For example, consider an electrolytic capacitor with five lifespan ratings. Taking the 2000-hour type as an example, it means that under rated voltage and at 125°C, the capacitance change does not exceed ±30% from its rated value, the dissipation factor change does not exceed 300% of its rated value, and the leakage current does not exceed its initial value. If the capacitor continues to meet these criteria after 2000 hours of continuous operation, its lifespan is considered to be 2000 hours. This fulfillment is based on batch compliance, meaning all capacitors of the 2000-hour type should meet these conditions .

Calculation of Electrolytic Capacitor Service Life

1. Theoretical Basis: The theoretical foundation for calculating electrolytic capacitor life is the Arrhenius equation. This equation shows that factors affecting lifespan include the capacitor's own materials and temperature .

2. General Life Estimation Formula: Based on the Arrhenius equation, the lifespan estimation formula is derived as: L = Lr × KT × KR × KV .

   L = Lr × 2^[(T0 - T)/10] × K^[ (I/I0)² × (ΔT0/10) ](Note: Formula representation based on text description)

• T0: Capacitor's rated maximum operating temperature (found in the datasheet).

• T: Capacitor's actual operating temperature (can be assessed based on the product's maximum ambient temperature).

• K: Ripple acceleration coefficient, usually taken as 2.

• I: Actual ripple current (for switch-mode power supplies, there are corresponding calculation formulas).

• I0: Rated ripple current (found in the datasheet).

• ΔT0: Allowable temperature rise of the capacitor core caused by the rated ripple current (found in the datasheet) .

• Lr: The basic time guaranteed by the capacitor supplier.

• KT: Temperature influence factor.

• KR: Ripple current influence factor.

• KV: Operating voltage influence factor (This value varies by manufacturer and should be confirmed with them; often temporarily disregarded for simplification).

  This leads to the following formula:

3. Simplified Formula: If the electrolytic capacitor is not used in circuits like switch-mode power supplies that cause significant ripple current, a simplified formula can be used :

   L = Lr × 2^[(T0 - T)/10]

Example Analysis

For instance, consider an electrolytic capacitor with a rated lifespan of 2000 hours at its maximum temperature of 105°C. Using the calculation formula, if the capacitor's actual maximum operating temperature is 60°C, its operational lifespan can be calculated as:

2000 × 2^[(105 - 60)/10] ≈ 2000 × 2^(4.5) ≈ 2000 × 22.627 ≈ 45254 hours ≈ 1885 days ≈ 5 years .

However, in practical product design, capacitor selection is often based on the product's required service life. For example, if the product's design life is 3 years (26280 hours), we can use the formula to calculate the maximum allowable temperature rise for the capacitor:

10 × log₂(26280 / 2000) ≈ 10 × log₂(13.14) ≈ 10 × 3.73 ≈ 37.3°C.

If the capacitor's maximum rated temperature is 105°C, then the capacitor's actual operating temperature must not exceed 105°C - 37.3°C = 67.7°C .