Equivalent Series Resistance (ESR) refers to the internal loss resistance of a capacitor. If an AC voltage is applied, the capacitor is charged and discharged with the frequency of the AC voltage. The behaviour depends not only on the capacity of the capacitor, but is also largely determined by the losses at each charging and discharging. Such losses are caused by the ohmic characteristics of a capacitor, and are designated as equivalent series resistance.
Particularly interesting is the ESR measurement of electrolytic capacitors in warm or hot circuits. The problem is the evaporation of the electrolyte in the electrolytic capacitor. Temperature rises through the evaporation of the electrolyte, resulting an increase of resistance to the current.
The rule for electrolytic capacitors is that their life is halved by a 10°C increase in temperature.« Back