It is hard to imagine what the modern world would have looked like without a direct current electric motor (however, an alternating one too). Any modern mechanism is equipped with an electric motor. It may have a different purpose, but its presence, as a rule, is critically important. It is expected that in the near future the role of the DC motor will only increase. Already today without this device it is impossible to create high-quality, reliable and noiseless equipment with adjustable operating 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 the experiments in 1821, the famous scientist Faraday accidentally discovered that a magnet and a conductor with a current somehow act on each other. In particular, a permanent magnet can cause rotation of a simple circuit from a current conductor. The results of these experiments were used for further studies.
Already in 1833, Thomas Davenport created a model of a train with a small electric motor capable of driving it.
In 1838, a passenger boat with 12 seats was built in the Russian Empire. When this swimming vehicle with an electric motor went along the Neva against the tide, it caused a real explosion of emotions in scientific circles and not only.
How a DC motor works
If we consider the work superficially, as is done at school in physics lessons, then it might 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 the electric motor, a whole series of complex physical phenomena proceeds which are still not fully understood and are explained by various hypotheses and assumptions.
In a simplified embodiment, 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 introduced through it. Moreover, if we consider the cross section of the conductor, then invisible concentric circles of circumference appear around it - this is the 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 technique that allows you to visually observe them. The easiest way is to make a hole in plywood or in a thick sheet of paper through which the wire is passed. 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 a magnetic field.
Actually, the principle of operation of a direct current electric motor is based on this phenomenon. A current conductor is placed between the north and south poles of the 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 located, and can be precisely determined by the so-called “gimlet” rule.
Ampere Force
The force that pushes a conductor with current out of the field of a permanent magnet is called the Ampere force - by the name of a famous researcher of electrical phenomena. His name also bears the unit of current.
To find the numerical value of this force, you need to multiply the current strength in the conductor under consideration by its length and the magnitude (vector) of the magnetic field induction.
The formula will look like this:
F = IBL.
The simplest engine model
Roughly speaking, in order to build the most primitive engine, it is necessary to place a frame of conductive material (wire) in a magnetic field and power it with current. The frame will rotate a certain angle and stall. This position on the slang of experts in the field of 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 device of a DC motor 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, another frame takes it out of the “stupor”.
Features of the device engines of different power
Even a person who is far from the world of electrical engineering will immediately realize that without a constant magnetic field there is simply no question of any direct current electric motor. As such sources, a variety of devices are used.
For low-power DC motors (12 volts or less), the permanent magnet is the most ideal solution. But this option is not suitable for units of high power and size: magnets will be too expensive and heavy. Therefore, for DC electric motors of 220 V and more, it is more expedient to use an inductor (field winding). For an inductor to become a source of a magnetic field, it must be energized.
Motor design
In the general case, the design of any DC motor includes the following elements: manifold, stator and anchor.
An anchor serves as a supporting element for the winding of an electric motor. It consists of thin sheets of steel for electrical purposes with recesses 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 type of material is characterized by a large size of artificially grown grain 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 plays the role of a magnet, considered earlier. To demonstrate the operation of the engine model in laboratory conditions, a stator with two poles is used for clarity and a better understanding of the principles. In real industrial motors, devices with a large number of pole pairs are used.
A collector refers to 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.
Engine types
There is no one universal engine that would be used in absolutely all branches of technology and the national economy and satisfy all the requirements in the field of safety and reliability during operation.
You should be very responsible in choosing a DC motor. Repair is an extremely complicated and expensive procedure that can only be performed by specialists with the appropriate qualifications. And if the design and capabilities of the engine do not meet the requirements, then considerable money will be spent on repairs.
There are four main types of DC motors: collector, inverter, unipolar, as well as universal collector DC motors. Each of these types has its positive and negative qualities. A brief description of each of them should be given.
DC Brush Motors
There are a large number of possible ways to implement engines of this type: one collector and an even number of circuits, several collectors and several winding circuits, three collectors and the same number of turns of the winding, four collectors and two turns of the winding, four collectors and four circuits at 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 he was known as a universal engine, the application of which is very extensive: from toy cars in radio control to very complex and high-tech machine tools with program control of German or Japanese production.
About inverter motors
In general, this type of engine is very similar to a collector one and has the same advantages and disadvantages. The only difference is in the starting mechanism: it is more advanced, which allows you to easily reverse the speed and adjust the rotor speed. Thus, the operational characteristics of this type of direct current electric motor are superior to the collector motors in a number of parameters.
But if you win in something, then in some things you will definitely see a loss. This is the 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, the repair of inverter type DC motors is quite difficult. Sometimes even experienced electricians can not 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 current and 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 you can see, has a rather complicated design and therefore often fails. The main application is scientific research in the field of physics of electricity and electric drive.
Features of universal collector motors
Fundamentally, this type of engine does not carry anything new. But it has a very important feature - the ability to work both from a direct current network and from an alternating current network. Sometimes this property can save significant money on the repair and modernization of equipment.
The frequency of the alternating current is strictly regulated and is 50 Hz. In other words, the direction of movement of negatively charged particles changes 50 times per second. Some mistakenly believe that the rotor of the electric motor should change the direction of rotation (clockwise - counterclockwise) 50 times per second. If this were true, then there could be no talk of any useful application of AC electric motors. What happens in reality: the current of the armature and stator windings is synchronized using simple 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 a direct current electric motor of this type is much lower than that of inverter and unipolar motors. Therefore, its application 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 provisions
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 operational characteristics. The power of DC motors increases from year to year, while their energy consumption drops.
According to scientists, the future will be determined by electrical equipment, and the oil era will end soon enough.