LIFE OF ALUMINUM ELECTROLYTIC CAPACITORS
The life of aluminum electrolytic capacitors is mainly dependent on environmental conditions (e.g.
ambient temperature, humidity etc.) and electrical factors (e.g. operating temperature, ripple current
etc.) Generally, the wear-out mechanism of aluminum electrolytic capacitors is based on evaporation
of electrolyte through the rubber seal. Consequently, the factor of temperature (ambient temperature
and internal heating due to ripple current) is the most critical to electrolytic capacitors life. The effect of
voltage on capacitor life is negligible, especially for low voltage electrolytic capacitors. The lifetime of
aluminum electrolytic capacitors can be expressed as following equations:
L
e
= L
o
Where:
K
t
K
r
-------- (1)
L
e
= Expected life at operating temperature T
e
(h)
L
o
= Specified life at temperature operating temperature T
o
(h)
K
t
= Ambient temperature acceleration term
K
r
= Ripple current acceleration term
K
t
= L
o
A
Where:
(T
o
-T
e
)/10
-------- (2)
T
o
= Maximum rated operating temperature ( C)
T
e
= Actual ambient temperature ( C)
A = Acceleration coefficient (for the range from 35 C to the maximum operating temperature,
A 2)
K
r
= 2
(- T/5)
Where:
-------- (3)
T = An increase in core temperature by internal heating due to ripple current
( T = core temperature – ambient temperature)
T can be estimated as follows:
S) -------- (4)
T = (I
2
R)/(
Where:
I = Ripple current of the capacitor (A rms)
R = Equivalent series resistance of the capacitor ( )
= Heat radiation coefficient of the aluminum can (W/ C
S = Surface area of the capacitor (cm
2
)
cm
2
)
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