How to calculate the wire cross-section for a transformer. Methods for calculating various transformer configurations. Parameter determination steps

Very often, a step-down transformer is required to power amateur radio designs or to power finished devices. Exact calculation power transformer is very complex, but for an approximate calculation you can use simplified formulas. In this article we will look at how to calculate a transformer assembled on the most common magnetic core made of W-shaped plates.

To calculate the transformer, we need to know: the desired voltage on the secondary winding and the load current. If the load current is unknown, but its power is known, then calculating the current is not difficult - you need to divide the power by the voltage on the secondary winding.

1. Calculation of the secondary winding current

I2 = 1.5*Iн, Where

• I2 - current in the secondary winding, A,
• In—load current, A.

2. Determination of power consumed from the secondary winding

P2 = U2*I2, Where

• P2 - power of the secondary winding, W,
• U2 - voltage of the secondary winding, V,
• I2 - secondary winding current, A.

If several secondary windings are needed, then we count the power of each winding, and then add up the powers of all secondary windings and substitute them into the following formula.

3. Determination of transformer power

Pt = 1.25*P2, Where

• RT - total power of the transformer, W,
• P2 - power of the secondary winding, W.

4. Calculation of the primary winding current

I1 = Pt/U1, Where

• I1 - current in the primary winding of the transformer, A,
• Pt—transformer power, W,
• U1 is the voltage of the primary winding, V.

5. Determination of the required cross-section of the magnetic core

S = 1.3* √ Pt, Where

• ² ,

It should be noted that the magnetic core must be selected so that the ratio of the width of the core (central plate) of the magnetic core to the thickness of the set is within 1 ÷ 2.

6. Calculation of the number of turns in the primary winding

W1 = 50*U1/S, Where

• W1 - number of turns of the primary winding, pcs.
• U1 - primary winding voltage, V,
• S – cross-sectional area of ​​the magnetic core, cm ² .

7. Calculation of the number of turns in the secondary winding

W2 = 55* U2/S, Where

• W2 - number of turns of the secondary winding, pcs.
• U1 - voltage of the secondary winding, V,
• S – cross-sectional area of ​​the magnetic core, cm ² .

8. Determination of the diameters of the wires of the transformer windings

d = 0.632*√ I, Where

• d—wire diameter, mm,
• I is the winding current, A (we substitute I1 and I2 for the primary and secondary windings, respectively).

The calculation is given for copper wire.

9. Checking the occupancy of the magnetic circuit windows

After selecting the magnetic circuit plates, you should check whether the wire will fit on the transformer frame.

So = 50*Pt, Where

• So is the area occupied by wound wires in one window of the magnetic circuit, mm 2,
• Pt — transformer power, W.

If the window area of ​​the selected magnetic circuit is greater than or equal to the calculated one, then the wire will fit.

The magnetic circuit plates must be assembled side by side, as shown in the figure above.

The magnetic core should be secured with a clip or studs with nuts; the studs should be wrapped in paper or other insulating material so that the studs do not short the plates. If the magnetic circuit is poorly tightened, it will hum.

The wires should be wound evenly and tightly (otherwise they may not fit). Between each row you need to lay thin paper or lavsan film in 1-2 layers and 3-4 layers between the windings.

For ease of winding, you can make a simple device, shown in the figure:

The device consists of two plywood racks fixed on a common base and a metal rod inserted into them, curved at one end in the form of a handle. With one hand we turn the handle, with the other we guide the wire; the spool of wire can be placed on another rod, but without the handle.

When designing transformers, the main parameter is its power. It is this that determines the dimensions of the transformer. In this case, the main determining factor will be the total power delivered to the load:

For transformer with big amount of the secondary windings, the total power can be determined by summing the powers consumed by the loads connected to all its windings:

(2)

With a completely resistive load (no inductive or capacitive components in the current), the power consumption is active and equal to the power output S 2. When calculating a transformer, an important parameter is the typical or overall power of the transformer. In addition to the total power, this parameter takes into account the power consumed by the transformer from the network through the primary winding. The typical transformer power is calculated as follows:

(3)

Let us determine the typical power for a transformer with two windings. Total power of the primary winding S 1 = U 1 I 1 where U 1 , I 1 - effective values ​​of voltage and current It is this power that determines the dimensions of the primary winding. In this case, the number of turns of the primary winding of the transformer depends on the input voltage, the cross-section of the wire depends on the maximum current flowing through it (rms value). The overall power of the transformer determines the required core cross-section s c. It can be calculated as follows:

(4)

The voltage on the primary winding of the transformer can be determined from the expression U 1 = 4k f W 1 fsB m, where s is the cross-sectional area of ​​the magnetic core, defined as the product of the core width and its thickness. The equivalent cross-sectional area of ​​a transformer core is usually smaller and depends on the thickness of the plates or tape and the distance between them, therefore, when calculating a transformer, the core fill factor is introduced, which is defined as the ratio of the equivalent cross-sectional area of ​​the magnetic core to its geometric area. Its value is usually equal to k c = 1 ... 0.5 and depends on the thickness of the tape. For extruded cores (made from ferrite, alsifer or carbonyl iron) k c = 1. Thus s = k c s c and the expression for the voltage of the primary winding of the transformer takes the following form:

U 1 = 4k f k c W 1 fs c B m(5)

A similar expression can be written for the secondary winding. In a transformer with two windings, the power of the primary winding and the typical power of the transformer are equal. The power of the primary winding can be determined by the following expression:

U 1 = U 1 I 1 = 4k f k c fs c B m W 1 I 1 (6)

In this case, the typical power of the transformer will be calculated using the following formula:

(7)

The ratio of the current in the winding wire to its cross-section is called the current density. In a correctly calculated transformer, the current density in all windings is the same:

(8) where s obm1, s obm2 - cross-sectional area of ​​the winding conductors.

Let's replace the currents I 1 = js obm1 and I 2 = js exchange2, then the sum in brackets of expression (7) can be written as follows: W 1 I 1 + W 2 I 2 = , j(s obm1 W 1 + s obm2 W 2) = js m, where s m - cross-section of all conductors (copper) in the window of the transformer core. Figure 1 shows a simplified transformer design, where the core area is clearly visible s s, area of ​​the magnetic circuit window s ok and the area occupied by the conductors of the primary and secondary windings s m.

Figure 1 Simplified transformer design

Let us introduce the coefficient of filling the window with copper. Its value is within k m = 0.15 ... 0.5 and depends on the thickness of the wire insulation, the design of the winding frame, interlayer insulation, and the method of winding the wire. Then js m = jk m s ok and the expression for the typical power of the transformer can be written as follows:

(9)

From expression (9) it follows that the typical power is determined by the product s With s OK. When increasing linear size transformer by m times, its volume (mass) will increase by m³ times, and its power will increase by m 4 times. Therefore, the specific weight and dimensions of transformers improve with increasing rated power. From this point of view, multi-winding transformers are preferable to several two-winding ones.

When developing the design of transformers, they try to increase the fill factor of the core window with windings, since this increases the value of the rated power S type. To achieve this goal, winding conductors with a rectangular cross-section are used. It should be noted that in practical calculations, formula (9) is transformed to a more convenient form.

(10)

When calculating a transformer for a given load power, based on expression (10), the product is determined s With s OK. Then, using the directory, select specific type and the size of the magnetic core of the transformer, for which this parameter will be greater than or equal to the calculated value. Then they begin to calculate the number of turns in the primary and secondary windings. Calculate the diameter of the wire and check whether the windings fit in the window of the magnetic circuit.

Literature:

Together with the article "Transformer power" read:

http://site/BP/KlassTransf/

http://site/BP/SxZamTransf/

A transformer is a type of electrical component that is designed to convert voltage and current from one quantity to another proportional to the input and output power consumption. This element of power equipment can usually contain one primary winding and one or more secondary windings.

Being a rather complex device, calculating a transformer sometimes takes a lot of time and not everyone can do it efficiently. But a lot depends on the correctness of the process. Operation stability finished device, efficiency, power consumption. In addition, if the calculation is incorrect, a wide variety of strange things can happen to the winding device:

• overheat;
• make ringing sounds when working;
• consume a large number of power at low efficiency, etc.

In more serious situations, it may even ignite, causing additional trouble. Therefore, many are interested in the question of how to calculate a transformer of one type or another so that it produces the required amount of electrical power and coefficient useful action was as close as possible to 1.

But right away, it’s worth assuring you that an efficiency equal to 1 is an unrealistic factor, because losses are always present, so when performing the calculation online or using the traditional method, seeing an indicator equal to 40% when calculating a power transformer on hardware is already good. For pulse devices, the calculation program will give at least 55-60%. Therefore, if you want to make the most efficient device, then choose a pulse type of transformer, but if you want to make a reliable power unit, where power consumption is not important, then, of course, we take transformer hardware into account.

Transformer calculation procedure

All transformer calculation programs process data using formulas known to us from scientific publications, so the correctness of its program can always be checked. But the need to know tabular values ​​may mislead you. Therefore, now we will look at some details of the calculation of transformers with a toroidal core on transformer iron or ferrite.

The toroid has best qualities compared to all other types of cores, since there are no gaps in it, and as a result, eddy current losses are minimized. Therefore, the efficiency of such transformers is significantly higher, so if you want to make a high-quality device, then use this type of core, although it is more difficult to wind a winding on it, but it’s worth it.

Parameter determination steps

First of all, for the calculation to be correct, you will need determine the main parameters future transformer. These include:

• voltage and current on the primary winding;
• the same indicators on the secondary winding.

Next, the number of turns on each winding is calculated, the type of wire is selected according to the table and the current calculation results obtained, but first you will need to measure the dimensions of the core, if any. Or, on the contrary, set the required power and calculate the parameters of the ring. This is what all online transformer calculation programs offer.

Choosing number of turns on the primary winding, it must be remembered that if their number is insufficient, it will get very hot and eventually burn out. And if it is sufficiently large, the voltage on the secondary will be small, so it is necessary to use strictly reference data and formulas from textbooks.

Let's consider an example of calculating a transformer wound on a toroidal core and powered from a network with a frequency of 50 Hz.

To simplify the process of calculating the device, you can use tabular data, which shows the formulas and variables used to determine the parameters of the winding product, summarized in the table below:

For the manufacture of cores of such network transformers 2 types of steel are used:

• E310-330 cold-rolled type and plate thickness in the range of 0.35-0.5 mm;
• E340-360 ordinary steel with a thickness of 0.05 - 0.1 mm.

It should be understood that the number of turns for each type of steel may be different, which is associated with the magnetic permeability of the core and other indicators. In the table, ω 1 and ω 2 are the number of turns for cold-rolled and conventional steel, respectively. Рг – overall power of the transformer; S – core parameters (sectional area), ∆ – maximum permissible current density in the windings; η is the efficiency of the device.

One of the features of manufacturing a toroidal transformer is that it uses external and interwinding insulation, so the conductors must have a sufficiently elastic coating. They are often chosen as such PELSHO or PESHO PEV-2 is also popular. The following types of materials are used as external insulation:

• varnished cloth;
• cambric tape;
• triacetate film;
• fluoroplastic film.

Benefits of using programs

One of the advantages of using online calculators to calculate transformer parameters is that there is no need for all of the above nuances. But the result is approximate, so it is important to remember this when using this or that program. Of course, there are better projects with calculations for transformers, which take into account the thickness of the insulating film, type of steel, and winding density.

Basic formulas and order of their application

Next, you need to set the basic parameters of the future transformer. These include the mains voltage Uc and the output voltage from the secondary winding Un. We also set the current in the load In, this indicator is often the most important, determining the characteristics of the device.

Some calculators, together with entering data into the form, also show the basic formulas by which the resulting value was determined. This greatly simplifies the process and at the same time allows for a more in-depth understanding of the calculation principle. In any case, when specifying the basic data in the form, the program first determines the nV power of the secondary winding using the well-known formula:

The next step when calculating the parameters of any toroidal transformer is to determine the cross-section of the core. It is calculated by the formula:

S calculated = √Рг/1.2.

For the right choice core, you must use the following formula for calculating the cross section:

S = (Dc - dc) hc /2.

Then, using the reference table of core parameters, we select the closest one in terms of characteristics. It is necessary to select a magnetic circuit with a higher power than that calculated by the formula.

The next step is performed by the program for calculating a welding or power transformer powered by 50Hz mains, is the determination of the number of turns per 1 volt. To do this, you need to use constant values ​​taken from the reference book. The fact is that each type of core has its own constant. For example, for a magnetic core made of E320 steel it is equal to 33.3, and the formula is as follows:

W 1-1 = ω 1 x Uc;

W 1-2 = ω 1 x U n.

When calculating the number of turns on the windings of a welding toroidal transformer, it is necessary to take into account the power dissipation, due to which the output voltage will be underestimated by 3%. Therefore, for the correctness of calculations, it is recommended to increase the number of turns on the secondary winding by exactly this difference.

The next step would be determination of wire diameter both windings. To do this, calculate the value of the current in the primary winding:

I 1=1.1(P2/Uc). And according to the formula:

d 1=1.13√ I 1/∆ the wire parameter is determined.

This calculation is valid for all types of transformers, both power and welding, powered from a network with a frequency of 50 Hz. The calculation program performs the same operations as given above. Only she can operate on data in any order. For example, by setting the number of turns, you can determine the voltage and power of the core; by entering the parameters of the core, you can find out the power and electrical characteristics transformer.

Pulse transformer calculation

As with a conventional power transformer, pulse transformers can also be calculated using online calculators and various programs. The formulas will be similar, but it will be necessary take into account magnetic permeability and other parameters of the ferrite core. Because the quality and correct operation of the finished device directly depends on its properties.

When performing calculations of welding pulse transformers using programs, many of them give hints, presenting bridge circuits of rectifiers and so on. All this makes the process much easier, since it is complicated using traditional methods. But, in general, the principle remains the same. What about calculator programs, you can find a large number of them on the Internet to perform calculations of any pulsed or conventional network devices of varying power and electrical parameters.

I’ll immediately make a reservation that I will consider single-phase transformers for powering ground-based stationary radio equipment with a power of tens to hundreds of watts, which has the most common application.

Before you start calculating a transformer, of which there can be a great variety, it is necessary to agree on the criteria for its quality, which will certainly affect the construction of calculation formulas. I believe that the main quality indicator of a power transformer for radio equipment is its reliability. A consequence of reliability is the minimum heating of the transformer during operation (in other words, it must always be cold!) and the minimum drop in output voltages under load (in other words, the transformer must be “hard”).

Other optimization criteria besides reliability, such as: copper savings, minimum dimensions or weight, high power density, ease of winding, cost minimization, limited service life (so that new ones are bought more often to replace burnt ones) I do not consider acceptable in engineering practice. I also consider methods of “knocking out” the maximum power core from an existing standard size unacceptable. - Such transformers do not work for a long time and get hot as hell.

If you want to save money, buy cheap Chinese goods or Soviet consumer goods. But remember: “The miser always pays twice!”

The transformer should work and not create problems. This is its main function.
Based on this, we will calculate it!
First of all, it is necessary to understand some minimal theory.

So: power transformer. Not ideal. Therefore, these imperfections need to be understood and taken into account correctly. There are two main imperfections in a power transformer.
1. Losses on the active resistance of the wire of the windings (depend on the material of the wire and on the density of the current flowing through it).
2. Magnetization reversal losses in the core - on a certain “magnetic resistance” (depending on the core material and the value of magnetic induction).

It is these two imperfections that must be reasonably minimal in order for the transformer to satisfy reliability requirements.

The active resistance of the windings and, as a consequence, their heating, is determined by the current density in the wire included in the calculation. Therefore, its value should be optimal. Based on a large practical experience I recommend using a current density value in copper wire of no more than 3.2 amperes per square millimeter of cross-section. When using silver wire, the current density can be increased to 3.5 amperes per square millimeter. But for an aluminum wire it should not exceed 2 amperes per square millimeter. The specified current density values ​​must absolutely not be exceeded! And from these values ​​we will derive formulas for determining the diameter of the winding wire, which we will use in the calculation.

It is possible to wind the windings with a thicker wire (at a lower current density). More subtle - absolutely not! However, it is not worth winding the windings with thicker wire, since then we risk not fitting the required number of turns into the core window. And a good transformer should have many turns in order to minimize magnetic losses and so that its core does not heat up.

Most cold-rolled electrical steels retain their linearity up to a magnetic induction value of 1.35 Tesla or 13,500 Gauss. But we must not forget that the voltage in an electrical outlet can vary from 198 to 242 volts, which corresponds to a normalized 10 percent deviation from the nominal value, both positive and negative. That is, if we want our transformer to operate reliably over the entire range of supply voltages, we must design it so that the core does not approach nonlinearity at any permissible supply voltage. Including at 242 volts. And therefore, at a nominal voltage of 220 volts, the magnetic induction should be selected no more than 1.2 Tesla or 12,000 Gauss.

Compliance with these two specified requirements will ensure high transformer efficiency and high stability of output voltages when the load current changes from zero to the maximum value. In other words, we will get a very “hard” transformer. That's what you need! But an increase in the calculated induction value of more than 1.2 Tesla will lead not only to heating of the core, but also to a decrease in the “rigidity” of the transformer. If we calculate the transformer for an induction value of more than 1.3 Tesla, then we will get a “soft” transformer, the output voltages of which smoothly drop as the load current increases from zero to its rated value. Such transformers are not suitable for all radio devices. However, in transistor circuits You can successfully use a rectified voltage stabilizer. But this is additional circuitry, additional dimensions, additional power dissipation, additional money and additional unreliability. Isn't it better to make a good transformer right away?

In a soft supply transformer, the voltage on some secondary windings depends on the current consumed in others - due to drawdown in the common circuits - on the active resistance of the primary winding and on the magnetic resistance. For example, if we power a push-pull transformer from a soft tube amplifier operating in class B or AB mode, then a change in consumption along the anode circuit will lead to additional fluctuations in the filament voltage of the lamps. And, since the filament voltage of the lamps also has a permissible spread of 10% of the nominal value, a soft transformer will introduce additional instability into this voltage of another 10, or even 15 percent. And this is inevitable, it will first reduce output power amplifier at high volumes (inertial volume drops), and over time will lead to an earlier loss of emission from the lamps.

Savings on a power transformer are reflected in more expensive losses in radio tubes and in the parameters of radio devices. This is truly true: “Saving is the path to ruin and poverty!”

Currently, the most common magnetic cores are of the following configurations:

We will carry out further calculations of the transformer using strict classical formulas from an electrical engineering textbook:

1. Subject to the agreements reached, the efficiency of the transformer (at the most common powers of 80 - 200 W) will be no lower than 95 percent, or even higher. Therefore, in the formulas we will use the efficiency value = 0.95.

2. Filling factor of the core window with copper for toroidal transformers is 0.35. For conventional frame armor or rod armor - 0.45. With wide frames and a large winding length of one layer (h), the value of Km can reach 0.5 ... 0.55, as, for example, in magnetic cores of type B69 and B35, the parameters of which are shown in the figure. With frameless industrial winding, Km can have values ​​of up to 0.6 ... 0.65. For reference: the theoretical limit of the Km value for layer placement of a round wire without insulation in a square window is 0.87.

Given practical implications Km are achievable only with even laying of the wire strictly turn to turn, thin interlayer and inter-winding insulation and termination of the terminals outside the core window (on the side extensions of the winding). When making frame windings under amateur conditions, in laboratory or pilot production conditions, it is better to take the value Km = 0.45 ... 0.5.

Of course, all this applies to conventional power transformers for lamp or transistor equipment, with output and supply voltages up to 1000 volts, where increased insulation requirements are not imposed on the windings and the termination of their terminals.

3. The overall power of the transformer, in watts, on a specifically selected core is determined by the formula:

Where:
η = 0.95 - transformer efficiency;
Sc And So- areas cross section core and window, respectively [sq. cm];
f- lower operating frequency of the transformer [Hz];
B= 1.2 - magnetic induction [T];
j- current density in the winding wire;
Km- coefficient of filling of the core window with copper;
Kc= 0.96 - coefficient of filling of the core section with steel;

4. Having specified the winding voltages, the number of required turns can be calculated using the following formula:

Where:
U 1, U 2, U 3, ... - winding voltages in volts, and n 1, n 2, n 3, ... - number of turns of windings.

If we have strictly followed the initial agreements, and we are making a rigid transformer, then the number of turns of both the primary and secondary windings is determined by the same formula. If we use a transformer at the maximum power value for the existing core size, calculated using this formula, or we design low-power transformers (less than 50 W), with a large number turns and thin wire windings, then the number of turns of the secondary windings should be increased by 1/√η once. Taking into account our agreement, this will be 1.026 or more than calculated by 2.6%.

As for the voltages of the filament windings, here it is worth recalling the instructions of the most important book on radio tubes: , issued for radio development engineers by the State Committee on Electronic Technology of the USSR in 1964.

You need to open this manual on page 13, carefully examine the graph in Figure 1, and understand from it that the optimal filament voltage of radio tubes to maintain their maximum reliability and, accordingly, durability is 95% of the nominal value. Which for lamps with a filament voltage of 6.3 volts will be exactly 6 volts. Therefore, there is no need to increase the number of turns of filament windings by 2.6%. Let it be as it is.

5. Determine the winding currents:
Primary current: I 1 = P / U 1
When using a full-wave rectifier, the average current of each half of the winding will be 1.41 times (root of two) less than the required rectified load current. If a bridge semiconductor rectifier is used, the winding current will be 1.41 times greater than the rectified load current. Therefore, we must not forget to substitute direct current consumption into the formulas for determining the diameters of wires, in the first case divided, and in the second, multiplied by 1.41.

6. We calculate the diameters of the winding wires based on the currents flowing in them using the following formulas (for copper, silver or aluminum):

We round the resulting values ​​upward to the nearest standard wire diameter.

7. We check the calculation. The power of the primary winding - the product of the supply voltage and the consumed current - must be equal to the sum of the powers of all secondary windings. That is: U 1 x I 1 = U 2 x I 2 + U 3 x I 3 + U 4 x I 4 + ...

Having wound the transformer, to carry out further calculations of the rectifier it is necessary to measure some of its parameters.

Active resistance of the primary winding.

Active resistance of secondary windings.

The exact values ​​of the voltages of the secondary windings, of course, check that the voltage in the network is 220 volts. If it differs from the nominal value (but is within the range of 198 - 242), then recalculate the measured values ​​proportionally.

No-load current of the primary winding (what current the transformer consumes from the network when there is no load on its secondary windings).

Eg,
A toroidal two-winding power transformer with a power of 530 Watts, which I myself manually wound in 1982 on a core from a burned-out household transitional 400-watt 127/220 volt autotransformer, called in the Yug-400 retail chain, had the following parameters:
Magnetic induction at a voltage of 220 volts - 1.2 Tesla,
The number of turns of the primary winding (220 volts) is 1100.
The diameter of the primary winding wire is 0.96 mm.
The number of turns of the secondary winding (127 volts) is 635.
The diameter of the secondary winding wire is 1.35 mm.
At the same time, the no-load current turned out to be 7 (seven!) milliamps.

For eighteen years, without turning off, my “bachelor” refrigerator “Saratov-II” (the same one during operation with which the autotransformer “Yug” burned out) was powered through this transformer after our area was transferred to a network voltage of 220 volts.

For comparison.
The “native”, industrial, winding of that same 220-volt “South” transformer contained 880 turns. Not surprisingly, it heated itself like a bastard, even being just an autotransformer, and eventually burned out. Yes, this is understandable, because the Soviet household industry was interested in increasing consumer demand. Well, this was achieved not by a wide range of products, but by a limited period of their work!

There is no need to save money - this is the same as spoiling yourself.

Good luck!

Determination of power transformer power

For the manufacture of transformer power supplies, a single-phase power transformer is required, which reduces AC voltage 220 volt power supply to the required 12-30 volts, which is then rectified by a diode bridge and filtered by an electrolytic capacitor.

These transformations electric current necessary, since any electronic equipment is assembled on transistors and microcircuits, which usually require a voltage of no more than 5-12 volts.

To assemble a power supply yourself, a novice radio amateur needs to find or purchase a suitable transformer for the future power supply. In exceptional cases, you can make a power transformer yourself. Such recommendations can be found on the pages of old books on radio electronics.

But nowadays it’s easier to find or buy a ready-made transformer and use it to make your own power supply.

Full payment and self-production transformer is quite a difficult task for a beginning radio amateur. But there is another way. You can use a used but serviceable transformer. To power most home-made designs, a low-power power supply with a power of 7-15 watts is enough.

If the transformer is purchased in a store, then, as a rule, there are no special problems with selecting the right transformer. The new product has all its main parameters indicated, such as power, input voltage, output voltage, as well as the number of secondary windings, if there is more than one.

But what if you come across a transformer that has already worked in some device and you want to reuse it to design your own power supply? How to determine the power of a transformer, at least approximately? The power of the transformer is a very important parameter, since the reliability of the power supply or other device you assemble will directly depend on it. As is known, consumed electronic device power depends on the current it consumes and the voltage required for its normal operation. Approximately this power can be determined by multiplying the current consumed by the device ( I n to the device supply voltage ( U n). I think many are familiar with this formula from school.

P=U n * I n

Where U n– voltage in volts; I n– current in amperes; P– power in watts.

Let's consider determining the power of a transformer at real example. We will train on the TP114-163M transformer. This is an armor-type transformer, which is assembled from stamped W-shaped and straight plates. It is worth noting that transformers of this type are not the best in terms of efficiency (Efficiency). But the good news is that such transformers are widespread, often used in electronics and can be easily found on the shelves of radio stores or in old and faulty radio equipment. In addition, they are cheaper than toroidal (or, in other words, ring) transformers, which have high efficiency and are used in fairly powerful radio equipment.

So, before us is the transformer TP114-163M. Let's try to roughly determine its power. As a basis for calculations, we will take recommendations from the popular book by V.G. Borisov "Young Radio Amateur".

To determine the power of a transformer, it is necessary to calculate the cross-section of its magnetic core. In relation to the TP114-163M transformer, the magnetic core is a set of stamped W-shaped and straight plates made of electrical steel. So, to determine the cross-section, it is necessary to multiply the thickness of the set of plates (see photo) by the width of the central lobe of the W-shaped plate.

When calculating, you must respect the dimensions. It is better to measure the thickness of the set and the width of the central petal in centimeters. Calculations must also be made in centimeters. So, the thickness of the set of the transformer under study was about 2 centimeters.

Next, measure the width of the central petal with a ruler. This is a more difficult task. The fact is that the TP114-163M transformer has a dense set and a plastic frame. Therefore, the central petal of the W-shaped plate is practically invisible; it is covered by the plate, and it is quite difficult to determine its width.

The width of the central petal can be measured at the side, the very first W-shaped plate in the gap between the plastic frame. The first plate is not complemented by a straight plate and therefore the edge of the central lobe of the W-shaped plate is visible. Its width was about 1.7 centimeters. Although the calculation given is indicative, but it is still desirable to carry out measurements as accurately as possible.

We multiply the thickness of the magnetic core set ( 2 cm.) and the width of the central lobe of the plate ( 1.7 cm.). We get the cross-section of the magnetic circuit - 3.4 cm 2. Next we need the following formula.

Where S– cross-sectional area of ​​the magnetic circuit; P tr– transformer power; 1,3 – average coefficient.

After some simple transformations, we obtain a simplified formula for calculating the power of a transformer based on the cross-section of its magnetic core. Here she is.

Let's substitute the value of the section into the formula S = 3.4 cm 2 which we received earlier.

As a result of calculations, we obtain an approximate value of transformer power of ~ 7 Watts. Such a transformer is quite enough to assemble a power supply for a 3-5 watt monophonic audio amplifier, for example, based on the TDA2003 amplifier chip.

Here is another one of the transformers. Labeled as PDPC24-35. This is one of the representatives of transformers - “babies”. The transformer is very miniature and, naturally, low-power. The width of the central petal of the W-shaped plate is only 6 millimeters (0.6 cm).

The thickness of the set of plates of the entire magnetic circuit is 2 centimeters. According to the formula, the power of this mini-transformer is equal to about 1 W.

This transformer has two secondary windings, the maximum permissible current of which is quite small, amounting to tens of milliamps. Such a transformer can only be used to power circuits with low current consumption.