The Expected Lifetime of Electrolytic Capacitors
Aluminum electrolytic capacitor is the shortest life parts in power supplies. Other parts, like resin, have also their life, but they are 20 – 30 or over years. So the life on electric devices generally are not problems.
Aluminum electrolytic capacitor is the most important parts in terms of reliabilty, and expected lifetime of power supplies can be estimated by calculating the estimation of expected lifetime of aluminum electrolytic capacitor.
Expected lifetime of aluminum electrolytic capacitor is determined by amount of excess electorlyte, speed of electrolyte evaporating through sealed rubber and temperature that determines the evaporating speed.
The relationship between ambient temperature and capacitor life has been confirmed to follow ARRHENIUS’ equation:
Expected lifetime of Electrolytic Capacitor : L = Lo x 2 (T1-T2) / 10
Lo : Lifetime Under Maximum Rated Operating Temperature
T1 : Allowable Maximum Temperature
T2 : Capacitor Temperature on operation
Life expectancy is determined by a coefficient depending on temperature, based on Lo.
Influence to Power Supplies
Expected lifetime of aluminum electrolytic capacitor is defined by the reduction of capacitance less than the allowable value, tanδ increase or leakage current increase.
Aluminum electrolytic capacitor is used for input/output smoothing circuit, auxiliary power supplies circuit or phase compasation circuit, and the influence of the degradation of aluminum electrolytic capacitor is different.
Table 1 shows the influence of aluminum electrolytic capacitor lifetime by each circuit.
|No.||Used Place||Influence to Power Supplies|
|1||Input Smoothing Circuit||Higher Ripple Voltage|
|2||Output Smoothing Circuit||Higher Ripple Voltage|
|3||Auxiliary Power Supplies Circuit||Power Supplies Stopped|
|4||Phase Compasation Circuit||Unstable Output Voltage|