Capacitor

Electrolytic Capacitor ESR Turns Ripple Current Into Heat

An aluminum electrolytic capacitor does not behave like an ideal capacitor. Its internal foil, electrolyte, tabs, and contacts add resistance, represented in a simple model as equivalent series resistance, or ESR. When AC ripple current flows through that resistance, the capacitor dissipates real power as heat. For power-supply filtering, this mechanism can matter as much as capacitance and voltage rating. A capacitor may have the expected number of microfarads and still run too hot if its ESR is too high for the ripple current imposed by the circuit.