Capacitor Charge Time Calculator
Calculate RC circuit charge and discharge times for capacitors with resistor values and target voltages.
Capacitor charging in an RC (resistor-capacitor) circuit follows an exponential curve. The time constant determines how quickly the capacitor charges or discharges.
The time constant:
tau = R x C
Where R is resistance in ohms and C is capacitance in farads.
Charging voltage formula:
V(t) = Vs x (1 - e^(-t/RC))
Where Vs is the supply voltage and t is time in seconds.
Discharging voltage formula:
V(t) = V0 x e^(-t/RC)
Where V0 is the initial voltage.
Key time milestones:
| Time Constants | Charge Level | Discharge Level |
|---|---|---|
| 1 tau | 63.2% | 36.8% |
| 2 tau | 86.5% | 13.5% |
| 3 tau | 95.0% | 5.0% |
| 4 tau | 98.2% | 1.8% |
| 5 tau | 99.3% | 0.7% |
A capacitor is considered fully charged after 5 time constants (5 tau).
Solving for time to reach a target voltage:
t = -RC x ln(1 - Vtarget/Vs) for charging
t = -RC x ln(Vtarget/V0) for discharging
Practical applications:
- Timer circuits (555 timer uses RC charging)
- Power supply filtering
- Debouncing switches
- Signal coupling and decoupling
- LED fade effects