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. It's fundamental for understanding motor performance in various 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 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 crucial for selecting the right motor for an application, designing mechanical systems, and troubleshooting performance issues.

4. Using the Calculator

Tips: Enter frequency in Hertz (Hz) and number of poles (must be an even number). Typical values are 50 or 60 Hz for frequency and 2, 4, 6, etc. for poles.

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 each AC cycle produces two magnetic pole changes (60 × 2 = 120).

Q2: What are typical RPM values for AC motors?
A: For 60Hz systems: 3600 RPM (2-pole), 1800 RPM (4-pole), 1200 RPM (6-pole). For 50Hz systems: 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 slip in induction motors?
A: Induction motors run slightly slower than synchronous speed (calculated here) due to slip, typically 2-5% slower than the calculated RPM.

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