1. What is the RPM Formula?

The RPM (Revolutions Per Minute) formula calculates the rotational speed of an electric motor based on the power supply frequency and the number of magnetic poles in the motor. This is a fundamental calculation 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 in Hertz (Hz)
• \( p \) — Number of poles in the motor (must be even number)
• 120 — Constant factor (60 seconds × 2 for alternating current)

Explanation: The formula accounts for the synchronous speed of an AC motor where the magnetic field rotates at a speed determined by the frequency and pole count.

3. Importance of RPM Calculation

Details: Accurate RPM calculation is crucial for motor selection, system design, and ensuring proper operation of machinery. It helps in matching motor speed to application requirements.

4. Using the Calculator

Tips: Enter frequency in Hz (typically 50 or 60 Hz for mains power), and number of poles (must be an even number like 2, 4, 6, etc.). All values must be valid (frequency > 0, poles ≥ 2 and even).

5. Frequently Asked Questions (FAQ)

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

Q2: What is the difference between synchronous and actual RPM?
A: This formula calculates synchronous speed. Actual RPM is slightly lower due to slip in induction motors.

Q3: What are typical pole numbers for motors?
A: Common configurations are 2-pole (~3600 RPM at 60Hz), 4-pole (~1800 RPM), and 6-pole (~1200 RPM).

Q4: How does voltage affect RPM?
A: Voltage doesn't directly affect synchronous RPM, but insufficient voltage may prevent a motor from reaching its rated speed.

Q5: Can this be used for DC motors?
A: No, DC motor speed depends on voltage and load, not on pole count and frequency.