One disadvantage of conventional DC machinery is the sparking which occurs at the brushes (“brush sparking“). This brush sparking is the main cause of high-frequency interference which the motor feeds back into the power network when operating and which can then interfere with other electrical appliances. This also limits the maximum speed, as at high speeds the brushes heat up and wear.

This problem is avoided by the brushless direct current machine, BLDC. The rotor here comprises a permanent magnet, and the stator is made up of several electromagnets. The rotor position is continuously measured, e.g. by the return induction current or by the resultant current or by means of Hall-effect sensors.

The electromagnets in the stator are commutated via a bridge circuit of MOSFET transistors or IGBT . We therefore also talk about EC-motors (electronically commutated motors).

Depending on the position of the permanent magnets of the rotors relative to the stator windings, we differentiate between “internal rotor“ and “external rotor“.

These motors are comparatively expensive, on account of their additional electronic components. However, they do offer a series of advantages when compared with conventional electric motors fitted with brushes; for example, longer service life and the potential of varying the rotating speed at the same motor voltage (practically identical torque). 

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