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Motor RPM Formula:
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The Motor RPM Formula calculates the rotational speed of an AC induction motor based on the electrical frequency and the number of magnetic poles in the motor. This fundamental relationship helps in motor selection and performance analysis.
The calculator uses the motor RPM equation:
Where:
Explanation: The formula derives from the fact that the magnetic field rotates at synchronous speed, which depends on the frequency of the AC power supply and the motor's pole configuration.
Details: Knowing a motor's RPM is crucial for proper application matching, determining gear ratios, predicting performance characteristics, and ensuring compatibility with driven equipment.
Tips: Enter frequency in Hz (typically 50 or 60 for mains power) and number of poles (common values are 2, 4, 6, or 8). The number of poles must be an even number.
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 poles (60 × 2 = 120).
Q2: What's the difference between synchronous and actual RPM?
A: This formula calculates synchronous speed. Actual RPM is slightly less due to slip in induction motors (typically 2-5% less than synchronous speed).
Q3: 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, it can be determined by counting the number of magnetic poles in the stator winding.
Q4: Does this formula work for DC motors?
A: No, DC motor speed depends on applied voltage and load. This formula is specific to AC induction motors.
Q5: What are typical RPM values for common motors?
A: For 60Hz systems: 3600 RPM (2-pole), 1800 RPM (4-pole), 1200 RPM (6-pole). For 50Hz systems: 3000 RPM, 1500 RPM, 1000 RPM respectively.