1. What is the RPM Formula?

The RPM (Revolutions Per Minute) formula calculates the rotational speed of an AC electric motor based on the power supply frequency and the number of magnetic poles in the motor.

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 magnetic poles in the motor

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 essential for proper equipment selection, speed control, and ensuring compatibility with driven machinery.

4. Using the Calculator

Tips: Enter frequency in Hz (typically 50 or 60 Hz) and number of poles (must be an even number, typically 2, 4, 6, or 8). All values must be valid (frequency > 0, poles ≥ 2).

5. Frequently Asked Questions (FAQ)

Q1: Why is the number 120 used in the formula?
A: The 120 comes from converting seconds to minutes (60) and accounting for the fact that one complete cycle involves two poles (60 × 2 = 120).

Q2: What are typical RPM values for AC motors?
A: Common values include ~3600 RPM (2-pole at 60Hz), ~1800 RPM (4-pole), ~1200 RPM (6-pole), and ~900 RPM (8-pole).

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

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

Q5: How does voltage affect motor speed?
A: In AC motors, speed is primarily determined by frequency and poles, not voltage (though voltage affects torque).