Homemade welding machine-transformer from latr. Homemade welding machines DIY welding from latra 9a

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

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

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

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

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

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

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

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

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

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

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

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

Wire layers must be insulated from each other. To save space, the winding should be laid as compact as possible. On a magnetic core made of small rings, the interlayer insulation must be applied thinner, for example, using ordinary adhesive tape. Take your time to wind the primary winding once. It's easier to do this in 2-3 approaches.

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

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

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

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

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

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

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

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

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

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

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

For the manufacture of a welding transformer, you can use a stator from an induction motor. The size of the core is determined in this case by the cross-sectional area of \u200b\u200bthe stator, which must be at least 20 cm 2.

Domestic color TVs used large, heavy network transformers, for example, TS-270, TS-310, ST-270. They have U-shaped magnetic circuits, they are easy to disassemble by unscrewing only two nuts on the tightening pins, and the magnetic circuit breaks up into two halves. For older transformers TS-270, TS-310, the section of the magnetic circuit has dimensions of 2x5 cm, S \u003d 10 cm2, and for newer transformers - TS-270, the section of the magnetopod S \u003d 11.25 cm2 with dimensions of 2.5x4.5 cm. the width of the window for old transformers is therefore several millimeters larger. Older transformers are wound with copper wire, and a wire may come in handy from their primary windings.

Welding transformer other possible types and designs

ST, in addition to special manufacture, can be obtained by re-equipping ready-made transformers for various purposes. Powerful transformers of a suitable type are used to create networks with a voltage of 36, 40 V, usually in places with increased fire hazard, humidity and for other needs. For these purposes, different types of transformers are used: different powers included in 220, 380 V according to a single or three-phase scheme.

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 take place 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 give 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 changing 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 value of the welding voltage U sv 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 material of the core 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 should 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 rewind 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 most often unknown, therefore, 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 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 wire of the primary winding 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 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 conclusions of the windings are tinned, marked, secured with cotton tape, and a cotton cambric is additionally put on the conclusions 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 therefore 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 consumed current 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 some more 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 check the quality of welding: the penetration depth and the 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 30 ... 25% higher than welding current.

The connection of the welding machine to the network must be made 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 length of the arc 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 spatter, and a decrease in the depth of penetration 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 C5 protective glass (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 the ready-made "LATR" type M2.

Note. All latras have a six-pin block 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, one must 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 burned-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 moisture and prevent it from 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 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: 13 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 allows welding metal 1 ... 20 mm thick.

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

Figure: 15 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: 18 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. nineteen)

Take two such corners about 270 mm long and connect 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 using chokes of all kinds, changing the magnetic flux due to the mobility of the windings or magnetic shunting, the use of active ballast resistors and rheostats. All 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, by 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 the 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 are alternately opened by current pulses formed 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 adjust the moment of turning on the thyristors 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.

As VT1, VT2, old-style transistors such as P416, GT308 have proven themselves well, 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, diagrams 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 "Household electrician and not only ..."

All the best, write to © 2005

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

LATRs are produced in different types, with maximum currents from 2 to 10A, not all of them are suitable for the manufacture of transformers for welding, only those with the size of the magnetic cores that allow you to lay the required number of turns. The most common among them is probably the LATR-1M autotransformer. Depending on the winding wire, it is designed for currents of 6.7-9A, although the dimensions of the autotransformer itself do not change from this. The LATR-1M magnetic core has the following dimensions: outer diameter D \u003d 127 mm, inner diameter d \u003d 70 mm, ring height h \u003d 95 mm, section S \u003d 27 cm 2, weight about 6 kg. A good welding transformer can be made of two LATR-1M rings, however, due to the small internal volume of the window, you cannot use too thick wires and you will have to save every millimeter of window space. A significant disadvantage of the LATR transformer, in comparison with the U-shaped transformer circuit, is also the fact that the coils cannot be made separately from the magnetic circuit. This means that you will have to wind, pulling each turn through the magnetic circuit window, which of course greatly complicates the manufacturing process.

There are LATRs with more voluminous magnetic drive rings. They are much better suited for making welding transformers, but less common. In other autotransformers, similar in parameters to LATR-1M, for example AOSN-8-220, the magnetic core has other dimensions: the outer diameter of the ring is larger, but the height and diameter of the window are smaller, d \u003d 65 mm. In this case, the window diameter must be expanded to 70 mm.

The ring of the magnetic circuit consists of pieces of iron tape wound on each other, fastened along the edges by spot welding. In order to increase the inner diameter of the window, it is necessary to detach the end of the tape from the inside and unwind the required amount. But don't try to rewind everything in one go. It is better to unwind one loop at a time, cutting off the excess each time. Sometimes in this way the windows of larger LATRs are also expanded, although this inevitably decreases the cross-sectional area of \u200b\u200bthe magnetic circuit.

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

Straddled Shoulder Transformer

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

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

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

The primary winding takes about 70-80 m of wire, which will have to be pulled through both windows of the magnetic circuit with each turn. In this case, you can not do without a simple device.

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

The primary wire can have a diameter of 1.6-2.2 mm. For magnetic circuits composed of rings with a window diameter of 70 mm, a wire with a diameter of not more than 2 mm can be used, otherwise there will be little space for the secondary winding. The primary winding contains, as a rule, 180-200 turns at normal mains voltage, which is sufficient for efficient operation with a 3 mm electrode.

A cambric is put on the end of the wire, which is attracted by HB electrical tape to the beginning of the first layer. The surface of the magnetic circuit has a rounded shape, so the first layers will contain fewer turns than the next ones to level the surface.

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

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

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

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

It may turn out that it was not possible to fit all the calculated turns of the secondary winding into the windows, and the output voltage turned out to be lower than the desired one. The operating current will not decrease much from this. To a greater extent, lowering the no-load voltage affects the arc ignition process. The arc ignites easily at voltages close to 50V and above. Although the arc can be ignited without any problems even at lower voltages. So if the manufactured transformer has an output of about 40V, then it may well be used for work. It is another matter if you come across electrodes designed for high voltages - some brands of electrodes operate from 70-80V.

Toroidal transformer

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

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

The advantageous difference between the toroidal circuit for a welding transformer is a higher efficiency. Each turn of the secondary winding will now have more than one volt of voltage, therefore, the "secondary" will have fewer turns, and the output power will be higher than in the previous circuit. However, the length of the turn on the toroidal magnetic circuit will be longer, and it is unlikely that it will be possible to save on the wire here. The disadvantages of this scheme include: the complexity of the winding, the limited volume of the window, the impossibility of using a wire of large cross-section, as well as the high intensity of heating. If in the previous version all the windings were separate and at least partially had contact with air, now the primary winding is completely under the secondary, and their heating is mutually reinforced.

It is difficult to use rigid wires for the secondary winding. It is easier to wind it with soft stranded or multi-strand wire. If you select all the wires correctly and carefully lay them, then the required number of turns of the secondary winding will fit into the space of the magnetic circuit window and the required voltage will be obtained at the output of the transformer.

Sometimes a toroidal welding transformer is made of several LATR rings in a different way, they are not placed on top of each other, but the iron strips of tape are rewound from one to the other. To do this, first, the inner turns of the strips are selected from one ring in order to expand the window. The rings of other LATRs are completely dissolved into strips of tape, which are then wound as tightly as possible on the outer diameter of the first ring. After that, the assembled single magnetic circuit is wrapped very tightly with insulating tape. Thus, a ring-magnetic circuit with a more voluminous inner space than all previous ones is obtained. In such it will be possible to fit a wire of significant cross-section. The required number of turns is calculated from the sectional area of \u200b\u200bthe assembled ring.

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

When using the content of this site, you need to put active links to this site, visible to users and search robots.

Do-it-yourself welding in this case does not mean welding technology, but home-made equipment for electric welding. Working skills are acquired through practical training. Of course, before you go to the workshop, you need to master the theoretical course. But you can only put it into practice if you have something to work on. This is the first argument in favor of taking care of the availability of appropriate equipment while mastering welding on your own.

Second, a purchased welding machine is expensive. Renting is also not cheap, because the probability of its failure with unskilled use is great. Finally, in the hinterland, getting to the nearest location where you can rent a welder can simply be long and difficult. Generally, it is better to start the first steps in welding metals with the manufacture of a welding machine with your own hands. And then - let him stand in the barn or garage until the occasion. It is never too late to spend money on branded welding, if it works.

What will we talk about

This article discusses how to make equipment at home for:

• Electric arc welding with alternating current of industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures approximately to the fence from corrugated board on a frame from a professional pipe or welded garage.
• Micro-arc welding of wire twists is very simple and useful when laying or repairing electrical wiring.
• Spot impulse resistance welding - can be very useful when assembling products from a thin steel sheet.

What we will not 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 home-made gas generator is a serious risk to life, plus carbide is expensive now, where it still goes on sale.

The second is inverter electric arc welding. Indeed, the semiautomatic welding inverter allows the novice amateur to cook quite critical designs. It is lightweight and compact and can be carried by hand. But the retail purchase of inverter components that allows you to consistently maintain a high-quality seam will cost more than the finished device. An experienced welder will try to work with simplified homemade products and refuse - "Give me a normal machine!" Plus, or rather minus - to make a more or less decent welding inverter, you need to have quite solid experience and knowledge in electrical engineering and electronics.

The third is argon-arc welding. From whose light hand the statement that it is a hybrid of gas and arc went to walk in Runet is unknown. In fact, this is a kind 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, the weld is chemically clean, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be cooked under argon, incl. dissimilar. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and to weld with a non-consumable electrode.

Equipment for argon arc welding is quite possible to make at home, but gas is very expensive. It is unlikely that aluminum, stainless steel or bronze will need to be cooked in the order of routine economic activity. And if you really need to, it is easier to rent argon welding - compared to how much (in money) gas will go back into the atmosphere, this is a penny.

Transformer

The basis of all "our" types of welding is a 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 works intermittently. If designed for maximum current as continuous transformers, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electric arc welding transformers is the main reason for the failure of amateur designers. Therefore, we will walk through the welding transformers in the following order:

1. a little theory - on the fingers, without formulas and zaum;
2. features of the magnetic cores of welding transformers with recommendations for choosing from those that accidentally turned up;
3. tests of available used;
4. calculation of the transformer for the welding machine;
5. preparation of components and winding of windings;
6. trial assembly and debugging;
7. commissioning.

Theory

An electrical transformer can be likened to a water supply storage tank. This is a rather deep analogy: a transformer operates due to the reserve of magnetic field energy in its magnetic circuit (core), which can be many times higher 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. Power losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in a liquid.

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

An important factor in our case is the external current-voltage characteristic (VVAC) of the transformer, or just its external characteristic (VX) - the 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, VX is rigid (curve 1 in the figure); they are like a shallow vast basin. If it is properly insulated and covered with a roof, then the water loss is minimal and the pressure is quite stable, no matter how the consumers turn the taps. But if there is a gurgle in the drain - sushi oars, the water is drained. As applied to transformers, the power engineer 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. For this:

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

Note: transformer steel with "angular" hysteresis is often called magnetic hardness. This is not true. Hard magnetic materials retain a strong residual magnetization, they are made by permanent magnets. And any transformer iron is soft magnetic.

It is impossible to cook from a transformer with a rigid VX: the seam is torn, burnt, the metal is splashed. The arc is inelastic: I almost moved it with the electrode, it goes out. Therefore, the welding transformer is made similar to an ordinary water tank. Its IQ is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage decreases smoothly. The normal scatter curve is approximated by a straight line falling at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly remove several times more power from the same iron, or, respectively. reduce the weight and dimensions and cost of the transformer. In this case, the induction in the core can reach the 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 heat up. Quite long: the thermal time constant of the welding transformers is 20-40 minutes. If you then let it cool down and there was no unacceptable overheating, you can continue to work. The relative drop in the secondary voltage ΔU2 (corresponding to it, the swing of the arrows in the figure) of normal dispersion increases smoothly with an increase in the swing of the welding current Iw, which makes it easy to keep the arc in any kind of work. The following properties are provided:

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

Note: reversible leakage losses means that some of the lines of force penetrate the secondary through the air bypassing the magnetic circuit. The name is not quite apt, as well as "useful scattering", since "Reversible" losses for the efficiency of a transformer are no more useful than irreversible ones, but they soften the VC.

As you can see, the conditions are completely different. So, by all means look for iron from a welder? Optional, for currents up to 200 A and peak power up to 7 kVA, but this will be enough on the farm. By design and design measures, as well as with the help of simple additional devices (see below), we will obtain curve 2a on any BX gland, somewhat more rigid than normal. In this case, the efficiency of energy consumption of welding is unlikely to exceed 60%, but for occasional work it is not scary for yourself. But on delicate works and low currents, it will be easy to keep the arc and welding current, without having much experience (ΔU2.2 and Ib1), at high currents Ib2 we will get an acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

There are also welding transformers with steeply dipping VX, curve 3. This is more like a pumping pump: either the output flow is in the nominal value regardless of the feed height, or it is not at all. They are even more compact and lightweight, but in order to withstand the welding mode on a steeply dipping VX, it is necessary to respond to fluctuations ΔU2.1 of the order of a volt in a time of about 1 ms. Electronics can do this, so transformers with "cool" VX are often used in semi-automatic welding machines. If from such a transformer you cook by hand, then the seam will go sluggish, undercooked, the arc is again inelastic, and when you try to ignite it again, the electrode now and then sticks.

Magnetic cores

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

The letters of the type are followed by the numbers denoting a, b and h in Fig. For example, for Ш20х40х90 the dimensions of the core cross-section (central rod) are 20x40 mm (a * b), and the window height h is 90 mm. Core cross-sectional area Sс \u003d a * b; window area Sok \u003d c * h is needed for accurate calculation of transformers. We will not use it: for an accurate calculation, you need to know the dependences of losses in steel and copper on the value of induction in the core of a given standard size, and for them - the steel grade. Where can we get it if we wind it on random hardware? We will calculate using a simplified method (see below), and then we will bring it to the test. It will take more work, but we will get welding on which you can actually work.

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

Another important parameter of the magnetic circuit is its mass, weight. Since the specific gravity of steel is unchanged, it determines the volume of the core, and, accordingly, the power that can be taken from it. For the manufacture of welding transformers, magnetic cores of mass are suitable:

• Oh, OL - from 10 kg.
• P, PL - from 12 kg.
• Ш, ШЛ - from 16 kg.

Why Sh and ShL are needed more heavily is understandable: they have an "extra" lateral rod with "shoulders". The OL can be easier, because there are no corners in it for which an excess of iron is needed, and the bends of the magnetic field lines are smoother and for some other reasons, which are already in the next. section.

Oh OL

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

LATR is a very useful thing, first. If the core is still alive, it is better to restore the LATR. Suddenly it is not needed, you can sell it, and the proceeds will be enough for welding suitable for your needs. Therefore, it is difficult to find "bare" LATR cores.

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

Another torus suitable for all its properties is the stator of the electric motor; welding from it will turn out even for an exhibition. But it is no easier to find it than LATR iron, and it is much more difficult to wind it on it. In general, a welding transformer from an electric motor stator is a separate topic, there are so many difficulties and nuances there. First of all - with a thick wire winding on the "donut". Having no experience in winding toroidal transformers, the probability of spoiling an expensive wire and not getting welding is close to 100%. Therefore, alas, with a cooking apparatus on a troidal transformer, you will have to wait.

Ш, ШЛ

Armor cores are structurally designed for minimal dispersion, and it is practically impossible to normalize it. Welding on a conventional W or SL will turn out to be too tough. In addition, the conditions for cooling the windings on Ш and ШЛ are the worst. The only armored cores suitable for a welding transformer are of increased height with spaced wafer windings (see below), on the left in Fig. The windings are separated by dielectric non-magnetic heat-resistant and mechanically strong spacers (see below) with a thickness of 1 / 6-1 / 8 of the core height.

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

If you turn up a lined Ш without a yoke, but with a notch of the plates between the core and the bulkhead (in the center), you are in luck. Signal transformer plates are loaded, and steel on them, in order to reduce signal distortion, goes to give normal VX initially. But the likelihood of such luck is very small: signal transformers for kilowatt powers are a rare curiosity.

Note: do not try to collect a high Ш or ШЛ from a pair of ordinary ones, as on the right in Fig. A solid straight gap, albeit very thin, is irreversible scattering and steeply dipping VX. Here, the dissipation losses are almost similar to the evaporation losses of water.

PL, PLM

Rod cores are most suitable for welding. Of these, those charged in pairs of identical L-shaped plates, see Fig., Their irreversible scattering is the smallest. Second, the windings P and PLov are wound in exactly the same halves, half turns for each. The slightest magnetic or current asymmetry - the transformer hums, heats up, but there is no current. Third, which may seem unobvious to those who have not forgotten the school rule of the gimbal - the windings are wound on the rods in one direction... Is there something wrong? Must the magnetic flux in the core be closed? And you twist the gimbals along the current, not along the turns. The directions of the currents in the semi-windings are opposite, and the magnetic fluxes are shown there. You can also check if the protection of the wiring is reliable: supply the network to 1 and 2 ', and close 2 and 1'. If the machine gun does not immediately knock out, then the transformer will howl and shake. However, who knows what you have with the wiring. Better not.

Note: you can also find recommendations - winding the windings of the welding P or PL on different rods. Like, VX softens. That's how it is, but a special core is needed for this, with rods of different sections (secondary housing on the smaller one) and recesses that release the lines of force into the air in the desired direction, see Fig. on right. Without this, we will get a loud, shaking and gluttonous, but not a boiling transformer.

If there is a transformer

A 6.3 A circuit breaker and an AC ammeter will also help determine the suitability of an old welder lying around God knows where and the devil knows how. An ammeter is needed either a non-contact induction (current clamp) or an electromagnetic switch for 3 A. A multimeter with alternating current limits will be unacceptable to lie, because the shape of the current in the circuit will be far from sinusoidal. Another - a liquid household thermometer with a long neck, or, better, a digital multimeter with the ability to measure temperature and a probe for this. A step-by-step test procedure and preparation for further operation of the old welding transformer is as follows:

Calculation of the welding transformer

In runet you can find different methods for calculating welding transformers. While seemingly inconsistent, most of them are correct, but with full knowledge of the properties of steel and / or for a specific series of standard types of magnetic cores. The proposed methodology developed in Soviet times, when instead of a choice there was a deficit of everything. For the transformer calculated according to it, VX falls a little steeply, somewhere between curves 2 and 3 in Fig. at the beginning. This is suitable for cutting, and for thinner work, the transformer is supplemented with external devices (see below), stretching the VX along the current axis to curve 2a.

The basis of the calculation is the usual: the arc burns stably under a voltage of Ud 18-24 V, and its ignition requires an instantaneous current 4-5 times higher than the rated welding current. Accordingly, the minimum no-load voltage Uхх of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. There is no other way: it is unacceptable for TB, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly switch from a short circuit mode (say, when closed by drops of metal) into a working one, is maintained without additional measures. True, such a transformer is prone to overheating, but since it is its own and in front of our eyes, and not in the far corner of a workshop or site, we will consider this permissible. So:

• According to the formula from clause 2 before. the list we find the overall power;
• We find the maximum possible welding current Iw \u003d Pg / Ud. 200 A are provided if 3.6-4.8 kW can be removed from iron. True, in the first case, the arc will be sluggish, and it will be possible to cook only with a two or 2.5;
• We calculate the operating current of the primary at the maximum allowable mains voltage for welding I1рmax \u003d 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 operating current of the protective circuit breaker as 1.2I1рmax;
• We accept the current density of the primary J1 \u003d 5 A / sq. mm and, using I1рmax, we find the diameter of its wire in copper d \u003d (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation is D \u003d 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, yok solution" mode, you can take J1 \u003d 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 primary: w \u003d k2 / Sс, where k2 \u003d 50 for Ш and П, k2 \u003d 40 for PL, ШЛ and k2 \u003d 35 for О, ОЛ;
• We find the total number of its turns W \u003d 195k3w, where k3 \u003d 1.03. k3 takes into account the energy losses of the winding for dissipation in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
• We set the stacking coefficient Ku \u003d 0.8, add 3-5 mm each to a and b of the magnetic circuit, calculate the number of layers of the winding, the average length of the turn and the length of the wire
• We calculate in a similar way the secondary at J1 \u003d 6 A / sq. mm, k3 \u003d 1.05 and Ku \u003d 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

Wire diameters in the calculation of windings are usually more than 3 mm, and varnished winding wires with d\u003e 2.4 mm are rare on the market. In addition, the welder's windings experience strong mechanical loads from electromagnetic forces, therefore, finished wires are needed with an additional textile winding: PELSH, PELSHO, PB, PBD. Finding them is even more difficult and very expensive. The length of the wire per welder is such that cheaper bare wires can be insulated on their own. An additional advantage - twisting several stranded wires to the desired S, we get a flexible wire, which is much easier to wind. Anyone who has tried to manually lay a tire of at least 10 squares on the frame will appreciate it.

Isolation

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

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

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

Winding

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

• We are preparing a wooden boss with a height in the height of the winding and with dimensions in diameter 3-4 mm larger than a and b of the magnetic circuit;
• We nail or fasten temporary plywood cheeks to it;
• We wrap the temporary frame in 3-4 layers with a thin plastic wrap with an approach to the cheeks and a twist on their outer side so that the wire does not stick to the tree;
• We wind a pre-insulated winding;
• On the winding, we impregnate twice until it flows through with liquid varnish;
• after the impregnation dries, carefully remove the cheeks, squeeze out the lug and tear off the film;
• we tie the winding in 8-10 places evenly around the circumference with a thin cord or propylene twine - it is ready for testing.

Lapping and homework

We load the core into a biscuit and tighten it with bolts, as expected. The winding tests are carried out completely similar to the tests of the 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 is more, the primary organization will be killed. Winding wire connections are made on bolts (!), Insulated with a heat-shrinkable tube (HERE) in 2 layers or cotton tape in 4-5 layers.

According to the test results, the number of turns of the secondary is corrected. For example, the calculation gave 210 turns, but in reality Iхх got into the norm at 216. Then we multiply the calculated turns of the secondary sections by 216/210 \u003d 1.03 approx. Do not neglect the decimal places, the quality of the transformer largely depends on them!

After finishing, the core is disassembled; tightly wrap the biscuit 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 we soak it again with liquid varnish; when dry - twice undiluted. This biscuit is ready, you can make a secondary one. When both are on the core, we once again test the transformer on Ixx (suddenly it curled somewhere), fix the biscuits and saturate the entire transformer with normal varnish. Phew, the most dreary part of the work is behind.

Pull VX

But we still have it too cool, don't you forget? You need to soften. The simplest way - a resistor in the secondary circuit - doesn't work for us. Everything is very simple: on a resistance of only 0.1 Ohm at a current of 200, 4 kW will dissipate by heat. If we have a welder for 10 or more kVA, and we need to weld thin metal, a resistor is needed. Whatever the current is set by the regulator, its emissions during arc striking are inevitable. Without active ballast, they will burn through the seam in places, and the resistor will extinguish them. But to us, weak, he will not be of any use to him.

The reactive ballast (inductance coil, choke) will not take away excess power: it will absorb current surges, and then smoothly give them to the arc, this will stretch the VX as it should. But then you need a choke with dispersion control. And for him - the core is almost the same as that of the transformer, and rather complicated mechanics, see fig.

We will go the other way: we will apply active-reactive ballast, in the old welders colloquially called the gut, see fig. on right. Material - steel wire rod 6 mm. The diameter of the turns is 15-20 cm. How many of them are shown in Fig. it can be seen that 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 clip-clothespin. By selecting the attachment point, it is possible, coupled with switching to secondary taps, to fine-tune the operating mode of the arc.

Note: active-reactive choke in operation can be heated red-hot, so it needs a non-combustible heat-resistant dielectric non-magnetic lining. In theory, a special ceramic lodgment. It is permissible to replace it with a dry sand pillow, or already formally in violation, but not rough, the welding gut is laid on bricks.

But other?

This means, first of all, the electrode holder and the return hose connector (clamp, clothespin). They, since we have a transformer at the limit, you need to buy ready-made, and such as in Fig. on the right, don't. For a welding machine for 400-600 A, the quality of contact in the holder is not perceptible, and it will also withstand just winding the return hose. And our home-made, working with an effort, can go awry for some unknown reason.

Further, the body of the device. It must be made of plywood; desirably bakelite impregnated as described above. The bottom - from 16 mm thick, the panel with the terminal block - from 12 mm, and the walls and lid - from 6 mm, so that they will not come off when carrying. Why not sheet steel? It is a ferromagnet and in the stray field of the transformer can disrupt its operation, because we are drawing out everything that is possible from it.

As for the terminal blocks, the terminals themselves are made from bolts from M10. The basis is the same textolite or fiberglass. Getinaks, bakelite and carbolite are not suitable, they will soon crumble, crack and exfoliate.

Trying a constant

DC welding has a number of advantages, but the VC of any DC welding transformer is tightened. And ours, designed for the minimum possible power reserve, will become unacceptably tough. The choke-gut will no longer help here, even if it worked on direct current. In addition, expensive 200 A rectifier diodes should be protected from current and voltage surges. We need a return-absorbing infra-low frequency filter, FINCH. Although it looks reflective, the strong magnetic coupling between the halves of the coil must be taken into account.

The scheme of such a filter, known for many years, is shown in Fig. But immediately after its implementation by amateurs, it turned out that the operating voltage of the capacitor C is small: voltage surges during arc ignition can reach 6-7 values \u200b\u200bof its Uхх, i.e. 450-500 V. Further, capacitors are needed to withstand the circulation of high reactive power, only and only oil-paper (MBGCH, MBGO, KBG-MN). About the mass and dimensions of single "cans" of these types (by the way, and not cheap) gives an idea of \u200b\u200bthe trace. fig., and on the battery they will need 100-200.

With the magnetic core, the coils are easier, although not entirely. For him, 2 PLs of the TS-270 power transformer from old tube TVs - "coffins" (data are available in reference books and in the Russian Internet), or similar, or SHL with similar or large a, b, c and h are suitable. SL is assembled from 2 submarines with a gap, see fig., 15-20 mm. Fix it with textolite or plywood gaskets. Winding - insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. They wind it in 2 wires. The end of one is connected to the beginning of the other, this will be the midpoint.

The filter is adjusted along an arc at the minimum and maximum values \u200b\u200bUхх. If the arc is at least sluggish, the electrode sticks, the gap is reduced. If the metal burns at maximum, they increase or, which will be more effective, cut off part of the side rods symmetrically. So that the core does not crumble from this, 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 micro-arc welding was mentioned at the beginning. The "equipment" for her is extremely simple: a step-down transformer 220 / 6.3 V 3-5 A. In the days of the tube, radio amateurs were connected to the filament winding of a standard power transformer. One electrode - the wire twisting itself (copper-aluminum, copper-steel can be used); the other is a graphite rod like the lead from a 2M pencil.

Now for micro-arc welding, more computer power supplies are used, or, for pulse micro-arc welding, capacitor banks, see the video below. With direct current, the quality of work, of course, improves.

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

Resistance welding in industry is mainly used for 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 a part is a coin or less, then the softest arc will burn it entirely.

The principle of operation of spot resistance welding is illustrated in Fig: copper electrodes compress the parts with force, a current pulse in the steel-steel ohmic resistance zone heats the metal to the point that electrodiffusion occurs; the metal does not melt. The current for this needs approx. 1000 A per 1 mm of thickness of the parts to be welded. Yes, a current of 800 A will take sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, for example, a galvanized corrugated fence, then the first strong gust of wind will remind you: "Man, but the current was rather weak!"

Nevertheless, contact spot welding is much more economical than arc welding: the open-circuit voltage of the welding transformer for it is 2 V. It is the sum of 2 contact potential differences steel-copper and the ohmic resistance of the penetration zone. The transformer for resistance welding is calculated similarly to it for arc welding, but the current density in the secondary winding is taken from 30-50 and more A / sq. mm. The secondary of a 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.

Runet has a lot of descriptions of homemade pulse-point welders from unusable microwave ovens. They are, in general, correct, but in repetition, as it is written in "1001 Nights", there is no benefit. And old microwave ovens are not piled up in the trash heaps. Therefore, we will deal with constructions less known, but, by the way, more practical.

In fig. - device of the simplest device for pulsed spot welding. It can weld sheets up to 0.5 mm; it fits perfectly for small crafts, and magnetic cores of this and larger standard size are relatively affordable. Its advantage, in addition to simplicity, is the clamping of the running rod of the welding tongs with a load. A third hand would not hurt to work with a contact-welding impulse, and if one has to squeeze the pliers with force, then it is generally inconvenient. Disadvantages - increased risk of accidents and injuries. If you accidentally give an impulse when the electrodes are brought together without the parts to be welded, then plasma will hit 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 16x2 copper bus. It can be drawn from strips of thin sheet copper (it turns out to be flexible) or made from a piece of a flattened pipe for supplying the refrigerant of a household air conditioner. Manually insulate the bus as described above.

Here in fig. - drawings of the pulsed spot welding apparatus are more powerful, for welding sheet up to 3 mm, and more reliable. Thanks to a rather powerful return spring (from the carapace of the bed), accidental convergence of the pliers is excluded, and the eccentric clamp provides a strong stable compression of the pliers, which significantly affects the quality of the welded joint. In which case the clamp can be instantly reset with one blow to the eccentric lever. The disadvantage is the insulating nodes of the ticks, there are too many of them and they are complicated. Another one is the aluminum pliers rods. Firstly, they are not as strong as steel ones, and secondly, they are 2 unnecessary contact differences. The heatsink on aluminum is certainly excellent though.

About electrodes

In amateur conditions, it is more expedient to insulate the electrodes at the installation site, as shown in Fig. on right. Houses are not a conveyor belt, the device can always be allowed to cool down so that the insulating sleeves do not overheat. Such a design will make it possible to make the rods from a durable and cheap steel professional pipe, and also lengthen the wires (up to 2.5 m this is permissible) and use a contact welding gun or remote pliers, see Fig. below.

In fig. on the right, one more feature of electrodes for spot resistance 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 should be equal to 3 thicknesses of the adjacent material to be welded, otherwise the penetration spot will be burned out either in the center (wide heel) or along the edges (narrow heel), and corrosion will go from the welded joint even on stainless steel.

The last thing about electrodes is their material and dimensions. Red copper burns out quickly, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, with current copper prices this 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. The length of the electrode under the conditions of heat transfer is not less than 3 of its diameters from the heel to the root (beginning of the shank).

How to give impetus

In the simplest home-made devices for pulse-contact welding, a current pulse is given manually: they simply turn on the welding transformer. This, of course, does not benefit him, and welding is either a lack of penetration or a burnout. However, it is not so difficult to automate the feeding and normalization of welding pulses.

A diagram of a simple, but reliable and proven by long practice of the welding pulse generator is given in Fig. The auxiliary transformer T1 is a conventional power transformer of 25-40 W. Winding voltage II - according to the backlight. You can instead put 2 anti-parallel LEDs with a damping resistor (normal, 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 (ordinary electrolytic) is needed for a voltage of 40 V. Diodes V1-V4 and V5-V8 are any rectifier bridges for 1 and from 12 A, respectively. Thyristor V9 - for 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 that regulates the pulse duration. T2 transformer - welding.

When designing, assembling or repairing something, you often have to connect parts. The types and methods of joining are different. For example, when joining metal products, a threaded connection (screw or bolt with nut), riveting, gluing, soldering and welding are used.

And if for the first three only mechanical tools are needed, then soldering irons are needed for soldering, and for welding, some craftsmen make homemade DC and AC welding machines. Many of these units have been operating without failures for decades.

Homemade AC machines

When assembling, repairing or designing household appliances or any equipment, it becomes necessary to weld several parts together. AC welding machines are expensive and not easy to buy. But it is perfectly acceptable to make them yourself. The schemes of such devices are very different.

One of the original designs is based on the LATR transformer (laboratory autotransformer). This device operates on a conventional network using alternating current. Its electrical characteristics are very high due to the special design of the magnetic circuit.

It is made of transformer strip iron (twisted into a roll) and has the shape of a ring or torus, although a conventional AC welding machine is assembled from plates similar to the letter "W". The characteristics of the toroidal product are 4.7 times higher, and the losses are almost minimal compared to the W-shaped core.

But such transformer tape iron is now in short supply, so it is easier to get a ready-made 9-ampere laboratory autotransformer (LATR) or a toroidal magnetic circuit from a burnt product. It must be rewound - remove the old or burnt secondary winding and wind a new one with a thicker wire. Using all of this, you will assemble a 75-155A AC apparatus in about 1-2 hours.

Back to the table of contents

Rewind LATR

To replace the windings, proceed as follows:

1. Remove the cover (if any).
2. Remove the reinforcement made of non-magnetic material (plastic, aluminum) together with the mechanical part.
3. Get rid of old or burnt windings:

• if the windings are not damaged, then the secondary is simply wound onto a special shuttle for use in other designs and designs. The shuttle 4-5x10-20 cm can be cut from plywood;
• if the windings are burnt out, then the wire is removed by any method: cut off, cut off.

1. The core is electrically insulated from the future winding by wrapping the iron with varnished cloth in two layers or by making overlays from a special electrical cardboard.
2. New windings are wound, insulating them from each other;
3. Assemble.

Only two windings are wound on devices made on the basis of the LATR transformer.

If the transformer burns out completely, you have to wind both windings.

The primary one is performed with a 1.2 mm wire of the PEV-2 type. The approximate length of this piece is 170 m. A shuttle is used for winding. The wire is completely wound around it.

And then, having secured the end, they begin to perform translational movements with the hand inside the toroid, wrapping the insulated core with a wire. The winding is done coil to coil. After winding, the primary winding is covered with insulation (the same varnished cloth).

For more reliable insulation and effective cooling of the apparatus, the air gap method between the windings can be applied. In this case, the primary winding need not be insulated from above - its own covering is enough.

The method is as follows:

• two rings are made of thick (3-5 mm) textolite with an external caliber 3-5 mm (on each side) larger than the diameter of the core with the wound "primary";
• the edges are chamfered (they are rounded off) to avoid damage to the insulation;
• rings are fixed at the top and bottom of the core with double-sided tape;
• the secondary winding is wound.

The secondary - 45 turns - is performed with several wires twisted together, or with a bus, which must be in glassy or HB insulation. The cross section is calculated depending on the required welding current and is 5-7 A per 1 sq. Mm. For a current of 170 A, you will need a bus or twist with a cross section of 35 mm or more. The secondary winding (for cooling) is distributed over the toroid with a gap, trying to distribute it evenly.

If you have a working autotransformer or you have purchased a new one, then the work is reduced only to rewinding one (secondary) winding, since the primary one is already wound with a wire of the required section and length.

It iterates over in the following sequence:

• first unscrew the metal or plastic casing (if any);
• remove the slider with a graphite current collector;
• remove reinforcement made of non-magnetic material (plastic, aluminum);
• identify (ring tester) and mark all network pins;
• the rest of the wires are wrapped with insulation or PVC tubes are put on them and laid on the side of the LATR perpendicular to the windings;
• then the secondary winding is mounted; turns, diameter and brand of copper wires are similar to the option described above (completely burnt out).

Welding machines, more precisely, their transformers, are recommended to be mounted together. The first person stretches the wire and lays it down, trying not to spoil the insulation and keep the distance between the turns. The second holds the end of the wire, preventing it from twisting.

If the insulation is broken and the ends of at least one turn touch, an interturn short circuit will occur, the transformer will overheat and the device will fail.

Welding machines with such a transformer operate at currents of 55-180 A.

Back to the table of contents

Wiring diagram

Any network-powered design has its own circuit. The above described welding machine also has it.

The rewound transformer is covered with an old casing (if it fits), a new one is prepared or dispensed with. It's not that dangerous. After all, the device has an output potential of no more than 50 V. And it is much easier to cool a transformer without a casing.

The terminals of the transformer windings on your device are connected as follows:

1. Primary (I) - connected to 220 V with a 2-4 mm flexible copper wire (VRP or SHRPS). An automatic switch (Q1) is required - an automatic circuit breaker like those in houses.
2. To the secondary (multi-ampere), carefully insulated, but also flexible, PRG wires of the corresponding section are attached.

One end is attached to the work piece and grounded (for electrical safety). On the other, a ballast resistor (to regulate the output current) and a homemade or standard electrode holder for the apparatus are fixed.

Back to the table of contents

Current regulators

The regulator is a 3-millimeter-gauge wire twisted in a spiral made of constantan or nichrome wire, approximately 5 m long. This is a kind of ballast connected in series to the electric holder circuit.

The spiral is fixed separately on a sheet of asbestos cement. The welding current of the machine can be changed in three ways:

1. Selection method. A large crocodile clip is attached to the regulating end. The current is changed by moving the clamp in a spiral. If the spiral is strengthened only at the ends (or straightened), then the adjustment will be smooth.
2. Switching method. Take the switch. Its common output is connected to the control wire. The rest of the leads are connected to the turns of the spiral. The current is regulated by discrete movement of the slider.
3. Replacement method. The current is changed by choosing electrodes (thick and thin, long and short). Regulation takes place within small limits. This method is almost never applied.

These machines change the welding current by adjusting the secondary winding. A large current is removed from it, therefore, it is unprofitable to change the current using the electronic method. It is necessary to install powerful parts, huge radiators and appropriate cooling.