To convert current they are used different kind special devices. Toroidal transformer TPP for welding machine and other devices, you can wind it with your own hands at home, it is an ideal energy converter.
Design
The first bipolar transformer was made by Faraday, and according to the data, it was a toroidal device. A toroidal autotransformer (brand Shtil, TM2, TTS4) is a device designed to convert alternating current from one voltage to another. They are used in various linear installations. This electromagnetic device can be single-phase or three-phase. Structurally consists of:
- Metal disk made of rolled magnetic steel for transformers;
- Rubber gasket;
- Primary winding terminals;
- Secondary winding;
- Insulation between windings;
- Shield winding;
- An additional layer between the primary winding and the shielding winding;
- Primary winding;
- Insulating core coating;
- Toroidal core;
- fuse;
- Fastening elements;
- Cover insulation.
A magnetic circuit is used to connect the windings.
This type of converter can be classified by purpose, cooling, type of magnetic circuit, windings. By purpose there is impulse, power, a frequency converter(TST, TNT, TTS, TT-3). For cooling – air and oil (OST, OSM, TM). By the number of windings - two-winding or more.
Photo - the principle of operation of the transformer A device of this type is used in various audio and video installations, stabilizers, and lighting systems. The main difference between this design and other devices is the number of windings and the shape of the core. Physicists believe that the ring shape is the ideal design for an anchor. In this case, the winding of the toroidal converter is carried out evenly, as well as the heat distribution. Thanks to this arrangement of the coils, the converter cools quickly and even during intensive operation does not require the use of coolers.
Photo - toroidal ring converter Advantages of a toroidal transformer:
- Small dimensions;
- The output signal on the torus is very strong;
- The windings have a short length, and as a result, reduced resistance and increased efficiency. But also because of this, a certain background sound is heard during operation;
- Excellent energy saving characteristics;
- Easy to install yourself.
The converter is used as a network stabilizer, Charger, as a power supply for halogen lamps, a ULF tube amplifier.
Photo - finished TPN25 Video: purpose of toroidal transformers
Principle of operation
The simplest toroidal transformer consists of two windings on a ring and a steel core. The primary winding is connected to the source electric current, and the secondary one – to the electricity consumer. Due to the magnetic circuit, the individual windings are connected to each other and their inductive coupling is strengthened. When the power is turned on, an alternating magnetic flux is created in the primary winding. Meshing with individual windings, this flux creates an electromagnetic force in them, which depends on the number of turns of the winding. If you change the number of windings, you can make a transformer to convert any voltage.
Photo - Operating principle Also, converters of this type are either buck or boost. The toroidal step-down transformer has high voltage at the terminals of the secondary winding and low at the primary. Increasing is the opposite. In addition, the windings can be of higher or lower voltage, depending on the characteristics of the network.
How to do
Even young electricians can make a toroidal transformer. Winding and calculation are not complicated. We suggest considering how to properly wind a toroidal magnetic circuit for a semi-automatic machine:
Considering that 1 turn carries 0.84 Volts, the winding circuit of a toroidal transformer is carried out according to the following principle:
So you can easily make your own 220 to 24 volt toroidal transformer. The described circuit can be connected to both arc welding and semi-automatic welding. The parameters are calculated based on the wire cross-section, number of turns, and ring size. The characteristics of this device allow for stepwise adjustment. Among the advantages of the assembly principle: simplicity and accessibility. Among the disadvantages: heavy weight.
Price overview
You can buy a toroidal transformer HBL-200 in any city Russian Federation and CIS countries. It is used for various audio equipment. Let's look at how much the converter costs.
Many home craftsmen are thinking about making a toroidal transformer with their own hands. This is explained by the fact that it performance characteristics significantly better than transformers with cores of other shapes. For example, with the same electrical characteristics, its weight can be up to one and a half times less. In addition, the efficiency of such a transformer is noticeably higher.
There are two main reasons why the production of a toroid is not always successful:
- It is difficult to find a suitable core.
- Manufacturing is labor intensive, winding the transformer is especially difficult.
Read also:
Calculation of a toroidal transformer
For a simplified calculation of a transformer on a toroidal magnetic circuit, you need to know the following initial data:
- The input voltage U1 supplied to the primary winding.
- Outside diameter D core.
- Its internal diameter is d.
- Magnetic core thickness – H.
Square cross section magnetic circuit S c determines the power of the transformer and, accordingly, the reliability of the future welding machine. Values of 45-55 cm 2 are considered optimal. Its value can be calculated using the formula:
S c = H * (D – d)/2.
An important characteristic of the core is the area of its window S0, since this parameter determines not only the convenience of winding winding wires and the intensity of excess heat removal, but also affects the nature of magnetic scattering. Optimal values this parameter is 80-110 cm 2. The formula allows you to calculate its value:
S 0 = π * d 2 / 4.
P = 1.9 * S c * S 0, where S c and S 0 are taken in square centimeters, and P is obtained in watts.
It is better to calculate the number of turns in the primary winding using the voltage on the secondary winding as an initial data:
W 1 = (U 1 * w 2) / U 2, where U 1 is the voltage supplied to the primary winding, and U 2 is removed from the secondary.
The fact is that it is better to regulate the welding current by changing the number of turns of the primary winding, since the current value in it is less than in the secondary. Let, for example, you need to obtain three values of output current 60 A, 80 A and 100 A with a transformer power of 5000 W.
These values welding current the following voltage values on the secondary winding will correspond:
U 21 = P / I 21 = 5000 W / 60 A = 83.3 V;
U 22 = P / I 22 = 5000 W / 80 A = 62.5 V;
U 23 = P / I 23 = 5000 W / 100 A = 50 V.
Let the secondary winding contain w 2 = 70 turns. Now you can calculate the number of turns in the corresponding stages of the primary winding for a network voltage U 1 = 220 V:
W 11 = (U 1 * w 2) / U 21 = 220 V * 70 / 83.3 V ≈ 185 turns;
W 12 = (U 1 * w 2) / U 22 = 220 V * 70 / 62.5 V ≈ 246 turns;
W 13 = (U 1 * w 2) / U 23 = 220 V * 70 / 50 V = 308 turns.
The last value should be increased by 5%:
W 13 = 308 * 1.05 ≈ 323 turns - this will be the required number in the primary winding, and taps should be made from the 185th and 246th turns.
For homemade transformers for welding, the permissible current density in the windings is j = 3 A/mm 2. Knowing it, you can find the cross-sectional area of the winding wires. In the example given earlier, the maximum current in the primary winding is:
I 1 m = P / U 1 = 5000 W / 220 V ≈ 23 A.
The cross-section of this wire should be:
S 1 = I 1 m / j = 23 A / 3 A/mm 2 ≈ 8 mm 2.
In the secondary winding, a wire with a cross-sectional area should be used:
S 2 = I 23 / j = 100 A / 3 A/mm 2 ≈ 33 mm 2.
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Selection and production of a toroidal core
The best material for the manufacture of a toroidal magnetic core is transformer strip steel. To make the core, this tape is rolled into a torus-shaped roll. rectangular section. If there is such a tape or a core made from it, then there will be no special problems in the manufacture of a magnetic core for a toroidal transformer.
If the internal diameter d is small, you can unwind part of the tape from the inside of the torus, and then wind it on the outer surface of the core. As a result, both diameters will increase, and the area of the internal part of the magnetic circuit will increase. True, the cross-sectional area of the core S 0 will decrease slightly. If necessary, you can add tape from another magnetic circuit.
A good ready-made toroidal core can be taken from a laboratory autotransformer LATR 1M designed for a current of 9 A. You just need to rewind its windings. It happens that the stator magnetic circuit of a suitable electric motor is used to make a toroidal core for a transformer.
Another way to manufacture a toroidal core is to use plates from a faulty powerful industrial or power transformer, which at one time powered a tube color TV, as a material. First, a hoop with a diameter of about 26 cm is made from these plates using rivets. Then, inside this hoop, they begin to insert the plates end-to-end, one after another, holding them with your hand from unwinding.
After obtaining the required cross-section S0, the magnetic circuit is ready. To increase S0, you can make two toroids of the same size and then connect them together. The edges of the toroids should be slightly rounded using a file. Two rings should be made from electrical insulating cardboard, having an internal diameter d and an external diameter D, as well as two strips for the internal and outer side Torah. After placing them on the toroid, the core is wrapped over the cardboard pads with kiper or woven insulating tape. The magnetic core is ready, and you can start winding the windings.
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 an alternating voltage appears on the primary winding, a magnetic current is excited inside the core. 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
A toroidal transformer, or simply a torus, is most often made at home as the main part for a home welding machine and more. 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 welding electrodes. Most often for household needs Electrodes with a diameter of 2−5 mm are quite sufficient. 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: than larger area cross-section 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 much higher current will flow on the secondary winding - 120-150 A. In both cases, the wire insulation must be heat-resistant.
In order to rewind and assemble correctly 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 insulating material is pre-cut into strips 1-2 cm wide. The insulation is laid in such a way that the inner part of the winding is covered with a double layer, and the outer part, 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 a torus is a complex and time-consuming process. In order to somehow alleviate it, they use special devices for winding.
- The so-called fork shuttle. It is pre-wound on it required amount wires, and then, using shuttle movements, the wires are sequentially wound onto the transformer core. This method is only suitable if the wire being wound is sufficiently thin and flexible, and the internal diameter of 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 this.
- 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 at a 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.
A toroidal transformer is an electrical voltage or current converter whose core is bent into a ring and closed. The cross-sectional profile differs from round; the name is still used for lack of a better one.
Differences between toroidal transformers
Michael Faraday is recognized as the author of toroidal transformers. It is possible to come across a utopian idea in Russian literature (especially in communist times): Yablochkov was the first to collect such a thing, comparing the indicated date - usually 1876 - with early experiments in electromagnetic induction(1830). The conclusion is: England is half a century ahead of Russia. Those interested in details will be referred to the review. Detailed information about the design of the world's first toroidal transformer is provided. The product is distinguished by the shape of the core. In addition to toroidal, it is customary to distinguish by shape:
- Armored. They are distinguished by the redundancy of the ferromagnetic alloy. To close the field lines (so that they pass inside the material), the yokes cover the windings with outside. As a result, the input and output are wound around a common axis. One on top of the other or next to each other.
- Rod. The transformer core runs inside the winding turns. The entrance and exit are spatially separated. Yokes absorb a small part of tension lines magnetic field, passing outside the turns. Actually needed to connect the rods.
Toroidal transformer
It’s difficult for a beginner, it’s worth explaining in more detail. The core is the part of the core that runs inside the turns. Wire is wound around the frame. The yoke is the part of the core that connects the rods. We need to transmit magnetic field lines. The yokes close the core, forming a solid structure. Closedness is required for the free propagation of a magnetic field within the material.
The topic Magnetic induction shows that inside a ferromagnet the field is significantly enhanced. The effect forms the basis for the functioning of transformers.
The composition of the yoke core is minimal. In armored armor, it additionally covers the windings from the outside along the length, as if protecting. The name comes from the analogy. Michael Faraday chose the torus rather intuitively. Formally, it can be called a rod core, although the guide of the axis of symmetry of the windings runs in an arc.
The support for the first magnet (1824) was a horse's shoe. Perhaps this fact gave the direction of flight of the scientist’s creative thought the right azimuth. If Faraday used any other material, the experiment would end in failure.
The torus is wound with a single ribbon. Such cores are called spiral, in contrast to armor and rod cores, which appear in the literature under the term lamellar. This will be misleading. Once again it should be said: a toroidal core, being wound with separate plates, is called spiral. You have to break it in parts when there is no tape. This is due to purely economic reasons.
Let's summarize: in its original form, the Faraday toroidal transformer had a round core. Today the form is unprofitable; it is impossible to ensure mass production with the appropriate technology. Although the deformation of the wire at the bend angles clearly leads to a deterioration in the characteristics of the product. Mechanical stress increases the ohmic resistance of the winding.
Toroidal transformer cores
The toroidal transformer is named for the shape of its core. Michael Faraday made a bagel using whole piece mild round steel. The design is inappropriate for modern stage for several reasons. The main focus is on minimizing losses. A solid core is disadvantageous; eddy currents are induced, strongly heating the material. The result is an induction melting furnace that easily turns steel into liquid.
To avoid unnecessary waste of energy and heating of the transformer, the core is cut into strips. Each is isolated from its neighbor, for example, with varnish. In the case of toroidal cores, they are wound in a single spiral or in strips. Steel usually has an insulating coating on one side that is a unit of micrometer thick.
The mentioned steels are used for construction, which are quite often toroidal in design. Those interested can familiarize themselves with GOST 21427.2 and 21427.1. For cores (as the name of the documents suggests), today anisotropic cold-rolled sheet steel is more often used. The name implies: the magnetic properties of the material are not the same along different coordinate axes. The field flow vector must coincide with the direction of the rolling (in our case it moves in a circle). Previously, another metal was used. The cores of high-frequency transformers can be made of 1521 steel. The features of the materials used were discussed within the site (see). Steel is marked in different ways; the designation includes the following information:
- The first place is given to the number characterizing the structure. For anisotropic steels, 3 is used.
- The second digit indicates the percentage of silicon:
- less than 0.8%.
- 0,8 – 1,8%.
- 1,8 – 2,8%.
- 2,8 – 3,8%.
- 3,8 – 4,8%.
- The third digit indicates the main characteristic. There may be specific losses, the value at a fixed field strength.
- Steel type. As the number increases, the specific losses are lower. Depends on metal production technology.
The relative position of the end and beginning of the tape loses its significance. To prevent the spiral from unwinding, the last turn is welded to the previous one. spot welding. Winding is carried out with tension; tapes assembled from several strips usually cannot be fitted tightly; the weld seam is overlapped. Sometimes the torus is cut into two parts (split core), but in practice this is required relatively rarely. The halves are pulled together with a bandage during assembly. During the manufacturing process, the finished toroidal core is cut with a tool, and the ends are ground. The coils of the spiral are held together with a binder to prevent it from unwinding.
Winding of toroidal transformers
It is standard practice to additionally insulate the toroidal core from the windings, even if varnished wire is used. Electrical cardboard (GOST 2824) with a thickness of up to 0.8 mm is widely used (other options are possible). Common cases:
- The cardboard is wound with the previous turn captured on a toroidal core. The method is characterized as full overlap (half the width). The end is glued or secured with keeper tape.
- The ends of the core are protected by cardboard washers with cuts 10–20 mm deep, 20–35 mm in increments, covering the thickness of the torus. The outer and inner edges are covered with stripes. Technologically, the washers are the last to be assembled; the cut teeth are bent. A keeper tape is wound spirally on top.
- The cuts can be made on strips, then they are taken with a margin so that they are greater than the height of the torus, the rings are strictly in width, and are placed on top of the bends.
- Thin strips and rings of textolite are secured to the toroidal core with fiberglass tapes with a full overlap.
- Sometimes the rings are made of electrical plywood, getinax, thick (up to 8 mm) textolite with a margin of outer diameter of 1-2 mm. The outer and inner edges are protected with cardboard strips with a bend at the edges. Between the first turns of the winding, the core remains air gap. The gap under the cardboard is needed in case the edges under the wire fray. Then the current-carrying part will never touch the toroidal core. A keeper tape is wound on top. Sometimes the outer edge of the rings is smoothed so that the winding at the corners goes smoothly.
- There is a type of insulation similar to the previous one; on the inside, along the rings on the outer ribs, there are grooves to the core, where the strips are placed. The elements are made of textolite. A keeper tape is wound on top.
The windings are usually made concentric (one above the other), or alternating (as in the first experiment of Michael Faraday in 1831), sometimes called disk windings. In the latter case, a fairly large number of them can be wound through one, alternately: now high voltage, now low. Pure electrical copper is used (99.95%) resistivity 17.24 – 17.54 nOhm m. Due to the high cost of the metal, refined aluminum is used for the manufacture of toroidal transformers of low and medium power. For other cases, restrictions on conductivity and plasticity affect.
In powerful transformers copper wire It comes with a rectangular cross-section. This is done to save space. The core must be thick, allowing significant current to pass through, so as not to melt; a round cross-section will lead to excessive growth in size. The gain in uniformity of field distribution over the material would be reduced to zero. A thick rectangular wire is quite convenient to lay, which cannot be said about a thin one. Otherwise (according to design features), winding is carried out in exactly the same ways as in the case of a conventional transformer. Coils are made cylindrical, screw, single-layer, multi-layer.
Definition of Toroidal Transformer Design
For those interested in the issue, we recommend studying the book by S.V. Kotenev, A.N. Evseev on calculating the optimization of toroidal transformers (Hot Line - Telecom publication, 2011). We remind you: the publication is protected by copyright law. Professionals will find the strength (means) to purchase a book if necessary. According to the chapters, the calculation begins by determining the idle speed parameters. It describes in detail how to find active and reactive currents and calculate key parameters.
The printed publication, despite some controversial presentation, simultaneously makes it clear why a transformer connected to the circuit, without a load, does not burn out (the current energy is consumed by magnetization). Although it would seem that the obvious outcome of the event was predicted.
The number of turns of the primary winding is selected from the condition of not exceeding the magnetic induction maximum value(before entering saturation mode, where the value does not change with increasing field strength). If the design is carried out for a 230 volt household network, a tolerance is taken in accordance with GOST 13109. In our case, this means an amplitude deviation within 10%. We remember: the entire industry switched to 230 volts in the 21st century (220 is not used, it is cited in the literature as a “legacy of a difficult past”).
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 important elements 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 on step-by-step rewinding of a 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 quality indicators 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 it happens short circuit in the windings, then the light will light up and prevent the consequences of the error; if everything is fine, then 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 core with a small window will not allow you to wind the required number of turns with 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 of insulated wire around the donut over all the windings, plug the transformer into 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 with a 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 recognized by the highest resistance for a given winding (the middle point will have the 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 calculations, the total load on the transformer in the amplifier was 3A, which corresponded with a margin for the load of the designed power supply.
Taking into account overall power 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 a separate spool. 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 that, how many turns we will need to wind to get 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. On this segment EMF was also induced (approximately ¼ turn), which was 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 yet touched the third secondary winding. 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 own experience on rewinding a transformer with your own hands, you should also not perceive the article as a scientific work.
I also advise you to find brochures in in electronic format 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!