Capacitor Charge Time Calculator
Calculate capacitor charge and discharge times from resistance, capacitance, and supply voltage.
Returns time constants, 5-tau charge time, and curve.
How Capacitor Charge Is Calculated
A capacitor stores electric charge on two conductive plates separated by an insulator (dielectric). The relationships between charge, voltage, and capacitance are fundamental to electronics.
Charge Formula:
Q = C × V
Where:
- Q = charge in Coulombs (C)
- C = capacitance in Farads (F)
- V = voltage across capacitor in Volts
Energy Stored in a Capacitor:
E = 0.5 × C × V²
RC Charging Time Constant:
τ = R × C
Voltage during charging: V(t) = V_source × (1 − e^(−t/τ))
After 5τ, capacitor is considered fully charged (99.3%). The time constant τ is the time to reach approximately 63.2% of the final voltage — a consequence of the exponential charging curve.
Worked Example: A 100 µF capacitor charged to 12V through a 10 kΩ resistor:
- Q = 100×10⁻⁶ × 12 = 1.2 × 10⁻³ C = 1.2 mC
- E = 0.5 × 100×10⁻⁶ × 12² = 0.5 × 100×10⁻⁶ × 144 = 7.2 × 10⁻³ J = 7.2 mJ
- τ = 10,000 × 100×10⁻⁶ = 1 second
- Fully charged after ~5 seconds
Common Capacitor Values:
- Decoupling: 100 nF (0.1 µF) ceramic
- Power supply filter: 470 µF–10,000 µF electrolytic
- Audio coupling: 1–100 µF
- Camera flash: 100–1000 µF at 300V (stores ~4.5–45 J)
Caution: Large capacitors can retain dangerous charge long after power is removed. Always discharge before handling.