Capacitor Ripple Current Calculator
A real capacitor has a small internal resistance, the equivalent series resistance or ESR, and the ripple current flowing through it turns into heat. That self-heating is the main cause of electrolytic capacitor wear-out, so every capacitor carries a ripple current rating. This calculator finds the power dissipated in the ESR, the ripple voltage it produces, and the resulting temperature rise when you supply the capacitor's thermal resistance from its datasheet. Use it to check a smoothing or output capacitor will stay within its ripple and temperature limits.
ESR ripple formula
Power P = I_ripple^2 * ESR (watts)
Ripple voltage V = I_ripple * ESR (volts)
Temperature rise dT = P * thermal resistance (C)
I_ripple is the RMS ripple current
Self-heating is power times thermal resistance. Supply ESR and thermal resistance from the capacitor datasheet at your operating frequency and temperature.
Capacitor ripple context
- Ripple current through the ESR produces heat that ages electrolytic capacitors.
- Power loss grows with the square of the ripple current, so it rises fast.
- Low-ESR parts cut both heating and output ripple voltage.
- ESR varies with frequency and temperature; use the datasheet value for your conditions.
- Keep the temperature rise within the part's ripple current rating for rated life.
Capacitor ripple: frequently asked questions
How is power dissipated in a capacitor's ESR?
Equivalent series resistance (ESR) turns ripple current into heat. The power lost is the ripple current (RMS) squared times the ESR: P = I_ripple squared times ESR. For example, 2 A RMS of ripple through 50 milliohms dissipates 0.2 watts inside the capacitor.
What is the ripple voltage across the ESR?
The ESR also creates a ripple voltage equal to the ripple current times the ESR: V = I_ripple times ESR. This adds to the capacitive ripple and is often the dominant ripple term in switching supplies, so a low-ESR capacitor gives cleaner output.
Why does ripple current heat a capacitor?
Real capacitors are not perfect: they have a small internal resistance, the ESR. When AC ripple current flows through that resistance it dissipates power as heat, raising the internal temperature. Excess self-heating shortens electrolytic capacitor life, so manufacturers publish a ripple current rating.
How much does self-heating raise the temperature?
The temperature rise is the dissipated power times the capacitor's thermal resistance to ambient in degrees Celsius per watt, a figure from the datasheet. This calculator estimates the rise when you supply that thermal resistance, since it varies by case size and mounting.
Does ESR change with frequency and temperature?
Yes. ESR generally falls as frequency rises up to a point, and electrolytic ESR rises sharply at low temperature. Datasheets specify ESR at a stated frequency and temperature, usually 100 kHz and 20 C for switching applications. Use the value matching your operating conditions.
Official sources
- NIST: SI electrical units and constants.
- IEEE Standards Association: passive component and capacitor standards.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.