Capacitor Discharge Resistor Calculator
Calculate safe discharge resistor values for capacitor circuits
Capacitor Discharge Resistor Calculator
Compliant with IEC 60384 Safety Standards
Results:
Discharge Resistor: 0.00 Ω
Time Constant (τ): 0.00 s
Power Rating: 0.00 W
Energy Dissipated: 0.00 J
Peak Current: 0.00 A
Calculation Details
How to Use the Capacitor Discharge Resistor Calculator
Step 1: Enter Capacitor Specifications
- Input the capacitance value in microfarads (µF)
- Enter the initial voltage across the capacitor
- Specify the desired discharge time in seconds
- Choose appropriate safety factor (2 recommended)
Step 2: Select Discharge Level
- Choose discharge level percentage
- 5% (3 time constants) is recommended for safety
- Lower percentages provide safer discharge
- Higher percentages discharge faster but less safe
Step 3: Calculate and Interpret
- Click "Calculate" to get resistor value
- Check power rating for resistor selection
- Verify energy dissipation requirements
- Use results for safe circuit design
Capacitor Discharge Theory
RC Time Constant
The time constant (τ) determines discharge rate:
- τ = R × C (seconds)
- After 1τ: 37% of initial voltage remains
- After 3τ: 5% of initial voltage remains
- After 5τ: 0.7% of initial voltage remains
Safety Considerations
- Always use appropriate safety factors
- Consider resistor power rating
- Ensure proper heat dissipation
- Follow electrical safety standards
Key Formulas:
Discharge Resistor: R = t / (C × ln(V₀/Vf))
Time Constant: τ = R × C
Power Rating: P = V₀² / (4 × R)
How to Calculate Capacitor Discharge Resistor
Basic Formula:
R = t / (C × ln(V₀/Vf))
Where:
R = Discharge resistor (Ω)
t = Discharge time (s)
C = Capacitance (F)
V₀ = Initial voltage (V)
Vf = Final voltage (V)
Step-by-Step Calculation Example
Given:
• Capacitance: 1000 µF (0.001 F)
• Initial Voltage: 400V
• Desired discharge time: 5 seconds
• Discharge to 5% (20V final voltage)
• Safety factor: 2
Step 1: Calculate basic resistor value
R = t / (C × ln(V₀/Vf))
R = 5 / (0.001 × ln(400/20))
R = 5 / (0.001 × ln(20))
R = 5 / (0.001 × 2.996)
R = 5 / 0.002996 = 1,669 Ω
Step 2: Apply safety factor
R_safe = R / Safety_Factor
R_safe = 1,669 / 2 = 835 Ω
Step 3: Calculate power rating
P = V₀² / (4 × R)
P = 400² / (4 × 835)
P = 160,000 / 3,340 = 47.9 W
Final Results:
Discharge Resistor: 835 Ω
Minimum Power Rating: 48 W
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