Homemade DC welding machine. How to make a welding machine with your own hands: a step-by-step description of how to calculate and assemble a welding machine (110 photos). Features of the manufacture of the core

From the article you will learn what it is to make them with your own hands is quite simple, if you have elementary knowledge in electrical engineering and necessary tools. As a basis for a welding machine, both a ready-made transformer and a home-made one can be taken.

Of course, such designs consume a lot of power, therefore, a strong voltage drop will be observed in the network. This may affect the operation of household electrical appliances. It is for this reason that designs based on semiconductor elements are much more effective. To put it simply, these are devices.

The simplest welding machine

So, the first thing to consider is the most simple designs that anyone can repeat. Of course, these are the devices based on transformers. The design discussed below allows you to work on voltages of 220 and 380 volts. The maximum electrode diameter used in welding is 4 mm. The thickness of the welded metal elements ranges from 1 to 20 millimeters. About that, you now know in full. And you can move from simple to complex.

Despite such excellent characteristics, the manufacture of the welding machine is made from readily available materials. You will need a three-phase step-down transformer for assembly. At the same time, its power should be about 2 kilowatts. It is also worth noting that you will not need all the windings. Therefore, in the event that one of them fails, there will be no problems with further design.

Alteration of the transformer

The bottom line is that you only need to make changes in the secondary winding. To facilitate the task, the article below shows a diagram of the welding machine, its connection to the network is also described.

So, the primary winding does not need to be touched, it has all the characteristics necessary for operation from a 220 volt AC mains. There is no need to disassemble the core, it is enough to disassemble the secondary winding directly on it, and wind a new one instead.

The transformer you have to choose has several windings. Three primary, the same number of secondary. But there are also medium windings. There are also three of them. It is instead of the middle one that it is necessary to wind the same wire that was used to make the primary one. Moreover, it is necessary to make taps from every thirtieth turn. About 300 turns in total should have each winding. Due to the correct winding of the wire, the power of the welding machine can be increased.

The secondary winding is wound on both extreme coils. It is difficult to specify the exact number of turns, since the more, the better. The wire is used with a cross section of 6-8 square millimeters. Together with it, a thin wire is wound at the same time. As a power cable, you need to use a stranded cable in reliable insulation. This is how they do it by hand.

If we analyze all the structures made using this technology, it turns out that the approximate amount of wire is about 25 meters. If there is no wire with a large cross section, you can use a cable with an area of ​​3-4 square millimeter. But in this case, it must be folded in half when winding.

Transformer connection

The design has a simple welding machine. A semi-automatic device can be made on its basis if one more winding is made to power the electric drive for supplying electrodes. Please note that the output of the transformer will be a very large current. Therefore, all switching connectors must be made as durable as possible.

To make terminals for connecting to the secondary winding terminals, you will need a copper tube. It should have a diameter of 10 millimeters and a length of 3-4 cm. It needs to be riveted from one end. You should get a plate in which you need to make a hole. Its diameter should be about one centimeter. Wires are inserted from the other end. Regardless of whether the welding machine is DC or AC, switching is made as rigid and reliable as possible.

It is desirable to clean them perfectly, if necessary, treat them in acid and neutralize it. To improve contact, the second edge of the tube should be slightly flattened with a hammer. The conclusions of the primary winding are best attached to the textolite board. Its thickness should be about three millimeters, it can be more. It is rigidly attached to the transformer. In addition, 10 holes need to be made in this board, each with a diameter of about 6 millimeters. Look at the scheme of the welding machine, how it is connected to the 220 and 380 Volt network.

They need to install screws, nuts and washers. The conclusions of all primary windings are connected to them. In the event that welding is required to work from a 220-volt household network, the extreme windings of the transformer are connected in parallel. The middle winding is connected in series with them. Welding will work ideally when powered by 380 volts.

To connect the primary windings to the mains, you need to use a different scheme. Both extreme windings are connected in series. Only after that, the middle winding is switched on in series with them. The reason for this lies in the following: the middle winding is additional; with its help, the voltage and current in the secondary circuit are reduced. Thanks to this, welding machines made by their own hands according to the above technology work in normal mode.

Manufacture of the electrode holder

Of course, an integral part of any welding machine is the electrode holder. There is no need to buy ready-made, if you can make it from improvised materials. You need a three-quarter pipe, its total length should be about 25 centimeters. At both ends, it is necessary to make small notches, about 1/2 of the diameter. With such a holder, the welding machine will work normally. There is a separate requirement for plastic structural elements - they must be located as far as possible from the transformer and holder.

They need to be done three to four centimeters from the edge. Then take a piece of steel wire with a diameter of 6 millimeters, weld it to the pipe opposite the larger recess. On the other hand, it is necessary to drill a hole, attach a wire to it, which will be connected to the secondary winding.

Network connection

It is worth noting that you need to connect the welding machine in accordance with all the rules. First, you need to use a knife switch, with which you can easily disconnect the device from the network. Please note that do-it-yourself welding machines, in terms of safety, should not be inferior to analogues manufactured by the industry. Secondly, the cross section of the wires for connecting to the network must be at least one and a half square millimeters. The current consumption of the primary winding is a maximum of 25 amperes. In this case, the current can be changed in the range of 60..120 amperes. Please note that this design is relatively simple, so it is only suitable for domestic use.

Spot welding machine

A spot type welding machine will also be useful. The designs of such devices are no less simple than the previous ones. However, the output current is very large. But it is possible to produce resistance welding of metals up to three millimeters thick. In most designs there is no adjustment of the output current. But you can do it if you wish. True, the whole homemade work becomes more complicated. The need to regulate the output current is eliminated, since the welding process can be controlled visually. Of course, inverter welding machines will be much more efficient. But point ones can do things that no other design can do.

For manufacturing, you will need a transformer with a power of about 1 kilowatt. The primary winding remains unchanged. Only the secondary will need to be redone. And if a transformer from a household microwave oven is used, then you need to knock out the secondary winding, instead winding several turns of large-section wire. If possible, it is better to use a copper bus. The output should be about five volts, but this will be enough for the full operation of the device.

Electrode holder design

Here it is slightly different from the one discussed above. For the manufacture you will need small duralumin blanks. Suitable rods with a diameter of 3 centimeters. The lower one must be motionless, completely isolated from the contacts. As an insulating material, you can use textolite washers, as well as varnished cloth. Any, even the simplest spot welding machine needs a reliable electrode holder, so pay maximum attention to its design.

The electrodes are made of copper, their diameter is 10-12 millimeters. They are firmly fixed in the holder with rectangular brass inserts. The initial position of the electrode holder - its halves are divorced. Springs can be used to give elasticity. Perfect for old cots.

Resistance welding work

It is necessary to connect such welding to the electrical network using a circuit breaker. It must have a rated current of 20 amps. Pay attention to the fact that at the input (where you have the counter) the machine must be either the same in terms of parameters or larger. To turn on the transformer, a simple magnetic starter is used. The operation of a contact-type welding machine is somewhat different from the one discussed above. And now you will find out these features.

To turn on the magnetic starter, it is necessary to provide a special pedal that you will press with your foot to generate current in the secondary circuit. Pay attention to what turns on and off contact welding only if the electrodes are fully brought together. If you neglect this rule, then a lot of sparks will appear, as a result, this will lead to burning of the electrodes, their failure. Try to pay attention to the temperature of the welding machine as often as possible. Take small breaks from time to time. Do not allow the unit to overheat.

inverter welding machine

It is the most modern, but more difficult to design. It also uses semiconductor transistors with high power. Perhaps these are the most expensive and scarce parts. First of all, the power supply is made. It is pulsed, so it is necessary to make a special transformer. And now in more detail about what such a welding machine consists of. See the specifications of its components below.

Of course, the transformer used in the inverter is much smaller than those discussed above. You will also need to make a throttle. So, you should get a ferrite core, a frame for making a transformer, copper tires, special brackets to fix the two halves of the ferrite core, electrical tape. The latter must be chosen based on the data of its thermal stability. Stick to these tips when making inverter welders.

winding transformer

The transformer is wound over the entire width of the frame. Only under this condition will it be able to withstand any voltage drop. For winding, either a copper bus or wires assembled in a bundle is used. Please note that aluminum wire cannot be used! It can't handle that much density. electric current which is present in the inverter. Such a welding machine for giving is able to help you out, and its weight is extremely small. The coils are wound as tightly as possible. The secondary winding is two wires with a thickness of about two millimeters, twisted together.

They should be isolated from each other as much as possible. If you have large stocks from old TVs, you can use them in the design. It takes 5 pieces, and you need to make one common magnetic circuit out of them. In order for the device to work with maximum efficiency, you need to pay attention to every little thing. In particular, the thickness of the wire of the output winding of the transformer affects its continuity.

Inverter design

To make a welding machine 200, you need to pay maximum attention to all the little things. In particular, power transistors must be mounted on a heatsink. Moreover, the use of thermal paste is welcomed to transfer heat from the transistor to the radiator. And it is recommended to change it from time to time, as it tends to dry out. In this case, heat transfer worsens, there is a possibility that semiconductors will fail. In addition, you need to do forced cooling. For this purpose, exhaust coolers are used. Diodes used to rectify alternating current must be mounted on an aluminum plate. Its thickness should be 6 millimeters.

The connection of the terminals is carried out using an uninsulated wire. Its cross section should be 4 mm. Please note that there is a maximum distance between the connection wires. They should not touch each other, no matter what impact the body of the welding machine experiences. The throttle must be fixed to the base of the welding machine with a metal plate.

Moreover, the latter should completely repeat the shape of the throttle itself. To reduce vibration, it is necessary to install a rubber seal between the housing and the throttle. Power wires inside the device are bred in different directions. Otherwise, there is a possibility that a short circuit will occur. It is necessary to install the fan in such a way that it blows all the radiators at the same time. Otherwise, if you cannot use one fan, you will have to install several.

But it is better to fully calculate in advance the installation location of all elements of the system. Please note that the secondary winding must be cooled as efficiently as possible. As you can see, not only radiators need effective airflow. On this basis, it is possible to make an argon welding machine at no cost. But its design will require the use of other materials.

Conclusion

Now you know how to make several types of welding machines. If you have design skills electronic means, it is better, of course, to stop at an inverter welding machine. You will spend time, but at the end you will get an excellent device that is not inferior even to expensive Japanese counterparts. Moreover, its production will cost mere pennies.

But if there is a need to make a welding machine, as they say, in haste, then it will be easier to connect two transformers from microwave ovens with modified secondary windings. Subsequently, the entire unit can be improved by adding an electric drive for supplying electrodes to it. You can also install a cylinder filled with carbon dioxide in order to weld metals in its environment.

When performing simple and small-scale welding work at home, everyone can assemble.

For assembly, you do not have to spend a lot of money, effort and time. Also, you do not need to purchase unreasonably expensive models of such equipment.

To make a mini welding machine with your own hands from improvised means, without much financial cost and effort, you need to understand how the equipment functions, after which you can start producing it at home.

First of all, it is worth determining the required current supply power of home-made equipment for welding. The connection of parts of a massive structure requires a greater current intensity, and welding work with thin metal surfaces requires a minimum.

The current value is related to the selected electrodes to be used in the process. When welding products up to 5 mm, it is necessary to use rods up to 4 mm, and in a design with 2 mm thickness, the rods should be 1.5 mm.

When using electrodes of 4 millimeters, the current strength is regulated up to 200 amperes, in 3 millimeters up to 140 amperes, in 2 millimeters - up to 70 amperes and for the smallest up to 1.5 millimeters - up to 40 amperes.

You can form an arc for the welding process yourself, using the mains voltage, which is obtained due to the operation of the transformer.

This equipment includes:

• magnetic circuit;
• winding - primary and secondary.

Also, the transformer can be made independently. For the magnetic circuit, plates made of steel or other durable material are used. The windings are necessary in order to directly perform welding work and be able to connect the welding unit to a 220 volt network.

Transformer for welding.

Specialized equipment has additional devices that improve the quality and power of the arc, which makes it possible to independently adjust the current values.

You should not go deep enough into this topic, since one of the easiest ways to assemble a do-it-yourself welding machine is.

Its feature is work with alternating current, which ensures the performance of a high-quality seam when welding metal surfaces. This equipment can handle any household work where it is necessary to weld metal or steel structures.

To make it you need to prepare:

1. Several meters of cable with a large thickness.
2. Material for the core, which will be located in the transformer.
   The material itself must have increased permeability with magnetization.

The best option is when the core in the form of a rod has the letter "P". In some cases, it is allowed to use this part in a more modified form, for example, a round stator made from a damaged electric motor.

Scheme of the device of the welding transformer.

However, it is worth paying attention that it is more difficult to wind the windings on this form. Best of all, when the core cross-section for classic do-it-yourself welding equipment used for domestic purposes had an area of ​​\u200b\u200babout 50 cm2.

In order for the equipment to have an affordable weight, it is not necessary to increase the cross section in volume, however, the technical effect will not be at the highest level. If the cross-sectional area does not suit you, then you can calculate it yourself using special schemes and formulas.

The primary winding must be made of copper wire, which will have enhanced characteristics: thermal resistance, since during the operation of the structure this part heats up very much.

Such a part must have cotton or fiberglass insulation. In extreme cases, it is possible to use insulated rubber wire or rubber cloth, but beware of PVC winding.

The insulation is also made by hand, using cotton or fiberglass, or rather, its parts are 2 cm wide. Thanks to these pieces, it will be possible to wrap the wire, and then impregnate it with any varnish with an electrical purpose. Such insulation will not overheat after regular operation.

Similarly to the above calculations, it will be possible to calculate which cross-sectional area of ​​\u200b\u200bthe winding - primary and secondary - will be the most optimal. Often the secondary winding has an area of ​​about 30 mm2, and the primary winding up to 7 mm2, using a rod 4 mm in diameter.

Besides in a simple way you need to determine how much a piece of copper wire will stretch and how many turns it will take to wind two windings. After that, the coils are wound, and the frame is made using the geometric parameters of the magnetic circuit.

The main thing is to make sure that there are no difficulties when putting on the magnetic circuit. First of all, you need to choose the right core size. It is best made using electrical cardboard or textolite.

Using the same analogy, it will be possible to make a structure for welding small parts. For the home, you can use a small “mini” welding machine.

Welding Machine Manufacturing

Today it is almost impossible and rather difficult to weld metal or process it in the proper way without using welding equipment. After you make a welding machine with your own hands, you can do any work with metal products.

Scheme of a transformer with a separate choke.

To make a high-quality unit, you need to have the knowledge and skills that will help you understand the circuit of a DC or AC welding machine, which are two options for assembling equipment.

For the purpose of home use, it is best to learn how to make mini welding.

It is more convenient to call a wizard or purchase a ready-made unit, but sometimes it can be too costly, since it is quite difficult to determine the number of volts per welding machine when choosing a model for various parameters, such as the weight for the welding machine.

There are several types of welding machines: working on alternating current, direct, having three phases or inverter. To choose one of the options and start the assembly, it is necessary to consider each scheme of the first 2 types. During the preparatory process, you need to pay attention to the voltage stabilizer.

On alternating current

To make home-made welding machines, you need to select a voltage indicator, the best is 60 volts, the current is best regulated from 120 to 160 amperes.

You can independently determine the cross-sectional value of the required wire for the manufacture of the primary winding of the transformer, which must be connected to a 220-volt network.

The cross section according to the area parameters should not be more than 7 mm2, since it is worth noting the possible voltage drop and possible additional load.

Based on the calculations, optimal size the diameter of the copper core under the primary winding, which reduces the action of the mechanism, is 3 millimeters. When choosing aluminum for the wire, the cross section is multiplied by a value of 1.6.

It is worth noting that the wires must be wrapped with a rag, as they must be insulated. The fact is that as the temperature rises, the wire can melt and a short circuit will occur.

In the absence of the necessary wire, it is possible to replace it with a slightly thinner residential wire, winding it in pairs. However, it must be remembered that the winding thickness will increase, due to which the dimensions of the welding equipment will be large. Under the secondary winding, a thick wire with a large number of strands of copper is used.

DC

Electrical circuit of a DC welder.

Some welding machines work with direct current. Thanks to this unit, it is possible to weld cast iron products and stainless steel structures.

It may take no more than half an hour to create a DC welding machine with your own hands. In order to convert homemade products with alternating current, it is necessary that the secondary winding be connected, which is assembled on a diode.

In turn, the diode must withstand a current of 200 amperes and have good cooling. To trim the current value, you can use capacitors that have certain characteristics and voltage features. After that, the unit is assembled sequentially according to the scheme.

Chokes are used to regulate the current, and contacts to attach the holder. Additional parts are used in the transmission of current from an external carrier to the welding site.

In order to operate the welding machine for its intended purpose, it is necessary, first of all, to kindle an electric arc. This process is easy and is carried out by the following actions: we bring the tip of the electrode under a certain slope from the side of the metal coating and strike it on the surface of the structure.

If the action is performed correctly and successfully, a flash occurs. Not large sizes, and the material is melted, after which the necessary elements can be welded.

When making a mini welding machine with your own hands, you must be guided by the recommendations for working with it. To weld elements, you need to hold the rod in such a position that it is at a certain distance from each other of the parts to be welded. This distance can be equal to the cross section of the selected electrode.

Often a metal such as carbon steel is connected with a direct polar current. However, some alloys can only be welded with reverse current polarity. In addition, it is necessary to carefully control the quality of the seam and how the structure is melted.

Scheme of a simple welding machine.

It is worth emphasizing that the alternating current, located, can be regulated efficiently and smoothly. Often, no difficulties arise with setting the unit to the required parameters.

With a small current strength indicator, the seam will come out of poor quality, but you should not set an increased value, as there is a risk of burning the surface.

If it is necessary to weld surfaces of small thickness, then the rods will fit with a size of 1 to 3 millimeters, while the current strength should vary with marks of 20-60 A. Using electrodes of a large cross section, metal products up to 5 millimeters can be welded, however, in this case, the current should be 100 A.

Upon completion of the welding process, using a homemade product, it is necessary to carefully remove the scale with light movements that appears on the seam, after which it is cleaned with a special brush.

Thanks to this action, you will be able to maintain a pleasant aesthetic appearance of your device. Do not worry if the cleaning of the equipment does not work out very well in the first couple. This skill is gained through experience and subject to the implementation of all recommendations for the competent operation of the structure.

Outcome

Summing up, it is worth noting that DC welding machines are much easier to assemble and they are also easy to use, due to their low power.

It's no secret that a do-it-yourself welding machine for a person familiar with electrical engineering is not so difficult to make. This makes sense especially if it is intended for use in a personal household, where it is used only from time to time. In this case, a home-made welding machine, the cost of which is much lower than the factory one, is quite capable of replacing it. Parts for its design can be freely removed from various electrical household devices that have failed or, if necessary, manufactured and assembled by yourself. Schemes of such devices can be different. The decisive factor here is usually the availability of parts and materials.

Choosing the Right Welding Machine

All electric arc welding machines are divided into inverter and transformer. It should be noted right away that the question of how to make a welding machine on your own depends largely on the ability to get parts from a certain household appliances. If all parts are purchased at market prices, then as a result, the cost will approach the price of a branded device, yielding to it in efficiency. That is why you need to have certain knowledge in the field of electrical engineering and know where which part is placed and where it can be removed for free or for a small price.

The number of turns on the primary winding should be about 240. At the same time, to ensure the possibility of adjusting the welding current in steps of 20 to 25 turns, several taps are made. The secondary winding is wound with copper wire with a cross section of 30 to 35 mm in an amount of 65 to 70 turns. To adjust the welding current on it, you also need to make taps. The insulation of the secondary winding must be especially reliable and heat resistant, so it should be given special attention. Each of the layers must be laid with additional insulation made of cotton fabric.

The transformer welding machine can use alternating or direct current for operation. The first of them is the simplest in terms of device, but more difficult to use. For direct current, it is quite easy to modify it by installing a diode bridge. Such a device is reliable, durable and unpretentious in use, but it has a significant weight and is sensitive to voltage drops in the mains. If it drops below 200 V, it becomes very difficult to start and maintain an electric arc.

Unlike a transformer inverter welding machine, due to the use of modern electronic parts, it has a relatively small weight. It can be worn on the shoulder by one person. Such a device has a current stabilization device, which greatly facilitates the work during welding. Reducing the voltage for it practically does not create interference, and it can operate from a household power outlet. However, the inverter apparatus is very sensitive to overheating and requires great care in operation, otherwise it easily fails.

Assembly of the transformer welding machine

The main part of such an apparatus is a transformer. Its main characteristic should be the ability to stably keep the operating current, and this is based on such an indicator as the external current-voltage characteristic of the power supply. In other words, the welding current should not differ significantly from the current produced by the short circuit.

To do this, the current must be limited in one of such ways as increasing the magnetic leakage of the transformer, ballast resistance or installing a choke. The transformer itself can be removed from the burnt high-frequency microwave oven. If there is no access to it, then you can make a welding transformer with your own hands.

To make the core, you need to purchase transformer iron plates. The core area should ideally be from 40 to 55 cm², with such indicators the winding will not overheat unnecessarily. Primary windings for self-made welding transformers should consist of thick heat-resistant copper wire with a cross section of at least 5 mm, and preferably more, enclosed in fiberglass or cotton insulation. Plastic or rubber insulation is not recommended for such purposes, since it is less resistant to overheating and breaks through more easily, which causes a short circuit in the primary winding.

It must be remembered that the secondary winding of the welding transformer must be wound on both sides of the core. It can be connected either in series or in anti-parallel. It must be remembered that the winding must be carried out on both sides in the same direction. After that, the transformer is placed in a metal case. Holes are cut from its end to cool the device, and an exhaust fan is installed, removed from the power supply of an outdated or broken computer. On the opposite side of the case, several dozen holes are drilled for air circulation. The cables and the electrode holder can then be connected.

How to assemble a homemade inverter welding machine?

An inverter welding machine can be completely assembled from parts from old TVs. This requires not only some general electrical knowledge, but also some knowledge of electronics. Its scheme is rather complicated. The inverter is a pulsed DC source, and for its manufacture, several ferrite cores are suitable, which are on horizontal transformers in old TVs. They are stacked in threes, and a winding of copper or aluminum wire is already wound on them.

Since the primary winding is most susceptible to overheating, small gaps must be left between the turns to facilitate the cooling process. It is worth remembering that aluminum wire must be taken with a larger cross section than copper, since its thermal conductivity is lower. To fix the inverter windings, a wire bandage made of 10 mm wide copper wire, superimposed on fiberglass insulation, is used.

Capacitors can also be removed from the TV, but just remember that it is not recommended to take paper capacitors from low-frequency circuits, since they will not be able to work for a long time under such loads. SCRs are better to take rather low-power ones and connect them in parallel than to take one powerful one, since a large thermal load falls on them and it is easier to cool them. SCRs are mounted on a metal plate with a thickness of at least 3 mm, which facilitates the removal of excess heat. Diodes for assembling a diode bridge can also be easily dialed from several old TVs. The bridge itself is also mounted on a heat sink plate.

Some parts for the inverter apparatus are not available on TVs, and they have to be made independently. First of all, it's a throttle. It is easy to make it without a frame of copper wire with a cross section of at least 4 mm, wound with 11 turns at intervals of at least 1 mm. Since the main thermal load will fall on the throttle, an additional air cooling system must be installed. In this capacity, it is quite possible to use an ordinary household fan mounted in the body of the welding machine in such a way that the air stream hits the throttle directly.

All elements of the electronic circuit are assembled on a fiberglass printed circuit board with a thickness of at least 1.5 mm. A heat sink is attached to the board itself, which facilitates cooling of the entire system. A round hole is cut out in the center of the board for installing a fan, since the device will not work for a long time without forced air cooling. The main advantage of the welding inverter is the ability to do mini-welding work by welding thin metal sheets. The welding seam itself comes out more accurate than that of a transformer apparatus. This is crucial for such a type of work as do-it-yourself car repair.

Welding machine, made by yourself, includes parts received for free or at a bargain price, but does its job well.

A welding machine is a welcome purchase for any household. The advantages of manual electric welding are obvious and indisputable: ease of use, the widest range of applications, high performance and reliability of connections - and all this with the ability to work almost anywhere where there is an electrical network. Problems with the choice and acquisition of welding machines today, it seems, do not exist. A lot of household and professional industrial welding machines have appeared on sale. Vieingly offer their products and all kinds of handicraft workshops and craftsmen. Yes, but the prices for factory-made devices "bite", as a rule, several times, exceeding the current average monthly income. Basically, it is this sad discrepancy between one's own wealth and price that always forces many people to take up welding with their own hands.

In modern literature, you can find a lot of material on welding. In recent years, a number of articles devoted to the improvement and calculation of elements of welding transformers (ST) have been published in Radioamator, which undoubtedly indicates the interest of readers in this topic. I propose the most important thing: how and from what to make welding transformers at home. All the welding transformer circuits described below have been practically tested and are really suitable for manual electric welding. Some of the schemes have been worked out "among the people" for decades and have become a kind of "classic" of independent "transformer building".

Like any transformer, the ST consists of primary and secondary (possibly with taps) windings wound on a large magnetic core made of transformer iron. The mode of operation distinguishes the CT from a conventional transformer: it operates in an arc mode, i.e. at almost maximum power. And hence the strong vibrations, intense heating, the need to use large-section wire. The ST is powered from a single-phase network of 220-240 V. The output voltage of the secondary winding in idle mode (x.x.) (when no load is connected to the output) for self-made STs is, as a rule, in the range of 45-50 V, less often up to 70 Q. In general, the output voltages for industrial welders are limited (80 VAC, 90 VDC). Therefore, large stationary units have an output of 60-80 V.

The main power characteristic of the ST is considered to be the output current of the secondary winding in the arc mode (welding mode). In this case, the electric arc burns in the gap between the end of the electrode and the metal to be welded. The gap is 0.5 ... 1.1 d (d is the electrode diameter), it is maintained manually. For portable structures, the operating currents are 40-200 A. The welding current is determined by the power of the ST. The choice of the diameter of the electrodes used and the optimal thickness of the welded metal depend on the output current of the ST.

The most common are electrodes with steel bars D3 mm ("troika"), which require currents of 90-150 A (usually 100-130 A). In skillful hands, the "troika" will burn even at 75 A. At currents greater than 150 A, such electrodes can be used for cutting metal (thin sheets of iron 1-2 mm can be cut at lower currents). When working with an electrode D3 mm, a current of 20-30 A flows through the primary winding of the ST (usually about 25 A).

If the output current is lower than required, then the electrodes begin to "stick" or "stick", welding their tips to the metal being welded: for example, the ST starts to work with a dangerous overload in short circuit mode. At currents greater than the allowable, the electrodes begin to cut the material: this can ruin the entire product.

For electrodes with an iron rod D2 mm, a current of 40-80 A is required (usually 50-70 A). They can accurately weld thin steel with a thickness of 1-2 mm. D4 mm electrodes work well at a current of 150-200 A. Higher currents are used for less common (D5-6 mm) electrodes and metal cutting.

In addition to power, an important property of ST is its dynamic response. The dynamic characteristic of the transformer largely determines the stability of the arc, and hence the quality of the welded joints. From the dynamic characteristics, one can distinguish steeply dipping and gently dipping. During manual welding, inevitable oscillations of the end of the electrode occur and, accordingly, a change in the length of the arc burning (at the moment of ignition of the arc, when adjusting the length of the arc, on irregularities, from hand trembling). If the dynamic characteristic of the ST is steeply falling, then with fluctuations in the length of the arc, slight changes in the operating current occur in the secondary winding of the transformer: the arc burns stably, the weld lies flat.

With a gently dipping or rigid characteristic of the ST: when the arc length changes, the operating current also changes sharply, which changes the welding mode - as a result, the arc burns unstably, the seam turns out to be of poor quality, it is difficult or even impossible to work with such a ST manually. For manual arc welding, a steeply falling dynamic characteristic of the ST is required. Sloping is used for automatic welding.

In general, in real conditions, it is hardly possible to somehow measure or quantify the parameters of the current-voltage characteristics, however, like many other parameters of the ST. Therefore, in practice, ST can be divided into those that weld better and those that work worse. When a CT works well, welders say, "Cooks soft." This should be understood as the high quality of the weld, the absence of metal spattering, the arc burns stably all the time, the metal is deposited evenly. All the CT designs described below are actually suitable for manual arc welding.

The mode of operation of ST can be characterized as short-term repetitive. In real conditions, after welding, as a rule, installation, assembly and other works follow. Therefore, the ST after working in the arc mode has some time for cooling in the cold mode. In the arc mode, the ST heats up intensively, and in the cold mode. cools, but much more slowly. The situation is worse when ST is used for cutting metal, which is very common. In order to cut thick rods, sheets, pipes, etc. with an arc, at a not too high current of a home-made transformer, it is necessary to overheat the ST too much.

Any industrially manufactured apparatus is characterized by such an important parameter as the operating time coefficient (PR), measured in%. For domestic factory portable devices weighing 40-50 kg, PR usually does not exceed 20%. This means that the ST can operate in the arc mode for no more than 20% of the total time, the remaining 80% it must be in the cold mode. For most home-made designs, the PR should be taken even less. We will consider the intensive mode of operation of the ST as such, when the arc burning time is of the same order as the break time.

Home-made CTs are performed according to different schemes: on P-, PU- and W-shaped magnetic cores: toroidal, with various combinations of winding arrangements. The SM manufacturing scheme and the number of turns of future windings are mainly determined by the core available - the magnetic circuit. In the future, the article will consider real schemes of home-made STs and materials for them. Now let's determine what winding and insulating materials will be needed for the future ST.

Given the high power, a relatively thick wire is used for the CT windings. Developing significant currents during operation, any ST gradually heats up. The heating rate depends on a number of factors, the most important of which is the diameter or cross-sectional area of ​​the winding wires. The thicker the wire, the better it passes current, the less it heats up and, finally, the better it dissipates heat. The main characteristic is the current density (A / mm2): the higher the current density in the wires, the more intense the heating of the ST. Winding wires can be copper or aluminum. Copper allows you to use 1.5 times the current density and heats up less: it is better to wind the primary winding with copper wire.

In industrial devices, the current density does not exceed 5 A/mm2 for copper wire. For homemade options ST satisfactory result can be considered and 10 A/mm2 for copper. With an increase in current density, the heating of the transformer is sharply accelerated. In principle, for the primary winding, you can use a wire through which a current with a density of up to 20 A / mm2 will flow, but then the ST will heat up to a temperature of 60 ° C after using 2 x 3 electrodes. If you think that you will have to weld a little, not quickly, and the best materials you still don’t have it, then you can wind the primary winding with a wire and with a strong overload. Although this, of course, will inevitably reduce the reliability of the apparatus.

In addition to the section, another important characteristic of the wire is the method of insulation. The wire can be varnished, wound in one or two layers of thread or fabric, which, in turn, can be impregnated with varnish. The reliability of the winding, its maximum overheating temperature, moisture resistance, and insulating qualities strongly depend on the type of insulation (see Table 1).

Table 1

Note. PEV, PEM - wires enamelled with high-strength varnish (viniflex and metalvin, respectively), are produced with thin (PEV-1, PEM-1) and reinforced insulating layers (PEV-2, PEM-2); PEL - wire enameled with oil-based varnish; PELR-1, PELR-2 - wires enamelled with high-strength polyamide varnish, respectively, with thin and reinforced insulation layers; PELBO, PEVLO - wires based on PEL and PEV wires with one layer, respectively, of natural silk, cotton yarn or lavsan; PEVTL-1, PEVTL-2 - wire enamelled with high-strength polyurethane enamel, heat-resistant, with thin and reinforced layers of insulation; PLD - wire insulated with two layers of lavsan; PETV - wire enamelled with heat-resistant high-strength polyester varnish; PSD type wires - with insulation made of alkali-free fiberglass, superimposed in two layers with gluing and impregnation with heat-resistant varnish (in brand designations: T - thinned insulation, L - with a surface varnish layer, K - with gluing and impregnation with silicone varnish); PETKSOT - wire insulated with heat-resistant enamel and fiberglass; PNET-imide is a wire insulated with high-strength polyamide-based enamel. Under the insulation thickness in the table, the difference between the maximum wire diameter and the nominal copper diameter is taken.

The best is fiberglass insulation impregnated with a heat-resistant varnish, but it is difficult to get such a wire, and if you buy it, it will cost a lot. The least desirable, but the most affordable material for homemade products are ordinary PEL wires, PEV Dtsii. Such wires are the most common, they can be removed from the coils of chokes, transformers of obsolete equipment. Carefully removing the old wires from the coil frames, it is necessary to monitor the condition of their coating and additionally isolate slightly damaged areas. If the coils with wire were additionally impregnated with varnish, their turns stuck together, and when trying to disconnect, the hardened impregnation often breaks off its own lacquer coating wires, exposing metal. In rare cases, in the absence of other options, "homemade" wind the primary windings even with a mounting wire in vinyl chloride insulation. Its disadvantages: extra volume of insulation and poor heat dissipation.

The quality of laying the primary winding of the CT should always be given the greatest attention. The primary winding contains more turns than the secondary, its winding density is higher, it heats up more. The primary winding is under high voltage, with its interturn circuit or insulation breakdown, for example, through moisture that has entered, the entire coil quickly "burns out". As a rule, it is impossible to restore it without disassembling the entire structure.

The secondary winding of the ST is wound with a single or stranded wire, the cross section of which provides the required current density. There are several ways to solve this problem. First, you can use a monolithic wire with a cross section of 10-24 mm2 made of copper or aluminum.

Such rectangular wires (commonly referred to as busbars) are used for industrial MTs. However, in most home-made designs, the winding wire has to be pulled many times through the narrow windows of the magnetic circuit. Try to imagine doing this about 60 times with 16mm2 solid copper wire. In this case, it is better to give preference to aluminum wires: they are much softer, and they are cheaper.

The second way is to wind the secondary winding with a stranded wire of a suitable cross section in ordinary vinyl chloride insulation. It is soft, easy to fit, securely insulated. True, the synthetic layer takes up extra volume in the windows and prevents cooling. Sometimes for these purposes they use old stranded wires in thick rubber insulation, which are used in powerful three-phase cables. The rubber is easy to remove, and instead wrap the wire with a layer of some thin insulating material. The third way - you can make a secondary winding from several single-core wires approximately the same as the primary winding. To do this, 2-5 wires D1.62.5 mm are carefully pulled together with adhesive tape and used as one stranded wire. Such a bus of several wires takes up little space and has sufficient flexibility, which makes it easy to install.

If it is difficult to get the right wire, then the secondary winding can be made from thin, the most common wires PEV, PEL D0.5-0.8 mm, although this will take an hour or two. First you need to choose a flat surface, where you must rigidly install two pegs or hooks with a distance between them equal to the length of the secondary winding wire of 2030 m. Then stretch several tens of strands of thin wire between them without deflection, you get one elongated bundle. Next, disconnect one of the ends of the beam from the support and clamp it into the chuck of an electric or manual drill. At low speeds, the entire bundle, in a slightly taut state, twists into a single wire. After twisting, the length of the wire will decrease slightly. At the ends of the resulting stranded wire, you need to carefully burn the varnish and clean the ends of each wire separately, and then securely solder everything together. After all, it is desirable to isolate the wire by wrapping it along its entire length with a layer, for example, adhesive tape.

For laying the windings, fastening the wire, inter-row insulation, insulating and fastening the magnetic circuit, you will need a thin, strong and heat-resistant insulating material. In the future, it will be seen that in many SM designs, the volume of the magnetic circuit windows, in which several windings with thick wires must be laid, is very limited. Therefore, in this "vital" space of the magnetic circuit, every millimeter is precious. With small core sizes, the insulating materials should occupy as little volume as possible, i.e. be as thin and flexible as possible. The widespread PVC iso1.6-2.4 mm in a simple varnish insulating tape can be immediately excluded from use in heated sections of ST. Even with a slight overheating, it becomes soft and gradually spreads or is pressed through by wires, and with significant overheating, it melts and foams. For insulation and bandage, you can use fluoroplastic, glass ... and lacquered fabric keeper tapes, and between rows - ordinary adhesive tape.

Adhesive tape can be attributed to the most convenient insulating materials. After all, having a sticky surface, small thickness, elasticity, it is quite heat-resistant and strong. Moreover, now adhesive tape is sold almost everywhere on reels of various widths and diameters. Coils of small diameters are the best suited for pulling through narrow windows of compact magnetic cores. Two or three layers of adhesive tape between the rows of wire practically do not increase the volume of the coils.

And finally, the most important element of any ST is the magnetic core. As a rule, for homemade products, magnetic circuits of old electrical appliances are used, which before that had nothing to do with ST, for example, large transformers, autotransformers (LATRs), electric motors. The most important parameter of the magnetic circuit is its cross-sectional area (S), through which the magnetic field flow circulates.

For the manufacture of ST, magnetic cores with a cross-sectional area of ​​​​25-60 cm2 (usually 30-50 cm2) are suitable. The larger the cross section, the more flux the magnetic circuit can transmit, the more power the transformer has and the fewer turns its windings contain. Although the optimal cross-sectional area of ​​​​the magnetic core, when the medium power CT has the best characteristics, is 30 cm2.

There are standard methods for calculating the parameters of the magnetic circuit and windings for commercial MT circuits. However, for homemade products, these techniques are practically not suitable. The fact is that the calculation according to the standard method is carried out for a given power of the ST, and only in a single variant. It is calculated separately optimal value section of the magnetic circuit and the number of turns. In fact, the cross-sectional area of ​​the magnetic circuit for the same power can be in a very wide range.

There is no connection between an arbitrary section and turns in standard formulas. For self-made CTs, any magnetic circuits are usually used, and it is clear that it is almost impossible to find a core with "ideal" parameters of standard methods. In practice, it is necessary to select the turns of the windings for the existing magnetic circuit, thereby setting the required power.

ST power depends on a number of parameters, which cannot be fully taken into account under normal conditions. However, the most important among them are the number of turns of the primary winding and the cross-sectional area of ​​the magnetic circuit. The ratio between the area and the number of turns will determine the operating power of the ST. To calculate the ST, designed for D3-4 mm electrodes and operating from a single-phase network with a voltage of 220-230 V, I propose to use the following approximate formula, which I obtained on the basis of practical data. Number of turns N=9500/S (cm2). At the same time, for a PT with a large area of ​​the magnetic circuit (more than 50 cm2) and a relatively high efficiency, it can be recommended to increase the number of turns calculated by the formula by 10–20%.

For STs manufactured on cores with a small area (less than 30 cm), it may be necessary, on the contrary, to reduce the number of calculated turns by 1020%. In addition, the useful power of the ST will be determined by a number of other factors: efficiency, secondary winding voltage, supply voltage in the network ... (Practice shows that the mains voltage, depending on the location and time, can vary between 190-250 V).

Equally important is the resistance of the power line. Being only a unit of an ohm, it practically does not affect the readings of a voltmeter with high resistance, but it can greatly dampen the power of the ST. The influence of line resistance can be especially pronounced in places remote from transformer substations (for example, cottages, garage cooperatives, in rural areas, where lines are laid with thin wires with a large number of connections). Therefore, initially it is hardly possible to accurately calculate the output current of the ST for different conditions - this can only be done approximately. When winding the primary winding, its last part is best done with 2-3 taps after 20-40 turns. Thus, you can adjust the power by choosing the best option for yourself, or adjust to the mains voltage. To obtain higher powers from ST, for example, to operate a D4 mm electrode at currents greater than 150 A, it is also necessary to reduce the number of turns of the primary winding by 20-30%.

But it should be remembered that with an increase in power, the current density in the wire also increases, and hence the intensity of heating of the windings. The output current of the ST can also be slightly increased by increasing the number of turns of the secondary winding so that the output voltage x.x. increased from the expected 50 V to higher values ​​(70-80 V).

Having included the primary winding in the network, it is necessary to measure the current x.x., it should not have much knowledge (0.1-2 A). (When the PT is connected to the network, a short but powerful current surge occurs). In general, current x.x. it is impossible to judge the output power of the CT: it can be different even for the same types of transformers. However, having studied the dependence curve of the current x.x. from the CT supply voltage, you can more confidently judge the properties of the transformer.

Fig.1

To do this, the primary winding of the ST must be connected through the LATR, which will allow you to smoothly change the voltage on it from 0 to 250 V. Volt-ampere characteristics ST in idle mode with different numbers of turns of the primary winding are shown in Fig. 1, where 1 - the winding contains few turns; 2 - ST operates at its maximum power; 3, 4 - moderate power ST. At first, the current curve gently, almost linearly increases to a small value, then the rate of increase increases - the curve smoothly bends upwards, followed by a rapid increase in current. When the current tends to infinity up to the operating voltage point of 240 V (curve 1), this means that the primary winding contains few turns, and it must be winded up (it should be borne in mind that the ST, switched on to the same voltage without LATR, will consume current approximately 30% more). If the operating voltage point lies on the bend of the curve, then the ST will produce its maximum power (curve 2, welding current of the order of 200 A). Curves 3 and 4 correspond to the case when the transformer has a power resource and an insignificant cold current: most homemade products are focused on this case. Real currents x.x. are different for different types of CT: most lie in the range of 100-500 mA. I do not recommend setting the current x.x. more than 2 A.

After getting acquainted with the general issues of manufacturing home-made welding transformers, we can proceed to a detailed examination of actually existing ST designs, the features of their manufacture and materials for them. Almost all of them I collected with my own hands or took a direct part in their manufacture.

Welding transformer on a magnetic circuit from LATRs

A common material for the manufacture of home-made welding transformers (ST) has long been burnt LATRs (laboratory autotransformer). Those who have dealt with them know well what it is. As a rule, all LATRs have approximately the same appearance: well ventilated tin case round shape with a tin or ebonite front cover with a scale from 0 to 250 V and a revolving handle. Inside the case there is a toroidal autotransformer, made on a magnetic circuit of a significant cross section. It is this core-magnetic circuit that will be needed from LATR for the manufacture of a new ST. Usually, two identical magnetic core rings from large LATRs are required.

LATRs were produced of various types with a maximum current from 2 to 10 A. Only those CTs are suitable for manufacturing, the dimensions of the magnetic circuits of which allow laying required amount turns. The most common among them is probably an autotransformer of the LATR 1M type, which, depending on the winding wire, is designed for a current of 6.7-9 A, although the dimensions of the autotransformer itself do not change from this. Magnetic circuit LATR 1M has following sizes: outer diameter D=127 mm; inner diameter d=70 mm; ring height h=95 mm; section S=27 cm2 and weight about 6 kg. You can make a good ST from two rings from LATR 1M, however, due to the small internal volume of the window, you cannot use too thick wires and you will have to save every millimeter of window space.

There are LATRs with more voluminous magnetic core rings, for example RNO-250-2 and others. They are better suited for making CTs, but are less common. For other autotransformers similar in parameters to LATR 1M, for example, AOSN-8-220, the magnetic circuit has a larger outer diameter of the ring, but a smaller height and window diameter d = 65 mm. In this case, the window diameter must be expanded to 70 mm. The ring of the magnetic core consists of pieces of iron tape wound on top of each other, fastened at the edges by spot welding.

In order to increase the inner diameter of the window, disconnect the end of the tape from the inside and unwind the required amount. But don't try to rewind in one go. It is better to unwind one turn, each time cutting off the excess. Sometimes the windows of larger LATRs are also expanded in this way, although this inevitably reduces the area of ​​the magnetic circuit.

Both rings must be insulated at the start of CT fabrication. At the same time, pay special attention to the corners of the edges of the rings - they are sharp, they can easily cut the superimposed insulation, and then close the winding wire. It is better to apply some strong and elastic tape along the corners, for example, a dense keeper or a cambric tube cut along. From above, the rings (each separately) are wrapped with a thin layer of fabric insulation.

Next, the isolated rings are connected together (Fig. 2). The rings are tightly pulled together with a strong tape, and on the sides they are fixed with wooden pegs, also then tightened with electrical tape, the core of the magnetic core for the ST is ready.

The next step is the most important - laying the primary winding. The windings of this ST are wound according to the scheme (Fig. 3) - the primary in the middle, two sections of the secondary - on the side arms. "Specialists" who know this type of transformer often call it "eared" in a kind of jargon because of the round "cheburashkin ears" protruding in different directions of the secondary winding sections.

The primary one takes about 70-80 m of wire, which will have to be pulled through both windows of the magnetic circuit with each turn. In this case, one cannot do without a simple device (Fig. 4). First, the wire is wound on a wooden reel and, in this form, is pulled through the windows of the rings without any problems. The winding wire can consist of pieces (even ten meters each) if you managed to get only one. In this case, it is wound in parts, and the ends are connected together. To do this, the tinned ends are connected (without twisting) and fastened with several turns of a thin copper core without insulation, then finally soldered and insulated. Such a connection does not crack the wire and does not take up a large volume.

The diameter of the wire of the primary winding is 1.6-2.2 mm. For magnetic circuits made up of rings with a window diameter of 70 mm, a wire with a diameter of not more than 2 mm can be used, otherwise there will be little space for the secondary winding. Contains a primary winding, as a rule, 180-200 turns at normal mains voltage.

So, suppose you have an assembled magnetic circuit in front of you, the wire is prepared and wound on a reel. Let's start winding. As always, we put a cambric on the end of the wire and draw it with electrical tape to the beginning of the first layer. The surface of the magnetic circuit has a rounded shape, so the first layers will contain fewer turns than the subsequent ones - to level the surface (Fig. 5).

The wire should be laid coil to coil, in no case allowing the wire to overlap the wire. Wire layers must be isolated from each other. (During operation, the MT vibrates strongly. If the wires in varnish insulation lie on top of each other without intermediate insulation, then as a result of vibration and friction against each other, the varnish layer may collapse and a short circuit will occur). To save space, the winding should be laid as compactly as possible. On a magnetic core of medium-sized rings, the interlayer insulation should be used thinner.

For these purposes, small rolls of adhesive tape are well suited, which easily pass through filled windows, and the tape itself does not take up extra volume. One should not strive to wind the primary winding quickly and in one go. This process is slow, and after laying hard wires, fingers begin to hurt. It is better to do this in 2-3 approaches - after all, quality is more important than speed.

When the primary winding is done, most of the work is done. Let's deal with the secondary winding. Let us determine the number of turns of the secondary winding for a given voltage. To begin with, we will turn on the already finished primary winding in the network. Current x.x. of this option, the ST is small - only 70-150 mA, the transformer hum should be barely audible. Wind 10 turns of any wire on one of the side arms and measure the output voltage on it.

Each of the side arms accounts for half of the magnetic flux created on the central arm, so here 0.6-0.7 V falls on each turn of the secondary winding. Based on the result, calculate the number of turns of the secondary winding, focusing on a voltage of 50 V ( about 75 turns).

The choice of material for the secondary winding is limited by the remaining space of the windows of the magnetic circuit. Moreover, each turn of a thick wire will have to be pulled along the entire length into a narrow window, and no "automation" here, alas, will help. I have seen transformers made on LATR 1M rings, into which craftsmen, with the help of a hammer and their own patience, pushed a thick monolithic copper wire with a section of twenty "squares".

Another thing, if you are new to this business, then you should not tempt fate, unwinding solid copper back is as difficult as winding it. Easier to wind aluminum wire section 16-20 mm2. The easiest way is to wind the usual stranded wire 10 mm2 in synthetic insulation - it is soft, flexible, well insulated, but it will heat up during operation. It is possible to make a secondary winding from several strands of copper wire, as described above. Wrap half of the turns on one shoulder, half on the other (Fig. 3). If there are no wires of sufficient length, you can connect them from pieces - it's okay. Having wound the windings on both arms, it is necessary to measure the voltage on each of them, it may differ by 2-3 V - the slightly different properties of the magnetic circuits of different LATRs affect, which does not particularly affect the properties of the ST. Then connect the windings on the arms in series, but you need to make sure that they are not in antiphase, otherwise the output will be a voltage close to 0. At a network voltage of 220-230 V, the ST of this design should develop a current in arc mode of 100-130 A, with short circuit current of the secondary circuit up to 180 A.

It may turn out that it was not possible to fit all the calculated turns of the secondary winding into the windows, and the output voltage turned out to be lower than required. The operating current will decrease slightly. IN more undervoltage x.x. affects the ignition process. The arc is easily ignited at a cold voltage close to 50 V and higher, although the arc can be ignited without any problems at lower voltages. I happened to work with ST with x.x. 37 V on alternating current, and at the same time the quality was quite satisfactory. So if the manufactured ST has an output voltage of 40 V, then it can be used for work. Another thing is if you come across electrodes designed for high voltages, - some brands of electrodes work from 70-80 V.

On rings from LATRs, ST can also be made according to the toroidal scheme (Fig. 6). This also requires two rings, preferably from large LATRs. The rings are connected and insulated: one ring-magnetic circuit with a significant area is obtained. The primary winding contains the same number of turns, but it is wound along the length of the entire ring and, as a rule, in two layers. The problem of the shortage of the internal space of the magnetic circuit window of such a CT scheme is even more acute than for the previous design. Therefore, it is necessary to isolate as thin layers and materials as possible. Do not use thick winding wires (recommended for primary winding D1.8 mm). In some installations, LATRs of especially large sizes are used; a toroidal ST can be made on only one ring of this type.

An advantageous difference between the toroidal circuit ST is a fairly high efficiency. For each turn of the secondary winding there is more than 1 V of voltage, therefore, the "secondary" will have fewer turns, and the output power is higher than in the previous circuit. However, the length of the turn on the toroidal magnetic circuit is longer, and it is unlikely that it will be possible to save on the wire here. The disadvantages of this scheme include the complexity of winding, the limited volume of the window, the impossibility of using a wire of large cross section, as well as the high intensity of heating. If in the previous version all the windings were separate and at least partially had contact with air, now the primary winding is completely under the secondary, and their heating is mutually enhanced.

It is difficult to use rigid wires for the secondary winding. It is easier to wind it with soft stranded or multi-core wire. If you correctly select all the wires and carefully lay them, then the required number of turns of the secondary winding will fit into the space of the magnetic circuit window, and the desired voltage will be obtained at the output of the ST. The arc burning characteristic of the toroidal CT can be considered better than that of the previous transformer.

Sometimes a toroidal ST is made from several rings of LATRs, but they are not placed on top of each other, but the iron strips of the tape are rewound from one to the other. To do this, first, internal turns of the strips are selected from one ring - to expand the window. The rings of other LATRs are completely unrolled into strips of tape, which are then wound as tightly as possible around the outer diameter of the first ring. After that, the assembled single magnetic core is wound very tightly with insulating tape. Thus, a ring-magnetic circuit is obtained with a more voluminous internal space than all the previous ones. In this you can fit a wire of considerable cross section, and make it much easier. The required number of turns is calculated from the cross-sectional area of ​​the assembled ring. The disadvantages of this design include the complexity of the manufacture of the magnetic circuit. Moreover, no matter how hard you try, you still won’t be able to manually wind the iron strips on top of each other as tightly as before. As a result, the magnetic circuit turns out to be flimsy. When the ST is operating, the iron in it vibrates strongly, emitting a powerful hum.

Sometimes the "native" windings of LATRs burn out only from one edge on the current collector or generally remain unharmed. Then there is a temptation to save yourself the extra effort and use a ready-made, perfectly laid primary winding of one ring. Practice shows that, in principle, this idea can be realized, however, the benefits of such an undertaking will be minimal. The winding LATR 1M has 265 turns of wire with a diameter of 1 mm. If you wind the secondary directly on it, then the transformer will develop exorbitant power for itself, quickly heat up and fail. After all, in reality, the "native" winding of the LATR can operate at low power - only for D2 mm electrodes that need a current of 50-60 A. Then a current of about 15 A should flow through the primary winding of the transformer.

For such a power, the primary winding of ST from one LATR should contain about 400 turns. They can be winded up by first varnishing the conductive path and isolating the native LATR winding. You can do it differently: do not wind the turns, but turn off the power with a ballast resistor included in the circuit of the primary or secondary winding. As an active resistance, you can use a battery of powerful wire resistors connected in parallel, for example, PEV50 ... 100, with a total resistance of 10-12 Ohms, included in the primary winding circuit. During operation, the resistors get very hot, to avoid this, they can be replaced with a choke (reactance). Wind the inductor on the frame of a 100-200-watt transformer with the number of turns 200-100. Although ST will have significantly the best feature if the ballast resistor (hundredths of an ohm) is turned on at the output of the secondary winding. To do this, use a piece of thick high-resistance wire wound into a spiral, the length of which is selected experimentally.

In some devices, LATRs of especially large sizes were used, only on one ring from this one can be wound a full-fledged ST. In the designs described above, it was necessary to use two rings each: this was done not so much because of the need to increase the area of ​​\u200b\u200bthe magnetic circuit, but to reduce the number of turns, otherwise they simply would not fit into narrow windows. In principle, a cross-sectional area and one ring are sufficient for a ST: it would have even better characteristics, since the magnetic flux density would be closer to optimal. But the problem is that smaller area magnetic cores inevitably require more turns, which increases coil volume and requires more window space.

Welding transformer on a magnetic circuit from the stator of an electric motor

From LATRs, let's move on to the next common source of obtaining good magnetic circuits for ST. Often, toroidal CTs are wound on the material of a magnetic conductor taken from a failed large asynchronous three-phase electric motor, which are most common in industry. For the manufacture of ST, motors with a power close to 4 kV A and more are suitable.

The electric motor consists of a rotor rotating on a shaft and a fixed stator pressed into the metal housing of the motor, which are connected by two side covers, pulled together by pins. Only the stator is of interest. The stator consists of a set of iron plates - a round magnetic circuit with windings installed on it. The shape of the stator magnetic circuit is not entirely circular, on the inside it has longitudinal grooves into which the motor windings are laid.

Different brands of engines, even of the same power, may have stators with different geometric dimensions. For the manufacture of STs, those with a larger case diameter and a correspondingly shorter length are better suited.

The most important part in the stator is the magnetic ring. The magnetic core is pressed into a cast iron or aluminum motor housing. Wires that need to be removed are tightly packed into the grooves of the magnetic circuit.

It is better to do this when the stator is still pressed into the housing. To do this, on one side of the stator, all winding outputs are cut off at the end with a sharp chisel. On the opposite side, the wire should not be cut - there the windings form something like loops, for which you can pull the remaining wires. Using a pry bar or a powerful screwdriver, the bends of the wire loops are pry up and pulled out several wires at a time. In this case, the end of the engine housing serves as a stop, creating a lever. The wires come out easier if you burn them first.

You can burn with a blowtorch, directing the jet strictly along the groove. Care must be taken not to overheat the stator iron, otherwise it will lose its electrical qualities. The metal case is then easy to destroy - a few blows of a good hammer, and it will crack - the main thing is not to overdo it.

If the motor core ring is bonded and separated from the windings and housing, then it is tightly insulated as usual. Sometimes you can hear that the remaining grooves of the windings must be filled with iron, supposedly to increase the area of ​​​​the magnetic circuit. In no case should this be done: otherwise the properties of the transformer will deteriorate sharply, it will begin to consume an exorbitantly large current, and its magnetic circuit will be very hot even in idle mode.

The stator ring has impressive dimensions: an inner diameter of about 150 mm, in which you can lay a wire of a significant cross section without worrying about space.

The cross-sectional area of ​​the magnetic circuit periodically changes along the length of the ring due to the grooves: inside the groove, its value is much smaller. It is this smaller value that should be guided by when calculating the number of turns of the primary winding (Fig. 7).

For example, I will give the parameters of a real-life CT made from the stator of an electric motor. For it, an asynchronous motor with a power of 4.18 kVA was used with an inner diameter of the magnetic circuit ring of 150 mm, an outer diameter of 240 mm and a height of the magnetic circuit ring of 122 mm. The effective cross-sectional area of ​​the magnetic core is 29 cm2. The set of plates of the magnetic circuit was initially not fastened, so it had to be welded with eight longitudinal seams along the outer side of the ring. As we feared, the welds did not cause any pronounced negative consequences associated with Foucault currents. The primary winding of the toroidal ST has 315 turns of copper wire with a diameter of 2.2 mm, the secondary is designed for a voltage of 50 V. The primary winding is wound in more than two layers, the secondary is laid on 3/4 of the length of the ring. ST in arc mode develops a current of 180-200 A at a supply voltage of 230 V.

When winding the secondary winding of a toroidal MT, it is desirable to lay it so that it does not overlap the last part of the primary, then the primary winding can always be wound up or unwound during the final adjustment of the MT.

Such a transformer can also be wound with windings spaced apart on different arms (Fig. 8). In this case, there is always access to each of them.

Welding transformer from television transformers

All the designs of welding transformers described above have common drawbacks: the need to wind the wire, each time pulling the turns through the window, as well as the shortage of magnetic circuit material - after all, not everyone can get rings from LATR or a suitable stator from an electric motor. Therefore, I designed and manufactured a CT of my own design, which does not require scarce materials. It does not have these disadvantages, and it is easy to implement at home. As source material for this design, a very common material is used - parts from television transformers.

In old domestic color TVs, large, weighty network transformers were used, for example, TS-270, TS-310, ST270. These transformers have U-shaped magnetic circuits, they can be easily disassembled by unscrewing just two nuts on the tie rods, and the magnetic circuit breaks into two halves. For older transformers TS-270, TS-310, the cross section of the magnetic circuit has dimensions of 2x5 cm, S=10 cm2, and for newer transformers TS-270, the cross section of the magnetopropod S=11.25 cm2 with dimensions of 2.5x4.5 cm. the window width of older transformers is several millimeters larger.

Older transformers are wound with copper wire, from their primary windings a wire with a diameter of 0.8 mm can be useful.

The new transformers are wound with aluminum wire. Today, this good in droves migrates to landfills, so problems with their acquisition are unlikely to arise. A few old or burned-out transformers can be bought inexpensively at any tele-repair shop. Here are their magnetic circuits (together with their own frames), with minor alterations, can be used to manufacture ST. For ST, you will need three identical transformers from TVs, while the total area of ​​\u200b\u200btheir combined magnetic circuit will be 30-34 cm2. How to connect them together is shown in Fig. 9, where 1,2,3 are magnetic cores with frames from television transformers. Three separate U-shaped cores are connected end-to-end to each other and pulled together with the same frame clamps. At the same time, the parts protruding beyond the end metal frames it is necessary to cut: on the central magnetic circuit on both sides, on the side ones - only on one inner side.

The result is a single large-section magnetic circuit, which is easy to assemble and disassemble. When disassembling television transformers, it is necessary to immediately mark the adjacent sides of the magnetic circuits so that during assembly the halves of different cores are not confused. They must fit in exactly the same position as they were assembled at the factory.

The window volume of the resulting magnetic circuit allows using a wire up to 1.5 mm in diameter for the primary winding, and a rectangular section of 10 mm2 or a stranded wire made from a bundle of thin wires with a diameter of 0.6-0.8 mm of the same section for the secondary bus. This, of course, is not enough for a full-fledged ST, however, it justifies itself in cases of short work, given the low cost of manufacturing this design.

The windings are wound on cardboard frames separately from the magnetic core. A cardboard frame can be made from a pair of "native" transformer frames, throwing out the side cheeks from one narrow side, and instead glue the wide cheeks together using additional strips of hard cardboard. When winding cardboard frames inside, it is imperative to tightly enclose several scraps of wooden planks, but not just one, otherwise the winding will tighten it and it will not come out back. Windings must be laid turn to turn, as tightly as possible. From the outside, after the first layer of wire and then every two, it is necessary to insert wooden inserts (Fig. 10) to ensure gaps and ventilation of the windings.

The secondary winding is best made from a 10 mm2 rectangular busbar, as it will take up the least volume. If you don’t have a bus, and you decide to make a secondary winding wire from a bundle of thin wires lying around, as described above, then be prepared for possible difficulties with its installation. In the case of a stranded wire of the secondary winding, it may turn out that it does not "fit" into the prescribed volume of the frame: mainly due to warping of the springy turns, but it is better not to pull them together, since the frame will collapse. In this case, you will have to completely abandon the cardboard frame.

The secondary winding must be wound on the magnetic circuit already assembled, with the primary winding coil installed, pulling each of its turns through the window. On a rigid magnetic circuit, a flexible wire can be pulled much tighter than on a cardboard frame, and more turns will enter the window.

When assembling the magnetic circuit, special attention should be paid to the reliability of fastening and tight fit of the individual halves of the PU-shaped core. As already mentioned, the mating halves of the magnetic circuit must be from the same transformers and installed on the same sides as at the factory. Under the nuts of the tie-down studs, it is imperative to place large-diameter washers and a grower. On my CT, the primary contains 250 turns of 1.5 mm varnished wire, the secondary contains 65 turns of 10 mm2 stranded wire, which provides an output of 55 V at a mains voltage of 230 V. With these data, the no-load current is 450 mA; current in arc mode in the secondary circuit 60-70 A; arcing performance is good. It was assembled on the basis of ST-270 parts. The welding transformer is used to work with an electrode with a diameter of 2 mm, the "three" burns steadily, but weakly on it.

The advantages of ST of this type are ease of manufacture and the prevalence of material for it. The main disadvantage is the imperfection of the magnetic circuit, which has a compressed gap between the two halves. During factory production, for transformers of this type, the gaps of the magnetic circuit are filled with a special filler. At home, they have to be pulled "dry", which, of course, worsens the characteristics and efficiency of the transformer. It is not possible to lay thick wires in a small volume window, which greatly reduces the coefficient of MT operation. It should be noted that the primary winding of this ST is heated more strongly than, for example, the winding with the same wire of the ST on LATRs - "eared". This is affected, firstly, by a large number of turns of the windings and, probably, by the imperfection of the magnetic system of the transformer. Nevertheless, ST can be successfully used for auxiliary purposes, especially for welding thin automotive metal. It is characterized by particularly compact dimensions and a low weight of 14.5 kg.

Other types of welding transformers

ST, in addition to special production, can be obtained by converting ready-made transformers for various purposes. Powerful transformers of a suitable type are used to create networks with a voltage of 36, 40 V, usually in places with increased fire hazard, humidity and for other needs. For these purposes, different types of transformers are used: different capacities, included in 220, 380 V in a single or three-phase circuit. The most powerful of the portable types, as a rule, have a power of up to 2.5 kVA. The wire and iron of such transformers are selected by power, based on continuous operation (current density 2-4 A / mm2), so they have significant cross sections. In the arc welding mode, the transformer is able to develop power several times higher than the nominal one, and its wire fearlessly endures short-term current overloads.

If you have a powerful single-phase transformer with terminals for switching on 220/380 V and a 36 V output (possibly 12 V), then there are no problems with its connection. You may have to wind a few turns of the secondary winding to increase the output voltage. Suitable transformers with a primary wire diameter of about 2 mm, having a magnetic circuit area of ​​up to 60 cm2.

There are transformers for a voltage of 36 V, designed to be connected to a three-phase 380 V network. Transformers with a power of 2.5 kVA are well suited for conversion, and a power of 1.25 and 1.5 kVA can only be used in short-term mode, since their windings with significant overloads quickly overheat.

To use three-phase transformers from a single-phase 220 V network, their windings must be connected to each other in a different way. Then, with a good voltage in the network, the power of the received ST will be enough to work with a D4 mm electrode.

Three-phase transformers were made on a W-shaped magnetic circuit with a cross section of one arm of at least 25 cm2 (Fig. 11).

Two windings are wound on each arm - inside the primary and secondary on top of it. Thus, the transformer has six windings. First you need to disconnect the windings from the previous circuit and find the beginning and end of each. In this case, the coils of the middle arm will not be needed at all, only the windings on the extreme arms will work. Two primary windings from the extreme shoulders must be connected to each other in parallel. Due to the fact that the magnetic flux must circulate in the magnetic circuit in one direction, the coils on opposite arms must create flows in opposite directions relative to, for example, the axis of the central arm: one up, the other down. Since the coils are wound in the same way, the currents in them must flow in opposite directions. This means that you need to connect them in parallel with different ends: connect the beginning of the 1st with the end of the 2nd, the end of the 1st with the beginning of the 2nd (Fig. 12).

Secondary windings are connected in series with each other by ends or beginnings (Fig. 12). If the windings are connected correctly, then the output voltage x.x. should not exceed 50V.

Transformers of this type are often built into a convenient metal case with handles and a hinged lid. Converting them into welding machines is quite common.

Most industrial single-phase MTs are made according to the U-shaped scheme, the magnetic circuit of which is assembled from a set of rectangular plates of the appropriate length and width. The windings on the U-shaped magnetic core can be arranged in two ways: in the first (Fig. 13, a) the transformer has a high efficiency, in the second (Fig. 13, b) the ST is easier to manufacture, and then, if necessary, add or remove some the number of turns in the already assembled transformer. In this case, the transformer is easier to repair, since only one winding burns out, and the second usually remains intact. When using the circuit (Fig. 13, a), when one winding ignites, the second one is always charred.

If there are suitable plates made of transformer iron, then ST on a U-shaped magnetic circuit is easy to make on your own. The windings are wound separately on the frame, and then installed on the assembled magnetic circuit. How a U-shaped magnetic circuit is assembled is easiest to see by disassembling any small transformer of a similar design. In large transformers, the plates are installed not through one, but in packages of 3-4 pieces, this is faster.

The magnetic circuit for ST can be used, for example, from U-shaped transformers removed from old equipment, if they have sufficient window volume and cross section of the magnetic circuit. But, as a rule, most instrument transformers have limited dimensions. It makes sense to assemble one magnetic circuit from two identical transformers, thus increasing the cross-sectional area. An increase in the cross section of the magnetic circuit gives a gain in turns: now they will have to be wound much less. And the fewer turns, the smaller the window can be installed windings. The reasonable limit is 5060 cm2.

ST can be made on an W-shaped magnetic core, provided that the required number of turns of thick winding wires fit into its windows. The author made a CT from the magnetic cores of two identical W-shaped transformers with the outer dimensions of the W-shaped plate 122x182 mm and the window size 31x90 mm. The cross-sectional area of ​​the magnetic circuit folded from a set of plates from two transformers exceeded 60 cm2, which made it possible to reduce the number of turns of its windings to a minimum. The primary winding of 176 turns of D1.68 mm wire and the secondary winding into two D2.5 mm wires with an output voltage of 46 V came in butt. At a mains voltage of 235 V, the ST developed an arc current of 160 A, although it heated up more than we would like .. .

As a rule, the cores of industrial transformers folded from plates can be easily disassembled: it is not difficult to remove old wires and wind new windings. Sometimes it makes sense to first install a secondary winding (low voltage) on the W-shaped magnetic circuit, and a primary winding (high voltage) on top of it. The characteristics of the CT do not deteriorate from this, but many problems are avoided. The number of turns of the secondary winding can be very approximate, focused on 40-60 V. The turns of the primary winding will have to be selected, adjusting the ST to the desired power. So, having calculated and laid first the low voltage winding, focusing on approximately 50 V, then you can always remove or add a certain number of turns from the upper primary winding of an already finished ST.

In units and equipment that have served their "life" you can find quite powerful and large transformers.

For stationary transformers, the limiting capabilities of either iron or winding wires are never used - everything is done with a margin. Wires often have significant cross sections, as they are designed for a current density 3-4 times less than that allowed for ST. Very often, large transformers have many secondary windings designed for different voltages and powers. The primary winding in the transformer is always one, and its wire is designed for full power. In this case, you can leave the primary winding completely or partially unwind, and remove all secondary windings by winding one thick wire in their place. If the primary winding is also unsuitable, but the magnetic circuit itself is suitable for the manufacture of ST, then all the windings will have to be wound.

In equipment, low voltages are more often used - 12; 27 V. Therefore, powerful transformers wound with thick wire can have an output of 2x12 V, 27 V and others, which are clearly insufficient for use as a ST. If there are two such transformers, then they can be combined, without redoing, into one welding one. To do this, the primary windings are connected in parallel, and the secondary windings are connected in series, and their voltages are summed up.

It may turn out that such a combined MT will have a poor, close to hard, characteristic. To correct the characteristics, it is necessary to include in the secondary winding circuit, in series with the arc, a ballast resistance - a piece of nichrome or other high-resistance wire. Possessing a resistance of the order of hundredths of an ohm, it will somewhat reduce the power of the ST, but it will allow you to work in manual mode.

Welding transformer current adjustment

An important design feature of any welding machine is the ability to adjust the operating current.

There are various ways to adjust the CT current. The easiest way to wind the windings is to make them with taps and, by switching the number of turns, change the current. However, this method can only be used to adjust the current, rather than adjust it over a wide range. Indeed, in order to reduce the current by 2-3 times, it will be necessary to increase the number of turns of the primary winding too much, which will inevitably lead to a voltage drop in the secondary circuit.

In industrial devices, they use different ways current regulation: shunting with various types of chokes; change in the magnetic flux due to the mobility of the windings or magnetic shunting, etc.; the use of stores of active ballast resistances and rheostats; use of thyristor, triac and other electronic circuits power regulation. Most industrial power control schemes are too complex to be fully implemented on homemade PTs. Let's consider the simplified methods actually used in home-made performance.

Recently, thyristor and triac power control circuits have gained some distribution.

Usually a triac is included in the primary winding circuit, a thyristor can only be used at the output. Power regulation occurs by the method of periodic shutdown for a fixed period of time of the primary or secondary winding of the ST at each half-cycle of current; the average value of the current decreases. Naturally, the current and voltage after that have a non-sinusoidal shape. Such schemes allow you to adjust the power over a wide range. A person versed in radio electronics can make such a circuit on his own, although this is very difficult.

In different magazines you can find many very simple circuits with the same principle of operation, consisting of only a few parts. They are intended mainly for adjusting the incandescence of light bulbs and electric heaters. As power regulators for ST, these circuits are of little use. Most of them are unstable: their scales are not linear, and the calibration changes with the mains voltage, the current through the thyristor gradually increases during operation due to the heating of the circuit elements, in addition, the output power of the ST is usually strongly extinguished even at the maximum unlocking position of the regulator.

Do not be surprised if, when connecting the triac circuit to the primary winding, the ST starts to "knock" already at cold speed. This knock is heard in the literal sense of the word, moreover, from ST, who previously worked on x.x. practically silent. This is not surprising, because with each unlocking of the triac, an instantaneous increase in voltage occurs, causing powerful short-term pulses of self-induction EMF and surges in the consumed current. Industrial apparatus, wound with thick wire in reliable insulation, endure this power defect without any consequences. For "feeble" home-made designs, I would not recommend using a triac for the primary winding.

For homemade designs, it is better to use a triac or thyristor regulator in the secondary winding circuit. This will save the ST from unnecessary loads. Almost the same circuit, but with a more powerful device, is suitable for this, although the arc burning process is somewhat worse when using regulators of this type. After all, now with a decrease in power, the arc begins to burn with separate increasingly short-term flashes. This method of adjusting the current, due to the complexity of manufacturing and low reliability, has not become widespread for home-made STs.

The most widely used is a very simple and reliable way to adjust the current using the ballast resistance included at the output of the secondary winding. Its resistance is on the order of hundredths, tenths of an ohm, and it is selected experimentally.

For these purposes, powerful wire resistances used in cranes and trolleybuses, or segments of heating element spirals (thermal electric heater), pieces of thick high-resistance wire have long been used. It is possible to reduce the current somewhat even with the help of a stretched steel door spring. The ballast resistance can be switched on stationary (Fig. 14) or so that later it would be relatively easy to select the desired current. Most high-power wire resistors are made in the form of an open spiral, mounted on a ceramic frame up to half a meter long, as a rule, wire from heating elements is also wound into a spiral.

One end of such a resistance is connected to the output of the ST, and the end of the "ground" wire or the electrode holder is equipped with a removable clamp, which is easy to transfer along the length of the resistance spiral, choosing the desired current (Fig. 15). The industry produces special resistance boxes with switches and powerful rheostats for STs. The disadvantages of this method of adjustment include the bulkiness of the resistances, their strong heating during operation, and inconvenience when switching.

But on the other hand, ballast resistances, although often having a rough and primitive design, improve the dynamic characteristic of the ST, shifting it towards a steeply falling one. There are STs that work extremely unsatisfactorily without ballast resistance.

In industrial devices, current regulation by turning on active resistance has not found distribution due to their bulkiness and heating. But reactive shunting is very widely used - inclusion in the secondary circuit of the inductor. Inductors have a variety of designs, often combined with the CT magnetic circuit as a whole, but they are made in such a way that their inductance, which means reactance, is mainly controlled by moving parts of the magnetic circuit.

At the same time, the throttle improves the arc burning process. Due to the design complexity, chokes are not used in the secondary circuit of self-made STs.

Adjusting the current in the secondary circuit of the ST is associated with certain problems. Thus, significant currents pass through the control device, which leads to its bulkiness. In addition, for the secondary circuit it is almost impossible to select such powerful standard switches that they can withstand currents up to 200 A. Another thing is the primary winding circuit, where the currents are five times less, the switches for which are consumer goods. Active and reactive resistances can be connected in series with the primary winding. Only in this case, the resistance of the resistors and the inductance of the inductors must be significantly greater than in the secondary winding circuit.

So, a battery of several PEV-50 ... 100 resistors connected in parallel with a total resistance of 6-8 Ohms is capable of reducing the output current of 100 A by half. You can collect several batteries and install a switch. If there is no powerful switch at your disposal, then you can get by with several.

By setting the resistors according to the scheme (Fig. 16), you can achieve a combination of 0; 4; 6; 10 ohm. Instead of resistors that will get very hot during operation, you can install a reactance choke.

The inductor can be wound on a frame from a 200-300 W transformer, for example, from a TV, by making taps every 40-60 turns connected to the switch (Fig. 17). You can turn off the power by turning on the secondary winding of a transformer (200-300 W) with a secondary winding rated at about 40 V as a choke. The choke can also be made on an open - straight core.

This is convenient when there is already a ready-made coil with 200-400 turns of suitable wire. Then inside it you need to fill a package of straight plates of transformer iron. The required reactance is selected depending on the thickness of the package, guided by the welding current ST.

For example: a choke made from a coil containing presumably about 400 turns of wire with a diameter of 1.4 mm is packed with an iron package with a total cross section of 4.5 cm2, a length equal to the length of the coil, 14 cm. This made it possible to reduce the CT current to 120 A, t .e. about 2 times. A choke of this type can also be made with a continuously adjustable reactance. It is necessary to make a structure for adjusting the depth of insertion of the core rod into the cavity of the coil (Fig. 18, where 1 is the core; 2 is the latch; 3 is the coil). A coil without a core has negligible resistance, with the core fully inserted, its resistance is maximum. The inductor, wound with a suitable wire, heats up a little, but its core vibrates strongly. This must be taken into account when screeding and fixing a set of iron plates.

It should be noted that for transformers with small currents x.x. (0.1 ... 0.2 A), the above-described resistances in the primary winding circuit have practically no effect on the output voltage of the c.x. ST, and this does not affect the ignition process of the arc. ST with current x.x. 1-2 A when ballast resistance is introduced into the primary circuit, the output voltage decreases already significantly. From my own experience, I can say that active and reactive resistances added in series to the primary winding do not have any pronounced negative effects on the ignition and burning of the arc.

Although the quality of the arc is still degraded, compared with the inclusion of a quenching resistor in the secondary winding circuit.

CTs can also combine regulators or current limiters of different types. For example, you can use the switching of turns of the primary winding in combination with the connection of an additional resistor or in another way.

Reliability of the welding transformer

The reliability of the welding machine depends both on design factors and on the mode and operating conditions. Reliable, carefully manufactured transformers work for many years, without problems withstanding short overloads and flaws in operation. Lightweight portable structures, with varnished wires, and even developing exorbitant power for themselves, as a rule, do not live long. They gradually wear out in the same way as, for example, clothes or shoes wear out over time. Although, given the significant amount of work performed and the low cost of their manufacture, this fully justifies their existence.

CT's worst enemies are overheating and moisture penetration. The most effective means against overheating are reliable winding wires with a current density of not more than 5-7 A / mm2. In order for the wire to cool quickly, it must have good contact with air. To do this, slots are made in the windings (Fig. 19).

First, the first layer is wound and wooden or getinax strips 5-10 mm thick are inserted from the outer sides, then the strips are inserted every two layers of wire: so each layer has contact with air on one side. If the ST is installed without airflow, then the slots should be oriented vertically. Then air will constantly circulate through them: warm air rises, and cold air is sucked in from below. It is even better if the CT is constantly blown by a fan. In fact, forced airflow has little effect on the heating rate of the transformer, but it significantly speeds up its cooling.

Toroidal transformers heat up the fastest and cool the worst. For a very hot ST, even a powerful airflow will not solve this problem, and here it will be necessary to maintain the temperature of the windings with a moderate mode of operation. The number of turns of the windings also affects the cooling of the transformer: the fewer turns, the higher it is.

In addition to the objective and understandable reasons for the failure of welding transformers, mainly related to the imperfection of the design, based on my experience, I want to note one more, seemingly implicit, but nevertheless very common way: how to ruin the ST.

The reason in this case, oddly enough, is the voltage drop in the mains ... ST ceases to weld normally if the mains voltage drops sharply or the power line has a significant intrinsic resistance of the order of several ohms. Unfortunately, both the first and the second are widespread in our country.

If, with a drop in voltage, you can at least accurately find out the cause by taking a voltmeter and measuring the voltage, then in the second case the situation is more complicated: a high-resistance voltmeter does not feel line resistance of a few ohms and shows normal voltage, but these few ohms can easily turn off the power of the ST, its own whose resistance in the arc mode is negligible. But what does the drop in power to the "combustion" of ST have to do with it? And here's the thing. When the owner of the "welding", having suffered quite a lot with the device that is not working from the 220 V network, realizes that he cannot change anything, but work oh, as it should be: earnings are lost or construction is underway, the solution is freezing, ... then in such cases very often the device is connected to a 380 V network.

The fact is that all wiring is usually done from a three-phase line: "zero" and three "phases". If you connect to "zero" and one "phase" - phase voltage, then this is the usual 220 V. If you connect to "phase" and "phase" - line voltage, then 380 V will be removed from two wires. Namely, make negligent welders with single-phase machines rated for 220 V.

At the same time, ST starts to work perfectly, however, very often for a very short time. "Fire" as weak homemade designs, and reliable industrial devices. But everything is very simple: if the voltage in the common power supply drops, for example, by 50 V, and the device does not want to work from 170 V, then 330 V remains between the "phases", which is deadly for any ST ...

Often, the owners of welding machines are simply too lazy to endure their "weldings" once again: after all, the mass is considerable, and they remain on the street, get wet in the rain, they are covered with snow ... After such an attitude, the turn-to-turn short circuit is quite common, the CT windings "burn out", and the whole structure falls apart.

But still, the main enemy of ST is overheating. Well, if you have to weld a lot and quickly, and the ST is wound with not so hot wires and heats up catastrophically quickly, ... you can offer one cardinal means of combating overheating.

You can not be afraid of overheating if the entire transformer is completely immersed in transformer oil. With a significant thermal conductivity, the oil not only removes heat from the windings, but also acts as an additional insulator. In its simplest form, this is a bucket of oil with a ST recessed in it, from where only four wires come out, such a "miracle" can sometimes be seen in rural yards. Some transformer oil can be drained, for example, from old refrigeration units. Although people say that in case of emergency, other types are also suitable, up to sunflower ... I don’t know about sunflower, I didn’t check it myself.

Another important design element of the CT is the outer case. When installing the CT in the case, special attention should be paid to its material and the possibility of air flow for cooling, while the top must be closed, protecting the transformer from rain. Cases or at least some of their parts are best made from non-magnetic materials (brass, duralumin, getinaks, plastics). CT creates a powerful magnetic field that attracts steel elements to it. If the case is made of tin or steel panels are screwed opposite the axis of the primary winding, then during operation this entire structure will be drawn inward and vibrate. The sound at the same time is sometimes such that it can only be compared with the work of a saw of a powerful "circular". Therefore, it is possible to install the ST either in a solidly curved rigid steel case, which is not so susceptible to vibrations, or to make panels opposite at least the primary winding from non-magnetic materials.

You can install a fan in the case or make it airtight and fill it with transformer oil.

And finally, the last recommendation. If you nevertheless made a ST, but are a beginner in welding, then it is better to invite a specialist to test it. Welding is a very difficult task, and a person without experience is unlikely to succeed immediately. Be sure to purchase or make a mask with glass number C-4 or E2. The electric arc emits powerful ultraviolet radiation, which negatively affects the skin and, first of all, the eyes. When the eyes are damaged, a yellow spot appears in the field of vision, which then gradually disappears, they say "catch a bunny."

If you manage to "catch" two such "bunnies" in a row at once, then immediately stop all experiments with an electric arc. When several "bunnies" appear before the eyes, they, as a rule, then disappear, and the person calms down, but later, after a few hours, this phenomenon is fraught with such consequences that it is better not to experience it yourself.

With this simple welding machine, you can cut thin metals, weld copper wires, and engrave metal surfaces. Other applications can be easily found. Such a mini welding machine can be powered by 12-24 V.

The welding machine is based on a high-voltage high-frequency converter. Built on the principle of a blocking generator with a deep transformer feedback. The generator generates short-term electrical impulses repeating at relatively large intervals. The clock frequency is in the range of 10-100 kHz.
The transformation ratio of this circuit will be 1 to 25. This means that if you apply a voltage of 20 V to the circuit, then the output should be about 500 V. This is not entirely true. Since any impulse transformer source or generator without load has powerful high-voltage impulses, reaching a voltage of 30,000 V! Therefore, if you disassemble any impulse Chinese charging, you will see a soldered resistor parallel to the output capacitor. This is also a network load, without a resistor, the output capacitor will quickly leak out due to overvoltage, or worse, it will explode.
Therefore, attention! The voltage at the output of the transformer is life threatening!

Diagram of a mini welding machine

Required details:

• The transformer is homemade, the manufacturing procedure is described below.
• Resistors - 0.5-2 W.
• The transistor was used FP1016 but is hard to find due to its specificity. Can be replaced with a transistor 2SB1587, KT825, KT837, KT835 or KT829 with a change in the polarity of the power supply. Another transistor with a collector current of 7 A or more, a collector-emitter voltage of 150 V or more, with a high gain (composite transistor) is also suitable.

The transistor must be equipped with a heat sink. Although this is not on the diagram, it would be nice to put a filter capacitor in parallel with the source so that all the interference from the operation of the blocking generator does not get into the source.

Transformer manufacturing

The transformer is wound on a piece of ferrite rod from a radio receiver.

• Collector winding - 20 turns of wire 1 mm.
• Base winding - 5 turns with a reason of 0.5-1 mm.
• High-voltage winding - 500 turns with an occasion of 0.14-0.25 mm.

All windings are wound in one direction. First, the collector winding, on top of it, the base winding. This is followed by a three-layer insulation of white electrical tape. Next, we wind the high-voltage winding, 1 layer of 125 turns, then insulation, then repeat. In total, 4 layers should be obtained, which is equal to 500 turns. From above, we also isolate with white electrical tape in several layers.

We collect the scheme. If everything is in order, everything should start without problems. Since the operating frequency of the generator exceeds the audio frequency, you will not hear a squeak during operation, so do not touch the transformer output with your hands.

Start the generator with a voltage of 12 volts and increase if necessary.
The arc is ignited from a distance of 1 cm, which indicates a voltage of 30 kV. The high frequency prevents the burning arc from breaking, as a result of which the arc burns very stably. When using a copper electrode in close contact with another electrode, a plasma medium (copper plasma) is formed, resulting in an increase in the temperature of arc welding-cutting.

Tests of the welding machine by cutting and welding

We cut an arc with a razor blade.

We fuse copper wires up to 1 mm thick.

A thick copper wire was used as the electrode. It is clamped in a wooden match, since dry wood is also a good insulator.

If you like this small welding machine, then you can make it larger and more powerful. But be extremely careful.
Also, to increase power, you can assemble a generator according to a push-pull scheme, and even on field-effect transistors, as here -. In this case, the power will be decent.
Also, do not look at the bright discharges of the arc with the naked eye, use special goggles.

Watch the video of making a welding machine on a blocking generator