How to assemble a welding machine at home? DIY mini welding machine for domestic use Homemade DIY welding

In construction, installation and repair work, a welding machine is used. Usually the design is purchased ready-made, but you can make it yourself. In this case, there is a significant savings in money. Moreover, this process can captivate those who like to engage in the manufacture of something new.

Connections, electrodes and windings

In order to assemble the welding machine with your own hands, you need to decide on the scheme on the basis of which the work will be carried out. Even before the start of the main work, it is worth considering how the unit will be powered. If the voltage is higher, then the use of the device may harm human health.

Usually, a single-phase 220 V network is used to power the equipment. In this case, it is necessary to use an additional winding (special ballast), with the help of which the periodically changing electric current is regulated during the welding period.

Before assembling a welding inverter with your own hands, you need to purchase:

• Transformer magnetic circuit.
• Remote capacitor devices.
• Welding mode switch.
• Several types of windings (primary, secondary, additional).
• Regulatory devices that help to establish the optimal welding mode.
• Special heat sensors.
• A device that notifies you with sounds about the optimal mode of operation.

Why Use Concrete

Before you make an inverter welding machine with your own hands, you need to make a case. It is made of specially prepared concrete, characterized by a high degree of plasticity. This material is able to quickly harden and become the desired shape.

The hull is made from fine-grained sand and cement in certain proportions. You should take 75 percent sand, 20 percent cement. In addition to these components, it is necessary to add an equal amount of PVA glue and glass wool. Sometimes the glue is replaced with a water-soluble latex material.

Novice craftsmen believe that the unit is quite easy to assemble with their own hands, in comparison with the creation of its body. With sequential work, the structure is assembled quite quickly.

The body must be at least 1 cm thick. The welding machine is cleaned, followed by drying, after which the body is started to be made. After waiting for the concrete to harden, the unit is externally processed using an organic monomer.

To cope with this task, experts recommend using styrene or methyl methacrylate. They help to heat treat the surface of the device. In this situation, a temperature above 70 degrees Celsius should be applied.

As a result of monomer polymerization, a waterproof layer is formed on the surface of the unit body. It is he who protects the surface of the structure from environmental influences.

Simple design

For the layout of the welding machine, you can use faulty household appliances. For example, you can use a failed microwave oven. Together with it, you should take electrical wiring, clamps, wooden parts and tips.

Taking all these components, it is possible in a short time, even with minimal knowledge in the field of technology, to produce the design of an apparatus for spot welding.

Parts inside the unit are fixed with self-tapping screws, washers or brackets of appropriate sizes. It is optimal to use a serviceable transformer of a broken microwave oven, from which equipment is made by hand.

Assembly process

They begin work by removing the secondary winding from the transformer. This operation requires accuracy. It is carried out with an angle grinder.

Next, the lamellar core is removed from the surface of the secondary winding. After carrying out the operation on the transformer, parts cut off on both sides can be found. With their help, the work will be better. Ideally, it is necessary to ensure that the insulating layer on the core is free of any defects.

Then the magnetic shunt is attached. During its normal functioning, the work of a do-it-yourself welding machine is carried out. Then the transformer is rewound using a thick wire made of copper material. If the core is damaged, it needs to be repaired. If the defect is minimal, then the site is isolated.

At the next stage, it is necessary to put the transformer on a wooden block, securing the top and bottom of the workstation with brackets. If the electrodes are attached qualitatively, then the unit will work better. If there are defects in the contacts, it will be difficult to weld the elements.

The fixation of the electrodes on the upper and lower parts of the bar is carried out with self-tapping screws. Then winding wires are connected to them. It is necessary to properly fix the copper terminals using pliers, which is usually very difficult for beginners. The structure is ready. Then it is necessary to check whether something can be welded using the unit, while it is important to follow the safety regulations.

Usually, it is not difficult to assemble a welding machine even for those people who have minimal technical knowledge. To do this, you can use the step-by-step instructions with photos at all stages, of which there are a large number on the Internet.

DIY welding machine photo

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

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

What will we be about

This article discusses how to make equipment at home for:

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

What we won't talk about

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

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

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

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

Transformer

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

1. a little theory - on the fingers, without formulas and zaumi;
2. features of the magnetic circuits of welding transformers with recommendations for choosing from randomly turned up ones;
3. testing of available second-hand;
4. calculation of a transformer for a welding machine;
5. preparation of components and winding of windings;
6. trial assembly and fine-tuning;
7. commissioning.

Theory

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

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

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

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

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

It is impossible to cook from a transformer with a rigid VX: the seam is torn, burnt, the metal is splashed. The arc is inelastic: I almost moved the electrode in the wrong way, it goes out. Therefore, the welding transformer is already made similar to a conventional water tank. Its VC is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage drops smoothly. The normal scattering curve is approximated by a straight line falling at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly remove several times more power from the same iron, or, respectively. reduce the weight and size of the transformer. In this case, the induction in the core can reach the saturation value, and even exceed it for a short time: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: thermal time constant of welding transformers 20-40 min. If you then let it cool down and there was no unacceptable overheating, you can continue to work. The relative drop in the secondary voltage ΔU2 (corresponding to the range of arrows in the figure) of normal dissipation gradually increases with an increase in the range of oscillations of the welding current Iw, which makes it easy to hold the arc in any type of work. These properties are provided as follows:

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

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

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

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

Magnetic circuits

Types of magnetic circuits suitable for the manufacture of welding transformers are shown in fig. Their names begin with a letter combination respectively. size. L means tape. For a welding transformer L or without L, there is no significant difference. If there is M in the prefix (SLM, PLM, SMM, PM) - ignore without discussion. This is iron of reduced height, unsuitable for a welder with all other outstanding advantages.

The letters of the nominal value are followed by numbers denoting a, b and h in fig. For example, for Sh20x40x90, the cross-sectional dimensions of the core (central rod) are 20x40 mm (a * b), and the window height h is 90 mm. Cross-sectional area of ​​the core Sc = 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 size, and for them - the steel grade. Where will we get it if we wind it on random hardware? We will calculate according to a simplified method (see below), and then we will bring it up during the tests. 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 colors on it, this is a marriage. Once this transformer overheated very much and the magnetic properties of its iron deteriorated irreversibly.

Another important parameter of the magnetic circuit is its mass, weight. Since the specific gravity of the 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 of:

• O, OL - from 10 kg.
• P, PL - from 12 kg.
• W, WL - from 16 kg.

Why Sh and ShL are needed harder is understandable: they have an “extra” side rod with “shoulders”. OL can be lighter, because there are no corners in it that require excess iron, and the bends of the magnetic lines of force are smoother and for some other reasons, which are already in the next. section.

Oh OL

The 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 LATR - a laboratory autotransformer. Laboratory, which means it should not be afraid of overloads, and the LATR iron provides a VX 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 you don’t need it, 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.

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

Another torus suitable for all properties is the stator of an electric motor; welding from it will turn out at least for an exhibition. But finding it is no easier than LATR's iron, and winding it up is much more difficult. In general, a welding transformer from an electric motor stator is a separate issue, there are so many complexities and nuances. First of all - with the winding of a thick wire on a "donut". Having no experience in winding toroidal transformers, the probability of damaging an expensive wire and not getting welding is close to 100%. Therefore, alas, it will be necessary to wait a little with the cooking apparatus on a triad transformer.

SH, SHL

Armor cores are structurally designed for minimal scattering, and it is almost impossible to normalize it. Welding on a regular Sh or ShL will be too hard. In addition, the cooling conditions of the windings on Sh and ShL are the worst. The only armored cores suitable for a welding transformer are of increased height with spaced biscuit 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 shifted (assembled from plates) for welding necessarily overlapped, i.e. yoke-plate pairs are alternately oriented back and forth relative to each other. The method of normalizing scattering by a non-magnetic gap for a welding transformer is unsuitable, because the loss is irreversible.

If a laminated Ш turns up without a yoke, but with a punching of the plates between the core and the jumper (in the center), you are in luck. The plates of signal transformers are mixed, and the steel on them, to reduce signal distortion, goes giving a normal VX initially. But the probability of such luck is very small: signal transformers for kilowatt power are a rare curiosity.

Note: do not try to assemble a high W or WL from a pair of ordinary ones, as on the right in fig. A continuous direct gap, albeit a very thin one, is irreversible scattering and a steeply falling VX. Here, the dispersion loss is almost similar to the evaporation loss of water.

PL, PLM

Rod cores are most suitable for welding. Of these, they are laminated in pairs of identical L-shaped plates, see Fig., Their irreversible scattering is the smallest. Secondly, the windings of P and Plov are wound in exactly the same halves, half turns for each. The slightest magnetic or current asymmetry - the transformer buzzes, heats up, but there is no current. The third thing that may seem non-obvious to those who have not forgotten the school rule of the gimlet is that the windings on the rods are wound in one direction. Does something not seem right? Does the magnetic flux in the core have to be closed? And you twist the gimlets according to the current, and not according to the turns. The directions of the currents in the half-windings are opposite, and the magnetic fluxes are shown there. You can also check if the wiring protection is reliable: apply the network to 1 and 2 ', and close 2 and 1 '. If the machine 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 still find recommendations - to wind the windings of the welding P or PL on different rods. Like, VX softens. That's how it is, but for this you need a special core, with rods of different sections (secondary on a smaller one) and notches that release lines of force into the air in the right direction, see fig. on right. Without this, we get a noisy, shaky and gluttonous, but not a cooking 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 a 3 A electromagnetic pointer. the shape of the current in the circuit will be far from sinusoidal. Another is a liquid household thermometer with a long neck, or, better, a digital multimeter with the ability to measure temperature and a probe for this. The 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. With seeming inconsistency, most of them are correct, but with full knowledge of the properties of steel and / or for a specific range of magnetic core ratings. The proposed methodology was developed in Soviet times, when there was a shortage of everything instead of a choice. For the transformer calculated from it, the VX drops 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), which stretch the VX along the current axis to curve 2a.

The calculation basis is usual: the arc stably burns under voltage Ud 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the nominal welding current. Accordingly, the minimum open-circuit voltage Uxx 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. Nothing more: it’s unacceptable according to TB, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly switch from a short circuit mode (say, when shorted by metal drops) to a working one, is maintained without additional measures. True, such a transformer is prone to overheating, but since it is ours and in front of our eyes, and not the far corner of a workshop or site, we will consider this acceptable. So:

• According to the formula from paragraph 2 before. the list we find the overall power;
• We find the maximum possible welding current Iw \u003d Pg / Ud. 200 A are provided if 3.6-4.8 kW can be removed from the iron. True, in the 1st case, the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
• We calculate the operating current of the primary at the maximum network voltage allowed for welding I1рmax = 1.1Pg (VA) / 235 V. In general, the norm for the network is 185-245 V, but for a home-made welder at the limit, this is too much. We take 195-235 V;
• Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
• We accept the current density of the primary J1 = 5 A/sq. mm and, using I1rmax, we find the diameter of its copper wire d = (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation D = 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, mortar yok" mode, you can take J1 \u003d 6-7 A / sq. mm, but only if the required wire is not available and is not expected;
• We find the number of turns per volt of the primary: w = k2 / Sс, where k2 = 50 for W and P, k2 = 40 for PL, SHL and k2 = 35 for O, OL;
• We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy losses of the winding due to leakage and in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
• We set the stacking factor Ku = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of winding layers, the average length of the coil and the wire footage
• We calculate the secondary in the same way at J1 = 6 A/sq. mm, k3 \u003d 1.05 and Ku \u003d 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.

Winding and finishing

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

isolation

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

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

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

winding

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

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

Finishing and domotka

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

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

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

Pull VX

But he is still too cool with us, remember? Needs to be softened. The simplest way - a resistor in the secondary circuit - does not suit us. Everything is very simple: at a resistance of only 0.1 ohms at a current of 200, 4 kW of heat will be dissipated. If we have a welder for 10 or more kVA, and we need to weld thin metal, a resistor is needed. Whatever the current is set by the regulator, its emissions when the arc is ignited are inevitable. Without an active ballast, they will burn the seam in places, and the resistor will extinguish them. But to us, low-powered ones, he will not be of any use to him.

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

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

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

But other?

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

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

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

Trying a constant

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

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

With a magnetic circuit, the coil is simpler, although not quite. For it, 2 PLA of the TS-270 power transformer from old tube TVs-“coffins” (the data is available in reference books and in Runet), or similar, or SL with similar or large a, b, c and h. From 2 PLs, a SL is assembled with a gap, see Fig., 15-20 mm. Fix it with textolite or plywood gaskets. Winding - insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. They wind it in 2 wires. The end of one is connected to the beginning of the other, this will be the middle point.

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

microarc

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

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

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

Contact welding in industry is mainly used for spot, seam and butt welding. At home, primarily in terms of energy consumption, a pulsed point is feasible. It is suitable for welding and welding thin, from 0.1 to 3-4 mm, steel sheet parts. Arc welding will burn through a thin wall, and if the part is a coin or less, then the softest arc will burn it entirely.

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

Nevertheless, 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. A transformer for contact welding is calculated similarly to it for arc welding, but the current density in the secondary winding is 30-50 or more A / sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, it cools well, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

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

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

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

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

About electrodes

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

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

The last point about the electrodes is their material and dimensions. Red copper quickly burns out, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, at current copper prices it is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. The length of the electrode according to the conditions of heat transfer is at least 3 of its diameters from the heel to the root (beginning of the shank).

How to give impetus

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

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

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

Do-it-yourself welding machines for the home are most often created by craftsmen from improvised materials.

If you do not have the opportunity or desire to buy a welding machine, then you can assemble it yourself using ready-made elements.

However, to speed up the assembly process, ready-made assemblies and parts can be used. The holder for the electrodes can also be made on your own from the materials available in the arsenal of the home master.

The simplest welding machine

In the household of a home master, a step-down transformer S-B22, IV-10, IV-8 can be found, the power of which is 1-2 kW. It lowers the voltage from 220 V to 36 V, serves to power the power tool.

Welding machines based on such transformers can be assembled even with a failed winding.

The welding machine is manufactured as follows:

Remove the secondary winding from the transformer.

• secondary windings are removed from the coils without damaging the primary ones;
• the middle primary coil is rewound with the same wire, creating taps with a total of 8-10 pieces after 30 turns. (for convenience, it is better to number each of them as they are created);
• two extreme coils are filled with a multi-core cable (three 6-8 mm wires with a thin phase, 12-13 m is spent on each coil);
• a copper pipe with a diameter of 10-12 mm is used for a terminal for a VO cable (one side compresses the wires, the second is flattened, drilled for fasteners with a diameter of 10 mm);
• on the top panel of the transformer, the M6 ​​fasteners are replaced by more powerful ones (M10), VO terminals are attached to them;
• A board with 10 holes for software is made from textolite, M6 fasteners are inserted into each hole.

Welding machines of this design are powered by a 380/220 V network. In the first case, the software of the extreme, then the middle coils are connected in series. In the second variant, the extreme windings are connected in parallel, the middle winding is connected in series to the same circuit. VO taps are put into the terminals of the textolite plate 1 - 10. The current is regulated by terminals 1 - 10.

It is not recommended to perform large volumes of work with this SA (maximum 15 “troika” electrodes).

For cutting metal, the second end of the cable leading to the holder is connected to the cutting terminal (on the side of the middle coil of the software). The characteristics of the VO current correspond to 60-120 A, in the software the current is always 25 A. When working with “two” electrodes, the transformer does not heat up above + 70 ° C, so the operating time is not limited. Welding/cutting modes are switched when the switch is off.

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Machine for welding from car batteries

In order to invent a diesel generator for a welding machine, it is necessary to connect a pair of batteries in a certain sequence.

The welding machine seriously loads the household power supply, providing a power surge of 30 V at a load of 3.5 kW. Instead of purchasing a welding diesel generator, the craftsmen created an original device circuit, the basis of which is 3-4 series-connected batteries from a car. The capacity of each of them must be at least 55-190 A / h; reliable clamps must be used to combine them into a common circuit.

This scheme is indispensable in the field, as even used batteries delivered to the object by the forces of a passenger vehicle will help out. It is necessary to take into account the strong heating of the AB cases after several hours of operation, check the level and density of the electrolyte daily during continuous use. In the heat, water evaporates intensively from the electrolyte, so control devices (hydrometer), distilled water, and acid should be kept at hand.

It is enough to put welding machines of this type on nightly recharging by connecting the appropriate device to a common circuit so that all batteries are charged at once. When welding with electrodes with a diameter of 3 mm, the working current is not more than 90-120 A, which does not exceed half the power. The electrolyte does not boil due to the high heat capacity. The output voltage completely depends on the number of batteries connected to the circuit, it is 42-54 V.

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Homemade toroidal welding machine

U-shaped, W-shaped transformers are significantly inferior to toroids in terms of weight and size ratio. A toroidal welding machine is one and a half times lighter than a W-shaped counterpart, however, the main difficulty in self-manufacturing lies in the lack of the necessary iron. Craftsmen share recommendations for the manufacture of a transformer from an industrial SA that has worked out its required resource. A similar replacement will be the transformer TCA 310 or TC 270. Its U-shaped plates are “halved” with a chisel, ruled on an anvil.

Welding machines of this type are assembled from 45 x 9 cm plates:

• a lamellar riveted hoop with a diameter of 26 cm is filled with plates end to end to each other (the work is done together, the partner fixes the recruited core, preventing the plates from straightening);
• when the inner diameter of the structure reaches 12 cm, the set is stopped;
• details are cut out of the electric cardboard: a strip 9 cm wide, rings with an inner diameter of 11 cm, an outer 27 cm;
• rings are applied to the sides of the structure assembled at the first stage, wrapped with cloth tape;
• winding I is laid on electrical tape - 170 turns (for 220 V) wires with a diameter of 2 mm brand PEV-2;
• winding II is laid on top of it - 30 turns with a wire with a diameter of 15-20 mm of brand PEV-3;
• winding III - 30 turns with wire brand MGTF 0.35;
• isolation from each other with a braid, the software is checked for the XX current: if it is less than 1-2 A, several turns are unwound, if the XX current is more than 2 A, two turns are added.

This welding machine has an original control circuit in the form of a phase regulator. The voltage taken from winding III is rectified by a diode bridge. The capacitor is charged through resistors up to 6 V, then a breakdown occurs through a dinistor assembled from a thyristor, a zener diode. The thyristor diode opens. The last resistor in the circuit limits the current, with a negative wave of alternating current, the response thyristor and diode open. Welding machines of this design are tuned by a resistor.

To create a welding machine, resistors with a power of 10 W or more are required.

The diagram uses:

• diodes for a current of 160-250 A, mounted on radiators with an area of ​​\u200b\u200b100 cm 2 or more;
• capacitor K50-6;
• resistors with power from 10 W;
• thyristors KU202 or KU201.

The welding machine confidently cooks with electrodes with a diameter of 4 mm, cuts metal. The holder for it can be made independently from an equal-shelf corner 10 cm long (shelves 2 cm each). A hole with a diameter of 4.1 mm is drilled 1 cm from the edge of the corner in the very corner, through which the burnt electrode can be pushed out with a new electrode. The lower part of the shelves is narrowed by the hand of the welder. A wire is welded into the inner corner, bent vertically upwards from it. From below, a piece of rubber hose is put on the structure. During operation, the electrode is inserted between the edges of the corner, pressed against them with a piece of welded wire.

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

Of course, you will have expenses, but incomparably less compared to the cost of purchasing a factory-made gadget. But how much fun you will get in the process of your favorite homemade work. 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. selection, calculation and production welding transformer (hereinafter - ST), which will help to optimize costs and save the budget.

A properly made do-it-yourself device is no worse than a factory one.

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

• arc;
• contact.

Do-it-yourself welding transformer: what we need

The range of tools and equipment for the manufacture and assembly of both types of ST is identical. We will 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(it is also a “grinder”, “zipper-machine”, etc.) with a set of discs (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 for marking on 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 ST. In general, it is like this:
  • complete electric soldering iron. We will perform soldering with solder POS-40;
  • screwdrivers (different sizes with a straight and cross slot);
  • keys:
    • wrench;
    • cap;
    • end;
  • pliers, side cutters, etc. with insulated handles;
• file set.

It is more convenient to carry out all work on a metalwork workbench with an electrically insulating coating, equipped with a metalwork vice.

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

• protective cover. Must 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 referred to as EMF) in the windings;
• wire and wire. Necessary for the installation of windings;
• coil frames. Windings are wound on them;
• contact pads. Powerful terminal block with clamps for welding wires, small blocks - for wiring the circuit;
• switches (switches). Carry out switching sections of the windings when selecting the value of the welding current;
• interturn insulation material. Reduces the possibility of electrical breakdown of the winding insulation;
• fasteners (bolts, screws, nuts, washers, etc.). They are necessary for mounting the gadget during assembly work;
• insulating tape(type Х/Б).

Important: PVC insulating tape cannot be used, because it is destroyed when heated.

Homemade welding transformer for arc welding

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

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

Only after that, you should 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 home-made welding transformer is very specific, since it does not correspond to typical schemes and generally accepted rules. The fact is that in the manufacture of homemade products, the parameters of their components are “adjusted” to the components already available (mainly to the magnetic circuit). Moreover, it often happens that:

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

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

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

• rod;
• armored.

Explanations for the figure:

• a - armored;
• b - rod.

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 laboriousness 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 - network winding on two sides of the core;
• b - the corresponding secondary (welding) winding, connected in anti-parallel;
• c - network winding on one side of the core;
• g - the secondary winding corresponding to it, connected in series.

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

We determine the power of the ST (according to the magnitude of the current in the secondary winding) from the following considerations. For electric welding in everyday life, coated electrodes are most often used Ø, mm: 2, 3, 4. We choose the “golden mean” for the most popular ones - 120 ... 130 A. The power of the ST is determined by the formula:

P = Uх.х. × Ist. × cos(φ) / η, where:

• Ux.x. - no-load voltage;
• Ist. - welding current;
• φ is the phase angle between voltage and current. Accept: cos(φ) = 0.8;
• η - efficiency. For homemade ST: efficiency = 0.7.

If we 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: 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 a given 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 circuit 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 from strips of transformer steel;
• c and d are the dimensions of the "window", cm;
• S \u003d a x b - cross-sectional area of ​​\u200b\u200bthe 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 selected by us and the parameters of the magnetic circuit can be made using the following formulas:
N1 = 7440 × U1/(Sout × I2). For windings on one arm (half of the windings on top of each other, connected in series);
N1 = 4960 × U1/(Sout × I2). The windings are spaced on different shoulders.

Conventions in both formulas:

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

The output voltage of the secondary winding of the ST in idle 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, taps are made on the windings.

Welding transformer winding and installation

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

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 ST 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 ST.

The secondary winding is carried out 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 windings, pay attention to the following:

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

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

Video

See how the task of assembling the device was implemented:

Do-it-yourself contact welding from a welding transformer

Contact 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 contact welding:

• point;
• butt;
• suture.

We will talk about homemade ST for the most popular: resistance spot welding (the other two require very sophisticated equipment).

Explanations for the figure:
1 - electrodes supplying welding current to the workpiece to be 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;
• the 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

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

Very often, during the operation of homemade products, it turns out that there is not enough power of the ST. 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 requirements as for CT arc welding. With special care, the turns of the secondary winding should be fixed. To do this, you can use its conclusions 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. Under no circumstances should the electrode diameter be smaller than the wire diameter. For low-power CTs, it is possible to use tips from powerful soldering irons.

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

:

• the welder needs to stand on a rubber mat;
• workers must wear rubber gloves;
• A welding mask is not required, but goggles must be worn on the face.

findings

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

• arc welding;
• contact welding.

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

Welding machines are of direct and alternating current.

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

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

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

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

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

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

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

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

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

When designing an amateur S.A., one should not strive to completely cover the range of welding currents. It is advisable at the first stage to assemble a welding machine for working with electrodes with a diameter of 2–4 mm, and at the second stage, if it is necessary to work at low welding currents, supplement it with a separate rectifier device with smooth regulation of the welding current. Amateur welding machines must meet a number of requirements, the main of which are the following: relative compactness and low weight; sufficient duration of operation (at least 5 - 7 electrodes de = 3 - 4 mm) from a 220v network.

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

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

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

So, the choice of the type of core. For the manufacture of welding machines, mainly rod-type magnetic cores are used, since they are more technologically advanced in design. The core is recruited from electrical steel plates of any configuration with a thickness of 0.35-0.55 mm, tightened with studs isolated from the core (Fig. 3). When selecting the core, it is necessary to take into account the dimensions of the "window" to fit the windings of the welding machine, and the cross-sectional area of ​​​​the core (core) S =axb, cm 2. As practice shows, you should not choose the minimum values ​​\u200b\u200bof S \u003d 25 - 35 cm, since the welding machine will not have the required power reserve and it will be difficult to obtain high-quality welding. Yes, and overheating of the welding machine after a short operation is also inevitable.

Figure 4. Scheme of a toroidal type magnetic circuit.

The cross section of the core should be S = 45 - 55 cm 2. The welding machine will be somewhat heavier, but will not let you down! Amateur welding machines on toroidal-type cores are becoming more widespread, which have higher electrical characteristics, about 4-5 times higher than those of the rod, and electrical losses are small. The labor costs for their manufacture are more significant and are associated primarily with the placement of the windings on the torus and the complexity of the winding itself.

However, with the right approach, they give good results. The cores are made from tape transformer iron rolled into a roll in the shape of a torus. An example is the core from the autotransformer "Latr" by 9 A. To increase the inner diameter of the torus ("window"), a part of the steel tape is unwound from the inside and wound on the outer side of the core. But, as practice shows, one "Latra" is not enough for the manufacture of high-quality S.A. (small section S). Even after working with 1 - 2 electrodes with a diameter of 3 mm, it overheats. It is possible to use two similar cores according to the scheme described in the article by B. Sokolov "Welding Kid" (Sam, 1993, No. 1), or to manufacture one core by rewinding two (Fig. 4).

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

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

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

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

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

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

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

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

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

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

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

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

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

Consider the arrangement of windings on a rod-type magnetic circuit. The network winding can be positioned in two main ways. The first method allows you to get a more "hard" welding mode. The network winding in this case consists of two identical windings W 1 W 2 located on different sides of the core, connected in series and having the same wire cross section. To adjust the output current, taps are made on each of the windings, which are closed in pairs (Fig. 6a, c).

The second method involves winding the primary (network) winding on one of the sides of the core (Fig. 6 c, d). In this case, the SA has a steeply falling characteristic, it welds “softly”, the arc length has less effect on the magnitude of the welding current, and, consequently, on the quality of welding. After winding the primary winding of the CA, it is necessary to check for the presence of short-circuited turns and the correctness of the selected number of turns. The welding transformer is connected to the network through a fuse (4 - 6A) and preferably an AC ammeter. If the fuse burns out or gets very hot, then this is a clear sign of a shorted coil. Therefore, the primary winding will have to be rewound, paying special attention to the quality of the insulation.

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

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

Figure 8. Measuring instrument connection diagram.

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

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

The scheme of their connection is shown in fig. 8. When welding with different electrodes, the values ​​of the welding current - Iw and the welding voltage Uw are taken, which must be within the required limits. If the welding current is small, which happens most often (the electrode sticks, the arc is unstable), then in this case, either by switching the primary and secondary windings, the required values ​​\u200b\u200bare set, or the number of turns of the secondary winding is redistributed (without increasing them) in the direction of increasing the number of turns wound over network winding. After welding, you can make a break or saw the edges of the welded products, and the quality of welding will immediately become clear: the depth of penetration and the thickness of the deposited metal layer. Based on the results of measurements, it is useful to make a table.

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

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

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

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

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

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

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

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

And finally, a few technological tips.

The connection of the welding machine to the network should be made with a wire with a cross section of 6-7 mm through an automatic machine for a current of 25-50 A, for example, AP-50. The electrode diameter, depending on the thickness of the metal to be welded, can be selected based on the following relationship: da= (1-1.5)L, where L is the thickness of the metal to be welded, mm.

The length of the arc is selected depending on the diameter of the electrode and is on average 0.5-1.1 d3. It is recommended to weld with a short arc of 2-3 mm, the voltage of which is 18-24 V. An increase in the length of the arc leads to a violation of the stability of its combustion, an increase in waste losses and spatter, and a decrease in the depth of penetration of the base metal. The longer the arc, the higher the welding voltage. The welding speed is chosen by the welder depending on the grade and thickness of the metal.

When welding in direct polarity, the plus (anode) is connected to the workpiece and the minus (cathode) to the electrode. If it is necessary that less heat is generated on the parts, for example, when welding thin-sheet structures, reverse polarity welding is used (Fig. 1). In this case, the minus (cathode) is attached to the workpiece to be welded, and the plus (anode) is attached to the electrode. This not only ensures less heating of the welded part, but also accelerates the process of melting the electrode metal due to the higher temperature of the anode zone and the greater heat supply.

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

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