In this article, we will briefly discuss two types of DC motors installed in power tools – conventional brushed motors with mechanical commutators and brushless electronically commutated motors, often referred to in Lithuania as "brushless" (from English - brushless).
The construction of conventional DC motors and brushless motors is similar. They consist of a stator and a rotor made of permanent magnets. The stator has a wound winding that creates a magnetic field in the air gap.
The main disadvantages of brushed motors are related to the mechanical commutator, which limits the motor's power and speed, increases inertia, and axial length. These motors also require constant maintenance, as their brushes wear out and need to be replaced. The commutator itself is noisy, sparks, and emits dust, which is generated by the wearing brushes. This dust can get into the motor bearings or even cause a short circuit.
It should be noted at this point that in most cases, conventional brushed motors can be replaced with brushless ones.
Such motors come in various power ratings – the smallest ones are used in computer hard drives, and the large ones in electric vehicles. Three-phase motors are the most popular, but there are also two-phase or multi-phase electronically commutated DC motors.
Early electronically commutated motors were characterized by high torque, but high-power, industrially applicable motors became possible only in 1980, with the adoption of powerful permanent magnets and semiconductor elements that create the motor's excitation field in the air gap, without an excitation winding and additional electricity consumption.
Thus, the main advantages of electronically commutated motors over brushed DC motors are:
a) better speed and torque characteristics;
b) higher efficiency;
c) longer service life;
d) quieter operation;
e) wider speed range.
In addition, the ratio of the torque generated by electronically commutated motors to the size of the motor itself is higher, which is particularly useful in applications where motor dimensions and weight have a critical impact.
References:
Pitrėnas, A. Research on the Control of an Electronically Commutated Motor. Master's Thesis. Department of Automation, Faculty of Electronics, Vilnius Gediminas Technical University, 2012.