Difference Between Start Capacitor, Run Capacitor, and Motor Capacitor
Capacitors play a vital role in single-phase induction motors and other AC systems. Many learners often get confused between start capacitors, run capacitors, and motor capacitors. This guide explains their differences in function, ratings, and applications with easy-to-understand examples.
📌 What is a Motor Capacitor?
A motor capacitor is a device connected to single-phase motors to improve starting torque, efficiency, and power factor. It may function as a start capacitor or run capacitor depending on the motor design.
⚡ Start Capacitor
- Function: Provides an initial phase shift and extra torque for starting motors.
- Capacitance Range: 50 µF to 500 µF.
- Voltage Rating: 250V to 330V.
- Applications: Air conditioners, compressors, refrigerators, pumps.
- Characteristic: Connected only during starting, then disconnected via centrifugal switch or relay.
🔋 Run Capacitor
- Function: Improves running efficiency, reduces power losses, and ensures continuous torque.
- Capacitance Range: 5 µF to 80 µF.
- Voltage Rating: 370V to 440V.
- Applications: Fans, blowers, HVAC units, continuous-duty motors.
- Characteristic: Remains in the circuit during motor operation.
📊 Key Differences: Start Capacitor vs Run Capacitor
| Feature | Start Capacitor | Run Capacitor |
|---|---|---|
| Purpose | Provides high starting torque | Improves efficiency and running performance |
| Capacitance | 50 µF – 500 µF | 5 µF – 80 µF |
| Voltage Rating | 250V – 330V | 370V – 440V |
| Operation | Used only at startup | Stays connected while motor runs |
| Applications | Compressors, pumps, AC units | Fans, HVAC systems, blowers |
🔎 Motor Capacitor vs Start/Run Capacitor
The term motor capacitor generally refers to both start and run capacitors since both are used in motor applications. The exact type depends on whether the motor requires extra starting torque or continuous phase shift.
❓ Frequently Asked Questions (FAQ)
1. Can I replace a start capacitor with a run capacitor?
No, start and run capacitors have different ratings and functions. Using the wrong one can damage the motor.
2. What happens if a run capacitor fails?
The motor may overheat, draw more current, produce noise, or fail to run efficiently.
3. How do I identify a start capacitor?
Start capacitors are usually larger in size, with high capacitance and lower voltage ratings.
Conclusion: The difference between start capacitor, run capacitor, and motor capacitor lies in their purpose, ratings, and application. Choosing the right capacitor ensures motor efficiency, safety, and long service life.
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