Capacitor ESR & Lifetime Calculator

Estimate ripple current heating and lifetime from ESR, and see how far a capacitor's real spec sits from its label.

Example: 1 A of ripple through 100 mΩ dissipates 100 mW, raising the core to 48 °C — about 29.7 years of life.

Inputs

ESR(Ω)

At the ripple frequency, not at 100 Hz — ESR falls with frequency.

Ripple current (RMS)(A)

Ambient temperature(°C)

Inside the enclosure, not room temperature.

Rated temperature(°C)

Rated life(h)

Thermal resistance(°C/W)

Case to ambient. Smaller cans are worse — 50+ °C/W for a small radial part.

Rated ripple current (optional)(A)

Result

Estimated life

29.7 years

Power dissipated: 100 mW
Self-heating: 3 °C
Core temperature: 48 °C
Life multiplier: 51.98×
In hours: 259921
Of rated ripple: 67%

Running 57 °C below the rating multiplies life by 52× — Arrhenius doubles it for every 10 °C. That is the single biggest lever you have.
ESR is not one number. It falls with frequency and with temperature, so the 100 Hz figure on a datasheet front page can be several times the value at a switching converter's ripple frequency. Use the curve at your actual frequency.
This is why electrolytics are the usual first failure in old equipment: they are consumables with a temperature-dependent shelf life, unlike the ceramics and semiconductors around them.

Life against core temperature

Core temp	Multiplier	Life
25 °C	256×	146 years
45 °C	64×	36.5 years
65 °C	16×	9.1 years
85 °C	4×	2.3 years
105 °C	1×	5000 h

Formula

P = I_ripple² × ESR    life = rated × 2^((T_rated − T_core)/10)

Worked example

1 A of ripple through 100 mΩ dissipates 100 mW, raising the core to 48 °C — about 29.7 years of life.

P = I_ripple² × ESR
(1 A)² × 100 mΩ
100 mW
ΔT = P × θ_CA
100 mW × 30 °C/W
3 °C
The heat is generated inside the can, so the core runs hotter than the case.
life = rated × 2^((T_rated − T_core)/10)
5000 × 2^((105 − 48)/10)
259921 hours

Frequently asked questions

Why do electrolytic capacitors wear out?

The electrolyte gradually dries out, and heat accelerates it. Life roughly halves for every 10 °C, which is why a 5000-hour part at 105 °C can last decades at 45 °C — and why capacitors near a hot regulator fail first.

What is ripple current rating and why does it matter?

The RMS current the capacitor can pass continuously without exceeding its internal temperature limit. It is a separate constraint from voltage and capacitance — a part comfortably within both still fails early if its ripple rating is exceeded, because the heating comes from inside.

How do I reduce ESR heating?

Use a lower-ESR part, or split the ripple across several capacitors in parallel. Paralleling helps twice over: each capacitor carries a fraction of the current, and since heating goes as the square, the dissipation per part falls faster than the current does.

Which ESR figure should I use?

The one at your ripple frequency and operating temperature, from the datasheet's curves. ESR falls substantially with both, so the headline 100 Hz figure at 20 °C can be several times the value that actually applies in a switching converter.

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