Autotransformers are electrical transformers with one coil and different voltage taps. Via these different voltage taps, the different reduced voltages are available. The single winding of an autotransformer acts both as primary and secondary winding simultaneously. This makes it possible to obtain a smaller and lighter construction compared to classical dual-winding transformers. Autotransformers are integrated in Sentera transformer fan speed controllers for motor speed control in steps via voltage reduction. Sentera has its own production line for autotransformers to guarantee optimal quality.