All electric motors are produced with plates on the housing, from which you can find out the main characteristics of the electric motor: its brand, rated power consumption, rotation speed, motor type, efficiency and cos(fi). This data is also indicated in the passport for the device.
Of all the parameters The most important factors for connection are: the power of the electric motor and the current consumed; this should not be confused with the starting current. It is these data that allow us to determine the sufficiency of power for the drive, the required cable cross-section for connecting the motor, and select the appropriate circuit breaker and thermal relay for protection.
But it happens that there is no passport or plate and to determine these values it will be necessary to make measurements. You will learn further in this article how to find out the power, operating current and reduce the starting current.
How to determine the power of an electric motor
The easiest way is to look at the plate and find the value in kilowatts. For example, in the picture it is 45 kW. Please note that this value on the plate indicates the active power consumed from the electrical network. The total power will be equal to the sum of active and reactive power. Electric meters in a house or garage count only the consumption of active electricity, and accounting is carried out only in enterprises using special meters. The higher the cos(fi) of an electric motor, the lower the reactive energy component of total power will be. Do not confuse cos(fi) with efficiency. This indicator shows how much electricity is converted into useful mechanical work, and how much into useless heat. For example, an efficiency of 90 percent means that a tenth of the electricity consumed is spent on heat losses and friction in the bearings.
You should keep in mind that the passport or plate indicates the rated power, which will be equal to this value only if the optimal load on the shaft is achieved. However, you should not overload the shaft for a number of reasons; it is better to choose a more powerful motor. At idle, the current will be much lower than the nominal value.
How to determine the rated power of an electric motor? On the Internet you will find many different formulas and calculations. For some, you need to measure the dimensions of the stator, for other formulas you will need to know the current value, efficiency and cos(fi). My advice is don't bother with all this. Practical measurements will still be better than these calculations. And you won’t need anything at all to carry them out.
How to determine the power of any electrical appliance in the house or garage? Of course, using an electricity meter. Before starting the measurement, unplug all electrical appliances from the sockets, lighting and everything connected to the electrical panel.
Further if you have an electronic meter like Mercury, everything is very simple, you just need to turn on the motor under load and drive for about 5 minutes. The electronic display should display the load value in kW currently connected to the meter.
If the engine is low power, then for higher accuracy you can count the disk revolutions. For example, in one minute it made 10 full revolutions, and the meter says 1200 revolutions = 1 kW/h. We multiply 10 by the number of minutes in an hour and get 600 revolutions per hour. Divide 1200 by 600 and we get 500 watts or 0.5 kW. The longer you measure, the more accurate the data will be. But the time must always be a multiple of a full minute. Then divide 60 by the number of minutes of measurement and multiply by the counted revolutions. After this, we divide the value of revolutions equal to one Kilowatt/hour for your electric meter model by the result obtained and obtain the required amount of power.
How to determine the current consumption of an electric motor
Knowing the power, you can easily calculate the amount of current consumed. For 3-phase motors connected in a 380-volt star configuration, it is necessary to multiply the power in kilowatts by 2. For example, with a power of 5 kilowatts, the current will be 10 Amperes. Again, keep in mind that the motor will take such current only under a load as close as possible to the nominal value. A semi-loaded electric motor, and even more so at idle, will consume significantly less current.
To determine the current in single-phase networks, it is necessary to divide the power by voltage. For example, when the engine is running, the voltage at its connection point is 230 Volts. This is important because after turning on the load, the voltage will most likely drop at the point where the electric motor is connected.
If, for example, the power of a 220 Volt motor was measured to be 1.5 kW or 1500 Watts. Divide 1500 by 230 Volts and we find that the operating current of the motor is approximately 6.5 Amperes.
Motor starting current
On startup of any type of electric motor, a starting current occurs from 2 to 8 times the value of the rated current in the operating mode of the electric motor. The magnitude of the starting current depends on the type of motor, rotation speed, connection diagram, presence of load on the shaft and other parameters. 
Starting current occurs because at the moment of startup a very strong magnetic field is induced in the windings, which is necessary to move and spin the rotor. When the motor is turned on, the resistance of the windings is low, and therefore, according to Ohm’s law, the current increases at a constant voltage in the circuit section. As the motor spins up, an emf or inductive reactance appears in the windings and the current begins to decrease to the rated value.
These bursts of reactive energy negatively affect the operation of other electrical consumers connected to the same power supply line, which causes the occurrence of voltage surges or surges that are especially destructive for electronics.
Reduce starting current by half This is possible by using a thyristor unit specially designed for this purpose, or better yet, using a soft start device (SPD). The UPD with a lower starting current starts the motor one and a half times faster compared to thyristor starting. 
Soft starters are suitable for both synchronous and asynchronous motors. UPZ are produced by enterprises in Ukraine and Russia.
To start a three-phase asynchronous motor Today frequency converters are also often used. Their widespread distribution is currently limited only by price. By changing the frequency of current and voltage, it is possible not only to make a smooth start, but also to regulate the speed of rotation of the rotor. There is no other way to regulate the rotation speed of an asynchronous motor by changing the frequency of the electric current. But you should know that the frequency converter creates interference in the electrical network, so use it to connect electronics and household appliances. 
Using a soft start device and a frequency converter allows you not only to maintain the stability of the power supply for you and your neighbors connected to the same power supply line, but also to extend the service life of electric motors.
Similar materials.
An electric motor is an electromechanical device based on electromagnetism, which allows the conversion of electrical energy, for example, into work or mechanical energy. This process is reversible and can be used to generate electricity. However, all these electrical machines are reversible and can be either a “motor” or a “generator” in the four quadrants of the torque plane.
Early developments
In 1821, after the discovery of the phenomenon of the connection between electricity and magnetism by the Danish chemist Oersted, Ampere's theorem and Biot-Savart's law, the English physicist Michael Faraday built two devices, which he called “electromagnetic rotation”: the continuous circular motion of the magnetic force around the wire is the actual demonstration of the first electric motor.
In 1822, Peter Barlow built what can be considered the first electric motor in history: the Barlow wheel. This device consists of a simple metal disk cut into a star, the ends of which are immersed in a cup containing mercury, providing a flowing stream. However, it only creates a force capable of turning it, preventing its practical use.
The first experimentally used commutator was invented in 1832 by William Sturgeon. The first commercially manufactured DC motor was invented by Thomas Davenport in 1834 and patented in 1837. These engines did not experience any industrial development due to the high cost of batteries at the time.
Electric motor with DC
A DC switched apparatus has a set of rotating windings wound around an armature mounted on a rotating shaft. The shaft also contains a commutator, a long-lasting rotary electrical switch that periodically changes the flow of current in the rotor windings as the shaft rotates. Thus, each DC bridge motor has alternating current passing through the rotating windings. Current flows through one or more pairs of brushes that are carried on the commutator; brushes connect an external power source to the rotating armature.
A rotating armature consists of one or more spools of wire wound around a laminated ferromagnetic core. The current from the brush flows through the commutator and one armature winding, making it a temporary magnet (electromagnet). The magnetic field produced by the armature interacts with the stationary magnetic field produced by either the PM or another winding (field coil) as part of the motor frame.
The force between the two magnetic fields tends to rotate the motor shaft. The commutator switches power to the coils as the rotor turns, keeping the magnetic poles from ever completely matching the stator's magnetic poles so that the rotor never stops (like a compass needle), but rather rotates as long as there is power.
Although most switches are cylindrical, some are flat disks consisting of several segments (usually at least three) mounted on an insulator.
Large brushes are desirable for a larger brush contact area, to maximize motor power, but small brushes are desirable for low mass, to maximize the speed at which the motor can operate without excessive kickback and brush sparking. Stiffer brush springs can also be used to produce brushes of a given mass at a higher speed, but at the expense of greater friction and wear on the accelerated brush and commutator. Therefore, DC motor design entails a trade-off between power output, speed, and efficiency/wear.
Design of DC motors:
- The valve circuit is a winding; it carries the load current, which can be a stationary or rotating part of an engine or generator.
- Field circuit - a set of windings that create a magnetic field so that electromagnetic induction can exist in electrical machines.
- Switching. A mechanical technique in which rectification can be achieved, or whereby direct current can be obtained.
There are four main types of DC motors:
- Electric motor with shunt winding.
- DC motor.
- Combined engine.
- Engine PM.
Basic calculation indicators
How to find out the power of an electric motor will be shown later in the article, using an example with initial data.
A good science project doesn't stop at building a power apparatus. It is very important to calculate the power of the electric motor and the various electrical and mechanical parameters of your device and calculate the formula for the power of the electric motor using unknown values and useful formulas.
To calculate the electric motor, we will use the International System of Units (SI). This is the modern metric system, officially adopted in electrical engineering.
One of the most important laws of physics is Ohm's fundamental law. He states that the current through a conductor is directly proportional to the applied voltage and is expressed as:
I=V/R
where I is current, in amperes (A);
V is the applied voltage, in volts (V);
R - resistance, in ohms (Ω).
This formula can be used in many cases. You can calculate the resistance of your motor by measuring the current drawn and the applied voltage. For any given resistance (in motors this is mostly coil resistance), this formula explains that the current can be controlled by the applied voltage.
The consumed electrical power of the engine is determined by the following formula:
Pin = I * V
where Pin is the input power, measured in watts (W);
I - current measured in amperes (A);
V is the applied voltage, measured in volts (V).
How to find out the power output
Motors are supposed to do some kind of work, and there are two important values that determine how powerful it is. This is the speed and turning force of the engine. The mechanical power output of the motor can be calculated using the following formula:
Pout = τ * ω
where Pout is the output power measured in watts (W);
τ - moment of force, measured in Newton meters (N m);
ω is the angular velocity measured in radians per second (rad/s).
ω = rpm * 2 * P / 60
where ω - angular velocity (rad/s);
rpm - rotation speed in revolutions per minute;
P is a mathematical constant (3.14);
60 is the number of seconds in a minute.
If the motor is 100% efficient, all electrical energy is converted into mechanical energy. However, such engines do not exist. Even precision small industrial motors have a maximum efficiency of 50-60%.
Measuring engine torque is a difficult task. This requires special expensive equipment. But it is possible to do this yourself with special information and formulas.
Mechanical efficiency indicators
Motor efficiency is calculated as the mechanical output power divided by the electrical input power:
E=Pout/Pin
hence,
Pout = Pin * E
after substitution we get:
T * ω = I * V * E
T * rpm * 2 * P / 60 = I * V * E
and the formula for calculating the moment of force will be:
T = (I * V * E * 60) / (rpm * 2 * P)
To determine the engine power, you need to connect it to a load to generate a torque. Measure current, voltage and RPM. You can now calculate the torque for this load at this speed, assuming you know the efficiency of the motor.
The 15 percent efficiency rating represents the engine's maximum efficiency, which only occurs at a certain speed. Efficiency can be anything between zero and maximum; in our example, below 1000 rpm may not be the optimal speed, so you can use 10% efficiency (E = 0.1) for calculations.
Example: speed 1000 rpm, voltage 6 V, and current 220 mA (0.22 A):
T = (0.22 * 6 * 0.1 * 60) / (1000 * 2 * 3.14) = 0.00126 N m
As a result, it is usually expressed in millinewtons times meters (mN m). 1000 mN m to 1 N m, so the calculated torque is 1.26 mN m. This could be further converted to (g-cm) by multiplying the result by 10.2, and. e. The torque is 12.86 g-cm.
In our example, the motor power input is 0.22 A x 6 V = 1.32 W, the mechanical power output is 1000 rpm x 2 x 3.14 x 0.00126 N m / 60 = 0.132 W.
The torque of the engine changes with speed. At no load, maximum speed and zero torque. Load adds mechanical resistance. The motor begins to draw more current to overcome this resistance, and the speed decreases. When this happens, the moment of force is maximum.
How accurate the torque calculation is is determined as follows. While voltage, current and speed may be measured accurately, motor efficiency may not be correct. This depends on the accuracy of your assembly, sensor position, friction, alignment of motors and generator axles, etc.
Speed, torque, power and efficiency are not constant values. Typically, the manufacturer provides the following data in special tables.
A linear motor is essentially an induction motor whose rotor is "turned" so that instead of producing a rotational force by a rotating electromagnetic field, it produces a linear force along its length by setting up a bias electromagnetic field.
Acoustic noise
Acoustic noise and vibration Electric motors usually arise from three sources:
- mechanical sources (for example, due to bearings);
- aerodynamic sources (for example, due to fans mounted on the shaft);
- magnetic sources (for example, due to magnetic forces such as Maxwell forces and magnetostriction acting on the stator and rotor structures).
The final source that may be responsible for noise from electric motors is called electrically excited acoustic noise.
Determination of electric motor power by shaft diameter. The use of electric motors has found its application not only in industry, but also in everyday life. An electric motor has many parameters, some of the important ones are power and electric current when connecting the motor. These parameters allow you to correctly select the diameter of the wiring required to power the motor, as well as automatic and relay protection. We’ll find out right now how to correctly determine the power of an electric motor, as well as how to find out the current.
In order to understand the power of the motor, as well as its current, it is enough to look at its passport, which contains all the technical characteristics, or at a special information plate pasted by the manufacturer on the electric motor at the time of its release. Moreover, it indicates the active power of the engine consumed from the electrical network.
All power consumption consists of both active power and the power of the reactive electric motor. For example, using home electric meters you can calculate the active electrical energy consumed. And when operating electric motors in industrial enterprises, control is exercised over reactive energy.
At home, we determine the power of an electric motor
This can be done through the use of an electricity meter. Before starting the measurement, you must turn off all electrical appliances from the network, including lighting, as well as equipment connected to the electrical panel, i.e. all electricity consumers must be turned off.
Turn on the electric motor and let it run under load for five minutes. Further measurements depend on the model of the electricity meter:
If the electricity meter is electronic, then the load will be determined in kW, which is currently connected to it;
If the meter is a disk induction model, it is metered in kW/h, and to measure power, you should record the last available meter readings and turn on the engine
For it to work for ten minutes. After turning it off, you need to find the difference in the readings and multiply the result by six, the resulting value expresses the active power of the electric motor.
To determine the electric current consumption of an electric motor you need to:
In single-phase electrical networks, you simply need to carry out mathematical calculations: divide the available power of the electric motor by a known voltage value;
In three-phase motors, you simply need to multiply the known power in kilowatts by two.
Turning on any electric motor is accompanied by the appearance of a starting current, the magnitude of which depends on the model of the electric motor, rotational speed and other indicators. The starting electric current occurs in order to push the rotor to spin it up.
At the moment of spin-up, inductive reactance appears, which leads to a decrease in the current value. Energy surges affect the operation of other electrical appliances that are powered from the same line and can contribute to the malfunction of electronics. Reducing the inrush current is achieved using special equipment. In this way, the power of the electric motor is determined and its current is known.
In addition, the use of special devices when starting electric motors contributes to their long operation.
Sometimes you have to face the need to determine engine power in the absence of a tag. For example, the relevant documents were lost, and the inscriptions on the device itself are impossible to read (they often wear out over time).
Meter measurements
The simplest option is to check the readings of a household electricity meter. First turn off absolutely all equipment that operates from the network (including lights), since otherwise the results will not correspond to reality. Make sure the meter is not spinning or flashing. Then record the readings, then turn on the engine and let it run for ten minutes. After turning off the device, take the results again. The difference between the first and last readings must be multiplied by six. The resulting number will be the power of the electric motor.
Tables
If you carefully search for information on the Internet, you will probably be able to find tables from which you can find out the type of motor and its power. However, for this you may need a large number of parameters, which you often have to measure yourself. Among them: shaft diameter, dimensions of fasteners, rotation speed, motor length, distance to the axis, flange diameter (in the case of a flanged motor).
Calculation by parameters
If necessary, the power of the electric motor can be obtained using arithmetic calculations. Doing them using a calculator is not difficult for anyone. You will need three parameters:
- the radius of the shaft (denoted by the letter A), which can be measured using a caliper;
- the number of shaft revolutions per second (denoted by the letter B);
- indicator of the draft force of the motor (denoted by the letter C).
The power of the electric motor will be equal to the number obtained by the formula: A*6.28*B*C.
Engine power is one of its most important characteristics. Without knowing it, it is impossible to select a thermal relay and circuit breaker with suitable parameters, or to determine the throughput and cross-section of suitable cables. Moreover, ignorance of the limit beyond which one cannot go during operation can lead to overloads and breakdowns.
There was a need to find out the power or shaft speed and other parameters of the electric motor, but after a careful inspection, there was no plate (nameplate) with its name and technical parameters on its body. You'll have to determine it yourself; there are several ways to do this, and we'll look at them below.
The power of an electric motor is the rate at which electrical energy is converted and is usually determined in watts.
To understand how this works, we need 2 quantities: current and voltage. Current strength is the amount of current that passes through a cross section over a certain period of time; it is usually determined in amperes. Voltage is a value equal to the work done to move a charge between two points in a circuit; it is usually determined in volts.
To calculate power, use the formula N = A/t, where:
N - power;
What about work;
Often the electric motor comes from the factory with technical parameters already specified. But the declared power does not always correspond to the actual one, and most likely it can only mean the maximum power of the electric flow.
So if your power tool indicates, for example, a power of 500 watts, this does not mean at all that the tool will consume exactly 500 watts.
Electric motors produce standard discrete power, such as 1.5, 2.2, 4 kW.
An experienced electrician can easily distinguish 1.5 from 2.2 kW just by looking at its dimensions. In addition, he will be able to determine the number of engine revolutions based on the stator size, number of pole pairs and shaft diameter.
A wrapper will be even more experienced in this matter; a specialist who rewinds electric motors will determine the technical parameters of your electric motor with 100% confidence.
If the motor rating plate is lost, to calculate the motor power, you need to measure the current on the rotor windings and use the standard formula to find the power consumption of the electric motor.
Basic methods for determining engine power
Determination of power by current. To do this, we connect the motor to the network and control the voltage. Then, one by one, we connect an ammeter to the circuit of each of the stator windings and measure the current consumed. After we have found the sum of consumed currents, the resulting number must be multiplied by a fixed voltage, as a result we get a number that determines the power of the electric motor in watts.
Determining power by size. You need to measure the diameter of the core (from the inside) and its length.
We multiply the synchronous speed of the shaft by the diameter of the core (in centimeters), multiply the resulting figure by 3.14, then divide it by the network frequency multiplied by 120. The resulting power value is in kilowatts.
Measuring by meter. The method is considered the simplest. To do this, for the purity of the experiment, we turn off all the loads in the house. Next, you need to turn on the engine for a certain time (for example, 10 minutes). On the brush, you can see the difference in kilowatts; from this you can easily calculate how many kilowatts the engine consumes. The most convenient way is to use a portable electric meter that shows consumption in kilowatts (watts) in real time.
To determine the real indicator of the power that the engine produces, it is necessary to find the shaft rotation speed, measured in the number of revolutions per second, and the engine tractive effort.
The rotational speed is multiplied sequentially by 6.28, an indicator of force and the radius of the shaft, which can be calculated using a caliper. The found power value is expressed in watts.
Determining the operating speed of the engine.
We determine power using calculation tables. Using a caliper, we measure the diameter of the shaft, the length of the motor (without the protruding shaft) and the distance to the axle. We measure the extension of the shaft and its protruding part, the diameter of the flange if there is one, as well as the distance of the mounting holes.
Using this data, using a pivot table, you can easily determine engine power and other characteristics