CONTENIDO:
- ¿Qué es el motor sin escobillas? ¿Como funciona?
- Diseño de motor sin escobillas y piezas principales.
- ¿Qué es un motor cepillado? ¿Como funciona?
- Pros y contras del motor de CC cepillado
- Aplicaciones principales. ¿Qué es mejor?
Diferencia entre motores con y sin escobillas en pocas palabras
Los motores eléctricos son dispositivos que convierten la energía eléctrica en mecánica. La eficiencia de ese proceso depende de su diseño y tipo de corriente (CA o CC).
Entonces, ¿cuál es la diferencia entre motores con y sin escobillas en pocas palabras?
- Los motores sin escobillas no tienen escobillas en el montaje y son más compactos. En cambio, deben estar equipados con dispositivos de conmutación adicionales (controladores, codificadores rotativos, accionamientos).
- Los motores cepillados son más baratos y sencillos. Se pueden conectar directamente a la fuente de CC y tienen un control elemental simple (como un interruptor).
- En variaciones sin escobillas, su rotor gira electrónicamente por otro lado; la armadura cepillada gira mecánicamente (corriente transmitida a través de las escobillas).
- Los sin escobillas tienen tres cables para la conexión y los cepillados tienen dos.
- Los motores sin escobillas tienen una mayor eficiencia (85-90%) que los cepillados (75% -80%). Esto quiere decir que con la misma potencia los primeros convierten una gran fuerza de rotación, porque no crean fricción y no pierden mucho calor durante su funcionamiento.
Por tanto, podemos sacar nuestra primera breve conclusión. Los motores sin escobillas tienen mayor rendimiento, eficiencia y mayor estabilidad. Por otro lado, los motores eléctricos cepillados tienen precios más bajos y son más fáciles de mantener.
Para una mayor diferencia, veámoslos en detalle.
¿Qué es el motor sin escobillas? ¿Como funciona?
El principio de funcionamiento de ambos tipos de motores es generalmente similar. Se basa en la interacción de un imán permanente en el rotor y un imán eléctrico en el estator.
El motor de CC sin escobillas (también llamado BLDC o simplemente BL) es un dispositivo síncrono y actúa como PMSM (motor síncrono de imán permanente). Por lo tanto, su principio de funcionamiento se basa en la regulación de frecuencia auto-sincronizada cuando su rotor y estator entran en contacto con la misma frecuencia.
Los motores BLDC vienen en dos tipos:
- Corredor
- In-runner
En el primer caso, el rotor se encuentra encima del estator y, en el segundo, debajo. Echemos un vistazo a cómo funciona en la versión out-runner como ejemplo.
In such design, the rotor has permanent magnets and stator has a coil arrangement that forms an electrical magnet. The basic principle of operation is based exactly on their interaction.
A power from source makes coils energized, and they create a magnetic field according to Faraday law. When it happens, these energized coils are attracted to opposite poles located on rotor. These coils are installed in the rotor, so it starts to rotate with them.
When they approach to opposite pole, power turns off and commutator starts to energize a next pair. The next pair of coils are also attracted, thereby moving the rotor further. Then such action is repeated continuously.
BLDC have a special design that allows user to supply power to any coil, so it can quickly change torque and rotation speed. Brushless motors have a compact size with high speed and precise positioning at the same time.
BL motors generate no friction; hence they produce more rotation force instead of heat. This is achieved due to the lack of brushes. Instead of them, integrated commutating devices monitor and regulate a rotor position, speed of rotation, and steady distribution of current across the coils.
Brushless motor design and main parts
A common motor of that type has a three-phase winding on the stator and a permanent magnet on the rotor. It is also made in single, dual, or three-phase variations. As was mentioned above, the stator winding creates a rotating magnetic field, which drives the magnetic rotor into motion. To form such magnetic field, a three-phase voltage is applied to the winding.
So how does the system know which coil is energized and which should be energized? For this purpose, a special electronic controller is used. Such integrated commutating device turn on current to orthogonal (perpendicular) windings. It also contains sensors that determine a rotor position. The most often hall sensors are used but sometimes photoelectrical, inductive sensors, and resolvers perform such tasks.
To change the direction of rotation, the controller changes connection of two phases. It also can work as stepper or servo motor.
Advantages and disadvantages of brushless DC motor
The main advantages of a brushless motor
- long service life;
- low noise level;
- high-efficiency indicators - about 90%;
- maximum rotation speed is achieved quickly;
- do not spark form during operation;
- additional cooling resources are not required;
- there are no mechanisms that need regular maintenance.
The main disadvantages of brushless motors
- complex management system;
- limited resource of electrical components;
- high price due to expensive components.
- need additional commutating devices to work (commutators, encoders, drives)
What is a brushed motor? How does it work?
Brushed motors are the most common DC motor. As noted above, its principle also consists in the attraction of two magnets with opposite poles.
The main parts of such motor are:
- Stator
- Rotor (armature)
- Brushes
- Commutator
Permanent or electrical magnets are placed on the stator and form a constant magnetic field. DC motors with electrical magnets are powered with the same dc source that armature.
Such motors can be of two main types:
- Shunt motors (with parallel connection)
- Serial motors (with serial connection)
Serial motors have a good start torque but its speed drops didactically with load. Opposite them, the parallel motors have worse start torque, but they can perform a constant speed irrespectively to acting load.
The rotor is connected to dc power source by brushes. Brushes are attached into commutator. Different windings are connected with different segments of such commutators. When they are energized, they create a magnetic field. When the rotor rotates, their magnetic fields change. This field switching is called commutation.
The current flows from the source to the windings, which as a result of the Lorentz law create a magnetic field and begin to interact with the magnets on the stator. The brushes (that made of generally of graphite) transfer power to the armature. To maintain their constant fit to the commutator, the springs exert pressure on them.
In the simplest mechanism with one loop of armature, an issue may happen when the armature becomes perpendicular to magnetic flux. In this case, its torque is equal to zero and the movement is interrupted for a short period. Therefore, for a smoother movement, additional loops are added to the design. The more of these loops, the smoother movement will be.
During the operation of such engines, Internal Electromotive (EMF) and Counter Electromotive (Back EMF) Forces often arise in accordance with the laws of Faraday and Lorenz. Because of this, a large amount of heat is generated. Therefore, in large and powerful motors, it is extremely needed to install additional cooling devices to avoid fire.
Pros and Cons of Brushed DC motor
The main advantages of brushed motors:
- low cost;
- simple design and wiring;
- easy maintenance;
- reliable to mechanical and vibration shocks.
The main disadvantages of brushed motors:
- brushes wear out quickly;
- have an electromagnetic noise;
- sparks form during operation;
- the mechanism overheats and smokes;
- low efficiency (about 60-80%);
- due to the high friction of the brushes, the service life is reduced.
Main applications. What is better?
Brushless motors, firstly, offer high performance and long life cycle. Such models are needed in areas where high rotation speed and resistance to overheating are required at the same time. Such equipment is used as part of the cooling system, in robotics, medical equipment, CNC machines, and other expensive and crucial industrial equipment. Brushless devices are more powerful than brushed ones with the same size. It is also used in areas when electric motors with a high lifespan and lack of maintenance are required.
The common brush dc motor has less power and stability. However, it is cheap and simple. Therefore, those devices perform not complicated and long-term tasks. Such equipment is used in the domestic sphere: in automobiles, hoisting mechanisms, in children's radio-controlled models, and some household tools (like a drill). They need regular maintenance due to brush friction and quick wear, but they are quite reliable to resistance in industrial harsh environments.
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