How to properly wind a transformer for a power supply. Making a toroidal transformer with your own hands. Direction of turns on different coils

Making a homemade transformer is a worthwhile endeavor so as not to waste money on buying transformers.

Selection of materials

Let's take a Russian wire, its insulation is stronger. The wire from old coils is used if there is no damage to the insulation. For insulation, paper or FUM film is suitable. For insulation between the windings, it is better to use varnish fabric and several layers of insulation. For superficial external insulation suitable cable paper, varnish fabric. You can also wind the transformer using PVC electrical tape.

The frame is made of fiberglass or similar material.

Calculations of parameters of a homemade transformer

On a simple transformer the primary winding has 440 turns for 220 volts. It turns out 1 volt for every two turns. Formula for counting turns by voltage:

N = 40-60 / S, where S is the cross-sectional area of ​​the core in cm 2.

The constant 40-60 depends on the quality of the core metal.

Let's make a calculation for installing the windings on the magnetic circuit. In our case, the transformer has a window 53 mm in height and 19 mm in width. The frame will be textolite. Two cheeks at the bottom and top 53 - 1.5 x 2 = 50 mm, frame 19 - 1.5 = 17.5 mm, window size 50 x 17.5 mm.

We calculate the required diameter of the wires. The power of the transformer core with your own hands is 170 watts in size. On the network winding the current is 170 / 220 = 0.78 amperes. Current density is 2 amperes per mm 2, standard wire diameter according to the table is 0.72 mm. The factory winding is made of 0.5 wire, the factory saved money on this.

• The winding of a simple high voltage transformer is 2.18 x 450 = 981 turns.
• Low voltage for filament 2.18 x 5 = 11 turns.
• Low voltage filament 2.18 x 6.3 = 14 turns.

Number of turns of the primary winding:

we take a wire of 0.35 mm, 50 / 0.39 x 0.9 = 115 turns per layer. Number of layers 981 / 115 = 8.5. It is not recommended to draw conclusions from the middle of the layer to ensure reliability.

Let's calculate the height of the frame with windings. Primary of eight layers with 0.74 mm wire, 0.1 mm insulation: 8 x (0.74 + 0.1) = 6.7 mm. It is better to shield the high-voltage winding from other windings to prevent high-frequency interference. In order to wind the transformer, we make a screen winding from one layer of 0.28 mm wire with two layers of insulation on each side: 0.1 x 2 + 0.28 = 0.1 x 2 = 0.32 mm.

The primary winding will take up space: 0.1 x 2 + 6.7 + 0.32 = 7.22 mm.

Step-up winding of 17 layers, thickness 0.39, insulation 0.1 mm: 17 x (0.39 + 0.1) = 6.8 mm. On top of the winding we make layers of insulation 0.1 mm.

It turns out: 6.8 + 2 x 0.1 = 7 mm. Height of the windings together: 7.22 + 7 = 14.22 mm. 3 mm left for filament windings.

You can make a calculation internal resistance windings To do this, the length of the turn is calculated, the length of the wire in the winding is taken, the resistance is determined, knowing resistivity according to the table for copper.

When calculating the resistance of the primary winding section, a difference of about 6 ohms is obtained. This resistance will give a voltage drop of 0.84 volts at a nominal current of 140 milliamps. To compensate for this voltage drop, we add two turns. Now during loading the sections are equal in voltage.

Making a transformer coil frame with your own hands

The angles on the parts and the accuracy in dimensions are important, which will affect the assembly of a simple transformer.

On the cheeks we allocate places for attaching the output contacts of the windings, and drill holes according to calculations. When the frame is assembled, now we round off the sharp edges that the winding wire will touch. We use a needle file for this purpose. The wires should not be bent sharply, as the insulation enamel will crack. Now let's check whether the plate is inserted into the frame window. It should not dangle or fit tightly. We put the frame on a special machine or get ready to wind the transformer by hand. Thick wires are always tossed around by hand.

Winding a transformer with your own hands

We lay the first layer of insulation. Insert the end of the wire into the hole in the output terminal. We begin to wind the wire, not forgetting about its tension. You can check this way: the wound coil will not bend under your finger. The wire cannot be stretched, as the insulation will be damaged. It is recommended to soak the finished coil with paraffin so as not to damage the wire. If the winding hums while the transformer is operating, the wire insulation wears off, the wire bends and breaks. For this reason, the tension of the wire during winding is of great importance.

During winding, we move the coils closer to each other and compact them. The first layer is the most important.

There is no need to leave empty space on the layer. The highest voltage on the last turns is for the primary 60 + 60 / 2, 18 + 55 V. The varnish insulation will withstand the voltage; if the wire falls into the void of the layer, the insulation may be damaged. We saturate the first layer, then the second and so on. The insulation between the windings must be treated conscientiously. It must withstand up to 1000 volts. At the top of the insulation, it is recommended to write the number of turns and the size of the wire; this will be useful during repairs.

The layers of a homemade transformer must have correct form. As you wind the coil, it will bend at the edges. To do this, the layers need to be equalized during winding without damaging the insulation.

It is better to make forced wire joints on the edge of the frame behind the core. Connect the wire by twisting with soldering, overlay with soldering. The length of the contact when connecting is made more than 12 wire diameters. The joint must be insulated with paper or varnish cloth. Soldering must be without sharp corners.

The terminal ends of the windings are made in different ways. The main thing is to have reliability and quality.

Completing the manufacture of the transformer with your own hands

We solder the lead ends of the windings, insulate the surface of a simple transformer, sign these characteristics on it and assemble the core. After this, you need to check this simple transformer with your own hands.

We measure the idle current of the homemade transformer; it should be minimal. Let's look at the heating. If the core heats up, then the iron is selected incorrectly. If the windings get hot, it means there is a short circuit. If it’s normal, then we short-circuit the secondary winding; there should be no crackling or strong buzzing.

An example of how to make a homemade transformer

Let's move on to the manufacture of the transformer itself. Based on the finished core, we will calculate the power of the transformer, turns and wire, wind the primary and secondary windings, and assemble the transformer completely.

To wind a transformer with a voltage of 220 to 12 volts, we need to select a magnetic core. We select a W-shaped magnetic core and a frame from an old transformer. To determine the power delivered a simple transformer, it is necessary to make a preliminary calculation.

Transformer calculation

We calculate the diameter of the primary winding wire. Transformer power P 1 = 108 W:

P 1 = U 1 x I 1

where: I 1 – current in the primary winding;

then the current in the primary winding is:

I 1 = P 1 / U 1 = 108 W / 220 V = 0.49 A.

Let's take I 1 = 0.5 ampere.

From the table of wire diameter depending on the current, select the permissible current 0.56 A, diameter 0.6 mm.

You can wind a homemade transformer with your own hands without a machine. This will take two to three hours, no more. Let's prepare strips of paper to lay between the layers of wire. We cut out a strip with a width equal to the distance between the cheeks of the transformer coil plus a couple of millimeters so that the paper lies tightly and the turns do not overlap each other at the edges.

We make the length of the strip with a margin of two centimeters for gluing. Lightly cut along the edges of the strip with scissors so that the paper does not tear when bending.

Then we glue a strip of paper onto the frame, smoothing it tightly.

Winding the primary winding

Now we take the wire from an old coil, which has a wire with good, non-cracked insulation. We insert the end of the wire into a flexible tube of insulation from an old used wire of the appropriate suitable diameter. We insert the end of the winding into the hole in the coil frame (they are already present in the old frame).

The coil winds tightly, turn to turn. Having wound 3-4 turns, you need to press the turns against each other so that the winding of the turns is tight. To wind the transformer after winding the first layer, it is necessary to count the number of turns in the row. We got 73 turns. We make a gasket with a strip of paper. We wind the second layer. During winding, you need to keep the wire taut at all times so that the winding is tight. After the second layer we also make a paper gasket. If the length of the wire is not enough, then we connect another wire to it by soldering. We tin the varnished wire by heating the end with a soldering iron on an aspirin tablet. At the same time, the varnish is easily removed.

When the winding of the primary winding is completed, we insulate the end of the wire into a tube and bring it out to the outside of the coil. We make winding insulation between the primary and secondary windings. You can wind the transformer further.

Secondary winding

Let's calculate the diameter of the wire of the secondary winding of a homemade transformer. Let us take the power of the secondary winding:

P 2 = 100 watts

P 2 = U 2 x I 2

U 2 = 18 volts;

The permissible current in the secondary winding will be equal to:

I 2 = P 2 / U 2 = 100 W / 18 V = 5.55 A.

From the table, diameter depending on current: diameter for a current of 5.55 A - the closest value in the table is 6.28 amperes. For such a current, a wire diameter of 2 mm is required.

We take the wire that we got when winding up the old transformer. We wind the secondary winding wire according to the same principle as primary winding. The wire of the secondary winding is much stiffer, therefore, in order for it to lie evenly when winding, it must be periodically upset with hammer blows through a wooden block so as not to damage the insulation. We got 3 layers of secondary winding. The result is a finished wound frame of a simple transformer.

DIY transformer assembly

To speed up assembly, we take two W-shaped plates. We insert them inside the frame alternately on both sides, two pieces at a time.

We are not installing the covering plates yet. They will be installed later. If you insert all the plates at once as a whole package, then gaps appear between the plates and the inductance of the entire core drops. After assembling the W-shaped plates of the homemade transformer, we insert the overlapping plates, also two pieces each.

After assembling the core, carefully tap its planes with a hammer to align the plates. Using racks and pins we will tighten the core. According to the rules, paper sleeves are put on the studs to reduce losses in the core.

We clean and tin the ends of the windings. Then we solder to the lead strips, which can be attached to the transformer frame. The result is a ready-made transformer with your own hands.

Write comments, additions to the article, maybe I missed something. Take a look at, I will be glad if you find anything else useful on mine.

If you need a power supply with a non-standard voltage, but you didn’t find the one you need, then don’t worry - you can make it yourself! If this is not a switching power supply, then one of the important elements of the power supply will be a high-quality transformer. You can make a transformer for the required voltages with your own hands; often, if all winding rules are followed, a homemade transformer will be much better than a factory-made one.

For winding a transformer, there are simplified calculation methods that have proven themselves quite well in amateur radio activities. We will discuss how to wind a transformer from scratch using one of these methods in the following articles, but in this one we will only touch upon step by step rewind transformer with an existing primary winding. So before reading a lengthy article, brew a couple of cups of coffee/tea and be patient :)

A few important points to know before you start rewinding the transformer:

1) Before measuring the voltages of the secondary windings, it would not be amiss to measure the voltage in the 220V network (write down in a notebook at what voltage the measurements were made). Changing the value of the supply network leads to a change in the voltage on the secondary windings of the transformer.

Changes in network voltage occur mainly due to its load by consumers in your home, depending on the time of day. A similar situation is observed when changing substations. For example, the voltage of the 220V network at your home, dacha or work may be different. Also, voltage drop on the secondary windings may be due to the quality indicators of the transformer.

This circumstance was mentioned for the reason that when designing the anode-heat transformer, I had to take this fact into account and make additional taps on the secondary winding (it is possible on the primary winding, for a certain network voltage). The transformer was intended for a radio tube tester and it was important to provide the device with certain supply voltages. If the required voltage did not match, the supply wires were connected to other taps of the secondary windings of the transformer.

2) All actions with a transformer connected to a 220V network must be carried out with a 60-80W incandescent light bulb connected to the break of one wire, between the power plug and the transformer. The light bulb acts as a fuse. If suddenly you have connected the windings incorrectly and a short circuit occurs in the windings, the light will light up and prevent the consequences of the error; if everything is fine, the light will not light. After making sure that everything is in order, the light bulb can be removed.

3) One more nuance regarding factory-made transformers. Often, in order to reduce production costs in order to save copper wire, the primary winding is not wound at the factory, as a result of which transformers operate with increased induction. In these cases, the magnetic circuit of the transformer will be on the verge of saturation: it will hum, get very hot and have a large no-load current. Also, the output voltages will drop significantly under load. After all, the current value XX is one of the important indicators of a high-quality transformer. The lower the current, the better.

To measure the no-load current, a microammeter is connected to the primary winding circuit. The microammeter is connected in series to one wire between the power plug and the transformer itself, while the load on the secondary windings must be turned off. Depending on the overall power of the transformer, the appropriate XX current for this transformer is determined.

4) When assembling the transformer, it is imperative to insulate the tension pins with a dielectric (cambric, paper tube) from the magnetic circuit plates. Assemble the package of magnetic circuit plates tightly without gaps.

A poorly assembled transformer can negate the correct design of the transformer windings, thereby increasing eddy currents (Foucault currents), and they will lead to a large no-load current with all its “charms”.

5) When rewinding a transformer, you should take into account the filling of the magnetic circuit window with copper wire. A situation may arise when an incorrectly selected magnetic circuit with a small window does not allow winding required amount turns of wire of the calculated diameter. Almost all Soviet brochures or manuals for radio amateurs on winding provide formulas for calculating the occupancy of a magnetic circuit window.

6) The number of wound turns of wire in the winding can be approximately determined without disassembling the transformer. For toroidal transformers, everything is much simpler in terms of counting turns per volt. It is enough to wind several turns onto the “donut” over all windings insulated wire, connect the transformer to the network and measure the voltage.

For W-shaped ones, almost everything is the same, but provided that there is a gap between the magnetic core and the coil. If it is possible to thread a wire and wrap it around the transformer coil, then in this case you can carefully insert a flexible, insulated long wire into the gap and make several turns (as long as the wire is enough). Laying the wire on the coil must be done tightly, with even turns to each other. Straighten the ends of the winding you just made so that they do not short out. All that remains is to insert the power plug into the socket and measure the voltage with a multimeter.

The voltage will correspond to the number of turns made by the wire. Then the simple laws of mathematics come into play for calculating the number of turns per volt. You count how many turns are wound, and measure the voltage, then calculate how many turns are needed for one volt. Then you multiply the resulting number of turns (per volt) by the required voltage in the winding - it’s simple!

How to determine the primary winding?

If you don't know how to connect a transformer, then the first thing you need to do is find the primary winding. The primary winding in a step-down transformer can be determined using a multimeter in resistance measurement mode. In most cases, the network winding has the highest resistance, as it is wound on a large number of turns.

Please note that the primary winding in low-power transformers is wound thin winding wire and is located (as a rule, but there are exceptions) closest to the magnetic core. Consider the contact petals on the transformer coil frame; the ends of the windings come out and are sealed onto the contact petals. This way you can visually assess the thickness of the wire and which winding terminals are closest to inside coil frame.

The high-voltage anode winding in a step-up anode-heat transformer may also have high resistance, but in any case, it is necessary to check through a light bulb and measure the voltage on other windings. For example, apply a voltage of 6.3V to the filament winding and measure the voltage on the other windings. The network (primary) winding is wound at 220-230V, it should have approximately the same voltage.

You can determine the windings using a multimeter in the “continuity” mode (also measuring resistance). On the contact pad of the transformer coil, place the probe on one petal and alternately touch the other petals with the second probe. When you find the second end of the winding, the multimeter notifies you of this with a sound signal (resistance readings on the screen). This way you “ring out” the windings. To avoid confusion, you should first draw the location of the contacts on the coils and mark them during the process of determining the windings for short circuits. If the winding has several terminals, then the beginning and end can be identified by the highest resistance for a given winding (the middle point will have an average resistance value).

By following simple steps to identify the windings, you can independently connect a transformer unknown to you. This is much easier if the transformer coils have factory markings on them. In this case, using information from the reference book, you can determine the parameters and numbering of the terminals of the transformer windings.

Rewinding a transformer with your own hands. Case Study

Now, having understood some points that you need to know, let's start rewinding the transformer. Next, an example of rewinding in a “live story format” will be described, if I were recording in chronological order all my actions are for you :). So, the “Record” button is turned on, the cassette film with a characteristic rustling winds the film from one reel to another. Evening, the table is lit desk lamp, and the smell of rosin is in the air... :)

A friend asked me to assemble a bipolar power supply to power the Yunost-21 synthesizer. It was necessary to obtain stable +/- 10 volts at the output. I did not find a specific transformer in my amateur radio stocks. It was decided to manufacture it ourselves to the required parameters. The basis for the modification was an armor-type transformer with an Ш-shaped magnetic core, which previously worked in the power supply of a single-channel amplifier. According to preliminary estimates total load per transformer in the amplifier was 3A, which corresponded with a margin for the load of the designed power supply.

Taking into account the overall power of the transformer and the thickness of the wire of the secondary winding, I figured that the primary winding should be wound with wire of a suitable diameter (measurements with a micrometer after winding the secondary winding confirmed this). Measuring the no-load current also confirmed the suitability of the selected transformer (there was no need to rewind the primary). All that remained was to deal with the secondary winding.

For a bipolar power supply, it is necessary to have two symmetrical windings designed for 1 Ampere load (the transformer for conversion already has them). We connect the transformer to a 220V network and measure the voltage at the taps of the windings. We write down the obtained values ​​on a draft for subsequent calculations. Next, we disassemble the transformer to rewind it.

Unscrew the studs and remove the transformer brackets. Before us is a W-shaped armor-type magnetic circuit. It consists of W-shaped plates and I-shaped plates, which alternate with each other and are rearranged in a certain way.

To make the disassembly process easier, carefully remove the varnish/paint. Removal paint coating(if necessary) is carried out extremely carefully so as not to damage the surface of the plates and not to leave a burr that can short-circuit the magnetic circuit plates. If possible, we do without these manipulations.

First, the I-shaped plates must be removed. Carefully pry it up with a knife or a flat thin screwdriver, pry it up and pull them all out. After this, we remove the W-shaped plates from the transformer coil frame one by one.

After the transformer coil has been separated from the magnetic circuit, we proceed to further actions. We are now faced with the task of counting the number of turns in the secondary windings. We do not touch the primary winding.

Based on the measurement results, the two secondary windings have the same voltages and are symmetrical to each other (they mirror the number of turns). If we find out the number of turns of one winding, we will know how many there are in the other. After counting, you won’t have to completely wind up all the turns; we’ll just calculate how much wire needs to be wound in order to get the desired voltage.

This counting of turns will help us verify the correctness of the previous measurements, when we wound wire onto a coil to count how many turns there are per volt.

Having sat down at the table in a calm atmosphere, we place in front of us a piece of paper, a pen (pencil) and a transformer coil. We begin to unwind the wire and count the turns being wound. After every ten winding turns, we mark a piece of paper with a mark, for example, a vertical line, which will correspond to 10 turns. We will do the same when winding wire onto a reel. This is necessary in order not to get confused and lose count. You can also use a simple calculator, adding the values ​​of the turns.

Some tips:

Before work, make sure that there are no sharp surfaces of furniture around you on which the winding wire may rub or get caught (do not damage the enamel insulation of the winding wires!);

Wind the wire onto separate coil. This way it will be laid evenly without damage, which will allow it to be reused;

It is also important to carefully wind the wire to avoid loops and creases formed in the process - this way we will keep the wire relatively straight and not damage enamel coating copper wire when it is bent.

Method of rewinding the secondary windings of a transformer

We have the first secondary winding measured at 2.02 volts. We wind the wire and count the turns. 2.02 volts corresponds to 12 turns. We divide 12 turns by 2.02 volts and get 5.94 turns per volt. Further, when calculating, we will multiply the voltage that we must obtain by 5.94 turns. The resulting value will be equal to how many turns we will need to wind to obtain the required voltage.

Let's continue winding the second secondary winding. According to measurements, it corresponded to a voltage of 19.08 volts. Let's check the previous calculations in practice. The second secondary winding turned out to be 112 turns. Divide 112 by 5.94 and we get 18.85 volts.

I assume that a small discrepancy appeared due to the fact that the values ​​of the second decimal place and the length of the wire for tapping the second end of the secondary winding were not taken into account. A piece of wire for tapping the secondary winding ran at a right angle from the bottom cheek of the coil frame to the top. An EMF is also induced on this segment (approximately ¼ of a turn), which is reflected in the discrepancy. Perhaps I was wrong by one turn and didn’t count it. This error should also be taken into account when designing a transformer.

We wind up the third secondary winding. It is worth noting that during measurements, the third winding, according to the voltmeter readings, had the same voltage value as the second secondary winding. This means that our fourth secondary winding corresponds to the voltage of the first winding and has the same number of turns.

The output of the designed bipolar power supply requires a voltage of plus/minus 10 volts of DC voltage. In order for the output of the power supply to be 10 volts, you need to take into account some points, namely the voltage drop across the elements of the power supply and “drawdowns” in the 220V power supply network. According to rough estimates, the transformer for powering the power supply circuit should produce 13-14 volts of alternating voltage. Based on this, we wind two secondary windings at 14 volts.

We have not touched the third secondary winding yet. The third and fourth windings give us a total of 21.1 volts, which is 124 turns for two windings. We multiply 14 volts by 5.94 turns and get the value 83.16 - this is the required number of winding turns to achieve 14 volts. From 124 turns (21.1V) we subtract 83.16 turns (14V) and get 40.84 - this is the value of the number of turns that should be wound in order to end up with a winding whose output will be 14 volts. We unwind and get the first necessary secondary winding.

To increase the reliability of the transformer and prevent electrical breakdown of the varnish insulation of the wire, it is necessary to tightly wrap the insulator around the coil over the first secondary winding. As an insulator, you can take the paper that is used to wrap the windings of a factory-made transformer like TS-180 or others; if you don’t have one, you can look for baking paper in your kitchen. We cut a strip of paper the width of the transformer coil with a small margin and make accordion-shaped cuts along the edges of 3-4 millimeters in size. We lay the paper and wrap it around the spool in several layers (no more than 2-3).

We wind 83.16 turns on top of the paper insulation for the second secondary winding of 14 volts. We wind it exactly turn to turn, trying to repeat the factory laying on the reel. At the end of winding, we wrap the coil with insulating paper, similar to how we did the interlayer insulation between the windings.

Now we assemble the transformer in the reverse order as we disassembled it. Don’t forget to isolate the tension pins from the magnetic circuit plates (after assembly you can ring them with a tester). When tightening a package of plates, the main thing is to maintain balance, not to overtighten (the thread may be damaged or the stud will burst) and not to tighten the nuts properly along the threads. Insufficient tightening of the magnetic circuit plates can lead to transformer hum and increased no-load current.

Now we connect the transformer to the network through a light bulb and measure the voltage at the ends of the windings. You may have to repeat the transformer assembly and disassembly procedure several times to achieve the desired result.

Thank you for reading this lengthy article! There are many examples of rewinding transformers on the Internet; this article described my own experience in rewinding a transformer with my own hands; you should also not take the article as a scientific work.

I also advise you to find brochures in electronic form from the Soviet period, where everything is sensibly and competently presented on this topic.

In the following articles I will try to describe in detail the calculation and winding of a transformer from scratch, I will tell you. Good luck!

About the author:

Greetings, dear readers! My name is Max. I am convinced that almost everything can be done at home with your own hands, I am sure that everyone can do it! In my free time I like to tinker and create something new for myself and my loved ones. You will learn about this and much more in my articles!

Rewinding transformers is a complex and labor-intensive type of technological operation when repairing this type of electrical equipment. All types of transformers produced by industry are highly reliable. These static electromagnetic devices have no moving parts and are designed for a long period of operation. Most common reasons failures may be, in particular:

• factory defects (components, assembly)
• critical deviation of operating modes
• violation of prescribed operating rules
• installation errors
• natural aging of insulating materials.

As a rule, in such cases there is a break in the transformer winding with its complete refusal. Another manifestation of a failure is an interturn short circuit on the housing, during which the power drops, and significant heating of the windings occurs. In these cases, the transformer requires a major overhaul with complete (partial) disassembly of the active part.

When a transformer fails, in most cases it is overhauled rather than replaced. This is due to economic reasons. Thus, restoring functionality by rewinding the transformer coil costs about 30% less than purchasing a new device. On the technical side, repairing a power transformer has positive aspect there is a possibility of modernizing the transformer with changing (improving) its consumer properties, technical parameters. The restored transformer can still serve for a long period.

The transformer rewinding service in Moscow provided by our company can be used to repair, modernize, or change the technical parameters of various types of this electrical equipment. Rewinding means the following types of work: disassembling the transformer, troubleshooting it, actually rewinding the transformer coils, applying insulation (impregnation with varnish), general assembly, bench testing.

Rewind technology pulse transformer different from other species. In order to reduce interference and losses, its design uses a complex sectional winding. Rewinding only the primary or secondary winding of a pulse transformer is impossible; both must be rewinded at once. When rewinding such devices, the sequence of operations must be strictly followed; the slightest deviations can significantly change its characteristics and even lead to failure.

In the event that there is a need to manufacture a device with non-standard voltage and current parameters, a careful calculation and rewinding of a transformer of a suitable (unified) type is made. In this case, the existing structural elements (winding frame, core) are taken as a basis and the old winding is replaced with a new one. For example, this way you can rewind the TS 180 transformer (secondary winding), which is equivalent to manufacturing a new one with the given characteristics.

In the process of rewinding a transformer, it becomes possible to improve its technical and operational parameters. Using the method of dividing the windings into sections instead of additional insulation improves heat removal, and therefore helps to increase the rated power of the transformer. Air cooling of the winding will be more effective the more separate sections there are. Application effective ways winding can, by reducing the cross-section of the wires, reduce the size of the windings (coils), their weight and the total cost of the device.

Prices for rewinding transformers

Transformer is translated from Latin as “converter”, “converter”. This is a static type electromagnetic device designed to convert alternating voltage or electric current. The basis of any transformer is a closed magnetic circuit, which is sometimes called a core. Windings are wound onto the core, of which there can be 2-3 or more, depending on the type of transformer. When on the primary winding occurs AC voltage, inside the core is excited magnetic current. It, in turn, causes an alternating current voltage with exactly the same frequency on the remaining windings.

The windings differ from each other in the number of turns, which determines the coefficient of change in voltage. In other words, if the secondary winding has half as many turns, then an alternating voltage appears on it, two times less than on the primary winding. But the current power does not change. It does possible work with high currents at relatively low voltage.

Depending on the shape of the magnetic circuit There are three types of transformers:

Plate materials

Transformer cores are made of either metal or ferrite. Ferrite, or ferromagnetic, is iron with a special structure crystal lattice. The use of ferrite increases the efficiency of the transformer. Therefore, most often the transformer core is made of ferrite. There are several ways to make a core:

• Made from stacked metal plates.
• Made from wound metal tape.
• In the form of a monolith cast from metal.

Any transformer can operate in both step-up and step-down modes. Therefore, all transformers are conditionally divided into two large groups. Boost: The output voltage is greater than the input. For example, it was 12 V, it became 220 V. Step-down: the output voltage is lower than the input. It was 220, but became 12 volts. But depending on which winding the primary voltage is supplied to, it can be turned into a boost voltage, which will turn 10 A into 100 A.

DIY toroidal transformer

The toroidal transformer, or simply torus, is most often made at home as the main part for the home welding machine and not only. In fact, this is the most common type of transformer, first manufactured by Faraday in 1831.

Advantages and disadvantages of the torus

Thor has undoubted advantages compared to other types:

The simplest torus consists of two windings on its ring-shaped core. The primary winding is connected to the source of electric current, the secondary winding goes to the electricity consumer. By means of a magnetic circuit, the windings are combined and their induction is enhanced. When the power is turned on, an alternating magnetic flux appears in the primary winding. Connecting to the secondary winding, this flux generates electromagnetic force in it. The magnitude of this force depends on the number of wound turns. By changing the number of turns, you can convert any voltage.

Calculation of the power of a toroidal transformer

Making a welding toroidal transformer at home begins with calculating its power. The main parameter of the future torus is the current that will be supplied to the welding electrodes. Most often, electrodes with a diameter of 2–5 mm are sufficient for domestic needs. Accordingly, for such electrodes the current power should be in the range of 110–140 A.

The power of the future transformer is calculated using the following formula:

U - open circuit voltage

I - current strength

cos f - power factor equal to 0.8

n - efficiency equal to 0.7

Next, the calculated power value is compared with the cross-sectional area of ​​the core using the appropriate table. For home welding transformers this value is usually 20−70 sq. cm depending on the specific model.

After this, using the following table, the number of turns of the wire is selected in relation to the cross-sectional area of ​​the core. The pattern is simple: the larger the cross-sectional area of ​​the magnetic circuit, the fewer turns are wound on the coil. The direct number of turns is calculated using the following formula:

U is the current voltage on the primary winding.

I - secondary winding current, or welding current.

S is the cross-sectional area of ​​the magnetic circuit.

The number of turns on the secondary winding is calculated using the following formula:

Toroidal core

Toroidal transformers have a rather complex core. It is best made from special transformer steel (an alloy of iron and silicon) in the form of a steel strip. The tape is pre-rolled into a dimensional roll. Such a roll, in fact, already has the shape of a torus.

Where can I get a ready-made core? A good toroidal core can be found on an old laboratory autotransformer. In this case, it will be necessary to unwind the old windings and wind new ones onto a ready-made core. Rewinding a transformer with your own hands is no different from winding a new transformer.

Features of torus winding

The primary winding is made of copper wire in glass cloth or cotton insulation. Under no circumstances should rubber-insulated wires be used. For a current on the primary winding of 25 A, the wound wire must have a cross-section of 5-7 mm. On the secondary, it is necessary to use a wire of a much larger cross-section - 30-40 mm. This is necessary due to the fact that a significant current will flow on the secondary winding greater strength- 120−150 A. In both cases, the wire insulation must be heat-resistant.

In order to properly rewind and assemble a homemade transformer, you need to understand some details of the process of its operation. It is necessary to correctly wind the wires. The primary winding is made using a wire of a smaller cross-section, and the number of turns themselves is much larger, this leads to the fact that the primary winding experiences very heavy loads and, as a result, can get very hot during operation. Therefore, the installation of the primary winding must be done especially carefully.

During the winding process, each wound layer must be insulated. To do this, use either a special varnished cloth or construction tape. The pre-insulating material is cut into strips 1-2 cm wide. The insulation is laid in such a way that inner part The windings are covered with a double layer, and the outer winding, respectively, with one layer. After this, the entire insulating layer is coated with a thick layer of PVA glue. The glue in this case has a dual function. It strengthens the insulation, turning it into a single monolith, and also significantly reduces the humming sound of the transformer during operation.

Winding devices

Winding the torus - difficult process, which takes a lot of time. In order to somehow alleviate it, they use special devices for winding.

• The so-called fork shuttle. The required amount of wire is first wound onto it, and then, using shuttle movements, the wire is sequentially wound onto the transformer core. This method is only suitable if the wire being wound is thin and flexible enough, and inner diameter The torus is so large that it allows the shuttle to be pulled through freely. At the same time, winding occurs quite slowly, so if you need to wind a large number of turns, you will have to spend a lot of time on it.
• The second method is more advanced and requires special equipment for its implementation. But with its help you can wind a transformer of almost any size and with very high speed. In this case, the quality of winding will be very high. The device is called a “breakable rim”. The essence of the process is as follows: the winding rim of the device is inserted into the hole of the torus. After this, the winding rim is closed into a single ring. Then the required amount of winding wire is wound onto it. And finally, the winding wire is wound from the rim of the device onto the torus coil. Such a machine can be made at home. His drawings are freely available on the Internet.

When building a receiver, amplifier or other radio equipment, a radio amateur has to deal with the work of remaking an old one or making a new transformer. Radio amateurs who are starting such work for the first time often do not have a clear idea of ​​how to wind, what material to choose and how to test the manufactured transformer. Information on these issues, gleaned from magazine articles and books, is usually insufficient, and the radio amateur has to most do work, relying on your own ingenuity or resorting to the help and advice of a more experienced comrade. This page will provide recommendations for making your own network transformer.

WINDING DEVICES

In factories with mass serial or continuous production, transformers are usually wound on special, often automated machines. It is, of course, difficult for radio amateurs to rely on a special winding machine, and therefore winding of transformers is usually done either directly by hand, or using simple winding devices.
Let's look at how you can make it from scrap materials and using ordinary tools. simple devices for winding.
The simplest such device is shown in Fig. 1. It consists of two racks / (or metal bracket), mounted on a board 2, and an axis 3 made of a thick (8-10 mm in diameter) metal rod, threaded through the holes in the racks and bent at one end in the form of a handle.
To wind the wire onto the finished frame 4, a wooden block 5 is made, slightly smaller in size than the frame window. A hole is drilled in the block to fit it onto the axle. The frame is put on the block, which is then placed on the axle and secured there with a pin 5. To prevent the frame from dangling and moving off the block, a sealing wedge 7 made of hard cardboard or cardboard must be inserted between them. thin plywood. To avoid axial play when winding, which is very important for even laying of the turns, on the free sections of the axis between the block and the racks it is necessary to put on pieces of tubes 8, which can be made from metal sheets, wrapping them around axis 3.
To remove the wound frame, you need to remove the pin 5 and pull out the axis 3.
A more convenient and reliable winding device is made from hand drill/ (Fig. 2), which must be clamped in a vice 2 or attached to the table so that nothing interferes with the free rotation of the drill handle. A metal rod 3 is clamped into the drill chuck, onto which a block with a frame is mounted. It is best to cut a rod with a diameter of 4-6 mm, and then the block with the frame can be clamped between two nuts 4. In this case, you can do without the block, clamping the frame with two cheeks made of plywood or PCB with holes in the center.
As a winding device, it is also convenient to use a ready-made machine for textile bobbins, a winder for rewinding film, a telephone inductor, etc. A film winder (after a little modification) is especially convenient, since it is made firmly and has a soft, play-free motion. Its alteration consists in replacing the short roller with a lock for film reels with a long axis with threads and wings for securing various frames.

No less important for winding work than the winding machine itself is the unwinding device, on which a coil of wire or the frame of an old transformer is placed, the wire of which is used for new winding. To prevent the insulation of the unwinding wire from deteriorating, and also to avoid shocks (which is important when laying turns in a row), the wire must run completely evenly.

The simplest device for unwinding wire is shown in Fig. 3. This is an ordinary metal rod / threaded into the holes of wooden posts 2 mounted on a board 3. Making a wooden block for the frame of the unwinding coil 4 is not necessary in this case. To prevent it from hitting or jumping when unwinding, you can roll up tube 5 of the required diameter from thick cardboard or paper, pass a rod through it and insert it tightly enough into the window of the frame.
It is better, however, to make a special unwinding device, shown in Fig. 4. A bracket / is bent from a strip of mild steel or other suitable material, which is attached to board 2 (or table). IN vertical racks The staples make holes (5-6 mm in diameter) with threads (M-5 or M-6 thread), into which bolts 3, sharpened from the ends to a cone, are screwed. A pin 4, cut along the entire length, is made from a metal rod with a diameter of 5-6 mm, shallow holes (3-4 mm) are drilled at the ends. The cones and the pin are equipped with corresponding nuts (preferably wings) 5 and jaws 6 for clamping the coil or frame with the wire.

Very important in the winding process is the ability to accurately count the number of turns. Simple but demanding special attention The method is to verbally count each revolution (or every other revolution) of the machine handle. If the winding must contain a large number of turns, then it is more convenient, after counting a hundred turns, to make a mark on paper (in the form of a stick), then summing up all the marks. In a machine with a gear drive, the gear ratio is taken into account, which should always be remembered.
Much better application a mechanical meter, which can be used as a bicycle speedometer or a counting mechanism from an electric meter, water meter, etc.
The meter can be connected to the machine using a flexible roller (a piece of thick-walled rubber tube) connecting the meter axis to the machine axis (Fig. 5a). In this case, each time you install a new frame, you have to disconnect the axle joint by removing the flexible roller, and after installing the new frame, put it on again. More convenient, but also more the hard way articulation is that the counter is connected to the machine through a pair of identical gears (Fig. 5, b). With this method, the counter is coupled to the machine all the time.

FRAME

The transformer frame (or inductor) is needed to isolate the windings from the core and to keep the windings, insulating gaskets and terminals in order. Therefore, it must be made of sufficiently durable insulating material. At the same time, it must be carried out from a sufficient thin material, in order not to take up much space in the core window. Usually the material for the frame is thick cardboard(presspan), fiber, textolite, getinaks, etc. Depending on the size of the transformer or inductor, the thickness of the sheet material for the frame is taken from 0.5 to 2.0 mm.
To glue the cardboard frame, you can use office universal glue or regular wood glue. The best glue nitro glue (enamel, rolled oats) should be considered to have good moisture resistance. Getinax or textolite frames are usually not glued together, but assembled “into a lock”.

The size of the core determines the shape and frame dimensions, after which its parts are drawn and then cut. If transformer plates with a middle core cut are used, then the height of the frame is made several millimeters less than the height of the window so that the core plates can be inserted without difficulty. To avoid errors, the dimensions of the core plates must be carefully measured (if they are unknown) and a sketch drawn on paper with the dimensions of individual parts of the frame. It is especially important to coordinate the individual parts of the frame when assembling it “into a castle”. Size ratios of frame and core plates for different types plates are given in Fig. 6.
A regular frame for a transformer can be made like this. First, the cheeks of the frame are cut out and a sleeve with cuffs on the end sides is cut out according to Fig. 7. Having made cuts at the folds, the pattern is rolled into a box, with side / glued to side 5. After this, both cheeks are put on the sleeve. Then you need to bend the flaps of the sleeve and, spreading the cheeks to the edges of the sleeve, glue the flaps to the outer planes of the cheeks. In the corners on outside cheeks, you can glue pieces of the same cardboard from which the frame sleeve was made. If the glue is strong and reliable enough, then the sleeve can be made without flaps, gluing the cheeks directly to the edges of the sleeve.

The prefabricated frame is more difficult to manufacture, but it has great strength and does not require gluing. Details of the prefabricated frame are shown in Fig. 8. They are manufactured as follows. The dimensions from the sketch are transferred by marking to a sheet of material (textolite, getinax, fiber). If the material is not too thick, then the parts are cut out with scissors. Then the grooves are cut into them using a file. In the cheeks /, after drilling several holes in them, windows are cut out. After this, having laid out the parts on the table, they adjust sides 2 and 3 of the sleeve so that when assembling the frame, all the cuts and protrusions of the “lock” come together. When marking and manufacturing parts 2, one of them can have a “key” part that is much larger in size (the contours are shown as dotted lines in Fig. 8) to accommodate contacts or petals for soldering winding leads. To avoid confusion of parts, they should be numbered before assembly. The order of assembly of the frame is clear from Fig. 9.

Immediately after making the cheeks, it is better to pre-drill holes for the leads in them “as a reserve”. When assembling the frame or gluing the cheeks, it is necessary to take into account which side of the transformer (or both) and which side of the cheeks the leads will be made in order to correctly position the sides of the cheeks that have holes for the leads. It is necessary to pay attention to the fact that the sides of the cheeks with holes in the case of a square core section are not covered by the core plates.
The finished glued or assembled frame must be prepared for winding, for which you should round off the corners of the sleeve and cheeks with a file, and also remove burrs. It is useful (but not necessary) to coat or impregnate the frame with shellac, bakelite, etc.

INSULATING GASKETS

In some cases, a large voltage is generated between adjacent rows of transformer windings, and then the insulation strength of the wire itself is insufficient. In such cases, between the rows of turns it is necessary to place insulating pads made of thin thick paper, tracing paper, cable, capacitor or tissue paper. The paper should be smooth and, when viewed against the light, there should be no visible pores or punctures.
The insulation between windings in a transformer must be even better than* between rows of turns, and the higher the voltage, the better. The best insulation is varnished fabric, but in addition to it, you also need dense cable or wrapping, which are also laid to level the surface for the convenience of winding the next winding on top. One layer of varnished cloth is always desirable, but two or three layers of tracing paper or cable paper can be substituted.
Having measured the distance between the cheeks of the finished frame, you can begin preparing the insulating strips of paper. To ensure that the outer turns of the winding do not fall between the edges of the strips and the cheeks, the paper is cut into slightly wider strips than the distance between the cheeks of the frame, and the edges are cut by 1.5-2 mm with scissors or simply folded. When winding, notched or folded strips cover the outermost turns of the winding. The length of the strips should ensure that the winding perimeter overlaps with the ends overlapping by 2-4 cm.

To insulate leads, solder points and winding taps, pieces of cambric or vinyl chloride tubes and pieces of varnished fabric are used.
To tighten and secure the beginning and end of thick windings (incandescent and output), pieces (10-15 cm) of keeper tape or strips, cut from varnished fabric and folded three or four times for strength, are prepared.
If the outer row of the winding is close to the core, then rectangular plates are cut out of a thin sheet of PCB or cardboard, which are inserted between the winding and the core after assembling the transformer.

WINDING AND OUTPUT WIRES

The windings of transformers that a radio amateur has to deal with are most often made of PE or PEL enamel insulated wire.
In power transformers, exclusively PE wire is used for the network and step-up windings, and for the incandescent windings of lamps, the same wire or, with a large diameter (1.5-2.5 mm), a wire with double paper insulation of the PBD brand.
The terminals of the ends and taps from windings made with thin wire are made with a wire of a slightly larger cross-section than the winding wire. For them it is better to take a flexible one stranded wire with elastic insulation (for example, vinyl chloride or rubber). If possible, it is advisable to take wires with different colors so that you can easily recognize any output from them. Leads from overstitching made with thick wire can be made with the same wire. Pieces of thin-walled insulating tubes must be placed on the ends or taps of these windings. The lead conductors must be of such length that they can be freely connected to the circuit elements or to the joint strip (comb).

WINDING

A reel with a wire intended for the next winding is clamped between the removable cheeks of the threaded pin of the unwinding device. A pin with a coil is installed in the cones of this device (Fig. 4). Depending on the diameter of the wire, the pressure of the cones and the degree of braking of the unwinding coil are adjusted.
The coil must be clamped so that it does not break when unwinding, since the success and ease of laying the wire turn to turn depends on this. The unwinding device is located in front of the winding machine no closer than 1 m (further is better).
The prepared transformer frame is clamped between two cheeks loosely mounted on a pin. The pin is then inserted into a drill chuck or clamped onto the shaft of a winding machine. The frame, as well as the coil with the wire, must be well centered so that it rotates evenly when winding and does not hit. The clamping brushes must be positioned in such a way that they do not cover the holes for the leads in the frame.
The coil with wire must be installed on the unwinding device and the winding machine on the table as shown in Fig. 10. The wire should go from the top of the coil to the top of the transformer frame. The machine or drill is located above the table at such a height that there is a distance of 15-20 cm between the axis of the machine and the plane of the table; then when winding, the left hand can be freely placed on the table without interfering with the rotation of the machine with the frame.
Before you start winding, you need to prepare insulating pads, lead conductors, an insulating tube for the leads, a sheet of paper and a pencil for making marks when counting turns, if you don’t have a counter, scissors for trimming the pads, a piece of fine sandpaper for stripping the insulation and a heated soldering iron for soldering leads. You yourself need to sit freely against the table (workbench) and practice hand interactions. With your right hand you need to rotate the winding machine so that the wire rests on the frame from above, and with your left hand you need to hold and pull the wire, directing its movement so that it lies evenly turn to turn (to do this, place your left hand on the table under the axis of the machine or device, pulling it forward as far as possible). The farther the wire is directed from the frame, the more accurately and easily the wire is laid.

The frame, verified and secured to a machine or drill, is wrapped in a thin paper strip. To strip
held, it can be slightly glued.
The lead conductor or the end of the winding wire itself can be secured in two ways. If the wire is thin, then the conclusion is made differently, flexible wire. Such a lead should be long enough so that, after passing it through the hole in the frame, it is possible to wrap it (in one turn) around the frame sleeve. Solder the stripped end of the wound wire to the tip of the output conductor, which has been previously stripped and tinned by 2-3 mm, and, having insulated the soldering point with a piece of paper or varnished cloth folded in half, winding begins (Fig. 11a). The insulating pad is pressed when winding with subsequent turns (Fig. 11.6). The lead threaded into the hole in the frame must be wrapped several times around the axis (pin) of the winding machine or tied to it so that during further winding it does not pull out of the frame. For greater reliability, the leads can be tied to the sleeve with several turns of strong thread. Another method is that the lead wire, after passing it through the holes in the cheek of the frame, is captured by a strip of release paper, the edge of which is folded under the wire (Fig. 11c). Then a strip, which should be the width of the frame, is wrapped around the sleeve and presses the lead wire. In this case, under the strip (at the end of the output wire) you need to place an insulating pad, which will then cover the junction of the output and wound wires.
To the tinned end of the output wire protruding from under the gasket, located at the other cheek of the frame, solder the stripped tip of the wound wire and wind it. In this case, the insulating pad will be pressed by the first turns of the winding, and the output end will be pressed by the turns of its first row (Fig. 11, d).

Winding must be done slowly at first, adjusting the hand so that the wire goes and lies turn to turn with some tension. During winding process this series The left hand should be moved evenly behind the laying of the turns, trying to maintain the angle of tension. Thus, subsequent turns of the first row press the previous ones. Each row should not be wound up to the cheek of the frame by 2-3 mm in order to prevent the turns from falling along the cheek. This is especially important when winding high-voltage windings (for example, step-up windings in power or anode windings in output transformers).
Before starting winding (when the first terminal is tucked in and soldered), the revolution counter must be set to zero or its readings must be recorded. In the absence of a counter, the revolutions are counted silently or out loud, and every hundred revolutions is marked on paper with a stick.
After winding each row, the wire must be left taut so that when applying the paper gasket, the wound part of the winding does not unravel. To do this, you can press the wire to the cheek of the frame with a clothes clip. The gasket must cover the entire row of windings. It is glued together or temporarily (until it is held in coils next row) is pressed against the winding with a rubber ring, which can be made from thin elastic cord.
The last output of the winding can be done in the same way as the first. Before winding the last complete or incomplete row, this output conductor, together with a paper gasket (Fig. 11.0), must be laid on the frame and, wrapping the frame with a strip of gasket, press the conductor with a rubber ring. After winding the last row, the wound wire is cut and, after stripping, soldered to the tinned tip of the output conductor (Fig. 11e). If the output end must come out of the cheek, near which the last row of the winding ends, then the output end blank is made in the form of a loop (Fig. 11, e), which is laid on the frame in the same way as a regular output conductor.
Branches from part of the turns of the winding, wound with a not too thin wire (from 0.3 mm or more), can be made in the form of a loop with the same wire (without cutting it), as shown in Fig. 12, a. In this case, the loop is passed through the hole of a folded paper strip, which is tightened after pressing it to the winding with subsequent turns (Fig. 12.6). You can do without a paper strip if you put an insulating tube on the loop-shaped outlet. Taps from a winding made with a thin wire (less than 0.3 mm) are usually made with a flexible lead conductor, which is soldered to the wire, as shown in Fig. 12, c.

The beginning and end of the thick wire windings are led out directly (without separate lead wires) through holes in the cheeks of the frame. You only need to put flexible insulating tubes on the ends coming out of the frame. The ends of the winding are secured using a narrow cotton tape. The tape is folded in half, forming a loop into which the first output end of the wire is passed. Then holding the tape with your hand and wrapping 6-8 turns tightly around it, tighten the loop (Fig. 13a). The second output end of the winding is also secured. In this case, without finishing the last 6-8 turns, a tape folded in a loop is placed on the frame, the last turns are wound, which press this tape to the frame, and, passing the end of the winding into the loop, the loop is tightened (Fig. 13.6). If the winding of thick wire contains a small number of turns (no more than 10), then the lead ends can be secured with tape by tightening on both sides, as shown in Fig. 13, c.
In multilayer windings of thick wire, it is recommended to make paper spacers after each row. If the frame is not particularly strong, then each subsequent row should be made one or two turns less, and then fill the voids between the winding and the cheeks of the frame with twine or thread. This is important in the case when there are still other windings on top.
If the wire breaks during winding or when the winding is made from separate pieces of wire, the ends of the wires are connected as follows. For wires of small diameter (up to 0.3 mm), the ends are cleaned by 10-15 mm with sandpaper, carefully twisted and soldered. The junction of the wires is then insulated with a piece of release paper or varnished cloth. The ends of thicker wires are usually soldered without twisting. Thin wires (0.1 mm or less) can be welded by twisting the ends by 10-15 mm (without stripping the insulation) and then placing them in the flame of an alcohol lamp, gas or several matches. The connection of the wires in this case is considered reliable if a small ball forms at the end of the twist.
Windings of thin wire with a number of turns of several thousand can be wound not turn by turn, but “in bulk.” However, the turns should be laid evenly so that the winding does not have bumps or dips. Approximately every millimeter of thickness of such winding, paper gaskets must be made.
To symmetry two windings or halves of windings, frames are often used, partitioned in the middle with a cheek. First, one half of the winding is wound, and then the frame is turned 180° and the other half is wound. Since the turns of each half of the winding will be wound in different directions, when connecting the halves in series, you need to connect their beginnings or ends. In this case, it is more convenient to make conclusions from the windings on opposite sides of the frame.
The windings of a transformer or inductor can be made without a frame. Winding is done basically in the same way as with the frame, but the spacers between the windings (or rows) are made very wide (three times wider than the winding).
After winding each section, the protruding edges of the gasket are cut at the corners with scissors or a blade safety razor and, bending them, close the wound section (Fig. 14). End sides of wound windings
then you need to fill it with tar (from dry elements and batteries).

From the outside, if the top row of turns of the last winding is wound with thick wire and done fairly neatly, the coil does not need to be wrapped in anything. If the upper winding is made of thin wire, and is not wound turn to turn, then the coil should be wrapped in paper or leatherette.
In order to easily understand the leads and taps when installing the transformer, it is advisable to use multi-colored lead conductors. For example, make the terminals of the transformer's network winding yellow, the beginning and end of the step-up winding - red, the tap from the middle of the step-up winding and the wire from the screen - black, etc. You can, of course, use single-color lead wires, but then you need to put a wire on each pin cardboard tag with the appropriate designation.

CORE ASSEMBLY AND TERMINAL INSTALLATION

Having finished winding the transformer, they begin to assemble its core. If the winding leads are made on one side of the cheek of the frame, then it is placed on the table with the leads down. If the conclusions are made on both sides of the cheeks, then the frame must be positioned so that the largest number of conclusions and the thickest of them are at the bottom; the upper terminals must be folded several times and tied temporarily to the winding so that they do not interfere with the assembly of the core (Fig. 15, i). This is especially important when the core plates are shaped with notches on the middle core.
The power transformer core plates are assembled without a gap into a ceiling (alternately left and right), as shown in Fig. 15.6. The cores of output transformers or filter chokes are often assembled with an air gap, inserting plates only on one side (Fig. 15e). To ensure that this gap remains unchanged, a strip of paper or cardboard is inserted into the joint between the plates and the core pads. In plates with a notch on the middle core, the thickness of the gap is determined by the thickness of the notch.
If the frame is not very strong, then you need to fill it with plates (especially at the end of assembly) very carefully, since otherwise you can cut the sleeve with the sharp edge of the middle core and damage the winding. To prevent this, it is advisable to insert and bend a protective strip of mild steel into the frame window (Fig. 15.6).

When assembling a core from plates with a perforation of the middle core, you need to use an auxiliary guide plate (Fig. 15d), cutting it, for example, from one core plate.
The frame window is filled with as many plates as possible. If the transformer has been disassembled and rewound, then when reassembling it, you must use all the previously removed plates. During the assembly process, the core should be pressed several times by inserting a ruler or rod into the frame window. The last plates, if they fit tightly, can be driven in with a hammer, lightly hitting them through a wooden lining. After this, turning the transformer in different directions and placing it on a flat surface, it is necessary to straighten the core with light blows of a hammer through a wooden lining.
The core, after its assembly, must be well tightened. If there are holes in the plates, then it is tightened with bolts through overhead strips or angles (Fig. 16, a and b). At the same time, you can install a pin with petals for soldering the output ends of the windings.
Core small size, assembled from plates without holes, can be tightened with one common bracket cut from thin mild steel (Fig. 16, c).

It is very convenient to use the chassis on which the transformer is to be installed to fasten the transformer and tighten its core. A window is cut out in the chassis to allow passage of the lower part of the coil with leads, a transformer is installed and the core is tightened with bolts through a common overhead frame (Fig. 16d). The output ends are connected to the corresponding sections of the circuit either directly or through a shield with contact petals installed on the chassis.

SIMPLE TESTS

The transformer, after its winding and assembly, must be tested.
Power transformers are tested by connecting the primary (mains) winding to the electrical network.
To check the absence short circuits in transformer windings, the following simple method can be recommended. The network is connected in series with the primary winding of the transformer being tested electric lamp L (Fig. 17), designed for the corresponding network voltage. For transformers with a power of 50-100 W, take a lamp of 15-25 W, and for transformers of 200-300 W, a lamp of 50-75 W. If the transformer is working properly, the lamp should burn at approximately “quarter incandescence.” If you short-circuit any of the windings of the transformer, the lamp will burn almost fully incandescent. In this way, the integrity of the windings, the correctness of the conclusions and the absence of short-circuited turns in the transformer are checked.

After this, making sure that the winding terminals are not shorted, the primary winding of the transformer must be connected directly to the network for one to two hours (by closing lamp L with the Vk switch). At this time, you can use a voltmeter to measure the voltage on all windings of the transformer and make sure that their values ​​correspond to the calculated ones.
In addition, it is necessary to test the reliability of the insulation between the individual windings of the transformer. To do this, one of the output ends of the step-up winding // must touch each of the outputs of the network winding / in turn. In this case, the voltage of the step-up winding, together with the voltage of the mains winding, will act on the insulation between these windings. In the same way, touching the output end of the step-up winding // to the output ends of other windings, the insulation of these windings is tested. The absence of a spark or weak sparking (due to the capacitance between the windings) indicates the adequacy of the insulation between the windings of the transformer.
The transformer test must be carried out carefully, being careful not to fall under high voltage step-up winding.
Other types of transformers (output transformers, etc.) with windings of a sufficiently large number of turns are tested in the same way. By measuring the voltage on the windings of the transformer, the transformation ratio can be determined.
Having verified as a result of the test that the manufactured transformer is in good working order, the latter can be considered ready for installation and installation.

A program for calculating a transformer can be