Brushless Fan Controller's

Brushless fan's are now in wide use in many applications many of which automotive. This is due to recent advances in so called "brushless motors". A brushless motor works in a similar way to the well known 3 phase induction motor, but rather than rely on self magnetisation of a steel rotor the rotor is made up of very powerful magnets, this greatly reduces the size of the motor for the same amount of power. Furthermore unlike an induction motor a modern brushless motor lends itself very well to be controlled at different speeds this is done with a variable frequency drive. Essentially a modern brushless motor is controlled with three-phase power that can be generated by an on-board electronic controller at variable frequencies. The higher the frequency the faster the motor goes round. Of course in automotive applications only DC power is available so it is quite commonplace for the brushless motor to include its own three-phase drive circuitry that is completely transparent to the user. The circuitry is managed by a microcomputer or microcontroller that generates the appropriate waveforms. Given that the motor has a controller designed to run it at a certain speed and the flexibility of the design it is a very simple matter to control the speed of the motor using an external command signal to tell the motors drive circuitry how fast to run the motor. This is very useful and important for controlling fans as it now means that customisable applications are possible. It is no longer necessary to guess at how fast the fan will go round and what its performance will be. Because of the built-in electronic controls providing the maximum power of the motor and electronics is not exceeded the fan can run at a very exact speed regulated by an external command signal. This means that the fan can be run at a lower speed using vastly less power where possible for example to run a fan at 80% of its maximum speed requires only 50% of the power required at maximum speed.

The ability to control the speed of a brushless fan allows for many new applications around thermal management and effective use of power or the ability to reduce performance to lower noise levels where this is beneficial and only use the fans maximum power when required. For example a fan can be driven based on the temperature of fluid exiting a radiator that the fan is cooling. The fan speed can be regulated to target a temperature range of the fluid which is particularly helpful where the fluid should not be over cooled or under cooled. This is far more flexible than a traditional thermostatic control.

Brushless fans also last much longer than brushed fans as the weak point in a brushed fans are usually the brushes which are subject to continuous friction and it is rare to find an automotive brushed fan that can function for more than 10,000 hours. A brushless fan has no such mechanical parts and there is no need for stationary and rotating parts to make contact therefore there is little to no wear inside the fan motor. The only point of mechanical friction is now the bearings. It is not unusual for a brushless fan to last for 40,000 hours. Of course as with brushed fans running a fan motor more slowly will prolong its life. Defining the life-cycle of a fan in hours is a convenience for the engineer choosing the fan but in reality with all things being equal the wear on the fan is down to the amount of revolutions the motor has undergone and usually a statement alongside the amount of running hours the fan will work for specifies that this is at maximum speed or another speed. So being able to slow down your fan is also a way of prolonging its life in the application as well as using less power and creating less noise. It is often easier to find fans with brushless motors that are sealed and therefore watertight making them much more durable in harsh applications or the motor may be more powerful than a brushed motor in the same package size giving higher performance of the same sized fan.

Sparky Lab's develops and supplies a range of controllers aimed at brushless fan motors. These can be as simple as telling the fan how fast to go in a fixed speed application particularly where a fan requires an input signal to run and simply powering the fan is not sufficient. Controllers are designed to work with most brushless fans on the market, the interfacing of Spal automotive fans and ebmpapst fans were given consideration during the design process and they are of such varied nature they would no doubt cover most fans on the market. Solutions range from production ready to quick turnaround prototype boards that may be slightly larger than a production solution but can be developed quickly into a customised solution as they are very flexible but still of production build standard. Once the prototype is approved and a control strategy agreed on, if production quantities warrant it a bespoke design can be produced in order to bring about the most cost effective and compact solution.
Email:
Simon@sparkylabs.co.uk