How to make resistance welding from an inverter. Do-it-yourself contact welding from an inverter. Necessary equipment for contact welding

Content:

Quite often there is a need for welding work at home. As a rule, these are small volumes performed on a case-by-case basis. Since factory-made welding machines are very expensive, many craftsmen prefer to make them different ways from improvised materials. A good option for a factory analogue is considered to be do-it-yourself resistance welding from an inverter, which provides high quality work at a relatively low cost.

The device and principle of contact welding

The principle of operation of any spot welding machine consists in heating metal parts in certain places with electric current, their subsequent melting, mixing with each other and solidification. As a result, a welding seam is formed in the places of solidification of both metals. During operation, both parts are reliably compressed and fixed by electrodes to which an electric current is supplied.

For execution contact welding at home, powerful power sources will be required, which can lead to overheating and failure of household electrical wiring. In this regard, it is recommended to check the condition of the wiring in advance and replace it if necessary.

By doing spot welding two blanks are interconnected along adjacent edges. This method is very effective for working with small parts, thin metal sheets and bars, with a diameter of up to 5 mm.

Surface joining is done in one of three ways:

In the fusion method, all parts to be welded are connected and heated by an electric current until they melt. This technology is widely used in working with non-ferrous metals, low-carbon steels, brass and copper blanks. In other areas, this method is used extremely rarely due to the high requirements for temperature regime and the absence of impurities at the joints. Homemade resistance welding from a welding machine works in the same way.
Continuous welding of workpieces by the flash method is carried out using welding tongs. The parts are connected at the moment the current is turned on. After the edges of the mounted parts are melted, they are upset, and the current supply is stopped. In this way, thin-walled pipelines and workpieces with different structures are welded. The main disadvantage of this method is the possibility of metal leakage from the weld and the appearance of carbon monoxide.
The third method is an intermittent melting, during which the workpieces are alternately dense or weakened in contact. The welding line is closed in the connection area with clamping tongs until their temperature rises to 950 degrees. This method is used if the power of the welding device is initially insufficient to perform continuous reflow.

Preparing parts and assembling spot welding

The standard design of the contact welding machine consists of a power section, a circuit breaker and a protective device. In turn, the power part includes a welding transformer and a thyristor starter, with the help of which the primary winding is connected. The entire inverter is not needed for a home-made welding machine, it is only necessary to take the main parts from it. This is a transformer with a power supply, a control system and a switch.

In the manufacture of spot welding, first of all, the secondary winding must be removed from the transformer, since it is not used at all during operation. The main thing when removing the winding is to keep the primary winding intact. Instead of a remote secondary winding, another is superimposed, made of thick copper wire, with a cross section of about 2-3 cm. Then it is wrapped with insulating paper and varnished for additional insulation and fixation.

Then the direction of each winding is checked using a conventional voltmeter. There should be no short circuits in the newly created circuit. After that, the current strength is determined. This procedure is mandatory for all such devices with two or more windings. The value of the current strength should not be more than 2 kiloamperes. In case of exceeding the established level, it must be reduced.

During the preparation of the transformer coil and the winding of the secondary winding, it is recommended to follow the mandatory rules. To calculate the number of turns, you can use the formula N \u003d 50 / S, in which N is the number of turns, and S is the core area (cm2). It will help speed up the calculations. Since parts from the inverter are used in the design, the parameters of the primary coil are first determined, necessary calculations and only then can the secondary winding be made.

Pay attention to the grounding of both windings. This is due to the high power of the received current, which can be deadly when in contact with live parts. Along with careful insulation, tight laying of turns is of great importance. Otherwise, inter-turn short circuits may occur and the wires will burn out as a result of overheating. It is necessary to take care of the cooling of the transformer. It may be necessary to install additional system cooling, which includes radiators blown by fans.

Additional elements of the welding machine

The next step after the manufacture of the transformer will be the manufacture of contact tongs. The quality of their manufacture largely determines how resistance welding from an inverter will work. The design of the pliers is selected depending on the specifics of future welding work. The gripper is manufactured according to the drive system and the dimensions of the parts to be connected.

The most important part of the pliers are the contact tips. You can use copper tips from a soldering iron or purchase already finished goods. It should also be taken into account that they should not melt during operation, therefore, refractory metal should be used for their manufacture. Usually rods with a diameter of about 15 mm are used. The diameter of the cable to be connected is always smaller than the diameter of the lugs.

The wires are connected to the electrodes using conventional copper lugs. Direct connection is carried out by bolts or soldering, which significantly reduces the likelihood of oxidation at the contact points. Soldering is most often used in low power devices, allowing you to eliminate incorrect connections that cause current disturbances at the output of the device.

The main advantage of bolted connections is the ability to quickly replace parts that have failed without additional soldering work. All bolts and nuts must be copper. If it is supposed to impose connecting seams with a large length, in this case the tips are equipped with special rollers.

After the manufacture of the tongs, the time comes to solve an equally difficult task - providing the necessary pressure of the electrodes at the point of welding of the parts. The main difficulty is due to the fact that it is impossible to manually create a high and uniform pressure. If other options are not considered, then it is best to initially abandon the manufacture of spot welding from an inverter, because the efficiency of such an apparatus will be extremely low.

In industry, this problem is successfully solved by using amplifiers based on pneumatic or hydraulic systems. At home, making such devices is almost impossible. For homemade spot welding, a compressed air system that is powered by a conventional pneumatic compressor. The most optimal maximum indicator required for normal operation will be the force at the ends of the electrodes, which is 100 kg or more. The change in pressure takes place with the help of a separate regulator, which can also be built into common system management.

At the final stage of the assembly of contact welding from the inverter, it remains only to mount the entire system. For installation, it is recommended to use already ready-made elements which greatly simplifies assembly and improves performance. All the missing parts are in the inverter, from which the transformer has already been taken.

The capacity of the capacitors installed in the inverter may not be sufficient for normal operation. Therefore, if necessary, they are replaced by other parts that are most suitable in their parameters. Next, stepwise current adjustment is performed, the accuracy of which is affected by specifications secondary winding. By such adjustments, it is possible to create equipment capable of operating in various modes.

It differs from the usual arc in that the metal does not melt at a high temperature of the electric arc that occurs between the electrode and the metal being welded, but due to the passage of current through the contact of two parts to be welded. These details can be thin sheets metal, wire, plates. They are firmly compressed by special mechanical devices and a pulsed current of high strength (1000 or more Amperes) is passed through the junction at a voltage of several volts.

Do-it-yourself spot welding assumes that at least 5 kW of power falls on 1 mm 2 of contact area, which corresponds to a current strength of up to 50A / mm 2. In this case, the mechanical pressure on the same square millimeter should be at least 3-8 kg. To achieve such parameters, a special design of the working tool in the form of pincers is required.

The working body is two conductive electrodes that compress the parts to be connected with the required force when the handles are pressed. After compression, a current pulse with a duration of 01–1 s is applied to the electrodes, which melts the metal to a plastic state. After the current supply is stopped, the mechanical effect is maintained and the molten metal merges into one whole and so solidifies, forming a strong connection that is not inferior to electric arc welding.

The welding scheme looks like this:

The main difficulty in the manufacture of a spot welding machine with your own hands is the assembly of a power source. It must provide short pulses of low voltage and high current, exceeding 1000A. The pulse duration is regulated by a thyristor circuit or manually by a conventional switch on the primary winding. For low-alloy steels, a longer pulse is needed, stainless steel is welded with short pulses so that the upper part does not have time to warm up and oxidize, which significantly reduces the anti-corrosion properties.

In the second case, welding with such an apparatus requires a certain skill - it is very difficult to guess the required pulse duration the first time, especially on different metals. But by trial and error on scraps of sheet steel or non-ferrous alloys, it is quite possible to achieve welding quality no worse than on industrial machines.

Spot welding, assembled with your own hands from an old welding machine, works quite efficiently and is quite able to solve a number of connection problems. sheet metal thickness from a few tenths to 2-3 mm. For a thicker sheet, it is difficult to create the required force with homemade pliers or a lever device.

Why is the old transformer chosen? A do-it-yourself spot welding machine involves its complete re-equipment, which, however, concerns only the secondary winding. After the alteration, ordinary MMA welding with such an apparatus becomes impossible, therefore an old, but still working apparatus is selected, at least the primary winding should be, if not in ideal, then in acceptable condition.

The secondary winding is removed completely and another is installed in its place, from a copper insulated bundle or busbar. It is necessary to isolate the wire very carefully, in several layers of non-combustible insulation. Fabric electrical tape is convenient for these purposes, which alternates with winding with ordinary automotive tape, which is used when painting the body.

The cross section of the wire of the secondary winding must be at least 1.8 cm 2. If you can find a suitable factory-made cable insulated, then it is better to use it. Good result they give both cables with a monolithic core, and stranded ones made of copper wires twisted into a bundle. Several turns of a cable or bus go to the secondary winding in such a way that when 220V is supplied to the primary circuit, a current of 6-8 V arises in the secondary. In this case, the current will reach 800-1000 A. This is quite enough for welding individual parts in the home workshop.

How to choose electrodes

For spot contact welding, it is best to use industrial electrodes made in accordance with GOST 14111-69. These can be bought online or in stores. welding equipment. When used on homemade equipment, they will last almost forever. But they are quite expensive, especially with pressed tips made of tungsten or other refractory material.

In most cases, craftsmen make electrodes on their own. Depending on the welding power, copper rods with a diameter of 5 to 15 mm are suitable. On the one hand, they are inserted into a metal sleeve with clamping bolts, fixed on the cable from the transformer. Like the cable, the electrodes are firmly clamped with bolts.

The second option for attaching the electrode is soldering. It is also quite reliable and effective method, providing reliable electrical contact, but changing the electrode in this case is more difficult. This does not affect productivity too much - the electrodes wear out very slowly, especially when amateur welding.

Reliable contact is much more important. If the connection is loose, then the wire and electrode will oxidize and overheat, and the current strength will be less than required. It is also necessary to make all connecting cables as short as possible - the diameter of the electrode and cable must be the same, otherwise there may be surprises in the form of burning insulation or burning of the rods.

It would be useful to recall that the same copper wires are selected for copper electrodes. Aluminium/copper combinations are unreliable and result in unreliable welding.

The working ends of the electrodes can be pointed (conical), oval or flat. In household homemade devices it is most convenient to use a flat lower and conical upper electrodes. This combination will provide both a high current density at the welding point and a reliable support for pressing parts.

Battery Spot Welding

There is information on the Internet on how to do spot welding with your own hands using a regular 12 V car battery. You can use it to connect small parts that are usually connected by soldering. But in many cases, welding gives best result strength and is more convenient for joining dissimilar metals.

Do-it-yourself spot welding from a battery is a simple design and can be done in a garage for several hours, with all the parts and tools, of course. It does not require any special tools or sophisticated equipment for installation.

There are three types of welding with a battery. The first, the simplest, one might say primitive, requires only a battery and two copper wires, the bare ends of which act as electrodes. As a rule, this method is used most often, but only for welding non-ferrous metals. It is with good reason that it can be called a point.

The other two methods - and with the help of an inverter - require batteries from several batteries and additional equipment. They are also used in domestic and camping conditions, but buy several of the same type of batteries to make them welding machine, is quite difficult. Any battery that can be removed from the car can be used for spot welding.

A simple device for performing welding work consists of two copper wires with a cross section of at least 1.5 mm 2, fixed in a terminal block. The distance between the stripped ends of the electrodes is 2-3 mm. Of course, as in any home-made design, there can be many options, but as a base it is best to use this particular type of design. How such a mini installation works is shown in the video:

Battery welding is designed to connect small pieces of thin sheet metal, but even with this, the battery is discharged quite intensively. If you removed it from the car, it is advisable to have a charger in the garage to return the batteries to their previous charge.

The examples given are the simplest. homemade designs spot welding machines. If you have your own developments - write to us on the site. We and our readers are very interested in the real development of amateur designers. Most interesting schemes we will publish it for sure.

When repairing a car or building work, there is often a need for a resistance welding machine that you would like to have, but its high price does not allow you to make such a purchase. We will tell you how to make such a unit from an inverter-type welding machine on your own. The contact type connection is based on pressure and heating of the metal using welding current with a short-term effect on the parts to be welded. Industrial devices this kind has been widely used for a long time, we will tell you how to assemble such an apparatus from an inverter at home.

Many types of equipment are due to their high efficiency, economy and speed. Some of them have high-tech control over the quality of work, can evaluate the thickness and parameters of the metal and regulate the current process. The contact welding machine of the Car-o-Liner CTR 41977 line performs all types of high-precision work on metal and is a source of powerful welding current. Swedish Car-o-liner units allow you to cook sheet metal, and are built on an inverter technology basis. Car-o-Liner devices allow welding metal under point pressure, and are designed, among other things, for body repair of cars.

Besides? there are other, much simpler, equipment for joining in the contact zone of sheets, such an example is the TOP resistance welding machine, which has the following parameters:

light weight (8 kg) and power (2 kW);
welds sheet metal up to 2 mm thick;
it is possible to weld a rod up to 4 mm;
carries out heating of the metal for the purpose of subsequent processing;
there is a soldering function with soldering high temperature melting;
in a set there are hard-alloy curly and straight electrodes;
there are specialized pliers with a hose of more than 2 m;

The use of such resistance welding machines with a reasonable price and high mobility allows you to carry out minor home and body repairs, as well as weld reinforcing mesh during construction work.

It is important to note that the low voltage at the terminals allows you to work in compliance with safety regulations.

The metal-sparing properties of resistance welding machines allow them to be used as a spotter in bodywork and other repairs of sheet metal. It should be discussed in more detail because most people are faced with damage to the car body. We are talking about dents that need to be pulled out and leveled.

In this case, special copper electrodes are used, which, after cleaning the body parts, are spot-welded to the dent. Then, with their help, irregularities are pulled out by additional heating and cooling of the metal. This very effective repair method allows you to pull out irregularities even in hard-to-reach places.

Necessary equipment for resistance welding

To assemble a contact welding machine with your own hands, you need to determine in advance how you want to use it. The small weight of the inverter unit, which we will take as the basis of the kit, allows you to assemble both a mobile and a stationary version. The fact is that the tongs that provide the necessary pressure at the welding point can be mounted on a stationary platform or on a flexible hose.

Fixed electrodes are more suitable for sheet metal in-line seam welding, while the mobile version is more versatile.

Separately, it is necessary to consider the criteria for choosing a welding inverter as a current source for the contact method of operation. It must have a wide range of current and voltage adjustments, and since the output waveform is pulsed, this parameter must also be configurable. Thus, the AKS contact welding machine must be equipped with refractory electrodes, which can be mounted in the following versions, namely:

a stationary version, in which sheets to be welded are superimposed on a fixed negative electrode, and they are pressed pointwise with a positive electrode;
mobile version using tongs that allow squeezing the parts to be joined at the welding point;
an option using a welding gun as a positive electrode, where the minus is a body part.

The use of a gun is typical for the work of a spotter during body repair, and in this case, replaceable copper tips are used, which make it possible to straighten defective areas. In order to save money, you can make a welding gun or tongs with your own hands, both in a stationary and mobile version. To do this, you will need the following materials and tools:

textolite for a gun or pincers;
start button;
fixing bolts with nuts;
copper or bronze tip as an electrode;
connecting cables and wires;
mini-cartridge with a bulb for illumination;
jigsaw, grinder and electric drill;
powerful electric soldering iron;
marking devices;
set of screwdrivers and wrenches.

It is important to ensure that the welding cable makes good contact with the handpiece holder or replacement tips to avoid overheating and loss of power.

Consideration should be given to quickly changing bronze or copper electrodes or tips, as operating conditions can change, and when repairing machine body sheet metal, replacement is part of the process.

Assembly of the contact welding kit and the sequence of work

When carrying out contact welding with your own hands, you need to understand that the whole process takes from 0.5 to 1.5 seconds, so the start button must be placed in the open circuit of the primary winding of the inverter. It is important to prevent metal burn through, and for this it is necessary to adjust the high-frequency output voltage of the inverter in an optimal way and experimentally select the welding duration. When joining sheets with an overlap, it is necessary to ensure their immobility relative to each other, as well as to press the electrode to the welding point with constant force.

The final assembly involves connecting all the nodes and checking the reliable, safe contact in the welding current circuit and the control button. Checking the performance of the device and adjusting the output parameters consists of the following steps:

setting the inverter to the minimum welding current;
checking the reliability of the connection of the cable, gun or tongs, as well as the start button;
on test parts, short-term, spot welding is carried out and, if necessary, the setting of the output parameters of the inverter is adjusted;
welding stops and the result is evaluated, in the case of burning the workpieces, the current and welding time at the contact point decrease;
welding is considered correct, in which the separation of the workpieces from each other occurs along the metal, and not along the welding point;
in the case of using the device as a spotter, it is necessary to ensure reliable welding of the tips to the surface of the repaired area.

It is very important to ensure the safety of the worker in order to avoid possible injury. electric shock and carry out welding in special clothing that protects against burns.

Summing up

We considered the possibility of assembling a resistance welding machine with our own hands using an inverter as a current source. This achieves significant cost savings, with a small investment of time and materials. The capabilities of such a contact welding machine are quite enough for personal needs and repair of the car body, as well as a reliable connection of sheet metal. Good luck with your work.

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

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

What will we be about

This article discusses how to make equipment at home for:

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

What we won't talk about

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

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

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

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

Transformer

The basis of all "our" types of welding is a welding transformer. The procedure for its calculation and design features significantly differ from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like transformers continuous action, 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.

Theory

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

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

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

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

Note: transformer steel with "angular" hysteresis is often referred to as magnetically hard. This is not true. Hard magnetic materials retain strong residual magnetization, they are made 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 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. Energy Consumption Efficiency welding in this case is unlikely to exceed 60%, but for episodic work for yourself this is not scary. But on fine work and low currents, it will not be difficult to hold the arc and the welding current, without having much experience (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 it, so transformers with a "steep" VX are often used in welding semiautomatic devices. 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 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.

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 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.

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.

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 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 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, are 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 desired wire no 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 obtained as a rule more than 3 mm, and the varnished winding wires with d> 2.4 mm in wide sale rare. 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.

winding

thin-walled homemade frame will not withstand the pressure of thick wire turns, vibrations and jerks during operation. Therefore, the windings of welding transformers are made frameless biscuit, and they are fixed on the core with wedges made of textolite, fiberglass or, in last resort, 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 of thin plastic wrap with a call on the cheeks and a twist on their outer side so that the wire does not stick to the tree;
We wind a pre-insulated winding;
After winding, we impregnate twice until it flows through with liquid varnish;
after the impregnation dries, carefully remove the cheeks, squeeze out the boss and tear off the film;
we tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.

Finishing and domotka

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

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

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

Pull VX

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

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

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

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

But other?

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

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

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

Trying a constant

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

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

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

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

microarc

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

Now for microarc welding use more than computer blocks power supply, or, for pulsed microarc welding, a capacitor bank, see the video below. At direct current, the quality of work, of course, improves.

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

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

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

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 operating time on Idling and cooling) many times lower.

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

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

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

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

About electrodes

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

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

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

How to give impetus

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

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

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

Many mistakenly believe that making a spot welding machine from an inverter with your own hands is very difficult. technological process. This is not entirely true.

With sufficient knowledge of electrical engineering and experience with a soldering iron, this work will be within your power. The resulting device will not differ from the factory ones in terms of its effectiveness.

welding transformer

To assemble a spot welding machine with your own hands, you will need:

U-shaped transformer (than larger size core, the better);
contactor (relay for current great strength. Must withstand 800-1000 amps);
25 volt relay;
25 volt transformer;
a set of copper cables;
copper tip.

The device control scheme will consist of:

power supply;
control circuits;
relay.

Machine control scheme

Transformer assembly

The main part of the spot welding machine (as, in principle, of any other electrical appliance) is a transformer.

It is he who will generate the voltage necessary for normal operation. Due to the fact that you may need a device with a large transformation ratio to assemble such a device with your own hands, it is best to borrow a transformer from a microwave (700-800 W). If this was not found, then the best option will be its analogue with a power of 1 kW.

microwave transformer

To make a transformer for a spot welding device with your own hands, you must follow this algorithm:

Knock down the secondary winding. Due to the fact that only the primary one is useful to us during work (located inside, wrapped with a thicker wire, but the winding layer is thinner), you can use any tool that comes to hand to remove the secondary one: a chisel, a chisel, a hacksaw, a hammer, or even electric drill. The main thing is not to damage the primary winding and not to violate its integrity.
Apply secondary winding. To do this, we need a tourniquet made of copper wire(section from 2.5 to 3 centimeters). It must be wrapped with tape. Each winding layer is covered with insulating paper and varnished.
Check winding directions. This can be done with the most common voltmeter. In addition to the directions of the windings, it is also worth checking for short circuits in the network. If there are none, you can proceed to the next paragraph.
Check current. If your design involves 2 or more transformer windings, you should definitely check the output current. If it is more than 2000 amperes, it must be reduced. Otherwise, it is fraught with serious voltage drops.

Spot welding from a microwave transformer

Manufacturing of electrodes

Making electrodes with your own hands is very simple. To do this, you will need copper rods with a diameter of 1.5 centimeters or more (they can be purchased on the market or in scrap metal). In this case, it is very important to remember one fundamental principle - the diameter of the electrode should in no case be inferior to the diameter of the cable.

If you are making a machine for weak welding, then you can even just disassemble two soldering irons and remove the tips from them. They themselves are good and workable electrodes.

Removing the tip from the soldering iron for spot welding

The wire that will be connected to the electrode should be as short as possible to minimize current loss.

To connect the wire to the electrode, you will need a regular copper ferrule. It must be connected to the wire by soldering or bolting - this will prevent the possibility of oxidation that inevitably occurs during the first use of the device. Contacts that have not been soldered beforehand can cause unwanted resistance, which will be especially felt if the machine is operated at low power.

The only advantage that bolted connections have is the ability to quick removal diodes. In all other cases, the device must be completely soldered. Also, such a connection is resorted to in cases where the diodes have to be changed more often. Replacement is much faster and more convenient. Of course, for such fasteners it is better to purchase bolts and nuts made of copper.

How to use the machine

The category of additional equipment can, without thinking, include a lever and switches. This is because only a good grip force will make a DIY spot welder efficient.

This is especially true when it comes to welding thick metal products. In production, the grip force of the lever can vary from 50 to 1000 kilograms. However, for welding at home, 30 will be enough. For this, you will need a sufficiently long lever (without it, it will be inconvenient to operate the spot welding machine with your own hands).

With the installation of the switch, it is still easier - it is necessary to mount it on the primary winding (since the current on the secondary will be too strong, the resistance of the device will interfere with its operation). Using this advice, you will be able to turn on the device only after the metals have come into contact with each other. This will significantly reduce energy costs and provide reliable protection from sparks.

It will also need to be tested to identify possible design defects. Such an apparatus is suitable for welding metal with a thickness of 2-3 millimeters (if the power of the transformer is 1 kilowatt) and five millimeter products if two or more transformers were connected.

We test the welding machine

How to protect yourself

When working with a spot welding machine, it is very important to adhere to safety regulations. Improper or careless use of this appliance can result in electric shocks, burns of varying severity, and all sorts of injuries.