Welding machine from laboratory autotransformer latr2. Self-made welding machine-transformer from latra Welding transformer from latra

From a compact and at the same time quite reliable, cheap and easy-to-manufacture "welder", not a single artisan, homely owner will refuse. Especially if he finds out that this device is based on an easily upgradeable 9 amp (familiar to almost everyone from school physics lessons) laboratory autotransformer LATR2 and a homemade thyristor mini-regulator with a rectifier bridge. They allow you not only to safely connect to a household lighting AC network with a voltage of 220V, but also to change the Ucv on the electrode, and therefore, to choose the required welding current value.

The operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which, triggered during its half-cycle, opens the corresponding thyristor for a certain period of time. As a result, adjustable 20-215 V appear on the primary winding of the welding T1. Transforming in the secondary winding, the required -Usv allow you to easily ignite the arc for welding on alternating (terminals X2, X3) or rectified (X4, X5) current.

A welding transformer based on the widespread LATR2 (a), its connection to the circuit diagram of a home-made adjustable device for welding on alternating or direct current (b) and a voltage diagram explaining the operation of the transistor regulator of the electric arc combustion mode.

Resistors R2 and R3 bypass the control circuits of thyristors VS1 and VS2. Capacitors C1, C2 reduce to an acceptable level of radio interference accompanying an arc discharge. A neon lamp with a current-limiting resistor R1 is used in the role of the HL1 indicator light, signaling that the device is switched on to the household power grid.

To connect the "welder" to the apartment wiring, a conventional plug X1 is used. But it is better to use a more powerful electrical connector, which is commonly called "Euro plug-Euro socket". And as a switch SB1, a VP25 "bag" is suitable, designed for a current of 25 A and allowing you to open both wires at once.

As practice shows, it makes no sense to install any kind of fuses (anti-overload machines) on the welding machine. Here you have to deal with such currents, when exceeded, the protection at the input of the network into the apartment will necessarily work.

For the manufacture of the secondary winding from the base LATR2 remove the casing, the current collector slider and the fastening fittings. Then, on the existing 250 V winding (127 and 220 V taps remain unclaimed), reliable insulation (for example, made of varnished cloth) is applied, on top of which a secondary (step-down) winding is placed.

And this is 70 turns of an insulated copper or aluminum bus with a diameter of 25 mm2. It is acceptable to make the secondary winding from several parallel wires with the same overall cross-section.

Winding is more convenient for two people. While one, trying not to damage the insulation of adjacent turns, carefully pulls and lays the wire, the other holds the free end of the future winding, protecting it from twisting.

The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which a circuit board made of 10-mm getinax or fiberglass with a SB1 packet switch, a thyristor voltage regulator (with a resistor R6), an HL1 light indicator for turning on the device into the network and output terminals for AC welding (X2, X3) or constant (X4, X5) current.

In the absence of a basic LATR2, it can be replaced with a home-made "welder" with a magnetic core made of transformer steel (core section 45-50 cm2). Its primary winding should contain 250 turns of PEV2 wire with a diameter of 1.5 mm. The secondary one is no different from that used in the modernized LATR2.

At the output of the low-voltage winding, a rectifier unit with VD3-VD10 power diodes for direct current welding is installed. In addition to these valves, more powerful analogs are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).

Power diodes and thyristors are installed on radiators, heat sinks, the area of \u200b\u200beach of which is at least 25 cm2. The axis of the adjusting resistor R6 is brought out from the casing. A scale with divisions corresponding to specific values \u200b\u200bof DC and AC voltage is placed under the handle. And next to it is a table of the dependence of the welding current on the voltage on the secondary winding of the transformer and on the diameter of the welding electrode (0.8-1.5 mm).

Of course, homemade electrodes made of carbon steel "wire rod" with a diameter of 0.5-1.2 mm are also acceptable. Workpieces with a length of 250-350 mm are covered with liquid glass - a mixture of silicate glue and crushed chalk, leaving unprotected 40-mm ends necessary for connecting to a welding machine. The coating is thoroughly dried, otherwise it will start to "shoot" during welding.

Reverse polarity is used when it is necessary to reduce heat generation, for example when welding thin metal sheets. Almost all the energy released by the electric arc is spent on the formation of a weld, and therefore the penetration depth is 40-50 percent greater than with a current of the same magnitude, but with straight polarity.

The welding voltage has little effect on the penetration depth. But the width of the seam depends on Usv: with increasing voltage, it increases.

Hence, an important conclusion for those involved in, say, welding when repairing a car body made of thin sheet steel: the best results will be obtained by direct current welding of reverse polarity with a minimum voltage (but sufficient for stable arc burning).

The arc must be kept as short as possible, the electrode is then consumed evenly, and the penetration depth of the metal being welded is maximum. The seam itself turns out to be clean and durable, practically free of slag inclusions. And you can protect yourself from rare splashes of the melt, which are difficult to remove after the product has cooled down, by rubbing the near-weld surface with chalk (the drops will roll off without adhering to the metal).

Excitation of the arc is carried out (after applying the corresponding -Usv to the electrode and "mass") in two ways. The essence of the first is in a light touch of the electrode to the parts to be welded, followed by its removal by 2-4 mm to the side. The second method resembles striking a match over a box: sliding the electrode over the surface to be welded, it is immediately taken away a short distance.

In any case, you need to catch the moment of the arc and only then, smoothly moving the electrode over the seam formed immediately, maintain its calm combustion.

Depending on the type and thickness of the metal to be welded, one or another electrode is chosen. If, for example, there is a standard assortment for a St3 sheet with a thickness of 1 mm, electrodes with a diameter of 0.8-1 mm are suitable (this is basically the design in question). For welding on 2-mm rolled steel, it is desirable to have a more powerful “welder” and a thicker electrode (2-3 mm).

For welding jewelry made of gold, silver, cupronickel, it is better to use a refractory electrode (for example, tungsten). It is possible to weld metals less resistant to oxidation using carbon dioxide protection.

In any case, work can be performed both with a vertically positioned electrode and tilted forward or backward. But sophisticated professionals say: when welding with an angle forward (meaning an acute angle between the electrode and the finished seam), a more complete penetration and a smaller width of the seam itself are provided. Welding with a backward angle is recommended only for overlapping joints, especially when you have to deal with profile rolled products (angle, I-beam and channel).

For direct connection with the "mass", a powerful crocodile clip is used, and with an electrode - a holder resembling a three-pronged fork. You can also use a car "cigarette lighter".

Personal safety must also be taken care of. When electric arc welding, try to protect yourself from sparks, and even more so from splashes of molten metal. It is recommended to wear loose-fitting canvas clothing, protective gloves and a mask that protects the eyes from the harsh radiation of an electric arc (sunglasses are not suitable here).

Of course, we must not forget about the "Safety regulations when working on electrical equipment in networks with a voltage of up to 1 kV". Electricity does not forgive carelessness!

M. VEVIOROVSKY, Moscow region Model constructor 2000 №1.

To make a laboratory autotransformer (LATRa) with their own hands, many are pushed by an excess of low-quality regulators on the electrical market. An industrial-type specimen can also be used, however, such specimens are too large and expensive. It is because of this that their use at home is difficult.

What is electronic LATR?

Autotransformers are needed to smoothly change the voltage current frequency 50-60 Hz during various electrical works. They are also often used when it is required to reduce or increase the alternating voltage for household or construction electrical equipment.

Transformers are electrical equipment, which is equipped with several inductively connected windings. It is used to convert electrical energy at the voltage or current level.

By the way, electronic LATR began to be widely used 50 years ago. Previously, the device was equipped with a collector contact. It was located on the secondary winding. So it turned out to smoothly adjust the output voltage.

When connected various laboratory devices, there was a variant of prompt voltage change. For example, if desired, it was possible to change the degree of heating of the soldering iron, adjust the speed of the electric motor, the brightness of the lighting and so on.

Currently, LATR has various modifications. In general, it is a transformer that converts alternating voltage from one magnitude to another. Such a device serves as a voltage stabilizer. Its main difference is the ability to adjust the voltage at the output of the equipment.

There are different types of autotransformers:

Single phase;
Three-phase.

The last type consists of three single-phase LATRs installed in a single structure. However, few people want to become its owner. Both three-phase and single-phase autotransformers are equipped with voltmeter and adjusting scale.

Scope of LATR

The autotransformer is used in various fields of activity, among them:

Metallurgical production;
Communal services;
Chemical and Oil Industry;
Manufacturing of equipment.

In addition, it is needed for the following work: the manufacture of household appliances, the study of electrical equipment in laboratories, adjustment and testing of equipment, the creation of television receivers.

In addition, LATR often used in educational institutions for conducting experiments in chemistry and physics lessons. It can even be found in the devices of some voltage stabilizers. Also used as additional equipment for recorders and machine tools. In almost all laboratory studies, it is LATR that is used in the form of a transformer, since it has a simple design and is easy to operate.

An autotransformer, in contrast to a stabilizer, which is used only in unstable networks and generates a voltage of 220V at the output with a different error of 2-5%, produces an exact set voltage.

According to climatic parameters, the use of these devices is allowed at an altitude of 2000 meters, but the load current has to be reduced by 2.5% for every 500 m rise.

The main disadvantages and advantages of an autotransformer

The main advantage of LATR is higher efficiency, because only some of the power is transformed. It is especially important if the input and output voltages are slightly different.

Their disadvantage is that there is no electrical insulation between the windings. Although in industrial power grids, the neutral wire has a grounding, therefore, this factor will not play a special role, in addition, less copper and steel are used for the windings for the cores, as a result, less weight and dimensions. As a result, you can save a lot.

The first option is a voltage changing device

If you are a novice electrician, then it is better to try first to make a simple LATR model, which will be regulated by a voltage device - from 0-220 volts. According to this scheme, the autotransformer has power - from 25-500 W.

To increase the power of the regulator to 1.5 kW, you need to put the thyristors VD 1 and 2 on the radiators. They are connected in parallel with the load R 1. These thyristors pass current in opposite directions. When the device is connected to the network, they are closed, and the capacitors C 1 and 2 begin to charge from the resistor R 5. They also, if necessary, change the voltage value during the load. In addition, this variable resistor, together with the capacitors, forms a phase-shifting circuit.

This technical solution makes it possible use two half-periods at once alternating current. As a result, full power is applied to the load, not half.

The only drawback of the circuit is that the shape of the alternating voltage during the load, due to the specificity of the thyristors, is not sinusoidal. All this leads to network interference. To fix the problem in the circuit, it is enough to build filters in series with the load. They can be taken out of a broken TV.

The second option is a voltage regulator with a transformer

A device that does not cause interference in the network and gives a sinusoidal voltage is more difficult to assemble than the previous one. LATR, the scheme of which has biopolar VT 1, in principle, you can also do it yourself. Moreover, the transistor serves as a regulating element in the device. The power in it depends on the load. It works like a rheostat. This model allows you to change the operating voltage not only with reactive loads, but also active ones.

However, the presented autotransformer circuit is also not ideal. Its disadvantage is that a functioning regulating transistor generates a lot of heat. To eliminate the disadvantage, you will need a powerful heat sink, the area of \u200b\u200bwhich is at least 250 cm ².

In this case, transformer T 1 is used. It must have a secondary voltage of about 6-10 V and power about 12-15 W... The diode bridge VD 6 rectifies the current, which subsequently passes to the transistor VT 1 in any half-period through VD 5 and VD 2. The base current of the transistor is regulated by a variable resistor R 1, thereby changing the characteristics of the load current.

Voltmeter PV 1 controls the size of the voltage at the output of the autotransformer. It is used with the calculation of voltage from 250-300 V. If there is a need to increase the load, then it is worth replacing the VD 5-VD 2 diodes and the VD 1 transistor with more powerful ones. Naturally, this will be followed by an expansion of the radiator area.

As you can see, to assemble LATR with your own hands, perhaps you just need to have a little knowledge in this area and purchase all the necessary materials.

I am sure: from a compact and at the same time quite reliable, cheap and easy-to-manufacture "welder" not a single artisan, homely owner will refuse. Especially if he finds out that this device is based on a 9-ampere laboratory autotransformer LATR2, which is easily modernized (familiar to almost everyone from school physics lessons) and a home-made thyristor mini-regulator with a rectifier bridge. They make it possible not only to safely connect to a 220 V AC household lighting network, but also to change u on the electrode, which means, to select the required welding current value.

The operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which is triggered during its half period. opens the corresponding thyristor for a certain period of time. As a result, the primary winding of the welding T1 turns out to be adjustable 20-215 V. Transforming in the secondary winding, the required -u makes it easy to ignite the arc for welding on alternating (X2, X3) or rectified (X4, X5) current.

Resistors R2 and R3 shunt the control circuits of thyristors VS1 and VS2. Capacitors C1. C2 is reduced to an acceptable level of radio interference accompanying an arc discharge. In the role of the HL1 indicator light, signaling that the device is switched on to the household power grid, a new lamp with a current-limiting resistor R1 is used.

To connect the "welder" to the apartment wiring, a conventional plug X1 is used. But it is better to use a more powerful electrical connector, which is commonly called “Euro plug-Euro socket”. And as a switch SB1, a VP25 "bag" is suitable, designed for a current of 25 A and allowing you to open both wires at once.

As practice shows, it makes no sense to install any kind of fuses (overload automatic devices) on the welding machine. Here you have to deal with such currents, when exceeded, the protection at the input of the network into the apartment will necessarily work.

For the manufacture of the secondary winding from the base LATR2 remove the casing, the current slider and the fastening fittings. Then, on the existing 250 V winding (127 and 220 V taps remain unclaimed), reliable insulation (for example, made of varnished cloth) is applied, on top of which a secondary (step-down) winding is placed. And this is 70 turns of an insulated copper or aluminum bus with a diameter of 25 mm2. It is acceptable to perform the secondary winding from several parallel wires with the same overall cross-section.

Winding is more convenient for two people. While one, trying not to damage the insulation of adjacent turns, carefully pulls and lay the wire, the other holds the free end of the future winding, protecting it from twisting.

The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which a circuit board made of 10 mm getinax or fiberglass with a packet switch SB1, a thyristor voltage regulator (with a resistor R6), an HL1 light indicator for switching on the device to the network and output terminals for AC welding (X2, X3) or constant (X4, X5) current.

In the absence of a basic LATR2, it can be replaced with a home-made "welder" with a magnetic core made of transformer steel (core section 45-50 cm2). Its primary winding should contain 250 turns of PEV2 wire with a diameter of 1.5 mm. Secondary is no different from that used in the modernized LATR2.

At the output of the low-voltage winding, a rectifier unit with power diodes VD3 - VD10 is installed for direct current welding. In addition to these valves, more powerful analogs are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).

A welding transformer based on the widespread LATR2 (a), its connection to the circuit diagram of a home-made adjustable welding machine for alternating or direct current (b) and a voltage diagram (c), explaining the operation of the resistor regulator of the electric arc combustion mode.

Although for welding you can use both alternating (terminals X2, X3) and constant (X4, X5) current, the second option, according to welders' reviews, is preferable to the first. Moreover, polarity plays an important role. In particular, when the "plus" is applied to the "ground" (welded object) and, accordingly, the electrode is connected to the terminal with the "minus" sign, the so-called forward polarity occurs. It is characterized by the release of more heat than with reverse polarity, when the electrode is connected to the positive terminal of the rectifier, and the "mass" - to the negative. Reverse polarity is used when it is necessary to reduce heat generation, for example when welding thin metal sheets. Almost all the energy released by the electric arc is spent on the formation of a weld, and therefore the penetration depth is 40-50 percent greater than with a current of the same magnitude, but with straight polarity.

And a few more very significant features. An increase in the arc current at a constant welding speed leads to an increase in the penetration depth. Moreover, if the work is carried out on alternating current, then the last of the named parameters becomes 15-20 percent less than when using direct current of reverse polarity. The welding voltage has little effect on the penetration depth. But the width of the seam depends on uw: with increasing voltage, it increases.

Excitation of the arc is carried out (after applying the corresponding Ucv to the electrode and "mass") in two ways. The essence of the first is in a light touch of the electrode to the parts to be welded, followed by its removal by 2-4 mm to the side. The second method resembles striking a match over a box: sliding the electrode over the surface to be welded, it is immediately taken away a short distance. In any case, you need to catch the moment of the arc and only then, smoothly moving the electrode over the seam formed immediately, maintain its quiet combustion.

An important thing is the welding cable. For the device under consideration, a copper stranded (total cross-section of about 20 mm2) in rubber insulation is the best fit. The required amount is two one and a half meter sections, each of which should be equipped with a carefully crimped and soldered terminal lug for connection to the "welder". For direct connection with the "mass", a powerful crocodile clip is used, and with an electrode - a holder resembling a three-pronged fork. You can also use a car cigarette lighter.

1.1. General information.

Depending on the type of current used for welding, a distinction is made between DC and AC welding machines. Welding machines using low direct currents are used when welding thin sheet metal, in particular, roofing and automotive steel. The welding arc in this case is more stable and at the same time welding can occur both on direct and on reverse polarity of the applied constant voltage.

Direct current can be welded with electrode wire without coating and with electrodes, which are designed for welding metals with direct or alternating current. To induce arc burning at low currents, it is desirable to have an increased open-circuit voltage U xx up to 70 ... 75 V on the welding winding. For AC rectification, as a rule, bridge rectifiers on powerful diodes with cooling radiators are used (Fig. 1).

Fig. 1 Schematic diagram of a bridge rectifier of a welding machine, indicating the polarity when welding thin sheet metal

To smooth out the voltage ripples, one of the CA terminals is connected to the electrode holder through a T-shaped filter, consisting of a choke L1 and a capacitor C1. The choke L1 is a coil of 50 ... 70 turns of a copper bus with a branch from the middle with a section of S \u003d 50 mm 2 wound on a core, for example, from a step-down transformer OSO-12, or more powerful. The larger the cross section of the iron of the smoothing choke, the less likely it is that its magnetic system will saturate. When the magnetic system enters saturation at high currents (for example, when cutting), the inductance of the inductor decreases abruptly and, accordingly, the current will not be smoothed. In this case, the arc will burn unstably. Capacitor C1 is a battery of capacitors such as MBM, MBG or the like with a capacity of 350-400 μF for a voltage of at least 200 V

Characteristics of powerful diodes and their imported counterparts are possible. Or follow the link to download a guide to diodes from the series "To help radio amateurs No. 110"

For rectification and smooth regulation of the welding current, circuits are used on powerful controlled thyristors, which allow you to change the voltage from 0.1 xx to 0.9U xx. In addition to welding, these regulators can be used to charge batteries, power electric heating elements and other purposes.

In AC welding machines, electrodes with a diameter of more than 2 mm are used, which allows welding products with a thickness of more than 1.5 mm. In the process of welding, the current reaches tens of amperes and the arc burns quite steadily. In such welding machines, special electrodes are used, which are intended only for welding with alternating current.

For normal operation of the welding machine, a number of conditions must be met. The output voltage must be sufficient to reliably ignite the arc. For an amateur welding machine U xx \u003d 60 ... 65V. For the safety of work, a higher open-circuit output voltage is not recommended; for industrial welding machines, for comparison, U xx can be 70..75 V.

Welding stress value I sv should ensure stable burning of the arc, depending on the diameter of the electrode. The magnitude of the welding voltage Uw can be 18 ... 24 V.

The rated welding current must be:

I sv \u003d KK 1 * d e where

I sv - the value of the welding current, A;

K 1 \u003d 30 ... 40 - coefficient depending on the type and size of the electrode d e, mm.

The short-circuit current should not exceed the rated welding current by more than 30 ... 35%.

It is noticed that stable arc burning is possible if the welding machine has a falling external characteristic, which determines the relationship between the current strength and the voltage in the welding circuit. (fig. 2)

Fig. 2 Falling external characteristic of the welding machine:

At home, as practice shows, it is quite difficult to assemble a universal welding machine for currents from 15 ... 20 to 150 ... 180 A. In this regard, when designing a welding machine, one should not strive to completely overlap the range of welding currents. It is advisable at the first stage to assemble a welding machine for working with electrodes with a diameter of 2 ... 4 mm, and at the second stage, if it is necessary to work at low welding currents, to supplement it with a separate rectifier device with smooth regulation of the welding current.

Analysis of the designs of amateur welding machines at home allows us to formulate a number of requirements that must be met in their manufacture:

Small size and weight
Powered by 220 V
The duration of operation should be at least 5 ... 7 electrodes d e \u003d 3 ... 4 mm

The weight and dimensions of the apparatus directly depend on the power of the apparatus and can be reduced by reducing its power. The operating time of the welding machine depends on the core material and the heat resistance of the insulation of the winding wires. To increase the welding time, it is necessary to use steel with a high magnetic permeability for the core.

1. 2. Selecting the type of core.

For the manufacture of welding machines, mainly rod-type magnetic cores are used, since they are more technological in design. The core of the welding machine can be drawn from plates of electrical steel of any configuration with a thickness of 0.35 ... 0.55 mm and pulled together with studs isolated from the core (Fig. 3).

Fig. 3 Rod type magnetic circuit:

When selecting a core, it is necessary to take into account the dimensions of the "window" to fit the windings of the welding machine, and the area of \u200b\u200bthe transverse core (yoke) S \u003d a * b, cm 2.

As practice shows, one should not choose the minimum values \u200b\u200bof S \u003d 25..35 cm 2, since the welding machine will not have the required power reserve and it will be difficult to obtain high-quality welding. And hence, as a consequence, the possibility of overheating the device after a short time. To avoid this, the cross-section of the core of the welding machine must be S \u003d 45..55 cm 2. Although the welding machine will be somewhat heavier, it will work reliably!

It should be noted that amateur welding machines on toroidal cores have electrical characteristics 4 ... 5 times higher than those of a rod, and hence small electrical losses. It is more difficult to make a welding machine using a toroidal type core than with a rod-type core. This is mainly due to the placement of the windings on the torus and the complexity of the winding itself. However, with the right approach, they give good results. The cores are made from tape transformer iron rolled into a torus-shaped roll.

Figure: 4 Toroidal magnetic circuit:

To increase the inner diameter of the torus ("window"), a part of the steel tape is unwound from the inside and wound onto the outside of the core (Fig. 4). After rewinding the torus, the effective cross-section of the magnetic circuit will decrease, so you will have to partially wind the torus with iron from another autotransformer until the cross-section S is equal to at least 55 cm 2.

The electromagnetic parameters of such iron are often unknown, so they can be determined experimentally with sufficient accuracy.

1. 3. Choice of wire windings.

For the primary (network) windings of the welding machine, it is better to use a special heat-resistant copper winding wire in cotton or fiberglass insulation. Wires in rubber or rubber-fabric insulation also have satisfactory heat resistance. It is not recommended to use wires in polyvinyl chloride (PVC) insulation for operation at elevated temperatures due to its possible melting, leakage from the windings and short-circuiting of turns. Therefore, PVC insulation from the wires must either be removed and the wires must be wrapped along the entire length with cotton insulating tape, or not removed at all, but wrapped over the insulation.

When selecting the cross-section of the winding wires, taking into account the periodic operation of the welding machine, a current density of 5 A / mm2 is allowed. The power of the secondary winding can be calculated using the formula P 2 \u003d I sv * U sv... If welding is carried out with an electrode de \u003d 4 mm, at a current of 130 ... 160 A, then the power of the secondary winding will be: Р 2 \u003d 160 * 24 \u003d 3.5 ... 4 kW, and the power of the primary winding, taking into account losses, will be about 5 ... 5.5 kW... Based on this, the maximum current in the primary winding can reach 25 A... Therefore, the cross-sectional area of \u200b\u200bthe primary winding wire S 1 must be at least 5..6 mm 2.

In practice, the cross-sectional area of \u200b\u200bthe wire is desirable to take a little more, 6 ... 7 mm 2. For winding, a rectangular bus or a copper winding wire with a diameter of 2.6 ... 3 mm is taken, excluding insulation. The cross-sectional area S of the winding wire in mm2 is calculated by the formula: S \u003d (3.14 * D 2) / 4 or S \u003d 3.14 * R 2; D is the diameter of bare copper wire, measured in mm. In the absence of a wire of the required diameter, winding can be carried out in two wires of a suitable section. When using an aluminum wire, its cross-section must be increased by 1.6..1.7 times.

The number of turns of the primary winding W1 is determined from the formula:

W 1 \u003d (k 2 * S) / U 1where

k 2 - constant coefficient;

S- cross-sectional area of \u200b\u200bthe yoke in cm 2

You can simplify the calculation by applying the special program Welding calculator for the calculation.

When W1 \u003d 240 turns, taps are made from 165, 190 and 215 turns, i.e. every 25 turns. A larger number of network winding taps, as practice shows, is impractical.

This is due to the fact that due to a decrease in the number of turns of the primary winding, both the power of the welding machine and U xx increase, which leads to an increase in the arc burning voltage and a deterioration in the quality of welding. By changing only the number of turns of the primary winding, it is not possible to overlap the range of welding currents without deteriorating the quality of welding. In this case, it is necessary to provide for switching the turns of the secondary (welding) winding W 2.

The secondary winding W 2 must contain 65 ... 70 turns of insulated copper bus with a cross section of at least 25 mm2 (preferably with a cross section of 35 mm2). Flexible stranded wire such as welding wire and three-phase power stranded cable are also suitable for winding the secondary winding. The main thing is that the cross-section of the power winding is not less than the required one, and the insulation of the wire is heat-resistant and reliable. With insufficient wire cross-section, winding in two or even three wires is possible. When using an aluminum wire, its cross section must be increased by 1.6 ... 1.7 times. The leads of the welding winding are usually led through copper lugs for terminal bolts with a diameter of 8 ... 10 mm (Fig. 5).

1.4. Features of winding windings.

There are the following rules for winding the windings of the welding machine:

Winding should be done on an insulated yoke and always in one direction (for example clockwise).
Each layer of the winding is insulated with a layer of cotton insulation (fiberglass, electric cardboard, tracing paper), preferably impregnated with bakelite varnish.
The terminals of the windings are tinned, marked, secured with cotton tape, and a cotton cambric is additionally put on the terminals of the network winding.
If the insulation of the wire is of poor quality, winding can be done in two wires, one of which is a cotton cord or a cotton thread for fishing. After winding one layer, the winding with cotton thread is fixed with glue (or varnish) and only after it has dried is the next row wound.

The mains winding on a bar-type magnetic circuit can be positioned in two main ways. The first method allows you to get a more "hard" welding mode. In this case, the mains winding consists of two identical windings W1, W2 located on different sides of the core, connected in series and having the same wire cross-section. To adjust the output current, taps are made on each of the windings, which are closed in pairs ( Figure: 6 a, b)

Figure: 6. Ways of winding CA windings on a rod-type core:

The second way of winding the primary (network) winding is winding a wire on one of the sides of the core ( fig. 6 c, d). In this case, the welding machine has a steeply dipping characteristic, it cooks "softly", the arc length has less effect on the value of the welding current, and, consequently, on the quality of welding.

After winding the primary winding of the welding machine, it is necessary to check for the presence of short-circuited turns and the correctness of the selected number of turns. The welding transformer is connected to the network through a fuse (4 ... 6 A) and if there is an alternating current ammeter. If the fuse burns out or gets very hot, this is a clear sign of a short-circuited loop. In this case, the primary winding must be rewound, paying particular attention to the quality of the insulation.

If the welding machine hums strongly, and the current consumption exceeds 2 ... 3 A, then this means that the number of turns of the primary winding is underestimated and it is necessary to wind up a certain number of turns. A working welding machine should consume no more than 1..1.5 A of current at idle, do not get warm or hum too much.

The secondary winding of the welding machine is always wound on both sides of the core. According to the first method of winding, the secondary winding consists of two identical halves, connected to increase the stability of the arc counter-parallel (Fig. 6 b). In this case, the cross-section of the wire can be taken slightly less, that is, 15..20 mm 2. When winding the secondary winding according to the second method, first, 60 ... 65% of the total number of its turns are wound on the side of the core free of windings.

This winding serves mainly to ignite the arc, and during welding, due to a sharp increase in the dissipation of the magnetic flux, the voltage across it drops by 80 ... 90%. The remaining number of turns of the secondary winding in the form of an additional welding winding W 2 is wound over the primary. Being power, it maintains the welding voltage, and therefore the welding current, within the required limits. The voltage across it drops in welding mode by 20 ... 25% relative to the open circuit voltage.

The winding of the windings of the welding machine on the toroidal type core can also be done in several ways ( Figure: 7).

Methods of winding the windings of the welding machine on a toroidal core.

Switching windings in welding machines is easier to do with copper lugs and terminals. Copper lugs at home can be made from copper tubes of a suitable diameter 25 ... 30 mm long, fixing the wires in them by crimping or soldering. When welding in various conditions (strong or low-current network, long or short supply cable, its cross-section, etc.), by switching the windings, the welding machine is set to the optimal welding mode, and then the switch can be set to the neutral position.

1.5. Setting up the welding machine.

Having made a welding machine, a home electrician must adjust it and check the quality of welding with electrodes of various diameters. The setup process is as follows. To measure welding current and voltage, you need: an alternating current voltmeter for 70 ... 80 V and an alternating current ammeter for 180 ... 200 A. The connection diagram of measuring devices is shown in ( Figure: 8)

Figure: 8 Schematic diagram of connecting measuring devices when setting up a welding machine

When welding with various electrodes, the values \u200b\u200bof the welding current - Iw and the welding voltage Uw are removed, which must be within the required limits. If the welding current is small, which happens most often (the electrode sticks, the arc is unstable), then in this case, by switching the primary and secondary windings, the required values \u200b\u200bare set, or the number of turns of the secondary winding is redistributed (without increasing them) towards an increase in the number of turns wound over the mains windings.

After welding, it is necessary to control the quality of welding: penetration depth and thickness of the deposited metal layer. For this purpose, the edges of the products to be welded are broken or sawn. It is advisable to draw up a table based on the measurement results. Analyzing the data obtained, the optimal welding modes are selected for electrodes of various diameters, keeping in mind that when welding with electrodes, for example, 3 mm in diameter, electrodes with a diameter of 2 mm can be cut, because cutting current is more than welding current by 30 ... 25%.

The welding machine must be connected to the network with a wire with a cross section of 6 ... 7 mm through an automatic machine for a current of 25 ... 50 A, for example AP-50.

The diameter of the electrode, depending on the thickness of the metal to be welded, can be selected based on the following ratio: de \u003d (1 ... 1.5) * B, where B is the thickness of the metal to be welded, mm. The arc length is selected depending on the diameter of the electrode and is on average (0.5 ... 1.1) de. It is recommended to perform welding with a short arc of 2 ... 3 mm, the voltage of which is 18 ... 24 V. An increase in the arc length leads to a violation of the stability of its combustion, an increase in losses for waste and spattering, and a decrease in the penetration depth of the base metal. The longer the arc, the higher the welding voltage. The welding speed is chosen by the welder depending on the grade and thickness of the metal.

When welding on straight polarity, the plus (anode) is connected to the workpiece and the minus (cathode) to the electrode. If it is necessary that less heat is generated on the part, for example, when welding thin-sheet structures, then welding is used in reverse polarity. In this case, the minus (cathode) is attached to the workpiece to be welded, and the plus (anode) is attached to the electrode. This not only provides less heating of the workpiece to be welded, but also accelerates the process of melting the electrode metal due to the higher temperature of the anode zone and greater heat supply.

Welding wires are connected to the welding machine through copper lugs for terminal bolts from the outside of the welding machine body. Poor contact connections reduce the power characteristics of the welding machine, deteriorate the quality of welding and can cause them to overheat and even fire the wires.

With a short length of welding wires (4..6 m), their cross-sectional area should be at least 25 mm 2.

During welding, it is necessary to observe fire safety rules, and when setting up the device and electrical safety - during measurements with electrical appliances. Welding must be carried out in a special mask with protective glass of the C5 brand (for currents up to 150 ... 160 A) and gloves. All switching in the welding machine must be done only after disconnecting the welding machine from the mains.

2. Portable welding machine based on "Latra".

2.1. Design feature.

The welding machine operates on a 220 V AC mains. The design of the device is the use of an unusual shape of the magnetic circuit, due to which the weight of the entire device is only 9 kg, and the dimensions are 125x150 mm ( Figure: nine).

For the magnetic circuit of the transformer, tape transformer iron is used, rolled into a roll in the form of a torus. As you know, in traditional designs of transformers, the magnetic core is recruited from W-shaped plates. The electrical characteristics of the welding machine, thanks to the use of a torus-shaped transformer core, are 5 times higher than those of machines with W-shaped plates, and the losses are minimal.

2.2. Improvements to "Latra".

For the core of the transformer, you can use a ready-made "LATR" type M2.

Note. All latras have a six-pin connector and voltage: at the input 0-127-220, and at the output 0-150 - 250. There are two types: large and small, and are called LATR 1M and 2M. Which one I don't remember which one. But, for welding, it is precisely a large LATR with rewound iron that is needed, or, if they are serviceable, then the secondary windings are wound with a bus and after that the primary windings are connected in parallel, and the secondary ones in series. In this case, it is necessary to take into account the coincidence of the directions of the currents in the secondary winding. Then it turns out something similar to a welding machine, although it cooks, like all toroidal ones, a little harsh.

You can use a torus-shaped magnetic core from a burnt-out laboratory transformer. In the latter case, first remove the fence and fittings from the Latra and remove the burnt winding. The cleaned magnetic circuit, if necessary, is rewound (see above), insulated with an electric cardboard or two layers of varnished cloth and the transformer windings are wound. The welding transformer has only two windings. For winding the primary winding, a piece of PEV-2 wire with a length of 170 m, a diameter of 1.2 mm ( Figure: ten)

Figure: ten Welding machine winding:

1 - primary winding;	3 - wire coil;
2 - secondary winding;	4 - yoke

For the convenience of winding, the wire is pre-wound on a shuttle in the form of a 50x50 mm wooden rail with slots. However, for greater convenience, you can make a simple device for winding toroidal power transformers

Having wound the primary winding, they cover it with a layer of insulation, and then the secondary winding of the transformer is wound. The secondary winding contains 45 turns and is wound with copper wire in cotton or glassy insulation. Inside the core, the wire is located turn to turn, and outside - with a small gap, which is necessary for better cooling. A welding machine manufactured according to the above method is capable of giving a current of 80 ... 185 A. A schematic diagram of the welding machine is shown on fig. eleven.

Figure: eleven Schematic diagram of the welding machine.

The work will be somewhat simplified if it is possible to purchase a working "Latr" for 9 A. Then they remove the fence, the current collector slider and the fasteners from it. Next, the terminals of the primary winding for 220 V are determined and marked, and the remaining terminals are reliably isolated and temporarily pressed against the magnetic circuit so that they are not damaged when winding a new (secondary) winding. The new winding contains the same number of turns and the same brand and the same wire diameter as in the above version. The transformer in this case gives a current of 70 ... 150 A.
The manufactured transformer is placed on an insulated platform in the previous casing, having previously drilled holes in it for ventilation (Fig. 12))

Figure: 12 Variants of the casing of the LATRA-based welding machine.

The conclusions of the primary winding are connected to the 220 V network with a SHRPS or VRP cable, while an AP-25 disconnecting machine should be installed in this circuit. Each terminal of the secondary winding is connected to a flexible insulated wire PRG. The free end of one of these wires is attached to the electrode holder, and the free end of the other is attached to the workpiece to be welded. This end of the wire must also be grounded for the safety of the welder. Adjustment of the current of the welding machine is made by connecting in series to the wire circuit of the electrode holder pieces of nichrome or constantan wire d \u003d 3 mm and 5 m long, rolled up with a "snake". The snake is attached to the asbestos sheet. All wire and ballast connections are made with M10 bolts. Moving the wire connection point along the "snake", set the required current. The current can be adjusted using electrodes of different diameters. For welding with such an apparatus, electrodes of the E-5RAUONII-13 / 55-2,0-UD1 type dd \u003d 1 ... 3 mm are used.

When carrying out welding work to prevent burns, it is necessary to use a fiber protective shield equipped with an E-1, E-2 light filter. A headdress, overalls and mittens are required. Protect the welding machine from dampness and prevent overheating. Approximate modes of operation with an electrode d \u003d 3 mm: for transformers with a current of 80 ... 185 A - 10 electrodes, and with a current of 70 ... 150 A - 3 electrodes. after using the specified number of electrodes, the device is disconnected from the network for at least 5 minutes (or better about 20).

3. Welding machine from a three-phase transformer.

The welding machine, in the absence of "LATRA", can also be made on the basis of a three-phase step-down transformer 380/36 V, with a capacity of 1..2 kW, which is designed to supply low voltage power tools or lighting (Fig. 13).

Figure: thirteen General view of the welding machine and its core.

Even a copy with one blown winding is suitable here. Such a welding machine operates from a 220 V or 380 V alternating current network and with electrodes up to 4 mm in diameter, it allows welding metal with a thickness of 1 ... 20 mm.

3.1. Details.

The terminals for the terminals of the secondary winding can be made from a copper tube d 10 ... 12 mm and a length of 30 ... 40 mm (Fig. 14).

Figure: fourteen Construction of the terminal of the secondary winding of the welding machine.

On one side, it should be riveted and a hole d 10 mm drilled in the resulting plate. Carefully stripped wires are inserted into the terminal tube and crimped with light hammer blows. To improve contact on the surface of the terminal tube, you can make notches with a core. On the panel located at the top of the transformer, the standard screws with M6 nuts are replaced by two screws with M10 nuts. It is advisable to use copper new screws and nuts. The terminals of the secondary winding are connected to them.

For the terminals of the primary winding, an additional board is made of sheet PCB with a thickness of 3 mm ( fig. 15).

Figure: fifteen General view of the scarves for the conclusions of the primary winding of the welding machine.

10 ... 11 holes d \u003d 6mm are drilled in the board and M6 screws with two nuts and washers are inserted into them. After that, the board is attached to the top of the transformer.

Figure: sixteen Schematic diagram of the connection of the primary windings of the transformer for voltage: a) 220 V; b) 380 V (secondary winding is not specified)

When the device is powered from a 220 V network, its two extreme primary windings are connected in parallel, and the middle winding is connected to them in series ( fig. 16).

4. Electrode holder.

4.1. Electrode holder from pipe d¾ ".

The simplest is the design of the electric holder, made of a pipe d¾ "and a length of 250 mm ( fig. 17).

On both sides of the pipe, at a distance of 40 and 30 mm from its ends, cut with a hacksaw recesses half the diameter of the pipe ( fig. 18)

Figure: eighteen Drawing of the body of the electrode holder from the pipe d¾ "

A piece of steel wire d \u003d 6 mm is welded to the pipe above the large recess. A hole d \u003d 8.2 mm is drilled on the opposite side of the holder, into which an M8 screw is inserted. A terminal is connected to the screw from the cable going to the welding machine, which is clamped with a nut. A piece of rubber or nylon hose with a suitable inner diameter is put on top of the pipe.

4.2. Electrode holder made of steel corners.

Convenient and simple in design, the electrode holder can be made from two steel corners 25x25x4 mm ( fig. 19)

They take two such corners with a length of about 270 mm and connect them with small corners and bolts with M4 nuts. The result is a box with a section of 25x29 mm. A window for the retainer is cut out in the resulting housing and a hole is drilled to install the axis of the retainers and electrodes. The latch consists of a lever and a small key made of 4 mm steel sheet. This part can also be made from a corner 25x25x4 mm. To ensure reliable contact of the latch with the electrode, a spring is put on the latch axis, and the lever is connected to the body with a contact wire.

The handle of the resulting holder is covered with insulating material, which is a piece of rubber hose. The electrical cable from the welding machine is connected to the housing terminal and fixed with a bolt.

5. Electronic current regulator for welding transformer.

An important design feature of any welding machine is the ability to adjust the operating current. such methods of current regulation in welding transformers are known: shunting with the help of chokes of various types, changing the magnetic flux due to the mobility of the windings or magnetic shunting, the use of active ballast resistors and rheostats. All of these methods have both advantages and disadvantages. For example, the disadvantage of the latter method is the complexity of the design, the bulkiness of the resistances, their strong heating during operation, and the inconvenience when switching.

The most optimal is the method of stepwise current regulation, by changing the number of turns, for example, connecting to the taps made when winding the secondary winding of the transformer. However, this method does not allow for wide current adjustment, therefore it is usually used to adjust the current. Among other things, the regulation of the current in the secondary circuit of the welding transformer is associated with certain problems. In this case, significant currents pass through the regulating device, which is the reason for the increase in its dimensions. For the secondary circuit, it is practically impossible to select powerful standard switches that would withstand currents up to 260 A.

If we compare the currents in the primary and secondary windings, it turns out that the current in the primary winding circuit is five times less than in the secondary winding. This suggests the idea of \u200b\u200bplacing a welding current regulator in the primary winding of the transformer, using thyristors for this purpose. In fig. 20 shows a diagram of a thyristor welding current regulator. With the utmost simplicity and accessibility of the element base, this regulator is easy to operate and does not require adjustment.

Power regulation occurs when the primary winding of the welding transformer is periodically disconnected for a fixed period of time at each half-cycle of the current. In this case, the average current value decreases. The main elements of the regulator (thyristors) are connected opposite and parallel to each other. They alternately open with current pulses generated by transistors VT1, VT2.

When the regulator is connected to the network, both thyristors are closed, the capacitors C1 and C2 begin to charge through the variable resistor R7. As soon as the voltage on one of the capacitors reaches the voltage of the avalanche breakdown of the transistor, the latter opens, and the discharge current of the capacitor connected to it flows through it. Following the transistor, the corresponding thyristor also opens, which connects the load to the network.

By changing the resistance of the resistor R7, you can regulate the moment when the thyristors turn on from the beginning to the end of the half-period, which in turn leads to a change in the total current in the primary winding of the welding transformer T1. To increase or decrease the adjustment range, you can change the resistance of the variable resistor R7 up or down, respectively.

Transistors VT1, VT2, operating in avalanche mode, and resistors R5, R6, included in their base circuits, can be replaced by dinistors (Fig. 21)

Figure: 21 Schematic diagram of replacing a transistor with a resistor with a dinistor, in the current regulator circuit of a welding transformer.

the anodes of the dinistors should be connected to the extreme terminals of the resistor R7, and the cathodes should be connected to the resistors R3 and R4. If the regulator is assembled on dinistors, then it is better to use devices of the KN102A type.

Transistors of the old type P416, GT308 have proven themselves well as VT1, VT2, however, these transistors, if desired, can be replaced with modern low-power high-frequency transistors with similar parameters. Variable resistor type SP-2, and fixed resistors type MLT. Capacitors of the MBM or K73-17 type for an operating voltage of at least 400 V.

All parts of the device are mounted on a textolite plate with a thickness of 1 ... 1.5 mm using a hinged mounting. The device has a galvanic connection to the mains, therefore all elements, including thyristor heat sinks, must be isolated from the case.

A properly assembled welding current regulator does not require special adjustment, you just need to make sure that the transistors work in an avalanche mode or, when using dinistors, in their stable turn on.

A description of other designs can be found on the website http://irls.narod.ru/sv.htm, but I want to warn you right away that many of them have at least controversial points.

Also on this topic you can see:

http://valvolodin.narod.ru/index.html - a lot of GOSTs, schemes of both self-made devices and factory

http://www.y-u-r.narod.ru/Svark/svark.htm the same site of a welding enthusiast

When writing the article, we used some of the materials from the book by V. M. Pestrikov "Home electrician and not only ..."

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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How to choose the right winding structure?

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

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

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

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Homemade welding machine from an autotransformer

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

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

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