Capacitor Charge Time Calculator
Calculate the RC time constant (τ = R × C) and voltage at each step during charging and discharging.
Returns exponential formula and a charge curve chart.
Capacitor charge and energy calculations are fundamental in electronics design — from power supply filtering to timing circuits and energy storage applications.
The core formulas:
Charge stored:
Q = C × V
Energy stored:
E = ½ × C × V²
Charge/discharge time constant:
τ (tau) = R × C
Voltage at time t during charging:
V(t) = V_source × (1 − e^(−t/τ))
What each variable means:
- Q — charge in Coulombs (C)
- C — capacitance in Farads (F); most capacitors are microfarads (µF) or picofarads (pF)
- V — voltage across the capacitor in Volts
- E — stored energy in Joules
- τ (tau) — time constant; after one time constant, the capacitor is 63.2% charged; after 5τ, it is 99.3% charged (fully charged for practical purposes)
- R — series resistance in Ohms
Worked example: A 470 µF capacitor is charged to 16V through a 1,000 Ω resistor.
Q = 470 × 10⁻⁶ × 16 = 7.52 mC (milliCoulombs) E = ½ × 470 × 10⁻⁶ × 16² = ½ × 470 × 10⁻⁶ × 256 = 0.0602 J (60.2 mJ) τ = 1,000 × 470 × 10⁻⁶ = 0.47 seconds Time to fully charge (5τ) = 5 × 0.47 = 2.35 seconds
Common capacitor values and uses:
- 100 pF: RF filtering
- 0.1 µF: power supply decoupling
- 10–100 µF: audio coupling, power filtering
- 1,000–10,000 µF: power supply bulk storage
- Supercapacitors: 1–3,000 F for energy backup systems