How to make a welding machine from latra. Contact welding - how to make equipment and pliers yourself? What we won't talk about

A home-made circuit of the welding machine is assembled on the basis of a nine-ampere laboratory adjustable autotransformer. In its design, it is possible to adjust the welding current. The presence of a diode bridge in the circuit of this welding machine allows welding with direct current.

The operating mode of the welding device is set by the variable resistance R5. Thyristors VS1 and VS2 open only in their half-cycle alternately due to the phase shift, on the radio components R5, C1 and C2.

Due to this, it is possible to change the input voltage on the primary winding in the range from 20 to 215 volts. As a result of the conversion, the secondary winding will have a reduced voltage, making it easy to start the welding arc on contacts X1 and X2 when welding with alternating current and on contacts X3 and X4 when welding in DC mode. The connection of the welding machine to the variable network is carried out with a standard plug. In the role of the SA1 toggle switch, you can use a paired machine for 25A.

To begin with, the protective cover, the electrically removable contact are carefully removed from the autotransformer and the mount is unscrewed. Next, good insulation is wound onto the existing 250 volt winding, on which 70 turns of the secondary winding are wound with copper wire with a cross-sectional area of 20 mm 2.

If there is no such wire at hand, you can wind from several wires with a smaller cross section. The upgraded autotransformer is placed in a homemade case with ventilation holes. It is also necessary to fit the regulator circuit, the bag, as well as contacts for welding with direct and alternating current.

In the absence of an autotransformer, you can do it yourself by winding both windings on a transformer steel core.

At the output of the secondary winding, in accordance with the scheme of the welding device, a diode bridge is connected, consisting of powerful rectifier diodes. Diodes must be installed on homemade radiators.

For this scheme of the welder, it is desirable to use a copper stranded wire in rubber insulation with a cross section of at least 20 mm 2.

I am sure: not a single artisan, homely owner will refuse from a compact and at the same time quite reliable, cheap and easy to manufacture “welder”. Especially if he finds out that this apparatus is based on an easily upgradeable 9-ampere (familiar to almost everyone from school physics lessons) laboratory autotransformer LATR2 and a self-made thyristor mini-regulator with a rectifier bridge. They allow not only to safely connect to a 220 V AC household lighting network, but also to change u on the electrode, which means choosing the desired welding current value.

Operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which, triggering during its half period. opens the corresponding thyristor for a certain period of time. As a result, adjustable 20-215 V are on the primary winding of the welding T1. Transforming in the secondary winding, the required -u make it easy to ignite the arc for welding on alternating (terminals X2, X3) or rectified (X4, X5) current.

Resistors R2 and R3 shunt the control circuits of thyristors VS1 and VS2. Capacitors C1. C2 is reduced to an acceptable level of radio interference accompanying the arc discharge. In the role of the light indicator HL1, signaling the inclusion of the device in the household electrical network, a neon light bulb with a current-limiting resistor R1 is used.

To connect the "welder" to the apartment wiring, a conventional plug X1 is applicable. But it is better to use a more powerful electrical connector, which is commonly called "Euro plug-Euro socket". And as the SB1 switch, the VP25 "bag" is suitable, designed for a current of 25 A and allowing you to open both wires at once.

As practice shows, it does not make sense to install any fuses (anti-overload machines) on the welding machine. Here you have to deal with such currents, if exceeded, the protection at the network input to the apartment will definitely work.

For the manufacture of the secondary winding, the casing-enclosure, the current collector slider and the mounting fittings are removed from the base LATR2. Then, on the existing 250 V winding (127 and 220 V taps remain unclaimed), reliable insulation is applied (for example, from varnished fabric), on top of which a secondary (lowering) winding is placed. And this is 70 turns of an insulated copper or aluminum bus, having a diameter of 25 mm2. It is acceptable to make the secondary winding from several parallel wires with the same overall cross section.

Winding is more convenient to carry out together. While one, trying not to damage the insulation of adjacent turns, carefully stretches and lays the wire, the other holds the free end of the future winding, preventing it from twisting.

The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which a circuit board made of 10 mm getinaks or fiberglass is placed with a packet switch SВ1, a thyristor voltage regulator (with resistor R6), a light indicator HL1 for turning on the device in the network and output terminals for welding on an alternating (X2, X3) or direct (X4, X5) current.

In the absence of a basic LATR2, it can be replaced with a home-made "welder" with a magnetic circuit made of transformer steel (core cross section 45-50 cm2). Its primary winding should contain 250 turns of PEV2 wire with a diameter of 1.5 mm. The secondary one is no different from the one used in the modernized LATR2.

At the output of the low-voltage winding, a rectifier unit with power diodes VD3 - VD10 is installed for DC welding. In addition to these valves, more powerful analogues are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).

Power diodes and thyristors are installed on radiators-heat sinks, the area of each of which is at least 25 cm2. The axis of the adjusting resistor R6 is brought out of the casing. A scale with divisions corresponding to specific values of direct and alternating voltage is placed under the handle. And next to it is a table of the dependence of the welding current on the voltage on the secondary winding of the transformer and on the diameter of the welding electrode (0.8-1.5 mm).

Welding transformer based on the widely used LATR2 (a), its connection to the circuit diagram of a self-made adjustable apparatus for welding on alternating or direct current (b) and a voltage diagram (c), explaining the operation of the resistor controller of the electric arc burning mode.

Of course, self-made electrodes made of carbon steel "wire rod" with a diameter of 0.5-1.2 mm are also acceptable. Blanks 250-350 mm long are covered with liquid glass - a mixture of silicate glue and crushed chalk, leaving the 40-mm ends unprotected, which are necessary for connecting to the welding machine. The coating is thoroughly dried, otherwise it will begin to “shoot” during welding.

Although both alternating (terminals X2, X3) and direct (X4, X5) current can be used for welding, the second option, according to welders, is preferable to the first. Moreover, polarity plays an important role. In particular, when a "plus" is applied to the "mass" (the object being welded) and, accordingly, the electrode is connected to the terminal with the "minus" sign, the so-called direct polarity takes place. It is characterized by the release of more heat than with reverse polarity, when the electrode is connected to the positive terminal of the rectifier, and the “mass” to the negative. Reverse polarity is used when it is necessary to reduce heat generation, for example, when welding thin sheets of metal. Almost all the energy released by the electric arc goes to the formation of a weld, and therefore the depth of penetration is 40-50 percent greater than with a current of the same magnitude, but with direct polarity.

And a few other very important features. An increase in the arc current at a constant welding speed leads to an increase in the penetration depth. Moreover, if the work is carried out on alternating current, then the last of these parameters becomes 15-20 percent less than when using direct current of reverse polarity. The welding voltage has little effect on the depth of penetration. On the other hand, the width of the seam depends on us: with increasing stress, it increases.

Hence an important conclusion for those involved in, say, welding work when repairing a car body made of sheet steel: the best results will be obtained by welding with direct current of reverse polarity at a minimum (but sufficient for stable arcing) voltage.

The arc must be kept as short as possible, the electrode is then consumed evenly, and the penetration depth of the welded metal is maximum. The seam itself is clean and strong, practically devoid of slag inclusions. And from rare splashes of the melt, which are difficult to remove after the product has cooled, you can protect yourself by rubbing the near-weld surface with chalk (the drops will roll off without sticking to the metal).

The arc excitation is carried out (after having previously supplied the corresponding Ucv to the electrode and the “mass”) in two ways. The essence of the first is in a light touch of the electrode on the parts to be welded, followed by its removal by 2-4 mm to the side. The second method is reminiscent of striking a match on a box: sliding the electrode over the surface to be welded, it is immediately taken away for a short distance. In any case, you need to catch the moment of the arc and only then, smoothly moving the electrode over the seam formed right there, maintain its calm burning.

Depending on the type and thickness of the metal to be welded, one or another electrode is selected. If, for example, there is a standard assortment for a St3 sheet with a thickness of 1 mm, electrodes with a diameter of 0.8-1 mm are suitable (this is basically what the design under consideration is designed for). For welding work on 2 mm rolled steel, it is desirable to have both a more powerful “welder” and a thicker electrode (2-3 mm).

For welding jewelry made of gold, silver, cupronickel, it is better to use a refractory electrode (for example, tungsten). Metals that are less resistant to oxidation can also be welded using carbon dioxide protection.

In any case, work can be performed both with a vertically located electrode, and tilted forward or backward. But sophisticated professionals say: when welding with a forward angle (meaning an acute angle between the electrode and the finished seam), more complete penetration and a smaller width of the seam itself are provided. Backward welding is recommended only for lap joints, especially when dealing with profiled steel (angle, I-beam and channel).

An important thing is the welding cable. For the device in question, copper stranded (total cross section is about 20 mm2) in rubber insulation is the best fit. The required quantity is two one and a half meter segments, each of which should be equipped with a carefully crimped and soldered terminal lug for connection to the "welder". For direct connection to the "mass" they use a powerful crocodile clip, and with the electrode - a holder resembling a three-pronged fork. You can also use the car "cigarette lighter".

From a compact and at the same time quite reliable, cheap and easy-to-manufacture “welder”, not a single artisan, homely owner will refuse. Especially if he finds out that this device is based on an easily upgradeable 9 amp(familiar to almost everyone from school physics lessons) laboratory autotransformer LATR2 and a home-made thyristor mini-regulator with a rectifier bridge. They allow not only to safely connect to a 220V AC household lighting network, but also to change Uw on the electrode, which means choosing the desired welding current value.

Operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which, triggering during its half-cycle, opens the corresponding thyristor for a certain period of time. As a result, adjustable 20-215 V are on the primary winding of the welding T1. Transforming in the secondary winding, the required -Us make it easy to ignite the arc for welding on alternating (terminals X2, X3) or rectified (X4, X5) current.

Welding transformer based on the widely used LATR2 (a), its connection to the circuit diagram of a self-made adjustable apparatus for welding on alternating or direct current (b) and a voltage diagram explaining the operation of the transistor arc burning mode controller.

Resistors R2 and R3 shunt the control circuits of thyristors VS1 and VS2. Capacitors C1, C2 reduce to an acceptable level of radio interference that accompanies the arc discharge. In the role of the light indicator HL1, signaling the inclusion of the device in the household electrical network, a neon lamp with a current-limiting resistor R1 is used.

To connect the "welder" to the apartment wiring, a conventional plug X1 is applicable. But it is better to use a more powerful electrical connector, which is commonly called a "Euro plug-Euro socket". And as the SB1 switch, the VP25 “bag” is suitable, designed for a current of 25 A and allowing you to open both wires at once.

For the manufacture of the secondary winding, the casing-guard, the current-collecting slider and the mounting fittings are removed from the base LATR2. Then, on the existing 250 V winding (127 and 220 V taps remain unclaimed), reliable insulation is applied (for example, from varnished fabric), on top of which a secondary (lowering) winding is placed.

And this is 70 turns of an insulated copper or aluminum bus, having a diameter of 25 mm2. It is acceptable to make the secondary winding from several parallel wires with the same overall cross section.

The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which is placed a circuit board made of 10 mm getinax or fiberglass with a batch switch SB1, a thyristor voltage regulator (with resistor R6), a light indicator HL1 for turning on the device in the network and output terminals for welding on an alternating (X2, X3) or direct (X4, X5) current.

At the output of the low-voltage winding, a rectifier unit with power diodes VD3-VD10 is installed for DC welding. In addition to these valves, more powerful analogues are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).

Reverse polarity is used when it is necessary to reduce heat generation, for example, when welding thin sheets of metal. Almost all the energy released by the electric arc goes to the formation of a weld, and therefore the depth of penetration is 40-50 percent greater than with a current of the same magnitude, but with direct polarity.

The welding voltage has little effect on the depth of penetration. But the width of the seam depends on Uw: with increasing voltage, it increases.

The arc excitation is carried out (after applying the corresponding -Usv to the electrode and the “mass”) in two ways. The essence of the first is in a light touch of the electrode on the parts to be welded, followed by its withdrawal by 2-4 mm to the side. The second method is reminiscent of striking a match on a box: sliding the electrode over the surface to be welded, it is immediately taken away for a short distance.

In any case, you need to catch the moment of the arc and only then, smoothly moving the electrode over the seam formed right there, maintain its calm burning.

Depending on the type and thickness of the metal to be welded, one or another electrode is selected. If, for example, there is a standard assortment for a St3 sheet 1 mm thick, electrodes with a diameter of 0.8-1 mm are suitable (this is what the design under consideration is mainly designed for). For welding work on 2 mm rolled steel, it is desirable to have both a more powerful "welder" and a thicker electrode (2-3 mm).

For a direct connection to the “ground”, a powerful crocodile clip is used, and with an electrode, a holder resembling a three-pronged fork is used. You can also use the car "cigarette lighter".

You also need to take care of your personal safety. When arc welding, try to protect yourself from sparks, and even more so from splashes of molten metal. It is recommended to wear loose-fitting canvas clothing, protective gloves and a mask that protects the eyes from the harsh radiation of the electric arc (sunglasses are not suitable here).

Of course, we must not forget about the "Safety regulations when performing work on electrical equipment in networks with voltages up to 1 kV". Electricity does not forgive carelessness!

M.VEVIOROVSKY, Moscow region Model designer 2000 No. 1.

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

The second - a purchased welding machine is expensive. Rent is also not cheap, because. the probability of its failure with unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be just long and difficult. 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 from a corrugated board on a frame from a professional pipe or a welded garage.
Microarc welding of strands of wires is very simple, and useful when laying or repairing electrical wiring.
Spot pulse resistance welding - can be very useful when assembling products from a thin steel sheet.

What we won't talk about

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

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

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

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

Transformer

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

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

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

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

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

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

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

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

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

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

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

Magnetic circuits

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

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 the beginning. This is suitable for cutting, and for thinner work, the transformer is supplemented with external devices (see below), which stretch the VX along the current axis to curve 2a.

The calculation basis is usual: the arc stably burns under voltage Ud 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the nominal welding current. Accordingly, the minimum open-circuit voltage Uxx of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. Nothing more: it’s unacceptable according to TB, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly switch from a short circuit mode (say, when shorted by metal drops) to a working one, is maintained without additional measures. True, such a transformer is prone to overheating, but since it is our own and in front of our eyes, and not in the far corner of a workshop or site, we will consider this acceptable. So:

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

Winding and finishing

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

isolation

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

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

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

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

Finishing and domotka

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

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

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

Pull VX

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

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

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

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

But other?

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

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

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

Trying a constant

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

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

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

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

microarc

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

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

Video: homemade twist welding machine

Video: do-it-yourself welding machine from capacitors

Contact! There is a contact!

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

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

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

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

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

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

About electrodes

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

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

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

How to give impetus

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

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

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

Resistance welding, in addition to the technological advantages of the application, has another important advantage - simple equipment for it can be made independently, and its operation does not require specific skills and initial experience.

1 Principles of design and assembly of resistance welding

Contact welding, assembled with one's own hands, can be used to solve a fairly wide range of non-serial and non-industrial tasks for the repair and manufacture of products, mechanisms, equipment from various metals both at home and in small workshops.

Resistance welding ensures the creation of a welded joint of parts by heating the area of their contact with an electric current passing through them while simultaneously applying a compressive force to the joint zone. Depending on the material (its thermal conductivity) and the geometric dimensions of the parts, as well as the power of the equipment used for their welding, the resistance welding process should proceed with the following parameters:

low voltage in the power welding circuit - 1–10 V;
in a short time - from 0.01 seconds to several;
high welding pulse current - most often from 1000 A or higher;
small melting zone;
the compressive force applied to the welding site must be significant - tens to hundreds of kilograms.

Compliance with all these characteristics directly affects the quality of the resulting welded joint. You can only make devices for yourself, as in the video. The easiest way is to assemble an alternating current welding machine with unregulated power. In it, the process of connecting parts is controlled by changing the duration of the supplied electrical impulse. To do this, use a time relay or cope with this task manually "by eye" using a switch.

Home-made spot welding is not very difficult to manufacture, and to make its main unit - a welding transformer - you can pick up transformers from old microwaves, TVs, LATRs, inverters, and the like. The windings of a suitable transformer will need to be rewound in accordance with the required voltage and welding current at its output.

The control circuit is selected ready-made or developed, and all other components, and, in particular, for the contact welding mechanism, are taken based on the power and parameters of the welding transformer. The contact welding mechanism is made in accordance with the nature of the upcoming welding work according to any of the known schemes. Usually make welding tongs.

All electrical connections must be of good quality and have good contact. And connections using wires are made from conductors with a cross section corresponding to the current flowing through them (as shown in the video). This is especially true of the power part - between the transformer and the clamp electrodes. If the circuit contacts are poor, there will be large energy losses at the joints, sparking may occur, and welding may become impossible.

2 Scheme of a device for welding metal up to 1 mm thick

To connect parts by contact, you can assemble according to the diagrams below. The proposed apparatus is designed for welding metals:

sheet, the thickness of which is up to 1 mm;
wire and rods, the diameter of which is up to 4 mm.

The main technical characteristics of the device:

supply voltage - alternating 50 Hz, 220 V;
output voltage (at the electrodes of the contact welding mechanism - on tongs) - variable 4–7 V (idle);
welding current (maximum pulsed) - up to 1500 A.

Figure 1 shows the circuit diagram of the entire device. The proposed contact welding consists of a power unit, a control circuit and an automatic switch AB1, which serves to turn on the power of the device and protect it in case of emergencies. The first unit includes a welding transformer T2 and a non-contact thyristor single-phase starter type MTT4K, which connects the primary winding T2 to the mains.

Figure 2 shows the winding diagram of the welding transformer indicating the number of turns. The primary winding has 6 outputs, by switching which it is possible to carry out stepwise coarse adjustment of the output welding current of the secondary winding. At the same time, output No. 1 remains permanently connected to the network circuit, and the remaining 5 serve for adjustment, and only one of them is connected to power for operation.

Scheme of the MTT4K starter, commercially available, in Fig.3. This module is a thyristor key, which, when its contacts 5 and 4 are closed, switches the load through contacts 1 and 3 connected to the open circuit of the primary winding Tr2. MTT4K is designed for a load with a maximum voltage of up to 800 V and a current of up to 80 A. Such modules are produced in Zaporozhye at Element-Converter LLC.

The control scheme consists of:

power supply;
direct control circuit;
relay K1.

Any transformer with a power of not more than 20 W, designed to operate from a 220 V network and outputting a voltage of 20–25 V on the secondary winding, can be used in the power supply. It is proposed to install a diode bridge of the KTs402 type as a rectifier, but any other with similar parameters or assembled from individual diodes.

Relay K1 is used to close contacts 4 and 5 of the MTT4K key. This happens when voltage is applied from the control circuit to the winding of its coil. Since the switched current flowing through the closed contacts 4 and 5 of the thyristor key does not exceed 100 mA, almost any low-current electromagnetic relay with a response voltage in the range of 15–20 V is suitable as K1, for example, RES55, RES43, RES32 and the like.

3 Control chain - what does it consist of and how does it work?

The control circuit performs the functions of a time relay. Turning on K1 for a given period of time, it sets the duration of the effect of an electric pulse on the parts to be welded. The control circuit consists of capacitors C1-C6, which must be electrolytic with a charging voltage of 50 V or higher, switches of the P2K type with independent fixation, a KN1 button and two resistors - R1 and R2.

The capacitance of the capacitors can be: 47 uF for C1 and C2, 100 uF for C3 and C4, 470 uF for C5 and C6. KH1 should be with one normally closed and the other normally open contacts. When AB1 is turned on, the capacitors connected via P2K to the control circuit and power supply start charging (only C1 in Fig. 1), R1 limits the initial charging current, which can significantly increase the life of the tanks. Charging occurs through the normally closed contact group of the KN1 button, which was switched at that time.

When KN1 is pressed, the normally closed contact group opens, disconnecting the control circuit from the power supply, and the normally open contact group closes, connecting the charged containers to the K1 relay. The capacitors are then discharged and the discharge current triggers K1.

The open normally closed contact group KN1 prevents the relay from being powered directly from the power supply. The greater the total capacitance of the discharging capacitors, the longer they are discharged, and, accordingly, K1 closes contacts 4 and 5 of the MTT4K key for longer, and the longer the welding pulse. When the capacitors are completely discharged, K1 will turn off and resistance welding will stop. To prepare it for the next impulse, KH1 must be released. The capacitors are discharged through the resistor R2, which must be variable and serves to more accurately control the duration of the welding pulse.

4 Power section - transformer

The proposed contact welding can be assembled, as shown in the video, on the basis of a welding transformer made using a magnetic circuit from a 2.5 A transformer. These are found in LATRs, laboratory instruments and a number of other devices. The old winding must be removed. At the ends of the magnetic circuit, it is necessary to install rings made of thin electric cardboard.

They are folded along the inner and outer edges. Then the magnetic circuit must be wrapped over the rings with 3 or more layers of varnished fabric. To perform the windings, wires are used:

For primary 1.5 mm in diameter, it is better in fabric insulation - this will contribute to good impregnation of the winding with varnish;
For a secondary diameter of 20 mm, stranded in organosilicon insulation with a cross-sectional area of at least 300 mm 2.

The number of turns is shown in Fig.2. Intermediate conclusions are drawn from the primary winding. After winding, it is impregnated with varnish EP370, KS521 or similar. A cotton tape (1 layer) is wound over the primary coil, which is also impregnated with varnish. Then the secondary winding is laid and varnished again.

5 How to make pincers?

Resistance welding can be equipped with tongs that are mounted directly into the body of the device itself, as in the video, or remote in the form of scissors. The first ones, from the point of view of performing high-quality, reliable insulation between their nodes and ensuring good contact in the circuit from the transformer to the electrodes, are much easier to manufacture and connect than remote ones.

However, the clamping force developed by such a design, if the length of the movable tong arm after the electrode is not increased, will be equal to the force created directly by the welder. Remote tongs are more convenient to use - you can work at some distance from the device. And the effort developed by them will depend on the length of the handles. However, it will be necessary to make sufficiently good insulation from textolite bushings and washers in the place of their movable bolted connection.

When making tongs, it is necessary to foresee the necessary reach of their electrodes in advance - the distance from the body of the apparatus or the place of the movable connection of the handles to the electrodes. This parameter will determine the maximum possible distance from the edge of the sheet metal to the place where welding is performed.

Tick electrodes are made from copper bars or beryllium bronze. You can use the tips of powerful soldering irons. In any case, the diameter of the electrodes must be no less than that of the wires supplying current to them. To obtain welding cores of the desired quality, the size of the contact pads (electrode tips) should be as small as possible.