So what does AC motor and DC motor mean? Simply put AC stands for Alternating Current – where electricity flows in one direction and then reverses to flow in the other direction and in the mains power grid it does this 50 times per second (a ‘frequency’ of 50 Hertz). DC means direct current, where electricity flows in one direction only. There is no frequency associated with DC because the flow remains constant in just one direction.
AC FansThese are run directly from the single phase 240V AC electricity grid that supplies homes and businesses. When this alternating electric current is run through a coil of wire it forms alternating magnetic fields. In a ceiling fan motor there are many coils joined together and these are called windings.
Typically an AC ceiling fan motor has two sets of fixed windings (the stator) and a capacitor connecting them together. AC motors are designed to use the magnetic fields generated in the stator windings to create a force in the rotor windings to make the motor rotate.
AC Fans can be controlled by limiting the power that gets to the motor, most commonly by connecting a capacitor in series with the motor using a switch fitted to the wall. With this simple method of control it is possible to easily connect to automation systems (which are really just computer controlled switches).
So to summarise, AC motors:
- are simple;
- easy to control;
- widely available;
- can be affected by noise;
- can be efficient but only limited improvements are possible.
DC FansThe term “DC motor” comes from describing the way electric current is applied to the windings. Many people incorrectly assume they are like DC motors used in cars and toys whereas DC fans should really be called “Inverter Driven Fans”. These days many appliances like air-conditioners and refrigerators, microwave ovens and washing machines are using inverter driven motors in place of conventional AC motors.
The control module in Hunter Pacific DC fans can also be called an ‘inverter drive’. It takes the incoming single source of AC power, converts it into DC and then splits that DC power into 3 separate sources of power for the motor. Each motor power source can be precisely controlled independently of the power coming from the mains grid.
Where AC motors have coils of wire connected to the same incoming power source, the DC motor has three separate coils that are connected to these controllable power sources. This is why DC ceiling fans must be connected using a control module and can’t be directly connected to simple wall switches and automation systems.
DC ceiling fan motors use magnets to push-pull against the magnetic fields formed in the coils of wire. The magnets are part of the rotor (rotating part) and the coils form part of the stator (stationary part). The effects of the magnets can be felt as a series of steps when the unpowered fan is rotated by hand.
To summarise, DC motors:
- have fixed magnets, which are more expensive but quieter ;
- have three independent windings;
- require a control module and remote control handset;
- are less affected by noise from the power grid;
- can be made highly efficient.
What does it all mean to the average user?It isn’t possible to make blanket statements that DC motors are always better than AC motors because the design of the fan determines how much power is required to generate the required airflow.
Some fan designs are highly efficient and give good results with both AC and DC motors (eg. Revolution and Revolution DC) and some designs (like the Radical and Rose) have been designed to take advantage of DC motors.
Although using less energy does amount to a cost saving on electricity bills the amount of saving may not justify the increased cost of a DC motor powered fan so it is better to base a purchasing decision on the airflow performance and ambience of the fan as a whole rather than simply deciding solely on whether it’s AC or DC.