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

Fig. 1. Homemade welding machine based on LATR.

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

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

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

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

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

Winding is more convenient for two people. While one, trying not to damage the insulation of adjacent turns, carefully pulls and lay the wire, the other holds the free end of the future winding, protecting it from twisting.
The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which a circuit board made of 10 mm getinax or fiberglass with a SB1 packet switch, a thyristor voltage regulator (with a resistor R6), an HL1 light indicator for switching on the device and output terminals for AC welding is placed (X2, X3) or constant (X4, X5) current.

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

At the output of the low-voltage winding, a rectifier unit with power diodes VD3-VD10 is installed for direct current welding. In addition to these valves, more powerful analogs are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).
Power diodes and thyristors are installed on heat sinks, heat sinks, each with an area of ​​at least 25 cm2. The axis of the adjusting resistor R6 is brought out from the casing. A scale with divisions corresponding to specific values ​​of direct and alternating voltage is placed under the handle. And next to it is a table of the dependence of the welding current on the voltage on the secondary winding of the transformer and on the diameter of the welding electrode (0.8-1.5 mm).

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

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

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

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

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

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

Depending on the type and thickness of the metal to be welded, one or another electrode is selected. If, for example, there is a standard assortment for a St3 sheet with a thickness of 1 mm, electrodes with a diameter of 0.8-1 mm are suitable (this is basically the design in question). For welding on 2-mm rolled steel, it is desirable to have a more powerful "welder" and a thicker electrode (2-3 mm).
For welding jewelry made of gold, silver, cupronickel, it is better to use a refractory electrode (for example, tungsten). It is possible to weld less oxidation-resistant metals using carbon dioxide protection.

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

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

Personal safety must also be taken care of. In electric arc welding, try to protect yourself from sparks, and even more so from splashes of molten metal. It is recommended to wear loose-fitting canvas clothing, protective gloves and a mask that protects the eyes from the harsh radiation of an electric arc (sunglasses are not suitable here).
Of course, we must not forget about the "Safety rules when performing work on electrical equipment in networks with a voltage of up to 1 kV". Electricity does not forgive carelessness!

An excellent welding machine can be made on the basis of a laboratory autotransformer LATR and a home-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, to select the required value of the welding current.

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

We need two identical magnetic circuit rings from large LATRs. Latars were produced in the USSR different types with a maximum current of 2 to 10 A. The welding transformer for its manufacture is suitable for those whose magnetic core sizes will make it possible to place 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 ring of the magnetic circuit 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.

The 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 on the sides they are fixed 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 placed 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 together, 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, so 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.

The layers of wire must be insulated from each other. To save space, the winding should be laid as compactly as possible. On a magnetic core made of small rings, the interlayer insulation must be applied thinner, for example, using ordinary tape. Do not rush 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. Wind 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 for each turn of the secondary winding there will be 0.6-0.7 V. 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. Easiest to reel stranded wire 10 mm2 in synthetic insulation. You can collect the 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 CT arms, 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 LATR magnetic circuit 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 strikes very easily at XX voltages, around 50 V or higher, although the arc can be struck 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 ring 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 accounts for 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 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 use soft stranded

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

The operating modes are set to potentiometers. Together with the 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 to the required voltage for welding on alternating or rectified current.

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 area cross section stator, which must be at least 20 cm 2.

In domestic color TVs, large, heavy network transformers were used, 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 down into two halves. For older transformers TS-270, TS-310, the section of the magnetic circuit has dimensions of 2x5 cm, S = 10 cm2, and for newer transformers - TS-270, the section of the magnetopod S = 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 copper wire, a wire may come in handy from their primary windings.

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 use different types transformers: of different capacities included in 220, 380 V according to one or three-phase scheme.

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 AC and DC welding machines. Many of these units have been operating without failures for more than a dozen years.

Homemade AC machines

When assembling, repairing or constructing 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's perfectly acceptable to make them yourself. The schemes of such devices are very different.

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

It is made of transformer strip iron (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 burned-out 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.

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LATR rewind

To replace the windings, proceed as follows:

1. Remove the casing (if any).
2. Remove reinforcement made of non-magnetic material (plastic, aluminum) together with the mechanical part.
3. Get rid of old or burnt out 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 out of 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 of special electrical cardboard.
2. New windings are wound, insulating them from each other;
3. Assemble.

On devices made on the basis of the LATR transformer, only two windings are wound.

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

The primary is performed with a 1.2-mm wire of the PEV-2 type. The approximate length of this piece is 170 m. A shuttle is used for winding. The wire is 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 a wound "primary";
• the edges are chamfered (they are rounded off) to avoid damage to the insulation;
• the 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 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 inter-turn short circuit will occur, the transformer will overheat and the device will fail.

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

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Wiring diagram

Any 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 is 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 copper flexible wire (VRP or SHRPS). An automatic switch (Q1) is required - an automatic switch, 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.

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Current regulators

The regulator is a 3 mm coiled wire made of constantan or nichrome wire about 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 change in current is produced 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 selecting 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 electronically. It is necessary to install powerful parts, huge radiators and adequate cooling.

The homemade welding machine from LATR 2 It is built on the basis of a nine-ampere LATR 2 (laboratory controlled autotransformer) and its design provides for the regulation of the welding current. The presence of a diode bridge in the construction of the welding machine allows direct current welding.

Current regulator circuit for a welding machine

The operating mode of the welding machine is regulated by a variable resistor R5. Thyristors VS1 and VS2 each open in their half-cycle alternately for a certain period of time due to the phase-shifting circuit built on the elements R5, C1 and C2.

As a result, it becomes possible to change the input voltage on the primary winding of the transformer from 20 to 215 volts. As a result of the transformation, an undervoltage appears on the secondary winding, allowing you to easily ignite the welding arc at terminals X1 and X2 when welding with alternating current and at terminals X3 and X4 when welding with direct current.

The welding machine is connected to the mains with an ordinary plug. In the role of switch SA1, you can use a twin 25A machine.

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Alteration of LATR 2 for a homemade welding machine

First, the protective cover, electrical contact and fastener are removed from the autotransformer. Next, good electrical insulation is wound on the existing 250 volt winding, for example, glass cloth, on top of which 70 turns of the secondary winding are laid. For the secondary winding, it is advisable to choose a copper wire with a cross-sectional area of ​​about 20 square meters. mm.

If there is no wire of a suitable cross-section, you can make a winding of several wires with with total area section 20 sq. mm. The modified LATR2 is mounted in a suitable homemade case with ventilation holes. It is also necessary to install a regulator board, a packet switch, as well as terminals for X1, X2 and X3, X4.

In the absence of LATR 2, the transformer can be made homemade by winding the primary and secondary windings on a transformer steel core. The core section should be approximately 50 square meters. see The primary winding is wound with a wire PEV2 with a diameter of 1.5 mm and contains 250 turns, the secondary one is the same which is wound on LATR 2.

At the output of the secondary winding, a diode bridge of powerful rectifier diodes is connected. Instead of the diodes indicated in the diagram, diodes D122-32-1 or 4 VL200 diodes (electric locomotive) can be used. Diodes for cooling must be installed on homemade radiators with an area of ​​at least 30 square meters. cm.

Another important point is the choice of cable for the welding machine. For this welder, it is necessary to use a copper multicore cable in rubber insulation with a cross section of at least 20 sq. Mm. You need two pieces of cable, 2 meters long. Each must be well crimped with terminal lugs to connect to the welding machine.

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 for welding thin sheet metal, in particular, roofing and automotive steel. The welding arc in this case is more stable and at the same time welding can occur both on direct and on reverse polarity of the applied constant voltage.

On direct current, you can weld 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 Principled electrical circuit bridge rectifier of the welding machine, indicating polarity when welding thin sheet metal

To smooth out 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 = 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 choke decreases abruptly and, accordingly, the current will not be smoothed. In this case, the arc will burn unstably. Capacitor C1 is a bank of capacitors such as MBM, MBG or the like with a capacity of 350-400 μF for a voltage of at least 200 V

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

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

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

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

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

The rated welding current must be:

I sv = KK 1 * d e, where

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

K 1 = 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 noted 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 makes it possible 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 = 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 technologically advanced 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 choosing 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 ​​the transverse core (yoke) S = a * b, cm 2.

As practice shows, one should not choose the minimum values ​​of S = 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 of work. To avoid this, the cross-section of the core of the welding machine should be S = 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 of tape transformer iron, rolled into a torus-shaped roll.

Rice. 4 Toroidal magnetic circuit:

To increase the inner diameter of the torus ("window"), 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 (mains) windings of the welding machine, it is better to use a special heat-resistant copper winding wire in cotton or fiberglass insulation. Wires in rubber or rubber-fabric insulation also have satisfactory heat resistance. It is not recommended to use wires in polyvinyl chloride (PVC) insulation for operation at elevated temperatures due to its possible melting, leakage from the windings and short-circuiting of turns. Therefore, PVC insulation from the wires must either be removed and the wires wrapped along the entire length of cotton insulating tape, or do not remove at all, but wrap the wire 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 = I sv * U sv... If welding is carried out with an electrode de = 4 mm, at a current of 130 ... 160 A, then the power of the secondary winding will be: Р 2 = 160 * 24 = 3.5 ... 4 kW, and the power of the primary winding, taking into account losses, will be of the order of 5 ... 5.5 kW... Based on this, the maximum current in the primary winding can reach 25 A... Therefore, the cross-sectional area of ​​the wire of the primary winding S 1 must be at least 5..6 mm 2.

In practice, it is advisable to take the cross-sectional area of ​​the wire 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 = (3.14 * D 2) / 4 or S = 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 cross-section. When using an aluminum wire, its cross-section must be increased by a factor of 1.6 ... 1.7.

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

W 1 = (k 2 * S) / U 1, where

k 2 - constant coefficient;

S- cross-sectional area of ​​the yoke in cm 2

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

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

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

The secondary winding W 2 must contain 65 ... 70 turns of an 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 winding.

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 (eg clockwise).
• Each layer of the winding is insulated with a layer of cotton insulation (fiberglass, electrical cardboard, tracing paper), preferably impregnated with bakelite varnish.
• The terminals of the windings are tinned, marked, secured with cotton tape, and a cotton cambric is additionally put on the terminals of the network winding.
• If the insulation of the wire is of poor quality, winding can be done in two wires, one of which is a cotton cord or 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 ( Rice. 6 a, b)

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

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

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

If the welding machine hums strongly, and the 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 heat up and not 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 arc stability in 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.

Winding the windings of the welding machine on a toroidal core can also be done in several ways ( Rice. 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 pipes 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, set the welding machine 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. Connection diagram measuring instruments shown on ( Rice. eight)

Rice. eight Schematic diagram connecting measuring devices when setting up the welding machine

When welding with various electrodes, the values ​​of 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 ​​are set, or the number of turns of the secondary winding is redistributed (without increasing them) in the direction of increasing 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, choose optimal modes welding for electrodes of various diameters, bearing in mind that when welding with electrodes, for example, 3 mm in diameter, electrodes with a diameter of 2 mm can be cut, because cutting current is more than welding current by 30 ... 25%.

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

The diameter of the electrode, depending on the thickness of the metal to be welded, can be selected based on the following ratio: de = (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 length of the arc leads to a violation of the stability of its combustion, an increase in losses for waste and spattering, 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 part and the minus (cathode) is connected 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 comply with 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. unusual shape magnetic circuit, thanks to which the weight of the entire device is only 9 kg, and the dimensions are 125x150 mm ( Rice. 9).

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 transformer core, you can use a 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, it is necessary to take into account the coincidence of the directions of the currents in the secondary winding. Then it turns out something similar to a welding machine, although it cooks, like all toroidal ones, a little harsh.

You can use a torus-shaped magnetic core from a burnt-out laboratory transformer. In the latter case, first remove the fence and fittings from the Latra and remove the burnt winding. The cleaned magnetic circuit, if necessary, is rewound (see above), insulated with an electric cardboard or two layers of varnished cloth and the transformer windings are wound. The welding transformer has only two windings. For winding the primary winding, a piece of PEV-2 wire with a length of 170 m, a diameter of 1.2 mm ( Rice. 10)

Rice. 10 Winding the windings of the welding machine:

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 electrical diagram of the welding machine is shown on rice. eleven.

Rice. 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 fastening fittings 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))

Rice. 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 carried out by connecting in series to the wire circuit of the electrode holder pieces of nichrome or constantan wire d = 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 = 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 = 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).

Rice. thirteen General view of the welding machine and its core.

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

3.1. Details.

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

Rice. 14 The design of the terminal of the secondary winding of the welding machine.

On one side, it should be riveted and a hole d 10 mm should be 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 new screws and nuts made of copper. The terminals of the secondary winding are connected to them.

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

Rice. 15 General view of the scarves for the conclusions of the primary winding of the welding machine.

10 ... 11 holes d = 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.

Rice. 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 out recesses with a hacksaw half the diameter of the pipe ( fig. 18)

Rice. eighteen Drawing of the body of the electrode holder from the pipe d¾ "

A piece of steel wire d = 6 mm is welded to the pipe above the large recess. A hole d = 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 of two steel corners 25x25x4 mm ( rice. nineteen)

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

Cover the handle of the resulting holder insulating material, which is used as a cut of a 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 adjusting the current in welding transformers are known: shunting with the help of 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 of these methods have both advantages and disadvantages. For example, the disadvantage of the latter method is the complexity of the design, the bulkiness of the resistances, their strong heating during operation, and the inconvenience when switching.

The most optimal is the method of stepwise current regulation, by changing the number of turns, for example, by connecting to the taps made when winding the secondary winding of the transformer. However, this method does not allow the current adjustment over a wide range, 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 ​​placing a welding current regulator in the primary winding of the transformer, using thyristors for this purpose. In fig. 20 shows a diagram of a thyristor-based 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 value of the current decreases. The main elements of the regulator (thyristors) are connected oppositely and parallel to each other. They alternately open with current pulses generated by transistors VT1, VT2.

When the regulator is connected to the network, both thyristors are closed, 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)

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

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

Transistors of the old type P416, GT308 have proven themselves well as VT1, VT2, but 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 using surface-mounted assembled on a textolite plate 1 ... 1.5 mm thick. The device has a galvanic connection with the mains, therefore all elements, including thyristor heatsinks, 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 structures 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 - many GOSTs, schemes how homemade devices and factory

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

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