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Electric Motor RPM Formula:
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The electric motor RPM formula calculates the rotational speed of an AC induction motor based on the frequency of the power supply and the number of magnetic poles in the motor. This fundamental relationship helps in motor selection and performance analysis.
The calculator uses the synchronous speed formula:
Where:
Explanation: The formula calculates the synchronous speed of the motor's magnetic field. Actual operating speed will be slightly less due to slip in induction motors.
Details: Knowing a motor's speed is crucial for proper equipment selection, matching motor speed to application requirements, and troubleshooting performance issues.
Tips: Enter the power supply frequency in Hz and the number of poles (must be an even number). Common pole configurations are 2, 4, 6, or 8 poles for most industrial motors.
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 is the difference between synchronous and actual RPM?
A: Synchronous speed is the theoretical maximum, while actual speed is typically 2-5% less due to slip in induction motors.
Q3: 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.
Q4: Can this formula be used for DC motors?
A: No, DC motor speed depends on voltage and load, not poles and frequency. This formula is specific to AC induction motors.
Q5: How does voltage affect motor speed?
A: Voltage doesn't directly affect synchronous speed, but insufficient voltage may prevent the motor from reaching its designed speed under load.