A magnet has N pole and S pole, cut in half in the middle, it becomes two magnets, also has N pole and S pole, that is, smash it into countless particles, each particle has N pole and S pole. Magical or not? A static thing, as if it has become a living dynamic! When the N pole and the S pole are close, they will attract each other. When the N pole and the N pole are close, they will repel each other. This is common sense from childhood, and nature is really charming!
What’s even more amazing is that a short circuit will occur when a wire is connected to a DC power supply. If a wire is wound into a spiral shape and connected to a DC power, the wound coil will not be short-circuited, but will also form an electromagnet , also has N pole and S pole. The N pole and S pole can be jointly determined by the winding direction and the current direction. If any condition changes, the direction of the electromagnet will change.
Once the winding is wound, it is not easy to change, but the current direction can be changed very easily, that is to say, the polarity of the electromagnet can be changed at any time by changing the current direction.
What will happen if the wound coil (as shown in the picture) is placed in the middle of the fixed permanent magnet, and direct current is applied to the wound coil?
The coil will turn! Congratulations, you got it right, the coil will turn. Why go where? The reason is that the same poles repel each other and opposite poles attract each other. If the current direction is continuously changed, the polarity of the coil will continue to change. In this case, the wound coil will continue to rotate. Weld a shaft for him, and install a small fan blade on the shaft. In summer, can you enjoy the shade!
Some people say how does this look like a motor? Congratulations, you got it right again! This is the primary model of a DC motor (permanent magnet type), the thing that changes the direction of the current is the commutator of the coil, and the two poles connected to the power supply are called the carbon brush of the DC motor.
In addition to the permanent magnet type, DC motors also have separate excitation and self-excitation, among which self-excitation is further divided into shunt excitation, series excitation and compound excitation, but no matter which one is, they are all evolved from the DC motor model, but each It has its own characteristics and uses different occasions, which will be discussed in the future.
Is there a three-phase power supply? No! Is there a rotating magnetic field? No! This is the biggest difference between DC motors and AC motors.
Some people ask, why do you say this today? I did experiments when I was in high school, because I found that the frequency of using low-power DC motors is too high now, and it may be higher in the future, so this is an expansion of the field! Because of its convenience, many electric tools and appliances are driven by DC motors. Household sweepers, electric toothbrushes, etc. are also important applications of DC motors.
DC motors are also relatively easy to damage, especially the brushes and commutators, which have poor overload capacity and high starting current. This is also the disadvantage of DC motors. If you understand the principle, you must know how to check and deal with them, and you should know how to maintain them.
