What Is Capacitor Energy?
A capacitor stores energy in the electric field between its plates. When a voltage is applied across a capacitor, charge accumulates on the plates, and the energy stored is proportional to both the capacitance and the square of the voltage. This stored energy can be released when the capacitor is discharged through a circuit.
Capacitors are fundamental components in electronics, used for energy storage, filtering, coupling, and timing applications. Understanding the energy stored in a capacitor is essential for designing safe and efficient circuits, particularly in high-voltage applications where the stored energy can be dangerous.
Energy Formula
Where E is energy in joules, C is capacitance in farads, and V is voltage in volts. The energy can also be expressed as E = Q²/(2C) or E = QV/2, where Q is the charge stored on the capacitor.
Common Capacitor Values
| Capacitance | Voltage | Energy Stored | Typical Use |
|---|---|---|---|
| 100 pF | 5 V | 1.25 nJ | RF filtering |
| 100 nF | 12 V | 7.2 μJ | Decoupling |
| 100 μF | 50 V | 0.125 J | Power supply filtering |
| 1 F | 5.5 V | 15.1 J | Supercapacitor backup |
| 3000 F | 2.7 V | 10.9 kJ | Ultracapacitor bank |
Applications
- Camera flash units use capacitors to store energy and release it as a brief, intense burst of light.
- Power supply smoothing capacitors store energy to fill in gaps between AC rectification cycles.
- Defibrillators store energy in capacitors and discharge it through the patient's heart to restore normal rhythm.
- Electromagnetic launchers (railguns, coilguns) use capacitor banks to deliver massive energy pulses.
Frequently Asked Questions
How much energy does a 1000 μF capacitor store at 50V?
Using E = 0.5 x C x V² = 0.5 x 0.001 x 2500 = 1.25 joules. This is enough energy to produce a noticeable shock, so capacitors at this voltage should be handled with care and discharged before servicing.
Can capacitors replace batteries?
Supercapacitors can replace batteries in some applications, but they generally store far less energy per unit mass. A lithium battery stores about 150 Wh/kg compared to about 5-10 Wh/kg for the best supercapacitors. However, capacitors can charge and discharge much faster and last millions of cycles.
Why does energy scale with voltage squared?
As voltage increases, both the charge stored and the voltage across which that charge was moved increase linearly. Since energy equals force times distance (or voltage times charge), and both scale with V, the total energy scales as V squared. This is analogous to kinetic energy scaling as velocity squared.