Speed fluctuation in regular ceiling fans

Ever experienced that your regular ceiling fan runs at a higher speed in the early hours of the morning or change speed on its own? This speed fluctuation stems from the inherent behaviour of the type of motor used in the ceiling fan. A regular ceiling fan is driven by Alternating Current Induction Motor (ACIM), for which, loosely speaking, the input supply voltage determines the rotation speed. The domestic input supply voltage (ideally 230V) depends on its load and the load varies over time depending on the use. In the early hours of the morning the industrial night shift winds down resulting in a decrease in load and this decrease in load cause a surge in the domestic input supply (>230V), subsequently, the ceiling fan would rotate faster. When the load is high, the input supply can reduce resulting in lowering the speed of the fan. As a ceiling fan user, these kinds of speed fluctuation results in energy waste and thermal discomfort.

Brush-Less Direct Current (BLDC) motorbased fans like Superfan do not have this problem as these fans operate at a steady speed in a wide range of voltage–90 to 400V.

How BLDC fans are immune to input supply voltage fluctuations?

BLDC ceiling fans like Superfan require electronic hardware with a micro-controller to run the motor. In BLDC motors electronic hardware supplies the input voltage to the motor and it is constant. In a simple broader view the input supply voltage that comes at the mains is decoupled from the BLDC ceiling fan motor–it does not see mains voltage rather sees only the voltage (constant) supplied by the electronics hardware. This inherent attribute makes the BLDC motor immune to speed fluctuations in a wider range of input supply voltage. This range is determined by the electronics hardware and typically it is 90–400 V.

This feature is also a reason why BLDC motor almost never fails. The fluctuations and surge of the input supply can cause a failure in the electronics hardware which protects the motor.