1. What is the RPM Formula?

The RPM (Revolutions Per Minute) formula calculates the rotational speed of an AC motor based on the frequency of the power supply and the number of magnetic poles in the motor. This relationship is fundamental in electrical engineering and motor design.

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

Explanation: The factor 120 comes from converting seconds to minutes (60) and accounting for the fact that each pair of poles produces one complete AC cycle (2). The number of poles must always be an even number.

3. Importance of RPM Calculation

Details: Knowing a motor's RPM is crucial for proper motor selection, system design, and ensuring equipment operates at desired speeds. It affects torque, power output, and efficiency.

4. Using the Calculator

Tips: Enter frequency in Hertz (Hz) and number of poles (must be even number). Common pole numbers are 2, 4, 6, or 8 for most AC motors.

5. Frequently Asked Questions (FAQ)

Q1: Why is the number of poles always even?
A: AC motors require pairs of north and south magnetic poles to function, so the pole count is always even (2, 4, 6, etc.).

Q2: What are typical RPM values for AC motors?
A: At 60Hz: 3600 RPM (2-pole), 1800 RPM (4-pole), 1200 RPM (6-pole). At 50Hz: 3000 RPM (2-pole), 1500 RPM (4-pole), 1000 RPM (6-pole).

Q3: Does this formula work for DC motors?
A: No, this formula is specific to synchronous AC motors. DC motor speed depends on voltage and load.

Q4: What is synchronous speed vs actual speed?
A: This formula gives synchronous speed. Actual speed is slightly less due to slip in induction motors.

Q5: How does frequency affect motor speed?
A: Speed is directly proportional to frequency. Doubling frequency doubles the speed (with poles constant).