Ripple current heats a capacitor from the inside, and every 10 °C of core temperature halves its life. Enter the ripple, ESR and ambient, and see how long the part actually lasts — and how much you buy by moving it somewhere cooler.
| Ambient | Core temp | Life | Years at your duty | vs target |
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Almost everything on a board is modelled with a constant failure rate: it fails randomly, and the rate does not change with age. Aluminium electrolytic capacitors are different. They wear out — the electrolyte escapes through the seal, capacitance falls, ESR rises, and the part eventually stops doing its job. Manufacturers publish a life in hours at a rated temperature because there genuinely is one.
ΔT = Iripple² · ESR · Rth
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Life = L0 · 2(Trated − Tcore)/10The exponent is the whole story: every 10 °C cooler doubles the life. A 2000-hour part at 105 °C gives about 2.6 years at a 70 °C core and about 14 years at 45 °C. The same component, the same circuit, a different position on the board.
The temperature that matters is the core, not the air around it, and ripple current heats the core from the inside. A capacitor carrying real ripple can run appreciably hotter than its surroundings, and that rise goes straight into the exponent.
It also worsens with age, which is the part that catches people: as the part dries out, ESR rises, so the same ripple current produces more heat, which accelerates the drying. It is a slow positive feedback, and it is why capacitors near end of life tend to fail suddenly rather than gracefully.
Run the board FIT calculator with a typical bill of materials and electrolytics come out as the single largest contributor to the failure rate. This tool is the mechanism behind that number. It is also why the thermal and IR drop tools matter beyond their own subject: a hot board is a short-lived board, and the coupling is exponential rather than linear.
If long life matters, the options in order of effect are: move the part away from heat sources, choose a higher rated temperature or a longer rated life, reduce the ripple it sees (more parallel capacitors, or a better filter upstream), or move to a polymer or hybrid part — which halves life per 20 °C rather than per 10, and is far less temperature-sensitive as a result.
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