Home
Back
Motor RPM Formula:
| From: | To: |
The motor 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.
The calculator uses the motor RPM equation:
Where:
Explanation: The formula shows that motor speed is directly proportional to frequency and inversely proportional to the number of poles.
Details: Knowing a motor's RPM is essential for proper motor selection, system design, and ensuring the motor operates within its specified speed range for optimal performance and longevity.
Tips: Enter the power supply frequency in Hz and the number of poles in the motor. Both values must be positive numbers (frequency > 0, poles ≥ 2 and typically an even number).
Q1: Why is the constant 120 used in the formula?
A: The 120 comes from converting seconds to minutes (60) and accounting for the fact that in AC motors, each complete cycle produces two poles (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 characteristics.
Q4: What is slip in induction motors?
A: Induction motors run slightly slower than synchronous speed (calculated by this formula) due to slip, which is typically 2-5% for most motors.
Q5: How do I determine the number of poles in a motor?
A: The number of poles is usually specified in the motor's documentation or nameplate. Alternatively, you can count the number of magnetic poles in the motor windings.