Life Time Estimation Formula on KY/KZE series Capacitors
Lx = Lo x 2(To – Tx)/10 x 2(∆To – ∆Tx)/5 = Lo x 2(105 – Tx)/10 x 2(5 – ∆Tx)/5
Where:
Lifetime (hours) of the capacitor to be estimated
Base lifetime (hours) of the capacitor shown in the catalog Maximum rated operating temperature ; 105ºC for KY/KZE Actual ambient temperature (ºC) of the capacitor within device (This is not the environment temperature of the device, but the
environment temperature of the capacitor that has been placed within the device.)
∆To = Rise (ºC) in core temperature of the capacitor due to rated (permissible)
maximum ripple current. Lx Lo To Tx
= = = =
The ∆To values designed for KY / KZE are 5 ºC maximum at 105 ºC.
∆Tx =
Actual rise (ºC) in the core temperature of the capacitor due to actual
ripple current at device operating conditions.
To calculate the ∆Tx from the surface temperature of the capacitors, refer to the table below.
∆Tx = (Ts - Tx) x Kc
Where: Ts = Surface temperature (ºC) of the aluminum case Tx = Actual ambient temperature (ºC) of the capacitor Kc = Coefficient standing for the ratio of the ∆Tx to the (Ts - Tx) For the Kc’s, refer to the table below:
Kc : Capacitor diameter φ5- φ8 φ10 φ12.5 φ16 φ18 (mm)
Kc 1.10 1.15 1.20 1.25 1.30
Also, to simply estimate the ∆Tx from the actual rms ripple current, use the following equation:
∆Tx = 5 x [ (actual rms ripple) / (rated rms ripple) ]^2
The actual and rated maximum rms ripple current shall be equaled in frequency by using frequency multipliers prescribed for each product series in the catalog.
July 2001
by Koh Ohno --- Engineering of Taiwan Chemi-Con
NIPPON CHEMI-CON CORPORATION
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