Transformer Based Speed Controllers are ideal for smooth and silent fan speed control. 
They are capable of running multiple fans at once (do not exceed 90% of rated amperage).
They are the only way to reduce the speed of larger fans without compromising the life of the fan motor.

Can be used with the following fans;
Max-Fan 250 / 355 / 400 / 500 / 630
Iso-Max 250 and 315

Transformer based controllers should not be used with fans that already have integrated speed control.

Why use a Transformer based Fan Speed Controller?

There are several ways to increase and decrease the mains supply voltage of fan motors in order to change the speed. The most common used variants are Transformer Based or Phase Controlled Modulator (Triac or Thyristor Controllers).

Transformer:
A Transformer only changes the amplitude of the sine wave. This means that there is no abrupt increase of the current or any change of the frequency, leading to a smooth speed control of the fan without any additional increase of the noise or the heating of the fan motor.

Phased Controlled Modulator (e.g. Triac or Thyristor Controller):
Phase controlled modulators, also known as phased cutting controllers, are an easy and cheap way of reducing the voltage. With these controllers, the supply of power to the fan motor is interrupted intermittently in order to reduce the speed of the fan. The abrupt rise of the voltage and current leads to harmonics in the motor current. The harmonics cause additional losses in the motor which leads to a higher input power and a higher warming of the motor windings. Furthermore, the harmonics also cause mechanical vibrations and noises.