Transformer fan speed controllers are intended for stepped speed control of the electric motors. They use autotransformer technology to reduce the motor voltage – and fan speed - in steps. Thanks to this technology, they generate a motor voltage with a perfect sinusoidal shape. This results in exceptionally quiet motor operation and extended service life.
Autotransformers are electrical transformers with a single coil. Via their different voltage taps, reduced voltages are available. A special impregnated coating reduces the electrical noise from the autotransformers. However, in quiet environments the typical humming noise caused by the transformer technology might be noticeable.
Transformer fan speed controllers are cost efficient and have proven to be very reliable and robust. They can also be used in circumstances with unstable power supply.
These type of fan speed controllers are easy to install. They don’t require any configuration. Some transformer fan speed controllers have an integrated rotary switch to manually adjust the fan speed. Other variants can be controlled remotely via Modbus RTU or via an analogue control signal.
Electronic or variable fan speed controllers offer infinitely variable speed control for AC fans. Typically, these controllers are used to optimise the speed of AC fans or pumps in HVAC applications. They use phase angle control - TRIAC technology - to reduce the motor voltage and to control fan speed. Triac fan speed controllers are typically available for motor currents up to 10 A. Thanks to this technology, these fan speed controllers are completely silent. They reduce the mains voltage by eliminating parts of it. The remaining motor voltage will not have a perfect sinusoidal shape. Microprocessor control makes it possible to optimise the zero-cross detection. This means that the TRIACs can be controlled more accurately. This results in a quiet motor operation.
Nevertheless, depending on the motor type some additional motor noise at low speed might occur due to the non-sinusoidal shape of the motor voltage. Increasing the minimum motor voltage will reduce the noise level.
Some electronic fan speed controllers have an integrated potentiometer to manually adjust the fan speed. Other variants can be controlled remotely via Modbus RTU or via an analogue control signal.
Electronic fan speed controllers do not require configuration in most circumstances. The low speed level can be adjusted via a trimmer or via Modbus RTU.
Frequency inverters or Variable Speed Drives provide infinitely variable speed control for AC fans. Just like electronic fan speed controllers... So what is the difference? A frequency inverter is using Pulse Width Modulation – IGBT technology – to adjust the motor voltage and frequency. This offers an almost perfect sinusoidal motor voltage and exceptionally quiet motor control in all circumstances. Depending on the settings, the frequency inverter itself can also operate very silently.
Due to the high switching frequency of the IGBT’s, special filters are required to reduce the EMC pollution in the power grid. This extra hardware has a cost. Precise motor control also means: more complex to configure. The conclusion is that frequency inverters are more expensive than electronic fan speed controllers, more complicated to configure and more critical to install, but they offer very precise motor control. These type of speed controllers are very energy efficient and capable of controlling high motor currents.
The requested motor speed can be adjusted via the integrated controls (potentiometer or push buttons). Next to that, it is also possible to adjust the motor speed remotely via Modbus RTU or an analogue control signal.