It's hard to even imagine what the modern world would look like without a DC electric motor (and an AC one, by the way). Any modern mechanism is equipped with an electric motor. It can have a different purpose, but its presence, as a rule, is critical. It is expected that the role of the DC motor will only increase in the near future. Even today, without this device, it is impossible to create high-quality, reliable and silent equipment with adjustable speeds. But this is the key to the development of the state, and the world economy as a whole.
From the history of the DC motor
During experiments in 1821, the famous scientist Faraday accidentally discovered that a magnet and a current-carrying conductor somehowinfluence each other. In particular, a permanent magnet can cause the rotation of a simple current-carrying conductor circuit. The results of these experiments were used for further research.
Already in 1833, Thomas Davenport created a model train with a small electric motor capable of driving it.
In 1838, a passenger boat for 12 seats was built in the Russian Empire. When this electric motor-powered boat went against the current along the Neva, it caused a real explosion of emotions in the scientific community and not only.
How a DC motor works
If you look at the work superficially, as they do at school in physics lessons, it may seem that there is absolutely nothing complicated in it. But this is only at first glance. In fact, the science of electric drive is one of the most difficult in the cycle of technical disciplines. During the operation of an electric motor, a number of complex physical phenomena occur, which are still not fully understood and are explained by various hypotheses and assumptions.
In a simplified version, the principle of operation of a DC motor can be described as follows. A conductor is placed in a magnetic field and a current is passed through it. Moreover, if we consider the cross section of the conductor, then invisible force concentric circles arise around it - this is a magnetic field that is formed by the current in the conductor. As already mentioned, these magnetic fields are invisible to the human eye. But there is a simple trick that allows you to visually observe them. The easiest way is to make a hole in plywood or a thick sheet of paper through which to pass the wire. In this case, the surface near the hole must be covered with a thin layer of finely dispersed magnetic metal powder (fine sawdust can also be used). When the circuit is closed, the powder particles line up in the shape of the magnetic field.
Actually, the principle of operation of a DC motor is based on this phenomenon. A current-carrying conductor is placed between the north and south poles of a U-shaped magnet. As a result of the interaction of magnetic fields, the wire is set in motion. The direction of movement depends on how the poles are positioned, and can be precisely determined by the so-called gimlet rule.
Ampere Strength
The force that pushes a current-carrying conductor out of the field of a permanent magnet is called the Ampère force - after a famous researcher of electrical phenomena. The unit of current is also named after him.
To find the numerical value of this force, you need to multiply the current in the conductor under consideration by its length and by the magnitude (vector) of the magnetic field.
The formula will look like this:
F=IBL.
Model of the simplest engine
Roughly speaking, to build the most primitive engine, you need to place a frame of conductive material (wire) in a magnetic field and power it with current. The frame will rotate to a certain angle and stop. This position on the slang of specialists inarea of the electric drive is called "dead". The reason for the stop is that the magnetic fields are, so to speak, compensated. In other words, this happens when the resultant force becomes equal to zero. Therefore, the DC motor device includes not one, but several frames. In a real industrial unit (which is installed on equipment), there can be very, very many such elementary circuits. So, when forces are balanced on one frame, the other frame brings it out of the "stupor".
Features of the device of engines of different power
Even a person who is far from the world of electrical engineering will immediately realize that without a source of a constant magnetic field, there is simply no question of any DC electric motor. A variety of devices are used as such sources.
For low power DC motors (12 volts or less), a permanent magnet is the ideal solution. But this option is not suitable for units of large power and size: the magnets will be too expensive and heavy. Therefore, for DC motors of 220 V or more, it is more expedient to use an inductor (field winding). In order for the inductor to become a source of a magnetic field, it must be powered.
Electric motor design
In general, the design of any DC motor includes the following elements:collector, stator and armature.
The armature serves as a bearing element for the motor winding. It consists of thin sheets of steel for electrical purposes with grooves around the perimeter for laying the wire. The material of manufacture in this case is very important. As already mentioned, electrical steel is used. This grade of material is characterized by a large artificially grown grain size and softness (as a result of low carbon content). In addition, the entire structure consists of thin, insulated sheets. All this does not allow parasitic currents to occur and prevents overheating of the armature.
The stator is a fixed part. It performs the role of the magnet discussed earlier. To demonstrate the operation of a model motor in the laboratory, for clarity and a better understanding of the principles, a stator with two poles is used. Real industrial motors use devices with a large number of pole pairs.
A collector is a switch (connector) that supplies current to the winding circuits of a DC motor. Its presence is strictly necessary. Without it, the engine will run jerkily, not smoothly.
Varieties of engines
There is no one universal engine that would be used in absolutely all branches of technology and the national economy and meet all the requirements in the field of safety and reliability during operation.
You should be very careful when choosing a DC motor. Repair is extremely difficult and expensivea procedure that can only be performed by suitably qualified personnel. And if the design and capabilities of the engine do not meet the requirements, then significant funds will be spent on repairs.
There are four main types of DC motors: brushed, inverter, unipolar, and universal brushed DC motors. Each of these types has its own positive and negative qualities. A brief description of each of them should be given.
DC brushed motors
There are a large number of possible ways to implement motors of this type: one collector and an even number of circuits, several collectors and several winding circuits, three collectors and the same number of winding turns, four collectors and two winding turns, four collectors and four circuits on anchor, and finally - eight collectors with an anchor without a frame.
This type of engine is characterized by comparative simplicity of execution and production. It is for this reason that it has become known as a universal motor, the application of which is very extensive: from toy radio-controlled cars to very complex and high-tech machine tools with German or Japanese production.
About inverter motors
In general, this type of engine is very similar to the collector and has the same advantages and disadvantages. The only difference is in the launch mechanism: it is moreperfect, which allows you to easily reverse the speed and adjust the rotor speed. Thus, the performance of this type of DC motor is superior to collector motors in a number of parameters.
But if there is a gain in something, then in some things there will be a loss. This is an undeniable law of the universe. So in this case: superiority is provided by a rather complex and capricious technique, which often fails. According to experienced specialists, repairing inverter-type DC motors is quite difficult to carry out. Sometimes even experienced electricians cannot diagnose a malfunction in the system.
Features of unipolar DC motors
The principle of operation remains the same and is based on the interaction of the magnetic fields of the conductor with the current and the magnet. But the current conductor is not a wire, but a disk rotating on an axis. The current is supplied as follows: one contact closes on the metal axis, and the other, through the so-called brush, connects the edge of the metal circle. Such an engine, as can be seen, has a rather complex design and therefore often fails. The main application is scientific research in the field of physics of electricity and electric drive.
Features of universal commutator motors
In principle, this type of engine does not carry anything new. But it has a very important feature - the ability to work asfrom the DC network, and from the AC network. Sometimes this property can save a lot of money on the repair and modernization of equipment.
Alternating current frequency is strictly regulated and is 50 Hertz. In other words, the direction of movement of negatively charged particles changes 50 times per second. Some mistakenly believe that the rotor of an electric motor must also change direction of rotation (clockwise - counterclockwise) 50 times per second. If this were true, then any useful application of AC electric motors would be out of the question. What happens in reality: the current of the armature and stator windings is synchronized using the simplest capacitors. And therefore, when the direction of the current on the armature frame changes, its direction on the stator also changes. Thus, the rotor constantly rotates in one direction.
Unfortunately, the efficiency of this type of DC motor is much lower than that of inverter and unipolar motors. Therefore, its use is limited to rather narrow areas - where it is necessary to obtain maximum reliability at any cost, without taking into account operating costs (for example, military engineering).
Final clauses
Technology does not stand still, and today many scientific schools around the world compete with each other and strive to create a cheap and economical engine with high efficiency and performance. The power of DC electric motors is growing from year to year, while theirpower consumption.
Scientists predict that the future will be determined by electrical equipment, and the era of oil will end pretty soon.
