Capacitor Discharge Time Calculator
Calculate how long it takes for a capacitor to discharge through a resistor
Capacitor Discharge Time Calculator
Compliant with IEEE 1584 Standards
Results:
Time Constant (τ): 0.00 seconds
Discharge Time: 0.00 seconds
Discharge Time (ms): 0.00 milliseconds
Discharge Time (μs): 0.00 microseconds
How to Use the Capacitor Discharge Time Calculator
Step 1: Enter Capacitor Value
- Input the capacitance value
- Select the appropriate unit (μF, nF, pF, or F)
- Common values range from 1 μF to 10,000 μF
Step 2: Enter Resistance Value
- Input the discharge resistance value
- Select the appropriate unit (Ω, kΩ, or MΩ)
- This is the resistance through which the capacitor discharges
Step 3: Enter Voltage Values
- Enter the initial voltage of the charged capacitor
- Enter the final voltage threshold (often near zero)
- Click "Calculate" to get the discharge time
Capacitor Discharge Fundamentals
Time Constant
The time constant (τ) is a fundamental parameter in capacitor discharge:
- Defined as τ = R × C (resistance × capacitance)
- After one time constant, voltage drops to 36.8% of initial value
- After five time constants, capacitor is considered fully discharged (≈0.7% of initial voltage)
Discharge Curve
- Capacitor discharge follows an exponential decay
- Voltage decreases more rapidly at the beginning
- The rate of discharge slows as the voltage decreases
Key Formulas:
Time Constant: τ = R × C
Voltage at time t: V(t) = V₀ × e^(-t/τ)
Discharge time: t = -τ × ln(V₁/V₀)
How to Calculate Capacitor Discharge Time
Step 1: Calculate time constant (τ):
τ = R × C
Step 2: Calculate discharge time:
t = -τ × ln(V₁/V₀)
Where:
R = resistance in ohms
C = capacitance in farads
V₀ = initial voltage
V₁ = final voltage
ln = natural logarithm
Example Calculation
For a 470 μF capacitor discharging through a 10 kΩ resistor:
Given:
- Capacitance (C) = 470 μF = 470 × 10⁻⁶ F
- Resistance (R) = 10 kΩ = 10,000 Ω
- Initial voltage (V₀) = 12 V
- Final voltage (V₁) = 1 V
Step 1: Calculate time constant (τ)
τ = R × C = 10,000 Ω × 470 × 10⁻⁶ F = 4.7 seconds
Step 2: Calculate discharge time
t = -τ × ln(V₁/V₀) = -4.7 × ln(1/12) = -4.7 × (-2.485) = 11.68 seconds
Therefore, it takes approximately 11.68 seconds for the capacitor to discharge from 12V to 1V.
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