If a person plans to perform small volumes of any simple tasks at home welding work, he can easily make a welding machine with his own hands, without spending money on purchasing a factory unit.

1

In order to make a welding unit from readily available materials and parts, it is necessary to clearly understand the key principles of its operation and only then begin assembly. First of all, you should decide on the current power of your homemade welding machine. To connect massive reinforcement, of course, a high current intensity is required, and for welding thin metal products (no more than 2 mm) - a lower one.

The current indicator is directly related to which electrodes are planned to be used. Welding of sheets and structures with a thickness of 3 to 5 mm is carried out with 3–4 mm rods, and with a thickness of less than 2 mm – with 1.5–3 mm rods. If you use four-millimeter electrodes, the current strength homemade installation should be 150–200 A, three-millimeter – 80–140 A, two-millimeter – 50–70 A. But for very thin parts (up to 1.5 mm), a current of 40 A is quite sufficient.

The formation of an arc for welding from mains voltage in any welding machine is achieved through the use of a transformer. This device includes in its design:

• windings (primary and secondary);
• magnetic circuit

It's easy to make a transformer yourself. The magnetic core, for example, is assembled from transformer steel plates or other material. The secondary winding is necessary directly for welding work, and the primary winding is connected to a 220-volt electrical network. Professional units necessarily have in their design some additional devices that improve and enhance the quality of the arc and allow you to smoothly adjust the current intensity.

Homemade welding machines, as a rule, are made without additional devices. The power of the transformer is selected based on the current strength. To obtain the calculated power, you need to multiply the current used for welding by 25. The resulting product, when multiplied by 0.015, gives us the required diameter of the magnetic core. And to calculate the required winding cross-section (primary), the power should be divided by two thousand and multiplied by 1.13.

Determining the cross-section of the secondary winding will have to “suffer” a little longer. Its value depends on the density of the welding current used. With a current strength of around 200 A, the density is 6A/square millimeter, from 110 to 150 A - 8, less than 100 A - 10. To set the required cross-section of the secondary winding you need:

• divide the welding current by its density;
• multiply the resulting value by 1.13.

The number of turns of wiring can be determined by dividing the cross-sectional area of ​​the magnetic circuit by 50. Another important point that those who plan to self-production welding machine, is that the welding process can be “soft” or “hard” depending on the voltage available at the output terminals (at their clamps) of the unit.

The specified voltage establishes the features of the external characteristics of the current for welding, which can be gently or steeply decreasing, as well as increasing. In self-assembled welders, experts advise using current sources that are described by a flat or steeply falling characteristic. They show minimal changes in current when the electric arc oscillates, which is optimal for welding at home.

2

Now that we know the main features of the welder, we can begin assembling a homemade welding machine. Now on the Internet there are many diagrams and instructions for performing such a task, which make it possible to create almost any equipment for welding - AC and DC, pulsed and inverter, automatic and semi-automatic.

We will not go into complex technical “wilds”, and will tell you how to make a welding machine of the simplest transformer type. It will operate on alternating current, providing an effective and quite decent welded joint in terms of seam quality. Such a unit will allow you to perform any household work, which require welding of metal and steel products. To make it you will need the following materials:

• a couple of tens of meters of thick (preferably copper) cable (wire);
• iron for core transformer device(iron must have a sufficiently high magnetic permeability).

It is most convenient to make the core a rod, in a traditional U-shape. In principle, it is also possible to use a core of a different configuration, for example, a round one from the stator of any burnt-out electric motor, but be prepared for the fact that it is much more difficult to wind windings onto a round structure. The recommended cross-sectional area of ​​the core for a standard household welding unit, made independently, is about 50 square centimeters.

This area is enough for the installation to use rods with a diameter of 3–4 millimeters.

There is no point in making a larger cross-section, since the unit will become much heavier, but you will not achieve a real technical effect. If you are not satisfied with the recommended cross-sectional area, you can calculate its value yourself using the diagram given in the first part of our article.

The primary winding must be made of high-performance copper wire thermal resistance(during welding, the winding is exposed to high temperatures). This wire, in addition, must have cotton or fiberglass insulation. As a last resort, it is allowed to use a wire in a rubber-fabric or ordinary rubber insulating sheath, but in no case in a polyvinyl chloride sheath.

By the way, you can make the insulation yourself by cutting two-centimeter wide strips of cotton or fiberglass. You wrap a copper cable with these strips, and then impregnate the wire with homemade insulation with any electrical varnish. Believe me, such insulation will not overheat when using 6-7 welding rods (when they are burned during the average duration of welding work).

The cross-sectional areas of the windings are calculated according to the principles that were outlined earlier. It seems that you will not have any problems with these calculations. Typically, the cross-sectional area of ​​the “secondary” wire is taken at the level of 25–30 square millimeters, the “primary” – 5–7 (values ​​for homemade units that will work with rods with a diameter of 3–4 millimeters).

It is also easy to determine the length of a piece of copper wire and the number of turns for both windings. And then they begin to wind the coils. Their frame is made according to the geometric parameters of the magnetic circuit. The dimensions are selected in such a way that the magnetic circuit fits onto the core, made of textolite or cardboard used in electrical engineering, without any difficulty.

The winding of the coils has a small peculiarity. The primary winding is wound in half, then half of the secondary is placed on it. After this, the second part of the coil is processed in a similar way. To improve the insulating properties, it is advisable to lay pieces of cardboard strips, fiberglass or thick paper between the layers.

After assembling a do-it-yourself welding installation, it must be adjusted. To do this, you need to plug it into the network and measure the voltage on the secondary winding. Its value should be 60–65 V. If the voltage is different, you will need to wind (or wind) part of the winding. Such procedures will have to be performed until the specified voltage value is achieved.

The primary winding of the assembled transformer is connected to an internal laying cable (IRP) or to a two-core hose wire (SHRPS), which will be connected to a 220 volt network. The secondary winding (its leads) is connected to insulated PRG wires, one of them is then in contact with the product being welded, and the welding rod holder is attached to the second. The homemade welding unit is ready!

3

In his practice, any radio amateur often needs to strongly heat or carefully weld one or another part. There is no point in using a conventional welding unit for these purposes, since even without it you can form a high-temperature flow quite simply and without expense.

If you have an old autotransformer lying around, which was previously used to regulate the supply voltage of Soviet lamp-based televisions, it is easy to adapt it to create a voltaic arc. To do this, you need to connect graphite electrodes between its terminals. Such a simple design will make it possible to perform simple welding work, for example, the following:

• repair or production of thermocouples: a welder made from an autotransformer allows you to repair thermocouples whose so-called “ball” breaks; there is simply no other equipment for such repair work;
• connecting the power buses to the filament element of a conventional magnetron;
• welding of any wires and cables;
• heating structures made of springs and similar parts to high temperatures;
• hardening of all kinds of devices made from (they are heated with an arc and then immersed in machine oil).

If you decide to make a welder based on an autotransformer, you need to handle it extremely carefully, since electrical network it has no galvanic isolation. This means that misuse homemade device may result in electric shock.

To perform all the above “minor” work, it is recommended to use an automatic transformer with a voltage (output) of 40–50 volts with low power (about 200–300 watts). Such a device is capable of delivering 10–12 amperes of operating current, which is quite enough for welding wires, thermocouples and other elements. The electrodes for the described mini-welding machine are ordinary pencil leads.

It is better if they are soft, however, medium and hard pencils are also suitable. Holders for such graphite rods can be made from old terminal blocks found on any electrical devices. The holder is connected to the winding (as you understand, secondary) of the autotransformer through one of the existing terminals, and the product that needs to be welded is also connected to it, but through a different terminal.

The handle of the electrode holder can be easily made from an ordinary fiberglass washer or from another heat-resistant element. Finally, let’s say that the arc on a welding machine from an autotransformer does not burn for very long. On the one hand, this is bad, on the other hand, it is very good, since the short duration of its operation eliminates the risk of overheating of the transformer device.

With this simple welding machine you can cut thin metals, weld copper wires, engrave on a metal surface. Other applications can be found without any problems. This mini welding machine can be powered with a voltage of 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 pulses, repeated 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 pulse transformer source or generator without load has powerful high-voltage pulses reaching a voltage of 30,000 V! Therefore, if you disassemble any Chinese pulse charger, 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 due to excess voltage, or worse, it will explode.
Therefore, attention! The voltage at the transformer output is dangerous to life!

Mini welding machine diagram

Required parts:

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

The transistor must have a heat sink installed. Although this is not on the diagram, it would be a good idea to place a filter capacitor in parallel with the source so that all interference from the operation of the blocking generator does not penetrate the source.

Transformer manufacturing

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

• The collector winding is 20 turns of 1 mm wire.
• Base winding - 5 turns with a 0.5-1 mm rein.
• High-voltage winding - 500 turns with a drive of 0.14-0.25 mm.

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

Let's put together a diagram. If everything is in order, everything should start without problems. Since the operating frequency of the generator exceeds the sound frequency, you will not hear a squeak during operation, so you should not touch the output of the transformer 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, indicating a voltage of 30 kV. The high frequency does not allow the burning arc to break, 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 and cutting.

Welding machine testing by cutting and welding

We cut the razor blade with an arc.

We fuse copper wires up to 1 mm thick.

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

If you liked this small welding machine, then you can make it larger in size and power. But be extremely careful.
Also, to increase power, you can assemble a generator using a push-pull circuit, and even using field-effect transistors, like here -. In this case, the power will be decent.
Also, do not look at the bright arc discharges with the naked eye; use special safety glasses.

Watch a video of making a welding machine using a blocking generator

A welding machine is used in construction, installation and repair work. Usually the design is purchased ready-made, but you can make it yourself. In this case, significant savings occur. Moreover, this process can captivate those who like to make something new.

Connections, electrodes and windings

In order to assemble a welding machine with your own hands, you need to decide on a diagram on the basis of which the work will be carried out. Even before starting the main work, it is worth considering how the unit will be powered. If the voltage is higher, then using the device may harm human health.

Typically, a single-phase 220 V network is used to power equipment. In this case, it is necessary to use an additional winding (special ballast), with the help of which the periodically changing electric current during the welding period.

Before assembling a welding inverter with your own hands, you need to purchase:

• Transformer magnetic circuit.
• Remote condenser devices.
• Welding mode switch.
• Several types of windings (primary, secondary, additional).
• Regulatory devices that help set the optimal welding mode.
• Special heat sensors.
• A device that notifies you with sounds about the optimal operating mode.

Why use concrete

Before you make an inverter welding machine with your own hands, you need to make a housing. It is made from specially prepared concrete, characterized by a high degree of plasticity. This material can quickly harden and become the desired shape.

The body is made from fine-grained sand and cement in certain proportions. You should take 75 percent sand, 20 percent cement. In addition to these components, you need to add equal amounts of PVA glue and glass wool. Sometimes the glue is replaced with a water-soluble latex material.

Novice craftsmen believe that it is quite easy to assemble the unit with their own hands, compared to creating its body. At consistent work The design comes together quite quickly.

The body should be at least 1 cm thick. The welding machine is cleaned and then dried, after which the body begins to be manufactured. After waiting for the concrete to harden, the external treatment of the unit is carried out using an organic monomer.

To cope with this task, experts recommend using styrene or methyl methacrylate. They help to perform heat treatment on the surface of the device. In this situation, temperatures above 70 degrees Celsius should be applied.

As a result of monomer polymerization, a waterproof layer is formed on the surface of the unit body. It is this that protects the surface of the structure from environmental influences.

Simple design

To assemble the welding machine, you can use faulty household appliances. For example, you can use a broken microwave oven. Along with it you should take electrical wiring, clamps, wooden parts and tips.

Taking all these components you can short term even with minimal knowledge in the field of technology, make the design of an apparatus for carrying out spot welding work.

The parts inside the unit are secured with self-tapping screws, washers or brackets of appropriate sizes. It is optimal to use a working transformer for a broken one microwave oven, from which equipment is made with your own hands.

Build process

Work begins by removing the secondary winding from the transformer. This operation requires care. It is carried out using an angle grinder.

Next, the plate core is removed from the surface of the secondary winding. After the operation on the transformer, you can find parts cut off on both sides. With their help, the work will be of better quality. Ideally, it is necessary to ensure that the insulating layer on the core is free of any defects.

Then the magnetic shunt is attached. During its normal functioning, the operation of a home-made welding machine is carried out. Then the transformer is rewound using a thick wire made of copper material. If the core is damaged, it must be repaired. If the defect is minimal, then the area is isolated.

At the next stage, it is necessary to place the transformer on a wooden block, securing the top and bottom of the workstation with brackets. If the electrodes are attached well, the unit will work better. If there are defects in the contacts, it will be difficult to weld the elements.

Fixation of the electrodes on the upper and lower parts of the bar is carried out with self-tapping screws. Then the winding wires are connected to them. It is necessary to secure the copper terminals correctly using pliers, which is usually very difficult for novice craftsmen. The structure is ready. Then you need to check whether anything can be welded using the unit, and it is important to follow safety regulations.

Usually, assembling a welding machine is not difficult even for those people who have minimal knowledge of technology. For this you can use step by step instructions with photos at all stages that exist large number on the Internet.

Photos of do-it-yourself welding machines

According to experts, making a welding machine with your own hands is not difficult.

However, to make it, you need to clearly understand why, for what work it will be used.

A homemade device is completed and assembled from available components and parts. A plasma mechanism can also be considered as an option for craftsmen.

Practice shows that when precise selection components, the device will serve for a long time and reliably.

It is important that electrical diagram was as simple as possible. Sometimes they even use a microwave transformer.

The device must operate from a household network AC voltage 220 V.

If you choose 380 V as the operating voltage, the circuit and design of the device will become noticeably more complicated.

Block diagram of the welding machine

For welding work, devices operating on alternating and direct current are used.

The circuit of any device includes a transformer (it is possible to use a transformer from a microwave), a rectifier, a choke, a holder, and an electrode. It is in this sequence that electric current flows through a closed circuit.

The circuit is completed when an electric arc occurs between the electrode and the metal workpieces to be connected.

To quality welded joint was high, it is necessary to ensure stable combustion of this arc.

And to set the required combustion mode, a current regulator is used.

DC machines are used for welding elements made of thin sheet metal. With this welding method, you can use any electrodes and electrode wire without ceramic coating.

The electrode holder is connected to the rectifier through a choke. This is done in order to smooth out voltage ripples.

The choke is a coil copper wires, which is wound on any core. The rectifier, in turn, is connected to the secondary winding of the transformer.

The transformer is connected to the household electrical network. The connection sequence is simple and clear.

AC voltage conversion is done using a step-down transformer.

According to Ohm's law, the voltage that is induced on the secondary winding of the transformer decreases, and the current increases from 4 amperes to 40 or more.

This is approximately the amount required for welding. In principle, this device can be called the simplest welding machine.

And use wires to attach the electrode holder to it. But it is impossible to use the holder for practical purposes, since the circuit does not contain other necessary elements.

And most importantly, it does not have a current regulator. As well as a rectifier and other elements.

The transformer is considered the main element of the welding machine. You can buy it or adapt one that is already in use.

Many craftsmen use a transformer from a microwave oven that has expired. Due to its dimensions and weight, a micropulse element always takes up a lot of space in the structure.

If we consider the welding unit as a whole, we can distinguish three main blocks that it includes:

• power unit;
• rectifier block;
• inverter block.

A homemade inverter device can be configured in such a way that it has minimal dimensions and weight.

Such devices, designed for use in the home, are sold in stores today.

The advantages of an inverter device over traditional units are obvious. First of all, it should be noted that the device is compact, easy to use, and reliable.

Only one component in the parameters of this device is of concern - its high cost.

The most general calculations confirm that making such a device with your own hands is easier and more profitable.

The main elements can almost always be found among electrical machines and devices that end up in storage rooms. Or in a landfill.

The simplest current regulator can be made from a piece of heating coil, which is used in household electric stoves. The choke is made from a piece of copper wire.

Radio amateurs have come up with the simplest pulse welding method. It is used to attach wires to a metal board.

No complicated devices - just a choke and a couple of wires. A current regulator is also not needed. Instead, a fuse-link is connected to the circuit.

One electrode is connected to the board through an inductor.

The second one is a crocodile clip. The plug with wires is plugged into a household outlet.

The clamp with the wire is sharply applied to the board in the place where it needs to be welded. A welding arc occurs and at this moment the fuses located in the electrical panel may blow out.

This does not happen because the fuse link burns out faster. And the wire remains securely welded to the board.

Product contents

The homemade one is assembled in order to perform small jobs around the household.

All elements, electronic devices, wires and metal structures must be assembled in a specific place. Where the product will be assembled.

The choke can be used from the fluorescent lamp fittings. You need to stock up more wires, preferably copper, of different sections.

If it was not possible to find a ready-made throttle, then you need to make it yourself.

To do this, you will need a steel magnetic core from an old starter and several meters of copper wires with a cross-section of 0.9 square.

power unit

The main element of the power supply in the inverter is the transformer.

It can be converted from a laboratory autotransformer or used to remake a transformer from a microwave oven that has already served its useful life.

It is very important not to damage the primary winding when removing the transformer from the microwave oven.

The secondary winding is removed and rebuilt. The number of turns and diameter of copper wires is calculated depending on the pre-selected power of the welding machine.

The spot welding method is well implemented by a device made on a transformer from a microwave oven.

The rectifier is used to convert AC voltage to DC voltage. The main elements of this device are diodes.

It is switched into certain circuits, most often bridge circuits. An alternating current is supplied to the input of such a circuit, and a direct current is removed from the output terminals.

Diodes are selected with such power to withstand the initially specified loads. To cool them, special radiators made of aluminum alloys are used.

When marking the installation board, it is advisable to provide space for a choke, which is designed to smooth out pulses. The rectifier is assembled on a separate board, made of getinax or textolite.

Inverter block

The inverter converts the direct current coming from the rectifier into alternating current, which has a high oscillation frequency.

The conversion is done using electronic circuits on thyristors or powerful transistors.

If a voltage of 220 volts with a frequency of 50 Hz is supplied to the input terminals of the transformer, then a direct current of up to 150 Amperes and a voltage of 40 volts is fixed at the output terminals of the inverter.

These current settings allow welding metal parts from various alloys.

The electronic regulator allows you to select the mode appropriate for a specific operation.

Practice shows that a homemade welding machine, in terms of its characteristics, is not inferior to factory products.

Some time ago, mini welding inverters appeared in the retail chain. To achieve this miniaturization manufacturing companies it took years.

While craftsmen have long been able to make a plasma welding machine made by themselves.

They were pushed to this step by local conditions - cramped conditions in the workshop and the significant weight of factory inverters. A plasma device is an excellent way out of this situation.

And the fact that instead of copper wires the secondary winding of the transformer is made of copper tin has also been known for a long time.

Assembly sequence of the welding machine

When placing elements on a metal or textolite base, you need to follow a certain order. The rectifier must be located next to the transformer.

The choke is on the same board as the rectifier. The current regulator should be located on the control panel. The body of the device can be made of sheet steel or aluminum.

Or adapt a chassis from an old oscilloscope or even a computer system unit. It is very important not to “sculpt” the elements as close to one another as possible.

It is necessary to make holes in the walls to install cooling fans and constant air flow.

The board with thyristors and other elements is placed as far as possible from the transformer, which gets very hot during operation. Exactly the same as the rectifier.

DIY welding in in this case This means not the technology for producing welding work, but homemade equipment for electric welding. Working skills are acquired through industrial practice. Of course, before going to the workshop, you need to master the theoretical course. But you can put it into practice only if you have something to work with. This is the first argument in favor of, when mastering welding on your own, first taking care of the availability of appropriate equipment.

Second, a purchased welding machine is expensive. Rent is also not cheap, because... the probability of its failure due to unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be simply long and difficult. All in all, It is better to start your first steps in metal welding by making a welding installation with your own hands. And then - let it sit in a barn or garage until the opportunity arises. It’s never too late to spend money on branded welding if things work out.

What are we going to talk about?

This article discusses how to make equipment at home for:

• Electric arc welding with alternating current of industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures up to approximately a corrugated fence on a frame made of corrugated pipe or a welded garage.
• Micro-arc welding of twisted wires is very simple and useful when laying or repairing electrical wiring.
• Spot pulse contact welding– can be very useful when assembling products from thin steel sheets.

What we won't talk about

First, let's skip gas welding. The equipment for it costs pennies compared to consumables, you can’t make gas cylinders at home, and a homemade gas generator is a serious risk to life, plus carbide is expensive now, where it is still on sale.

The second is inverter electric arc welding. Indeed, a semi-automatic inverter welding allows a novice amateur to weld quite important structures. It is light and compact and can be carried by hand. But purchasing at retail the components of an inverter that allows for consistent high-quality welding will cost more than a finished machine. And an experienced welder will try to work with simplified homemade products, and refuse - “Give me a normal machine!” Plus, or rather minus - in order to make a more or less decent welding inverter, you need to have fairly solid experience and knowledge in electrical engineering and electronics.

The third is argon-arc welding. With whose light hand the claim that it is a hybrid of gas and arc has gone for a walk in RuNet, unknown. In fact, this is a type of arc welding: the inert gas argon does not participate in the welding process, but creates a cocoon around the working area, isolating it from air. As a result welding seam It turns out chemically pure, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be cooked under argon, incl. heterogeneous. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and weld with a non-consumable electrode.

It is quite possible to make equipment for argon-arc welding at home, but gas is very expensive. Cook as usual economic activity aluminum, stainless steel or bronze are unlikely to be needed. And if you really need it, it’s easier to rent argon welding - compared to how much (in money) gas will go back into the atmosphere, it’s pennies.

Transformer

The basis of all “our” types of welding is welding transformer. The procedure for its calculation and design features differ significantly from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like transformers continuous action, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electrical transformers for arc welding is the main reason for the failures of amateur designers. Therefore, let’s take a walk through welding transformers in the following order:

1. a little theory - on the fingers, without formulas and brilliance;
2. features of magnetic cores of welding transformers with recommendations for choosing from random ones;
3. testing of available used equipment;
4. calculation of a transformer for a welding machine;
5. preparation of components and winding of windings;
6. trial assembly and fine-tuning;
7. commissioning.

Theory

An electrical transformer can be likened to a water supply storage tank. This is a pretty deep analogy: a transformer operates due to its energy reserve magnetic field in its magnetic circuit (core), which can be many times greater than that instantly transmitted from the power supply network to the consumer. And the formal description of losses due to eddy currents in steel is similar to that for water losses due to infiltration. Electricity losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in the liquid.

Note: the difference is in losses due to evaporation and, accordingly, magnetic field scattering. The latter in the transformer are partially reversible, but smooth out the peaks of energy consumption in the secondary circuit.

An important factor in our case is the external current-voltage characteristic (VVC) of the transformer, or simply its external characteristic(VX) – dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, the VX is rigid (curve 1 in the figure); they are like a shallow, vast pool. If it is properly insulated and covered with a roof, then water losses are minimal and the pressure is quite stable, no matter how consumers turn the taps. But if there is gurgling in the drain - sushi oars, the water is drained. In relation to transformers, the power source must keep the output voltage as stable as possible to a certain threshold less than the maximum instantaneous power consumption, be economical, small and light. To do this:

• The steel grade for the core is selected with a more rectangular hysteresis loop.
• Design measures (core configuration, calculation method, configuration and arrangement of windings) reduce dissipation losses, losses in steel and copper in every possible way.
• The magnetic field induction in the core is taken less than the maximum permissible current form for transmission, because its distortion reduces efficiency.

Note: transformer steel with “angular” hysteresis is often called magnetically hard. This is not true. Magnetically hard materials retain strong residual magnetization, they are made permanent magnets. And any transformer iron is soft magnetic.

You cannot cook from a transformer with a hard VX: the seam is torn, burned, and the metal splatters. The arc is inelastic: I moved the electrode slightly wrong and it goes out. Therefore, the welding transformer is made to look like a regular water tank. Its CV is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage gradually drops. The normal scattering curve is approximated by a straight line incident at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly extract several times more power from the same hardware, or resp. reduce the weight, size and cost of the transformer. In this case, the induction in the core can reach a saturation value, and for a short time even exceed it: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: the thermal time constant of welding transformers is 20-40 minutes. If you then let it cool down and there is no unacceptable overheating, you can continue working. The relative drop in the secondary voltage ΔU2 (corresponding to the range of the arrows in the figure) of normal dissipation gradually increases with increasing range of fluctuations of the welding current Iw, which makes it easy to hold the arc during any type of work. The following properties are provided:

1. The steel of the magnetic circuit is taken with hysteresis, more “oval”.
2. Reversible scattering losses are normalized. By analogy: the pressure has dropped - consumers will not pour out much and quickly. And the water utility operator will have time to turn on the pumping.
3. The induction is chosen close to the overheating limit; this allows, by reducing cosφ (a parameter equivalent to efficiency) at a current significantly different from the sinusoidal one, to take more power from the same steel.

Note: reversible scattering loss means that part of the power lines penetrates the secondary through the air, bypassing the magnetic circuit. The name is not entirely apt, just like “useful scattering”, because “reversible” losses for the efficiency of a transformer are no more useful than irreversible ones, but they soften the I/O.

As you can see, the conditions are completely different. So, should you definitely look for iron from a welder? Optional, for currents up to 200 A and peak power up to 7 kVA, but this is enough for the farm. Using design and design measures, as well as with the help of simple additional devices (see below), we will obtain on any hardware a VX curve 2a that is somewhat stiffer than normal. The efficiency of welding energy consumption is unlikely to exceed 60%, but for occasional work this is not a big deal. But on delicate work and low currents, maintaining the arc and welding current will not be difficult, without having great experience(ΔU2.2 and Iсв1), at high currents Iсв2 we will obtain acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

There are also welding transformers with a steeply falling VX, curve 3. This is more like a booster pump: either the output flow is at nominal level, regardless of the feed height, or there is none at all. They are even more compact and lightweight, but in order to withstand the welding mode at a steeply falling VX, it is necessary to respond to fluctuations ΔU2.1 of the order of a volt within a time of about 1 ms. Electronics can do this, which is why transformers with a “steep” VX are often used in semi-automatic welding machines. If you cook from such a transformer manually, then the seam will be sluggish, undercooked, the arc will again be inelastic, and when you try to light it again, the electrode will stick every now and then.

Magnetic cores

The types of magnetic cores suitable for the manufacture of welding transformers are shown in Fig. Their names begin with the letter combination respectively. standard size. L means tape. For a welding transformer L or without L, there is no significant difference. If the prefix contains M (SHLM, PLM, ShM, PM) - ignore without discussion. This is iron of reduced height, unsuitable for a welder despite all its other outstanding advantages.

After the letters of the nominal value there are numbers indicating a, b and h in Fig. For example, for W20x40x90, the cross-sectional dimensions of the core (central rod) are 20x40 mm (a*b), and the window height h is 90 mm. Core cross-sectional area Sc = a*b; window area Sok = c*h is needed for accurate calculation of transformers. We will not use it: for an accurate calculation, we need to know the dependence of losses in steel and copper on the value of induction in a core of a given standard size, and for them, the grade of steel. Where will we get it if we run it on random hardware? We will calculate using a simplified method (see below), and then finalize it during testing. It will take more work, but we will get welding that you can actually work on.

Note: if the iron is rusty on the surface, then nothing, the properties of the transformer will not suffer from this. But if there are spots of tarnish on it, this is a defect. Once upon a time, this transformer overheated very much and the magnetic properties of its iron were irreversibly deteriorated.

Another important parameter magnetic circuit - its mass, weight. Since the specific density of steel is constant, it determines the volume of the core, and, accordingly, the power that can be taken from it. Magnetic cores with the following weight are suitable for the manufacture of welding transformers:

• O, OL – from 10 kg.
• P, PL – from 12 kg.
• W, SHL – from 16 kg.

Why Sh and ShL are needed heavier is clear: they have an “extra” side rod with “shoulders”. OL may be lighter because it does not have corners that require excess iron, and the bends of the magnetic force lines are smoother and for some other reasons, which will be discussed later. section.

Oh OL

The cost of toroid transformers is high due to the complexity of their winding. Therefore, the use of toroidal cores is limited. A torus suitable for welding can, firstly, be removed from the LATR - a laboratory autotransformer. Laboratory, which means it should not be afraid of overloads, and the hardware of LATRs provides a VH close to normal. But…

LATR is a very useful thing, first of all. If the core is still alive, it is better to restore the LATR. Suddenly you don’t need it, you can sell it, and the proceeds will be enough for welding suitable for your needs. Therefore, “bare” LATR cores are difficult to find.

Secondly, LATRs with a power of up to 500 VA are weak for welding. From LATR-500 iron you can achieve welding with a 2.5 electrode in the mode: cook for 5 minutes - it cools down for 20 minutes, and we heat up. As in Arkady Raikin’s satire: mortar bar, brick yok. Brick bar, mortar yok. LATRs 750 and 1000 are very rare and useful.

Another torus suitable for all properties is the stator of an electric motor; Welding from it will turn out to be good enough for an exhibition. But it is no easier to find than LATR iron, and it is much more difficult to wind on it. In general, a welding transformer from an electric motor stator is separate topic, there are so many complexities and nuances there. First of all, with a thick wire wound around the donut. Having no winding experience toroidal transformers, the probability of ruining an expensive wire and not getting welded is close to 100%. Therefore, alas, we will have to wait a little longer with the cooking apparatus on a triode transformer.

Sh, ShL

Armor cores are structurally designed for minimal dissipation, and it is almost impossible to standardize it. Welding on a regular Sh or ShL will turn out to be too tough. In addition, the cooling conditions for the windings on Ш and ШЛ are the worst. The only armored cores suitable for a welding transformer are those of increased height with spaced biscuits windings (see below), on the left in Fig. The windings are separated by dielectric non-magnetic heat-resistant and mechanically strong gaskets (see below) with a thickness of 1/6-1/8 of the core height.

For welding, the core Ш is welded (assembled from plates) necessarily across the roof, i.e. yoke-plate pairs are alternately oriented back and forth relative to each other. The method of normalizing dissipation by a non-magnetic gap is unsuitable for a welding transformer, because the losses are irreversible.

If you come across a laminated Sh without a yoke, but with a cut in the plates between the core and the lintel (in the center), you are in luck. The plates of the signal transformers are laminated, and the steel on them, to reduce signal distortion, is used to initially give normal VX. But the likelihood of such luck is very low: signal transformers with kilowatt power are a rare curiosity.

Note: do not try to assemble a high Ш or ШЛ from a pair of ordinary ones, as on the right in Fig. A continuous straight gap, albeit a very thin one, means irreversible scattering and a steeply falling CV. Here, dissipation losses are almost similar to water losses due to evaporation.

PL, PLM

Rod cores are most suitable for welding. Of these, those laminated in pairs of identical L-shaped plates, see Fig., their irreversible scattering is the smallest. Secondly, the P and PL windings are wound in exactly the same halves, with half turns for each. The slightest magnetic or current asymmetry - the transformer hums, heats up, but there is no current. The third thing that may not seem obvious to those who have not forgotten the school gimlet rule is that the windings are wound onto the rods in one direction. Does something seem wrong? Does the magnetic flux in the core have to be closed? And you twist the gimlets according to the current, and not according to the turns. The directions of the currents in the half-windings are opposite, and magnetic fluxes are shown there. You can also check if the wiring protection is reliable: apply the network to 1 and 2’, and close 2 and 1’. If the machine does not immediately knock out, the transformer will howl and shake. However, who knows what's going on with your wiring. Better not.

Note: You can also find recommendations - to wind the windings of the welding P or PL on different rods. Like, VH is softening up. That’s how it is, but for this you need a special core, with rods of different sections (the secondary is on the smaller one) and recesses that release power lines into the air in in the right direction, see fig. right. Without this, we will get a noisy, shaking and gluttonous, but not cooking transformer.

If there is a transformer

A 6.3 A circuit breaker and an AC ammeter will also help determine the suitability of an old welder lying around God knows where and God knows how. You need either a non-contact induction ammeter (current clamp) or a 3 A pointer electromagnetic ammeter. A multimeter with alternating current limits will not lie, because the shape of the current in the circuit will be far from sinusoidal. Also, a long-neck liquid household thermometer, or, better yet, a digital multimeter with the ability to measure temperature and a probe for this. The step-by-step procedure for testing and preparing for further operation of an old welding transformer is as follows:

Calculation of a welding transformer

In RuNet you can find different methods for calculating welding transformers. Despite the apparent inconsistency, most of them are correct, but with full knowledge of the properties of steel and/or for a specific range of standard values ​​of magnetic cores. The proposed methodology developed in Soviet times, when instead of choice there was a shortage of everything. For a transformer calculated using it, the VX drops a little steeply, somewhere between curves 2 and 3 in Fig. at the beginning. This is suitable for cutting, but for thinner work the transformer is supplemented with external devices (see below) that stretch the VX along the current axis to curve 2a.

The basis of calculation is usual: the arc burns stably under a voltage Ud of 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the rated welding current. Accordingly, the minimum open-circuit voltage Uхх of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. Nothing more: it is unacceptable according to technical regulations, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly transition from short-circuit mode (say, when short-circuited by drops of metal) to working mode is maintained without additional measures. True, such a transformer is prone to overheating, but since it is our own and in front of our eyes, and not in the far corner of a workshop or site, we will consider this acceptable. So:

• According to the formula from paragraph 2 previous. list we find the overall power;
• We find the maximum possible welding current Isv = Pg/Ud. 200 A is guaranteed if 3.6-4.8 kW can be removed from the iron. True, in the first case the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
• We calculate the operating current of the primary at the maximum permissible network voltage for welding I1рmax = 1.1Pg(VA)/235 V. In fact, the norm for the network is 185-245 V, but for a homemade welder at the limit this is too much. We take 195-235 V;
• Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
• We assume the current density of the primary J1 = 5 A/sq. mm and, using I1рmax, we find the diameter of its copper wire d = (4S/3.1415)^0.5. Its total diameter with self-insulation is D = 0.25 + d, and if the wire is ready - tabular. To operate in the “brick bar, mortar yoke” mode, you can take J1 = 6-7 A/sq. mm, but only if the required wire is not available and is not expected;
• We find the number of turns per volt of the primary: w = k2/Sс, where k2 = 50 for Sh and P, k2 = 40 for PL, ShL and k2 = 35 for O, OL;
• We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy loss of the winding due to leakage and in copper, which is formally expressed by the somewhat abstract parameter of the winding’s own voltage drop;
• We set the laying coefficient Kу = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of winding layers, average length coil and meter of wire
• We calculate the secondary similarly at J1 = 6 A/sq. mm, k3 = 1.05 and Ku = 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.

Winding and finishing

The diameters of the wires in the calculation of windings are usually greater than 3 mm, and varnished winding wires with d>2.4 mm are rarely widely sold. In addition, the welder windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSH, PELSHO, PB, PBD. They are even more difficult to find, and they are very expensive. The meterage of the wire for the welder is such that it is possible to insulate cheaper bare wires yourself. Additional benefit– having twisted several stranded wires to the required S, we get a flexible wire, which is much easier to wind. Anyone who has tried to manually lay a tire of at least 10 square meters on a frame will appreciate it.

Isolation

Let's say there is a 2.5 sq.m. wire available. mm in PVC insulation, and for the secondary you need 20 m by 25 squares. We prepare 10 coils or coils of 25 m each. We unwind about 1 m of wire from each and remove the standard insulation, it is thick and not heat-resistant. We twist the exposed wires with a pair of pliers into an even, tight braid, and wrap it in order of increasing insulation cost:

1. Using masking tape with an overlap of 75-80% turns, i.e. in 4-5 layers.
2. Calico braid with an overlap of 2/3-3/4 turns, i.e. 3-4 layers.
3. Cotton electrical tape with an overlap of 50-67%, in 2-3 layers.

Note: the wire for the secondary winding is prepared and wound after winding and testing the primary, see below.

Winding

Thin-walled homemade frame will not withstand the pressure of thick wire turns, vibrations and jerks during operation. Therefore, the windings of welding transformers are made of frameless biscuits, and they are secured to the core with wedges made of textolite, fiberglass or, in extreme cases, bakelite plywood impregnated with liquid varnish (see above). The instructions for winding the windings of a welding transformer are as follows:

• Cooking wooden boss the height of the winding and its dimensions in diameter are 3-4 mm larger than a and b of the magnetic circuit;
• We nail or screw temporary plywood cheeks to it;
• We wrap the temporary frame in 3-4 layers of thin polyethylene film, covering the cheeks and wrapping them on the outside so that the wire does not stick to the wood;
• We wind the pre-insulated winding;
• Along the winding, we impregnate it twice with liquid varnish until it drips through;
• Once the impregnation has dried, carefully remove the cheeks, squeeze out the boss and peel off the film;
• We tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.

Finishing and finishing

We mix the core into a biscuit and tighten it with bolts, as expected. Winding tests are carried out in exactly the same way as tests of a questionable finished transformer, see above. It is better to use LATR; Iхх at an input voltage of 235 V should not exceed 0.45 A per 1 kVA of the overall power of the transformer. If it’s more, the primary is wound up. Winding wire connections are made with bolts (!), insulated with heat-shrinkable tube (HERE) in 2 layers or with cotton electrical tape in 4-5 layers.

Based on the test results, the number of turns of the secondary is adjusted. For example, the calculation gave 210 turns, but in reality Ixx fit into the norm at 216. Then we multiply the calculated turns of the secondary sections by 216/210 = 1.03 approx. Do not neglect decimal places, the quality of the transformer largely depends on them!

After finishing, we disassemble the core; We wrap the biscuit tightly with the same masking tape, calico or “rag” tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now saturate it with liquid varnish again; when it dries - twice undiluted. This galette is ready, you can make a secondary one. When both are on the core, we test the transformer again now at Ixx (suddenly it curled somewhere), fix the biscuits and impregnate the entire transformer with normal varnish. Phew, the most dreary part of the work is over.

Pull VX

But he’s still too cool for us, remember? Needs to be softened. The simplest method - a resistor in the secondary circuit - does not suit us. Everything is very simple: at a resistance of only 0.1 Ohm at a current of 200, 4 kW of heat will be dissipated. If we have a welder with a capacity of 10 kVA or more, and we need to weld thin metal, we need a resistor. Whatever current is set by the regulator, its emissions when the arc is ignited are inevitable. Without active ballast, they will burn the seam in places, and the resistor will extinguish them. But for us, weaklings, it will be of no use.

The reactive ballast (inductor, choke) will not take away excess power: it will absorb current surges, and then smoothly release them to the arc, this will stretch the VX as it should. But then you need a throttle with dispersion adjustment. And for it, the core is almost the same as that of a transformer, and the mechanics are quite complex, see fig.

We will go the other way: we will use active-reactive ballast, colloquially called gut by old welders, see fig. right. Material – steel wire rod 6 mm. The diameter of the turns is 15-20 cm. How many of them are shown in Fig. Apparently, for power up to 7 kVA this gut is correct. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is attached to it with a clothespin clamp. By selecting the connection point, it is possible, coupled with switching to secondary taps, to fine-tune the operating mode of the arc.

Note: An active-reactive choke can become red-hot during operation, so it requires a fireproof, heat-resistant, dielectric, non-magnetic lining. In theory, a special ceramic cradle. It is acceptable to replace it with a dry sand cushion, or formally with a violation, but not grossly, the welding gut is laid on bricks.

What about the rest?

This means, first of all, an electrode holder and a connecting device for the return hose (clamp, clothespin). Since our transformer is at its limit, we need to buy them ready-made, but those like those in Fig. right, no need. For a 400-600 A welding machine, the quality of contact in the holder is hardly noticeable, and it will also withstand simply winding up the return hose. And our homemade one, working with effort, can go haywire, seemingly for some unknown reason.

Next, the body of the device. It must be made of plywood; preferably bakelite impregnated, as described above. The bottom is 16 mm thick, the panel with the terminal block is 12 mm thick, and the walls and cover are 6 mm thick, so that they don’t come off during transportation. Why not sheet steel? It is ferromagnetic and in the stray field of a transformer can disrupt its operation, because we get everything we can out of him.

As for the terminal blocks, the terminals themselves are made from M10 bolts. The base is the same textolite or fiberglass. Getinax, bakelite and carbolite are not suitable; pretty soon they will crumble, crack and delaminate.

Let's try a permanent one

Welding with direct current has a number of advantages, but the input voltage of any welding transformer becomes more severe at constant current. And ours, designed for the minimum possible power reserve, will become unacceptably stiff. The choke-intestine will no longer help here, even if it worked on direct current. In addition, it is necessary to protect expensive 200 A rectifier diodes from current and voltage surges. We need a reciprocal-absorbing infra-low frequency filter, FINCH. Although it looks reflective, you need to take into account the strong magnetic coupling between the halves of the coil.

The circuit of such a filter, known for many years, is shown in Fig. But immediately after its implementation by amateurs, it became clear that the operating voltage of capacitor C is low: voltage surges during arc ignition can reach 6-7 values ​​of its Uхх, i.e. 450-500 V. Further, capacitors are needed that can withstand the circulation of high reactive power, only and only oil-paper ones (MBGCH, MBGO, KBG-MN). The following gives an idea of ​​the weight and dimensions of single “cans” of these types (by the way, not cheap ones). Fig., and a battery will need 100-200 of them.

With a coil magnetic circuit it is simpler, although not entirely. 2 submarines are suitable for it power transformer TS-270 from old tube “coffin” TVs (data is in reference books and in RuNet), or similar ones, or SHL with similar or larger a, b, c and h. From 2 submarines, an SL is assembled with a gap, see figure, of 15-20 mm. It is fixed with textolite or plywood spacers. Winding - insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. Wind it into 2 wires. The end of one is connected to the beginning of the other, this will be the middle point.

The filter is adjusted in an arc at the minimum and maximum values ​​of Uхх. If the arc is sluggish at minimum, the electrode sticks, the gap is reduced. If the metal burns at maximum, increase it or, which will be more effective, cut off part of the side rods symmetrically. To prevent the core from crumbling, it is impregnated with liquid and then normal varnish. Finding the optimum inductance is quite difficult, but then welding works flawlessly on alternating current.

Microarc

The purpose of microarc welding is discussed at the beginning. The “equipment” for it is extremely simple: a step-down transformer 220/6.3 V 3-5 A. In tube times, radio amateurs connected to the filament winding of a standard power transformer. One electrode – the twisting of the wires itself (copper-aluminum, copper-steel is possible); the other is a graphite rod like a 2M pencil lead.

Nowadays, for micro-arc welding, they use more computer power supplies, or, for pulsed micro-arc welding, capacitor banks, see the video below. On direct current, the quality of work, of course, improves.

Video: homemade machine for welding twists

Video: DIY welding machine from capacitors

Contact! There is contact!

Resistance welding in industry is mainly used in spot, seam and butt welding. At home, primarily in terms of energy consumption, pulsed point is feasible. It is suitable for welding and welding thin, from 0.1 to 3-4 mm, steel sheet parts. Arc welding will burn through a thin wall, and if the part is the size of a coin or less, then the softest arc will burn it entirely.

The principle of operation of resistance spot welding is illustrated in the figure: copper electrodes forcefully compress the parts, a current pulse in the steel-to-steel ohmic resistance zone heats the metal until electrodiffusion occurs; metal does not melt. The current needed for this is approx. 1000 A per 1 mm of thickness of the parts being welded. Yes, a current of 800 A will grab sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, say, a galvanized corrugated fence, then the first strong gust of wind will remind you: “Man, the current was rather weak!”

However, resistance spot welding is much more economical than arc welding: the no-load voltage of the welding transformer for it is 2 V. It consists of 2-contact steel-copper potential differences and the ohmic resistance of the penetration zone. The transformer for resistance welding is calculated in the same way as for arc welding, but the current density in the secondary winding is 30-50 or more A/sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, is well cooled, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

There are many descriptions on the RuNet of homemade pulse-spot welders from unusable microwave ovens. They are, in general, correct, but repetition, as written in “1001 Nights,” is of no use. And old microwaves don’t lie in heaps in trash heaps. Therefore, we will deal with designs that are less known, but, by the way, more practical.

In Fig. – device of the simplest apparatus for pulsed spot welding. They can weld sheets up to 0.5 mm; it is perfect for small crafts, and magnetic cores of this and larger sizes are relatively affordable. Its advantage, in addition to its simplicity, is the clamping of the running rod of the welding pliers with a load. To work with a contact welding pulser, a third hand would not hurt, and if one has to forcefully squeeze the pliers, then it is generally inconvenient. Disadvantages – increased risk of accidents and injuries. If you accidentally give a pulse when the electrodes are brought together without the parts being welded, then the plasma will shoot out from the tongs, metal splashes will fly, the wiring protection will be knocked out, and the electrodes will fuse tightly.

The secondary winding is made of a 16x2 copper busbar. It can be made from strips of thin sheet copper (it will be flexible) or made from a piece of flattened coolant supply tube household air conditioner. The bus is isolated manually as described above.

Here in Fig. – drawings of a pulse spot welding machine are more powerful, for welding sheets up to 3 mm, and more reliable. Thanks to a fairly powerful return spring (from the armored mesh of the bed), accidental convergence of the pliers is excluded, and the eccentric clamp provides strong, stable compression of the pliers, on which the quality of the welded joint significantly depends. If something happens, the clamp can be instantly released with one blow on the eccentric lever. The disadvantage is the insulating pincer units, there are too many of them and they are complex. Another one is aluminum pincer rods. Firstly, they are not as strong as steel ones, and secondly, they are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.

About electrodes

In amateur conditions, it is more advisable to insulate the electrodes at the installation site, as shown in Fig. right. There is no conveyor at home; you can always let the device cool down so that the insulating bushings do not overheat. This design will allow you to make rods from durable and cheap steel corrugated pipe, and also lengthen the wires (up to 2.5 m is permissible) and use a contact welding gun or external pliers, see fig. below.

In Fig. On the right, another feature of electrodes for resistance spot welding is visible: a spherical contact surface (heel). Flat heels are more durable, so electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 times the thickness of the adjacent material being welded, otherwise the weld spot will be burned either in the center (wide heel) or along the edges (narrow heel), and corrosion will occur from the welded joint even on stainless steel.

The last point about electrodes is their material and size. Red copper burns out quickly, so commercial electrodes for resistance welding are made of copper with a chromium additive. These should be used; at current copper prices it is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. According to heat transfer conditions, the length of the electrode is at least 3 of its diameters from the heel to the root (the beginning of the shank).

How to give impetus

In the simplest homemade pulse-contact welding machines, the current pulse is given manually: they simply turn on the welding transformer. This, of course, does not benefit him, and welding is either insufficient or burnt out. However, automating the supply and normalization of welding pulses is not so difficult.

A diagram of a simple but reliable welding pulse generator, proven by long practice, is shown in Fig. Auxiliary transformer T1 is a regular 25-40 W power transformer. The voltage of winding II is indicated by the backlight. You can replace it with 2 LEDs connected back-to-back with a quenching resistor (usual, 0.5 W) 120-150 Ohm, then the voltage II will be 6 V.

Voltage III - 12-15 V. 24 is possible, then capacitor C1 (regular electrolytic) is needed for a voltage of 40 V. Diodes V1-V4 and V5-V8 - any rectifier bridges for 1 and from 12 A, respectively. Thyristor V9 - 12 or more A 400 V. Optothyristors from computer power supplies or TO-12.5, TO-25 are suitable. Resistor R1 is a wire-wound resistor; it is used to regulate the pulse duration. Transformer T2 – welding.