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Supercapacitors Service Life

Supercapacitors have a finite lifetime. This is affected by the circumstances under which they are used, including environmental conditions such as temperature, humidity, and vibration, and electrical conditions such as applied voltage, charging, and discharging. The guaranteed service life for supercapacitors is specified in the catalog as high temperature load characteristics.

●Ambient temperature and service life
As shown in Fig. 1, the service life of supercapacitors is greatly affected by the ambient temperature at which they are used. A lower temperature during actual use can be expected to result in a longer service life.
耐久性試験-dCap(温度パラメータ)耐久性試験-DCIR(温度パラメータ)
[Fig.1] Durability test (temperature parameter)


●Applied voltage and service life
As shown in Fig. 2, the service life of supercapacitors is greatly affected by the applied voltage at which they are used. A lower applied voltage during actual use can be expected to result in a longer service life.
耐久性試験-dCap(電圧パラメーター)耐久性試験-DCIR(電圧パラメータ)
[Fig.2] Durability test (voltage parameter)


●Self-heating due to charging and discharging
Because supercapacitors have internal resistance, the internal heat generated by charging and discharging affects their lifespans. Applications which entail continuous charging or discharging at large currents are particularly likely to accelerate degradation due to the accompanying increase in temperature. This rise in temperature due to heating should be taken into consideration as heat generation varies greatly according to charge/discharge pattern. Also, consideration should be given to voltage drop as it generates heat at the beginning or end of discharge when larger currents are used.

●Estimating service life
Two factors that contribute greatly to shortening the service life of supercapacitors are temperature and continuously applied voltage. As Fig. 3 shows, there is a linear relationship between change in electrical properties and the square root of test time. This can be expressed with the following formula.
   
ΔCap: Rate of change on electrostatic capacitance
k: Life acceleration factor
t: Test time [hours]

The variable k changes depending on temperature and voltage combination. Service life can be estimated by calculating k from actual usage conditions. Both k and α differ depending on temperature and voltage. Contact us for details.

 
耐久性試験の√tプロット例
[Fig. 3] Example of √t plotted on durability test

 
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