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Do-it-yourself contact welding from a welding inverter. Spot welding from an inverter with your own hands. Control circuit - what it consists of and how it works

A spotter is a welding unit used specifically for organizing spot welding, and also allows you to carry out work on straightening thin sheet blanks. This type of welding is especially common in workshops whose employees are engaged in straightening work that requires preliminary disassembly of the body. Using a spotter allows you to avoid the mandatory dismantling of the load-bearing parts of the car and straighten surfaces without reverse hammer(Figure below in the text).

In this case, the welding procedure is used for the purpose of point-fixing an additional holder on the restored surface, by pulling which it is possible to straighten the existing dent.

Spot Welding Properties

The design of this device is somewhat different from typical units with a continuously burning arc. You can make a spotter from a welding machine with your own hands only if you know the basic principles of the formation of the operating current. The fact is that with the contact welding method, heating occurs not by melting the metal, but by concentrating heat in a point zone between the workpiece and the electrode.

In the case of an incorrectly selected resistance welding mode (with a lack of experience on the part of the operator), sticking of the electrode is often observed, which can lead to unpleasant consequences in the form of a short circuit or even breakdown of the unit. That is why the spot welding machine is manufactured so that the welding time is strictly limited and does not exceed a second.

In addition, such a device is designed for small values ​​of effective voltage (since ignition of the arc is not required in this case) and for significant operating currents. In this regard, the transformer (CT) included in its composition must also withstand high current loads, sufficient for high-quality heating of the welding site.

Features of the conversion

You can make a spot welding machine with your own hands without unnecessary effort if you use the option of remaking it from unnecessary materials welding device. When preparing for work, you will need to pay attention to the following points:

• For an ordinary CT, the voltage when operating at idle (no-load), as a rule, is selected to be no more than 70 Volts;
• In a situation with a spot welding unit, this figure should not exceed 6 Volts;
• To implement this condition, a new secondary winding will be required, designed for a reduced output voltage.

Note! You can also make a new low-voltage coil by winding it over the existing secondary winding (if space allows).

Otherwise, it is better to unwind the old “secondary” and use its wire to form a new working winding.

Before doing spot welding with an updated transformer, it is advisable to familiarize yourself with the existing types of these electrical products and try to choose the most suitable one.

Cores used in welding transformers may have several various designs(picture below).

Among them, the most notable are following types TT:

• With the so-called “W-shaped” or armored core;
• With a rod base (in the shape of the letter “O”);
• And finally, with a core made in the form of a torus.

Of all the listed options, the most suitable for the purposes under consideration is a transformer with a toroidal core, which has small dimensions and relatively light weight (see the figure below).

Additional Information. The cross-section of such a core in any transformer will be determined by the expected welding current.

For do-it-yourself spot welding to work properly, the output current of the unit must be at least 1000 Amperes. The latter means that a sufficiently thick wire must be used in the CT output winding. This requirement is fully satisfied by the selected version of the toroidal core, since there is plenty of space for placing the output winding in it.

Secondary winding

Selecting parameters

When remaking a CT, the main attention should be paid to the parameters of the secondary winding, which determine the output characteristics of the device (its load current, in particular). In this case, it is important to select a bus cross-section that would provide a current density of about 8 A/mm² (with a cross-sectional area of ​​about 120 mm²). Since it is very difficult to handle such a thick busbar when winding on a torus, they are most often limited to a value of 80 mm².

Note! The specified cross-section can be obtained by putting together several wires of slightly less thickness.

To facilitate the conditions for converting a CT into a point unit, it is advisable to pre-calculate the amount of wire required for rewinding it. After this, it will be possible (based on the space occupied by the winding) to decide whether it will fit into the free space remaining on the torus or not.

Important! In the case where the new winding does not fit into the torus, the old secondary coil will have to be completely disassembled (dismantled).

To make it easier to handle new wires during the winding process, it is recommended to wrap them with fabric-based insulating tape. To determine the exact number of turns that affect the output voltage, we recommend using the method of test winding with a wire not large section in isolation.

Since the winding in this case is not connected to the load, the cross-section of the test wire is not very important. Experience has shown that during rough tests it is sufficient to use no more than 10 turns. After winding them, the transformer should be connected to the network and the voltage produced by the test coil should be measured, after which it is divided by the number of turns. The result is a figure indicating the number of turns required to produce one volt of output.

Since in this case it is necessary to obtain 6 Volts, multiplying the number obtained from the test connection by 6, we obtain the required number of turns.

In order to make a new device with your own hands, you must first calculate the amount of wire required for rewinding the CT. After this, it will be possible (based on the space occupied by the bus winding) to determine whether it will fit into the free space remaining on the torus.

Winding diagrams and placement

The connection diagram and the order of placement of the “secondary” depend on the type of core selected. Given the toroidal base of the CT that we have declared, it is more convenient to divide it into two half windings connected in series (3 Volts each).

In order to increase the load capacity (increase the welding current), you can make two windings of 6 Volts each and connect them in parallel. In this case, the output voltage will not change, and the load current can be doubled. This design option allows us to solve the problem of the large cross-section of the secondary bus, which can then be reduced by half.

Various types of connections of such windings are shown in the picture below.

The order in which they are connected is very important to obtain the required output parameters, and mistakes made in this case can lead to completely different indicators. So, in particular, if you make a mistake during installation and turn on two windings in opposite directions, as a result they will be short-circuited to one another and will produce zero voltage at the output, which is equivalent to a short circuit.

At the ends of ready-made secondary windings, special tips should be equipped by crimping.

Control circuit

To control the welding process, short pulses are used, generated in a special electronic circuit. When manufacturing a spotter based on an old unit, it is also necessary to provide a control unit that allows switching a significant output current.

To solve this problem, manually generated pulses are applied to the primary winding of the CT (the simplest control circuit is shown in the figure below).

The disadvantages of such management include:

• Using the button shown in the figure, the mains voltage is switched, which is extremely dangerous;
• When mechanical contacts open, strong sparking occurs;
• Even if you replace the mains switch with a traction relay from the starter, controlled by a push-button mechanism, then such a circuit, despite the improvement, will still be unfinished.

Note! To implement the traction principle, it is allowed to use a combination of “powerful starter plus automotive relay” (and the latter can be of any brand).

When this combination is selected, the relay is activated when a voltage of 12 Volts is applied, and its switching causes the power contactor to operate. However, this control option is not without drawbacks, since in this case it is not possible to precisely control the impact interval (pulse width).

For those who know the basics of electronics and know how to handle a soldering iron, something more complex in design, but reliable in operation, is suitable. electronic circuit controls (see photo below).

Here, operating pulses are supplied to the input winding of the CT from an electronic device - a thyristor, which opens when voltage is applied to its control electrode. The capacitor (C1) included in its circuit, with the button contact open, is charged through the elements V1-V4 of the diode bridge. When the button is pressed, the capacitance is discharged through resistor R1 and directly through the control electrode circuit of the thyristor, which causes it to turn on.

The electronic device will remain on until the capacitor is completely discharged (this interval can be adjusted with variable resistor R1). For the subsequent start operation, the button must first be released and then pressed again (its shutter speed determines the welding interval).

Transformer T1 can be of any type (with a voltage on the secondary winding of 12 Volts). The parameters of the thyristor must satisfy the operating conditions, that is, allow it to operate at voltages up to 400 Volts and currents of at least 50 Amperes. An electronic product of the T132-50 brand is quite suitable for these purposes.

In the final part of the review, we recall that welding equipment The “spotter” type is most often in demand for body repair and similar work with sheet metal. In this regard, when choosing the output power of a home-made unit, it is necessary to take into account the thickness sheet material, with which you will mainly work.

Video

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

If you have sufficient knowledge of electrical engineering and experience working with a soldering iron, you will be able to do this job. The resulting device will not differ from the factory ones in terms of its efficiency.

Transformer for welding

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

• U-shaped transformer (the larger the core size, the better);
• contactor (relay for high current. Must withstand 800-1000 amperes);
• 25 volt relay;
• 25 volt transformer;
• set of copper cables;
• copper tip.

The device control circuit will consist of:

• power supply;
• control circuits;
• relay.

Device control circuit

Transformer assembly

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

It is this that will generate the voltage necessary for normal operation. Due to the fact that to assemble such a device with your own hands you may need a device with a high transformation ratio, it is best to borrow a transformer from a microwave (700-800 W). If one was not found, then the best option there will be an 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 (it is located inside, wrapped with a thicker wire, but the winding layer is thinner), to remove the secondary one, you can use any tool that comes to hand: 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 compromise its integrity.
• Apply a secondary winding. To do this we need a tourniquet made from copper wire(section from 2.5 to 3 centimeters). It must be wrapped with electrical tape. Each layer of the winding is covered with insulating paper and varnished.
• Check winding directions. This can be done with the most ordinary voltmeter. In addition to the directions of the windings, it is also worth checking for short circuits online. If there are none, you can move on to the next point.
• Check current strength. If your design involves 2 or more transformer windings, you should definitely check the output current. If it is more than 2000 amps, it must be reduced. Otherwise, this 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 (they can be purchased at 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 simply disassemble two soldering irons and remove the tips from them. They themselves are quite good and efficient electrodes.

Removing the tip from the soldering iron for spot welding

The wire that will be connected to the electrode must have a minimum length to minimize current loss.

The only advantage that bolted connections have is the ability to quickly remove diodes.

In all other cases, the device must be completely re-soldered. This connection is also used in cases where diodes have to be changed more often. Replacement is much faster and more convenient. Of course, for such fastenings it is better to purchase bolts and nuts made of copper.

How to use the device Go to category additional equipment

You can, without thinking, include the lever and switches. This is due to the fact that only good compression force will make a homemade spot welding machine effective.

This is especially true when it comes to welding thick metal products. In production, the compression force of the lever can vary from 50 to 1000 kilograms. However, for welding at home, 30 will be enough. To do this, you will need a fairly long lever (without it, operating the spot welding machine with your own hands will be inconvenient). Installing the switch is even simpler - you need to mount it on the primary winding (since the secondary will have too strong a current, which will be interfered with by the resistance of the device). 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 the device will fit

for welding metal 2-3 millimeters thick (if the transformer power 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 welder, it is very important to adhere to safety regulations. Incorrect or careless use of this device may result in electric shocks, burns of varying severity, and all kinds of injuries.

Content: Quite often there is a need to carry out welding work at home. As a rule, these are small volumes performed occasionally. Since factory-made welding machines are very expensive, many craftsmen prefer to make them different ways from scrap materials. A good option for a factory analogue is considered to be do-it-yourself contact welding from an inverter, which ensures high quality

The device and principle of operation of resistance welding

The principle of operation of any spot welding machine is to heat metal parts with electric current in certain places, then melt them, mix them together and solidify. As a result, a weld seam is formed in the places where both metals solidify. During operation, both parts are reliably compressed and fixed by electrodes to which electric current is supplied.

To perform contact welding at home you will need powerful sources power supply, 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.

When performing spot welding, two workpieces are joined together along adjacent edges. This method very effective for working with small parts, thin metal sheets and rods with a diameter of up to 5 mm.

Surfaces are connected in one of three ways:

• When using the reflow method, all parts to be welded are joined and heated by the action electric current until they melt. This technology is widely used in working with non-ferrous metals, low-carbon steels, brass and copper workpieces. In other areas, this method is used extremely rarely due to the high requirements for temperature conditions and the absence of impurities at the joints. Homemade resistance welding from a welding machine works in exactly the same way.
• Continuous welding of workpieces using the reflow method is performed using welding tongs. The connection of parts occurs at the moment the current is turned on. After the edges of the mounted parts have melted, they are upset and the current supply is stopped. Thin-walled pipelines and workpieces with different structures are welded using this method. The main disadvantage of this method is the likelihood of metal leaking out of the weld and the appearance of carbon monoxide.
• The third method is intermittent melting, which ensures alternately tight or loose contact between the workpieces. The welding line is closed in the joint area with clamping pliers 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 a resistance 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 homemade welding machine; you only need to take the main parts from it. This is a transformer with a power supply, a control system and a switch.

When making spot welding, first of all, you need to remove the secondary winding 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 the removed secondary winding, another one is placed, made of thick copper wire, with a cross-section of approximately 2-3 cm. Then it is wrapped in insulating paper and varnished for additional insulation and fixation.

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

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

Pay attention to the grounding of both windings. It's connected with high power the resulting current, which can be fatal if it comes into contact with live parts. Along with careful insulation, great importance has a dense laying of turns. Otherwise, interturn short circuits may occur and the wires will burn out as a result of overheating. It is also necessary to take care of cooling 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 manufacturing the transformer will be the manufacture of contact clamps. 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 gripping device is manufactured in accordance with the drive system and the dimensions of the parts to be connected.

The most important part of the pliers is the contact tips. You can use copper tips from a soldering iron or purchase ready-made products. It should also be taken into account that they should not melt during operation, so a refractory metal should be used for their manufacture. Typically rods with a diameter of about 15 mm are used. The diameter of the connected cable is always less than the diameter of the lugs.

The wires are connected to the electrodes using ordinary 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, eliminating incorrect connections that cause current disturbances at the output of the device.

Main advantage bolted connections is the ability to quickly replace failed parts without additional soldering work. All bolts and nuts must be copper. If it is intended to apply connecting seams over a long distance, in this case the tips are equipped with special rollers.

After manufacturing the pliers, the time comes to solve an equally difficult task - ensuring the necessary pressure of the electrodes at the point of welding the parts. The main difficulty lies in the fact that it is impossible to create high and uniform pressure manually. If other options are not considered, then it is best to initially refuse to make spot welding from an inverter, because the efficiency of such a device will be extremely low.

In industry, this problem is successfully solved by using amplifiers based on pneumatic or hydraulic systems. It is almost impossible to make such devices at home. For homemade spot welding, the best option is a compressed air system driven by a conventional pneumatic compressor. The most optimal maximum indicator required for normal operation will be a force at the ends of the electrodes of 100 kg or more. The pressure changes using a separate regulator, which can also be built into the overall control system.

At the final stage of assembling resistance welding from the inverter, all that remains is to mount the entire system. For installation it is recommended to use already ready-made elements, which significantly simplifies assembly and improves performance characteristics. All the missing parts are in the inverter, from which the transformer was already taken.

The capacity of the capacitors installed in the inverter may not be sufficient for normal operation. Therefore, if necessary, they are replaced with 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 making such adjustments, it is possible to create equipment capable of operating in different modes.

Do-it-yourself welding in this case does not mean welding technology, but homemade equipment for electric welding. Working skills are acquired through industrial practice. Of course, before going to the workshop, you need to master the theoretical course. But you can put it into practice only if you have something to work with. This is the first argument in favor of, when mastering welding on your own, first taking care of the availability of appropriate equipment.

Second, a purchased welding machine is expensive. Rent is also not cheap, because... the probability of its failure due to unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be simply long and difficult. All in all, It is better to start your first steps in metal welding by making a welding installation with your own hands. And then - let it sit in a barn or garage until the opportunity arises. It’s never too late to spend money on branded welding if things work out.

What are we going to talk about?

This article discusses how to make equipment at home for:

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

What we won't talk about

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

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

Third - argon-arc welding. With whose light hand the claim that it is a hybrid of gas and arc has gone for a walk in RuNet, unknown. In fact, this is a type of arc welding: the inert gas argon does not participate in the welding process, but creates working area a cocoon that insulates it from the air. As a result, the welding seam is chemically pure, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be cooked under argon, incl. heterogeneous. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and weld with a non-consumable electrode.

It is quite possible to make equipment for argon-arc welding at home, but gas is very expensive. It is unlikely that you will need to cook aluminum, stainless steel or bronze as part of routine economic activity. And if you really need it, it’s easier to rent argon welding - compared to how much (in money) gas will go back into the atmosphere, it’s 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 failures of amateur designers. Therefore, let’s take a walk through welding transformers in the following order:

1. a little theory - on the fingers, without formulas and abstruse ideas;
2. features of magnetic cores of welding transformers with recommendations for choosing from random ones;
3. testing of available used equipment;
4. calculation of a transformer for a welding machine;
5. preparation of components and winding of windings;
6. trial assembly and fine-tuning;
7. commissioning.

Theory

An electrical transformer can be likened to a water supply storage tank. This is a rather deep analogy: a transformer operates due to the reserve of magnetic field energy in its magnetic circuit (core), which can be many times greater than 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 the liquid.

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

An important factor in our case is the external current-voltage characteristic (VVC) of the transformer, or simply its external characteristic(VX) – 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 water losses are minimal and the pressure is quite stable, no matter how consumers turn the taps. But if there is gurgling in the drain - sushi oars, the water is drained. In relation to transformers, the power source must keep the output voltage as stable as possible to a certain threshold less than the maximum instantaneous power consumption, be economical, small and light. For this:

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

Note: transformer steel with “angular” hysteresis is often called magnetically hard. This is not true. Magnetically hard materials retain strong residual magnetization; they are made by permanent magnets. And any transformer iron is soft magnetic.

You cannot cook from a transformer with a hard VX: the seam is torn, burned, and the metal splatters. The arc is inelastic: I moved the electrode slightly wrong and it goes out. Therefore, the welding transformer is made to look like a regular water tank. Its CV is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage gradually drops. The normal scattering curve is approximated by a straight line incident at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly extract several times more power from the same hardware, or resp. reduce the weight, size and cost of the transformer. In this case, the induction in the core can reach a saturation value, and for a short time even exceed it: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: the thermal time constant of welding transformers is 20-40 minutes. If you then let it cool down and there is no unacceptable overheating, you can continue working. The relative drop in the secondary voltage ΔU2 (corresponding to the range of the arrows in the figure) of normal dissipation gradually increases with increasing range of fluctuations of the welding current Iw, which makes it easy to hold the arc during any type of work. The following properties are provided:

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

Note: reversible scattering loss means that part of the power lines penetrates the secondary through the air, bypassing the magnetic circuit. The name is not entirely apt, just like “useful scattering”, because “reversible” losses for the efficiency of a transformer are no more useful than irreversible ones, but they soften the I/O.

As you can see, the conditions are completely different. So, should you definitely look for iron from a welder? Not necessary, for currents up to 200 A and peak power up to 7 kVA, but this is enough for the farm. We use design and design measures, as well as using simple additional devices(see below) we obtain on any iron BX, curve 2a, somewhat more rigid than normal. The efficiency of welding energy consumption is unlikely to exceed 60%, but for occasional work this is not a problem. But on delicate work and low currents, holding the arc and welding current will not be difficult, without much experience (ΔU2.2 and Iw1), at high currents Iw2 we will get 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 nominal level, regardless of the feed height, or there is none at all. They are even more compact and lightweight, 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, which is why transformers with a “steep” VX are often used in semi-automatic welding machines. If you cook from such a transformer manually, then the seam will be sluggish, undercooked, the arc will again be inelastic, and when you try to light it again, the electrode will stick every now and then.

Magnetic cores

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

After the letters of the nominal value there are numbers indicating a, b and h in Fig. For example, dimensions W20x40x90 cross section core (central rod) 20x40 mm (a*b), and window height h – 90 mm. Core cross-sectional area Sc = a*b; window area Sok = c*h is needed for accurate calculation of transformers. We will not use it: for an accurate calculation, we need to know the dependence of losses in steel and copper on the value of induction in a core of a given standard size, and for them, the grade of steel. Where will we get it if we run it on random hardware? We will calculate using a simplified method (see below), and then finalize it during testing. It will take more work, but we will get welding that you can actually work on.

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

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

• O, OL – from 10 kg.
• P, PL – from 12 kg.
• W, SHL – from 16 kg.

Why Sh and ShL are needed heavier is clear: they have an “extra” side rod with “shoulders”. OL may be lighter because it does not have corners that require excess iron, and the bends of the magnetic force lines are smoother and for some other reasons, which will be discussed later. section.

Oh OL

The cost of toroid transformers is high due to the complexity of their winding. Therefore, the use of toroidal cores is limited. A torus suitable for welding can, firstly, be removed from the LATR - a laboratory autotransformer. Laboratory, which means it should not be afraid of overloads, and the hardware of LATRs provides a VH close to normal. But…

LATR is a very useful thing, first of all. 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, “bare” LATR cores are difficult to find.

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

Another torus suitable for all properties is the stator of an electric motor; Welding from it will turn out to be good enough for an exhibition. But it is no easier to find than LATR iron, and it is much more difficult to wind on it. In general, a welding transformer from an electric motor stator is a separate topic, there are so many complexities and nuances. First of all, with a thick wire wound around the donut. Having no experience in winding toroidal transformers, the probability of damaging an expensive wire and not getting welded is close to 100%. Therefore, alas, you will have to wait a little longer with the cooking apparatus on a triode transformer.

Sh, ShL

Armor cores are structurally designed for minimal dissipation, and it is almost impossible to standardize it. Welding on a regular Sh or ShL will turn out to be too tough. In addition, the cooling conditions for the windings on Ш and ШЛ are the worst. The only armored cores suitable for a welding transformer are those of increased height with spaced biscuits 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.

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

If you come across a laminated Sh without a yoke, but with a cut in the plates between the core and the lintel (in the center), you are in luck. The plates of the signal transformers are laminated, and the steel on them, to reduce signal distortion, is used to initially give normal VX. But the likelihood of such luck is very low: signal transformers with kilowatt power are a rare curiosity.

Note: do not try to assemble a high Ш or ШЛ from a pair of ordinary ones, as on the right in Fig. A continuous straight gap, albeit a very thin one, means irreversible scattering and a steeply falling CV. Here, dissipation losses are almost similar to water losses due to evaporation.

PL, PLM

Rod cores are most suitable for welding. Of these, those laminated in pairs of identical L-shaped plates, see Fig., their irreversible scattering is the smallest. Secondly, the P and PL windings are wound in exactly the same halves, with half turns for each. The slightest magnetic or current asymmetry - the transformer hums, heats up, but there is no current. The third thing that may not seem obvious to those who have not forgotten the school gimlet rule is that the windings are wound onto the rods in one direction. Does something seem wrong? 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 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, the transformer will howl and shake. However, who knows what's wrong with your wiring. Better not.

Note: You can also find recommendations - to wind the windings of the welding P or PL on different rods. Like, VH is softening up. That’s right, but for this you need a special core, with rods different sections(secondary on the smaller one) and recesses releasing power lines into the air in the desired direction, see fig. on right. Without this, we will get a noisy, shaking and gluttonous, but not cooking transformer.

If there is a transformer

6.3 A circuit breaker and ammeter alternating current They will also help determine the suitability of an old welder lying around God knows where and God knows how. You need either a non-contact induction ammeter (current clamp) or a 3 A pointer electromagnetic ammeter. A multimeter with alternating current limits will not lie, because the shape of the current in the circuit will be far from sinusoidal. Also, a long-neck liquid household thermometer, or, better yet, 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 an old welding transformer is as follows:

Calculation of a welding transformer

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

The basis of calculation is usual: the arc burns stably under a voltage Ud of 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the rated welding current. Accordingly, the minimum open-circuit voltage Uхх of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. Nothing more: it is unacceptable according to technical regulations, 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 transition from short-circuit mode (say, when shorted by drops of metal) to working mode 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 previous. list we find the overall power;
• We find the maximum possible welding current Isv = Pg/Ud. 200 A is guaranteed if 3.6-4.8 kW can be removed from the iron. True, in the first 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 permissible network voltage for welding I1рmax = 1.1Pg(VA)/235 V. In fact, the norm for the network is 185-245 V, but for a homemade 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 assume the current density of the primary J1 = 5 A/sq. mm and, using I1рmax, we find the diameter of its copper wire d = (4S/3.1415)^0.5. Its total diameter with self-insulation is D = 0.25+d, and if the wire is ready - tabular. To operate in the “brick bar, mortar yok” mode, you can take J1 = 6-7 A/sq. mm, but only if the right wire no and not expected;
• We find the number of turns per volt of the primary: w = k2/Sс, where k2 = 50 for Sh 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 loss of the winding due to leakage and in copper, which is formally expressed by the somewhat abstract parameter of the winding’s own voltage drop;
• We set the laying coefficient Kу = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of layers of the winding, the average length of the turn and the footage of the wire
• We calculate the secondary similarly at J1 = 6 A/sq. mm, k3 = 1.05 and Ku = 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.

Winding and finishing

The diameters of the wires in the calculation of windings are usually greater than 3 mm, and varnished winding wires with d>2.4 mm are rarely widely sold. In addition, the welder windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSH, PELSHO, PB, PBD. They are even more difficult to find, and they are very expensive. The meterage of the wire for the welder is such that it is possible to insulate cheaper bare wires yourself. An additional advantage is that you can twist several times to the desired S stranded wires, we get a flexible wire, which is much easier to wind. Anyone who has tried to manually lay a tire of at least 10 square meters on a frame will appreciate it.

Isolation

Let's say there is a 2.5 sq.m. wire available. mm in PVC insulation, and for the secondary you need 20 m by 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 exposed wires with a pair of pliers into an even, tight braid, and wrap it in order of increasing insulation cost:

1. Using masking tape with an overlap of 75-80% turns, i.e. in 4-5 layers.
2. Calico braid with an overlap of 2/3-3/4 turns, i.e. 3-4 layers.
3. Cotton electrical 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 of frameless biscuits, and they are secured to the core with wedges made of textolite, fiberglass or, in extreme cases, bakelite plywood impregnated with liquid varnish (see above). The instructions for winding the windings of a welding transformer are as follows:

• We prepare a wooden boss with a height equal to the height of the winding and with dimensions in diameter 3-4 mm larger than a and b of the magnetic circuit;
• We nail or screw temporary plywood cheeks to it;
• We wrap the temporary frame in 3-4 layers of thin plastic film with an approach to the cheeks and a turn to their outer side so that the wire does not stick to the wood;
• We wind the pre-insulated winding;
• Along the winding, we impregnate it twice with liquid varnish until it drips through;
• Once the impregnation has dried, carefully remove the cheeks, squeeze out the boss and peel 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 finishing

We mix the core into a biscuit and tighten it with bolts, as expected. Winding tests are carried out in exactly the same way as tests of a questionable 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 wound up. Winding wire connections are made with bolts (!), insulated with heat-shrinkable tube (HERE) in 2 layers or cotton tape in 4-5 layers.

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

After finishing, we disassemble the core; wrap the biscuit tightly 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 saturate it with liquid varnish again; when it dries - twice undiluted. This galette is ready, you can make a secondary one. When both are on the core, we test the transformer again now at 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’s still too cool for us, haven’t you forgotten? Needs to be softened. The simplest way– a resistor in the secondary circuit is not suitable for us. Everything is very simple: at a resistance of only 0.1 Ohm at a current of 200, 4 kW of heat will be dissipated. If we have a welder with a capacity of 10 kVA or more, and we need to weld thin metal, we need a resistor. Whatever current is set by the regulator, its emissions when the arc is ignited are inevitable. Without active ballast, they will burn out the seam in places, and the resistor will extinguish them. But for us, weaklings, it will be of no use.

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

We will go the other way: we will use active-reactive ballast, colloquially called 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. Apparently, for power up to 7 kVA this gut is correct. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is attached to it with a clothespin clamp. By selecting the connection point, it is possible, coupled with switching to secondary taps, to fine-tune the operating mode of the arc.

Note: An active-reactive choke can become red-hot during operation, so it requires a fireproof, heat-resistant, dielectric, non-magnetic lining. In theory, a special ceramic cradle. It is acceptable to replace it with dry sand cushion, or already formally with a violation, but not grossly, the welding gut is laid on bricks.

But other?

This means, first of all, an electrode holder and a connecting device for the return hose (clamp, clothespin). Since our transformer is at its limit, we need to buy them ready-made, but those like those in Fig. right, no need. For a 400-600 A welding machine, the quality of contact in the holder is hardly noticeable, and it will also withstand simply winding up the return hose. And our homemade one, working with effort, can go haywire, seemingly for some unknown reason.

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

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

Let's try a permanent one

Welding with direct current has a number of advantages, but the input voltage of any welding transformer becomes more severe at constant current. And ours, designed for the minimum possible power reserve, will become unacceptably stiff. The choke-intestine will no longer help here, even if it worked on direct current. In addition, it is necessary to protect expensive 200 A rectifier diodes from current and voltage surges. We need a reciprocal-absorbing infra-low frequency filter, FINCH. Although it looks reflective, you need to take into account the strong magnetic coupling between the halves of the coil.

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

With a coil magnetic circuit it is simpler, although not entirely. Suitable for it are 2 PL power transformers TS-270 from old tube “coffin” TVs (the data is in reference books and in RuNet), or similar ones, or SLs with similar or larger a, b, c and h. From 2 submarines, an SL is assembled with a gap, see figure, of 15-20 mm. It is fixed with textolite or plywood spacers. Winding – insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. They wind it in 2 wires. The end of one is connected to the beginning of the other, this will be the middle point.

The filter is adjusted in an arc at the minimum and maximum values ​​of Uхх. If the arc is sluggish at minimum, the electrode sticks, the gap is reduced. If the metal burns at maximum, increase it or, which will be more effective, cut off part of the side rods symmetrically. To prevent the core from crumbling, it is impregnated with liquid and then normal varnish. Finding the optimum inductance is quite difficult, but then welding works flawlessly on alternating current.

Microarc

The purpose of microarc welding is discussed 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 connected to the filament winding of a standard power transformer. One electrode – the twisting of the wires itself (copper-aluminum, copper-steel is possible); the other is a graphite rod like a 2M pencil lead.

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

Video: homemade twist welding machine

Video: DIY welding machine from capacitors

Contact! There is contact!

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

The principle of operation of resistance spot welding is illustrated in the figure: copper electrodes forcefully compress the parts, a current pulse in the steel-to-steel ohmic resistance zone heats the metal until electrodiffusion occurs; metal does not melt. The current needed for this is approx. 1000 A per 1 mm of thickness of the parts being 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!”

However, resistance spot welding is much more economical than arc welding: the no-load voltage of the welding transformer for it is 2 V. It consists of 2-contact steel-copper potential differences and the ohmic resistance of the penetration zone. The transformer for resistance welding is calculated in the same way as 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, is well cooled, and its utilization factor (the ratio of welding time to idling and cooling time) is many times lower.

There are many descriptions on the RuNet of homemade pulse-spot welders made from unusable microwave ovens. They are, in general, correct, but repetition, as written in “1001 Nights,” is of no use. And old microwaves don’t lie in heaps in trash heaps. Therefore, we will deal with designs that are less known, but, by the way, more practical.

In Fig. – construction of a simple apparatus for pulsed spot welding. They can weld sheets up to 0.5 mm; It is perfect for small crafts, and magnetic cores of this and larger sizes are relatively affordable. Its advantage, in addition to its simplicity, is the clamping of the running rod of the welding pliers with a load. To work with a contact welding pulser, a third hand would not hurt, and if one has to forcefully squeeze the pliers, then it is generally inconvenient. Disadvantages – increased risk of accidents and injuries. If you accidentally give a pulse when the electrodes are brought together without the parts being welded, then the plasma will shoot out 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 busbar. It can be assembled from strips of thin sheet copper (it will turn out flexible) or made from a piece of flattened refrigerant supply tube of a household air conditioner. The bus is isolated manually as described above.

Here in Fig. – drawings of a pulse spot welding machine are more powerful, for welding sheets 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 strong, stable compression of the pliers, on which the quality of the welded joint significantly depends. If something happens, the clamp can be instantly released with one blow on the eccentric lever. The disadvantage is the insulating pincer units, there are too many of them and they are complex. Another one is aluminum pincer rods. Firstly, they are not as strong as steel ones, and secondly, they are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.

About electrodes

In amateur conditions, it is more advisable to insulate the electrodes at the installation site, as shown in Fig. on right. There is no conveyor at home; you can always let the device cool down so that the insulating bushings do not overheat. This design will allow you to make rods from durable and cheap steel corrugated pipe, and also lengthen the wires (up to 2.5 m is permissible) and use a contact welding gun or external pliers, see fig. below.

In Fig. On the right you can see another feature of electrodes for resistance spot welding: 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 times the thickness of the adjacent material being welded, otherwise the weld spot will be burned either in the center (wide heel) or along the edges (narrow heel), and corrosion will occur from the welded joint even on stainless steel.

The last point about electrodes is their material and size. Red copper burns out quickly, so commercial 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. According to heat transfer conditions, the length of the electrode is at least 3 of its diameters from the heel to the root (the beginning of the shank).

How to give impetus

In the simplest homemade pulse-contact welding machines, the current pulse is given manually: they simply turn on the welding transformer. This, of course, does not benefit him, and the welding is either insufficient or burnt out. However, automating the supply and standardization of welding pulses is not so difficult.

A diagram of a simple but reliable welding pulse generator, proven by long practice, is shown in Fig. Auxiliary transformer T1 is a regular 25-40 W power transformer. The voltage of winding II is indicated by the backlight. You can replace it with 2 LEDs connected back-to-back with a quenching resistor (usual, 0.5 W) 120-150 Ohm, then the voltage II will be 6 V.

Voltage III - 12-15 V. 24 is possible, then capacitor C1 (regular 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 - 12 or more A 400 V. Optothyristors from computer power supplies or TO-12.5, TO-25 are suitable. Resistor R1 is a wire-wound resistor; it is used to regulate the pulse duration. Transformer T2 – welding.