How to make a welding machine. Homemade welding machine at home. electric motor welder

It's no secret that a do-it-yourself welding machine for a person familiar with electrical engineering is not so difficult to make. This makes sense especially if it is intended for use in a personal household, where it is used only from time to time. In this case, a home-made welding machine, the cost of which is much lower than the factory one, is quite capable of replacing it. Parts for its design can be freely removed from various electrical household devices that have failed or, if necessary, manufactured and assembled by yourself. Schemes of such devices can be different. The decisive factor here is usually the availability of parts and materials.

Choosing the Right Welding Machine

All electric arc welding machines are divided into inverter and transformer. It should be noted right away that the question of how to make a welding machine on your own depends largely on the ability to get parts from a certain household appliances. If all parts are purchased at market prices, then as a result, the cost will approach the price of a branded device, yielding to it in efficiency. That is why you need to have certain knowledge in the field of electrical engineering and know where which part is placed and where it can be removed for free or for a small price.

The number of turns on the primary winding should be about 240. At the same time, several taps are made to allow adjustment of the welding current in increments of 20 to 25 turns. The secondary winding is wound with copper wire with a cross section of 30 to 35 mm in an amount of 65 to 70 turns. To adjust the welding current on it, you also need to make taps. The insulation of the secondary winding must be especially reliable and heat-resistant, so it should be given Special attention. Each of the layers must be laid with additional insulation made of cotton fabric.

The transformer welding machine can use alternating or direct current for operation. The first of them is the simplest in terms of device, but more difficult to use. For direct current it is quite easy to modify it by installing a diode bridge. Such a device is reliable, durable and unpretentious in use, but it has a significant weight and is sensitive to voltage drops in the mains. If it drops below 200 V, it becomes very difficult to start and maintain an electric arc.

Unlike a transformer inverter welding machine, due to the use of modern electronic parts, it has a relatively small weight. It can be worn on the shoulder by one person. Such a device has a current stabilization device, which greatly facilitates the work during welding. Reducing the voltage for it practically does not create interference, and it can operate from a household power outlet. However, the inverter apparatus is very sensitive to overheating and requires great care in operation, otherwise it easily fails.

Assembly of the transformer welding machine

The main part of such an apparatus is a transformer. Its main characteristic should be the ability to stably keep the operating current, and this is based on such an indicator as the external current-voltage characteristic of the power supply. In other words, the welding current should not differ significantly from the current produced by the short circuit.

To do this, the current must be limited in one of such ways as increasing the magnetic leakage of the transformer, ballast resistance or installing a choke. The transformer itself can be removed from a burnt high-frequency microwave oven. If there is no access to it, then you can make a welding transformer with your own hands.

To make the core, you need to purchase transformer iron plates. The core area should ideally be from 40 to 55 cm², with such indicators the winding will not overheat unnecessarily. Primary windings for self-made welding transformers should consist of thick heat-resistant copper wire with a cross section of at least 5 mm, and preferably more, enclosed in fiberglass or cotton insulation. Plastic or rubber insulation is not recommended for such purposes, since it is less resistant to overheating and breaks through more easily, which causes a short circuit in the primary winding.

It must be remembered that the secondary winding of the welding transformer must be wound on both sides of the core. It can be connected either in series or in anti-parallel. It must be remembered that the winding must be carried out on both sides in the same direction. After that, the transformer is placed in a metal case. Holes are cut from its end to cool the apparatus, and placed exhaust fan taken from the power supply of an obsolete or broken computer. On the opposite side of the case, several dozen holes are drilled for air circulation. The cables and the electrode holder can then be connected.

How to assemble a homemade inverter welding machine?

An inverter welding machine can be completely assembled from parts from old TVs. This requires not only some general electrical knowledge, but also some knowledge of electronics. Its scheme is rather complicated. The inverter is a pulsed DC source, and for its manufacture, several ferrite cores are suitable, which are on horizontal transformers in old TVs. They are stacked in threes, and a winding of copper or aluminum wire is already wound on them.

Since the primary winding is most susceptible to overheating, small gaps must be left between the turns to facilitate the cooling process. It is worth remembering that aluminum wire must be taken with a larger cross section than copper, since its thermal conductivity is lower. To fix the inverter windings, a wire bandage made of 10 mm wide copper wire, superimposed on fiberglass insulation, is used.

Capacitors can also be removed from the TV, but just remember that it is not recommended to take paper capacitors from low-frequency circuits, since they will not be able to work for a long time under such loads. SCRs are better to take rather low-power ones and connect them in parallel than to take one powerful one, since a large thermal load falls on them and it is easier to cool them. SCRs are mounted on a metal plate with a thickness of at least 3 mm, which facilitates the removal of excess heat. Diodes for assembling a diode bridge can also be easily dialed from several old TVs. The bridge itself is also mounted on a heat sink plate.

Some parts for the inverter apparatus are not available on TVs, and they have to be made independently. First of all, it's a throttle. It is easy to make it without a frame of copper wire with a cross section of at least 4 mm, wound with 11 turns at intervals of at least 1 mm. Since the main thermal load will fall on the throttle, you need to put additional system air cooling. In this capacity, it is quite possible to use an ordinary household fan mounted in the body of the welding machine in such a way that the air stream hits the throttle directly.

All elements of the electronic circuit are assembled on printed circuit board from fiberglass with a thickness of at least 1.5 mm. A heat sink is attached to the board itself, which facilitates cooling of the entire system. cut out in the center of the board round hole to install a fan, because without forced air cooling the device will not work for a long time. The main advantage of the welding inverter is the ability to do mini-welding, welding thin metal sheets. The welding seam itself comes out more accurate than that of a transformer apparatus. This is crucial for such a type of work as do-it-yourself car repair.

A do-it-yourself welding machine includes parts obtained for free or at a bargain price, but it does its job quite well.

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

However, to make it, you need to have a clear idea for what, for what work it will be used.

A home-made device is completed and assembled from available components and parts. As an option for craftsmen, a plasma mechanism can also be considered.

Practice shows that with an accurate selection of components, the device will serve for a long time and reliably.

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

The device must be operated from a 220 V AC household mains.

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

Structural diagram of the welding machine

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

The circuit of any apparatus includes a transformer (it is possible to use a transformer from a microwave oven), a rectifier, a choke, a holder, an electrode. It is in this sequence that the flow occurs electric current along a closed circuit.

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

In order for the quality of the welded joint to be high, it is necessary to ensure stable burning of this arc.

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

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

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

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

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

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

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

Approximately this value is required for welding. In principle, this device can be called the simplest welding machine.

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

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

The transformer is considered the main element of the welding machine. It can be bought or adapted already used.

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

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

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

A home-made inverter apparatus can be arranged in such a way that it has minimal dimensions and weight.

Such devices, designed for use in the household, are now sold in stores.

The advantages of the inverter apparatus over traditional units are obvious. First of all, it should be noted the compactness of the device, ease of use, reliability.

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

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

The main elements, in practice, can always be found among electrical machines and devices that ended up in storerooms. Or in a landfill.

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

Radio amateurs came up with the simplest pulse welding method according to the scheme. It is used to attach wires to a metal board.

No complicated fixtures - just a choke and a couple of wires. The current regulator is also not needed. Instead, a fusible link is included in the circuit.

One electrode is connected to the board through a choke.

As the second, a crocodile clip is used. The plug with wires is included in the socket of a household network.

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

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

Product package

Homemade is going to do small jobs in the household.

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

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

If the throttle in finished form could not be found, then it must be made independently.

This will require a steel magnetic circuit from an old starter and several meters of copper wires with a cross section of 0.9 squares.

power unit

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

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

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

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

The spot welding method is well implemented by an apparatus made on a microwave transformer.

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

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

Diodes are selected with such power to withstand the initially specified loads. For their cooling, special radiators made of aluminum alloys are used.

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

Inverter block

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

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

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

These current parameters allow you to weld metal parts from various alloys.

The electronic regulator allows you to select the mode corresponding to a particular operation.

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

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

While craftsmen have long been able to make a do-it-yourself plasma welding machine.

This step was prompted by local conditions - tightness in the workshop and the significant weight of factory inverters. A plasma machine is a great way out of this situation.

And the fact that instead of copper wires the secondary winding of the transformer is made of copper sheet has also long been known.

Assembly sequence of the welding machine

When placing elements on a metal or textolite basis, a certain order must be observed. The rectifier must be located near the transformer.

The inductor is on the same board as the rectifier. The current regulator must be located on the control panel. The body of the apparatus can be made of sheet steel or aluminium.

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

It is imperative to make holes in the walls for the installation of cooling fans and a constant flow of air.

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

1. What will we be about
2. What we won't talk about
3. Transformer
4. Trying a constant
5. microarc
6. Contact! There is a contact!

Do-it-yourself welding in this case does not mean welding technology, but home-made equipment for electric welding. Work skills are acquired through work experience. Of course, before going to the workshop, you need to learn the theoretical course. But it can only be put into practice if you have something to work on. This is the first argument in favor of, independently mastering the welding business, first take care of the availability of appropriate equipment.

The second - a purchased welding machine is expensive. Rent is also not cheap, because. the probability of its failure with unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be just long and difficult. All in all, it is better to start the first steps in metal welding with the manufacture of a welding machine with your own hands. And then - let him stand in a barn or garage until the case. It's never too late to spend money on branded welding, if things go well.

What will we be about

This article discusses how to make equipment at home for:

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

What we won't talk about

First, skip the gas welding. Equipment for it costs pennies compared to consumables, gas cylinders cannot be made at home, and a home-made gas generator is a serious risk to life, plus carbide is now, where it is still on sale, expensive.

The second is inverter arc welding. Really, welding inverter- a semi-automatic device allows a novice amateur to cook quite responsible designs. It is light and compact and can be carried by hand. But the retail purchase of inverter components, which allows you to consistently conduct a high-quality seam, will cost more than a finished device. And with simplified homemade products, an experienced welder will try to work, and refuse - “Give me a normal device!” Plus, or rather minus - to make a more or less decent welding inverter, you need to have a fairly solid experience and knowledge in electrical engineering and electronics.

The third is argon-arc welding. From whose light hand the assertion that it is a hybrid of gas and arc went for a walk 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 the air. As a result, the welding seam is chemically clean, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be boiled under argon, incl. heterogeneous. 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.

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

Transformer

The basis of all "our" types of welding is a welding transformer. The procedure for its calculation and design features significantly differ from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like continuous transformers, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electrical transformers for arc welding is the main reason for the 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 zaumi;
2. features of the magnetic circuits of welding transformers with recommendations for choosing from randomly turned up ones;
3. testing of available second-hand;
4. calculation of a transformer for a welding machine;
5. preparation of components and winding of windings;
6. trial assembly and fine-tuning;
7. commissioning.

Theory

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

Note: the difference is in evaporation losses and, accordingly, magnetic field scattering. 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 (VVC) of the transformer, or simply its external characteristic(VH) - dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, the VX is rigid (curve 1 in the figure); they are like a shallow vast pool. If it is properly insulated and covered with a roof, then 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 paddles, the water is drained. With regard to transformers, the power man must keep the output voltage as stable as possible up 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, winding configuration and arrangement) 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 transfer of the current form, because. its distortion reduces the efficiency.

Note: transformer steel with "angular" hysteresis is often referred to as magnetically hard. This is not true. Hard magnetic materials retain strong residual magnetization, they are made permanent magnets. And any transformer iron is magnetically soft.

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 the electrode in the wrong way, it goes out. Therefore, the welding transformer is already made similar to a conventional water tank. Its VC is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage drops smoothly. The normal scattering 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 size of the transformer. In this case, the induction in the core can reach the saturation value, and even exceed it for a short time: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: thermal time constant of welding transformers 20-40 min. 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? U2 (corresponding to the range of the arrows in the figure) of normal dissipation increases smoothly with an increase in the range of oscillations of the welding current Iw, which makes it easy to hold the arc in any type of work. These properties are provided as follows:

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

Note: reversible scattering loss means that part of the lines of force penetrates the secondary through the air, bypassing the magnetic circuit. The name is not entirely successful, as well as "useful scattering", because. "Reversible" losses are no more useful for the efficiency of a transformer than irreversible ones, but they soften the VX.

As you can see, the conditions are completely different. So, is it necessary to look for iron from a welder? Optional, for currents up to 200 A and peak power up to 7 kVA, and this is enough on the farm. By calculation and constructive measures, as well as with the help of simple additional devices (see below), we will obtain, on any hardware, a BX curve 2a that is somewhat more rigid than the normal one. Energy Consumption Efficiency welding in this case is unlikely to exceed 60%, but for episodic work for yourself this is not scary. But on fine work and low currents, it will not be difficult to hold the arc and the welding current, without having much experience (? U2.2 and Isv1), at high currents Isv2 we will get an acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

• According to the formula from paragraph 2 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 the iron. True, in the 1st case, the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
• We calculate the operating current of the primary at the maximum network voltage allowed for welding I1rmax \u003d 1.1Pg (VA) / 235 V. In general, the norm for the network is 185-245 V, but for a home-made welder at the limit, this is too much. We take 195-235 V;
• Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
• We accept the current density of the primary J1 = 5 A/sq. mm and, using I1rmax, we find the diameter of its copper wire d = (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation D = 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, mortar yok" 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 of the primary: w = k2 / Sс, where k2 = 50 for W and P, k2 = 40 for PL, SHL and k2 = 35 for O, OL;
• We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy losses of the winding due to leakage and in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
• We set the stacking factor Ku = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of winding layers, the average length of the coil and the wire footage
• We calculate the secondary in the same way at J1 = 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

The diameters of the wires in the calculation of the windings are usually obtained more than 3 mm, and varnished winding wires with d> 2.4 mm are rare in wide sale. In addition, the welder's windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSh, PELSHO, PB, PBD. Finding them is even more difficult, and they are very expensive. The footage of the wire per welder is such that cheaper bare wires can be insulated on their own. An additional advantage is that by 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 on the frame at least 10 squares will appreciate it.

isolation

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

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

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

winding

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

• We are preparing a wooden boss with a height in winding height 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 film with a call on 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;
• After winding, we impregnate twice until it flows through with liquid varnish;
• after the impregnation dries, carefully remove the cheeks, squeeze out the boss and tear off the film;
• we tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.

Finishing and domotka

We shift the core into a biscuit and tighten it with bolts, as expected. The winding tests are carried out in exactly the same way as those of the dubious 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 more, the primary is homemade. 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 Ixx got back to normal at 216. Then we multiply the calculated turns of the secondary sections by 216/210 = 1.03 approx. Do not neglect the decimal places, the quality of the transformer largely depends on them!

After finishing, we disassemble the core; we tightly wrap the biscuit with the same masking tape, calico or “rag” electrical tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now once again impregnate 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 for Ixx (suddenly it curled somewhere), fix the biscuits and impregnate the entire transformer with normal varnish. Phew, the most dreary part of the work is over.

Pull VX

But he is still too cool with us, remember? Needs to be softened. The simplest way - a resistor in the secondary circuit - does not suit us. Everything is very simple: at a resistance of only 0.1 ohms at a current of 200, 4 kW of heat will be dissipated. 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 when the arc is ignited are inevitable. Without an active ballast, they will burn the seam in places, and the resistor will extinguish them. But to us, low-powered ones, he will not be of any use to him.

The reactive ballast (inductor, 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 dissipation control. And for him - the core is almost the same as that of the transformer, and rather complex mechanics, see fig.

We will go the other way: we will use an active-reactive ballast, colloquially referred to as the gut by old welders, 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 connected to it with a clip-clothespin. By selecting the connection point, it is possible, together with switching to secondary outlets, to fine-tune the operating mode of the arc.

Note: an active-reactive inductor can get red hot in operation, so it needs a fireproof, heat-resistant, non-magnetic dielectric lining. In theory, a special ceramic lodgment. It is acceptable to replace it with a dry sand cushion, or already formally with a violation, but not rough, the welding gut is laid on bricks.

But other?

This means, first of all, an electrode holder and a connection device for the return hose (clamp, clothespin). They, since we have a transformer at the limit, need to be bought ready-made, but such as in fig. right, don't. For a 400-600 A welding machine, the quality of the contact in the holder is not very noticeable, and it will also withstand simply winding the return hose. And our self-made, working with an effort, can go wrong, it seems to be unclear why.

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

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

Trying a constant

DC welding has a number of advantages, but the VX of any DC welding transformer is tightened. And ours, designed for the minimum possible power reserve, will become unacceptably tough. The inductor-gut will not help here, even if it worked on direct current. In addition, expensive 200 A rectifier diodes must be protected from current and voltage surges. We need a return-absorbing filter of infra-low frequencies, Finch. Although it looks reflective, you need to take into account the strong magnetic connection between the halves of the coil.

The scheme of such a filter, known for many years, is shown in Fig. But immediately after its introduction by amateurs, it turned out that the operating voltage of the capacitor C is small: voltage surges during ignition of the arc can reach 6-7 values ​​of its Uхх, i.e. 450-500 V. Further, capacitors are needed to withstand the circulation of large 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 ​​the following. fig., and the battery will need 100-200 of them.

With a magnetic circuit, the coil is simpler, although not quite. For it, 2 PLA of the TS-270 power transformer from old tube TVs-"coffins" (the data is available in reference books and in Runet), or similar, or SL with similar or large a, b, c and h. From 2 PLs, a SL is assembled 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 middle point.

The filter is adjusted along the arc at the minimum and maximum Uхх values. If the arc is sluggish at the minimum, the electrode sticks, the gap is reduced. If the metal burns at the maximum, increase it or, which will be more efficient, cut off part of the side rods symmetrically. So that the core does not crumble from this, it is impregnated with liquid, and then with normal varnish. Finding the optimum inductance is quite difficult, but then welding works flawlessly on alternating current.

microarc

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

Now more computer power supplies are used for microarc welding, or, for pulsed microarc welding, capacitor banks, see the video below. At 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!

Contact welding in industry is mainly used for spot, seam and butt welding. At home, primarily in terms of energy consumption, a pulsed point is feasible. It is suitable for welding and welding thin, from 0.1 to 3-4 mm, steel sheet parts. arc welding it will burn through a thin wall, and if the 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 parts with force, a current pulse in the steel-steel ohmic resistance zone heats the metal to the point where electrodiffusion occurs; metal does not melt. This requires approx. 1000 A per 1 mm thickness of the parts to be welded. Yes, a current of 800 A will grab sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, say, a galvanized corrugated fence, then the very first strong gust of wind will remind you: “Man, the current was rather weak!”

However, resistance spot welding is much more economical than arc welding: voltage idle move welding transformer for it - 2 V. It consists of 2 contact potential differences steel-copper and ohmic resistance of the penetration zone. A transformer for contact welding is calculated similarly to it for arc welding, but the current density in the secondary winding is 30-50 or more A / sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, it cools well, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

In RuNet there are many descriptions of home-made pulsed spot welders from unusable microwaves. They are, in general, correct, but in repetition, as it is written in "1001 Nights", there is no use. And old microwave ovens don't lie around in heaps. Therefore, we will deal with less well-known designs, but, by the way, more practical.

On fig. - the device of the simplest apparatus for pulsed spot welding. They can weld sheets up to 0.5 mm; for small crafts, it fits perfectly, and magnetic cores of this and larger sizes are relatively affordable. Its advantage, in addition to simplicity, is the clamping of the welding tongs running rod with a load. A third hand would not hurt to work with a contact welding impulse, and if one has to squeeze the tongs with force, then it is generally inconvenient. Disadvantages - increased accident and injury hazard. If you accidentally give an impulse when the electrodes are brought together without welded parts, then plasma will strike from the tongs, metal splashes will fly, the wiring protection will be knocked out, and the electrodes will fuse tightly.

The secondary winding is made of a 16x2 copper bus. It can be made from strips of thin sheet copper (it will turn out flexible) or made from a segment of a flattened refrigerant supply pipe for a domestic air conditioner. The tire is isolated manually, as described above.

Here in fig. - drawings of a pulsed spot welding machine are more powerful, for welding a sheet up to 3 mm, and more reliable. Thanks to a fairly powerful return spring (from the armored mesh of the bed), accidental convergence of the pliers is excluded, and the eccentric clamp provides 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 on the eccentric lever. The disadvantage is the insulating knots of the pliers, there are too many of them and they are complex. Another one is aluminum pincer bars. Firstly, they are not as strong as steel ones, and secondly, these are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.

About electrodes

In amateur conditions, it is more expedient to isolate the electrodes at the installation site, as shown in fig. on right. There is no conveyor at home, the apparatus can always be allowed to cool down so that the insulating sleeves do not overheat. This design will make it possible to make rods from a durable and cheap steel professional pipe, and also extend the wires (up to 2.5 m is acceptable) and use a contact welding gun or remote tongs, see fig. below.

On fig. On the right, one more feature of electrodes for resistance spot welding is visible: a spherical contact surface (heel). Flat heels are more durable, so electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 thicknesses of the adjacent welded material, otherwise the penetration spot will burn 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 point about the electrodes is their material and dimensions. Red copper quickly burns out, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, at current copper prices it is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. The length of the electrode according to the conditions of heat transfer is at least 3 of its diameters from the heel to the root (beginning of the shank).

How to give impetus

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

A diagram of a simple, but reliable and long-term proven welding pulse shaper is shown in fig. Auxiliary transformer T1 is a conventional power transformer for 25-40 watts. Winding voltage II - according to the backlight. Instead of it, you can put 2 LEDs connected in anti-parallel with a quenching resistor (normal, 0.5 W) 120-150 Ohms, then the voltage II will be 6 V.

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

Finally

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

Video: do-it-yourself welding in 15 minutes (on saline solution)

It is very convenient to work in any metal processing workshop if you have a welding machine at hand. With it, you can securely connect metal parts or structures, cut holes, or even simply cut blanks in the right place.

Such useful tool you can do it yourself, the main thing is to understand everything well, and the skill to make beautiful and reliable seam will come with experience.

AC output current

At home, in the country, at work, such devices are most often found. Many photos of welding equipment show that it is made by hand.

The most important components for such an apparatus are a wire for two windings and a core for them. In fact, this is a transformer for lowering the voltage.

Wire dimensions

The device will work quite well with an output voltage of 60 volts and a current of up to 160 amperes. Calculations show that for the primary winding, you need to take a copper wire with a cross section of 3, and preferably 7 square millimeters. For aluminum wire, the cross section should be 1.6 times larger.

Wire insulation must be fabric because the wires get very hot during operation and the plastic will simply melt.

It is necessary to lay the primary winding very carefully and carefully because it has many turns and is located in a high voltage zone. It is desirable that the wire be without breaks, but if desired length not at hand, then the pieces must be securely connected and soldered.

Secondary winding

For the secondary winding, you can take copper, or aluminum. The wire can be either single-core or consisting of several conductors. Cross section from 10 to 24 square millimeters.

It is very convenient to wind the coil separately from the core, for example, on a wooden blank, and then collect transformer steel plates into a finished, reliably insulated winding.

stranded wire

How to make a stranded wire of a suitable cross section for a welding machine? There is such a way. At a distance of 30 meters (more or less, depending on the calculations), two hooks are securely attached. Between them, the required amount of thin wire is stretched, from which a stranded conductor will be composed. Then one end is removed from the hook and inserted into an electric drill.

At low speeds, the wire bundle twists evenly, its total length will decrease somewhat. Clean the ends of the wire (separately each core), tin and solder well. Then insulate the entire wire, preferably with a textile-based insulating material.

Core

Good performance is shown by home-made welding machines based on transformer steel cores. They are recruited from plates with a thickness of 0.35-0.55 millimeters.

It is important to choose the right size of the window in the core so that both coils fit in it, and the cross-sectional area (its thickness) is 35-50 square centimeters. Bolts are installed at the corners of the finished core, and everything is tightly tightened with nuts.

The primary winding consists of 215 turns. To be able to regulate the welding current of the finished machine, conclusions can be drawn from winding on 165 and 190 turns.

All contacts are mounted on a plate made of insulating material and sign. The scheme is as follows: the more turns of the coil, the greater the current at the output. The secondary winding consists of 70 turns.

inverter

You can assemble another welding device with your own hands - this is an inverter. It has a number of positive differences from the transformer. The very first thing that catches your eye is its light weight. Just a few kilos. You can work without removing the device from your shoulder. Then, working direct current, this allows you to create a more accurate seam, and the arc does not jump so much. Easier for beginner welders.

Parts for assembling such a device are sold in stores and on the market. You just need to know the label. The quality of the transistors requires special attention because they are in the most stressed area of ​​​​the inverter design circuit. To cool the device, forced ventilation is used in the form of cooling radiators and exhaust fans.

Thus, if you compile a catalog of home-made welding machines, you will get a long list of transformers of various designs, inverters, semi-automatic welding machines and automatic machines. Such devices allow you to work with cast iron and steel, aluminum and copper, stainless steel and thin sheet iron.

The reliability and durability of their work depends on the accuracy of calculations, the availability of materials, parts, correct assembly, as well as compliance with safety rules at all stages of the creation and operation of such devices.

Photo of a welding machine at home

Figure 1. Scheme of a bridge rectifier for a welding machine.

Welding machines are of direct and alternating current.

S.A. direct current are used for welding at low currents of thin sheet metal (roofing steel, automotive, etc.). DC welding arc is more stable, direct and reverse polarity welding is possible. At direct current, it is possible to cook with electrode wire without coating and electrodes intended for welding, both at direct current and at alternating current. To make the arc burning stable at low currents, it is desirable to have an increased open-circuit voltage Uxx of the welding winding (up to 70 - 75 V). To rectify alternating current, the simplest "bridge" rectifiers on powerful diodes with cooling radiators are used (Fig. 1).

To smooth out voltage ripples, one of the conclusions of S.A. A is connected to the electrode holder through the L1 choke, which is a coil of 10 - 15 turns of a copper bus with a cross section of S = 35 mm 2, wound on any core, for example, from. For rectification and smooth regulation of the welding current, more complex circuits are used using powerful controlled thyristors. One of the possible circuits based on thyristors of the T161 (T160) type is given in the article by A. Chernov “And it will charge and weld” (Model designer, 1994, No. 9). The advantage of DC regulators is their versatility. The range of voltage change by them is 0.1-0.9 Uxx, which allows them to be used not only for smooth adjustment of the welding current, but also for charging batteries, power supply of electric heating elements and other purposes.

Figure 2. Scheme of the falling external characteristic of the welding machine.

Rice. 1. Bridge rectifier for welding machine. S.A. connection shown. for welding thin sheet metal on the "reverse" polarity - "+" on the electrode, "-" on the workpiece to be welded U2: - output alternating voltage of the welding machine

AC welding machines are used for welding with electrodes whose diameter is more than 1.6 - 2 mm, and the thickness of the welded products is more than 1.5 mm. In this case, the welding current is significant (tens of amperes) and the arc burns quite steadily. Electrodes designed for welding only on alternating current are used. For normal operation of the welding machine, it is necessary:

1. Provide output voltage for reliable arc ignition. For amateur S.A. Uxx \u003d 60 - 65v. A higher no-load output voltage is not recommended, which is mainly due to the safety of operation (Uxx industrial welding machines - up to 70 - 75 V).
2. Provide the welding voltage Usv necessary for stable arc burning. Depending on the diameter of the electrode - Usv \u003d 18 - 24v.
3. Ensure the rated welding current Iw = (30 - 40) de, where Iw is the value of the welding current, A; 30 - 40 - coefficient depending on the type and diameter of the electrode; de - electrode diameter, mm.
4. Limit the short-circuit current Ikz, the value of which should not exceed the rated welding current by more than 30 - 35%.

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

S.A. shows that for a rough (stepped) overlapping of the range of welding currents, it is necessary to switch both the primary windings and the secondary ones (which is structurally more difficult due to the large current flowing in it). In addition, mechanical devices for moving the windings are used to smoothly change the welding current within the selected range. When the welding winding is removed relative to the mains, the leakage magnetic fluxes increase, which leads to a decrease in the welding current.

Figure 3. Scheme of a rod-type magnetic circuit.

When designing an amateur S.A., one should not strive to completely cover 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, supplement it with a separate rectifier device with smooth regulation of the welding current. Amateur welding machines must meet a number of requirements, the main of which are the following: relative compactness and low weight; sufficient duration of operation (at least 5 - 7 electrodes de = 3 - 4 mm) from a 220v network.

The weight and dimensions of the device can be reduced by reducing its power, and increasing the duration of operation by using steel with high magnetic permeability and heat-resistant insulation of the winding wires. These requirements are easy to meet, knowing the basics of designing welding machines and adhering to the proposed technology for their manufacture.

Rice. 2. Falling external characteristic of the welding machine: 1 - a family of characteristics for different welding ranges; Iw2, Iwv, Iw4 - ranges of welding currents for electrodes with a diameter of 2, 3 and 4 mm, respectively; Uxx - no-load voltage of SA. Ikz - short circuit current; Ucv - welding voltage range (18 - 24 V).

Rice. 3. Rod-type magnetic circuit: a - L-shaped plates; b - plates U-shaped; c - plates from strips of transformer steel; S \u003d axb- cross-sectional area of ​​\u200b\u200bthe core (core), cm 2 s, d- window dimensions, cm.

So, the choice of 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 is recruited from electrical steel plates of any configuration with a thickness of 0.35-0.55 mm, tightened with studs isolated from the core (Fig. 3). When selecting the core, it is necessary to take into account the dimensions of the "window" to fit the windings of the welding machine, and the cross-sectional area of ​​​​the core (core) S =axb, cm 2. As practice shows, the minimum values ​​\u200b\u200bS = 25 - 35 cm should not be chosen, since the welding machine will not have the required power reserve and it will be difficult to obtain high-quality welding. Yes, and overheating of the welding machine after a short operation is also inevitable.

Figure 4. Scheme of a toroidal type magnetic circuit.

The cross section of the core should be S = 45 - 55 cm 2. The welding machine will be somewhat heavier, but will not let you down! Amateur welding machines on toroidal-type cores are becoming more widespread, which have higher electrical characteristics, about 4-5 times higher than those of the rod, and electrical losses are small. The labor costs for their manufacture are more significant and are associated primarily with 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 roll in the shape of a torus. An example is the core from the autotransformer "Latr" by 9 A. To increase the inner diameter of the torus ("window"), a part is unwound from the inside steel tape and wound on the outer side of the core. But, as practice shows, one "Latra" is not enough for the manufacture of high-quality S.A. (small section S). Even after working with 1 - 2 electrodes with a diameter of 3 mm, it overheats. It is possible to use two similar cores according to the scheme described in the article by B. Sokolov "Welding Kid" (Sam, 1993, No. 1), or to manufacture one core by rewinding two (Fig. 4).

Rice. 4. Toroidal type magnetic circuit: 1.2 - autotransformer core before and after rewinding; 3 design S.A. based on two toroidal cores; W1 1 W1 2 - network windings connected in parallel; W 2 - welding winding; S =axb- cross-sectional area of ​​the core, cm 2, s, d- inner and outer diameters of the torus, cm; 4 - electrical circuit S.A. based on two joined toroidal cores.

Amateur S.A., made on the basis of stators of asynchronous three-phase electric motors of high power (more than 10 kW), deserve special attention. The choice of the core is determined by the cross-sectional area of ​​the stator S. The stamped stator plates do not fully correspond to the parameters of electrical transformer steel, therefore it is not advisable to reduce the cross section S to less than 40 - 45 cm.

Figure 5. Scheme of fastening the leads of the SA windings.

The stator is freed from the body, the stator windings are removed from the internal grooves, the groove jumpers are cut with a chisel, the inner surface is protected with a file or an abrasive wheel, the sharp edges of the core are rounded and wrapped tightly, with an overlap of cotton insulating tape. The core is ready for winding windings.

Winding selection. For primary (network) windings, it is better to use a special copper winding wire in cotton. (fiberglass) insulation. Satisfactory heat resistance is also possessed by wires in rubber or rubber-fabric insulation. Unsuitable for operation at elevated temperatures (and this is already being incorporated into the design of an amateur S.A.) wires in polyvinyl chloride (PVC) insulation due to its possible melting, leakage from the windings and their short circuit. Therefore, PVC insulation from the wires must either be removed and wrapped around the wires along the entire length of the coil. with insulating tape, or do not remove, but wrap the wire over the insulation. Another proven method of winding is also possible. But more on that below.

When selecting the section of the winding wires, taking into account the specifics of the work of S.A. (periodic) allow a current density of 5 A / mm 2. At a welding current of 130 - 160 A (electrode de \u003d 4 mm), the power of the secondary winding will be P 2 \u003d Iw x 160x24 \u003d 3.5 - 4 kW, the power of the primary winding, taking into account losses, will be about 5-5.5 kW, and therefore, the maximum current of the primary winding can reach 25 A. Therefore, the cross section of the wire of the primary winding S 1 must be at least 5 - 6 mm. In practice, it is desirable to use a wire with a cross section of 6 - 7 mm 2. Either it is a rectangular bus, or a copper winding wire with a diameter (without insulation) of 2.6 - 3 mm. (Calculation according to the well-known formula S \u003d piR 2, where S is the area of ​​\u200b\u200bthe circle, mm 2 pi \u003d 3.1428; R is the radius of the circle, mm.) If the cross section of one wire is insufficient, winding in two is possible. When using aluminum wire, its cross section must be increased by 1.6 - 1.7 times. Is it possible to reduce the cross section of the wire of the network winding? Yes, you can. But at the same time, S.A. will lose the required power reserve, will heat up faster, and the recommended core cross section S = 45 - 55 cm in this case will be unreasonably large. The number of turns of the primary winding W 1 is determined from the following relationship: W 1 \u003d [(30 - 50): S] x U 1 where 30-50 - constant factor; S- core section, cm 2, W 1 = 240 turns with taps from 165, 190 and 215 turns, i.e. every 25 turns.

Figure 6. Scheme of winding methods for SA windings on a rod-type core.

More taps of the network winding, as practice shows, is not practical. And that's why. By reducing the number of turns of the primary winding, both the power SA and Uxx increase, which leads to an increase in the arcing voltage and a deterioration in the quality of welding. Therefore, only by changing the number of turns of the primary winding, it is impossible to achieve overlapping of the range of welding currents without deteriorating the quality of welding. To do this, it is necessary to provide for switching turns of the secondary (welding) winding W 2.

The secondary winding W 2 must contain 65 - 70 turns of a copper insulated bus with a cross section of at least 25 mm (better with a cross section of 35 mm). A flexible stranded wire (for example, welding) and a three-phase power stranded cable are quite suitable. The main thing is that the cross section of the power winding should not be less than required, and the insulation should be heat-resistant and reliable. If the wire section is insufficient, winding in two or even three wires is possible. When using aluminum wire, its cross section must be increased by 1.6 - 1.7 times.

Rice. 5. Fastening the leads of the SA windings: 1 - SA housing; 2 - washers; 3 - terminal bolt; 4 - nut; 5 - copper tip with wire.

The difficulty of acquiring switches for high currents, and practice shows that it is easiest to lead the welding winding leads through copper lugs under terminal bolts with a diameter of 8 - 10 mm (Fig. 5). Copper lugs are made from copper tubes of suitable diameter 25 - 30 mm long and are attached to the wires by crimping and preferably by soldering. Let us dwell in particular on the order of winding the windings. General rules:

1. Winding must be carried out on an insulated core and always in the same direction (for example, clockwise).
2. Each layer of the winding is insulated with a layer of cotton. insulation (fiberglass, electric cardboard, tracing paper), preferably impregnated with bakelite varnish.
3. The conclusions of the windings are tinned, marked, and fixed. braid, on the conclusions of the network winding additionally put on h.b. cambric.
4. In case of doubt about the quality of the insulation, winding can be carried out using a cotton cord, as it were, in two wires (the author used a cotton thread for fishing). After winding one layer, the winding with cotton the thread is fixed with glue, varnish, etc. and after drying, the next row is wound.

Figure 7. Scheme of winding methods for SA windings on a toroidal type core.

Consider the arrangement of windings on a rod-type magnetic circuit. The network winding can be positioned in two main ways. The first method allows you to get a more "hard" welding mode. The network winding in this case consists of two identical windings W 1 W 2 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 (Fig. 6a, c).

The second method involves winding the primary (network) winding on one of the sides of the core (Fig. 6 c, d). In this case, the SA has a steeply falling characteristic, it welds “softly”, the arc length has less effect on the magnitude of the welding current, and, consequently, on the quality of welding. After winding the primary winding of the CA, 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 - 6A) and preferably an AC ammeter. If the fuse burns out or gets very hot, then this is a clear sign of a shorted coil. Therefore, the primary winding will have to be rewound, paying special attention to the quality of the insulation.

Rice. 6. Ways of winding SA windings on a rod-type core: a - network winding on both sides of the core; b - the secondary (welding) winding corresponding to it, connected in anti-parallel; c - network winding on one side of the core; g - the secondary winding corresponding to it, connected in series.

If the welding machine is very buzzing, and the current consumption exceeds 2 - 3 A, then this means that the number of primary windings is underestimated and it is necessary to rewind a certain number of turns. A serviceable SA consumes no more than 1 - 1.5 A of idle current, does not heat up and does not buzz very much. The secondary winding CA is always wound on two sides of the core. For the first winding method, the secondary winding also consists of two identical halves, connected in anti-parallel to increase the stability of the arc (Fig. 6), and the wire cross section can be taken somewhat less - 15 - 20 mm 2.

Figure 8. Measuring instrument connection diagram.

For the second winding method, the main welding winding W 2 1 is wound on the side of the core free from windings and makes up 60 - 65% of the total number of turns of the secondary winding. It serves mainly to ignite the arc, and during welding, due to a sharp increase in the magnetic leakage flux, the voltage on it drops by 80 - 90%. Additional welding winding W 2 2 is wound over the primary. Being power, it maintains the welding voltage within the required limits, and, consequently, the welding current. The voltage on it drops in the welding mode by 20 - 25% relative to the open circuit voltage. After manufacturing SA, it is necessary to set it up and check the quality of welding with electrodes of various diameters. The setup process is as follows. To measure the welding current and voltage, it is necessary to purchase two electrical measuring instruments - an AC ammeter for 180-200 A and an AC voltmeter for 70-80V.

Rice. 7. Ways of winding SA windings on a toroidal type core: 1.2 - uniform and sectional winding of the windings, respectively: a - network b - power.

The scheme of their connection is shown in fig. 8. When welding with different electrodes, the values ​​of the welding current - Iw and the welding voltage Uw are taken, 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, either 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) in the direction of increasing the number of turns wound over network winding. After welding, you can make a break or saw the edges of the welded products, and the quality of welding will immediately become clear: the depth of penetration and the thickness of the deposited metal layer. Based on the results of measurements, it is useful to make a table.

Figure 9. Scheme of welding voltage and current meters and the design of the current transformer.

Based on the data in the table, the optimal welding modes are selected for electrodes of various diameters, remembering that when welding with electrodes, for example, with a diameter of 3 mm, electrodes with a diameter of 2 mm can be cut, because. cutting current is 30-25% more than welding current. The difficulty of purchasing the measuring instruments recommended above made the author resort to making a measuring circuit (Fig. 9) based on the most common 1-10 mA direct current milliammeter. It consists of voltage and current meters assembled in a bridge circuit.

Rice. 9. circuit diagram welding voltage and current meters and current transformer design.

The voltage meter is connected to the output (welding) winding S.A. The setting is carried out using any tester that controls the output voltage of welding. With the help of variable resistance R.3, the pointer of the device is set to the final division of the scale at the maximum value of Uxx. The scale of the voltage meter is quite linear. For greater accuracy, you can remove two or three control points and calibrate the measuring device for measuring voltages.

It is more difficult to set up a current meter because it is connected to a self-made current transformer. The latter is a toroidal type core with two windings. The dimensions of the core (outer diameter 35-40 mm) are of no fundamental importance, the main thing is that the windings fit. Core material - transformer steel, permalloy or ferrite. The secondary winding consists of 600 - 700 turns of insulated copper wire PEL, PEV, preferably PELSHO with a diameter of 0.2 - 0.25 mm and is connected to a current meter. The primary winding is a power wire passing inside the ring and connected to the terminal bolt (Fig. 9). Setting up the current meter is as follows. To the power (welding) winding S.A. connect a calibrated resistance from a thick nichrome wire for 1 - 2 seconds (it gets very hot) and measure the voltage at the output of S.A. By determine the current flowing in the welding winding. For example, when connecting Rn = 0.2 ohm Uout = 30v.

Mark a point on the instrument scale. Three to four measurements with different R H are enough to calibrate the current meter. After calibration, the instruments are mounted on the C.A case, using generally accepted recommendations. When welding in various conditions(strong or low-current network, long or short supply cable, its cross section, etc.) adjust S.A. by switching the windings. on optimal mode welding, and then the switch can be set to the neutral position. A few words about contact-spot welding. To the design of S.A. This type has a number of specific requirements:

1. The power given off at the time of welding should be maximum, but not more than 5-5.5 kW. In this case, the current consumed from the network will not exceed 25 A.
2. The welding mode must be "hard", and therefore, the winding of the windings S.A. should be carried out according to the first option.
3. The currents flowing in the welding winding reach values ​​of 1500-2000 A and above. Therefore, the welding voltage should be no more than 2-2.5V, and the open-circuit voltage should be 6-10V.
4. The cross section of the wires of the primary winding is at least 6-7 mm, and the cross section of the secondary winding is at least 200 mm. Such a cross-section of wires is achieved by winding 4-6 windings and their subsequent parallel connection.
5. It is not advisable to make additional taps from the primary and secondary windings.
6. The number of turns of the primary winding can be taken as the minimum calculated due to the short duration of the work of S.A.
7. It is not recommended to take a core (core) section less than 45-50 cm.
8. Welding tips and submarine cables to them must be copper and pass the appropriate currents (tip diameter 12-14 mm).

Special class amateur S.A. represent devices made on the basis of industrial lighting and other transformers (2-3 phase) for an output voltage of 36V and a power of at least 2.5-3 kW. But before taking on the alteration, it is necessary to measure the cross section of the core, which must be at least 25 cm, and the diameters of the primary and secondary windings. It will immediately become clear to you what you can expect from the alteration of this transformer.

And finally, a few technological tips.

The connection of the welding machine to the network should 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 electrode diameter, depending on the thickness of the metal to be welded, can be selected based on the following relationship: da= (1-1.5)L, where L 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 d3. It is recommended to weld 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 waste losses 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 in direct 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 parts, for example, when welding thin-sheet structures, reverse polarity welding is used (Fig. 1). 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 ensures less heating of the welded part, but also accelerates the process of melting the electrode metal due to the higher temperature of the anode zone and the greater heat supply.

Welding wires are connected to the SA through copper lugs under the terminal bolts on the outside of the body of the welding machine. Poor contact connections reduce the power characteristics of the SA, worsen the quality of welding and can cause them to overheat and even ignite the wires. With a small length of welding wires (4-6 m), their cross section must be at least 25 mm. When performing welding work, it is necessary to follow the rules of fire and electrical safety when working with electrical appliances.

Welding work should be carried out in a special mask with protective glass grade C5 (for currents up to 150-160 A) and gloves. All switching of the SA should be carried out only after disconnecting the welding machine from the mains.