What’s the difference between a brushless motor and a brushed? The brushless motor is a DC motor with a permanent magnet rotor and a rotating magnetic field stator. Unlike a brush engine, there is no need for electric crawling contacts (brushes) on the rotor shaft to function. Switching the circulating current to the stator windings, and thus the variation in the orientation of the magnetic field generated by them, takes place electronically.
This results in less mechanical resistance, eliminating the possibility of sparking at increasing rotational speed, and greatly reducing the need for periodic maintenance. A very similar engine is the stepper motor, which differs from the brushless motor because the stator windings are not fed all at once, but cyclically so that the magnetic fields generated by them result in rotation of the rotor by obtaining a precise positioning of the same.
In a brush motor, the mechanical contact of the brushes with the rotating manifold on the rotor axis closes the electrical circuit between power and windings on the rotor by periodically reversing the direction of current circulation in the rotor winding turns, thus realizing the ‘inversion of the electrodynamic forces that act on the spires themselves.
In a brushless motor the rotor is free of winding and is equipped with permanent magnets, while the magnetic field generated by windings on the stator is variable. Since the motor operates in DC, to realize the rotation of the magnetic field generated in the stator, an electronic circuit consisting of a power transistor bank controlled by a microcontroller controlling the current switching, commands the current reversal and therefore the rotation of the magnetic field. Since the controller needs to know the rotor position with respect to the stator to determine the orientation to be given to the magnetic field, it is usually connected to a Hall effect sensor such as Pick-up or a more precise cable shaft resolver.
The performance of these machines is on average higher than with asynchronous DC motors and the yield can reach 0.98
There are naval applications of such engines with superconducting technologies that have powers of MW order. Recently, they are widely used in industrial applications and used in automatic machines that require precise and fast movements with extremely compact dimensions and great versatility, also provided by highly sophisticated programmable control equipment that give complete engine control and diagnostics.
This type of engine is used in Formula E.
What are the advantages of a brushless engine compared to a brush engine?
The first significant advantage is the engine’s expected life, since the brushes are the “weak point” of an electric motor. The absence of brushes also eliminates the main source of electromagnetic noise present in DC motors.
The footprint is limited in relation to the power they can deliver and above all the torque that these engines can deliver. In terms of efficiency, brushless motors always work in optimum performance. Not having to generate the rotor magnetic field have greater efficiencies. The absence of sparks is critical when the engine operates in saturated volatile organic compounds such as fuels.
In these types of motors, permanent magnets are positioned on the rotor and are made with special materials that allow a very low rotor inertia, which allows for extremely precise control both in speed and acceleration.
Recently, due to the commercial thrust associated with the demand for highly energy-efficient products in the civil sector, they have been introduced on the refrigeration and air conditioning market, where they can achieve high benefits in terms of consumption for large users (for example: large organized distribution that can be installed on fans operating on refrigerator counter heat exchangers; large offices that can fit them in fan coils used in distributed air conditioning systems).
With the cost savings of electronic control systems produced by economies of scale, the greater convenience and consequent extension of the use of brushless motors has also become important for the operation of bicycles, motorcycles and electric traction vehicles.
And what are the disadvantages of a brushless engine?
The main disadvantage of these types of engines is the higher cost. Unlike brush motors, in fact, the control is carried out electronically by a controller, an electronic device provided by the engine manufacturer or by third parties, so at the cost of the engine, the cost of the control system is increased. For brush motors, the “control” is made by a potentiometer or a rheostat (low efficiency but extremely cheap systems) for speed regulation. Variable resistance, potentiometer or a rheostat can be used to vary the current absorbed by the motors. This control system can also be used for multiple parallel motors, while any brushless motor must be controlled by its “controller” device.