1. What is the Electric Motor RPM Formula?

The RPM (Revolutions Per Minute) formula calculates the rotational speed of an AC electric motor based on the frequency of the power supply and the number of poles in the motor. This is fundamental for understanding motor performance and selecting the right motor for specific applications.

2. How Does the Calculator Work?

The calculator uses the RPM formula:

Where:

• \( RPM \) — Revolutions per minute
• \( f \) — Frequency of power supply (Hz)
• \( p \) — Number of poles in the motor
• 120 — Constant factor (60 seconds × 2 for alternating current)

Explanation: The formula shows that motor speed is inversely proportional to the number of poles and directly proportional to the frequency of the power supply.

3. Importance of RPM Calculation

Details: Knowing a motor's RPM is crucial for proper equipment selection, ensuring compatibility with driven machinery, and understanding performance characteristics like torque and power output.

4. Using the Calculator

Tips: Enter frequency in Hertz (typically 50 or 60 Hz) and number of poles (always an even number, common values are 2, 4, 6, or 8). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is the number of poles always even?
A: AC motors require pairs of north and south poles to function, so the number of poles is always even.

Q2: What are typical RPM values for motors?
A: For 60Hz power: 2-pole=3600 RPM, 4-pole=1800 RPM, 6-pole=1200 RPM. For 50Hz power: 2-pole=3000 RPM, 4-pole=1500 RPM.

Q3: Is this formula accurate for all motor types?
A: This gives synchronous speed. Actual speed is slightly less (slip speed) for induction motors due to slip.

Q4: How does voltage affect RPM?
A: Voltage doesn't directly affect RPM in AC induction motors. RPM is primarily determined by frequency and poles.

Q5: Can I use this for DC motors?
A: No, DC motor speed depends on voltage and load, not on poles and frequency.