# How do I compute the lifetime of an electrolytic capacitor?

I am considering using a KZE series (by United Chemi-Con) electrolytic capacitor, which has a specified lifespan of 5,000 hours at 105°C with rated ripple current. Now, for an example assume I am using it at room temperature (25°C) with half the rated ripple current and half the applied working voltage. How long would the capacitor last? In future, how would I calculate it?

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Your wall thermometer may say 25'C, but I guarantee that, in operation, your capacitor is warmer. – davidcary Apr 8 '11 at 21:07
@davidcary, you're right. So, let's assume a 470µF 25V cap which according to the KZE datasheet has an ESR of 0.041 ohms (@25°C) and a ripple current maximum of 1,250mA. We can calculate at, let's say 600mA ripple current, the cap will dissipate 14mW (I^2 * R.) So, where does the cap heat up from, as this is tiny? Am I missing something? – Thomas O Apr 8 '11 at 22:34
For some strange reason, people try to hide most capacitors in opaque boxes full of other heat-generating stuff -- fast CPUs, or quickly-discharging batteries, or transistors switching heavy currents, or etc. The temperature of the cap (and everything else in that box) is at least the product of the total heat energy generated by everything inside that box, multiplied by the thermal resistance of that box. I don't know anyone who can look at a schematic and accurately guess the actual interior temperature. In my experience, it's always at least 10'C hotter than anyone expected. – davidcary Apr 17 '11 at 0:29