A simple spot welding machine. How to make spot welding from a microwave transformer yourself How to make spot welding from simple welding

The resistance spot welding machine is very easy to manufacture. It comes in a variety of configurations - from small portable to fairly large. Before proceeding with the assembly of the design of a home-made device, remember the Joule-Lenz law, which quantifies the thermal effect of an electric current (Q \u003d I² X R X t). Given that the amount of heat generated in a conductor is directly proportional to the conductor's resistance, current squared, and time, poorly made connections to thin wires will waste a significant amount of energy. Therefore, the quality of the electrical circuit should be given special attention.

In this article, we will answer in detail the question: "How to make spot welding at home?".

Due to its simplicity and convenience, spot welding has become widespread.

There are three types of resistance welding: spot, seam, butt. A spot welding machine welds parts at one or more points at the same time. The structure of the welding point depends on the size and shape of the contact surface of the electrode and determines the strength of the connection. The spot welding machine is a kind of resistance welding, which is why its technology is based on the thermal effect of electric current.

Brief Spot Welding Technology

Welding spot technology involves several stages. The parts to be joined, aligned in the desired position, must be placed between the electrodes of the welding equipment, pressing them against each other.

The need to press the parts is due to the formation of a sealing belt around the molten core. At the moment of the welding pulse, the formed belt prevents the splash of molten metal from the welding zone.

Next, you should heat the parts to the state of thermoplasticity, this is necessary for their deformation. To ensure high-quality spot welding at home, it is necessary to maintain a constant speed of movement of the electrodes, the required pressure value and ensure full contact of the parts to be joined.

The spot welding machine heats the parts thanks to a short-term pulse generated as a result of the passage of the welding current. This pulse contributes to the melting of the metal at the points of contact with the electrode, forming a common liquid core of the parts. The diameter of the formed nucleus reaches 4-12 mm.

As soon as the action of the current stops, the parts will continue to be held until the molten core cools and crystallizes. Spot welding technology at home is very economical and can provide mechanical strength to the seams. As for the tightness of the seam, this cannot be achieved with such equipment.

Welding processes, equipment used, as well as safety precautions are strictly regulated by GOSTs. You can check out some of them:

GOST R. ISO 17659-2009 (will help define the terms for welding joints);
• GOST 5264-80 and GOST 11534-75 are designed for manual welding;
• GOST 10157-79 and GOST 5583-78 regulate the technical conditions;
• GOST 15878-79 regulates structural resistance welding joints;
• GOST 2601-84 (metal welding, basic concepts);
• GOST 19521-74: Welding of metals and classification.

Homemade design of the spot welding machine

Such equipment cannot be called powerful. Using it, you can weld a sheet of metal with a thickness of 0.2 mm or a steel wire with a diameter of 0.3 mm. Such parameters make it possible to weld thermocouples, as well as weld thin foil parts. The welding electrode is made of a pistol, since the clamping force of small-sized parts to be welded is small.

Making welding equipment according to this scheme is quite simple. The main unit of equipment is the T2 welding transformer. The welding electrode is connected to the secondary winding of the transformer using a flexible cable. As for the more massive welded part, it is connected to the lower end.

The welding machine is connected to the mains using a V5…V8 rectifier bridge. The second diagonal of this bridge is provided to turn on the thyristor V9, when it is opened, the voltage is applied to the primary winding T2. In this case, contact welding pliers act as a gun. Their technological feature lies in the attachment of a gun to one end of the secondary winding of the transformer, as for the second end, it is attached to the spot welding product itself. Thus, the pliers can perform welding work anywhere on the product using a single electrode. Pliers for contact welding can work from single-phase or three-phase current. The transformer, from which the resistance welding pliers are powered, produces a current of several kilo amperes.

In the handle of the welding gun there is a button S3, when pressed, the thyristor is controlled. When an auxiliary source is connected to the network, the charging of the capacitor C1 immediately begins. Transformer T1 and rectifier bridge V1…V4 are an auxiliary source.

Detailed scheme of the point apparatus

The welding machine T1 is turned on by closing the diagonal of the bridge V5 ... V9 with an opened thyristor. The thyristor will remain open until the capacitor C1 is completely discharged. Variable resistor R1 is provided to adjust the discharge time of the capacitor. To prepare the next welding pulse, the S3 button must be released, at this time the capacitor C1 is charged. The next pulse is formed when pressed again.

Transformer T1 can be any low-power (5 ... 10 W). The maximum duration of welding, at the specified ratings of C1 and R1, will be 0.1 seconds. This provides welding current - 300 ... 500 A, which is quite sufficient when welding small parts.
In this example, the transformer is made of iron. The thickness of the set is 70 mm; the PEV-2 0.8 wire containing 300 turns was used as the primary winding. The diameter of the stranded wire of the secondary winding is 4 mm.

Do-it-yourself welding machine

The basis of the welding machine is a three-phase step-down transformer. Without disassembling the core, it is necessary to bite the copper bus and remove the secondary windings from all coils. Primary wires remain intact, and the middle wire must be rewound with the same wire, forming taps every 30 turns. There should be 8-10 of them in total.

Using a three-phase power multicore cable, wind the secondary winding around the two extreme coils until they are completely filled. The cable should consist of wires D - 6-8 mm., And one of them should be thinner. It is well insulated and able to withstand high current. Due to the flexibility of the wire, winding can be carried out without prior disassembly of the equipment. You will need approximately 25 meters of cable. If necessary, it can be replaced with a wire of a smaller cross section, in this case, when winding, the cores must be folded in half.

It will be difficult to cope with such a task alone. It is recommended to do the work together: one pulls the wire, the second lays the turns. For the manufacture of clamps, you will need a copper tube D - 10 - 12 mm and a length of 30 - 40 mm. One side of the tube must be riveted, a hole D - 10 mm should be drilled in the resulting plate. Wires are inserted on the other side, which should be carefully cleaned. Using a hammer, it is necessary to compress the stripped wires. To improve contact on the surface of the tube, notches must be made.

The standard screws with nuts located on the top of the transformer must be removed and replaced with two new ones with an M10 thread, attach the secondary winding terminals to them. A separate textolite board must be attached to the transformer. This is necessary for the conclusions of the primary winding. Before attaching the board, you need to drill 11 holes D - 6 mm in it. and insert screws with two washers and nuts into them.

Here is such an aesthetic appearance, it can have, do-it-yourself spot welding

A 3/4 pipe 250 mm long acts as an electric holder, on both sides of which notches are cut. To ensure free pressing of the electrode, a piece of steel wire is welded to the holder. A hole is drilled on the opposite side and a piece of the same cable is attached that was used in the secondary winding. The pipe must be hidden by a rubber hose of suitable diameter.

Please note: the welding machine is used for a small amount of welding work, so after working with 10-14 electrodes, it must be allowed to cool down.

A multi-point welding machine, unlike a spot welding machine, works with workpieces of certain sizes and shapes. A universal multi-point resistance welding machine is quite rare. Reconfiguring this device is a rather complicated and lengthy process.

Spot welding electrodes

No contact welding can be carried out without a specific welding attribute, which is called contact welding electrodes. For resistance spot welding, special electrodes are used, which are made of alloys with high thermal conductivity. The electrodes perform the function of compressing the metal and supplying current to the product. The heat concentration in spot welding depends on the tip, so a very thin tip is subject to rapid wear and requires constant regrinding. The most common tip shape is a cone. In order for the electrodes to serve for a long time, the following conditions must be observed:

• Do not use thin tips for heavy welding;
• Use specially designed electrodes for a certain material;
• Use water jacket;
• Store electrodes in places where they will not be damaged;

In amateur radio practice, contact welding is not often used, but it still happens. And when such a case comes, but there is neither the desire nor the time to make a good and large spot welding machine. Yes, if you do it, then then it will lie around idle, since the next application of it may not come.
For example, you need to connect several batteries in a chain. They are connected with a thin metal tape, without soldering, since batteries are generally not recommended for soldering. For such purposes, I will show you how to assemble a simple do-it-yourself spot welding machine in 30 minutes.

• We need an AC transformer with a secondary voltage of 15-25 volts. Load capacity doesn't matter.
• Capacitors. I took 2200 microfarads - 4 pieces. More is possible, depending on the power you need to get.
• Any button.
• Wires.
• Copper wire.
• Diode assembly for rectification. You can also use one diode for half-wave rectification.

Scheme of the apparatus for resistance spot welding

The operation of the device is very simple. When you press the button, which is installed on the welding plug, the capacitors are charged up to 30 V. After that, a potential appears on the welding plug, since the capacitors are connected in parallel with the plug. In order to weld metals, we connect them and press them with a fork. When the contacts are closed, a short circuit occurs, as a result of which sparks jump and the metals are welded together.

Assembling the machine for welding

Solder the capacitors together.
We make a welding fork. To do this, take two pieces of thick copper wire. And solder to the wires, isolate the soldering points with electrical tape.
The body of the plug will be an aluminum tube with a plastic plug through which the welding leads will stick out. So that the conclusions do not fail, we put them on glue.

We also put a plug on the glue.

Solder the wires to the button and attach the button to the plug. We wrap everything with tape.

That is, four wires go to the welding plug: two for the welding electrodes and two for the button.
We assemble the device, solder the plug and the button.

Turn on, press the charge button. Capacitors are charging.

We measure the voltage across the capacitors. It is approximately equal to 30 V, which is quite acceptable.
Trying to weld metals. In principle, tolerable, given that I took not quite new capacitors. The tape is holding up pretty well.

But if you need more help, then you can modify the scheme like this.

The first thing that catches your eye is a larger number of capacitors, which significantly increases the power of the entire apparatus.
Further, instead of a button - a resistor with a resistance of 10-100 ohms. I decided that it was enough to play around with the button - everything charges itself in 1-2 seconds. Plus, the button does not stick. After all, the instantaneous charge current is also decent.
And the third is a choke in the plug circuit, consisting of 30-100 turns of thick wire on a ferrite core. Thanks to this inductor, the instantaneous welding time will be increased, which will increase its quality, and the life of the capacitors will be extended.

Capacitors operating in such a resistance welding machine are doomed to early failure, since such overloads are not desirable for them. But they are more than enough for several hundred welding joints.

Watch assembly and test videos

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

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

What will we be about

This article discusses how to make equipment at home for:

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

What we won't talk about

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

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

The third is argon-arc welding. With whose light hand the assertion that it is a hybrid of gas and arc went for a 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, 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:

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

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 transmitted from the power supply network to the consumer. And the formal description of losses due to eddy currents in steel is similar to that for water losses due to infiltration. Electricity losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in a liquid.

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

External characteristics of electrical transformers

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 man must keep the output voltage as stable as possible up to a certain threshold, less than the maximum instantaneous power consumption, be economical, small and light. For this:

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

Note: transformer steel with "angular" hysteresis is often referred to as magnetically hard. This is not true. Hard magnetic materials retain strong remanence, 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 VX 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 the arrows in the figure) of normal dissipation increases smoothly with an increase in the range of oscillations of the welding current Iw, which makes it easy to hold the arc in any type of work. These properties are provided as follows:

• The steel of the magnetic circuit is taken with a hysteresis, more "oval".
• 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.
• 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 BX curve 2a that is somewhat more rigid than the normal one. In this case, the efficiency of welding energy consumption is unlikely to exceed 60%, but for episodic work, this is not a problem for yourself. But on 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.

Magnetic cores of transformers

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 labor, 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 it does not have corners 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.

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.

Armor cores are structurally designed for minimal scattering, and it is practically 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.

Plates of armored magnetic circuits and biscuit windings

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 losses are almost similar to the losses of water due to evaporation.

Winding of transformer windings on a rod core

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

Winding and finishing

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

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

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. The 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.

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.

Reactive Coil Adjustment

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.

Homemade welding transformer ballast

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

Primitive welding electrode holder

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.

Scheme of electric arc welding with direct current

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.

Oil-paper capacitors

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.

Armored magnetic core with non-magnetic gap

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

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.

Scheme of spot welding

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

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

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

A simple home-made resistance welding installation

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

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

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

About electrodes

Resistance welding electrode in an insulating sleeve

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.

Gun and remote tongs for contact welding

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.

Scheme of a simple pulse shaper for contact welding

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.

Spot welding machines are not as often used in everyday life as arc welding machines, but sometimes it is impossible to do without them. Considering that the cost of such equipment starts from $450-$470, the profitability of its purchase is questionable.

The way out of this situation is do-it-yourself contact spot welding. But, before telling you how to make such a device yourself, let's look at what spot welding is and how it works.

Briefly about spot welding

This type of welding refers to contact (thermomechanical). Note that this category also includes seam and butt welding, but it is not possible to implement them at home, since complex equipment will be required for this purpose.

The welding process includes the following steps:

• parts are combined in the required position;
• fix them between the electrodes of the apparatus, which press the parts;
• heating is carried out, as a result of which, due to plastic deformation, the parts are firmly connected to each other.

A production spot welding machine (such as shown in the photo) is capable of performing up to 600 operations within a minute.

Process Technology

In order to heat the parts to the required temperature, a short-term impulse of a high-power electric current is applied to them. As a rule, the impulse lasts from 0.01 to 0.1 seconds (the time is selected based on the characteristics of the metal from which the parts are made).

With a pulse, the metal melts, and a common liquid core forms between the parts, until it hardens, the surfaces to be welded must be kept under pressure. Due to this, cooling, the molten core crystallizes. A drawing illustrating the welding process is shown below.

Designations:

• A - electrodes;
• B - welded parts;
• C - welding core.

The pressure on the parts is necessary so that, with a pulse, a sealing belt is formed along the perimeter of the core of the molten metal, which does not allow the melt to flow out of the zone where welding takes place.

To provide the best conditions for the crystallization of the melt, the pressure on the parts is removed gradually. If it is necessary to “forge” the welding site in order to eliminate inhomogeneities inside the seam, increase the pressure (do this at the final stage).

Please note that in order to ensure a reliable connection, as well as the quality of the seam, it is first necessary to process the surfaces of the parts in the places where welding will take place. This is done to remove oxide film or corrosion.

When it is required to ensure a reliable connection of parts with a thickness of 1 to 1.5 mm, capacitor welding is used. The principle of its operation is as follows:

• a block of capacitors is charged with an electric current of small force;
• the capacitors are discharged through the connected parts (the pulse strength is sufficient to provide the necessary welding mode).

This type of welding is used in those industries where it is necessary to connect miniature and subminiature components (radio engineering, electronics, etc.).

Speaking about spot welding technology, it should be noted that it can be used to connect dissimilar metals together.

Examples of homemade designs

On the Internet there are many examples of the creation of machines that produce spot welding. Here are some of the most successful designs. Below is a diagram of a simple spot welding device.

For implementation, we need the following radio components:

• R - variable resistance with a nominal value of 100 ohms;
• C - a capacitor designed for a voltage of at least 25 V with a capacity of 1000 μF;
• VD1 - thyristor KU202, the letter index can be K, L, M or N, you can also use PTL-50, but in this case the capacitance "C" must be reduced to 1000 microfarads;
• VD2-VD5 - diodes D232A, foreign analogue - S4M;
• VD6-VD9 - diodes D226B, they can be replaced by a foreign analogue 1N4007;
• F - 5 A fuse.

It is necessary to make a digression to tell how to make a TR1 transformer. It is made on the basis of Sh40 iron, with a set thickness of 70 mm. For the primary winding, a PEV2 wire Ø0.8 mm is required. The number of turns in the winding is 300.

To make the secondary winding, you will need a stranded copper wire Ø4 mm. It can be replaced with a tire, provided that its cross section is at least 20 mm 2. The number of turns of the secondary winding is 10.

Video: do-it-yourself resistance welding

As for TR2, any of the low-power transformers (from 5 to 10 W) will do. At the same time, on winding II, used to connect the backlight lamp "H", there must be an output voltage in the range of 5-6 V, and windings III - 15 V.

The power of the manufactured apparatus will be relatively low, ranging from 300 to 500 A, the maximum pulse time is up to 0.1 sec (provided that the ratings "R" and "C" are the same as in the above diagram). This is quite enough for welding steel wire Ø0.3 mm or sheet metal if its thickness does not exceed 0.2 mm.

Let's give a diagram of a more powerful apparatus, in which the welding electric current of the pulse will be in the range from 1.5 kA to 2 kA.

We list the components used in the circuit:

• resistance ratings: R1-1.0 kOhm, R2-4.7 kOhm, R3-1.1 kOhm;
• capacitances in the circuit: C1-1.0 uF, C2-0.25 uF. Moreover, C1 must be designed for a voltage of at least 630 V;
• VD1-VD4 diodes - D226B diodes, replacement with a foreign analogue 1N4007 is allowed, instead of diodes, you can put a diode bridge, for example, KTs405A;
• thyristor VD6 - KU202N, it must be placed on a radiator with an area of ​​at least 8 cm 2;
• VD6 - D237B;
• F - 10 A fuse;
• K1 is any magnetic starter that has three pairs of working contacts, and the winding is designed for ~ 220 V, for example, you can install PME071 MVUHLZ AC3.

Now we will tell you how to make a TR1 transformer. The autotransformer LATR-9 is taken as a basis, such as shown in the photo.

The winding in this autotransformer has 266 turns, it is made of copper wire Ø1.0 mm, we will use it as the primary one. We carefully disassemble the structure so as not to damage the winding. The shaft and the mobile roller contact attached to it are dismantled.

Next, we need to isolate the contact track, for this purpose we clean it of dust, degrease it and varnish it. When it dries out additionally, we isolate the entire winding using varnished cloth.

As a secondary winding, we use a copper wire with a cross-sectional area of ​​​​at least 80 mm 2. It is important that the insulation of this wire is heat resistant. When all conditions are met, we make them a winding of three turns.

Setting up the assembled device is reduced to grading the scale of a variable resistor that regulates the pulse time.

We recommend that before starting welding, set the optimal time for the pulse empirically. If the duration is excessive, the parts will be burned through, and if less than necessary, the strength of the connection will be unreliable.

As already mentioned above, the device is capable of delivering a welding electric current with a power of up to 2000 A, which allows you to weld steel wire Ø3 mm or sheet steel, the thickness of which does not exceed 1.1 mm.

Do-it-yourself spot welding can become a very necessary device in a home workshop. Such a device allows you to connect various metal elements, repair various structures at home. And most importantly, hand-made production helps to avoid the significant costs associated with the purchase of ready-made welding devices.

Do-it-yourself spot welding is a rather complicated structure and to create it you need certain skills in electrics and plumbing, but with all the complexity, you can safely get to work, armed with knowledge of the principles of installation. Home craftsmen came up with various schemes and manufacturing technologies that were implemented and tested in real conditions. Positive feedback on the performance of the devices indicates the possibility of assembling sufficiently reliable structures.

The main essence of the process

Spot welding is a type of contact welding, i.e. is a combination of metals by penetration of their melts into each other with point contact under load.

The principle of implementation of such a process is based on the fact that the workpieces to be joined are tightly combined and pressed on both sides by electrodes, to which a short-term welding current is applied.

Due to its own electrical resistance, when a high current passes, the materials are heated to their melting point, and the melts of the two workpieces are mutually mixed under load, which ensures a strong connection.

To reduce the heating zone (reduce the required power of the welding pulse), a minimum contact area is provided - point-type electrodes are used.

Apparatus design

The spot welding machine includes two main parts - the source of the welding pulse and the contact block. The power source must ensure the supply in automatic mode of a pulse with a current of about 150-250 A for 0.02-0.1 s when powered from a conventional 220 V power supply. A desirable condition is the ability to control the current for welding workpieces of various thicknesses and from different metals.

The following requirements are imposed on the contact block: summing up the welding signal using a point electrode, pressing the workpieces to be welded, holding the workpieces until the melt is completely solidified after the pulse is removed. Basically, the following design solutions are used: clamping workpieces between two point electrodes; one electrode is flat and the other is point; spotter - the workpiece itself plays the role of the lower electrode.

Required tool

To make a spot welding machine with your own hands, you will need the following equipment and tools:

• welding machine;
• Bulgarian;
• electric drill;
• hacksaw for metal;
• milling cutter;
• soldering iron;
• file;
• chisel;
• hammer;
• pliers;
• screwdriver;
• metal scissors;
• calipers;
• metal ruler;
• wrenches.

Power supply manufacturing

A home-made spot welding machine is usually assembled on the basis of a welding pulse source using the principle of a capacitor discharge. A simple diagram of such a source. A welding machine with such a power supply is capable of welding a sheet up to 0.5 mm thick, it can be used for batteries in order to reliably connect Li-Ion batteries.

The required current strength in the form of a short-term pulse is created at the output of the secondary winding of the transformer Tr3, while the desired signal is provided by the discharge of capacitors C8-C9 to the primary winding. Thyristors T1 and T2 provide control of the capacitor discharge. The accumulation of charge on the capacitor plates is carried out when the auxiliary circuit of the Current transformer is turned on. Diodes D6-D7 are used to rectify the electrical signal.

The principle of discharging capacitors is carried out as follows. During the period of the disconnected main circuit, the capacitors C8-C9 are charged through the Current winding. When the main circuit is turned on (starting the welding machine), the capacitors are discharged to the Tr3 winding, while the discharge parameters are regulated by T1-T2 thyristors, and the signal duration is provided by the Ru1-Ru2, R34 and C10 system. The cycle is completely repeated when the device is turned off. The recommended characteristics of the parts are given, and the parameters of the transformer Current are as follows: type 220/220 V, PEV-2 wire with a diameter of 0.5 mm is used for both windings, the number of turns is 90.

For welding workpieces up to 3-4 mm thick, the discharge power should be increased. A diagram of a more powerful current source is presented, which, according to the principle of operation, does not differ from the previous case. The duration of the pulse is regulated by the time relay, and the MTT4K contactless starter is included in the primary winding circuit of the output transformer, due to the increase in power.

Power transformer winding

The output transformer is a fundamental part of the entire design of the welding machine, providing the necessary current supplied to the electrode. It is desirable to do it yourself as follows. The core will come from an ordinary failed transformer - it is important that it has a steel plate construction and has a total cross section of one element of about 65 cm².

The primary winding is wound on the first rack from a wire of the PEV or PETV brand with a diameter of 2.9 mm with a number of turns - 20. Transformer (cable) paper is applied under the winding and on top of it. The ends of the winding are fixed on a terminal block placed on the top of the core.

The output (secondary) winding is wound on the second leg of the core in the form of two turns of a flat tire. Such a bus can be assembled from 15-17 copper flat wires with a total cross section of 200 mm² and wrapped for insulation with fluorolon film or fabric insulating tape. It is recommended to lay transformer paper on top and bottom of the winding, and bring the ends of the winding to the terminal block.

If all the above conditions are met, then an output transformer should be obtained with the following parameters: power 3000 V A; primary voltage - 220V, secondary voltage - 15V, current - up to 220 A.

Assembly of the contact block

For domestic spot welding equipment, incl. spotter, the most commonly used block design is for pistol-shaped contact. The gun for the electrode is assembled in the following sequence. Two plates of getinax or textolite 8-12 mm thick are selected, from which figures are cut in the form of a pistol 23-25 ​​cm long. The shape is arbitrary, taking into account ease of use. It is advisable to provide the following geometry: barrel width - 42-45 mm, handle width 50-55 mm, handle length - 100-110 mm.

In the front part of the halves (trunk), symmetrical longitudinal semicircular grooves with a radius of 5-7 mm are made to install the electrode. The length of the machined channel is 55-60 mm. At a distance of 30-35 mm from the extreme cut of the barrel, a rectangular groove is machined on a longitudinal groove for installing a nut, into which the electrode will then be screwed. A sample is made in the trigger section and a hole is drilled for mounting and fastening the starting push-button switch. To align the two halves of the gun, holes for screws are drilled: in the handle - 4 pieces, in the barrel and back - 2 pieces each. To ensure the cable supply, grooves are made in the handle and between the trigger and the electrode channel.

The electrode is made of a copper bar with a diameter of 8-10 mm, and a thread corresponding to the fixing nut is cut on its tail end. The front end of the rod is sharpened in the form of a cone of the order of 15-20 mm, and the top of the cone is rounded. The total length of the electrode is selected in the order of 50-60 mm.

The welding gun is assembled in the following order. A nut is screwed onto the tail of the electrode, and a lead wire is soldered to its end, which is connected to the start button. A push-button switch is placed in the trigger part with the button output into the hole. The button is connected to the electrode, and the lead wire is connected. The whole scheme fits into the corresponding grooves and grooves; halves of the gun are combined and twisted.