How to determine the main parameters of an electric motor? Selection of an electric motor based on the parameters of an existing one Determination of motor characteristics using tables

If the technical documentation for the engine is lost, and the inscriptions on the body are erased or unreadable, the question arises: how to determine the power of an electric motor without a tag? There are several methods that we will tell you about, and you will just have to choose the one that is most convenient in your case.

Practical measurements

The most accessible way is to check the readings of a household electricity meter. First, you should turn off absolutely all household appliances and turn off the lights in all rooms, since even a burning 40W light bulb will distort the readings. Make sure that the counter does not spin or the indicator does not blink (depending on its model). You are lucky if you have a Mercury meter - it shows the load value in kW, so you only need to turn on the engine for 5 minutes at full power and check the readings.

Induction meters record in kW/h. Record the readings before turning on the engine, let it run for exactly 10 minutes (it is better to use a stopwatch). Take new meter readings and find out the difference by subtraction. Multiply this figure by 6. The resulting result displays the engine power in kW.

If the engine is low-power, calculating the parameters will be somewhat more difficult. Find out how many revolutions (or pulses) are equal to 1 kW/h - you will find the information on the meter. Let's say it's 1600 rpm (or indicator flashes). If the meter makes 20 revolutions per minute when the engine is running, multiply this figure by 60 (the number of minutes in an hour). This turns out to be 1200 rpm. Divide 1600 by 1200 (1.3) - this is the engine power. The result is more accurate the longer you measure the readings, but a small error is still present.

Definition from tables

How to find out the power of an electric motor by shaft diameter and other indicators? On the Internet it is not difficult to find technical tables with which you can find out the type of motor and, accordingly, its power. You will need to clear the following settings:

• shaft diameter;
• its rotation frequency or number of poles;
• mounting dimensions;
• flange diameter (if the engine is flanged);
• height to the center of the shaft;
• motor length (without protruding part of the shaft);
• distance to the axis.

Calculation by number of revolutions per minute

Visually determine the number of stator windings. Use a tester or milliammeter to find out the number of poles - no need to disassemble the motor. Connect the device to one of the windings and rotate the shaft evenly. The number of needle deflections is the number of poles. Please note that the shaft rotation speed with this calculation method is slightly lower than the result obtained.

Determination by dimensions

Another way is to carry out measurements and calculations. Many of those who are interested in how to find out the power of a three-phase motor prefer it. You will need the following data:

• Core diameter in centimeters (D). It is measured from the inside of the stator. The length of the core is also required, taking into account the ventilation holes.

• Gross rotation frequency (n) and mains frequency (f).

Using them, calculate the polar division index. D multiplied by n and by Pi - let's call this reading A. 120 multiplied by f - this is B. Divide A by B.

Determination by the power produced by the engine

Here again you will have to arm yourself with a calculator. Find out:

• number of shaft revolutions per second (A);
• indicator of engine draft force (B);
• shaft radius © - this can be done using a caliper.

The electric motor power in W is determined using the following formula: Ax6.28xBxC.

Why do you need to know engine power?

Of all the technical characteristics of an electric motor (efficiency, rated operating current, speed, etc.), the most significant is power. Knowing the main data, you can:

• Select a thermal relay and automatic circuit breaker with suitable ratings.
• Determine the throughput and cross-section of electrical cables for connecting the unit.
• Operate the engine according to its parameters, avoiding overload.

We described how to measure the power of an electric motor in different ways. Use the one that is optimal in your case. Using any of the methods, you will select a unit that will best meet your requirements. But the most effective option, saving your time and eliminating the need to search for information and carry out measurements and calculations, is to keep the technical passport in a safe place and make sure that the data plate is not lost.

The most common type of industrial power plants are asynchronous electric motors. One of their most important parameters is the power of the electric motor, which, depending on the model, can vary widely. Power determines the type of power system to which the motor can be connected, as well as the type and performance of the equipment with which it will be interfaced. For this reason, without knowing the power of the electric motor, it is almost impossible to use it.

Determining the power of an electric motor by the size of the stator core

If there is no technical passport, you can calculate the power of the electric motor based on the dimensions of the stator core and the rotation speed. To do this, use the formula P 2H = C * D 1 2 / N 1 * 10 -6 kW. Here:
C—constant power;
D is the size of the internal diameter of the stator core in cm;
l is the stator length in cm;
N 1 - value of synchronous rotation speed in rpm.

Constant power depends on the speed and dimensions of the motor. It is determined by the value of the pole division as the dependence of power on the number of poles and the size of the pole division τ, if U1< 500В.

τ = πD 1 / 2р cm.
2p here is the number of poles in the motor.

The result obtained using this formula must be rounded to the most appropriate value in the table. This is the simplest and most accessible method by which the power of an electric motor can be calculated.

Selection of the required electric motor power

Correctly selected electric motor power allows you to obtain optimal technical and economic indicators of the electric drive in terms of cost, size, efficiency and other parameters. With a stable load on the electric motor, its power can be determined simply by selecting from the catalog, based on the ratio P n ≥ P load. Here P n is the power of the selected engine, and P load is the expected load power.

Electric motor power consumption

Figure 1. Label with parameters on the motor housing When working with electric motors, you need to know how the power consumption of the electric motor is determined from the nameplate. The power value P is not the electrical power of the motor, but the mechanical power on the shaft, indicated in kW.

To find the power consumption, you need to pay attention to the efficiency and cosφ of the motor indicated on the nameplate. Moreover, efficiency can be designated either simply by the letters efficiency, or by the letter η, as can be seen on the nameplate. First, you need to find the active power consumed by the motor from the network using the formula P a = P / efficiency.

That is, in our case (Fig. 1), the active power consumed by the electric motor from the network is equal to P a = 0.75 kW/0.75 = 1 kW. Now, to find the total power consumption, you need to use the formula S = P a /cosφ = 1/0.78 = 1.28 kW.

Electric motor power factor

Motor power factor, or cos φ, is the ratio of active to apparent motor power. The power factor of the electric motor is determined by the formula cosφ = P/S. Here:
P - active power in W;
S is the apparent power in VA.

In most cases, active power is less than apparent power, causing the coefficient to be less than unity. Only when the load is exclusively active will cosφ become equal to unity.

The lower the consumer's power factor, the more powerful the transformers, power stations, and supply power lines must be. In addition, motors with a low coefficient have lower efficiency and higher energy losses.

An electric motor is an electromechanical converter in which electricity is converted into mechanical energy, the final effect of which is the release of heat. An electric motor is necessary for the operation of all electric machines. To select such a motor, you need to take into account all the parameters of the device and its characteristics, since these indicators are necessary to determine the purpose of the motor and the load on it through the network. This completely determines the durability and quality of the electric machine.

Content

Components of an electric machine

The basis for an electric machine is the rule of electrical induction with magnetic induction. Such a device includes a stator or, as it is called, a constant part (typical for asynchronous, synchronous machines of variable current) or an inductor (for devices of constant current) and a rotor, it is called an active or moving part (for asynchronous and synchronous machines of variable current) or an armature (constant current devices). Magnets (of a constant state) are actively used as a constant part for current machines with low power.

Motor power

Electrical power is a physical quantity that is characterized by the rate of transformation or transmission of electrical energy. To make it easier to understand, electricians imagine the movement of current as the movement of liquid through a pipe, and voltage as the difference in the position of the tiers of this liquid. Electricity, while carrying out work, moves from high to low power, just like liquid. This means that electrical power is the amount of work that is done in 1 second, or the speed at which the work itself is performed. The sum of the electric current that passes through the cross section of the circuit for one second is the current strength in the circuit itself.

It follows that electrical power is equal in proportion to the voltage and current in the circuit. To determine the current power, the unit used is the watt, abbreviated as W.
For physical calculations, it was customary to use the standard formula N=A/t, where N is power, A is work, t is time.
There are many variations of this formula with different letter symbols.

Determine engine power

If you constantly use electric machines, you have often come across nameplates that, in fact, indicate all the characteristics, including power options. If you look at the image of the nameplate, you can see the power value among the different parameters. As you can see, against the inscription the maximum power is 1000 W. But this is not its electrical power, as the consumer often thinks.

The label below shows the maximum permissible electrical current. They often write the recommended power on the nameplate and designate it in kilowatts.

So, how is it possible to calculate the usable power of a specific motor from its own electrical network. To do this, you need to look at other indicators on the same nameplate of the device under study - these are efficiency and cosφ. Where efficiency is sometimes denoted by the abbreviation efficiency, or the letter η. First, you need to take into account the relationship between the useful power of the mechanics on the shaft and efficiency. Having these values, you can easily calculate the power consumed by the engine from the electrical network. We find out by the relationship: Ra=P/η. But these are not results yet. It must be remembered that electrical appliances consume both active and reactive energy from the network. When calculating the total power used by the engine, it is necessary to obtain the ratio from the power triangle.

How to determine the power of an electric motor

So, let's move on to the options. Namely, to determine the power of the electric motor:

• by current. We connect the motor to an electrical network with a certain load (voltage). Alternately connecting an ammeter to each coil in our sequence, we measure the operating electric current of the engine in amperes. We determine the amount of currents obtained as a result of current measurements. We multiply the amount by the voltage indicator, and as a consequence - the consumed power of the electric engine in watts;
• by size. We determine the endomentricular caliber of the core of the fixed part, its length together with the ventilation channels in centimeters. We find out the frequency of changing current in the network to which a certain electric motor is connected and the simultaneous rotation frequency of the shaft. To determine the constant separation, we reproduce the core caliber by the simultaneous repetition of the shaft and multiply by 3.14 and in the same order divide by 120 (3.14 D n/(120 f)) and the network repeatability. Thus, we learned the division of the device, characterized as polar. We find how many poles, multiplying the frequently encountered repetition rate of the network electricity by 60, and divide the resulting number by the repetition rate of the shaft revolution. We multiply the taken values ​​by two. Based on the solution, we look in the table “determining the dependence of a constant engine C on the number of poles” and find our number to be constant. We multiply the resulting constant by the squared core caliber, its simultaneous rotation frequency and length. We multiply the resulting number by 10^(-6) (P = C D² l n 10^(-6)). Defined the value of electrical power in kilowatts;
• power produced by the electric motor. We find the rotation speed of the shaft of the device under study using a tachometer in rotations per second. Then we take a dynamometer and determine the traction force of the electric motor. And as a result, to determine the power in watts, we multiply the speed by 6.28, also by the force and radius of the shaft, the latter we measure with a ruler.

Note! For each motor there is a network for a certain number of phases. An example is a three-phase motor, which is designed only to be powered from a three-phase alternating current network.

Let's look at 5 popular methods how to calculate car engine power using data like:

• engine speed,
• engine volume,
• torque,
• effective pressure in the combustion chamber,
• fuel consumption,
• injector performance,
• machine weight
• acceleration time to 100 km.

Each of the formulas that will be used to produce engine power calculation the car is quite relative and cannot determine with 100% accuracy the real horsepower of the driving car. But by making calculations for each of the above garage options, based on one or another indicator, you can calculate, at least, the average value, whether it’s a stock or a tuned engine, literally with 10 percent error.

Power- the energy generated by the engine is converted into torque on the output shaft of the internal combustion engine. This is not a constant value. Next to the maximum power values, the speed at which it can be achieved is always indicated. The maximum point is reached at the highest average effective pressure in the cylinder (depending on the quality of filling with fresh fuel mixture, combustion completeness and heat losses). Modern engines produce the greatest power on average at 5500–6500 rpm. In the automotive industry, engine power is measured in horsepower. Therefore, since most results are displayed in kilowatts, you will need

How to calculate power through torque

The simplest calculation of car engine power is possible determine by the dependence of torque and revolutions.

Torque

The force multiplied by the leverage of its application, which the engine can produce to overcome certain resistance to movement. Determines how quickly the motor reaches maximum power. Calculation formula for torque based on engine volume:

Micro = VHxPE/0.12566, Where

• VH – engine displacement (l),
• PE – average effective pressure in the combustion chamber (bar).

Engine speed

Crankshaft rotation speed.

The formula for calculating the power of an internal combustion engine of a car is as follows:

P = Mkr * n/9549 [kW], Where:

• Mcr – engine torque (Nm),
• n – crankshaft speed (rpm),
• 9549 is a coefficient so that the revolutions can be substituted in rpm, and not in alpha cosines.

Since according to the formula, we get the result in kW, then, if necessary, you can also convert to horsepower or simply multiply by a factor of 1.36.

Using these formulas is the easiest way to convert torque to power.

And in order not to go into all these details, a quick calculation of the power of an internal combustion engine online can be done using our calculator.

If you do not know the torque of your car’s engine, then to determine its power in kilowatts you can also use a formula of this type:

Ne = Vh * pe * n/120(kW), where:

• Vh - engine volume, cm³
• n - rotation speed, rpm
• pe is the average effective pressure, MPa (for conventional gasoline engines it is about 0.82 - 0.85 MPa, for forced ones - 0.9 MPa, and for diesel engines from 0.9 and to 2.5 MPa, respectively).

To obtain engine power in “horses” rather than kilowatts, the result should be divided by 0.735.

Calculation of engine power based on air flow

The same approximate calculation of engine power can be determined by air flow. The function of such a calculation is available to those who have an on-board computer installed, since it is necessary to record the flow rate when the car engine, in third gear, is spun up to 5.5 thousand revolutions. We divide the resulting value from the mass air flow sensor by 3 and get the result.

Gw [kg]/3=P[hp]

This calculation, like the previous one, shows gross power (bench test of the engine without taking into account losses), which is 10-20% higher than the actual one. It is also worth considering that the readings of the mass air flow sensor are highly dependent on its contamination and calibrations.

Calculation of power by weight and acceleration time to hundreds

Another interesting way to calculate engine power using any type of fuel, be it gasoline, diesel or gas, is by acceleration dynamics. To do this, using the weight of the car (including the pilot) and acceleration time to 100 km. And in order for the Power Calculation Formula to be as close to the truth as possible, it is also necessary to take into account slipping losses depending on the type of drive and the speed of reaction of different gearboxes. The approximate loss at start for front-wheel drive will be 0.5 seconds. and 0.3-0.4 for rear-wheel drive cars.

Using this internal combustion engine power calculator, which will help determine the engine power based on the dynamics of acceleration and weight, you can quickly and accurately find out the power of your iron horse without delving into the technical characteristics.

Calculation of internal combustion engine power based on injector performance

An equally effective indicator of the power of a car engine is. Previously, we looked at its calculation and relationship, therefore, it will not be difficult to calculate the amount of horsepower using the formula. The estimated power is calculated according to the following scheme:

Where, the load factor is no more than 75-80% (0.75...0.8), the mixture composition at maximum performance is somewhere around 12.5 (rich), and the BSFC coefficient will depend on what kind of engine you have, naturally aspirated or turbocharged (atmo - 0.4-0.52, for turbo - 0.6-0.75).

Having found out all the necessary data, enter the indicators into the appropriate cells of the calculator and by clicking the “Calculate” button you will immediately receive a result that will show the real engine power of your car with a slight error. Please note that you do not necessarily need to know all the parameters presented; you can clear the power of the internal combustion engine using a separate method.

The value of the functionality of this calculator lies not in calculating the power of a stock car, but if your car has been tuned and its weight and power have undergone some changes.

Electric motors have long been included in various gearmotors. They find their application in both three-stage type MTs3U and two-stage type MTs2U. Electric motors have almost 90% efficiency and do not require constant maintenance. An important parameter is the exceptional environmental friendliness of the electric motor; there are no harmful emissions at all, which makes it indispensable for indoor installation. In short, electric motors are currently recognized as 3 or even 4 times more efficient than traditional internal combustion engines.

But sometimes, in the event of an electric motor failure, the buyer finds out that absolutely no accompanying documentation is attached to it. Marking nameplates, even if they have been preserved, may be in a worn-out, shabby state, so that it is simply impossible to see anything on them. How, then, can you determine the engine power and its speed? Here are some step-by-step tips to help you do this.

It should be borne in mind that the number of revolutions refers to the so-called asynchronous speed. Synchronous speed is the speed of rotation of the magnetic field. Asynchronous speed is slightly lower than synchronous due to the presence of mass in the rotating element, as well as the influence of friction forces, which can significantly reduce the efficiency of the motor. However, in practice these differences are almost never of decisive importance.

There are currently 3 main categories of asynchronous electric motors on the market. The first category of the catalog is motors operating at 1000 rpm. In practice, this number is about 950-970 revolutions, but for clarity, it is still rounded to the nearest thousand. The second category is motors producing 1500 rpm. This is also rounded as the actual range is 1430-1470. The third is 3000 rpm. Although in reality such a motor produces 2900-2970 rotations.

Methods for determining the characteristics of an electric motor.

To determine which of these groups the engine belongs to, you do not need to disassemble it, as some experts advise, in order to secure a work order. The fact is that disassembly of an electric motor can only be carried out by a sufficiently qualified master. In fact, it is enough to open the protective cover (another name is the bearing shield) and find the winding coil. There may be several such coils, but one is enough. If a coupling half or pulley is attached to the shaft, you will also need to remove the lower shield.

If the coils are connected using parts that interfere with viewing the information, these parts must not be disconnected under any circumstances. You need to try to determine by eye the ratio of the size of the coil and the stator.

The stator is the stationary part of the electric motor, while the moving part is called the rotor. Depending on the design features, either the coil itself or magnets can act as a rotor.

If the coil covers half of the stator ring, such an engine belongs to the third group, that is, it is capable of delivering up to 3000 revolutions. If the size of the coil is a third of the size of the ring, this is a motor of the second type; accordingly, it is capable of developing 1500 rpm. Finally, if the coil only covers a quarter of the ring, it is type 1. The electric motor develops a power of 1000 rpm.

There is another way to determine the rotation speed of the rotor shaft. To do this, you also need to remove the cover and find the upper part of the winding. The location of the winding sections determines the speed. Typically the outer section occupies 12 slots. If you count the total number of slots and divide by 12, you can get the number of poles. If the number of poles is 2, the motor has a rotation speed of about 3000 rpm. If there are 4 poles, this corresponds to 1500 rpm. If 6, then 1000 rpm. If 8, then 700 rpm.

The third way to determine the number of revolutions is to carefully examine the tag on the engine itself. The number on the marking at the end corresponds to the number of poles. For example, for marking AIR160S6, the last digit 6 indicates how many poles the coil uses.

The easiest way to measure the speed is with a special tachometer. But due to the narrow specialization of application, this method cannot be considered as generally available. Thus, even if no technical documentation has been preserved, there are at least 4 ways to determine the speed of an electric motor.