Capacitor Energy Calculator
Calculate the energy stored in a capacitor and the stored charge.
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Capacitors store energy in their electric field. The energy depends on both capacitance and voltage squared, so doubling the voltage quadruples the stored energy. This calculator is essential for power supply design, flash photography circuits, energy harvesting and understanding how supercapacitors can replace batteries in certain applications.
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Frequently asked questions
E = 0.5 × 0.001 × 25 = 0.0125 joules or 12.5 millijoules. That is enough to briefly flash a small LED but not much else.
Q = CV. A 1000 µF capacitor at 5V holds 0.005 coulombs (5 mC). That is 5 milliampere-seconds of charge - enough to power a 5 mA circuit for 1 second.
Supercapacitors (1-3000 F) can replace batteries for short-duration tasks. A 100F supercapacitor at 2.7V stores 364.5 joules, equivalent to a small AAA battery for about 10 seconds of moderate load.
Energy is proportional to V² but only linear with C. Doubling voltage quadruples energy, while doubling capacitance only doubles it. A 100 µF cap at 100V stores more energy than a 10,000 µF cap at 10V.
Very dangerous at high voltages. A 450V 1000 µF capacitor stores 101.25 J - potentially lethal. Always discharge capacitors before working on electronics. Even a 100 µF cap at 400V stores 8 J, enough to cause burns.