Why do BLDC motors have variable numbers of turns per pole?
BLDC motors can have a variable number of turns per pole for a few important reasons:
Torque & Speed Requirements
The number of turns per pole influences the torque & speed characteristics of the motor. More turns per pole will improve torque but lower maximum speed. Fewer turns per pole reduce torque yet allow for faster speeds.
The number of turns per pole can be varied to optimize the motor for the application’s specific torque & speed needs.
Ex: A motor utilized in a high-speed application such as a drone will have fewer turns per pole than a motor used in a high-torque use such as an electric vehicle.
Winding Factor
The winding factor indicates how effectively the windings are dispersed in the stator slots. It is determined by the number of slots per pole and phase (q).
Certain slot and pole combinations produce a higher winding factor & more efficient usage of the windings. The winding factor can be customized for a specific slots/poles configuration by adjusting the number of turns per pole.
Cogging Torque
Cogging torque is an unwanted torque produced when the rotor magnets contact with the stator slots. It may produce vibration and loudness.
The number of turns per pole influences the cogging torque. Specific combinations of turns per pole & slots/poles will produce increased cogging torque. By changing the turns per pole, the cogging torque can be reduced.
Adjusting the number of turns per pole enables BLDC motors to be tuned for torque, speed, winding factor, & cogging torque based on the application requirements. The ideal number of turns is determined by the slot/pole design and required performance parameters.
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