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

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

What are we going to talk about

This article discusses how to make equipment at home for:

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

What we will not talk about

First, let's skip gas welding. The equipment for it costs pennies in comparison with consumables, you can't make gas cylinders at home, and a home-made gas generator is a serious risk to life, plus carbide is expensive now, where it still goes on sale.

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

The third is argon-arc welding. From whose light hand the statement that it is a hybrid of gas and arc went to walk in Runet is unknown. In fact, this is a kind of arc welding: the inert gas argon does not participate in the welding process, but creates a cocoon around the working area, isolating it from the air. As a result, the weld is chemically clean, free from impurities of metal compounds with oxygen and nitrogen. Therefore, it is possible to cook under argon non-ferrous metals, incl. dissimilar. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and to weld with a non-consumable electrode.

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 as part of routine economic activities. And if you really need to, then it is easier to rent argon welding - compared to how much (in money) gas will go back into the atmosphere, this is a penny.

Transformer

The basis of all "our" types of welding is a welding transformer. The procedure for its calculation and design features differ significantly from those of power supply (power) and signal (sound) transformers. The welding transformer works in intermittent mode. If designed for maximum current as continuous transformers, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electric arc welding transformers is the main reason for the failure of amateur designers. Therefore, we will walk through the welding transformers in the following order:

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

Theory

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

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

An important factor in our case is the external current-voltage characteristic (VVAC) of the transformer, or simply its external characteristic (VX) - the dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, VX is rigid (curve 1 in the figure); they are like a shallow vast basin. If it is properly insulated and covered with a roof, then the water loss is minimal and the pressure is quite stable, no matter how the consumers turn the taps. But if there is a gurgle in the drain - sushi oars, the water is drained. With regard to transformers, the power engineer must keep the output voltage as stable as possible to a certain threshold, less than the maximum instantaneous power consumption, be economical, small and light. For this:

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

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

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

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

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

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

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

Magnetic cores

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

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

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

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

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

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

Oh OL

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

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

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

Another torus suitable for all its properties is the stator of an electric motor; welding from it will turn out even for an exhibition. But finding it is no easier than LATR iron, and it is much more difficult to wind on it. In general, a welding transformer from an electric motor stator is a separate topic, there are so many difficulties and nuances there. First of all - with the winding of a thick wire on the "donut". Without experience in winding toroidal transformers, the probability of spoiling an expensive wire and not getting welding is close to 100%. Therefore, alas, with a cooking apparatus on a troidal transformer, you will have to wait.

Ш, ШЛ

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

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

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

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

PL, PLM

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

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

If there is a transformer

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

Calculation of the welding transformer

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

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

• According to the formula from clause 2 before. the list we find the overall power;
• We find the maximum possible welding current Iw = Pg / Ud. 200 A are provided if 3.6-4.8 kW can be removed from iron. True, in the 1st case, the arc will be sluggish, and it will be possible to cook only with a two or 2.5;
• We calculate the operating current of the primary at the maximum allowable mains voltage for welding I1pmax = 1.1Pg (VA) / 235 V. In fact, 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 I1рmax, we find the diameter of its wire in copper d = (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation is D = 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, yok solution" mode, you can take J1 = 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 Ш and П, k2 = 40 for ПЛ, ШЛ and k2 = 35 for О, ОЛ;
• We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy losses of the winding for dissipation in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
• We set the stacking coefficient Ku = 0.8, add 3-5 mm each to a and b of the magnetic circuit, calculate the number of layers of the winding, the average length of the turn and the length of the wire
• We calculate in a similar way the secondary at J1 = 6 A / sq. mm, k3 = 1.05 and Ku = 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.

Winding and finishing

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

Isolation

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

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

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

Winding

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

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

Lapping and homework

We load the core into a biscuit and tighten it with bolts, as expected. The winding tests are carried out completely similar to the tests of the dubious finished transformer, see above. Better to use LATR; Iхх at an input voltage of 235 V should not exceed 0.45 A per 1 kVA of the overall power of the transformer. If it is more, the primary organization will be killed. Winding wire connections are made on bolts (!), Insulated with a heat-shrinkable tube (HERE) in 2 layers or cotton tape in 4-5 layers.

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

After finishing, the core is disassembled; We wrap the biscuit tightly with the same masking tape, calico or "rag" tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now we soak it again with liquid varnish; when dry - twice undiluted. This biscuit is ready, you can make a secondary one. When both are on the core, we once again test the transformer on Ixx (suddenly it curled somewhere), fix the biscuits and saturate the entire transformer with normal varnish. Phew, the most dreary part of the work is behind.

Pull VX

But we still have it too cool, have you forgotten? It needs to be softened. The simplest way - a resistor in the secondary circuit - is not suitable for us. Everything is very simple: at a resistance of only 0.1 Ohm at a current of 200, 4 kW will dissipate by heat. If we have a welder for 10 or more kVA, and we need to weld thin metal, a resistor is needed. Whatever the current is set by the regulator, its emissions during arc striking are inevitable. Without active ballast, they will burn through the seam in places, and the resistor will extinguish them. But for us, weak 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 dispersion control. And for him - the core is almost the same as that of the transformer, and rather complicated mechanics, see fig.

We will go the other way: we will use active-reactive ballast, in the old welders, in common parlance, called the gut, see fig. on right. Material - steel wire rod 6 mm. The diameter of the loops is 15-20 cm. How many of them are shown in Fig. it can be seen that this gut is correct for power up to 7 kVA. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is attached to it with a clip-clothespin. By selecting the attachment point, you can, together with switching to the secondary taps, fine-tune the operating mode of the arc.

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

But other?

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

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

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

Trying a constant

DC welding has a number of advantages, but the VC of any DC welding transformer is toughened. And ours, designed for the minimum possible power reserve, will become unacceptably tough. The choke-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 infra-low frequency filter, FINCH. Although it looks reflective, the strong magnetic coupling between the halves of the coil must be taken into account.

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

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

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

Microarc

The purpose of micro-arc welding was mentioned at the beginning. The “equipment” for it is extremely simple: a step-down transformer 220 / 6.3 V 3-5 A. One electrode - the wire twisting itself (copper-aluminum, copper-steel can be used); the other is a graphite rod, like the lead from a 2M pencil.

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

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

Resistance welding in industry is mainly used for spot, seam and butt welding. At home, primarily in terms of energy consumption, 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 a part is a coin or less, then the softest arc will burn it entirely.

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

Nevertheless, resistance 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 steel-copper potential differences and the ohmic resistance of the penetration zone. The transformer for resistance welding is calculated similarly to it for arc welding, but the current density in the secondary winding is taken from 30-50 and more A / sq. mm. The secondary of the contact welding transformer contains 2-4 turns, is well cooled, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

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

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

Secondary winding - 16x2 copper bus. It can be drawn from strips of thin sheet copper (it will turn out to be flexible) or made from a piece of a flattened pipe for supplying the refrigerant of a household air conditioner. Manually insulate the bus as described above.

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

About electrodes

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

In fig. on the right, one more feature of electrodes for spot resistance welding is visible: a spherical contact surface (heel). Flat heels are more durable, which is why electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 times the thickness of the adjacent material to be welded, otherwise the penetration spot will be burned out either in the center (wide heel) or along the edges (narrow heel), and corrosion will go from the welded joint even on stainless steel.

The last thing about electrodes is their material and dimensions. Red copper quickly burns out, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, with current copper prices this is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A / sq. mm. The length of the electrode under the conditions of heat transfer is not less than 3 of its diameters from the heel to the root (the beginning of the shank).

How to give impetus

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

A diagram of a simple, but reliable and proven by long-term practice of the welding pulse generator is given in Fig. The auxiliary transformer T1 is a conventional power transformer of 25-40 W. Winding voltage II - according to the backlight lamp. You can instead put 2 LEDs connected in antiparallel with a damping resistor (normal, 0.5 W) 120-150 Ohm, then the voltage II will be 6 V.

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

The welding machine is a fairly popular device both among professionals and among home craftsmen. But for domestic use, sometimes it makes no sense to buy an expensive unit, since it will be used in rare cases, for example, if you need to weld a pipe or put up a fence. Therefore, it will be wiser to make a welding machine with your own hands, investing a minimum amount of money in it.

The main part of any electric arc welder is the transformer. This part can be removed from old, unnecessary household appliances and made a homemade welding machine out of it. But in most cases, the transformer needs a little tweaking. There are several ways to make a welder, which can be both the simplest and more complex, requiring knowledge in electronics.

To make a mini welder, you will need a pair of transformers taken from an unnecessary microwave oven. It is easy to find a microwave oven from friends, acquaintances, neighbors, etc. The main thing is that it has a power in the range of 650-800 W, and the transformer is in good working order. If the stove has a more powerful transformer, then the device will turn out with higher current rates.

So, the transformer removed from the microwave has 2 windings: primary (primary) and secondary (secondary).

Resale has more turns and a smaller wire cross-section. Therefore, in order for the transformer to become suitable for welding, it must be removed and replaced with a conductor with a larger cross-sectional area. To remove this winding from the transformer, it must be cut off from both sides of the part using a metal hacksaw.

This must be done with special care so as not to accidentally hit the primary winding with the saw.

When the coil is cut off, its remains will need to be removed from the magnetic circuit. This task will be much easier if the windings are drilled to relieve the metal stress.

Do the same with the other transformer. As a result, you will have 2 parts with a primary winding of 220 V.

Important! Remember to remove the current shunts (shown by arrows in the photo below). This will increase the power of the device by 30 percent.

For the manufacture of the secondary, you will need to purchase 11-12 meters of wire. It must be stranded and have cross section not less than 6 squares.

To make a welding machine, for each transformer, you will need to wind 18 turns (6 rows in height and 3 layers in thickness).

You can wind both transformers with one wire or separately. In the second case, the coils must connect in series.

The winding should be done very tightly so that the wires do not dangle. Further, the primary windings need connect in parallel.

The pieces can be screwed onto a small piece of wood to be tied together.

If you measure the voltage on the secondary of the transformer, then in this case it will be 31-32 V.

With such a homemade welder, metal with a thickness of 2 mm is easily welded with electrodes with a diameter of 2.5 mm.

It should be remembered that such a homemade apparatus should be cooked with rest breaks, since its windings are very hot. On average, after each used electrode, the device should cool down for 20-30 minutes.

It will not be possible to cook thin metal with a unit made from a microwave, since it will cut it. To adjust the current, a ballast resistor or choke can be connected to the welder. The role of the resistor can be performed by a piece of steel wire of a certain length (selected experimentally), which is connected to the low-voltage winding.

AC welder

This is the most common type of metal welding machine. It is easy to make at home, and it is unpretentious to operate. But the main drawback of the device is large mass of step-down transformer, which is the basis of the unit.

For home use, it is enough that the device produces a voltage of 60 V and can provide a current of 120-160 A. Therefore for the primary, to which the 220 V household network is connected, you will need a wire with a cross section of 3 mm 2 to 4 mm 2. But the ideal option is a conductor with a cross section of 7 mm 2. With such a cross-section, voltage drops and possible additional loads will not be terrible for the device. From this it follows that the secondary needs a conductor with a diameter of 3 mm. If we take an aluminum conductor, then the calculated cross-section of the copper is multiplied by a factor of 1.6. For the secondary housing a copper bar with a cross section of at least 25 mm 2 is required

It is very important that the winding conductor is covered with rag insulation, since the traditional PVC sheath melts when heated, which can cause a turn-to-turn short circuit.

If you have not found a wire with the required section, then you can make yourself from several thinner conductors. But this will significantly increase the thickness of the wire and, accordingly, the dimensions of the unit.

First thing, the base of the transformer is made - the core... It is made from metal plates (transformer steel). These plates should have a thickness of 0.35-0.55 mm. The studs connecting the plates must be well insulated from them. Before assembling the core, its dimensions are calculated, that is, the dimensions of the “window” and the cross-sectional area of ​​the core, the so-called “core”. To calculate the area, use the formula: S cm 2 = a x b (see the figure below).

But from practice it is known that if you make a core with an area of ​​less than 30 cm 2, then such an apparatus will be difficult to obtain a high-quality seam due to a lack of power reserve. And it will heat up very quickly. Therefore, the cross-section of the core must be at least 50 cm 2. Despite the fact that the weight of the unit will increase, it will become more reliable.

For core assembly, it is better to use L-shaped plates and place them as shown in the following figure until the thickness of the part reaches the desired value.

At the end of the assembly, the plates must be fastened (at the corners) with bolts, then cleaned with a file and insulated with fabric insulation.

Now you can start transformer winding.

One nuance should be taken into account: the ratio of turns on the core should be 40% to 60%. This means that on the side where the primary is located, there should be fewer turns of the secondary. Due to this, at the start of welding, the winding with more turns will be partially cut off due to the occurrence of eddy currents. This will increase the current strength, which will have a positive effect on the quality of the seam.

When the winding of the transformer is complete, the mains cable is connected to the common wire and to the 215 turn tap. The welding cables are connected to the secondary winding. After that, the contact welding machine is ready for work.

DC apparatus

To cook cast iron or stainless steel, a DC apparatus is required. It can be made from a conventional transformer unit, if to its secondary winding connect rectifier... Below is a diagram of a diode bridge welding machine.

Diagram of a welding machine with a diode bridge

The rectifier is assembled on D161 diodes, capable of withstanding 200A. They must be installed on radiators. Also, to equalize the ripple of the current, you will need 2 capacitors (C1 and C2) of 50 V and 1500 μF. This wiring diagram also has a current regulator, the role of which is played by the choke L1. Welding cables are connected to contacts X5 and X4 (straight or reverse polarity), depending on the thickness of the metal to be connected.

Inverter from computer power supply

It is impossible to make a welding machine from a computer power supply. But it is quite possible to use its case and some parts, as well as the fan. So, if you make an inverter with your own hands, then it can easily be placed in a power supply unit from a computer. All transistors (IRG4PC50U) and diodes (KD2997A) must be installed on radiators without using gaskets. For cooling parts, it is desirable use a powerful fan such as Thermaltake A2016. Despite its small size (80 x 80 mm), the cooler is capable of developing 4800 rpm. The fan also has a built-in speed controller. The latter are regulated using a thermocouple, which must be fixed to a radiator with installed diodes.

Advice! It is recommended to drill several additional holes in the PSU case for better ventilation and heat dissipation. Overheating protection installed on the radiators of transistors is configured to operate at a temperature of 70-72 degrees.

Below is a schematic electrical diagram of a welding inverter (in high resolution), according to which you can make an apparatus that fits in the power supply case.

The following photos show what components a homemade inverter welding machine consists of, and how it looks after assembly.

Electric motor welder

To make a simple welding machine from the stator of an electric motor, it is necessary to select the motor itself that meets certain requirements, namely, that its power is from 7 to 15 kW.

Advice! It is best to use a 2A series motor as it will have a large magnetic circuit window.

You can get the required stator in places where scrap metal is accepted. As a rule, it will be cleared of wires and after a couple of blows with a sledgehammer, it splits. But if the case is made of aluminum, then in order to remove the magnetic circuit from it, need to anneal the stator.

Preparation for work

Place the stator with the hole facing up and place bricks under the part. Next, fold the wood inside and set it on fire. After a couple of hours of frying, the magnetic core will easily separate from the case. If there are wires in the housing, they can also be removed from the grooves after heat treatment. As a result, you will get a magnetic circuit, cleaned of unnecessary elements.

This blank follows well soak with oil varnish and let it dry. A heat gun can be used to speed up the process. The impregnation with varnish is done so that after removing the screeds, the package does not spill out.

When the disc is completely dry using a grinder, remove the screeds laid out on it. If the ties are not removed, they will act as short-circuited turns and take up the power of the transformer, as well as cause it to heat up.

After cleaning the magnetic circuit from unnecessary parts, you will need to make two end plates(see figure below).

The material for their manufacture can be either cardboard or press board. You also need to make two sleeves from these materials. One will be internal and the other will be external. Next, you need:

• install both end caps on the blank;
• then insert (put on) the cylinders;
• wrap all this structure with kiper or glass tape;
• soak the resulting part with varnish and dry.

Making a transformer

After carrying out the above steps, it will be possible to make a welding transformer from the magnetic circuit. For these purposes, you need a wire covered with fabric or glass enamel insulation. To wind the primary winding, you need a wire with a diameter of 2-2.5 mm. The secondary winding will require about 60 meters of copper bus bar (8 x 4 mm).

So, the calculations are done as follows.

1. Twenty turns of wire with a diameter of at least 1.5 mm should be wound on the core, after which a voltage of 12 V must be applied to it.
2. Measure the current flowing in this winding. The value should be about 2 A. If the value is greater than the required one, then the number of turns must be increased, if the value is less than 2A, then decrease.
3. Calculate the number of turns obtained and divide it by 12. As a result, you get a value that indicates how many turns are needed per 1 V of voltage.

For primary winding a conductor with a diameter of 2.36 mm, which needs to be folded in half, is suitable. In principle, you can take any wire with a diameter of 1.5-2.5 mm. But first you need to calculate the cross-section of the conductors in the loop. First you need to wind the primary winding (220 V), and then the secondary. Its wire must be insulated along its entire length.

If you make a tap in the secondary winding in the section where 13 V is obtained and put a diode bridge, then this transformer can be used instead of a battery if you want to start the car. For welding, the voltage on the secondary winding should be in the range of 60-70 V, which will allow the use of electrodes with a diameter of 3 to 5 mm.

If you have laid both windings, and there is free space in this design, then you can add 4 turns of a copper bus (40 x 5 mm). In this case, you will receive a spot-welding coil that allows you to join sheet metal up to 1.5 mm thick.

For case making using metal is not recommended. It is better to make it from PCB or plastic. In the places where the coil is attached to the case, it is necessary to lay rubber gaskets to reduce vibration and better isolation from conductive materials.

Homemade spot welding machine

A ready-made device for spot welding has a rather high price, which does not justify its internal “stuffing”. It is arranged very simply, and it will not be difficult to make it yourself.

To make a spot welding machine yourself, you need one microwave transformer with a power of 700-800 watts. It is necessary to remove the secondary winding from it in the manner described above, in the section where the manufacture of a welding machine from a microwave was considered.

A spot welder is made in the following way.

1. Make 2-3 turns inside the manit conductor with a cable with a conductor diameter of at least 1 cm.This will be a secondary winding that allows you to get a current of 1000 A.
   
   
2. It is recommended to install copper lugs at the ends of the cable.
   
   
3. If we connect 220 V to the primary winding, then on the secondary winding we get a voltage of 2 V with a current of about 800 A. This will be enough to melt an ordinary nail in a few seconds.
   
   

   

4. Followed by make a case for the device... A wooden board works well for the base, from which several elements should be made, as shown in the following figure. The dimensions of all parts can be arbitrary and depend on the dimensions of the transformer.
   
   

   

5. To give the cabinet a more aesthetic appearance, sharp corners can be removed using a hand router with an edge molding cutter installed on it.
   
   

   

6. On one part of the welding gun, cut a small wedge... Thanks to him, the ticks will be able to rise higher.
   
   

   

7. Cut out the holes for the switch and the power cable on the back of the case.
   
   
8. When all the parts are ready and sanded, they can be painted black or varnished.
   
   
9. From an unnecessary microwave, you will need to disconnect the power cable and the limit switch. You will also need a metal doorknob.
   
   

   

10. If your home does not have a switch and a copper rod, as well as copper clamps, then these parts must be purchased.
    
    
11. Cut 2 small rods from the copper wire, which will act as electrodes, and fix them in the clamps.
    
    

    

12. Screw the switch to the back of the device.
    
    
13. Screw the back wall and 2 posts to the base, as shown in the following photos.
    
    

    

14. Fix the transformer to the base.
    
    
15. Further, one mains wire is connected to the primary winding of the transformer. The second mains wire is connected to the first terminal of the switch. Then you need to attach the wire to the second terminal of the switch and connect it to the other terminal of the primary. But a break should be made on this wire and installed in it breaker removed from the microwave... It will act as a button for turning on the welding. These wires must be long enough to accommodate the breaker at the end of the clamp.
16. Attach the cover of the machine with the handle attached to the uprights and the back wall.
    
    
17. Secure the side walls of the case.
    
    
18. The welding gun can now be installed. First, drill at their ends along the hole into which the screws will be screwed.
    
    
19. Next, attach the switch to the end.
    
    
20. Insert the pliers into the housing, placing a square block between them to align. Drill holes in the pliers through the sidewalls and insert long nails into them to serve as pivots.
    
    

    

21. Attach copper electrodes to the ends of the pliers and align them so that the ends of the rods are opposite each other.
    
    

    

22. In order for the upper electrode to rise automatically, screw in 2 screws and attach an elastic band to them, as shown in the following photo.
    
    

    

23. Switch on the unit, connect the electrodes and press the start button. You should see an electrical discharge between the copper rods.
    
    
24. To check the operation of the unit, you can take metal washers and weld them.
    
    

    

In this case, the result was positive. Therefore, the creation of a spot welding machine can be considered complete.

If you have the necessary locksmith and electrical installation tools (below we will tell you about them in detail), and you have the appropriate professional skills, then you can make do-it-yourself welding transformer.

Your expenses, of course, will be, but incomparably less compared to the costs of purchasing a factory-made gadget. But how much pleasure will you get in the process of your favorite work on creating homemade products? And the delight, at the moment of the successful start of electric welding, in general, cannot be compared with anything!

We will give you a lot of useful tips in the article. by choice, calculation and manufacture welding transformer (hereinafter - ST), which will help you optimize costs and save your budget.

A properly made device with your own hands is no worse than a factory one.

The article will talk about two types of welding transformers. For welding:

• arc;
• contact.

DIY welding transformer: what we need

The range of tools and equipment for the manufacture and assembly of both types of CT is identical. We need the following:

• electrical voltage indicator... To control the absence of the latter on electrical contacts, and thereby ensure safety when performing electrical work;
• Angle grinder(she is "Bulgarian", "whack-machine", etc.) with a set of disks (cutting, grinding, etc.);
• electric drill with a set of drills for metal and a core;
• tester or voltmeter alternating current with a measurement limit of 400 V;
• any " scriber". It is used when marking for metal;
• locksmith clamps... For fixing parts when marking "in place";
• electric tool set... The specific composition of the kit depends on the materials that will be used in the manufacture of CT. In general, it is as follows:
  • complete electric soldering iron. Soldering will be performed with POS-40 solder;
  • screwdrivers (different sizes with straight and Phillips slot);
  • keys:
    • nut;
    • captive;
    • end;
  • pliers, side cutters, etc. with insulated handles;
• set of files.

It is more convenient to carry out all work on a locksmith's workbench with an electrical insulating coating, equipped with a locksmith's vice.

For the manufacture of CTs, components and materials are required that differ from each other depending on the type of transformer. In general, you need the following:

• protective cover... Should provide:
  • protection against electric shock;
  • exclude the possibility of any objects getting inside the gadget;
• magnetic circuit... Provides a powerful electromagnetic flux, which induces an electromotive force (hereinafter - EMF) in the windings;
• wire and wire... Required for mounting windings;
• bobbins... Windings are wound on them;
• terminal blocks... Powerful terminal block with clamps for welding wires, small blocks - for wiring the circuit;
• switches (switches)... The switching of the sections of the windings is carried out when selecting the value of the welding current;
• material for turn-to-turn insulation... Reduces the possibility of electrical breakdown of winding insulation;
• fasteners (bolts, screws, nuts, washers, etc.)... They are necessary for the installation of the gadget during assembly work;
• insulating tape(type X / B).

Important: insulating tape "PVC" can not be used, because when heated, it is destroyed.

Homemade arc welding transformer

Before proceeding with further work on the manufacture of CT, you should decide: what exactly you will create. You need:

• choose the design and electrical schematic diagram of the future device;
• make an electrical and, if necessary, a constructive calculation of its parameters.

Only after that should you select the necessary equipment, materials and prepare, if necessary, a special tool.

How to calculate a welding transformer. Scheme

The question of how to calculate a self-made welding transformer is very specific, since it does not correspond to typical schemes and generally accepted rules. The fact is that when making homemade products, the parameters of their components are "adjusted" to the components already available (mainly for the magnetic circuit). Moreover, it often happens that:

• transformers are not assembled from the best transformer iron;
• windings are wound with the wrong wire and many other negative factors.

As a result, the homemade products heat up and “hum” (the core plates vibrate at the frequency of the mains: 50 Hz), but, at the same time, they “do their job” - they weld the metal.

By the shape of the cores, transformers of the following main types are distinguished:

• rod;
• armored.

Explanations for the figure:

• a - armored;
• b - core.

Transformers pivotal type compared to transformers armored type, allow high current densities in the windings. Due to this, they have a higher efficiency, but the labor intensity of their manufacture is much higher. However, they are used more often.

On the rod core, the winding schemes shown in the figure are used.

Explanations for the figure:

• a - mains winding on both sides of the core;
• b - the corresponding secondary (welding) winding, connected in counter-parallel;
• c - mains winding on one side of the core;
• d - the corresponding secondary winding, connected in series.

For example, let's calculate the CT assembled according to the "c" - "g" scheme. Its secondary winding consists of two equal parts (halves). They are located on opposite arms of the magnetic circuit, and are connected in series with each other. The calculations consist in determining the theoretical and choosing the actual dimensions of the magnetic circuit.

We are determined with the power of the CT (by the value of the current in the secondary winding) from the following considerations. For electric welding in everyday life, coated electrodes Ø, mm are most often used: 2, 3, 4. We choose the "golden mean" for the most popular - 120 ... 130 A. The power of the CT is determined by the formula:

P = Uх.х. × Iw. × cos (φ) / η, where:

• Uх.х. - no-load voltage;
• Iw. - welding current;
• φ is the phase angle between voltage and current. We accept: cos (φ) = 0.8;
• η - efficiency. For homemade STs: efficiency = 0.7.

If you calculate the magnetic circuit according to the reference book, then its cross section for the selected current is 28 sq. Cm. In practice, the cross-section of the magnetic circuit for the same power can vary within the range: 25 ... 60 sq. Cm.

For each section, it is necessary to determine (according to the reference book) the number of turns of the primary winding to provide the specified power at the output. We only note that the larger the cross-sectional area of ​​the magnetic circuit (S), the less turns of both coils will be needed. This is an essential point, since a large number of turns may not fit into the "window" of the magnetic circuit.

It is possible to use the magnetic core of an old transformer (for example, from a microwave oven, of course, after some reconstruction - replacement of the secondary winding).

If you do not have an old transformer, then you should purchase transformer iron, from which you will make the CT core.

Explanations for the figure:

• a - L-shaped plates;
• b - U-shaped plates;
• c - plates made of strips of transformer steel;
• c and d - dimensions of the "window", cm;
• S = a x b - cross-sectional area of ​​the core (yoke), sq. Cm.

The calculation of the number of turns of the primary windings at a mains supply voltage of 220 ... 240 V, the welding currents we have chosen and the parameters of the magnetic circuit can be made according to the following formulas:
N1 = 7440 × U1 / (Sfrom × I2). For windings on one shoulder (half of the windings on top of each other, connected in series);
N1 = 4960 × U1 / (Sfrom × I2). The windings are spaced apart on different shoulders.

Legend in both formulas:

• U1 - power supply voltage;
• N1 is the number of turns of the primary winding;
• Siz - section of the magnetic circuit (sq. Cm);
• I2 - set secondary welding current (A).

The output voltage of the secondary winding of the CT in no-load mode for self-made welding transformers is, as a rule, in the range of 45 ... 50V. Using the following formula, you can determine its number of turns:
U1 / U2 = N1 / N2.

For the convenience of selecting the strength of the welding current, bends are made on the windings.

Welding transformer winding and installation

For the primary winding of the transformer, a special heat-resistant copper wire with cotton or fiberglass insulation is used.

Taking into account the power selected above, the electric current in the primary winding can reach 25 A. Based on these considerations, the primary winding of the CT should be wound with a wire having a cross section of ≥ 5 ... 6 sq. Mm. This, among other things, will significantly increase the reliability of the CT.

The secondary winding is made with copper wire, the cross-section of which is 30 ... 35 sq. Mm. Particular attention should be paid to the choice of insulation of the secondary winding wire, since a large welding current flows through it. It must be very reliable - special attention should be paid to heat resistance.

When installing the windings, pay attention to the following:

• winding is done in one direction;
• an insulating layer of additional insulation (recommended - cotton) is laid between the rows of windings.

The assembled CT should be placed in a protective casing with ventilation holes.

Video

See how the task of assembling the device was implemented:

Do-it-yourself contact welding from a welding transformer

Resistance welding creates a welded joint of parts due to the following simultaneous effects on them:

• heating the area of ​​their contact with an electric current passing through it;
• a compressive force is applied to the joint area.

There are three types of resistance welding:

• point;
• butt;
• suture.

We will tell you about a homemade CT for the most popular: spot resistance welding (the other two require very sophisticated equipment).

Explanations for the figure:
1 - electrodes supplying the welding current with the items being welded;
2 - welded products with lap joint;
3 - welding transformer.

For resistance welding, depending on the thickness and thermal conductivity of the materials of the parts to be welded, the following values ​​of its main parameters are selected:

• electric voltage in the power (welding circuit), V: 1 ... 10;
• value of the welding current (amplitude of the welding pulse), A: ≥ 1000;
• heating time (passage of the welding current pulse), sec: 0.01… 3.0;

In addition, the following must be provided:

• insignificant melting zone;
• significant compressive force applied to the weld.

Scheme and calculation

The calculation of CT resistance welding is performed according to the same algorithm as for arc welding (see above). When choosing data from the reference book (current and voltage of the secondary winding for spot welding of the selected grade of metal of a given thickness), it should be borne in mind that the current strength of the secondary winding for such transformers is of the order of 1000 ... 5000 A. represents only a few turns (sometimes one) of a thick wire. Therefore, the following transformer primary winding circuit is recommended to adjust the welding current.

Very often, in the process of using homemade products, it turns out that there is not enough ST power. In this case, it is possible to connect a second transformer in accordance with the proposed scheme.

Winding and installation

These operations are performed according to the same basic rules and in compliance with the requirements as for ST arc welding. With special care, the turns of the secondary winding should be secured. To do this, you can use its leads by passing them in a heat-resistant insulator.

Copper rods are used as electrodes.

Should be considered that the larger the diameter of the electrode, the better. In no case should the electrode diameter be less than the wire diameter. For low-power STs, it is possible to use tips from powerful soldering irons.

During operation, monitor the condition of consumables: the electrodes must be periodically sharpened - otherwise they lose their shape. Over time, they are completely grinded and need to be replaced.

:

• the welder needs to stand on a rubber mat;
• the worker must wear rubber gloves;
• a welding mask is optional, but protective goggles must be worn on the face.

conclusions

We've given you enough information to make a homemade welding transformer:

• arc welding;
• contact welding.

When doing simple and small-scale welding at home, everyone can assemble.

You don't have to spend a lot of money, effort and time to assemble. Also, there is no need to purchase unreasonably expensive models of such equipment.

To make a mini welding machine with your own hands from improvised means, without special financial costs and efforts, you need to understand how the equipment functions, after which you can start producing it at home.

First of all, it is worth determining the required current supply power of homemade welding equipment. Joining parts of a massive structure requires a higher current intensity, and welding work with thin metal surfaces is minimal.

The current value is related to the selected electrodes to be used in the process. When welding products up to 5 millimeters, rods up to 4 millimeters must be used, and in a structure with 2 millimeters thick, the rods must be 1.5 millimeters.

When using electrodes of 4 millimeters, the current strength is regulated up to 200 amperes, at 3 millimeters up to 140 amperes, at 2 millimeters - up to 70 amperes, and for the smallest ones up to 1.5 millimeters - up to 40 amperes.

You can form an arc for the welding process yourself, using the mains voltage, which is obtained due to the operation of the transformer.

The set of this equipment includes:

• magnetic circuit;
• winding - primary and secondary.

Also, the transformer can be made independently. For the magnetic core, plates of steel or other durable material are used. The windings are necessary to directly carry out welding work and be able to connect the welding unit to a 220 volt network.

Transformer for welding.

Specialized equipment has additional devices that increase the quality and power of the arc, which makes it possible to independently adjust the current strength.

You should not go deep enough into this topic, since one of the easiest ways to assemble a welding machine with your own hands is.

Its feature is work with alternating current, which ensures the performance of a high-quality seam when welding metal surfaces. Such equipment can cope with any household work where it is necessary to weld metal or steel structures.

To make it you need to prepare:

1. Several meters of thick cable.
2. Material for the core that will be located in the transformer.
   The material itself must have increased permeability with magnetization.

The best option is when the rod-shaped core has the letter "P". In some cases, it is allowed to use this part in a more modified form, for example, a round stator made from a damaged electric motor.

Diagram of the device of the welding transformer.

However, it is worth noting that it is more difficult to wind the windings on such a shape. It is best when the cross-section of the core for classic DIY welding equipment used for domestic purposes had an area of ​​about 50 cm2.

In order for the equipment to have an accessible weight, it is not necessary to increase the cross-section in volume, however, the technical effect will not be at the highest level. If the cross-sectional area does not suit you, then you can calculate it yourself using special schemes and formulas.

The primary winding should be made of copper wire, which will have increased characteristics: thermal resistance, since during the operation of the structure, this part heats up very much.

Such a part must have cotton or fiberglass insulation. In extreme cases, it is possible to use an insulated rubber wire or rubber cloth, but beware of PVC winding.

Insulation is also made by hand, using cotton or fiberglass, or rather parts of it, 2 cm wide. Thanks to these pieces, it will be possible to wrap the wire, and then soak it with any varnish for electrical purposes. This insulation will not overheat after regular operation.

Similar to the above calculations, it will be possible to calculate which sectional area of ​​the winding - primary and secondary - will be the most optimal. Often the secondary winding has an area of ​​about 30 mm2 and the primary winding up to 7 mm2, using a rod 4 mm in diameter.

In addition, in a simple way, you need to determine how much a piece of copper wire will stretch and how many turns it will take to wind two windings. After that, the coils are wound, and the frame is made using the geometric parameters of the magnetic circuit.

The main thing is to make sure that there are no difficulties when putting on the magnetic circuit. First of all, it is necessary to choose the correct size of the core. It is best to make it with the help of electrical cardboard or textolite.

Using the same analogue, it will be possible to manufacture a structure for welding small parts. For the home, you can use a small welding machine "mini".

Welding machine manufacturing

Today it is almost impossible and rather difficult to weld metal or process it in a proper way without using welding equipment. After you make a do-it-yourself welding machine, you can perform any work with metal products.

Transformer circuit with a separate choke.

To make a quality unit, you need to have the knowledge and skills that will help you understand the circuit of a DC or AC welding machine, which are two options for assembling equipment.

For home use, it's best to learn how to do mini welding.

It is more convenient to call a master or purchase a ready-made unit, but sometimes it is too expensive, since it is rather difficult to determine the number of volts per welding machine for choosing a model for various parameters, such as the mass for the welding machine.

There are several types of welding machines: AC, DC, three-phase or inverter. To choose one of the options and start assembling, it is necessary to consider each scheme of the first 2 types. During the preparatory process, you need to pay attention to the voltage stabilizer.

AC

To make homemade welding machines, you need to select a voltage indicator, the best is 60 volts, the current is best regulated from 120 to 160 amperes.

You can independently determine the value of the cross-section of the required wire for the manufacture of the primary winding of the transformer, which must be connected to a 220 volt network.

The cross-sectional area parameters should not be more than 7 mm2, since it is worth noting a possible voltage drop and possible additional load.

Based on calculations, the optimal size of the diameter of the copper core for the primary winding, which reduces the action of the mechanism, is 3 millimeters. When choosing aluminum for the wire, the cross section is multiplied by a value of 1.6.

It is worth noting that the wires need to be wrapped with a rag as they need to be insulated. The fact is that with an increase in temperature, the wire can melt and a short circuit occurs.

In the absence of the required wire, it is possible to replace it with a conductor a little thinner, winding it in pairs. However, it must be remembered that the thickness of the winding will increase, due to which the size of the welding equipment will be large. Under the secondary winding, a thick wire with a large number of copper conductors is used.

DC

Electric circuit of a direct current welder.

Some welding machines operate with direct current. Thanks to this unit, cast iron and stainless steel structures can be welded.

It may take no more than half an hour to create a DC welding machine with your own hands. In order to convert homemade products with alternating current, it is necessary that the secondary winding be connected, which is assembled on a diode.

In turn, the diode must be able to handle 200 amperes and be well cooled. To trim the current value, you can use capacitors that have certain characteristics and voltage features. After that, the unit is assembled sequentially according to the scheme.

Chokes are used to regulate the current, and the contacts are used to attach the holder. Additional parts are used in transferring current from an external carrier to the welding site.

To operate the welding machine for its intended purpose, it is necessary, first of all, to ignite an electric arc. This process is easy and is performed by the following actions: bring the tip of the electrode at a certain inclination from the side of the metal coating and strike it along the surface of the structure.

If the action is done correctly and successfully, a small flash occurs, and the material melts, after which the necessary elements can be welded.

When making a mini welding machine with your own hands, you must be guided by the recommendations for working with it. To weld the elements, you need to keep the rod in such a position that it is at a certain distance from each other of the parts to be welded. This distance can be equal to the cross section of the selected electrode.

Often, a metal such as carbon steel is joined with direct polar current. However, some alloys can only be welded in reverse current polarity. In addition, it is necessary to carefully monitor the quality of the seam and how the structure is melted.

Diagram of a simple welding machine.

It is worth emphasizing that the alternating current present can be regulated efficiently and smoothly. Often, no difficulties arise with adjusting the unit to the required parameters.

With a small indicator of the current strength, the seam will come out of poor quality, but an increased value should not be set, since there is a risk of burning the surface.

If it is necessary to weld surfaces of small thickness, then the rods are suitable with a size of 1 to 3 millimeters, while the current strength should vary from 20-60 A. be 100 A.

Upon completion of the welding process, using homemade products, it is necessary to carefully remove the scale with light movements that appears on the seam, after which it is cleaned with a special brush.

Thanks to this action, you will be able to maintain a pleasant aesthetic appearance of your device. Do not worry if the cleaning of the equipment will not work very well in the first couples. This skill is gained from experience and subject to all recommendations for the correct operation of the structure.

Outcome

Summing up, it is worth noting that DC welding machines are much easier to assemble and they are also convenient to operate, due to their low power.

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

Welding machines are available in DC and AC.

S.A. direct current are used when welding at low currents of thin sheet metal (roofing steel, automobile, etc.). DC arc is more stable, direct and reverse polarity can be welded. On direct current, you can weld with electrode wire without coating and with electrodes intended for welding, both on direct current and on alternating current. To give stability to arc burning at low currents, it is desirable to have an increased open-circuit voltage Uxx of the welding winding (up to 70 - 75 V). For rectifying alternating current, the simplest "bridge" rectifiers on powerful diodes with cooling radiators are used (Fig. 1).

To smooth out voltage ripples, one of S.A. And they are connected to the electrode holder through a choke L1, 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 with the use of powerful controlled thyristors. One of the possible circuits on thyristors of the T161 (T160) type is given in the article by A. Chernov "Both will charge and weld" (Modelist-constructor, 1994, No. 9). The advantages of DC regulators are their versatility. The range of voltage variation by them is 0.1-0.9 Uxx, which makes it possible to use them not only for smooth adjustment of the welding current, but also for charging batteries, powering electric heating elements and other purposes.

Figure 2. Diagram of the falling external characteristics of the welding machine.

Rice. 1. Bridge rectifier for the welding machine. Connection of S.A. is shown. for welding thin sheet metal on "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, the diameter of which is more than 1.6 - 2 mm, and the thickness of the products to be welded is more than 1.5 mm. In this case, the welding current is significant (tens of amperes) and the arc burns quite steadily. The electrodes used are intended for welding only on alternating current. For normal operation of the welding machine, you must:

1. Provide output voltage for reliable arc ignition. For amateur S.A. Uxx = 60 - 65v. A higher open-circuit output voltage is not recommended, which is mainly associated with ensuring the safety of work (Uxx industrial welding machines - up to 70 - 75 V).
2. Provide welding voltage Uw, required for stable arc burning. Depending on the diameter of the electrode - Uw = 18 - 24v.
3. Provide a 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 Isc, 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 and voltage in the welding circuit (Fig. 2).

S.A. shows that for a rough (stepwise) overlap of the range of welding currents, it is necessary to switch both the primary windings and the secondary windings (which is structurally more complicated 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 removing the welding winding relative to the mains, magnetic leakage fluxes increase, which leads to a decrease in the welding current.

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

When designing an amateur SA, 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, to 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 the 220V network.

The weight and dimensions of the apparatus can be reduced due to a decrease in its power, and an increase in the duration of operation - due to the use of steel with high magnetic permeability and heat-resistant insulation of the winding wires. These requirements are easy to fulfill, 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 ranges of welding; Isv2, Isvz, Isv4 - ranges of welding currents for electrodes with a diameter of 2, 3 and 4 mm, respectively; Uxx- open circuit voltage CA. 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 made of strips of transformer steel; S = axb- cross-sectional area of ​​the core (core), cm 2 s, d- window dimensions, see.

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

Figure 4. Diagram of a toroidal type magnetic circuit.

The section of the core should be S = 45 - 55 cm 2. The welding machine will be a little heavier, but it won't let you down! Amateur welding machines with toroidal cores, which have higher electrical characteristics, are about 4 - 5 times higher than that of a rod one, are becoming more widespread, and electrical losses are small. Labor costs for their manufacture are more significant and are primarily associated 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 of tape transformer iron, rolled into a torus-shaped roll. An example is a core made of an autotransformer "Latr" for 9 A. To increase the inner diameter of the torus ("window"), a part of the steel tape is unwound from the inside and wound onto the outer side of the core. But, as practice shows, "Latra" alone is not enough to produce high-quality SA. (small cross 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 B. Sokolov's article "Welding baby" (Sam, 1993, No. 1), or to manufacture one core by rewinding two (Fig. 4).

Rice. 4. Toroidal magnetic circuit: 1.2 - autotransformer core before and after rewinding; 3 design by S.A. based on two toroidal cores; W1 1 W1 2 - mains 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.

Special attention should be paid to amateur SA made on the basis of stators of asynchronous three-phase electric motors of high power (more than 10 kW). 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 inappropriate to reduce the cross-section S to less than 40 - 45 cm.

Figure 5. Scheme of fastening the conclusions of the CA windings.

The stator is freed from the housing, the stator windings are removed from the inner grooves, the groove bridges 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 off and wrapped tightly, overlapping with cotton insulating tape. The core is ready for winding the windings.

Selection of windings. For primary (network) windings, it is better to use a special copper winding wire in h.b. (fiberglass) insulation. Wires in rubber or rubber-fabric insulation also have satisfactory heat resistance. Unsuitable for work at elevated temperatures (and this is already incorporated into the design of an amateur SA) 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 the wires wrapped along the entire length of the h.b. with insulating tape, or do not remove, but wrap the wire over the insulation. Another method of winding that has been tested in practice is also possible. But more on that below.

When selecting the cross-section of the winding wires, taking into account the specifics of the work of S.A. (periodic) we assume a current density of 5 A / mm 2. With a welding current of 130 - 160 A (electrode de = 4 mm), the power of the secondary winding will be P 2 = Iw x 160x24 = 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 advisable 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) 2.6 - 3 mm. (Calculation according to the well-known formula S = piR 2, where S is the area of ​​the circle, mm 2 pi = 3.1428; R is the radius of the circle, mm.) If the section of one wire is insufficient, winding in two is possible. When using an aluminum wire, its cross-section must be increased by 1.6 - 1.7 times. Is it possible to reduce the cross-section of the mains winding wire? Yes, you can. But at the same time S.A. will lose the required power reserve, it will heat up faster, and the recommended core section S = 45 - 55 cm in this case will be unjustifiably large. The number of turns of the primary winding W 1 is determined from the following ratio: W 1 = [(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. Diagram of ways of winding CA windings on a rod-type core.

A larger number of network winding taps, as practice shows, is impractical. And that's why. By reducing the number of turns of the primary winding, both the power of the SA and Uxx increase, which leads to an increase in the arc voltage and a deterioration in the quality of welding. Consequently, it is impossible to achieve overlapping of the range of welding currents only by changing the number of turns of the primary winding without deteriorating the quality of welding. To do this, it is necessary to provide for switching the turns of the secondary (welding) winding W 2.

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

Rice. 5. Fastening of the CA winding leads: 1 - CA case; 2 - washers; 3 - terminal bolt; 4 - nut; 5 - copper tip with a wire.

The difficulty of acquiring switches for high currents, and practice shows that it is most simple to lead the leads of the welding winding through copper lugs under terminal bolts with a diameter of 8-10 mm (Fig. 5). Copper lugs are made from copper tubes of a suitable diameter 25-30 mm long and fixed to the wires by crimping and preferably soldering. Let's pay special attention to the order of winding winding. General rules:

1. Winding should be done on an insulated core and always in one direction (eg clockwise).
2. Each layer of the winding is insulated with a layer of h.b. insulation (fiberglass, electrical cardboard, tracing paper), preferably impregnated with bakelite varnish.
3. The conclusions of the windings are tinned, marked, fixed with h.b. braid, on the conclusions of the network winding, they additionally put on h.b. cambric.
4. In case of doubts about the quality of 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 h.b. thread is fixed with glue, varnish, etc. and after drying, the next row is wound.

Figure 7. Diagram of ways of winding CA windings on a toroidal core.

Consider the order of arrangement of the windings on a rod-type magnetic circuit. The mains winding can be positioned in two main ways. The first method allows you to obtain a more "hard" welding mode. The mains 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 CA has a steeply dipping characteristic, it cooks "softly", the arc length has less effect on the value of the welding current, and, consequently, on the quality of welding. After winding the primary winding of the 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 alternating current ammeter. If the fuse burns out or gets very hot, then this is a clear sign of a short-circuited loop. Consequently, the primary winding will have to be rewound, paying particular attention to the quality of the insulation.

Rice. 6. Methods of winding CA windings on a rod-type core: a - mains winding on both sides of the core; b - the corresponding secondary (welding) winding, connected in counter-parallel; c - mains winding on one side of the core; d - the corresponding secondary winding, connected in series.

If the welding machine hums strongly, and the current consumption exceeds 2 - 3 A, then this means that the number of the primary winding is underestimated and it is necessary to wind up some more turns. A serviceable AC consumes no more than 1 - 1.5 A no-load current, does not heat up and does not buzz much. The secondary winding CA is always wound on both sides of the core. For the first method of winding, the secondary winding also consists of two identical halves, included to increase the stability of arc burning (Fig. 6) counter-parallel, and the wire cross-section can be taken slightly less - 15 - 20 mm 2.

Figure 8. Wiring diagram for measuring devices.

For the second method of winding, the main welding winding W 2 1 is wound on the side of the core free of 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 across it drops by 80 - 90%. An additional welding winding W 2 2 is wound over the primary. Being power, it maintains the welding voltage, and therefore the welding current, within the required limits. The voltage across it drops in welding mode by 20 - 25% relative to the open circuit voltage. After the manufacture of S.A, it is necessary to adjust it and check the quality of welding with electrodes of various diameters. The setup process is as follows. To measure welding current and voltage, it is necessary to purchase two electrical measuring devices - an alternating current ammeter for 180-200 A and an alternating current voltmeter for 70-80 V.

Rice. 7. Methods of winding CA windings on a toroidal core: 1.2 - uniform and sectional winding of windings, respectively: a - network b - power.

Their connection diagram is shown in Fig. 8. When welding with different electrodes, the values ​​of the welding current - Iw and the welding voltage Uw, which must be within the required limits, are removed. 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 ​​are set, or the number of turns of the secondary winding is redistributed (without increasing them) in the direction of increasing the number of turns wound over network winding. After welding, you can make a break or sawing of the edges of the welded products, and immediately the quality of the welding becomes clear: the penetration depth and the thickness of the deposited metal layer. It is useful to draw up a table based on the measurement results.

Figure 9. Diagram of welding voltage and current meters and current transformer design.

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

Rice. 9. Schematic diagram of welding voltage and current meters and current transformer design.

The voltage meter is connected to the output (welding) winding of S.A. Adjustment is carried out using any tester that monitors the output voltage of the welding. With the help of variable resistance R.3, the arrow 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 to measure voltages.

It is more difficult to set up a current meter as it connects to a self-made current transformer. The latter is a toroidal core with two windings. The dimensions of the core (outer diameter 35-40 mm) are not of fundamental importance, the main thing is that the windings fit. The core material is transformer steel, permalloy or ferrite. The secondary winding consists of 600 - 700 turns of PEL, PEV insulated copper wire, better than PELSHO with a diameter of 0.2 - 0.25 mm and is connected to a current meter. The primary winding is the power wire that runs inside the ring and connects to the terminal bolt (Figure 9). Setting up a 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 determining the current flowing in the welding winding. For example, when connecting Rн = 0.2 ohm, Uout = 30v.

Mark a point on the scale of the instrument. Three to four measurements with different R H are enough to calibrate the current meter. After calibration, the devices are installed on the S.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 tuned 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. this type has a number of specific requirements:

1. The power delivered 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, consequently, the winding of the windings of S.А. should be carried out according to the first option.
3. The currents flowing in the welding winding reach values ​​of 1500-2000 A and higher. 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. Achieve this cross-section of wires by winding 4-6 windings and their subsequent parallel connection.
5. It is impractical 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 S.A.
7. It is not recommended to take a section of the core (core) less than 45-50 cm.
8. Welding lugs and submarine cables to them must be copper and carry appropriate currents (lug diameter 12-14 mm).

A special class of 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 core section, which should be at least 25 cm, and the diameters of the primary and secondary windings. It will immediately become clear to you what can be expected from the alteration of this transformer.

And in conclusion, a few technology 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 diameter of the electrode, depending on the thickness of the metal to be welded, can be selected based on the following ratio: 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 perform welding with a short arc of 2-3 mm, the voltage of which is 18-24 V. An increase in the length of the arc leads to a violation of the stability of its combustion, an increase in losses for waste and spatter, and a decrease in the depth of penetration of the base metal. The longer the arc, the higher the welding voltage. The welding speed is chosen by the welder depending on the grade and thickness of the metal.

When welding on straight polarity, the plus (anode) is connected to the part and the minus (cathode) is connected to the electrode. If it is necessary that a smaller amount of heat is generated on the part, for example, when welding thin-sheet structures, welding is used in reverse polarity (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 provides less heating of the workpiece to be welded, but also accelerates the process of melting the electrode metal due to the higher temperature of the anode zone and greater heat supply.

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

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