Homemade welding machine-transformer from latr. Self-made welding machines and devices Welding machine from an autotransformer

Burnt LATRs (laboratory autotransformers) have long been a widespread material for the manufacture of home-made welding transformers. Inside the LATR body there is a toroidal autotransformer made on a magnetic circuit of a significant section. It is this magnetic circuit that will be needed from LATR for the manufacture of a welding transformer. A transformer usually requires two identical magnetic circuit rings from large LATRs.

LATRs are produced in different types, with maximum currents from 2 to 10A, not all of them are suitable for the manufacture of transformers for welding, only those with the size of the magnetic cores that allow you to lay the required number of turns. The most common among them is probably the LATR-1M autotransformer. Depending on the winding wire, it is designed for currents of 6.7-9A, although the dimensions of the autotransformer itself do not change from this. The LATR-1M magnetic core has the following dimensions: outer diameter D = 127 mm, inner diameter d = 70 mm, ring height h = 95 mm, section S = 27 cm 2, weight about 6 kg. A good welding transformer can be made of two LATR-1M rings, 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. A significant disadvantage of the LATR transformer, in comparison with the U-shaped transformer circuit, is also the fact that the coils cannot be made separately from the magnetic circuit. This means that you will have to wind, pulling each turn through the window of the magnetic circuit, which, of course, greatly complicates the manufacturing process.

There are LATRs with more voluminous magnetic drive rings. They are much better suited for making welding transformers, but less common. In other autotransformers, similar in parameters to LATR-1M, for example AOSN-8-220, the magnetic circuit has other dimensions: the outer diameter of the ring is larger, but the height and diameter of the window are smaller, d = 65 mm. In this case, the window diameter must be expanded to 70 mm.

The ring of the magnetic circuit consists of pieces of iron tape wound on top of each other, fastened along the edges by spot welding. In order to increase the inner diameter of the window, it is necessary to detach the end of the tape from the inside and unwind the required amount. But don't try to rewind everything in one go. It is better to unwind one turn at a time, cutting off the excess each time. Sometimes in this way the windows of larger LATRs are also expanded, although this inevitably decreases the cross-sectional area of the magnetic circuit.

In principle, a cross-sectional area and one ring would be sufficient for a welding transformer. But the problem is that smaller magnetic cores inevitably require more turns, which increases the volume of the coils and requires more window space.

Staggered shoulder transformer

At the beginning of the manufacture of the transformer, it is necessary to insulate both rings. In this case, special attention should be paid to the corners of the edges of the rings - they are sharp, they can easily cut the imposed insulation, and then close the winding wire with themselves. It is better to first smooth the corners a little with a file, and then apply some strong and elastic tape along it, for example, a dense keeper tape or a cambric tube cut along the length. On top of the rings, each separately, they are wrapped with a thin layer of fabric insulation.

Then the insulated rings are connected together. The rings are tightly tightened with a strong tape, and on the sides they are fixed with wooden pegs, also then tightened with tape, - the magnetic core for the transformer is ready.

The next step is the most critical - laying the primary winding. The windings of this welding transformer are wound according to the scheme: primary in the middle, two secondary sections on the side arms.

The primary winding 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, you can not do without a simple device.

First, the wire is wound on a wooden reel and in this form is easily pulled through the ring windows.

The primary wire can have a diameter of 1.6-2.2 mm. For magnetic circuits made up of rings with a window diameter of 70 mm, you can use a wire with a diameter of no more than 2 mm, otherwise there will be little space for the secondary winding. The primary winding contains, as a rule, 180-200 turns at normal mains voltage, which is sufficient for efficient operation with a 3 mm electrode.

A cambric is put on the end of the wire, which is attracted by HB 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 next ones to level the surface.

The wire lays down coil to coil, in no case allowing the wire to overwhelm the wire. The layers of wire must be insulated from each other. Again, to save space, the winding should be placed as compactly as possible. On a magnetic core made of medium-sized rings, the interlayer insulation should be used thinner. One should not strive to wind the primary winding quickly. This process is slow, and after laying the hard wires, your fingers begin to ache. It is better to do this in 2-3 approaches - after all, quality is more important than speed.

If the primary winding is made, most of the work is done, leaving the secondary. But first you need to determine the number of turns of the secondary winding for a given voltage. To get started, connect the ready-made primary to the network. The no-load current of this version of the transformer is small - only 70-150 mA, the hum of the transformer should be barely audible. We wind 10 turns of any wire on one of the side arms and measure the output voltage across them. Each of the side arms accounts for half of the magnetic flux created on the central arm, so here 0.6-0.7V falls on each turn of the secondary winding. Based on the result obtained, the number of turns of the secondary winding is calculated, focusing on a voltage of 50V (about 75-80 turns).

The choice of material for the secondary winding is limited by the remaining space of the magnetic circuit windows. Moreover, each turn of a thick wire will have to be pulled along its entire length into a narrow window. The easiest way is to wind it with an ordinary stranded wire 16 mm 2 in synthetic insulation - it is soft, flexible, well insulated, and will only slightly warm up during operation. It is possible to make a secondary winding from several strands of copper wire.

Half of the turns of the secondary winding is wound on one shoulder, half on the other. If there are no wires of sufficient length, you can connect them from pieces - it's okay. Having wound the windings on both arms, you need to measure the voltage on each of them, it may differ by 2-3V - the somewhat excellent properties of the magnetic cores of different LATRs affect, which does not particularly affect the properties of the arc during welding. Then the windings on the shoulders are connected in series, but care must be taken that they are not in antiphase, otherwise the output will produce a voltage close to zero (see article Winding of a welding transformer). At a mains voltage of 220-230V, a welding transformer of this design must develop a current of 100-130A in arc mode. Short-circuit current of the secondary circuit - up to 180A.

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 the desired one. The operating current will not decrease much from this. To a greater extent, lowering the no-load voltage affects the arc ignition process. The arc ignites easily at voltages close to 50V and above. Although the arc can be ignited without any problems at lower voltages. So if the manufactured transformer has an output of about 40V, then it can be used for work. It's another matter if you come across electrodes designed for high voltages - some brands of electrodes operate from 70-80V.

Toroidal transformer

On the LATR rings, you can also make a welding transformer according to a different - toroidal scheme. This also requires two rings, preferably from large LATRs. The rings are connected and insulated: one ring-magnetic circuit with a significant cross-sectional area is obtained.

The primary winding contains the same number of turns as in the previous circuit, but winds along the length of the entire ring and, as a rule, lies in two layers. The problem of the lack of internal space of the magnetic circuit window of such a transformer circuit is even more acute than for the previous design. Therefore, it is necessary to insulate here with as thin layers and materials as possible. Thick winding wires cannot be used here either. Although some installations use LATRs of particularly large dimensions, only one such ring can be used to manufacture a toroidal welding transformer.

The advantageous difference between the toroidal circuit for a welding transformer is a higher efficiency. Each turn of the secondary winding will now have more than one volt of voltage, therefore, the "secondary" will have fewer turns, and the output power will be higher than in the previous circuit. However, the length of the turn on the toroidal magnetic circuit will be 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 the winding, the limited volume of the window, the inability to use 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 reinforced.

It is difficult to use rigid wires for the secondary winding. It is easier to wind it with a soft stranded or multi-strand wire. If you select all the wires correctly 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 required voltage will be obtained at the output of the transformer.

Sometimes a toroidal welding transformer is made of several LATR rings in a different way, they are not placed on top of each other, but the iron strips of tape are rewound from one to the other. To do this, first, the inner turns of the strips are selected from one ring in order to expand the window. The rings of other LATRs are completely dissolved into strips of tape, which are then wound as tightly as possible on the outer diameter of the first ring. After that, the assembled single magnetic circuit is wrapped very tightly with insulating tape. Thus, a ring-magnetic circuit with a more voluminous inner space than all previous ones is obtained. In such it will be possible to fit a wire of significant cross-section. The required number of turns is calculated from the sectional area of the assembled ring.

The disadvantages of this design include the laboriousness of manufacturing a magnetic circuit. Moreover, no matter how hard you try, it will still not be possible to manually wind the iron strips on each other as tightly as before. As a result, the magnetic core is flimsy. When working in welding mode, the iron in it vibrates strongly, emitting a powerful hum.

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When constructing or repairing equipment or household appliances, it is often necessary to weld any elements. To connect the parts, you will need to use a welding machine. Today, you can easily purchase a similar design, but you should know that you can also make homemade welding machines.

Welding machines are available in DC and AC. The latter are used to weld small-thickness metal blanks at low currents. The DC arc is more stable, and it is possible to weld in forward and reverse polarity. In this case, you can use electrode wire without coating or electrodes. To make the arc stable, it is recommended to overestimate the open-circuit voltage of the welding winding at low currents.

To rectify alternating current, ordinary bridge rectifiers on large semiconductors with cooling heatsinks should be used. In order to smooth out voltage ripples, one of the terminals must be connected to the electrode holder through a special choke, which is a coil of several tens of turns of a copper bus with a cross section of 35 mm. Such a bus can be wound on any core, it is best to use a core from a magnetic starter.

To straighten and smoothly regulate the welding current, more complex circuits with the use of large thyristors for control should be used.

The advantages of constant current regulators include their versatility. They have a wide range of voltage configurations, and therefore such elements can be used not only for gradual current regulation, but also for charging batteries, powering electrical elements for heating and other circuits.

AC welding machines can be used to connect workpieces with electrodes larger than 1.6 mm in diameter. The thickness of the workpieces to be joined can be more than 1.5 mm. In this case, there is a large welding current, and the arc is burning steadily. Electrodes that are made for AC welding only can be used.

Stable arc burning can be obtained if the welding attachment has a falling external characteristic, which determines the relationship between current and voltage in the welding chain.

What should be considered in the process of manufacturing welding machines?

For a stepwise overlap of the welding current spectrum, it is necessary to switch both the primary and secondary windings. For a smooth configuration of the current within the selected spectrum, the mechanical properties of the movement of the windings should be used. If you remove the welding winding with respect to the mains, magnetic leakage fluxes will increase. It should be understood that this can lead to a decrease in the welding current. In the process of making a homemade structure for welding, you do not need to strive for a complete overlap of the range of welding currents. It is recommended to first collect for work with electrodes 2-4 mm. If it is necessary in the future to work at low welding currents, the structure can be supplemented with a separate straightening device with a gradual adjustment of the welding current.

Homemade designs must meet several requirements, the main ones of which are the following:

Comparative compactness and light weight. Such parameters can be reduced by reducing the power of the structure.
Sufficient duration of operation from a 220 V power network. It can be increased by using steel with high magnetic permeability and heat-resistant insulation of wires for winding.

Such requirements can be easily met if you know the basics of the construction of welding structures and adhere to the technology of their manufacture.

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How to choose the type of core for the structure to be manufactured?

In the process of manufacturing such structures, rod magnetic wires are used, they are more technologically advanced. The core is made of electrical steel plates of any configuration, the material thickness should be 0.35-0.55 mm. The elements will need to be pulled together with pins, which are covered with insulating material.

In the process of choosing a core, the dimensions of the “window” should be taken into account. The windings of the elements must be placed in the structure. It is not recommended to use cores with a cross section of 25-35 mm, since in this case the manufactured structure will not have the necessary power supply, as a result of which high-quality welding will be quite difficult. In this case, overheating of the device cannot be ruled out either. The core should have a cross section of 45-55 mm.

In some cases, welded structures with toroidal cores are produced. These devices have higher electrical performance and low electrical losses. It is much more difficult to make such devices, since the windings will need to be placed on the torus. You should be aware that winding in this case is quite difficult to perform.

The cores are made from tape transformer iron, which is rolled into a torus-shaped roll.

To increase the inner diameter of the torus, you need to unwind a part of the metal strip from the inside, and then wind it on the outside of the core.

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How to choose the right winding structure?

For the primary winding, it is recommended to use a copper wire, which is covered with an insulating material made of fiberglass. You can also use wires that are covered with rubber. It is not allowed to use cords that are covered with PVC insulation.

A large number of network winding taps is not recommended. By reducing the number of turns of the primary winding, the power of the welding machine will increase. This will lead to an increase in the arc voltage and a deterioration in the quality of joining the workpieces. By changing the number of turns of the primary winding, it will not be possible to achieve overlapping of the welding current spectrum without deteriorating welding properties. For this, it will be necessary to provide for switching the turns of the secondary welding winding.

The secondary winding must contain 67-70 turns of a copper busbar with a cross section of 35 mm. A stranded mains cable or a flexible stranded cord can be used. The insulating material must be heat-resistant and reliable.

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Homemade welding machine from an autotransformer

The welding device operates on a 220 V power supply. The design has excellent electrical performance. Thanks to the use of a new form of magnetic wire, the weight of the device is about 9 kg with dimensions of 150x125 mm. This is achieved by using a strip iron that is rolled into a torus-shaped roll. In most cases, a standard W-shaped plate package is used. The electrical performance of a transformer structure on a magnetic wire is approximately 5 times higher than that of similar plates. Electrical losses will be minimal.

Elements that will be needed in order to make a do-it-yourself welding machine:

magnetic wire;
autotransformer;
electrical cardboard or varnish cloth;
wires;
wooden lath;
insulating material;
transformer;
cable;
casing;
switch.

An excellent welding machine can be made on the basis of a laboratory autotransformer LATR and a home-made thyristor mini-controller with a rectifier bridge. They make it possible not only to safely connect to a standard 220 V network, but also to change the voltage at the electrode, and therefore, to select the required value of the welding current.

A toroidal autotransformer (ATR) is located inside the housing, which is made on a large-section magnetic circuit. It is this core-magnetic circuit that will be needed from LATR for the manufacture of a new welding transformer (ST).

We need two identical magnetic circuit rings from large LATRs. LATRs were produced in the USSR of various types with a maximum current from 2 to 10 A. Welding transformers for its manufacture are suitable for those whose magnetic core sizes will make it possible to accommodate the required number of turns. The most common among them is the ATP type LATR 1M.

The magnetic circuit from LATR 1M has the following dimensions: outer diameter 127 mm; inner 70 mm; ring height 95 mm; section 27 cm2 and weight 6 kg. From two rings from this LATR, you can make an excellent welding transformer.

In many ATRs, the magnetic core has a larger outer diameter of the ring, but the height and diameter of the window are smaller. In this case, it must be increased to 70 mm. The ring of the magnetic circuit is made of pieces of iron tape wound on top of each other, welded along the edges.

In order to adjust the inner diameter of the window, it is necessary to detach the end of the tape from the inside and unwind the required amount. Don't try to do this in one go.

The welding transformer is the beginning of the manufacturing operation, firstly, it is required to insulate both rings. Paying attention to the corners of the edges of the rings, if they are sharp, they can easily damage the applied insulation, and then short-circuit the winding wire. It is better to glue some kind of elastic tape or cambric cut along the corners. From above, the ring is wrapped with a small layer of insulation. Next, the insulated rings are fastened together.

The rings are tightly twisted with a dense tape, and on the sides they are fixed with pegs tightened with electrical tape. The CT core is now ready.

Moving on to the next item the manufacture of a welding transformer, namely the laying of the primary winding.

Welding transformer winding - wound as shown in figure three - primary winding in the middle, both secondary sections are placed on the side arms. The primary winding requires about 70-80 meters of wire, which will have to be pulled with each turn through both windows of the magnetic circuit. In this case, I can recommend using the device shown in Figure 4. First, the wire is wound on it and in this form is easily pulled through the windows of the rings. The winding wire can be lumpy, ten meters each, but it is better to use a whole one.

In this case, it is wound in parts, and the ends are fastened without twisting and soldered together, and then isolated. The diameter of the wire used in the primary winding is 1.6-2.2 mm. in the amount of 180-200 turns.

We start winding CT. At the end of the wire, we attach the cambric with electrical tape to the beginning of the first layer. The surface of the magnetic circuit is rounded, so the first layers will have fewer turns than each subsequent one for leveling the surface, see Figure 5. The wire must be laid turn to turn, in no case overwhelming the wire on the wire.

The layers of wire must be insulated from each other. To save space, the winding should be laid as compactly as possible. On a magnetic core made of small rings, the interlayer insulation must be applied thinner, for example, using ordinary tape. Do not rush to wind the primary winding once. It's easier to do this in 2-3 approaches.

Determine the number of turns of the CT secondary winding for the required voltage. To begin with, we connect the already wound primary winding to an alternating voltage of 220 volts. The idle current of this version of the CT is low - only 70-150 mA, the hum of the CT should be quiet. Wind 10 turns of wire on one of the side arms and measure the output voltage across it with a voltmeter. Each of the side arms receives only half of the magnetic flux generated on the central arm, so here for each turn of the secondary winding there will be 0.6-0.7 V. Based on the result obtained, we calculate the required number of turns in the secondary winding, focusing on the voltage level at 50 volts, usually about 75 turns. The easiest way is to wind it with a 10 mm2 stranded wire in synthetic insulation. You can collect the secondary winding from several strands of copper wire. Half the turns should be wound on one shoulder, half on the other.

Having wound the windings on both CT arms, you need to check the voltage on each of them, a difference of 2-3 volts is allowed, but no more. Then the windings on the shoulders are connected in series, but so that they are not in antiphase, otherwise the output will be about zero.

With a standard mains voltage, a welding transformer on a LATR magnetic circuit can produce a current in arc mode up to 100-130 A, with a short-circuit current of the secondary circuit reaches 180 A.

The arc strikes very easily at XX voltages, around 50 V or higher, although the arc can be struck without too much trouble at lower voltages. On the LATR rings, you can also assemble CTs according to the toroidal scheme.

This will also require two rings, preferably from large LATRs. The rings are connected and insulated: one large magnetic ring is obtained. The primary winding contains the same number of turns as described above, but it is already wound around the entire ring and usually in two layers. It is necessary to isolate the layers with as thin materials as possible. Thick winding wires cannot be used either.

The advantage of the ST toroidal circuit is its high efficiency. For each turn of the secondary winding there is 1 V of voltage, therefore, the secondary winding will contain fewer turns, and the output power is higher than in the previous case.

The obvious disadvantages include the problem with winding, the limited volume of the window and the inability to use a large diameter wire.

It is problematic to use rigid wires for the secondary. Better to use soft stranded

The arc burning characteristic of a toroidal ST is an order of magnitude higher than that of the previous version.

Scheme of a welding machine based on CT on a magnetic circuit from Latrov

The operating modes are set to potentiometers. Together with the capacitors C2 and C3, it forms classical phase-shifting chains, each of which will operate in its own half-cycle and open its thyristor for a given period of time. As a result, the primary winding of the CT will be regulated by 20 - 215 V. Being transformed in the secondary winding, they easily ignite the arc for welding on alternating or rectified current to the required voltage.

For the manufacture of a welding transformer, you can use a stator from an induction motor. The size of the core is determined in this case by the cross-sectional area of the stator, which must be at least 20 cm 2.

In domestic color TVs, large, heavy network transformers were used, for example, TS-270, TS-310, ST-270. They have U-shaped magnetic circuits, they are easy to disassemble by unscrewing only two nuts on the tightening pins, and the magnetic circuit breaks down into two halves. For older transformers TS-270, TS-310, the section of the magnetic circuit has dimensions of 2x5 cm, S = 10 cm2, and for newer transformers - TS-270, the section of the magnetopod S = 11.25 cm2 with dimensions of 2.5x4.5 cm. the width of the window for old transformers is therefore several millimeters larger. Older transformers are wound with copper wire, and a wire can come in handy from their primary windings.

Welding transformer other possible types and designs

ST, in addition to special manufacture, can be obtained by re-equipping 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 according to a single or three-phase scheme.

The homemade welding machine from LATR 2 It is built on the basis of a nine-ampere LATR 2 (laboratory controlled autotransformer) and its design provides for the regulation of the welding current. The presence of a diode bridge in the construction of the welding machine allows direct current welding.

Current regulator circuit for a welding machine

The operating mode of the welding machine is regulated by a variable resistor R5. Thyristors VS1 and VS2 each open in their half-cycle alternately for a certain period of time due to the phase-shifting circuit built on the elements R5, C1 and C2.

As a result, it becomes possible to change the input voltage on the primary winding of the transformer from 20 to 215 volts. As a result of the transformation, an undervoltage appears on the secondary winding, which makes it easy to ignite the welding arc at terminals X1 and X2 for AC welding and at terminals X3 and X4 for DC welding.

The welding machine is connected to the mains with an ordinary plug. In the role of switch SA1, you can use a twin 25A machine.

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Alteration of LATR 2 for a homemade welding machine

First, the protective cover, electrical contact and fastener are removed from the autotransformer. Next, good electrical insulation is wound on the existing 250 volt winding, for example, glass cloth, on top of which 70 turns of the secondary winding are laid. For the secondary winding, it is advisable to choose a copper wire with a cross-sectional area of about 20 square meters. mm.

If there is no wire of a suitable cross-section, you can make a winding of several wires with a total cross-sectional area of 20 sq. Mm. The modified LATR2 is mounted in a suitable homemade case with ventilation holes. It is also necessary to install a regulator board, a packet switch, as well as terminals for X1, X2 and X3, X4.

In the absence of LATR 2, the transformer can be made homemade by winding the primary and secondary windings on a transformer steel core. The core section should be approximately 50 square meters. see The primary winding is wound with a wire PEV2 with a diameter of 1.5 mm and contains 250 turns, the secondary one is the same which is wound on LATR 2.

At the output of the secondary winding, a diode bridge of powerful rectifier diodes is connected. Instead of the diodes indicated in the diagram, diodes D122-32-1 or 4 VL200 diodes (electric locomotive) can be used. Diodes for cooling must be installed on homemade radiators with an area of at least 30 square meters. cm.

Another important point is the choice of cable for the welding machine. For this welder, it is necessary to use a copper multicore cable in rubber insulation with a cross section of at least 20 sq. Mm. You need two pieces of cable, 2 meters long. Each must be well crimped with terminal lugs to connect to the welding machine.

Resistance welding, in addition to the technological advantages of its use, has another important advantage - simple equipment for it can be manufactured independently, and its operation does not require specific skills and initial experience.

1 Principles of design and assembly of resistance welding

Contact welding, assembled by hand, can be used to solve a fairly wide range of non-serial and non-industrial tasks for the repair and manufacture of products, mechanisms, equipment from various metals both at home and in small workshops.

Resistance welding ensures the creation of a welded joint of parts by heating the area of their contact with an electric current passing through them while simultaneously applying a compressive force to the joint area. Depending on the material (its thermal conductivity) and the geometric dimensions of the parts, as well as the power of the equipment used to weld them, the contact welding process should proceed with the following parameters:

low voltage in the power welding circuit - 1–10 V;
in a short time - from 0.01 seconds to several;
high welding pulse current - most often from 1000 A or higher;
small melting zone;
the compressive force applied to the weld should be significant - tens to hundreds of kilograms.

Compliance with all these characteristics directly affects the quality of the resulting welded joint. You can only make devices for yourself, as in the video. The easiest way is to assemble an AC welding machine with an unregulated power. In it, the process of joining parts is controlled by changing the duration of the supplied electrical impulse. To do this, use a time relay or cope with this task manually "by eye" using a switch.

Homemade spot resistance welding is not very difficult to manufacture, and to complete its main unit - a welding transformer - you can pick up transformers from old microwave ovens, televisions, latvians, inverters and the like. The windings of a suitable transformer will need to be rewound in accordance with the required voltage and the welding current at its output.

The control scheme is selected ready-made or developed, and all other components and, in particular, for the contact welding mechanism are taken based on the power and parameters of the welding transformer. The contact-welding mechanism is made in accordance with the nature of the forthcoming welding works according to any of the known schemes. Welding tongs are usually made.

All electrical connections must be of good quality and have good contact. And connections using wires are made of conductors with a cross section corresponding to the current flowing through them (as shown in the video). This is especially true for the power section - between the transformer and the clamp electrodes. With poor contacts of the circuit of the latter, there will be large losses of energy at the joints, sparking may occur, and welding may become impossible.

2 Diagram of a device for welding metal up to 1 mm thick

To connect parts by contact, you can assemble according to the diagrams below. The proposed device is designed for welding metals:

sheet, the thickness of which is up to 1 mm;
wires and rods up to 4 mm in diameter.

Main technical characteristics of the device:

supply voltage - alternating 50 Hz, 220 V;
output voltage (on the electrodes of the contact welding mechanism - on the tongs) - variable 4–7 V (idle);
welding current (maximum pulse) - up to 1500 A.

Figure 1 shows a schematic electrical diagram of the entire device. The offered resistance welding consists of a power section, a control circuit and an AB1 circuit breaker, which is used to turn on the power of the device and protect it in case of emergency. The first unit includes a welding transformer T2 and a non-contact thyristor single-phase starter of the MTT4K type, which connects the primary winding of T2 to the mains.

Figure 2 shows a diagram of the windings of a welding transformer with an indication of the number of turns. The primary winding has 6 terminals, by switching which you can perform a stepwise coarse adjustment of the output welding current of the secondary winding. In this case, terminal No. 1 remains permanently connected to the network circuit, and the remaining 5 are used for adjustment, and only one of them is connected to the power supply for operation.

The scheme of the MTT4K starter, produced in series, is shown in Fig. 3. This module is a thyristor switch, which, when its contacts 5 and 4 are closed, switches the load through contacts 1 and 3 connected to the open circuit of the primary winding of Tr2. MTT4K is designed for a load with a maximum voltage of up to 800 V and a current of up to 80 A. Such modules are produced in Zaporozhye at Element-Converter LLC.

The control scheme consists of:

power supply unit;
direct control circuit;
relay K1.

Any transformer with a power of no more than 20 W can be used in the power supply unit, designed to operate from a 220 V network and outputting a voltage of 20-25 V on the secondary winding. It is proposed to install a diode bridge of the KTs402 type as a rectifier, but any other with similar ones can be used parameters or assembled from individual diodes.

Relay K1 is used to close contacts 4 and 5 of the MTT4K key. This occurs when voltage is applied from the control circuit to the winding of its coil. Since the switched current flowing through closed contacts 4 and 5 of the thyristor switch does not exceed 100 mA, almost any low-current electromagnetic relay with an operating voltage within 15-20 V is suitable as K1, for example, RES55, RES43, RES32 and the like.

3 Control chain - what does it consist of and how does it work?

The control circuit functions as a time relay. Turning on K1 for a given period of time, it sets the duration of the effect of an electric pulse on the parts to be welded. The control circuit consists of C1-C6 capacitors, which must be electrolytic with a charging voltage of 50 V or higher, P2K switches with independent latching, KH1 buttons and two resistors - R1 and R2.

The capacitance of the capacitors can be: 47 μF for C1 and C2, 100 μF for C3 and C4, 470 μF for C5 and C6. KH1 must be with one normally closed and the other normally open contacts. When AB1 is turned on, the capacitors, connected with P2K to the control circuit and the power supply (in Fig. 1, this is only C1), begin to charge, R1 limits the initial charging current, which significantly increases the service life of the capacitors. Charging occurs through the normally closed contact group of the KN1 button, which was switched at that time.

When KH1 is pressed, the normally closed contact group opens, disconnecting the control circuit from the power supply, and the normally open one closes, connecting the charged capacities to the K1 relay. The capacitors are discharged and the discharge current triggers K1.

An open normally closed contact group KH1 prevents the relay from being energized directly from the power supply. The greater the total capacity of the discharging capacitors, the longer they are discharged, and, accordingly, K1 closes contacts 4 and 5 of the MTT4K key longer, and the longer the welding pulse. When the capacitors are completely discharged, K1 will shut off and resistance welding will stop working. To prepare it for the next impulse, KH1 must be released. The capacitors are discharged through the resistor R2, which must be variable and serves to more accurately regulate the duration of the welding pulse.

4 Power section - transformer

The proposed resistance welding can be assembled, as shown in the video, on the basis of a welding transformer made using a magnetic circuit from a 2.5 A transformer. Such ones are found in LATRs, laboratory instruments and a number of other devices. The old winding must be removed. On the ends of the magnetic circuit, it is necessary to install rings made of thin electrical cardboard.

They are folded along the inner and outer edges. Then the magnetic core must be wrapped over the rings with 3 or more layers of varnished cloth. To make the windings, wires are used:

For primary 1.5 mm in diameter, it is better in fabric insulation - this will contribute to a good impregnation of the winding with varnish;
For a secondary diameter of 20 mm, stranded in organosilicon insulation with a cross-sectional area of at least 300 mm 2.

The number of turns is shown in Fig. 2. Intermediate conclusions are made from the primary winding. After winding it is impregnated with EP370, KS521 varnish or the like. A cotton tape (1 layer) is wound over the primary coil, which is also impregnated with varnish. Then the secondary winding is laid and the varnish impregnation is done again.

5 How to make pliers?

Contact welding can be equipped with pliers, which are mounted directly into the body of the device, as in the video, or external in the form of scissors. The first, from the point of view of performing high-quality, reliable insulation between their nodes and ensuring good contact in the circuit from the transformer to the electrodes, is much easier to manufacture and connect than remote ones.

However, the clamping force developed by such a structure, if the length of the movable arm of the pliers is not increased after the electrode, will be equal to the force generated directly by the welder. Remote pliers are more convenient to use - you can work at some distance from the device. And the effort developed by them will depend on the length of the handles. However, it will be necessary to make good enough insulation from textolite bushings and washers in the place of their movable bolted connection.

When making pliers, it is necessary to foresee in advance the necessary overhang of their electrodes - the distance from the body of the apparatus or the place of the movable connection of the handles to the electrodes. This parameter will determine the maximum possible distance from the edge of the sheet metal to the place where welding is performed.

Tick electrodes are made from copper or beryllium bronze rods. You can use the tips of powerful soldering irons. In any case, the diameter of the electrodes must be no less than that of the wires supplying them with current. To obtain welding cores of the desired quality, the size of the contact pads (electrode tips) should be as small as possible.