BLDC motors have become popular today as we have household appliances like washing machines and ceiling fans coming with such motors.
The primary advantage of BLDC motors is that they support variable speeds, the bedrock of inverter motor technology. However, BLDC motors have their demerits. Therefore, we shall concentrate on the general drawbacks of brushless DC motors.
BLDC motors work with magnets. The rare earth permanent magnets are expensive than conventional magnets. Hence, it translates into higher motor costs.
Affects high-speed performance
The BLDC surface-mounted motors of permanent magnets cannot achieve high speeds as the mechanical strength of the assembly between the magnets and the rotor yoke limits its performance significantly.
Limited Constant Power Range
A machine requires a large constant power range to achieve higher efficiency. Permanent magnet brushless DC motors cannot achieve maximum speeds more than twice the base speed. Hence, these motors have a limited constant power range.
BLDC motors operating at low speeds can cause vibrations in the appliance. However, the vibrations reduce at high speeds.
Related: BLDC Motor vs Induction Motor
Comparatively difficult wiring
In the case of brushed DC motors, all you do is connect the positive terminal to the positive wire and the negative terminal to the negative for the motor to start functioning. The wiring and operation in a BLDC motor are complex because of the involvement of electronic controls and their links to all electromagnets.
The inherent natural vibration frequency of the BLDC motor can come closer to the vibrational frequency of the appliance’s body, resulting in a resonance phenomenon.
One should exercise care when cooling the motor, especially with a compact motor assembly. There are chances of demagnetizing the permanent magnets because of high temperature and large reverse magnetomotive force. However, one should also note that the critical demagnetization force varies for each permanent magnet material.
Safety concerns during manufacturing
The primary disadvantage of permanent rare earth magnets is that they can attract scattered metal objects. Brushless DC motors used in vehicles can be dangerous during a crash as there can be high voltage at the motor terminals if the wheels spin freely and the motor is still exited by permanent magnets. It can cause injuries to passengers or even rescuers.