Capacitors store electrical energy in the electric field between two conductive plates. They are essential in switch-mode power supplies, camera flash units, motor starters and signal filters. The two most important questions: how much charge does the capacitor store? And how much energy is held within it? Our calculator answers both.
Step by Step: How to Use the Capacitor Calculator
- Enter the capacitance: For example 100 µF = 0.0001 F or 10 nF = 0.00000001 F.
- Enter the voltage: Operating voltage, for example 12 V or 400 V.
- Calculate charge: Q = C × U = 0.0001 × 12 = 0.0012 C = 1.2 mC.
- Calculate energy: E = ½ × C × U² = ½ × 0.0001 × 144 = 0.0072 J = 7.2 mJ.
- Discharge time constant (optional): τ = R × C. At R=1kΩ, C=100µF: τ = 0.1 s (after 5τ = 0.5 s the capacitor is more than 99% discharged).
Practical Examples
Camera flash capacitor, 330µF, 330V: Energy = ½ × 0.00033 × 108,900 = 17.97 J. A substantial amount of energy for a brief flash of light!
Power supply buffer capacitor, 2200µF, 24V: Q = 0.0022 × 24 = 52.8 mC. Energy = ½ × 0.0022 × 576 = 0.634 J. Enough to smooth out brief load spikes.
Motor start capacitor, 25µF, 230V: Q = 0.000025 × 230 = 5.75 mC. The phase-shifted current reliably starts single-phase motors.
Capacitor Formulas
- Charge: Q = C × U (coulombs)
- Energy: E = ½ × C × U² (joules)
- Discharge time constant: τ = R × C (seconds)
- Series connection: 1/C_total = 1/C1 + 1/C2
- Parallel connection: C_total = C1 + C2
Frequently Asked Questions (FAQ)
How do I choose the right capacitor?
Key parameters: capacitance value (F), voltage rating (always choose at least 20% above the operating voltage), package type (electrolytic, film, ceramic), temperature range, lifespan (ESR). Electrolytic capacitors: high capacitance, polarity-sensitive.
What is ESR and why does it matter?
ESR = Equivalent Series Resistance. Low ESR means less power loss and better high-frequency performance. Critical in switch-mode power supplies – poor ESR values lead to heating and premature failure of the capacitor.
Can capacitors be dangerous?
Yes, especially large electrolytic capacitors in power supplies (450V, several mF). The stored energy is sufficient to deliver a serious electric shock. Always plan for a discharge resistor and confirm the capacitor is discharged before working on the circuit.
