When constructing or repairing equipment or household appliances, quite often there is a need to weld some 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 come in direct and alternating current. The latter are used to weld metal workpieces of small thickness at low currents. The DC welding arc is more stable, and it is possible to weld with direct and reverse polarity. In this case, you can use electrode wire without coating or electrodes. To make the arc burning stable, at low currents it is recommended to increase the open circuit voltage of the welding winding.
To rectify alternating current, you should use ordinary bridge rectifiers on large semiconductors with cooling radiators. 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 dozen turns of a copper busbar 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, you should use more complex circuits using large thyristors for control.
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 gradually adjusting current, but also for charging batteries, powering electrical elements for heating and other circuits.
AC welding machines can be used to connect workpieces with electrodes whose diameter is more than 1.6 mm. The thickness of the joined workpieces can be more than 1.5 mm. In this case, there is a high welding current, and the arc burns stably. Electrodes that are made for welding exclusively with alternating current can be used.
A stable arc can be obtained if the welding fixture has a falling external characteristic, which determines the relationship between the current and voltage in the welding chain.
What should be considered in the manufacturing process of welding machines?
To stepwise cover the spectrum of welding currents, switching of both primary and secondary windings is necessary. 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 in relation to the network winding, the magnetic leakage fluxes will increase. Please be aware that this may result in a reduction in welding current. In production homemade design for welding there is no need to strive to completely cover the spectrum of welding currents. It is recommended that you first assemble it to work with 2-4 mm electrodes. If you need to work with small welding currents in the future, the design can be supplemented with a separate device for straightening with gradual adjustment of the welding current.
Self-made structures must satisfy certain requirements, the main ones being the following:
- Relatively compact and light weight. Such parameters can be reduced by reducing the power of the structure.
- Sufficient operating time from a 220 V power supply. 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 constructing welding structures and adhere to the technology for their manufacture.
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How to choose the type of core for the structure being manufactured?
In the manufacturing process of such structures, rod magnetic wires are used; they are more technologically advanced. The core is made from electrical steel plates of any configuration, the thickness of the material should be 0.35-0.55 mm. The elements will need to be tightened with studs that are covered with insulating material.
When choosing a core, you should take into account the size of the “window”. The structure must accommodate the windings of the elements. It is not recommended to use cores with cross section 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 to produce. In this case, overheating of the device also cannot be ruled out. The core should have a cross-section of 45-55 mm.
In some cases, they are produced welding structures with toroidal cores. These devices have higher electrical performance and low electrical losses. Making such devices is much more difficult, since the windings will need to be placed on the torus. You should know that winding in this case is quite difficult.
The cores are made of transformer strip iron, which is rolled into a torus-shaped roll.
To increase the internal diameter of the torus, with inside you need to unwind part of the metal tape, 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 copper wire, which is covered with fiberglass insulating material. You can also use wires that are covered with rubber. It is not allowed to use cords that are covered with polyvinyl chloride insulation.
It is not recommended to make a large number of taps of the network winding. 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 arc voltage and deterioration in the quality of the workpiece connection. By changing the number of turns of the primary winding, it will not be possible to overlap the spectrum of welding currents without deteriorating the welding properties. To do this, it will be necessary to provide for switching the turns of the secondary welding winding.
The secondary winding should contain 67-70 turns of a copper busbar with a cross-section of 35 mm. Stranded can be used network cable or flexible stranded cord. The insulating material must be heat-resistant and reliable.
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Homemade welding machine from an autotransformer
The welding device operates from 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 strip iron, which is rolled into a torus-shaped roll. In most cases, a standard package of W-shaped plates is used. The electrical performance of a transformer design on a magnetic wire is approximately 5 times higher than that of similar plates. Electrical losses will be minimal.
Elements that will be needed to make a welding machine with your own hands:
- magnetic wire;
- autotransformer;
- electrical cardboard or varnish fabric;
- wires;
- wooden slats;
- insulating material;
- transformer;
- cable;
- casing;
- switch.
A common material for the manufacture of homemade welding transformers has long been burnt LATRs (laboratory autotransformers). Inside the LATR housing there is a toroidal autotransformer made on a magnetic core of large cross-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 core rings from large LATRs.
LATRs are produced different types, with maximum currents from 2 to 10A, not all of them are suitable for the manufacture of transformers for welding, only those whose magnetic core sizes allow the required number of turns to be laid. 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 this does not change the dimensions of the autotransformer itself. The LATR-1M magnetic core has the following dimensions: outer diameter D=127 mm, inner diameter d=70 mm, ring height h=95 mm, cross-section S=27 cm 2, weight about 6 kg. From two rings from LATR-1M you can make a good welding transformer, 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 a transformer made from LATRs, compared to the U-shaped transformer circuit, is also that it is impossible to manufacture the coils 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 larger magnetic conductor rings. They are much better suited for making welding transformers, but are less common. For other autotransformers similar in parameters to LATR-1M, for example AOSN-8-220, the magnetic circuit has different dimensions: the outer diameter of the ring is larger, but the height and diameter of the window d = 65 mm are smaller. In this case, the window diameter must be expanded to 70 mm.
The magnetic circuit ring consists of pieces of iron tape wound on each other, fastened at the edges spot welding. In order to increase the inner diameter of the window, it is necessary to disconnect the end of the tape from the inside and unwind the required amount. But don’t try to rewind everything at once. It is better to unwind one turn at a time, cutting off the excess each time. Sometimes the windows of larger LATRs are expanded in this way, although this inevitably reduces the cross-sectional area of the magnetic core.
In principle, the 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.
Transformer with spaced arms
At the beginning of transformer manufacturing, it is necessary to insulate both rings. Special attention In this case, you should pay attention to the corners of the edges of the rings - they are sharp, they can easily cut the applied insulation, and then short-circuit the winding wire. It is better to first smooth out the corners somewhat with a file, and then apply some kind of strong and elastic tape along it, for example, a thick keeper tape or a cambric tube cut lengthwise. On top of the rings, each separately, is wrapped with a thin layer of fabric insulation.Next, the isolated rings are connected together. The rings are tightly pulled together with strong tape, and fixed on the sides with wooden pegs, also then tied with tape - the magnetic core for the transformer is ready.
The next step is the most important - laying the primary winding. The windings of this welding transformer are wound according to the scheme: primary in the middle, two sections of secondary 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, there is no way to do without a simple device.
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 primary winding wire can have a diameter of 1.6-2.2 mm. For magnetic cores 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 left for the secondary winding. The primary winding contains, as a rule, 180-200 turns at normal mains voltage, which is enough for effective operation with a 3 mm electrode.
A cambric is put on the end of the wire, which is attracted by cotton 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 subsequent layers to level the surface.
The wire is laid turn to turn, in no case allowing wire to overlap 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 circuit made of small rings, the interlayer insulation should be used thinner. You should not try to wind the primary winding quickly. This process is slow, and after laying the hard wires, your fingers begin to hurt. It’s 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 begin, 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 onto one of the side arms and measure the output voltage on them. Each of the side arms accounts for half of the magnetic flux created on the central arm, so here there is 0.6-0.7V for 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 secondary winding material is limited by the remaining space of the magnetic circuit windows. Moreover, each turn of thick wire will have to be stretched along the entire length of narrow window. The easiest way is to wind it with ordinary stranded wire 16 mm 2 in synthetic insulation - it is soft, flexible, well insulated, and will only heat up slightly during operation. You can make a secondary winding from several strands of copper wire.
Half of the turns of the secondary winding are wound on one arm, half on the other. If there are no wires of sufficient length, you can connect them from pieces - no problem. Having wound the windings on both arms, you need to measure the voltage on each of them, it can differ by 2-3V - the slightly different properties of the magnetic cores of different LATRs affect it, which does not particularly affect the properties of the arc during welding. Then the windings on the arms are connected in series, but care must be taken that they are not out of phase, otherwise the output voltage will be close to zero (see the article Winding of a welding transformer). With a network voltage of 220-230V, a welding transformer of this design should develop a current of 100-130A in arc mode. Current during a short circuit of the secondary circuit is 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 desired. This will not decrease the operating current much. IN to a greater extent a decrease in open circuit voltage affects the arc ignition process. The arc ignites easily at voltages close to 50V and higher. Although the arc can be ignited without any problems even at more low voltage. 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
Using rings from LATRs, you can also make a welding transformer using a different - toroidal scheme. For this you also need two rings, preferably from large LATRs. The rings are connected and insulated: one ring-magnetic core with a significant cross-sectional area is obtained.
The primary winding contains the same number of turns as in the previous circuit, but is wound along the length of the entire ring and, as a rule, lies in two layers. The problem of the lack of internal space in 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 in some installations LATRs are used especially large sizes, only on one ring of this can a toroidal welding transformer be made.
The advantageous difference between the toroidal circuit for a welding transformer is its 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 a toroidal magnetic circuit will be longer, and it is unlikely that it will be possible to save on wire here. The disadvantages of this scheme include: complexity of winding, limited window volume, inability to use wire large section, as well as greater heating intensity. If in the previous version all windings were located separately and at least partially had contact with air, now the primary winding is completely under the secondary, and their heating is mutually reinforcing.
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 select all the wires correctly and carefully lay them out, 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 transformer output.
Sometimes a toroidal welding transformer is made from several rings of LATRs in a different way, they are not placed on top of each other, but the iron strips of the tape are rewinded from one to another. To do this, first the inner turns of strips are selected from one ring to widen the window. The rings of other LATRs unravel completely into strips of tape, which are then wound as tightly as possible around the outer diameter of the first ring. After this, the assembled single magnetic circuit is wrapped very tightly with insulating tape. Thus, a ring-magnetic core with a larger volume is obtained internal space than all the previous ones. This one can accommodate a wire of significant cross-section. The required number of turns is calculated based on the cross-sectional area of the assembled ring.
The disadvantages of this design include the complexity of manufacturing the magnetic core. Moreover, no matter how hard you try, you still won’t be able to manually wind the iron strips around each other as tightly as before. As a result, the magnetic circuit turns out to be flimsy. When working in welding mode, the iron in it vibrates strongly, producing a powerful hum.
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When designing, assembling or repairing something, you often have to connect parts. The types and methods of connections are different. For example, when connecting metal products, a threaded connection (screw or bolt with a nut), riveting, gluing, soldering and welding are used.
And if for the first three you only need mechanical tools, then soldering irons are needed for soldering, and for welding some craftsmen make homemade DC and AC welding machines. Many of these units have been operating without failures for decades.
Homemade AC devices
When assembling, repairing or designing household appliances or any equipment, it becomes necessary to weld several parts together. AC welding machines are expensive and not easy to buy. But it is perfectly acceptable to make them yourself. The circuits of such devices are very different.
One of original designs made on the basis of the LATR transformer (laboratory autotransformer). This device operates from a regular network using alternating current. Its electrical characteristics are very high due to the special design of the magnetic circuit.
It is made of transformer strip iron (rolled) and has the shape of a ring or torus, although a conventional AC welding machine is assembled from plates similar to the letter “W”. The characteristics of a toroidal product are 4.7 times higher, and losses are almost minimal compared to an W-shaped core.
But such transformer strip iron is now in short supply, so it is easier to get a ready-made 9-amp laboratory autotransformer (LATR) or a toroidal magnetic circuit from a burnt product. It needs to be rewound - remove the old or burnt secondary winding and wind a new one with a thicker wire. Using all this, you will assemble a 75-155 Amp AC unit in about 1-2 hours.
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Rewind LATR
To replace the windings proceed as follows:
- Remove the casing (if there is one).
- Reinforcement made of non-magnetic material (plastic, aluminum) is removed along with the mechanical part.
- Get rid of old or burnt windings:
- if the windings are not damaged, then the secondary is simply wound onto a special shuttle for use in other developments and designs. A shuttle measuring 4-5x10-20 cm can be cut from plywood;
- if the windings are burned out, then the wire is removed by any method: cut off, torn off.
- The core is electrically insulated from the future winding by wrapping the iron in two layers of varnished cloth or making overlays from special electrical cardboard.
- New windings are wound, isolating them from each other;
- Assembly is carried out.
Devices made on the basis of the LATR transformer are wound with only two windings.
If the transformer burns out completely, you have to wind both windings.
The primary is performed with a 1.2 mm wire of the PEV-2 type. The approximate length of this piece is 170 m. A shuttle is used for winding. The wire is wound completely around it.
And then, having secured the end, they begin to perform translational movements with their hand inside the toroid, wrapping the insulated core with wire. Winding is done turn to turn. After winding, the primary winding is covered with insulation (the same varnished fabric).
For more reliable insulation and efficient cooling of the device, you can use the air gap method between the windings. In this case, the primary winding does not need to be insulated from above - its own coating will suffice.
The method is:
- two rings are made of thick (3-5 mm) PCB with an external gauge 3-5 mm (on each side) larger than the diameter of the core with a wound “primary”;
- the edges are chamfered (they are rounded) to avoid damage to the insulation;
- the rings are secured at the top and bottom of the core with double-sided tape;
- the secondary winding is wound.
The secondary one - 45 turns - is performed with several wires twisted together, or a busbar, which must be in glassy or CB insulation. The cross section is calculated depending on the required welding current and is 5-7 A per 1 sq. mm. For a current of 170 A you will need a busbar or twist with a cross section of 35 mm or larger. The secondary winding (for cooling) is distributed over the toroid with a gap, trying to distribute it evenly.
If you have a working autotransformer or have purchased a new one, then the work comes down to only rewinding one (secondary) winding, since the primary is already wound with wire of the required cross-section and length.
It moves in the following sequence:
- First, unscrew the metal or plastic casing (if there is one);
- remove the slider with the graphite current collector;
- remove reinforcement from non-magnetic material (plastic, aluminum);
- identify (call the tester) and mark all network outputs;
- the remaining wires are wrapped with insulation or PVC tubes are put on them and laid on the side of the LATR perpendicular to the windings;
- then the secondary winding is mounted; the turns, diameter and brand of copper wires are similar to the option described above (completely burnt).
Welding machines, or rather their transformers, are recommended to be installed by two people. The first person pulls the wire and lays it down, trying not to spoil the insulation and maintain a distance between the turns. The second holds the end of the wire, preventing it from twisting.
If the insulation is broken and the ends of at least one turn touch, an interturn short circuit will occur, the transformer will overheat and the device will fail.
Welding machines with such a transformer operate at currents of 55-180 A.
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Wiring diagram
Any design that operates from the network has its own circuit. The welding machine described above also has it.
The rewound transformer is covered with an old casing (if it fits), a new one is prepared or dispensed with without a fence. It's not that dangerous. After all, the device has an output potential of no more than 50 V. And it is much easier to cool a transformer without a casing.
The terminals of the transformer windings are connected to your device as follows:
- Primary (I) - connected to 220 V with a 2-4 mm flexible copper wire (VRP or ShRPS). An automatic switch (Q1) is required - an automatic switch like those found in houses.
- Carefully insulated, but also flexible PRG wires of the appropriate cross-section are attached to the secondary (multi-ampere) one.
One end is attached to the workpiece and grounded (for electrical safety). On the other, a ballast resistor is mounted (to regulate the output current) and a homemade or standard electrode holder for the device.
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Current regulators
The regulator is a spiral-twisted 3-mm caliber wire made of constantan or nichrome wire approximately 5 m long. This is a kind of ballast connected in series to the electrical holder circuit.
The spiral is fixed separately on a sheet of asbestos cement. The welding current of the machine can be changed in three ways:
- Selection method. A crocodile clip is attached to the regulating end large size. The current is changed by moving the clamp in a spiral. If you strengthen the spiral only at the ends (or straighten), the adjustment will be smooth.
- Switching method. Take the switch. Its common terminal is connected to the control wire. The remaining terminals are connected to spiral turns. The current is controlled by discrete movement of the slider.
- Replacement method. The current is changed by selecting electrodes (thick and thin, long and short). Regulation occurs within small limits. This method is almost never used.
These machines change the welding current by adjusting the secondary winding. A large current is removed from it, so changing the current electronically is unprofitable. It is necessary to install powerful parts, huge radiators and appropriate cooling.
A homemade welding machine circuit is assembled on the basis of a nine-amp laboratory adjustable autotransformer. Its design has the ability to adjust the welding current. The presence of a diode bridge in the circuit of this welding machine allows welding with direct current.
The operating mode of the welding device is set by variable resistance R5. Thyristors VS1 and VS2 open only during their half-cycle alternately due to the phase shift on the radio components R5, C1 and C2.
Thanks to this, it is possible to change the input voltage on the primary winding in the range from 20 to 215 volts. As a result of the transformation on the secondary winding there will be undervoltage, allowing you to easily ignite the welding arc on contacts X1 and X2 when welding with alternating current and on contacts X3 and X4 when welding in direct current mode. The welding machine is connected to an alternating network using a standard plug. In the role of toggle switch SA1, you can use a paired 25A machine.
To begin with, carefully remove the protective casing and electrical contact from the autotransformer and unscrew the fastening. Next, good insulation is wound onto the existing 250 volt winding, onto which 70 turns of the secondary winding are wound with copper wire with a cross-sectional area of 20 mm 2.
If such a wire is not at hand, you can wind it from several wires with a smaller cross-section. The modernized autotransformer is placed in a homemade housing with ventilation holes. It is also necessary to fit the regulator circuit, packet, as well as contacts for welding with direct and alternating current.
If you don’t have an autotransformer, you can make one yourself by winding both windings on a transformer steel core.
At the output of the secondary winding, in accordance with the circuit of the welding device, a diode bridge consisting of powerful rectifier diodes is connected. Diodes must be installed on homemade radiators.
For this welder circuit, it is advisable to use a stranded copper wire in rubber insulation with a cross-section of at least 20 mm 2.
When designing or repairing appliances and household equipment, a problem often arises: how to weld certain parts. Buying a welding machine is not entirely easy, but making it yourself...
In this article you can get acquainted with a simple homemade welding machine made according to an original design.
Welding machine operates from a 220 V network and has high electrical characteristics. Thanks to the use of a new form of magnetic circuit, the weight of the device is only 9 kg with overall dimensions of 125 x 150 mm. This is achieved by using transformer strip iron rolled into a torus-shaped roll, instead of the traditional package of W-shaped plates. The electrical characteristics of a transformer on a brake magnetic circuit are approximately 5 times higher than those of a W-shaped transformer, and electrical losses are minimal.
To get rid of the search for scarce transformer iron, you can purchase a ready-made 9 A LATR or use a brake magnetic circuit from a burnt-out laboratory transformer. To do this, remove the fence, fittings and remove the burnt winding. The freed magnetic circuit must be insulated from future winding layers with electrical cardboard or two layers of varnished cloth.
The welding transformer has two independent windings. The primary one uses PEV-2 1.2 mm wire, 170 m long. For ease of work, you can use a shuttle (a 50 x 50 mm wooden strip with slots at the ends), on which the entire wire is pre-wound. A layer of insulation is placed between the windings. Secondary winding - copper wire in cotton or glass insulation - has 45 turns over the primary. Inside the wire is placed turn to turn, and on the outside with a small gap - for uniform placement and better cooling.
It is more convenient to do the work together: one carefully, without touching the adjacent turns, so as not to damage the insulation, stretches and lays the wire, and an assistant holds the free end, protecting it from twisting. A welding transformer made in this way will produce a current of 50 - 185 A.
If you purchased a 9 A Latr and upon inspection it turns out that its winding is intact, then the matter becomes much simpler. Using the finished winding as the primary, you can assemble a welding transformer in 1 hour, giving a current of 70 - 150 A. To do this, you need to remove the fence, current collection slider and mounting hardware. Then identify and mark the 220 V terminals, and the remaining ends, securely insulated, are temporarily pressed to the magnetic circuit so as not to damage them when working with the secondary winding. Installation of the latter is carried out in the same way as in the previous version, using copper wire of the same cross-section and length.
The assembled transformer is placed on an insulated platform in the same casing, having previously drilled holes in it for ventilation. The wires of the primary winding are connected to a 220 V network using a ShRPS or VRP cable. A disconnecting circuit breaker must be provided in the circuit.
The secondary winding leads are connected to flexible insulated wires PRG, the electrode holder is attached to one of them, and the part to be welded is attached to the other. The same wire is grounded for the safety of the welder.
Current regulation is provided for by connecting in series the wire circuit of the ballast electrode holder - nichrome or constantan wire with a diameter of 3 mm and a length of 5 m, coiled like a snake, which is attached to asbestos cement sheet. All connections of wires and ballast are made using M10 bolts. Using the selection method, moving the wire connection point along the snake, the required current is set. It is possible to regulate the current using electrodes of different diameters. Electrodes with a diameter of 1 - 3 mm are used for welding.
All necessary materials for a welding transformer can be purchased at a retail chain. And for a person familiar with electrical engineering, making such a device is not difficult.
When working, to avoid burns, it is necessary to use a fiber protective shield equipped with an E-1, E-2 light filter. A hat, overalls and mittens are also required. The welding machine should be protected from dampness and not allowed to overheat. Approximate operating mode with an electrode with a diameter of 3 mm: for a transformer with a current of 50 - 185 A - 10 electrodes, and with a current of 70 - 150 A - 3 electrodes, after which the device must be disconnected from the network for at least 5 minutes.
