Capacitor Size Calculator
Calculate required capacitor size for motors and energy storage applications
Calculate Capacitor Requirements
Energy required to start the motor or application
Operating voltage of the circuit or motor
Required Capacitance
Formula used: C = 2E/V²
Application: Motor startup, energy storage, power supply filtering
Example Calculation
Electric Motor Startup
Problem: Determine capacitor size for motor startup
Given: Startup energy = 64 µJ, Operating voltage = 16 V
Required: Capacitance needed for the startup capacitor
Step-by-Step Solution
1. Convert energy to Joules: E = 64 µJ = 64 × 10⁻⁶ J
2. Apply the formula: C = 2E/V²
3. Substitute values: C = 2 × (64 × 10⁻⁶) / (16)²
4. Calculate: C = 128 × 10⁻⁶ / 256 = 0.5 × 10⁻⁶ F
Result: C = 0.5 µF
Recommendation: Use a 1 µF, 25V capacitor for safety margin
Common Capacitor Codes
Key Formulas
Energy Storage
E = ½CV²
Energy stored in a capacitor
Capacitor Sizing
C = 2E/V²
Required capacitance for given energy
Voltage Rating
V = √(2E/C)
Minimum voltage for energy storage
Selection Tips
Choose voltage rating 150-200% of operating voltage
Electrolytic caps for high capacitance values
Film caps for stable, low-loss applications
Consider temperature and lifetime ratings
Understanding Capacitor Sizing
What is Capacitor Size?
Capacitor "size" refers to the capacitance value (measured in Farads) rather than physical dimensions. It indicates the capacity to store electrical energy and is determined by the startup energy requirements and operating voltage of your application.
Energy Storage Principle
Capacitors store energy in an electric field between their plates. The amount of energy depends on both the capacitance and the square of the voltage. This relationship is fundamental to determining the right capacitor for energy storage applications.
Common Applications
- •Motor startup capacitors for single-phase motors
- •Power supply filtering and energy storage
- •Camera flash circuits and strobe lights
- •Backup power for memory circuits
Calculation Method
Energy Formula: E = ½CV²
Rearranged for C: C = 2E/V²
Where:
- • C = Capacitance (Farads)
- • E = Energy (Joules)
- • V = Voltage (Volts)
Design Considerations
- ✓Voltage rating must exceed operating voltage
- ✓Consider temperature coefficient and stability
- ✓Account for capacitance tolerance (±10-20%)
- ✓Evaluate ESR (Equivalent Series Resistance)
Safety and Selection Guidelines
Voltage Rating Safety
Always select capacitors with voltage ratings significantly higher than the operating voltage. A safety factor of 1.5-2x is recommended to account for voltage spikes and ensure long-term reliability.
Capacitor Type Selection
Choose electrolytic capacitors for high capacitance values (>1µF), ceramic capacitors for stability and low loss, and film capacitors for precision applications requiring low ESR and high reliability.