Make a welding machine. Welding machines from improvised materials

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. Indeed, a semi-automatic welding inverter allows a novice amateur to cook quite important structures. 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. Whose light hand went for a walk in RuNet, the statement that it is a hybrid of gas and arc is unknown. In fact, this is a kind of arc welding: the inert gas argon does not participate in the welding process, but creates around working area a cocoon that isolates it from the air. As a result, the weld is chemically clean, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be 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 differ significantly from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like 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 peaks in energy consumption during secondary circuit.

An important factor in our case is external volt-ampere characteristics(ВВХ) of a transformer, or simply its external characteristic (ВХ) - the dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, 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 by 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 lines of force permeates 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. In this case, the efficiency of welding energy consumption is unlikely to exceed 60%, but for episodic work, this is not a problem for yourself. But on thin work and low currents, it will not be difficult to hold the arc and the welding current, without having much experience (? U2.2 and Ib1), at high currents Ib2 we will get an acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.

• 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 turn 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 - twisting to the desired S is somewhat stranded wires, 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

A thin-walled home-made 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. Can be replaced with 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 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!”

Nevertheless, contact spot welding is much more economical than arc welding: the open circuit voltage of the welding transformer for it is 2 V. It is the sum of 2 contact potential differences of steel-copper and the 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 piece of flattened refrigerant supply pipe 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)

Direct current will require a high power source of electric current, which converts the standard voltage of the household network and ensures the constancy of the value of the electric current to ignite and maintain the electric arc.

A DC welding machine has a number of advantages: soft arc ignition and the ability to connect thin-walled parts.

Block diagram of the apparatus for welding

The power supply is installed in a housing made of plastic or sheet metal. The power supply unit of the unit is equipped with all the components necessary for operation: connectors, switches, terminals and regulators. The body of the unit for welding work is equipped with special holders and wheels for transportation.

Read also:

The main condition in the design of the unit used for welding is an understanding of the principle of operation of the apparatus and the essence of the welding process itself. In order to design your own welding machine, you need to understand the principles of ignition and combustion of an electric arc and the basic principles of melting an electrode for welding.

The high power power supply includes the following components:

• rectifier;
• inverters;
• current and voltage transformer;
• regulators that improve the quality characteristics of the resulting electric arc;
• additional devices.

The main component of any welding unit is a transformer. Auxiliary devices may have different scheme organizations depending on the design of the device.

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welding transformer

The DC welding machine in its design includes a transformer as the main element, which provides a decrease in the normal mains voltage from 220 V to 45-80 V.

This structural element operates in arc mode with maximum power.

The transformers used in the design must withstand high currents during operation, the rated strength of which is 200 A. The current-voltage indicators of the transformer must fully comply with the special requirements that ensure the operating modes of arc welding.
Some homemade transformer welding machines are simple in design. They do not have additional devices for adjusting current parameters. Adjustment of the technical parameters of such a device is carried out in several ways:

• with the help of a highly specialized regulator;
• by switching the number of coil turns.

The transformer of the welding unit consists of the following structural elements:

• magnetic circuit made of transformer steel plates;
• two windings - primary and secondary, this transformer component has terminals for connecting devices for adjusting operating current parameters.

The transformer used in the welding machine does not have adjusting devices that provide current regulation and its limitation on the working winding. The primary winding of the welding transformer is equipped with terminals for connecting control circuits and devices that allow adjustment welding device depending on operating conditions and input current parameters.

The main part of the transformer is the magnetic circuit. Most often when designing homemade welding machines magnetic cores from a decommissioned engine, an old power transformer are used. Each design of the magnetic circuit has its own nuances in the design. The main parameters characterizing the magnetic core are the following:

• the size of the magnetic circuit;
• the number of turns of windings on the magnetic circuit;
• voltage level at the input and output of the device;
• current consumption level;
• maximum current received at the output of the device.

These basic characteristics determine the suitability of the transformer for use as a device to promote the formation of an arc, as well as a device that promotes the formation of a quality weld.

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Possible details when creating a machine for welding

When creating a do-it-yourself welding machine, the stability of the electric arc is achieved by the constancy of the potential. The stability of the arc ensures the quality of the resulting seams. Potential constancy is achieved by using high-power rectifiers, which are made on diodes that can withstand currents up to 200 A, such as, for example, V-200.

These diodes are large and require the mandatory use of massive radiators to organize high-quality heat dissipation. This circumstance must be taken into account in the manufacture of the structure body. The best option when creating a structure, a diode special bridge will be used. Diodes can be mounted in parallel, which allows a significant increase in output current.

Assembling the structure with your own hands, you need to adjust all its components. With poor-quality selection or incorrect calculation, the design can affect the quality of welding.

Sometimes, with the appropriate selection of parts and accessories, a truly unique device can be obtained that has soft and easy ignition of an electric arc, and parts can be welded even with very thin walls, with almost no liquid metal splashing.

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Schematic diagram of a homemade welding unit

You can make a home-made welding machine based on transistor or thyristor control. Thyristors are more reliable. These elements of the control design are capable of withstanding an output short and are able to recover from this state fairly quickly. These control system components do not require the installation of powerful cooling radiators. This is due to the fact that structural elements have low heat dissipation.

A control system based on transistors is able to get out of working condition much faster, since transistors burn out much faster when overloads occur and are more capricious in operation. The circuit created on the basis of thyristors is simple and highly reliable.

A control unit based on these elements has the following advantages:

• smooth adjustment;
• presence of direct current.

When welding steel with a thickness of 3 mm, the current consumed is about 10 A. The welding current is supplied by pressing a special lever on the plug that holds the electrode.

This design allows you to increase safety in the process of work, work with high voltage, which ensures the stability of the arc. In the case of using reverse polarity in the work, it is possible to carry out welding work with very thin sheet metal.

A welding machine is highly specialized equipment, but almost every man has had to look for a similar unit more than once in his life to repair home appliances or a car. It is easy enough to make a welding machine with your own hands, but it should be understood that the equipment is suitable for working on small structures. This will be arc welding from an AC or DC source.

Argon and gas welding require special knowledge and equipment. It is possible to make a gas generator at home, but if the master does not have a specialized education, there is a high risk of making a mistake. It is easier to rent an argon-arc welding machine, it costs ten times cheaper than making equipment yourself.

The welding machine for home use is a simplified design with the simplest component parts and an uncomplicated assembly scheme. The main part is a welding transformer, which you can make yourself or use a node household appliance(for example, a microwave oven).

The welding inverter unit is arranged according to the scheme:

• power supply;
• rectifier;
• inverter.

You can make a transformer yourself using spent wire cables and a copper tape of the required length.

If the transformer uses a round copper wire, the operation of the machine is limited to 2-3 welding rods. Transformer oil is used for cooling.

The seam on the parts to be joined is formed due to heat, the source of which is an electric arc that occurs between two electrodes. One of the electrodes is the material to be welded. A short circuit, which is required to heat up the electrode (cathode), will lead to a stable discharge with a temperature of up to 6000°C. Under its action, the metal will begin to melt. This is a rough description of the welding process for non-specialists who in everyday life just need to quickly fix the necessary profile, part.

Product package

Welding inverters are rarely made on their own. This electronic device requires repeated testing, specific knowledge and experience. It is easier to make a homemade product based on a transformer and, since it should work from a household network (usually 220 V), this device will be quite enough to perform minor home repairs.

The welding inverter for a 220 V network is assembled according to the scheme that is used for devices operating from an industrial three-phase network. You need to know that these devices will have an efficiency of 60% higher than equipment adapted to a single-phase network.

The welder is made from a transformer without additional components, the package includes:

• transformer (you can do it yourself);
• insulating material;
• welding rod holder;
• PRG cable.

More complex inverter products are equipped with:

• transformer;
• inverter;
• ventilation system;
• ampere regulator.

After assembly, the voltage of the secondary winding is measured: the values ​​\u200b\u200bshould not go beyond the parameters of 60-65 V.

Power supply for a simple welder

Homemade welding transformers are simple equipment for rare repairs. The stator can serve as a magnetic circuit. The primary winding will be connected to the network, the secondary winding is designed to receive an electric arc and perform work. The winding of the transformer consists of copper wire or tape (up to 30 meters).

Primary winding is done with a copper strip with cotton insulation. You can use a "bare" magnetic circuit and insulate it separately. Strips of cotton fabric are wrapped around the wire and impregnated with any varnish for electrical work. The secondary winding is wound after the primary is insulated. The cross section of the primary winding is 5-7 square meters. mm, secondary section - 25-30 sq. mm. After isolation, the parameters are tested: more turns may be required.

An inverter-type welding machine has a more complex device, can operate on direct or alternating current and provides best quality seam. But if in everyday life you only need to spend spot welding(for example, when repairing household appliances), then the manufacture of an inverter welder is impractical. If a vacuum cleaner or microwave oven transformer is used, it is important not to damage the primary winding. The secondary winding in 80% of cases must be removed and redone so that the unit does not overheat.

Rectifier block

The rectifier unit converts the AC signal voltage to DC and consists of a small number of small parts:

• diode bridges;
• capacitors;
• throttle;
• voltage boost.

The rectifier is assembled on the principle of a bridge circuit, where an alternating current is supplied at the input, and a constant current is output from the output terminals. Both devices - a transformer and a rectifier for a welder - are equipped with a forced cooling unit. You can use the cooler from the computer power supply.

Inverter block

The inverter unit converts direct current from the rectifier into alternating current and outputs voltage up to 40 V, current strength up to 150 A.

The inverter works as follows:

1. From the outlet, alternating current (frequency 50-60 Hz) is supplied to the rectifier, where the frequency is equalized. The current is supplied to transistors, where the constant signal is converted into an alternating signal with an increase in the oscillation frequency up to 50 kHz.
2. Lowering the voltage of the high-frequency flow at the step-down transformer from 220 to 60 V. This increases the current strength. Due to the increase in frequency, only the minimum allowable number of turns is used in the inverter coil.
3. At the output rectifier, the last conversion of the electric current into a constant one with high power and low voltage takes place, which is optimally suited for high-quality welding.

In the welding device, in addition to the main stages, the current strength is adjusted, optimal ventilation is ensured. You can make an inverter yourself, guided by a detailed diagram.

Required Tool

To assemble the welding machine and manufacture, you will need the following tools and devices:

• hacksaw;
• fasteners;
• soldering iron;
• knife, chisel, tweezers and screwdrivers;
• sheet metal for the frame;
• electrodes;
• assembly elements for transformer, asynchronous stator.

The parts of the device are assembled on a textolite basis; sheets of aluminum or industrial steel are used for the body.

Manufacturing

All parts in the home-made manufacturing scheme of a transformer welder will be arranged in the following order:

• rectifier;
• network filter;
• converter;
• transformer;
• power rectifier.

A power filter and a rectifier can be excluded from the circuit, but the electric arc will be poorly controlled, and the seam will be of poor quality (uneven, with large torn edges that will require stripping).

Assembly steps:

1. Winding transformer coils. For an inverter welder that will work on AC and DC, a high-frequency transformer with a conversion module is required.
2. Lacquering of the winding insulation.
3. Assembly of the magnetic circuit. The best option- asynchronous stator from an electric motor with a power of 4-5 kW.
4. Soldering coil and output connections.
5. Checking the transformer.
6. Assembly of the diode bridge and connection in the circuit. You will need 5 diodes of the KVRS5010 or B200 class.
7. Installation of a cooling radiator for each diode bridge.
8. Mounting the choke on the same board with a rectifier.
9. Setting the current regulator on the control panel.
10. Ensuring ventilation of the entire structure. Fans are installed in the body of the machine for welding around the perimeter.
11. The output to the working electrodes and the holder is installed on the front wall, the power cord on the opposite.
12. Between the board with the power supply and the power unit, it is recommended to install a sheet metal threshold, a voltage capacitor, which will stabilize the current in the arc.

The weight of the assembled apparatus for minor repairs is from 10 kg. It is recommended to make a diode bridge with a choke in a separate case to reduce weight. This assembly will need to be connected to a stainless steel welding machine. With an alternating mains voltage, semi-automatic equipment is practically not required for welding an iron profile, repairing bodywork or spot tacks.

On alternating current

A homemade AC welding machine has the following advantages:

1. Reliable seam. On alternating current, the arc does not deviate from the original axis, this helps beginners to make an even and high-quality seam.
2. An easy way to assemble the device.
3. Budget cost of components.
4. It is necessary to connect only to a single-phase network, a household outlet is enough.

The main disadvantage of the contact welding machine is the spattering of metal during operation due to the interruption of the sinusoid of the electric arc and the rapid overheating of the transformer. For welding parts up to 2 mm thick, the electrode diameter should be 1.5-3 mm. Welding of sheets from 4 mm is carried out with rods of 3-4 mm at a machine current of at least 150 amperes.

DC

Homemade DC machines are widely used for the home, but require skill, time and more small parts to assemble. Among the advantages of the equipment:

• a stable arc allows you to cook complex and thin-walled structures;
• absence of unclaimed plots;
• no metal spatter, no deburring or seam cleaning required.

It is recommended that a complete do-it-yourself DC welding machine be checked several times for overheating of the transformer, capacitor and diode bridge in test mode before main operation.

into construction homemade devices for welding, you can make changes and constantly refine them. You can make a unit that runs on direct current, a minimal design that runs on an alternating signal with a minimum power of up to 40A, or a massive stationary unit for installation in a workshop.

If a person plans to perform small amounts of any simple welding work at home, he may well make a welding machine with his own hands, without spending money on purchasing a factory unit.

1

In order to make a welding unit from readily available materials and parts, it is necessary to clearly understand the key principles of its operation and only after that proceed with assembly. First of all, you should decide on the current power of a homemade welding machine. To connect massive fittings, of course, a high current intensity is required, and for welding thin metal products (no more than 2 mm) - less.

The current strength indicator is directly related to which electrodes are planned to be used. Welding of sheets and structures with a thickness of 3 to 5 mm is carried out with rods of 3-4 mm, and with a thickness of less than 2 mm - with rods of 1.5-3 mm. If you use 4 mm electrodes, the current homemade installation should be 150-200 A, three-millimeter - 80-140 A, two-millimeter - 50-70 A. But for very thin parts (up to 1.5 mm), a current of 40 A is enough.

The formation of an arc for welding from mains voltage in any welding machine is obtained through the use of a transformer. This device includes in its design:

• windings (primary and secondary);
• magnetic core.

The transformer is easy to make yourself. The magnetic circuit, for example, is assembled from plates of transformer steel or other material. The secondary winding is necessary directly for welding, and the primary is connected to a 220-volt electrical network. Professional units necessarily have in their design some additional devices that improve and enhance the quality of the arc, allow you to smoothly adjust the current strength.

Homemade welding machines, as a rule, are made without additional devices. The value of the power of the transformer is chosen based on the current strength indicator. To get the calculated power, you need to multiply the current used for welding by 25. The resulting product, when multiplied by 0.015, gives us the required diameter of the magnetic circuit. And to calculate the required cross-section of the winding (primary), the power should be divided by two thousand and the resulting value multiplied by 1.13.

With the determination of the cross section of the secondary winding, you will have to "torment" a little longer. Its value depends on the density of the welding current used. With a current strength in the region of 200 A, the density is 6A / square millimeter, from 110 to 150 A - 8, less than 100 A - 10. To set the required cross-section of the secondary winding, you need:

• divide the welding current by its density;
• multiply the resulting value by 1.13.

The number of turns of wire can be determined by dividing the cross-sectional area of ​​the magnetic circuit by 50. Another important point, which you need to know for those who plan to independently manufacture a welding machine, is that the welding process can be "soft" or "hard" depending on the voltage available at the output terminals (at their terminals) of the unit.

The specified voltage sets the features of the external current characteristic for welding, which can be gently or steeply falling, as well as increasing. In welders of their own assembly, experts advise using such current sources that are described by a gently sloping or steeply falling characteristic. They show minimal changes in current during fluctuations in the electric arc, which is optimal for welding at home.

2

Now that we know the main features of the welder, we can begin to assemble a homemade welding machine. Now on the Internet there are many schemes and instructions for performing such a task, which make it possible to create almost any equipment for welding - AC and DC, pulsed and inverter, automatic and semi-automatic.

We will not go into complex technical "wilds" and will tell you how to make a welding machine of the simplest transformer type. It will work on alternating current, providing an efficient and quite decent welded joint in terms of the quality of the seam. Such a unit will allow you to perform any household work that requires welding of metal and steel products. For its manufacture you will need the following materials:

• a couple of tens of meters of thick (preferably copper) cable (wire);
• iron for the core of the transformer device (iron must be characterized by a sufficiently large magnetic permeability).

The core is most convenient to make a rod, traditional U-shaped. In principle, it is allowed to use a core of a different configuration, for example, a round one from the stator of any burnt electric motor, but be prepared for the fact that it is much more difficult to wind windings on a round winding design. The recommended cross-sectional area of ​​​​the core for a standard household welding machine made by yourself is about 50 square centimeters.

This area is enough for the installation to be able to use rods with a diameter of 3-4 mm.

It makes no sense to make a larger section, since the unit will become much heavier, but you will not achieve a real technical effect. If you are not satisfied with the recommended cross-sectional area, you can calculate its value yourself using the diagram given in the first part of our article.

The primary winding must be made of copper wire with high thermal resistance characteristics (during welding, the winding is exposed to high temperatures). This wire, in addition, must have cotton or fiberglass insulation. In extreme cases, it is allowed to use a wire in a rubber-fabric or ordinary rubber insulating sheath, but in no case in PVC.

Insulation, by the way, can be made independently by cutting strips of two centimeters wide from cotton or fiberglass. With these strips you wind copper cable, after which you impregnate the wire with home-made insulation with any varnish for electrical purposes. Believe me, such insulation will not overheat during the operation of 6-7 welding rods (when they are burned during the average duration of welding).

The cross-sectional areas of the windings are calculated according to the principles that were described earlier. It seems that with these calculations you will not have problems. Usually, the cross-sectional area of ​​\u200b\u200bthe "secondary" wire is taken at the level of 25-30 square millimeters, the "primary" - 5-7 (values ​​\u200b\u200bfor home-made units that will work with rods with a diameter of 3-4 mm).

It is also simple to determine the length of a piece of copper wire and the number of turns for both windings. And then they start winding the coils. Their frame is made according to the geometric parameters of the magnetic circuit. The dimensions are selected in such a way that the magnetic core is put on without any difficulty on a core made of textolite or cardboard used in electrical engineering.

Coil winding has a small feature. The primary winding is wound halfway, then half of the secondary winding is applied to it. After that, the second part of the coil is treated in the same way. To improve the insulating properties, it is desirable to lay pieces of cardboard strips, fiberglass or thick paper between the layers.

After assembling the do-it-yourself welding installation, it is mandatory to set it up. To do this, you need to turn it on to the network and measure the voltage indicator on the secondary winding. Its value must be equal to 60–65 V. If the voltage is different, you will need to wind (or rewind) part of the winding. Such procedures will have to be performed until the specified voltage value is reached.

The primary winding of the assembled transformer is connected to an internal laying cable (VRP) or to a two-wire hose wire (SHRPS), which will be connected to a 220 volt network. The secondary winding (its conclusions) is connected to insulated PRG wires, one of them then contacts the workpiece to be welded, and the holder of the welding rods is attached to the second. Homemade welding unit is ready!

3

Any radio amateur in his practice often needs to heat up or carefully weld one or another part. There is no point in using a conventional welding unit for these purposes, since even without it it is possible to form a high-temperature stream quite simply and without cost.

If you have an old autotransformer lying around, which was previously used to regulate the supply voltage of Soviet TVs on lamps, it is easy to adapt it to create a voltaic arc. To do this, connect graphite electrodes between its terminals. Such a simple design will make it possible to perform the simplest welding work, for example, such:

• repair or manufacture of thermocouples: a welder from an autotransformer allows you to repair thermocouples in which the so-called "ball" breaks, other equipment for such repair work simply does not exist;
• connection of power buses with the filament element of a conventional magnetron;
• welding of any wires and cables;
• heating to high temperatures of structures made of (springs and similar parts);
• hardening of all kinds of devices made of (they are heated with an arc, and then immersed in engine oil).

If you decide to make a welder based on an autotransformer, you need to handle it very carefully, since electrical network it has no galvanic isolation. This means that the misuse homemade device may result in electric shock.

To perform all the above "minor" work, it is recommended to use an automatic transformer with a voltage (output) of 40–50 volts with low power (about 200–300 watts). Such a device is capable of delivering 10–12 amperes of operating current, which is quite enough for welding wires, thermocouples and other elements. The electrodes for the described welding mini-machine are ordinary pencil leads.

It is better if they are soft, however, pencils of medium and high hardness will also work. Holders for such graphite rods can be made from old terminal blocks available on any electrical appliances. The holder is connected to the winding (as you yourself understand, secondary) of the autotransformer through one of the available outputs, and the product to be welded is also connected to it, but through another output.

The handle of the electrode holder is easy to make from a conventional fiberglass washer or from another heat-resistant element. Finally, let's say that the arc on the welding machine from the autotransformer does not burn for a very long time. On the one hand, this is bad, on the other hand, it is very good, since the short duration of its operation eliminates the risk of overheating of the transformer device.

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

Welding machines are permanent 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. Their voltage variation range 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, powering 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 - U-shaped plates; 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") with inside part of the steel tape is unwound 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 - circuit diagram 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 is a constant coefficient; 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. Schematic diagram of welding voltage and current meters and the design of the current transformer.

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 measuring device for voltage measurement.

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.), S.A. is adjusted by switching the windings. to the optimal welding mode, and then the switch can be set to the neutral position. A few words about contact-spot welding. To the design of S.A. of this type There are 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 with outer side 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.