Vacuum Cleaner Motors
The Working Principle of a Universal Motor
The Working Principle of a Universal Motor
The universal motor is a versatile and widely used electromechanical device that can operate on both AC (alternating current) and DC (direct current) power sources.universal motor It finds applications in household appliances, power tools and small industrial machines. In this article, we will explore the structure and working principle of this electromechanical device, highlighting its unique features and application.
The main parts of a universal motor are the field winding and armature conductors. The field winding produces a magnetic field when an electric current passes through it. The armature conductors are connected to the field winding through a commutator and brushes. Commutation and mechanical balance are issues that require significant attention when designing this type of motor.
When a universal motor is fed with an AC supply, the direction of the current in the armature and field winding changes simultaneously. As a result, the electromagnetic force experienced by the armature conductors also reverses. This change in the direction of the force causes the rotor to rotate continuously. Moreover, the speed of this rotation can be controlled by changing the voltage or current supplied to the motor.
However, it is important to note that AC power supply makes this motor less efficient than DC. This is because it induces a transformer EMF in the switched sections of the core, which interferes with the switching process. This results in arcing at the commutator and high maintenance brush wear.
In order to avoid this problem, a special commutation scheme is used. This involves the use of brushes and a commutator that reverses the current flow between the rotor and field windings. This reduces the frequency of the current passing through the armature and fields windings, which in turn increases the efficiency of the motor.
Moreover, it is possible to control the speed of a universal motor by varying its voltage or current. When the motor is running with no load, its speed is constant and stable. In closed loop, the motor responds quickly to a load disturbance and matches its reference value after a delay of about 2.45 s. However, when the load is constant, the motor loses its speed and stalls after a short time.
In this circuit, the zero-cross detector signal is fed to a frequency to voltage converter. The converter has a low pass filter to make it compatible with the motor and tachometer's characteristics. This circuit also incorporates a simple tachometer and adds a power supply to prevent the motor from frying if you connect it to a low-voltage source.
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