If a person plans to perform living conditions small volumes of any simple welding work, he may well produce welding machine with your 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, high current intensity is required, and for welding thin metal products(no more than 2 mm) – smaller.

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 of a home-made installation should be 150–200 A, three-millimeter electrodes should be 80–140 A, two-millimeter electrodes should be 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 What those who are planning to independently manufacture a welding machine need to know 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 the core of a 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 from copper wire with high performance 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. With these strips you wrap copper cable, after which you 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, which 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 geometric parameters 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 insulating properties It is advisable to place 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 reached.

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.

No work with iron can be done without a welding machine. It allows you to cut and join metal parts any size and thickness. Good decision- do the welding yourself, because good models They are expensive, and cheap ones are of poor quality. To implement the idea self-made you need to get a welder special equipment, allowing you to hone the quality skills of a specialist in real conditions.

Types and characteristics of the tool

After everything necessary conditions preparatory stage successfully met, the opportunity opens up to make a model of the welding device with your own hands. Today there are many schematic diagrams that can be used to make a device. They follow one of the following approaches:

• Direct or alternating current.
• Pulse or inverter.
• Automatic or semi-automatic.

It is worth paying attention to the device, which belongs to the transformer type. An important characteristic of this device is its operation on alternating current, allowing it to be used in domestic conditions. AC machines are capable of ensuring the standard quality of seams welded joints. A unit of this type can easily find its use in everyday life. when servicing real estate located in the private sector.

In order to assemble such a device, you must have:

• About 20 meters of cable or large-section wire.
• A metal base of high magnetic permeability that will be used as the core of the transformer.

The optimal core configuration has a U-shaped core base. In theory, a core of any other configuration could easily be suitable, for example, a round shape taken from a stator that has become unusable for an electric motor. But in practice, winding a winding on such a base is much more difficult.

The cross-sectional area for a core belonging to a home-made household welding machine is 50 cm 2. This will be enough to use rods from 3 to 4 mm in diameter in the installation. Usage larger section will only lead to an increase in the mass of the structure, and the efficiency of the device will not become higher.

Manufacturing instructions

For the primary winding it is necessary to use copper wire with high performance heat resistance, since when performing welding work it will be exposed to high temperature. The wire used must be selected according to fiberglass or cotton insulation, intended for stationary use in high temperature zones.

For the winding of the transformer, it is not allowed to use wire with PVC insulation, which will immediately become unusable when heated. In some cases, the insulation for the transformer winding is made independently.

To perform this procedure, you need to take a piece of cotton fabric or fiberglass, cut it into strips about 2 cm wide, wrap them around the prepared wire and impregnate the bandage with any varnish that has electrical properties. Such insulation in terms of thermal characteristics is not inferior to any factory analogue.

The coils are wound according to a certain principle. First, half of the primary winding is wound, followed by half of the secondary. Then proceed to the second coil using the same technique. To improve the quality of the insulating coating, fragments of strips of cardboard, fiberglass or pressed paper are inserted between the layers of windings.

Equipment setup

Next you need to configure. It is performed by connecting the equipment to the network and taking voltage readings from the secondary winding. The voltage on it should be from 60 to 65 volts.

Precise adjustment of the parameters is carried out by reducing or increasing the length of the winding. To obtain a high-quality result, the voltage on the secondary winding should be adjusted to the specified parameters.

A VRP cable or a ShRPS wire, which will be used to connect to the network, is connected to the primary winding of the finished welding transformer. One of the terminals of the secondary winding is fed to the terminal to which ground will subsequently be connected, and the second is fed to the terminal connected to the cable. The last procedure is completed and the new welding machine is ready for use.

Production of small-sized units

An autotransformer from a Soviet-style TV is easily suitable for making a small welding machine. It can easily be used to produce a voltaic arc. In order for everything to work out correctly, graphite electrodes are connected between the terminals of the autotransformer. This simple design allows you to perform several simple work using welding, such as:

• Making or repairing thermocouples.
• Heating high-carbon steel products to maximum temperature.
• Hardening of tool steel.

A homemade welding machine, created on the basis of an autotransformer, has a significant drawback. It must be used with additional precautions. Without galvanic isolation from the electrical network, it is a rather dangerous device.

The optimal parameters of an autotransformer suitable for creating a welding machine are considered to be an output voltage ranging from 40 to 50 volts and low power from 200 to 300 watts. This device is capable of delivering from 10 to 12 amperes of operating current, which will be sufficient for welding wires, thermocouples and other elements.

As electrodes for a DIY mini welding machine, you can use leads from a simple pencil. The terminals found on various electrical appliances can serve as holders for improvised electrodes.

To carry out welding work, the holder is connected to one of the terminals of the secondary winding, and the part to be welded to the other. The handle for the holder is best made from a fiberglass washer or other heat-resistant material. It should be noted that the arc of such a device acts for a fairly short time, preventing the used autotransformer from overheating.

A welding machine cannot be called an essential home tool, such as a screwdriver or a hammer. However, there are situations when a welding machine is really necessary. In this material we will look at how to assemble a simple welding machine at home.

First of all, we suggest watching a video on how to make a welding machine.

So, we will need:
- water container;
- salt;
- water;
- two metal plates;
- wire with plug;
- two wires;
- welding electrode.

According to the author of the homemade product, the creation process takes only 15 minutes, so let's not waste time and move on to making a homemade welding machine. First of all, we need to take one metal plate and screw one of the two wires to it.

We repeat the process with the second plate and the second wire.

The next thing is to add two tablespoons of salt to the water and stir everything thoroughly.

We immerse two plates and wires wound on them into the resulting mixture.

For safety reasons, it is recommended to secure the metal plates with clothespins.

The plates actually allow you to adjust the welding current. How exactly does it work? The deeper we immerse the plates, the more current we get.

We must connect one wire coming from one of the plates to the phase, and the second wire to the welding electrode.

We also take neutral wire and connect it to the item that we need to cook.

A completely logical question arises - how can one determine where the phase is and where the zero is, if for some reason there are no special measuring devices at home. There is an old one the right way: You just need to touch the wire to the ground. The wire that will spark when it touches the ground is the phase wire.

Make welding inverter with your own hands, even without deep knowledge of electronics and electrical engineering, it is quite possible, the main thing is to strictly adhere to the diagram and try to understand well the principle on which such a device works. If you make an inverter whose technical characteristics and efficiency differ little from those of serial models, you can save a decent amount.

You should not think that a homemade machine will not give you the opportunity to effectively carry out welding work. Such a device, even assembled according to a simple scheme, will allow you to weld with electrodes with a diameter of 3–5 mm and an arc length of 10 mm.

Characteristics of a homemade inverter and materials for its assembly

Having assembled a welding inverter with your own hands in a fairly simple way electrical diagram, you will receive efficient device, having the following technical characteristics:

• voltage consumption – 220 V;
• the current supplied to the input of the device is 32 A;
• The current generated at the device output is 250 A.

During operation, the diodes of such a bridge become very hot, so they must be mounted on radiators, which can be used as cooling elements from old computers. To install a diode bridge, you need to use two radiators: the upper part of the bridge is attached to one radiator through a mica spacer, and the lower part is attached to the second through a layer of thermal paste.

The terminals of the diodes from which the bridge is formed must be directed in the same direction as the terminals of the transistors, with the help of which direct current will be converted into high-frequency alternating current. The wires connecting these terminals should be no longer than 15 cm. Between the power supply and the inverter unit, which is based on transistors, there is a sheet of metal attached to the body of the device by welding.

Power block

The basis of the power unit of the welding inverter is a transformer, due to which the voltage of the high-frequency current is reduced and its strength is increased. In order to make a transformer for such a block, it is necessary to select two Ш20x208 2000 nm cores. You can use newsprint to provide a gap between them.

The windings of such a transformer are made not of wire, but of copper strip 0.25 mm thick and 40 mm wide.

To ensure thermal insulation, each layer is wrapped with tape from cash register which demonstrates good wear resistance. The secondary winding of the transformer is formed from three layers of copper strips, which are insulated with each other using fluoroplastic tape. The characteristics of the transformer windings must correspond to the following parameters: 12 turns x 4 turns, 10 sq. mm x 30 sq. mm.

Many people try to make the windings of a step-down transformer from thick copper wire, but this is the wrong solution. Such a transformer operates on high-frequency currents, which are forced onto the surface of the conductor without heating it inner part. That is why the best option for forming windings is a conductor with a large surface area, that is, a wide copper strip.

Plain paper can also be used as a thermal insulation material, but it is less wear-resistant than cash register tape. This tape will darken due to elevated temperatures, but its wear resistance will not be affected by this.

The transformer of the power unit will become very hot during its operation, so to force it to cool, it is necessary to use a cooler, which can be a device previously used in the computer system unit.

Inverter unit

Even a simple welding inverter must perform its main function - convert the direct current generated by the rectifier of such a device into high-frequency alternating current. To solve this problem, power transistors are used that open and close at high frequencies.

Schematic diagram of the inverter unit (click to enlarge)

It is better to assemble the inverter unit of the device, which is responsible for converting direct current into high-frequency alternating current, based on not one powerful transistor, but several less powerful ones. This constructive solution will allow you to stabilize the frequency of the current, as well as minimize noise effects when performing welding work.

The electronic also contains capacitors connected in series. They are necessary to solve two main problems:

• minimizing resonant emissions of the transformer;
• reducing losses in the transistor unit that occur when it is turned off and due to the fact that the transistors open much faster than they close (at this moment current losses may occur, accompanied by heating of the switches of the transistor unit).

Cooling system

The power elements of the homemade welding inverter circuit become very hot during operation, which can lead to their failure. To prevent this from happening, in addition to the radiators on which the hottest units are mounted, it is necessary to use fans responsible for cooling.

If you have it in stock powerful fan, you can get by with it alone by directing the air flow from it to a step-down power transformer. If you use low-power fans from old computers, you will need about six of them. At the same time, three such fans should be installed next to the power transformer, directing the air flow from them to it.

To prevent overheating of a homemade welding inverter, you should also use a temperature sensor by installing it on the hottest radiator. Such a sensor, if the radiator reaches critical temperature will turn off the flow electric current at him.
For the inverter ventilation system to work effectively, its housing must have properly designed air intakes. The grilles of such intakes, through which air flows will flow into the device, should not be blocked by anything.

DIY inverter assembly

For a homemade inverter device, you need to choose a reliable housing or make it yourself using sheet metal thickness of at least 4 mm. As a base on which the welding inverter transformer will be mounted, you can use a getinax sheet with a thickness of at least 0.5 cm. The transformer itself is mounted on such a base using staples that you can make yourself from copper wire with a diameter of 3 mm.

To create electronic circuit boards for the device, you can use foil-coated PCB with a thickness of 0.5–1 mm. When installing magnetic cores that will heat up during operation, it is necessary to provide gaps between them necessary for free air circulation.

For automatic control you will need to purchase and install a PWM controller in it, which will be responsible for stabilizing the welding current and voltage. To make it convenient for you to work with your homemade device, you need to install controls in the front part of its body. Such organs include the toggle switch for turning on the device, the variable resistor knob, with which you adjust welding current, as well as cable clamps and signal LEDs.

Diagnostics of a homemade inverter and its preparation for operation

Doing it is half the battle. No less important task is its preparation for work, during which the correct functioning of all elements is checked, as well as their settings.

The first thing you need to do when checking a homemade welding inverter is to apply a voltage of 15 V to the PWM controller and one of the cooling fans. This will allow you to simultaneously check the functionality of the controller and avoid overheating during such a test.

After the capacitors of the device are charged, a relay is connected to the electrical supply, which is responsible for closing the resistor. If you apply voltage directly to the resistor, bypassing the relay, an explosion may occur. After the relay operates, which should happen within 2-10 seconds after voltage is applied to the PWM controller, you need to check whether the resistor has shorted.

When the relays of the electronic circuit operate, rectangular pulses should be generated on the PWM board and supplied to the optocouplers. This can be checked using an oscilloscope. The correct assembly of the diode bridge of the device also needs to be checked; for this, a voltage of 15 V is applied to it (the current should not exceed 100 mA).

The transformer phases may have been incorrectly connected when assembling the device, which can lead to incorrect operation of the inverter and the occurrence of strong noise. To prevent this from happening, the correct phase connection must be checked using a dual-beam oscilloscope. One beam of the device is connected to the primary winding, the second to the secondary. The phases of the pulses, if the windings are connected correctly, should be the same.

The correct manufacturing and connection of the transformer is checked using an oscilloscope and connecting electrical devices with different resistances to the diode bridge. Based on the noise of the transformer and the readings of the oscilloscope, they conclude that it is necessary to improve the electronic circuit of the homemade inverter apparatus.

To check how long you can continuously work on a homemade inverter, you need to start testing it from 10 seconds. If the device’s radiators do not heat up during operation for such a duration, you can increase the period to 20 seconds. If such a time period does not negatively affect the condition of the inverter, you can increase the operating time of the welding machine to 1 minute.

Maintenance of a homemade welding inverter

For the inverter device to serve long time, it must be properly maintained.

If your inverter stops working, you need to open its cover and blow out the insides with a vacuum cleaner. Those places where dust remains can be thoroughly cleaned with a brush and a dry cloth.

The first thing you need to do when diagnosing a welding inverter is to check the voltage supply to its input. If there is no voltage, you should check the functionality of the power supply. The problem in this situation may also be that the fuses of the welding machine have blown. Another weak link of the inverter is the temperature sensor, which, in the event of a breakdown, must not be repaired, but replaced.

When performing diagnostics, it is necessary to pay attention to the quality of connections of the electronic components of the device. You can identify poorly made connections visually or using a tester. If such connections are identified, they must be corrected to avoid future overheating and failure of the welding inverter.

Only if you pay due attention to the maintenance of the inverter device can you count on it to serve you for a long time and enable you to perform welding work as efficiently and efficiently as possible.

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1. What are we going to talk about?
2. What we won't talk about
3. Transformer
4. Let's try a permanent one
5. Microarc
6. Contact! There is contact!

DIY welding in in this case this means not the technology of 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 alternating current industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures up to about 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 resistance 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 home-made products, and refuse - “Give me a normal machine!” Plus, or rather minus, is that in order to make a more or less decent welding inverter, you need to have quite a lot of 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 abstruse ideas;
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(ВХ) – 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 to be 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? U2 (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. Induction is chosen close to the overheating limit, this allows by reducing cos? (a parameter equivalent to efficiency) at a current significantly different from sinusoidal, 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 the 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. We use design and design measures, as well as using simple additional devices(see below) we obtain on any iron BX, curve 2a, somewhat more rigid 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, holding the arc and welding current will not be difficult, without much experience (?U2.2 and Iw1), at high currents Iw2 we will get an acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

• According to the formula from paragraph 2 previous. list we find the overall power;
• We find the maximum possible welding current Iw = 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 full 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 layers of the winding, the average length of the turn and the footage of the 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 winding calculations are usually greater than 3 mm, and varnished winding wires with d>2.4 mm are rare in general sale. 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. An additional advantage is that by twisting several stranded wires to the required S, we get a flexible wire that 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

A thin-walled homemade frame will not withstand the pressure of turns of thick wire, 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 dry sand cushion, or already 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 high circulation reactive power, only and only oil and paper (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 made 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 significantly depends welded joint. 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, doesn’t do him any good, and the welding either lacks fusion or burns 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.

In conclusion

And finally, something that may seem like a joke: welding in a salt solution. In fact, this is not idle entertainment, but for some purposes it is quite useful. And you can make welding equipment for salt welding with your own hands on a table in 15 minutes, see video:

Video: DIY welding in 15 minutes (with saline solution)