Induction motors Vs BLDC motors: The technology explained

A few years back there was a major transition from incandescent bulbs to LED due to the huge reduction in power consumption achieved by LEDs. It was just not another technology but a revolution in the industry because the same amount of lumens could be achieved with very less power consumption.

The ceiling fan industry is also in the cusp of such a transition. BLDC is the new revolution in the fan industry. And it is only a matter of time before all old inefficient induction motor fans will be replaced by smart super efficient BLDC fans.

BLDC technology has been in the market for many years now and it is widely used in industries where high torque motors are required. What was missing so far is its application in ceiling fans. But, this is rapidly changing as of today.

Here, we throw some light on the difference in working of an ordinary induction motor fan as compared to a brushless DC fan.

Induction Motor Fan( How it works?)

An induction fan composes of two main components responsible for rotating motion of the fan:
1. Stator
2. Rotor

An induction fan has coils/Windings on Stator and Rotor. An Electric flux is generated when you pass current through the stator winding. This current flows through the coil depending on the arrangement of the stator. Everything is done in a sequence to make a rotational moment by creating a magnetic field. The conduction of current through the coils in rotor causes the motor to rotate.

The speed of an induction fan is controlled by a regulator, which are of two types:

1. Resistance Based: In this, the regulator the resistance is varied to adjust the amount of voltage going to the fan. These regulators are highly inefficient because a lot of heat is dissipated due to resistance resulting in power losses.

2. The modern regulator is basically an on/off device that constantly keeps chopping the voltage so as to change the speed of the fan.

BLDC Fan( How it works?)

A BLDC fan takes in AC voltage and internally converts it into DC using SMPS.

The main difference between BLDC and ordinary DC fans is the commutation method. A commutation is basically the technique of changing the direction of current in the motor for the rotational movement. In a BLDC motor, as there are no brushes so the commutation is done by the driving algorithm in the Electronics. The main advantage is that over a period of time, due to mechanical contact in a brushed motor the commutators can undergo wear and tear, this thing is eliminated in BLDC Motor making the motor more rugged for long-term use.

To explain, BLDC technology in simpler terms, BLDC uses a combination of Permanent Magnets and Electronics to achieve the kind of efficiency and performance it delivers. A BLDC fan composes of 3 main components:

1. Stator
2. Rotor
3. Electronics.

The assembly of the motor can be explained in the following images:

bldc pcb
Fig.1 – Electronics

bldc stator and rotor
Fig.2 – Stator- Rotor Assembly

The electronics contains a driving algorithm which drives the BLDC motor. As discussed earlier in a BLDC motor the position of magnets in the fan is sensed by electronics that either uses a Hall effect sensor or back EMF. Modern BLDC motors use Back EMF for commutation due to proven disadvantages of hall effect sensor over period of time.

To explain it in easier terms, we can take an example of a donkey who has a carrot fixed over his head as per shown in the picture below:

Consider the Stator to be the Carrot and the donkey to be the Magnets. The polarity of the stator will keep changing, due to attraction the magnets will create rotational moment, just like how the donkey tries hard to reach the carrot in the picture.

bldc donkey

To increase the torque of the motor, modern motors excite the other 2 phases too to create repulsion hence increasing the torque of the motor.

Permanent magnets used in rotor are responsible for mass reduction in power consumption compared to windings used in the stator in an ordinary induction fan. One added advantage in a BLDC fans due to use of an electronic circuit is that you can add several additional features to increase convenience, few example of the same are sleep mode, timer mode also it is compatible with Home automation systems. Most of the BLDC Ceiling fans are operated by remote unlike traditional regulator reducing the purchase cost of regulator.

Compared to regular induction fan, a BLDC fan can save upto Rs 1000-1500/ Year/fan. And because there is no heating of the motor, the life of a BLDC fan is also expected to be much higher than ordinary fans.