Capacitor EnergyStorage Calculator
Calculate energy (Joules), charge (Coulombs), and theoretical discharge time. Essential for pulse power, flash circuits, and backup power design.
Calculation Parameters
Enter values to calculate energy
For theoretical discharge time calculation
Enter capacitance and voltage to calculate
Governing Equations
E = ½CV²Q = CVt = E / Pτ = RCEngineering Insights
Energy scales exponentially with voltage (E ∝ V²). For high-density energy storage, increasing operating voltage is often more efficient than increasing capacitance.
Hold-Up Time Design
For power supply applications, useful energy is the difference between initial and minimum operating voltage:
E = 0.5 × C × (V²start - V²min)Safety Considerations
- •Capacitors above 50V can deliver lethal currents. Always install bleed resistors for discharge.
- •Electrolytic capacitors exhibit dielectric absorption—they can recover voltage after being shorted.
- •Always verify capacitor polarity before connecting power to electrolytic types.
Related Resources
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Worked Energy & Charge Examples
Stored energy and charge for common capacitor ratings, calculated from E = ½CV² and Q = CV.
| Capacitance | Voltage | Energy | Charge |
|---|---|---|---|
| 100 µF | 12 V | 0.0072 J | 0.0012 C |
| 470 µF | 25 V | 0.147 J | 0.01175 C |
| 1,000 µF | 50 V | 1.25 J | 0.05 C |
| 2,200 µF | 63 V | 4.37 J | 0.139 C |
| 4,700 µF | 100 V | 23.5 J | 0.47 C |
| 10,000 µF | 100 V | 50.0 J | 1.00 C |
Anything at or above roughly 1 joule can deliver a harmful shock. Discharge through a rated bleeder resistor, never by shorting the terminals.
Frequently Asked Questions
How do you calculate the energy stored in a capacitor?
Use E = 1/2 C V squared, with capacitance in farads and voltage in volts, which gives energy in joules. A 1,000 µF capacitor charged to 50 V holds 0.5 x 0.001 x 2,500 = 1.25 J. Because voltage is squared, doubling the voltage stores four times the energy while doubling the capacitance only doubles it.
How long does a capacitor take to discharge?
Discharge follows the time constant tau = R x C, in seconds. After one time constant the capacitor retains about 37 percent of its voltage, and after five time constants it is below 1 percent, which is normally treated as fully discharged. A 100 µF capacitor bleeding through a 10 kΩ resistor has a time constant of 1 second, so it is effectively discharged in about 5 seconds.
How much charge does a capacitor hold?
Charge is Q = C x V, measured in coulombs. A 470 µF capacitor at 25 V holds 0.00047 x 25 = 0.01175 C, or 11.75 millicoulombs. Charge scales linearly with voltage, unlike stored energy, which scales with the square of it.
How much stored energy is dangerous?
Stored energy above roughly 1 joule is widely treated as capable of delivering a harmful shock, and energies in the tens of joules can be lethal. Large electrolytic and film capacitors hold their charge long after power is removed. Always discharge through a suitably rated bleeder resistor rather than shorting the terminals with a screwdriver, which damages the capacitor and can produce an arc flash.