Main dimensions of electric motors. How to determine the power and speed of an asynchronous electric motor from the stator winding How to find out the power and speed of an electric motor

Most often, the engine power is indicated in the technical data sheet for the device and is duplicated on the case, where there is a special sticker or strip with the main technical parameters.

However, it often happens that the data on the case is not readable, and the technical passport has long been lost.

How, then, can we find out the power parameters of the electric motor?

Definition by meter:

If there are no markings on the body of the electric motor, you can calculate its power in several ways. The simplest method is to calculate using an electricity meter: you will need to disconnect all other devices from this device, connect the electric motor and run it under load for 5-7 minutes. Most modern meters provide a load indicator in kilowatts, and the resulting indicator will be the result of the claim.

Calculation using tables:

Another way to determine motor power is to calculate using data from tables. To do this, you will need to measure the diameter of the shaft, the length of the motor without taking into account the protruding part of the shaft, as well as the distance to the axis. Using these parameters, you can find out which series this motor belongs to and find its technical characteristics, including power. On the Internet you can find technical tables for DC and AC motors, where you can easily find the type of device and its power based on the value found.

Calculation by dimensions:

This method requires the following steps:

• Measure the diameter of the core in the stator along the inside, as well as the length taking into account the ventilation holes. The value is expressed in centimeters.
• Calculate the frequency of the network to which the electric motor is connected and the synchronous frequency of the shaft rotation.
• Find out the pole division indicator: for this purpose, the core diameter is multiplied by the synchronous shaft speed, and the found value is multiplied by 3.14 and divided by the network frequency multiplied by 120.

Formula for calculating pole constant value:

• Find the number of poles by multiplying the current frequency by 60 and dividing by the shaft rotation frequency.
• Multiply the found number by 2, then refer to the table for determining the dependence of the constant on the number of poles and identify the corresponding indicator.
• The found constant value is multiplied by the square of the core diameter, the length and the shaft rotation speed, after which the result is multiplied by the formula below:

The found value is expressed in kW.

Calculation of power produced by an electric motor.

To calculate the real power indicator with which the electric motor operates, it is necessary to find the shaft rotation speed, expressed in the number of revolutions per second, the traction force of the motor. 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.

Determine the current consumption:

For those who need to know not only the power, but also the amount of current consumed, there are also several ways to obtain such data. For each of them, an important criterion in the determination process is the number of phases.
If you have a single-phase network, divide the power rating by the voltage value.
If the motor is 3-phase, the calculation scheme is even simpler: double the power value - this will be the indicator in Amperes.

As you have seen, it is quite simple to find out the motor power and current consumption, even if this data is lost. Choose the easiest way for you to solve the problem and let your equipment always work properly and have high efficiency!

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 corresponding 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.

Table 4

This section of calculations must be completed by indicating the selected electric motor. For example: “Electric motor selected 4A 112M4 UZ GOST 19523-81 with power Р motor = 5.5 kW with synchronous motor shaft speed n dv = 1500 rpm.

2.2. Determination of gear ratio

After selecting the electric motor, determine the gear ratio

(2.6)

Where n dv - engine shaft rotation speed under load (asynchronous);

n 1 =n dv / u o.p. – rotation speed of the input (high-speed) shaft of the gearbox;

n 2 =n out – rotation speed of the output (low-speed) shaft of the gearbox.

The gear ratio must be consistent with the standard value given in Table 5; in this case the deviation Δ u, according to GOST, should not exceed 4% for cylindrical gears and 2.5% for bevel gears.

. (2.7)

Table 5

Standard gear ratios u according to GOST 2185-66

Note. The 1st row is preferable to the 2nd.

If the error exceeds the standard value, then you should accept an engine of the same power, but with a different rotation speed, or change the open gear ratio (within acceptable limits) and repeat the calculations.

2.3. Determination of power and torque on shafts

Gearbox input shaft rotation speed n 1 =n dv / u o.p.

The rotation speed of the gearbox output shaft is determined taking into account the accepted standard gear ratio u st

The powers (kW) transmitted by the shafts are determined taking into account the efficiency of the constituent links of the kinematic chain (see Fig. 4):

R 1 = R dv ∙ η op ∙ η P

R 2 = R 1 ∙ η salary ∙ η P ∙η m (2.8)

Torques (N∙m) on the gearbox shafts can be determined by the following dependencies:

for input shaft -
, (2.9)

for output shaft -

(2.10)

Where T i– torque transmitted by the shaft, N. m;

[τ cr]– permissible torsional stresses;[ τ cr]=15…20 MPa.

The obtained values ​​of the diameters of the gearbox shafts should be rounded to the nearest larger value from the range of normal linear dimensions according to GOST 6636-69. For the convenience of further calculations, the found gearbox parameters are summarized in the table:

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

1.1 kW

1.5 kW

• When you receive an electric motor for repair with a missing plate, you have to determine the power and speed by the stator winding. First of all, you need to determine the speed of the electric motor. The easiest way to determine the speed in a single-layer winding is to count the number of coils (coil groups).

• According to the table, single-layer windings have 3000 and 1500 rpm. the same number of coils, 6 each, you can visually distinguish them by their step. If a line is drawn from one side of the coil to the other side, and the line passes through the center of the stator, then this is a 3000 rpm winding. drawing No. 1. Electric motors have a 1500 rpm step less.

How to determine the power of an asynchronous electric motor.

• To determine the power of an electric motor, you need to measure the height of the axis of rotation of the electric motor shaft, the outer and inner diameter of the core, as well as the length of the engine core and compare it with the dimensions of electric motors of the unified series 4A, AIR, A, AO...

• Linking rated powers with installation dimensions of 4A series asynchronous electric motors: