Aluminum Electrolytic Capacitors

®ALUMINUM ELECTROLYTICCAPACITORS2-2 Estimation of life considering the ripple current.The ripple current affects the life of a capacitorbecause the internal loss (ESR) generates heat. Thegenerated heat will be :P I 2 R………………(2)Where l : Ripple current (Arms)R : ESR ()With increase in the temperature of the capacitor:I 2 •Δ T R………………(3)A • HWhere Δ T : Temperature increase in the capacitorcore(deg.)I : Ripple current (Arms)R : ESR ()A :Surface area of the capacitor (cm 2 )H : Radiation coefficient (Approx. 1.5 2.0 10 -3 W/cm 2 )The above equation (3) shows that the temperature ofa capacitor increases in proportion to the square ofthe applied ripple current and ESR, and in inverseproportion to the surface area. Therefore, the amountof the ripple current determines the heat generation,which affects the life. The value of Δ T varies dependingon the capacitor types and operating conditions.The usage is generally desirable if Δ T remainsless than 5. The measuring point for temperatureincrease due to ripple current is shown below ;Measuring pointTECHNICAL NOTET0TΔT0ΔTL Lr 2 10 K 10 ………(5)Where Lr : Life at the upper category temperaturewith the rated ripple current (h)ΔT0 : Temperature increase at capacitor core,at the upper category temperature (deg.)(3) The life equation considering the ambient temperatureand the ripple current will be a conversion ofthe above equation (5), as below :T0TI ΔT0 1 L Lr 2 10 K I 0 10 ……(6)Where l 0 : Rated ripple current at the upper categorytemperature (Arms)I : Applied ripple current (Arms)Since it is actually difficult to measure the temperatureincrease at the capacitor core, the following table isprovided for conversion from the surface temperatureincrease to the core temperature increase.2 The life expectancy formula shall in principle beapplied to the temperature range between the ambienttemperature of 40 and upper categorytemperature. The expected life time shall be aboutfifteen years at maximum as a guide in terms ofdeterioration of the sealant.(Table aFig. 2-1 Life Expectancy Chart)Test results:(1) The life equation considering the ambient temperatureand the ripple current will be :T0T ΔTL Ld 2 K 10………………(4)Where Ld : Life at DC operation (h) K : Ripple acceleration factor(K2, within allowable ripple current)T0 : Upper category temperature ()T : Operating temperature ()Δ T : Temperature increase at capacitor core(deg.) 10Ambient temperature of capacitor ()1301251201151101051009590858075706560558 9314210115126712345678910111285˚C: 1000hour guaranteed85˚C: 2000hour guaranteed105˚C: 1000hour guaranteed105˚C: 2000hour guaranteed105˚C: 3000hour guaranteed105˚C: 5000hour guaranteed105˚C: 20000hour guaranteed125˚C: 1000hour guaranteed125˚C: 1250hour guaranteed125˚C: 2000hour guaranteed125˚C: 3000hour guaranteed125˚C: 5000hour guaranteed(2) The life equation based on the life with the ratedripple current applied under the maximum guaranteedtemperature will be a conversion of the above equation(4), as below :h (10 3 h)504525 10 20 50 100 131 175Year 1 3 5 10 15CAT.No.2010/2011Ea