How to make a homemade welding machine with your own hands. Do-it-yourself welding machine: simple instructions for creating and using the device. Mains voltage and number of phases
No work with iron can do without a welding machine. It allows you to cut and connect metal parts of any size and thickness. Good decision- do welding with your own hands, because good models are expensive and cheap ones are of low quality. To implement the idea self-manufacturing It is necessary for a welder to acquire special equipment that allows you to hone the quality skills of a specialist in real conditions.
Types and characteristics of the tool
After all the necessary conditions for the preparatory stage are successfully met, it becomes possible to make a model of the welding device with your own hands. Today there are many schematic diagrams by which the device can be manufactured. They operate in one of the following ways:
- Direct or alternating current.
- Pulse or inverter.
- Automatic or semi-automatic.
It is worth paying attention to the apparatus belonging to the transformer type. An important characteristic This device is AC-powered, allowing it to be used in a domestic environment. AC devices are capable of providing the nomenclature quality of welded joints. A unit of this type can easily find its application in everyday life. when servicing real estate located in the private sector.
In order to assemble such a device, you must have:
- About 20 meters of cable or wire of large cross section.
- High magnetic permeability metal base to be used as the core of the transformer.
The optimal core configuration has a U-shaped rod base. In theory, a core of any other configuration can easily fit, for example, a round shape taken from a stator that has become unusable. But in practice, winding the winding on such a base is much more difficult.
The cross-sectional area for a core belonging to a home-made household welding machine is 50 cm 2. This will be enough to use rods from 3 to 4 mm in diameter in the installation. Usage larger section will only lead to an increase in the mass of the structure, and the efficiency of the apparatus will not become higher.
Manufacturing instructions
For the primary winding, you must use copper wire with high heat resistance, since during welding it will be exposed to high temperatures. The wire used must be selected according to fiberglass or cotton insulation designed for stationary use in the high temperature zone.
For the winding of the transformer, it is not allowed to use a wire with PVC insulation, which, when heated, will instantly become unusable. In some cases, insulation for the transformer winding is made independently.
To perform this procedure, you need to take a blank made of cotton fabric or fiberglass, cut it into strips about 2 cm wide, wrap the prepared wire with them and impregnate the bandage with any varnish that has electrical properties. Such insulation in terms of thermal characteristics will not yield to any factory analogue.
Coils are wound according to a certain principle. First, half of the primary winding is wound, followed by half of the secondary. Then proceed to the second coil using the same technique. To improve quality insulating coating fragments of strips of cardboard, fiberglass or pressed paper are inserted between the winding layers.
Hardware setup
Next, you need to configure. It is produced by turning on the equipment in the network and taking voltage readings from the secondary winding. The voltage on it should be from 60 to 65 volts.
Precise adjustment of the parameters is carried out by reducing or increasing the length of the winding. To obtain a qualitative result, the voltage on the secondary winding should be adjusted to the specified parameters.
A VRP cable or a SHRPS wire is connected to the primary winding of the finished welding transformer, which will be used to connect to the network. One of the outputs of the secondary winding is fed to the terminal, to which the “mass” will subsequently be connected, and the second is fed to the terminal connected to the cable. The last procedure is over and a new welding machine ready for operation.
Small unit production
For the manufacture of a small welding machine, an autotransformer from a Soviet-style TV is easily suitable. It can be easily used to obtain a voltaic arc. In order for everything to work out correctly, graphite electrodes are connected between the terminals of the autotransformer. This simple design allows you to perform several simple jobs using welding, such as:
- Making or repairing thermocouples.
- Heating up to the maximum temperature of high-carbon steel products.
- Hardening of tool steel.
A home-made welding machine, created on the basis of an autotransformer, has a significant drawback. It must be used with extra precautions. Without galvanic isolation from the electrical network, it is a rather dangerous device.
The optimal parameters of an autotransformer suitable for creating a welding machine are considered to be an output voltage in the range from 40 to 50 volts and low power from 200 to 300 watts. This device is capable of delivering from 10 to 12 amperes of operating current, which will be sufficient when welding wires, thermocouples and other elements.
As electrodes for a do-it-yourself mini welding machine, you can use leads from a simple pencil. Holders for improvised electrodes can serve as terminals that are on various electrical appliances.
For welding, the holder is connected to one of the terminals of the secondary winding, and the workpiece to be welded to the other. The handle for the holder is best made from fiberglass washer or other heat-resistant material. It should be noted that the arc of such a device operates for a rather short time, preventing the autotransformer used from overheating.
If you have the necessary plumbing and electrical installation tools (we will talk about them in detail below), and you have the appropriate professional skills, then you can easily make welding transformer with your own hands.
Of course, you will have expenses, but incomparably less compared to the cost of purchasing a factory-made gadget. But how much fun you will get in the process of your favorite homemade work. And the delight, at the moment of the successful start of electric welding, in general, cannot be compared with anything!
We will give you a lot of useful tips in the article. selection, calculation and production welding transformer (hereinafter - ST), which will help to optimize costs and save the budget.
A properly made do-it-yourself device is no worse than a factory one.
The article will talk about two types of welding transformers. For welds:
- arc;
- contact.
Do-it-yourself welding transformer: what we need
The range of tools and equipment for the manufacture and assembly of both types of ST is identical. We will need the following:
- electrical voltage indicator. To control the absence of the latter on electrical contacts, and thereby ensure safety when performing electrical work;
- angle grinder(it is also a “grinder”, “zipper-machine”, etc.) with a set of discs (cutting, grinding, etc.);
- electric drill with a set of drills for metal and a core;
- tester or voltmeter alternating current with a measurement limit of 400 V;
- any " scriber". It is used for marking on metal;
- locksmith clamps. For fixing parts when marking "in place";
- electric tool set. The specific composition of the kit depends on the materials that will be used in the manufacture of ST. In general, it is like this:
- complete electric soldering iron. We will perform soldering with solder POS-40;
- screwdrivers (different sizes with a straight and cross slot);
- keys:
- wrench;
- cap;
- end;
- pliers, side cutters, etc. with insulated handles;
- file set.
All work is more convenient to perform on locksmith workbench with an electrically insulating coating, equipped with a bench vise.
For the manufacture of ST, components and materials are required that differ depending on the type of transformer. In general, you need the following:
- protective cover. Must provide:
- protection against electric shock;
- exclude the possibility of any objects getting inside the gadget;
- magnetic circuit. Provides powerful electromagnetic flux, which induces an electromotive force in the windings (hereinafter - EMF);
- wire and wire. Necessary for the installation of windings;
- coil frames. Windings are wound on them;
- contact pads. Powerful terminal block with clamps for welding wires, small blocks - for wiring the circuit;
- switches (switches). Carry out switching sections of the windings when selecting the value of the welding current;
- interturn insulation material. Reduces the possibility of electrical breakdown of the winding insulation;
- fasteners (bolts, screws, nuts, washers, etc.). They are necessary for mounting the gadget during assembly work;
- insulating tape(type Х/Б).
Important: PVC insulating tape cannot be used, because it is destroyed when heated.
Homemade welding transformer for arc welding
Before proceeding with further work on the manufacture of ST, you should decide what exactly you will create. You need:
- choose the design and electrical circuit diagram of the future device;
- make an electrical and, if necessary, constructive calculation of its parameters.
Only after that, you should select the necessary equipment, materials and prepare, if necessary, a special tool.
How to calculate a welding transformer. Scheme
The question of how to calculate a home-made welding transformer is very specific, since it does not correspond typical schemes And generally accepted rules. The fact is that in the manufacture of homemade products, the parameters of their components are “adjusted” to the components already available (mainly to the magnetic circuit). Moreover, it often happens that:
- transformers are not assembled from the best transformer iron;
- windings are not wound with the most suitable wire and many other negative factors.
As a result, homemade products heat up and “buzz” (the core plates vibrate at the mains frequency: 50 Hz), but, at the same time, they “do their job” - they weld metal.
According to the shape of the cores, transformers of the following main types are distinguished:
- rod;
- armored.
Explanations for the figure:
- a - armored;
- b - rod.
transformers pivotal type, compared to transformers armored type, allow high current densities in the windings. Due to this, they have a higher efficiency, but the laboriousness of their manufacture is much higher. However, they are used more often.
On the rod core, the winding schemes shown in the figure are used.
Explanations for the figure:
- a - network winding on two sides of the core;
- b - the corresponding secondary (welding) winding, connected in anti-parallel;
- c - network winding on one side of the core;
- g - the secondary winding corresponding to it, connected in series.
For example, let's perform the calculation of ST assembled according to the scheme "c" - "g". Its secondary winding consists of two equal parts (halves). They are located on opposite arms of the magnetic circuit, and are connected to each other in series. The calculations consist in determining the theoretical and choosing the actual dimensions of the magnetic circuit.
We determine the power of the ST (according to the magnitude of the current in the secondary winding) from the following considerations. For electric welding in everyday life, coated electrodes are most often used Ø, mm: 2, 3, 4. We choose the “golden mean” for the most popular ones - 120 ... 130 A. The power of the ST is determined by the formula:
P = Uх.х. × Ist. × cos(φ) / η, where:
- Ux.x. - no-load voltage;
- Ist. - welding current;
- φ is the phase angle between voltage and current. Accept: cos(φ) = 0.8;
- η - efficiency. For homemade ST: efficiency = 0.7.
If we calculate the magnetic circuit according to the reference book, then its cross section for the selected current is 28 sq.cm. In practice, the cross section of the magnetic circuit for the same power can vary within: 25 ... 60 sq.cm.
For each section, it is necessary to determine (according to the reference book) the number of turns of the primary winding to provide a given power at the output. We only note that the larger the cross-sectional area of the magnetic circuit (S), the less turns of both coils will be needed. This is an essential point, since a large number of turns may not fit into the "window" of the magnetic circuit.
It is possible to use the magnetic circuit of an old transformer (for example, from a microwave oven, of course, after some reconstruction - replacement of the secondary winding).
If you do not have an old transformer, then you should purchase transformer iron, from which you will make the CT core.
Explanations for the figure:
- a - L-shaped plates;
- b - U-shaped plates;
- c - plates from strips of transformer steel;
- c and d are the dimensions of the "window", cm;
- S \u003d a x b - cross-sectional area of \u200b\u200bthe core (yoke), sq. cm.
The calculation of the number of turns of the primary windings at a mains supply voltage of 220 ... 240 V, the welding currents selected by us and the parameters of the magnetic circuit can be made using the following formulas:
N1 = 7440 × U1/(Sout × I2). For windings on one arm (half of the windings on top of each other, connected in series);
N1 = 4960 × U1/(Sout × I2). The windings are spaced on different shoulders.
Conventions in both formulas:
- U1 – power supply voltage;
- N1 is the number of turns of the primary winding;
- Siz - cross section of the magnetic circuit (sq.cm);
- I2 - given welding current of the secondary winding (A).
The output voltage of the secondary winding of the ST in idle mode for self-made welding transformers is, as a rule, in the range of 45 ... 50V. Using the following formula, you can determine its number of turns:
U1/U2 = N1/N2.
For the convenience of selecting the strength of the welding current, taps are made on the windings.
Welding transformer winding and installation
For the primary winding of the transformer, a special heat-resistant copper wire is used, which has cotton or fiberglass insulation.
Taking into account the power selected above, the electric current in the primary winding can reach 25 A. Based on these considerations, the primary winding of the ST should be wound with a wire having a cross section of ≥ 5 ... 6 sq. mm. This, among other things, will significantly increase the reliability of the ST.
The secondary winding is carried out copper wire, the cross section of which is: 30 ... 35 sq. mm. Particular attention should be paid to the choice of insulation of the secondary winding wire, since a large welding current flows through it. It must be very reliable Special attention should be given to heat resistance.
When installing windings, pay attention to the following:
- winding is done in one direction;
- an insulating layer of additional insulation is laid between the rows of windings (we recommend cotton).
The assembled CT should be placed in a protective casing with holes for ventilation.
Video
See how the task of assembling the device was implemented:
Do-it-yourself contact welding from a welding transformer
Contact welding creates a welded joint of parts due to the following simultaneous effects on them:
- heating the area of their contact with an electric current passing through it;
- a compressive force is applied to the joint area.
There are three types of contact welding:
- point;
- butt;
- suture.
We will talk about homemade ST for the most popular: resistance spot welding (the other two require very sophisticated equipment).
Explanations for the figure:
1 - electrodes supplying welding current to the workpiece to be welded;
2 - welded products with lap joint;
3 - welding transformer.
For resistance welding, depending on the thickness and thermal conductivity of the materials of the parts to be welded, the following values its main parameters:
- electric voltage in the power (welding circuit), V: 1…10;
- the value of the welding current (amplitude of the welding pulse), A: ≥ 1000;
- heating time (passage of the welding current pulse), sec: 0.01…3.0;
In addition, the following must be provided:
- insignificant melting zone;
- significant compressive force applied to the weld.
Scheme and calculation
Calculation of ST of resistance welding is performed according to the same algorithm as for arc welding (see above). When choosing data from the reference book (current strength and voltage of the secondary winding for spot welding of a selected metal grade of a given thickness), it should be borne in mind that the current strength of the secondary winding for such transformers is about 1000 ... 5000 A. The secondary winding is usually designed for units of volts and It is just a few turns (sometimes one) of a thick wire. Therefore, to adjust the welding current, the following circuit of the primary winding of the transformer is recommended.
Very often, during the operation of homemade products, it turns out that there is not enough power of the ST. In this case, it is possible to connect a second transformer in accordance with the proposed scheme.
Winding and installation
These operations are performed according to the same basic rules and requirements as for CT arc welding. With special care, the turns of the secondary winding should be fixed. To do this, you can use its conclusions by passing them in a heat-resistant insulator.
Copper rods are used as electrodes.
Should be considered that the larger the diameter of the electrode, the better. Under no circumstances should the electrode diameter be smaller than the wire diameter. For low-power CTs, it is possible to use tips from powerful soldering irons.
During operation, monitor the condition of consumables: the electrodes must be periodically undermined - otherwise they lose their shape. Over time, they wear down completely and need to be replaced.
:- the welder needs to stand on a rubber mat;
- workers must wear rubber gloves;
- A welding mask is not required, but goggles must be worn on the face.
conclusions
We have given you enough information to make a homemade welding transformer:
- arc welding;
- contact welding.
Housework always requires a certain set of tools, fixtures, as well as a variety of equipment. This is especially felt by the owners of private houses and those involved in various types of repairs in their own workshops and garages. The acquisition of expensive equipment is not always justified, since its use will not be permanent, but it is quite possible for every craftsman to assemble a welding machine with his own hands.
Before starting the process, it is necessary to determine the power of the device, because its dimensions and capabilities will depend on this. To get acquainted with the assembly procedure, you can watch the corresponding video, which shows how you can make a practical welding machine with your own hands. Its manufacture will require some theoretical training, as well as experience in electromechanical work. The assembly of the electric device at home is carried out according to preliminary calculations, taking into account both the input and output parameters of the device.
This electric device is useful not only for welders who perform some work at home or in the garage, but also for ordinary craftsmen who use a welding device to build various devices.
Features of homemade transformers
Self-assembled devices differ from factory equipment in their technical design. Do-it-yourself welding is made from available elements and assemblies, for which a welding transformer circuit is used. With exact observance of the parameters of the component parts, the electric device will serve reliably for many years. Before you make a welding transformer device with your own hands, you need to decide on the available components. The basis is a transformer consisting of a magnetic circuit, as well as primary and secondary windings. It can be purchased separately, adapted to an existing one, or made independently. To make a welded electric device with your own hands, transformer iron and wire for windings will be added to a variety of tools from improvised materials. The manufactured transformer must be able to be connected to a 220 V household power supply and have an output voltage of about 60-65 V for welding thick metals.
Features of homemade rectifiers
Self-made rectifiers allow you to weld thin sheet metal with high quality seam connections.
Scheme of a welding machine using rectification electric current quite simple. It contains a transformer to which a rectifier unit is connected, as well as a choke. This simplest design ensures stable burning of the welded electric arc. A coil of copper wires wound around a core is used as a choke. The rectifying device is connected directly to the outputs of the step-down transformer winding.
Depending on the goals, you can independently build a mini welded electric device. It will perfectly cope with metals of small thickness, which do not require the use of high currents when connecting. A spotter can be made from a welded electric device, which will greatly expand the possibilities of its application.
How to make a welding machine
A self-made electric welding device is designed to perform small jobs around the house, household or in the garage. At the first stage, the necessary calculations are performed and assembly parts and assemblies are prepared. To assemble a welding transformer with your own hands, it is advisable to determine in advance the place of assembly of the device. This will streamline the manufacturing process. Next to it, the layout units are folded, allowing you to assemble the simplest electric welding machine with your own hands. In addition to the main voltage converter, you will need a choke that can be used from the elements of a fluorescent lamp. In the absence of a finished element, it is made independently from a magnetic circuit from a powerful starter and wire from copper conductors with a cross section of about 1 mm square. A self-made electric welding machine will differ from its counterparts not only in appearance, but also in characteristics. To decide how to make it, check out similar devices in the photo or video.
Calculation of the welding transformer
Electric welding homemade devices made according to the simplest scheme, which does not involve the use of additional nodes. The power of the assembled electric apparatus will depend on the required value of the welded electric current. Welding in the country with a do-it-yourself electric device will directly depend on the technical characteristics of your own product.
When calculating the power for welding, take the strength of the required welding current and multiply this value by 25. The resulting value, when multiplied by 0.015, will show the required cross-sectional diameter of the magnetic circuit for welding. Before making calculations for the windings, you will have to remember other mathematical operations. To get the cross section of the higher voltage winding, the power value is divided by two thousand, after which it is multiplied by 1.13. The calculation method for the primary and secondary windings is different.
To obtain the winding values \u200b\u200bof the lowest voltage of the transformer, you will have to spend a little more time. The size of the cross section of the secondary winding depends on the density of the welded electric current. For values of 200 A, this will be 6 A / mm sq., With numbers 110-150 A - up to 8, and up to 100 A - 10. When determining the cross section of the lower winding, the strength of the welded electric current is divided by density, after which it is multiplied by 1.13.
The number of turns is calculated by dividing the cross-sectional area of the transformer magnetic circuit by 50. In addition, the output voltage will affect the final result of welding. It affects the characteristic of the process and can be increasing in current, gently sloping or steeply falling. This affects the fluctuations of the arc during operation, in which the minimum current changes are important when working at home.
Scheme of the welding transformer
The figure below shows a diagram of a welding transformer of the simplest form.
You can find wiring diagrams that will be supplemented with devices for rectification and other elements to improve the welded electrical apparatus. However, the main component is still a conventional transformer. The wiring diagram for connecting its wires is quite simple. The connection of the welded device is carried out through a switching electric device and fuses to a 220 V household electrical network. The use of electrical protective devices is mandatory, as this will protect the network from overloads in emergency conditions.
a - network winding on two sides of the core;
b - the corresponding secondary (welding) winding, connected in anti-parallel;
c - network winding on one side of the core;
g - the secondary winding corresponding to it, connected in series.
Defining parameters
To make an electric welding machine, you need to understand the principle of operation. It converts the input voltage (220 V) to a lower one (up to 60-80 V). In this process, the low strength of the electric current in the primary winding (about 1.5 A) increases in the secondary (up to 200 A). This direct dependence of the operation of transformers is called the step-down current-voltage characteristic. The operation of the device depends on these indicators. On its basis, calculations are carried out, and the design of the future apparatus is determined.
Rated operating mode
Before welding, it is necessary to determine its future nominal mode of use. It shows how long do-it-yourself welding fixtures can continuously cook and how much they must cool. This indicator is also called the duration of the inclusion. For homemade electrical appliances, it is located in the region of 30%. This means that out of 10 minutes, he is able to continuously work 3, and rest 7 minutes.
Rated operating voltage
The operation of a transformer welded device is based on lowering the input voltage to the nominal operating value. When manufacturing a welding machine, you can make any value of the output parameters (30-80 V), which directly affects the range of working electric currents. Unlike a 220 V power supply, the output value can be about 1.5-2 Volts in products for spot electric welding. This is due to the need to obtain high level current.
Mains voltage and number of phases
The current connection diagram of the welding transformer homemade type designed for connection to a household single-phase power supply. For powerful welding devices, an industrial network with three phases at 380 V is used. The rest of the calculations are performed from the value of this input parameter. Do-it-yourself mini welding uses the inclusion in the home electrical network and does not require large supply voltages.
Open circuit voltage
A do-it-yourself household welder must have a voltage x / x sufficient to ignite an electric arc. The larger this value, the easier it will appear. The manufacture of the device must comply with current safety regulations, which limit the output voltage to a maximum of 80 V.
Rated welding current of the transformer
Before you make an electric welding machine yourself, you need to decide on the size of the rated current. The possibility of performing the work itself on metals of various thicknesses will depend on it. With household electric welding, a value of 200 A is enough, which allows you to make a fully functional device. Exceeding this indicator will require an increase in the power of the electric transformer, which affects both the growth of its dimensions and weight.
Assembly process
The manufacture of a home-made welding machine begins with the necessary calculations. The input and output voltages, as well as the required electric current, are taken into account. This directly affects the size of the device and the number of necessary materials. An electric welding machine, like other equipment, is not very difficult to make with your own hands. With the right calculation and the use of high-quality components, it can reliably serve for decades. For the base, a wire with copper conductors is used, as well as a core made of magnetically permeable iron. The remaining components are not so significant and can be selected from those that can be easily obtained.
How to start the preparatory stage
After the calculation part is completed, materials are prepared, and a workplace is equipped for assembling the structure. To build a home-made welding machine, you will need wires for the primary as well as the secondary winding, for the core - a suitable transformer iron, insulating materials (varnished cloth, textolite, glass tape, electric cardboard). In addition, you should take care in advance of the winding machine for the manufacture of windings, metal elements for the frame and a switching electric device. During the assembly process, you will need a set of conventional locksmith tools. Choose a more spacious workplace to freely wind the coils and engage in the assembly process.
Construction assembly
After completing preparations, proceed directly to the manufacture of the electric device. Homemade electric welding requires a lot of time during assembly. It is not as heavy as long and painstaking, requiring precise observance of the calculated values. The procedure begins with the manufacture of a frame for the windings. For this, textolite plates of small thickness are used. Inner part ducts should be suitable for a transformer core with a small gap.
After assembling the two frames, it is necessary to insulate them to protect the electrical wire. This is done using any electrically insulating material of a heat-resistant type (varnished cloth, glass tape or electric cardboard).
A wire with heat-resistant insulation is wound onto the resulting frames. This will protect the product from possible breakdown during overheating in operation. It is necessary to accurately count the number of turns so that there is no difference with the calculated values. Each wound layer is necessarily isolated from the next. Reinforced insulation is laid between the primary and secondary windings. Remember to make the necessary taps on the required number of turns. After winding is completed, external insulation is performed.
At the next stage, the wound windings are mounted on the transformer core, and its blending is performed (assembly of a single structure). At the same time, it is undesirable to drill sheets of transformer iron during installation. Metal plates are connected in a checkerboard pattern and are well tightened. Assembling a simple U-shaped welder with your own hands is not particularly difficult. At the end of the assembly procedure, the integrity of the windings is checked for possible damage. Finishing stage is the assembly of the housing and the connection of the electrical switching device. Additional equipment includes a rectifier unit, as well as an electric current regulator.
Be attentive to all processes, from calculations to the assembly of home-made welding. The final parameters of the manufactured device will depend on this.
Today it is difficult to imagine the construction and creation of various metal structures without the use of welding transformers. The high reliability of structural connections and the ease of performing work have allowed the welding machine to firmly take its place in the arsenal of any builder. You can buy such a transformer at any hardware store. But not always factory model can meet certain needs and requirements. Therefore, many are trying to make a transformer for welding on their own. The manufacture of a home-made welding transformer takes place in several stages, starting with calculations and ending with installation.
To understand the whole process of manufacturing a transformer for welding with your own hands, you need to understand the principle of its operation, which consists in converting a voltage of 220 Volts to a lower voltage of up to 80 Volts. At the same time, the current strength increases from 1.5 Amperes to 160 - 200 Amperes, and in industrial ones up to 1000 Amperes. This dependence for a welding transformer is also called a step-down current-voltage characteristic and is one of the fundamental characteristics of the device. It is on the basis of this dependence that the entire design of the welding transformer is built and all the necessary calculations are performed, as well as various models welding machines.
Types of homemade transformers for welding
More than two hundred years have passed since the discovery of the electric arc phenomenon and the creation of the first welding machine. During all this time, the welding transformer and welding methods have been improved. Today you can see several various designs welding machines, of varying complexity and principle of operation. Among them, the most popular for do-it-yourself manufacturing are a welding transformer for contact welding and for arc welding.
Arc welding transformers were most widely used among craftsmen. There are several reasons for this popularity. First, simple and robust construction apparatus. Secondly, a wide range of applications. Thirdly, simplicity and portability. But in addition to the advantages described above, manual arc welding has a number of disadvantages, among which the main ones are low efficiency and the dependence of the quality of the weld on the skill of the welder.
Manual arc welding is most often widely used for various repair and construction work, the manufacture of metal structures and parts of structures, and pipe welding. With the help of arc welding, both cutting and welding of metal of various thicknesses is possible.
The design of such transformers is quite simple. The device consists of the transformer itself, the current regulator, the holder for the electrodes and the ground clamp. Separately, it is worth highlighting the central element - the transformer. Its design can be of several types, but the most popular are home-made welding transformers with a toroidal and U-shaped magnetic circuit. Around the magnetic circuit there are two windings of copper or aluminum wire - primary and secondary. Depending on the performance, the thickness of the wire on the windings changes, as well as the number of turns.
This type of welding is also called contact welding, and contact welding transformers are somewhat different from arc welding machines. The key difference is in the welding method. So if in arc welding melting occurs with the help of an electric arc that occurs between the electrode and the surface to be welded, then in resistance welding, the spot heating of the welding spot is performed by electricity using two sharpened copper electrodes and exposure high pressure for connection. As a result, the metal of the blanks at the point of impact is melted and merges.
Spot welding found wide application in the automotive industry, in construction when creating a frame from reinforcement for reinforced concrete structures, welding thin sheets of aluminum, stainless steel, copper and other metals that require special conditions for welding.
The design of transformers for spot welding also has certain differences. Firstly, it concerns the absence of deposited electrodes. Instead, pointed copper contacts are used, between which the elements to be welded are located. Secondly, the transformers in such devices are less powerful and are made with a U-shaped core. Thirdly, contact welding machines have a set of capacitors in their design, which is not necessary for arc welding.
But regardless of whether you plan to make an arc welding or contact transformer, you need to know their performance. And understand what each of them is responsible for and how one or another characteristic can be changed.
The operation of a welding transformer is determined by its operating characteristics. Knowing and understanding what this or that characteristic is responsible for, you can easily calculate the welding transformer and assemble the device with your own hands.
Mains voltage and number of phases
This characteristic indicates the mains voltage from which the welding transformer will be powered. Most often, home-made welding transformers are designed for a voltage of 220 V, but sometimes it can be 380 V. When performing calculations and creating a circuit, this parameter is one of the main ones.
Rated welding current of the transformer
This characteristic is the main one for any welding transformer. The possibility of welding and cutting a metal workpiece depends on the value of the rated welding current. In home-made and household welding transformers, the rated current value does not exceed 200 A. But this is more than enough, especially since the higher this figure, the higher the weight of the transformer itself. For example, in industrial welding transformers, the welding current can reach 1000 A, and the weight of such devices will be more than 300 kg.
Limits of regulation of welding current
When welding metal of various thicknesses, a certain current strength is required, otherwise the metal will not melt. For this, a regulator is provided in the design of welding transformers. Most often, the adjustment limits are set based on the need to use electrodes of a certain diameter. For home-made arc welding machines, the adjustment limits range from 50 A to 200 A. For contact welding transformers, the control limits start from 800 A to 1000 A or more.
Electrode diameter
To weld metal of different thicknesses using the same arc welding machine, it is necessary to adjust the rated welding current, as well as use electrodes of different diameters. It must be clearly understood that welding with thin electrodes requires a low current strength, and for thicker ones, on the contrary, a large one. The same applies to the thickness of the metal. The table below shows a summary of the diameters of the electrodes used, depending on the thickness of the metal and the current strength of the transformer.
Important! For contact welding transformers, the diameter of the electrodes is also important. But in this case, two parameters are used - the diameter of the electrode itself and the diameter of its cone-shaped part.
Rated operating voltage
As we already know, a welding transformer works by lowering the input voltage to a lower value. The output voltage is called nominal and does not exceed 80 volts. For arc welding transformers, the rated voltage range is between 30 - 70 Volts. Moreover, this characteristic is not adjustable and is set initially. Transformers for spot welding, unlike arc ones, have an even lower rated voltage of the order of 1.5 - 2 Volts. Such indicators are quite natural, given the relationship between voltage and current strength. The higher the current, the lower the voltage.
Rated operating mode
This performance is one of the key. The nominal operating mode indicates how long you can work continuously and how much you need to let it cool down. For home-made welding transformers, the nominal mode is in the range of 30%. That is, out of 10 minutes, 3 can be cooked continuously and 7 minutes left to rest.
Power input and output
In fact, these two indicators have little effect. But knowing both of these indicators, it is possible to calculate the efficiency of the welding transformer. The smaller the difference between input and output power, the better. It should be noted that when performing calculations, the value of power consumption must be known and taken into account.
Open circuit voltage
This indicator is important for arc welding transformers. He is responsible for the appearance of the arc. The higher this indicator, the easier it is to induce a welding arc. But the open circuit voltage is limited by safety rules and should not exceed 80 volts.
Scheme of the welding transformer
Creating a transformer for welding with your own hands, you can not do without it circuit diagram. In fact, there are no particular difficulties in this, especially since the device of the transformer itself is quite simple. The diagram below shows the simplest arc welding transformer.
Important! For those who are poorly versed or not at all versed in electrical diagrams, you should first familiarize yourself with GOST 21.614 “Conditional graphic images of electrical equipment and wiring in the original”. And only then proceed to create a circuit for a welding transformer.
With the development of electrical engineering and technology, the welding transformer circuit has been improved. Today at homemade devices for welding, you can see diode bridges and various welding current regulators. In the diagram below of an arc welding transformer, you can see how a diode bridge is integrated into it.
Important! The most popular among home-made arc welding transformers is toroidal. Such a device has excellent performance characteristics, which are an order of magnitude higher than those of transformers with a U-shaped core. This applies primarily to high efficiency and rated current, which has a beneficial effect on the overall weight of the device.
Unlike those described above, the spot welding transformer circuit is more complex and may include capacitors, thyristors, and diodes. This filling allows you to more finely adjust the current strength, as well as the time of contact welding. Approximate scheme transformer for contact welding can be seen below.
In addition to the above diagrams of welding machines, there are others. Finding them will not be difficult. They are posted both on the Internet and in various magazines and books about electrical engineering. Having acquired the scheme you like best, you can proceed to the calculations and assembly of the welding transformer.
As already described, the transformer consists of a core and two windings. It is these structural elements that are responsible for the main performance characteristics of the transformer for welding. Knowing in advance what the rated current should be, the voltage on the primary and secondary windings, as well as other parameters, a calculation is performed for the windings, core and wire section.
When performing calculations of a transformer for welding, the following data are taken as a basis:
- voltage of the primary winding U1. In fact, this is the mains voltage from which the transformer will operate. Can be 220V or 380V;
- rated voltage of the secondary winding U2. The voltage of electricity, which should be after lowering the incoming and not exceeding 80 V. Required to start the arc;
- rated current of the secondary winding I. This parameter is selected based on which electrodes will be welded and what is the maximum thickness of the metal that can be welded;
- cross-sectional area of the core Sc. The reliability of the device depends on the core area. The optimal cross-sectional area is from 45 to 55 cm2;
- window area So. The area of the core window is selected based on good magnetic dissipation, excess heat removal, and ease of winding the wire. Parameters from 80 to 110 cm2 are considered optimal;
- winding current density (A/mm2). This is a rather important parameter responsible for the electrical losses in the transformer windings. For homemade welding transformers, this figure is 2.5 - 3 A.
As an example of calculations, we take the following parameters for a welding transformer: mains voltage U1=220 V, secondary winding voltage U2=60 V, rated current 180 A, core cross-sectional area Sc=45 cm2, window area So=100 cm2, current density in winding 3 A.
P \u003d 1.5 * Sc * So \u003d 1.5 * 45 * 100 \u003d 6750 W or 6.75 kW.
Important! In this formula, a coefficient of 1.5 is applicable for transformers with a P, Sh type core. For toroidal transformers, this coefficient is 1.9, and for PL, ShL type cores 1.7.
Important! As in the first formula, the coefficient 50 is used for transformers with a P, Sh type core. For toroidal transformers, it will be equal to 35, and for PL, ShL type cores 40.
Now we calculate the maximum current strength on the primary winding according to the formula: Imax \u003d P / U \u003d 6750/220 \u003d 30.7 A. It remains to calculate the turns based on the data obtained.
To calculate the turns, we use the formula Wx \u003d Ux * K. For the secondary winding, this will be W2 = U2 * K = 60 * 1.11 = 67 turns. For the primary calculation, we will perform a little later, since a different formula is used there. Quite often, especially for toroidal transformers, the current regulation steps are calculated. This is done to output the wire on a certain turn. The calculation is performed according to the following formula: W1st \u003d (220 * W2) / Ust.
Ust - output voltage of the secondary winding.
W2 - turns of the secondary winding.
W1st - turns of the primary winding of a certain stage.
But first it is necessary to calculate the voltage of each stage Ust. To do this, we use the formula U=P/I. For example, we need to make four steps adjustable for 90 A, 100 A, 130 A and 160 A for our 6750 W transformer. Substituting the data into the formula, we get U1st1 \u003d 75 V, U1st2 \u003d 67.5 V, U1st3 \u003d 52 V, U1st4 \u003d 42.2 V.
We substitute the obtained values into the form for calculating the turns for the adjustment steps and get W1st1=197 turns, W1st2=219 turns, W1st3=284 turns, W1st4=350 turns. Adding another 5% to the maximum value of the obtained turns for the 4th stage, we get the real number of turns - 385 turns.
Finally, we calculate the cross section of the wire on the primary and secondary windings. To do this, we divide the maximum current for each winding by the current density. As a result, we get Sprim = 11 mm2 and Ssecond = 60 mm2.
Important! The calculation of the resistance welding transformer is performed in a similar way. But there are a number of significant differences. The fact is that the rated current of the secondary winding for such transformers is about 2000 - 5000 A for low-power and up to 150,000 A for powerful ones. In addition, for such transformers, adjustment is made up to 8 steps using capacitors and a diode bridge.
Installation of a welding transformer
Having all the calculations and the scheme on hand, you can begin to assemble the transformer. All work will be not so much difficult as painstaking, since you will have to count the number of turns and not go astray. Despite the fact that the most popular among homemade devices is toroidal transformer for welding, consider the installation using the example of a transformer with a U-shaped core. This type of transformer is somewhat easier to assemble, unlike the toroidal and the second most popular among homemade products.
We start work with creating frames for windings. For this we use textolite plates. This material is used to create stamped boards. From the plates we cut out the details for two boxes. Each box will consist of two top covers with slots for four walls. The area of the internal slots will correspond to the cross-sectional area of the core with a slight increase for the walls of the box. An example of how the parts of the box should look can be seen in the photo.
Having assembled the frames for the windings, we isolate them with heat-resistant insulation. Then we start winding the windings.
It is advisable to take wires for windings with heat-resistant glass insulation. This, of course, will be somewhat more expensive compared to conventional wiring, but as a result there will be no headache regarding possible overheating and breakdown in the windings. After we have wound one layer of wiring, we isolate it and only after that we begin to wind the next one. Do not forget to make taps on a certain number of skeins. At the end of the creation of the windings, we wind a layer of top insulation. We fix copper bolts at the ends of the bends.
Important! Before installing and fixing the bolts at the ends of the wires, we stretch the latter through additional holes cut in the upper plate of the textolite frame.
Now we proceed to the assembly and blending of the magnetic circuit of the welding transformer. For it, iron is used, created specifically for this. The metal has certain indicators of magnetic induction, and the wrong brand can ruin everything. Metal core plates can be removed from old transformers or purchased separately. The wafers themselves are about 1mm thick, and assembling the entire core will only require patiently joining all the wafers together. Upon completion, all windings should be checked with a tester for errors.
Upon completion of the assembly of the transformer, we do diode bridge and install the current regulator. For the diode bridge, we use B200 or KBPC5010 type diodes. Each diode is rated at 50 A, so a welding transformer with a rated current of 180 A will require 4 of these diodes. All diodes are fixed to aluminum radiator and are connected in parallel with the inductor to the taps from the windings. All that's left is assemble the body and place a welding transformer there.
A good do-it-yourself welding transformer may not work the first time. There are many reasons for this, starting with errors in calculations and ending with a lack of experience in assembling and installing electrical equipment. But everything comes with experience, and by rewinding the transformer windings once or twice, you can get the desired result.
- What will we be about
- What we won't talk about
- Transformer
- Trying a constant
- microarc
- Contact! There is a contact!
Do-it-yourself welding in this case does not mean welding production technology, but home-made equipment for electric welding. Job skills are acquired field trip. Of course, before going to the workshop, you need to learn the theoretical course. But it can only be put into practice if you have something to work on. This is the first argument in favor of, independently mastering the welding business, first take care of the availability of appropriate equipment.
The second - a purchased welding machine is expensive. Rent is also not cheap, because. the probability of its failure with unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be just long and difficult. All in all, it is better to start the first steps in metal welding with the manufacture of a welding machine with your own hands. And then - let him stand in a barn or garage until the case. It's never too late to spend money on branded welding, if things go well.
What will we be about
This article discusses how to make equipment at home for:
- Electric arc welding with alternating current of industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures up to about a fence made of corrugated board on a frame made of a professional pipe or a welded garage.
- Microarc welding of strands of wires is very simple, and useful when laying or repairing electrical wiring.
- Spot pulse resistance welding - can be very useful when assembling products from a thin steel sheet.
What we won't talk about
First, skip the gas welding. Equipment for it costs pennies compared to consumables, gas cylinders cannot be made at home, and a home-made gas generator is a serious risk to life, plus carbide is now, where it is still on sale, expensive.
The second is an inverter arc welding. Really, welding inverter- a semi-automatic device allows a novice amateur to cook quite responsible designs. It is light and compact and can be carried by hand. But the retail purchase of inverter components, which allows you to consistently conduct a high-quality seam, will cost more than a finished device. And with simplified homemade products, an experienced welder will try to work, and refuse - “Give me a normal device!” Plus, or rather minus - to make a more or less decent welding inverter, you need to have a fairly solid experience and knowledge in electrical engineering and electronics.
The third is argon-arc welding. Whose light hand went for a walk in RuNet, the statement that it is a hybrid of gas and arc is unknown. In fact, this is a kind of arc welding: the inert gas argon does not participate in the welding process, but creates around working area a cocoon that isolates it from the air. As a result Weld it turns out chemically pure, 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 profound analogy: a transformer operates at the expense of a supply of energy magnetic field in its magnetic circuit (core), which can be many times greater than instantly transmitted from the power supply network to the consumer. And the formal description of losses due to eddy currents in steel is similar to that for water losses due to infiltration. Electricity losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in a liquid.
Note: the difference is in evaporation losses and, accordingly, magnetic field scattering. The latter in the transformer are partially reversible, but they smooth out the peaks of energy consumption in the secondary circuit.
An important factor in our case is external volt-ampere characteristics(ВВХ) of a transformer, or simply its external characteristic (ВХ) - the dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, the VX is rigid (curve 1 in the figure); they are like a shallow vast pool. If it is properly insulated and covered with a roof, then the water loss is minimal and the pressure is quite stable, no matter how the consumers turn the taps. But if there is a gurgle in the drain - sushi paddles, the water is drained. With regard to transformers, the power man must keep the output voltage as stable as possible up to a certain threshold, less than the maximum instantaneous power consumption, be economical, small and light. For this:
- The steel grade for the core is chosen with a more rectangular hysteresis loop.
- Constructive measures (core configuration, calculation method, winding configuration and arrangement) in every possible way reduce dissipation losses, losses in steel and copper.
- The induction of the magnetic field in the core is taken less than the maximum allowable for the transfer of the current form, because. its distortion reduces the efficiency.
Note: transformer steel with "angular" hysteresis is often referred to as magnetically hard. This is not true. Hard magnetic materials retain strong remanence, they are made by permanent magnets. And any transformer iron is magnetically soft.
It is impossible to cook from a transformer with a rigid VX: the seam is torn, burnt, the metal is splashed. The arc is inelastic: I almost moved the electrode in the wrong way, it goes out. Therefore, the welding transformer is already made similar to a conventional water tank. Its VX is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage drops smoothly. The normal scattering curve is approximated by a straight line falling at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly remove several times more power from the same iron, or, respectively. reduce the weight and size of the transformer. In this case, the induction in the core can reach the saturation value, and even exceed it for a short time: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: thermal time constant of welding transformers 20-40 min. If you then let it cool down and there was no unacceptable overheating, you can continue to work. The relative drop in the secondary voltage? U2 (corresponding to the range of the arrows in the figure) of normal dissipation increases smoothly with an increase in the range of oscillations of the welding current Iw, which makes it easy to hold the arc in any type of work. These properties are provided as follows:
- The steel of the magnetic circuit is taken with a hysteresis, more "oval".
- The reversible scattering losses are normalized. By analogy: the pressure has dropped - consumers will not pour out a lot and quickly. And the operator of the water utility will have time to turn on the pumping.
- Induction is chosen close to the limiting overheating, this allows by reducing cos? (a parameter equivalent to efficiency) at a current that is significantly different from sinusoidal, 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 thin work and low currents, it will not be difficult to hold the arc and the welding current, without having much experience (? U2.2 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.
- According to the formula from paragraph 2 before. the list we find the overall power;
- We find the maximum possible welding current Iw \u003d Pg / Ud. 200 A are provided if 3.6-4.8 kW can be removed from the iron. True, in the 1st case, the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
- We calculate the operating current of the primary at the maximum network voltage allowed for welding I1rmax \u003d 1.1Pg (VA) / 235 V. In general, the norm for the network is 185-245 V, but for a home-made welder at the limit, this is too much. We take 195-235 V;
- Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
- We accept the current density of the primary J1 = 5 A/sq. mm and, using I1rmax, we find the diameter of its copper wire d = (4S / 3.1415) ^ 0.5. Its full diameter with self-isolation D = 0.25 + d, and if the wire is ready - tabular. To work in the "brick bar, mortar yok" mode, you can take J1 \u003d 6-7 A / sq. mm, but only if the required wire is not available and is not expected;
- We find the number of turns per volt of the primary: w = k2 / Sс, where k2 = 50 for W and P, k2 = 40 for PL, SHL and k2 = 35 for O, OL;
- We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy losses of the winding due to leakage and in copper, which is formally expressed by a somewhat abstract parameter of the winding's own voltage drop;
- We set the stacking factor Ku = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of winding layers, the average length of the turn and the wire footage
- We calculate the secondary in the same way at J1 = 6 A/sq. mm, k3 \u003d 1.05 and Ku \u003d 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.
Winding and finishing
The diameters of the wires in the calculation of the windings are usually obtained more than 3 mm, and varnished winding wires with d> 2.4 mm are rare in wide sale. In addition, the welder's windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSh, PELSHO, PB, PBD. Finding them is even more difficult, and they are very expensive. The footage of the wire per welder is such that cheaper bare wires can be insulated on their own. Additional advantage- 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 of thin plastic wrap with a call on the cheeks and a twist on their outer side so that the wire does not stick to the tree;
- We wind a pre-insulated winding;
- After winding, we impregnate twice until it flows through with liquid varnish;
- after the impregnation dries, carefully remove the cheeks, squeeze out the boss and tear off the film;
- we tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.
Finishing and domotka
We shift the core into a biscuit and tighten it with bolts, as expected. The winding tests are carried out in exactly the same way as those of the dubious finished transformer, see above. It is better to use LATR; Iхх at an input voltage of 235 V should not exceed 0.45 A per 1 kVA of the overall power of the transformer. If more, the primary is homemade. Winding wire connections are made on bolts (!), insulated heat shrink tube(HERE) in 2 layers or cotton tape in 4-5 layers.
According to the test results, the number of turns of the secondary is corrected. For example, the calculation gave 210 turns, but in reality Ixx got back to normal at 216. Then we multiply the calculated turns of the secondary sections by 216/210 = 1.03 approx. Do not neglect the decimal places, the quality of the transformer largely depends on them!
After finishing, we disassemble the core; we tightly wrap the biscuit with the same masking tape, calico or “rag” electrical tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now once again impregnate with liquid varnish; when dry - twice undiluted. This biscuit is ready, you can make a secondary one. When both are on the core, we once again test the transformer for Ixx (suddenly it curled somewhere), fix the biscuits and impregnate the entire transformer with normal varnish. Phew, the most dreary part of the work is over.
Pull VX
But he is still too cool with us, remember? Needs to be softened. The simplest way - a resistor in the secondary circuit - does not suit us. Everything is very simple: at a resistance of only 0.1 ohms at a current of 200, 4 kW of heat will be dissipated. If we have a welder for 10 or more kVA, and we need to weld thin metal, a resistor is needed. Whatever the current is set by the regulator, its emissions when the arc is ignited are inevitable. Without an active ballast, they will burn the seam in places, and the resistor will extinguish them. But to us, low-powered ones, he will not be of any use to him.
The reactive ballast (inductor, choke) will not take away excess power: it will absorb current surges, and then smoothly give them to the arc, this will stretch the VX as it should. But then you need a choke with dissipation control. And for him - the core is almost the same as that of the transformer, and rather complex mechanics, see fig.
We will go the other way: we will use an active-reactive ballast, colloquially referred to as the gut by old welders, see fig. on right. Material - steel wire rod 6 mm. The diameter of the turns is 15-20 cm. How many of them are shown in fig. it can be seen that for power up to 7 kVA this gut is correct. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is connected to it with a clip-clothespin. By selecting the attachment point, it is possible, together with switching to secondary outlets, to fine-tune the operating mode of the arc.
Note: an active-reactive inductor can get red hot in operation, so it needs a fireproof, heat-resistant, non-magnetic dielectric lining. In theory, a special ceramic lodgment. It is acceptable to replace it with a dry sand cushion, or already formally with a violation, but not rough, the welding gut is laid on bricks.
But other?
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 large circulation 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 it will burn through a thin wall, and if the part is a coin or less, then the softest arc will burn it entirely.
The principle of operation of spot resistance welding is illustrated in Fig: copper electrodes compress parts with force, a current pulse in the steel-steel ohmic resistance zone heats the metal to the point where electrodiffusion occurs; metal does not melt. This requires approx. 1000 A per 1 mm thickness of the parts to be welded. Yes, a current of 800 A will grab sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, say, a galvanized corrugated fence, then the very first strong gust of wind will remind you: “Man, the current was rather weak!”
Nevertheless, contact spot welding is much more economical than arc welding: the open circuit voltage of the welding transformer for it is 2 V. It is the sum of 2 contact potential differences of steel-copper and the ohmic resistance of the penetration zone. A transformer for contact welding is calculated similarly to it for arc welding, but the current density in the secondary winding is 30-50 or more A / sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, it cools well, and its utilization factor (the ratio of welding time to 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 pliers is excluded, and the eccentric clamp provides a strong stable compression of the pliers, which significantly affects the quality of the welded joint. In which case, the clamp can be instantly reset with one blow on the eccentric lever. The disadvantage is the insulating knots of the pliers, there are too many of them and they are complex. Another one is aluminum pincer bars. Firstly, they are not as strong as steel ones, and secondly, these are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.
About electrodes
In amateur conditions, it is more expedient to isolate the electrodes at the installation site, as shown in fig. on right. There is no conveyor at home, the apparatus can always be allowed to cool down so that the insulating sleeves do not overheat. This design will make it possible to make rods from a durable and cheap steel professional pipe, and also extend the wires (up to 2.5 m is acceptable) and use a contact welding gun or remote tongs, see fig. below.
On fig. On the right, one more feature of electrodes for resistance spot welding is visible: a spherical contact surface (heel). Flat heels are more durable, so electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 thicknesses of the adjacent welded material, otherwise the penetration spot will burn out either in the center (wide heel) or along the edges (narrow heel), and corrosion will go from the welded joint even on stainless steel.
The last point about the electrodes is their material and dimensions. Red copper quickly burns out, so purchased electrodes for resistance welding are made of copper with a chromium additive. These should be used, at current copper prices it is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. The length of the electrode according to the conditions of heat transfer is at least 3 of its diameters from the heel to the root (beginning of the shank).
How to give impetus
In the simplest home-made pulse-contact welding machines, a current pulse is given manually: they simply turn on the welding transformer. This, of course, does not benefit him, and welding is either lack of fusion, or burnout. However, it is not so difficult to automate the feed and normalize the welding pulses.
A diagram of a simple, but reliable and long-term proven welding pulse shaper is shown in fig. Auxiliary transformer T1 is a conventional power transformer for 25-40 watts. Winding voltage II - according to the backlight. Instead of it, you can put 2 LEDs connected in anti-parallel with a quenching resistor (normal, 0.5 W) 120-150 Ohms, then the voltage II will be 6 V.
Voltage III - 12-15 V. It can be 24, then capacitor C1 (ordinary electrolytic) is needed for a voltage of 40 V. Diodes V1-V4 and V5-V8 - any rectifier bridges for 1 and from 12 A, respectively. Thyristor V9 - for 12 or more A 400 V. Optothyristors from computer power supplies or TO-12.5, TO-25 are suitable. Resistor R1 - wire, they regulate the pulse duration. Transformer T2 - welding.
Finally
And finally, something that may seem like a joke: welding in saline solution. In fact, this is not idle entertainment, but the thing is quite useful for some purposes. And you can make welding equipment for salt welding with your own hands on the table in 15 minutes, see the video:
Video: do-it-yourself welding in 15 minutes (on saline solution)
