The designer and famous scientist Yuri Negulyaev once invented an almost indispensable device - a welding inverter. We propose to consider how to make a welding inverter with your own hands using a pulse transformer and powerful MOSFET transistors.

The most important thing when designing or repairing a purchased or home-made inverter is its circuit diagram. We took it for the manufacture of our inverter from the Negulyaev project.

Manufacturing of transformer and inductor

For work we need the following equipment:

1. ferrite core.
2. Frame for the transformer.
3. Copper bus or wire.
4. Bracket for fixing the two halves of the core.
5. Heat-resistant insulating tape.

First you need to remember a simple rule: the windings are wound only on the full width of the frame, with this design the transformer becomes more resistant to voltage drops and external influences.

A high-quality pulse transformer is wound with a copper bus or a bundle of wires. Aluminum wires of the same cross section are not able to withstand a sufficiently high current density in the inverter.

In this version of the transformer, the secondary winding must be wound in several layers, according to the sandwich principle. A bundle of wires with a cross section of 2 mm, twisted together, will serve as a secondary winding. They must be isolated from each other, for example, with a varnish coating.

winding rings

There must be two or three times more insulation between the primary and secondary windings so that the mains voltage, which in rectified form is 310 volts, does not get to the secondary winding. For this, fluoroplastic heat-resistant insulation is best suited.

The transformer can also be made not on a standard core, using for this purpose 5 horizontal-scan transformers of faulty TVs, combined into one common core. It is also necessary to remember about the air gap between the windings and the core of the transformer, this facilitates its cooling.

An important note, the uninterrupted operation of the device directly depends not only on the magnitude of the direct current, but also on the thickness of the wire of the secondary winding of the transformer. That is, if you wind a winding thicker than 0.5 mm, we will get a skin effect, which does not have a very good effect on the operating mode and thermal characteristics of the transformer.

A current transformer is also made on a ferrite core, which will then be fixed on a positive power wire, the conclusions from this transformer come to the control board to monitor and stabilize the output current.

A choke is used to reduce the ripple at the output of the device and to reduce the amount of noise emissions into the power supply network. It is also wound on a ferrite frame of arbitrary design, with a wire or bus, the thickness of which corresponds to the thickness of the wire of the secondary winding.

The design of the welding machine

Consider how to design a sufficiently powerful pulsed welding inverter at home.

If we repeat the design according to the Negulyaev system, then the transistors are screwed to the radiator with a plate specially cut for this, thus improving heat transfer from the transistor to the radiator. Between the heatsink and the transistors, it is necessary to lay a thermally conductive, current-impermeable gasket. This provides short circuit protection between the two transistors.

Rectifier diodes are attached to a 6 mm thick aluminum plate, mounting is carried out in the same way as mounting transistors. Their outputs are connected to each other by an uninsulated wire with a cross section of 4 mm. Be careful not to touch wires.

The throttle is attached to the base of the welding machine with an iron plate, the dimensions of which repeat the shape of the throttle itself. To reduce vibration, a rubber seal is laid between the throttle and the housing.

Video: do-it-yourself welding inverter

All power conductors inside the inverter housing must be separated in different directions, otherwise there is a possibility of a short circuit. The fan cools several heatsinks at the same time, each dedicated to a different part of the circuit. This design allows you to get by with just one fan mounted on the rear wall of the case, which saves space.

To cool a home-made welding inverter, you can use a fan from a computer case, it is optimally suited both in terms of dimensions and power. Since the ventilation of the secondary winding plays a big role, this should be taken into account when placing it.

Scheme: disassembled welding inverter

The weight of such an inverter will range from 5 to 10 kg, while its welding current can be in the range from 30 to 160 amperes.

How to set up inverter operation

Making a homemade welding inverter is not so difficult, especially since it is an almost completely free product, except for the cost of some parts and materials. But to set up the assembled device, you may need the help of specialists. How can you do it yourself?

Instructions facilitating self-configuration of the welding inverter:

1. First you need to apply mains voltage to the inverter board, after which the unit will begin to emit a characteristic squeak of a pulse transformer. Also, voltage is supplied to the cooling fan, this will prevent the structure from overheating and the operation of the device will be much more stable.
2. After the power capacitors are fully charged from the mains, we need to close the current limiting resistor in their circuit. To do this, you need to check the operation of the relay, making sure that the voltage across the resistor is zero. Remember, if you connect the inverter without a current-limiting resistor, an explosion may occur!
3. The use of such a resistor significantly reduces current surges when the welding machine is connected to a 220 volt network.
4. Our inverter is capable of delivering current in excess of 100 amps, this value depends on the specific circuit used in the development. It is not difficult to find out this value using an oscilloscope. It is necessary to measure the frequency of incoming pulses to the transformer, they should be in the ratio of 44 and 66 percent.
5. The welding mode is checked directly on the control unit by connecting a voltmeter to the output of the optocoupler amplifier. If the inverter is low-power, the average peak voltage should be about 15 volts.
6. Then the correct assembly of the output bridge is checked, for this, a voltage of 16 volts is supplied to the input of the inverter from any suitable power supply. At idle, the unit consumes a current of about 100 mA, this must be taken into account when conducting control measurements.
7. For comparison, you can check the operation of an industrial inverter. Using an oscilloscope, measure the pulses on both windings, they must match each other.
8. Now it is necessary to control the operation of the welding inverter with connected power capacitors. We change the supply voltage from 16 volts to 220 volts by connecting the device directly to the electrical network. Using an oscilloscope connected to the output MOSFET transistors, we control the waveform, it should correspond to the tests at low voltage.

Video: welding inverter under repair.

A welding inverter is a very popular and necessary device in any activity, both in industrial enterprises and in the household. In addition, due to the use of a built-in rectifier and current regulator, using such a welding inverter, you can achieve better welding results compared to the results that can be achieved using traditional machines whose transformers are made of electrical steel.

Do-it-yourself welding inverter was assembled by hundreds of craftsmen. As practice shows, there is nothing super complicated in this process. If you have experience and desire, you can acquire the necessary details and spend some time working.

For the manufacture of the device, it is necessary to stock up with all the necessary parts and accessories.

The transformer-type welding machine was so bulky and problematic in operation that the thyristor-based inverters that replaced it quickly gained general popularity.

Further development of manufacturing technologies for semiconductor components made it possible to create powerful field-effect transistors. With their advent, inverters have become even lighter and more compact. Improved conditions for adjusting and stabilizing the welding current make it easy to work even for beginners.

Inverter design selection

As a case, you can use an old computer unit.

The layout of a homemade welding inverter is unoriginal and similar to most other designs. Most parts can be replaced with analogues. It is necessary to determine the dimensions of the device and start manufacturing the case if all the main elements are present.

You can use ready-made heatsinks (from old computer power supplies or other devices). In the presence of an aluminum bus with a thickness of 2-4 mm and a width of more than 30 mm, they can be made independently. You can use any fan from old devices.

All dimensional parts must be placed on a flat surface, view the connection possibilities according to the schematic diagram.

Then determine the installation location of the fan so that hot air from some parts does not heat others. In a difficult situation, two exhaust fans can be used. The cost of coolers is small, the weight is also insignificant, the reliability of the entire device will increase significantly.

The largest and heaviest parts are a transformer and a choke to smooth out ripples. It is desirable to place them in the center or symmetrically along the edges so that their weight does not pull the device in one direction. Working with a device worn on the shoulder and constantly sliding to one side during welding is extremely inconvenient.

With a satisfactory arrangement of all parts, it is necessary to determine the dimensions of the bottom of the device and cut it out of the available material. The material must be non-conductive, usually getinax, fiberglass. In the absence of these materials, wood treated with fire retardant and moisture protection agents can be used. The latter option has some advantages. Screws can be used to fasten parts, rather than threaded connections. This will somewhat simplify and reduce the cost of the manufacturing process.

Electrical diagram of the inverter

All inverters have a similar block diagram:

• input diode bridge that converts AC voltage to DC;
• DC to AC high frequency converter;
• a device for lowering high-frequency voltage to a working one;
• converter to direct voltage with a filter to smooth out ripples.

The scheme chosen for home-made manufacturing is arranged according to the classical method. The heart of the circuit is the oblique bridge, which provides the best performance at maximum simplicity and cost. The power circuit is controlled by the TL494 controller. Control functions and adjustment of the welding current are carried out by the PIC16F628 microcontroller. Protection of the device from overheating is also implemented through it. Depending on the maximum current and the parts used, several firmware versions of the device are possible with different maximum allowable welding current.

The power supply for the logic elements of the circuit and low-voltage equipment is based on the TNY264 PWM controller.

The schematic diagram, despite the large number of elements, is made quite simply. The entire control system is made on several boards:

• power element board, two options;
• rectifier;
• two control boards.

Rectifier diodes with protective circuits, power transistors, transformer, measuring resistance are installed on the board of power elements. The required version of the board must be selected according to the available components for the welding inverter.

The inverter machine requires a power control board.

On the rectifier board, bridge elements, smoothing capacitors, soft start relays, resistances that compensate for changes in parameters due to temperature (thermistors) are installed.

The following circuits are located on the power control boards:

• PWM controller with decoupling elements on optocouplers;
• digital indicator with control buttons;
• elements of the power supply;
• microcontroller.

Before assembling the boards, the tracks for installing power elements must be reinforced with copper wire with a cross section of 2.5-4 mm. For tinning the tracks, it is advisable to use refractory solder.

Transformer and choke for inverter

In the manufacture of a core for a welding inverter transformer, you can use horizontal transformers from old TVs. You will need six transformers of the TVS110PTs15.U type. The tightening bracket must be removed from the transformers (unscrew the two M3 nuts and remove the bracket). The winding can be sawn on both sides with a hacksaw or grinder, observing the necessary precautions. If, after removing the winding, the core does not separate into two parts, you need to clamp it in a vise and separate it with a light blow. The surfaces of the parts must be cleaned of epoxy. After preparing the magnetic cores, you need to make a frame. The optimal material for the frame will be fiberglass with a thickness of 1-2 mm, but you can use getinaks or cardboard. Technical characteristics of the assembled magnetic core:

Transformers can be borrowed from an old TV.

• average length of the magnetic line kp=182 mm;
• window dimensions S 0 =6.2 cm 2 ;
• cross section of the magnetic circuit S m =11.7 cm 2;
• coercive force H c =12 A/m;
• residual magnetic induction B g =0.1 T;
• magnetic induction B s =0.45 T (if H=800 A/m), B m =0.33 T (if H=100 A/m and t=60° C).

The cross section and number of turns of the windings must be calculated based on the maximum allowable operating current for the device.

Windings must be placed across the entire width of the window to reduce overhead.

As a winding material, you can use copper foil or litz wire of the desired section to eliminate the skin effect. The insulating material between the layers and windings can be wax paper, varnished cloth, FUM tape.

If it is necessary to control the welding current, a current transformer can be made. For its manufacture, you will need two rings of the K30x18x7 type. They need to be wound with 85 turns of copper wire in varnish insulation with a cross section of 0.2-0.5 mm. The ring is put on any of the output wires of the device.

Using an inverter in a three-phase network

Sometimes when the network is overloaded, there is not enough power for the normal operation of the inverter. If possible, a single-phase inverter can be converted to a three-phase one.

When connected to a single-phase network (the plug is plugged into a socket), the K1 starter is turned on. One pair of its contacts connects the wires coming from the plug to the regular switch (on / off) of the inverter. Another pair will connect the tracks cut on the board from the switch to the stationary rectifier.

Starter K1 must have contacts with a maximum allowable current of at least 25 A.

To connect the voltage from a three-phase rectifier, a K2 starter is used. The maximum allowable current of its contacts must be at least 10A. To connect to a three-phase network, it is advisable to use a 3p + N + E socket (three phase wires, zero and ground). The device can be built into the inverter or made as a separate unit. Production in the form of a separate block is optimal when working in one place. With frequent movements, carrying two devices is not convenient.

Conclusion on the topic

Making a welding inverter with your own hands is not so difficult. With a lack of experience, you can always consult with specialists.

The result is an excellent device with additional features not found in industrial inverters.

Repairing a do-it-yourself device will not create any special problems, and using the tool in your work will be a pleasure.

Today, a widely demanded welding machine is a welding inverter. Its advantages are functionality and performance. You can make a mini welding machine with your own hands without much financial investment (spending only on consumables), if you have an understanding of how electronics are arranged and work. Today, good inverters are expensive, and cheap ones can disappoint with poor welding quality. Before constructing such a tool on your own, you need to carefully study the circuit.

The first stage of assembly - winding the transformer

For winding the transformer, copper sheet 4 cm wide and 0.3 mm thick is suitable. Copper wire can work under high heat. As a thermal layer, you can take paper for a cash register. You can use copier paper, but it is less durable and may tear when wound.

Lakotkan is considered the best insulator. At least one of its layers for insulation is always desirable. Textolite plates can be placed in the windings for the electrical safety of the device. The better the insulation between the windings, the higher the voltage. The length of the paper strips should be such as to cover the perimeter of the winding with a margin of 2-3 cm at the end.

It is impossible to use a thick wire for winding, since the inverter operates on high-frequency currents. The core of the thick wire will not be used, which can lead to overheating of the transformer. It won't even last 5 minutes.

To avoid this "skin" effect, you need to use a conductor with a larger area and a minimum thickness. Such a surface conducts current well and does not overheat.

When rewinding, it is advisable to use 3 copper strips, which must be separated from each other with a fluoroplastic plate. Everything again needs to be wrapped with tape for the cash register as a thermal layer. This paper has a drawback - when heated, it darkens. But with all this, she does not break.

Instead of copper sheet, you can use PEV wire up to 0.7mm. It consists of many veins, which is its main advantage. However, this winding method is worse than copper, since such wires have large air gaps and do not fit well with each other. The total cross-sectional area decreases and heat transfer slows down. When working with SEW, the design of a home-made welding machine with your own hands can have 4 windings:

• primary, consisting of one hundred turns (PEV thickness 0.3 mm);
• three secondary windings: the first includes 15 turns, the second -15, the third -20.

The transformer and the whole mechanism must be equipped with a fan. A cooler from a system unit with a current of 220 volts 0.15A or more is suitable.

Do-it-yourself welding inverter circuit: design features

First you need to think about the ventilation of the inverter mechanism, which will protect the system from overheating. To do this, it is good to use heatsinks from Pentium 4 and Athlon 64 system blocks. Today they can be purchased quite cheaply.

After winding the transformer, it is attached to the base of the welding machine. This will require several brackets that can be made of wire (copper with a diameter of at least 3 mm).

For the manufacture of boards, you will need foil textolite (about 1 mm thick). In each of the boards you need to make small slots. They will help reduce the load on the diode outputs. They must be attached towards the terminals of the transistors. As a layer between the radiators and the outputs, put a board that will connect the bridge mechanism to the power strings. Each step of assembling the device can be verified according to the approximate scheme of a home-made welding inverter:

Capacitors must be soldered onto the board. There may be about 14 of them. Thanks to them, transformer emissions will go into the power circuit.

To eliminate resonant current surges from the transformer, it is necessary to install snubbers, which will contain capacitors C15, C16. Only high quality, proven devices should be used, since the function of snubbers is very significant in the inverter - they reduce the resonant surges of the transformer and reduce the losses of the IGBT when disconnected. The best are the models SVV-81, K78-2. All power is transferred to the snubber, reducing heat generation by several times.

In the case when during the soldering process it is necessary to control and adjust the temperature or other parameters, there is a need not for a simple soldering iron, but for a more complex tool. To do this, it is not at all necessary to go to the store, you can assemble a soldering station with your own hands at home.

How to make your own main tool of a soldering station - a soldering iron, you can learn here.

All components of the device must be installed on the base. For its production, a getinax plate ½ cm thick is suitable. Cut a round hole for the fan in the center of the plate, which will need to be protected with a grill.

There must be air space between the wires.

On the front of the base, you need to bring out the LEDs, resistor and toggle switch knobs, cable clamps. This entire mechanism must be equipped with a “casing” from above, for the manufacture of which vinyl plastic or textolite (at least 4 mm thick) is suitable. A button is mounted on the electrode holder, which, together with the connected cable, must be well insulated.

The assembly process itself is not that complicated. The most important step is setting up the welding inverter. Sometimes this requires the help of a wizard.

1. First, the inverter must connect 15V power to PWM. simultaneously connect one convector to the power supply in order to reduce the heating of the device and make its operation quieter.

To close the resistor connect relay. It is connected when the charging of the capacitors is over. This procedure significantly reduces voltage fluctuations when the inverter is connected to a 220V network. If you do not use a resistor when connecting directly, an explosion may occur.

Then check how the relays work closing the resistor a few seconds after connecting the current to the PWM board. Diagnose the board itself for the presence of rectangular pulses after the relays work.

Then 15V power is supplied to the bridge. to check its serviceability and correct installation. The current strength should not be higher than 100mA. Move set to idle.

Check the correct installation of the transformer phases. To do this, you can use a 2-beam oscilloscope. Connect power to the bridge from capacitors through a 220V 200W lamp, before that set the PWM frequency to 55kHz, connect an oscilloscope, look at the signal form, make sure that the voltage does not rise more than 330V.

In order to determine the frequency of the device, you need to gradually reduce the PWM frequency until a slight inversion appears on the lower IGBT key. Fix this indicator, divide it by two, add the value of the oversaturation frequency to the resulting sum. The final sum will be the working frequency oscillation of the transformer.

The bridge should consume current in the region of 150mA. The light from the bulb should not be bright, a very bright light may indicate a breakdown in the winding or errors in the design of the bridge.

The transformer should not produce any noise effects. If they are present, then it is worth checking the polarity. You can connect test power to the bridge through some household appliance. You can use a kettle with a power of 2200 watts.

The conductors that come from the PWM should be short, twisted and placed away from sources of interference.

Gradually increase current inverter with a resistor. Be sure to listen to the device and observe the oscilloscope readings. The lower key should not rise more than 500V. The standard indicator is 340V. In the presence of noise, IGBTs may fail to work.

Start welding from 10 seconds. Check radiators, if cold, extend welding to 20 seconds. Then you can increase the welding time to 1 minute or more.
After using several electrodes, the transformer heats up. After 2 minutes, the fan cools it and you can start working again.

Assembling a homemade welding inverter with your own hands on video

Do-it-yourself welding inverter: diagrams and assembly instructions

It is quite possible to make a welding inverter with your own hands, even without in-depth knowledge in electronics and electrical engineering, the main thing is to strictly adhere to the scheme and try to understand well how such a device works. If you make an inverter, the technical characteristics and efficiency of which will differ little from those of serial models, you can save a decent amount.

Homemade welding inverter

You should not think that a home-made device will not give you the opportunity to effectively carry out welding work. Such a device, even assembled according to a simple scheme, will allow you to weld with electrodes with a diameter of 3-5 mm and an arc length of 10 mm.

Characteristics of a homemade inverter and materials for its assembly

Having assembled a welding inverter with your own hands according to a fairly simple electrical circuit, you will receive an effective device with the following technical characteristics:

• the value of the consumed voltage - 220 V;
• the strength of the current supplied to the input of the device - 32 A;
• the current generated at the output of the device is 250 A.

The scheme of an inverter-type welding machine with such characteristics includes the following elements:

• power unit;
• power key drivers;
• power block.

Before you start assembling a homemade inverter, you need to prepare working tools and elements for creating electronic circuits. So, you will need:

• Screwdriver Set;
• soldering iron for connecting elements of electronic circuits;
• hacksaw for metal work;
• threaded fasteners;
• sheet metal of small thickness:
• elements from which electronic circuits will be formed;
• copper wires and strips - for winding transformers;
• thermal paper from the cash register;
• fiberglass;
• textolite;
• mica.

For home use, inverters are most often assembled that operate from a standard 220 V electrical network. However, if necessary, you can make a device that will operate from a three-phase electrical network with a voltage of 380 V. Such inverters have their advantages, the most important of which is a higher Efficiency compared to single-phase devices.

Power Supply

One of the most important elements of the welding inverter power supply is a transformer, which is wound on a SH7x7 or 8x8 ferrite. This device, which provides a stable voltage supply, is formed from 4 windings:

• primary (100 turns of PEV wire with a diameter of 0.3 mm);
• the first secondary (15 turns of PEV wire with a diameter of 1 mm);
• the second secondary (15 turns of PEV wire with a diameter of 0.2 mm);
• third secondary (20 turns of PEV wire with a diameter of 0.3 mm).

To minimize the negative impact of voltage drops that regularly occur in the electrical network, the winding of the transformer windings should be performed across the entire width of the frame.

Power transformer winding process

After completing the primary winding and insulating its surface with fiberglass, a layer of shielding wire is wound around it, the turns of which should completely cover it. The turns of the shield wire (it must have the same diameter as the primary winding wire) are made in the same direction. This rule is also relevant for all other windings formed on the transformer frame. The surfaces of all windings wound on the transformer frame are also insulated from each other using fiberglass or ordinary masking tape.

In order for the voltage supplied from the power supply to the relay to be in the range of 20–25 V, it is necessary to select resistors for the electronic circuit. The main function of the welding inverter power supply is to convert AC to DC. For these purposes, the power supply uses diodes assembled according to the "oblique bridge" scheme.

Inverter power supply circuit (click to enlarge)

During operation, the diodes of such a bridge get very hot, so they must be mounted on radiators, which can be used as cooling elements from old computers. To mount the diode bridge, it is necessary to use two radiators: the upper part of the bridge is attached to one radiator through a mica gasket, the lower part through a layer of thermal paste to the second one.

The conclusions of the diodes from which the bridge is formed must be directed in the same direction as the conclusions of the transistors, with the help of which the direct current will be converted into high-frequency alternating current. The wires connecting these terminals should be no longer than 15 cm. Between the power supply and the inverter unit, which is based on transistors, there is a sheet of metal attached to the body of the device by welding.

Attaching diodes to a heatsink

Power block

The basis of the power unit of the welding inverter is a transformer, due to which the value of the high-frequency voltage decreases, and its strength increases. In order to make a transformer for such a block, it is necessary to select two cores Ш20х208 2000 nm. Newsprint can be used to provide a gap between them.

The windings of such a transformer are not made of wire, but of a copper strip 0.25 mm thick and 40 mm wide.

Each layer is wrapped with cash register tape to provide thermal insulation, which demonstrates good wear resistance. The secondary winding of the transformer is formed from three layers of copper strips, which are isolated from each other using a fluoroplastic tape. The characteristics of the transformer windings must comply with the following parameters: 12 turns x 4 turns, 10 kv. mm x 30 sq. mm.

Many people try to make step-down transformer windings from thick copper wire, but this is not the right solution. Such a transformer operates on high-frequency currents, which are forced out to the surface of the conductor without heating its interior. That is why, for the formation of windings, the best option is a conductor with a large surface area, that is, a wide copper strip.

Homemade inverter output choke

Plain paper can also be used as a thermal insulation material, but it is less wear-resistant than cash register tape. From elevated temperature, such a tape will darken, but its wear resistance will not suffer from this.

The transformer of the power unit will become very hot during its operation, therefore, for its forced cooling, it is necessary to use a cooler, which can be used as a device previously used in the computer system unit.

inverter unit

Even a simple welding inverter must perform its main function - to convert the direct current generated by the rectifier of such an apparatus into high-frequency alternating current. To solve this problem, power transistors are used that open and close at a high frequency.

Schematic diagram of the inverter unit (click to enlarge)

The inverter unit of the apparatus, which is responsible for converting direct current to high-frequency alternating current, is best assembled on the basis of not one powerful transistor, but several less powerful ones. Such a constructive solution will allow to stabilize the current frequency, as well as to minimize noise effects during welding.

The electronic circuit of the welding inverter also contains capacitors connected in series. They are necessary to solve two main tasks:

• minimization of resonant emissions of the transformer;
• reducing losses in the transistor block that occur when it is turned off and due to the fact that the transistors open much faster than they close (at this moment, current losses may occur, accompanied by heating of the transistor block keys).

Assembled inverter electronics

Cooling system

The power elements of the home-made welding inverter circuit become very hot during operation, which can lead to their failure. To prevent this from happening, in addition to the radiators on which the most heated blocks are mounted, it is necessary to use fans responsible for cooling.

If you have a powerful fan available, you can get by with one by directing the air flow from it to a step-down power transformer. If you are using low-power fans from older computers, you will need about six of them. At the same time, three such fans should be installed next to the power transformer, directing the air flow from them to it.

A powerful fan will ensure good cooling of the device elements

To prevent overheating of a homemade welding inverter, you should also use a temperature sensor by installing it on the hottest radiator. Such a sensor, if the radiator reaches a critical temperature, will turn off the flow of electric current to it.
In order for the inverter ventilation system to work effectively, properly executed air intakes must be present in its case. The grilles of such intakes, through which air flows will flow into the device, should not be blocked by anything.

Do-it-yourself inverter assembly

For a home-made inverter device, you need to choose a reliable case or make it yourself, using sheet metal with a thickness of at least 4 mm. As a base on which the welding inverter transformer will be mounted, you can use a sheet of getinax with a thickness of at least 0.5 cm. The transformer itself is mounted on such a base using brackets that you can make yourself from copper wire with a diameter of 3 mm.

Sliding body of factory production

To create electronic circuit boards of the device, you can use foil textolite with a thickness of 0.5–1 mm. When installing magnetic circuits that will heat up during operation, it is necessary to provide for gaps between them necessary for free air circulation.

To automatically control the operation of the welding inverter, you will need to purchase and install a PWM controller in it, which will be responsible for stabilizing the welding current and voltage. To make it convenient for you to work with your home-made device, it is necessary to mount controls in the front of its case. Such bodies include a toggle switch for turning on the device, a variable resistor knob with which the welding current is regulated, as well as cable clamps and signal LEDs.

Inverter Front Panel Layout Example

Diagnostics of a homemade inverter and its preparation for work

Making an inverter welding machine is half the battle. An equally important task is its preparation for work, during which the correct functioning of all elements is checked, as well as their settings.

The first thing to do when testing a homemade welding inverter is to apply 15 V to the PWM controller and one of the cooling fans. This will allow you to simultaneously check the performance of the controller and avoid its overheating during such a test.

Checking the output voltage with a tester

After the capacitors of the device are charged, a relay is connected to the electrical supply, which is responsible for closing the resistor. If voltage is applied directly to the resistor, bypassing the relay, an explosion may occur. After the relay trips, which should happen within 2-10 seconds after the voltage is applied to the PWM controller, you need to check if the resistor has closed.

When the relays of the electronic circuit work, the PWM board should form rectangular pulses to the optocouplers. This can be checked using an oscilloscope. The correct assembly of the diode bridge of the device must also be checked; for this, a voltage of 15 V is applied to it (the current strength should not exceed 100 mA).

The transformer phases may have been connected incorrectly during the assembly of the device, which may lead to incorrect operation of the inverter and strong noise. To prevent this from happening, the correct connection of the phases must be checked; for this, a two-beam oscilloscope is used. One beam of the device is connected to the primary winding, the second - to the secondary. The phases of the pulses, if the windings are connected correctly, should be the same.

Using an oscilloscope to diagnose the inverter

The correctness of the manufacture and connection of the transformer is checked using an oscilloscope and connecting electrical devices with various resistances to the diode bridge. Focusing on the noise of the transformer and the readings of the oscilloscope, they conclude that it is necessary to refine the electronic circuit of a home-made inverter apparatus.

To check how much you can continuously work on a homemade inverter, you need to start testing it from 10 seconds. If the radiators of the device do not heat up during operation of this duration, you can increase the period up to 20 seconds. If such a time period did not negatively affect the state of the inverter, you can increase the duration of the welding machine up to 1 minute.

Maintenance of a homemade welding inverter

In order for the inverter device to serve for a long time, it must be properly maintained.

In the event that your inverter has stopped working, you need to open its cover and blow out the insides with a vacuum cleaner. Those places where dust remains can be thoroughly cleaned with a brush and a dry cloth.

The first thing to do when diagnosing a welding inverter is to check the voltage supply to its input. If the voltage is not supplied, you should diagnose the performance of the power supply. The problem in this situation may also be that the fuses of the welding machine have blown. Another weak link of the inverter is the temperature sensor, which, in the event of a breakdown, must not be repaired, but replaced.

Often failing thermal sensor, usually located on a diode block or inductor

When performing diagnostics, it is necessary to pay attention to the quality of the connections of the electronic components of the device. Poorly made connections can be determined visually or using a tester. If such connections are identified, they must be corrected so as not to encounter further overheating and failure of the welding inverter.

Only if you pay due attention to the maintenance of the inverter device, you can count on the fact that it will serve you for a long time and will enable you to perform welding work as efficiently and efficiently as possible.

Do-it-yourself welding inverter - save on the purchase of expensive equipment

Welding machines have firmly entered the everyday life of home craftsmen. Traditional transformers are inexpensive, easy to repair, and such a design can be made by hand.

However, they have a drawback - for welding metal thicker than a car body, high currents are required. This gives a load from the primary side of 220 volts, about 3-5 watts.

It will not be possible to weld a pipe in an apartment; according to technical conditions, the input of the meter is limited to a power of 3.5-5 W. Yes, and in a private house a power outage is guaranteed.

For work at home, it is better to use a welding inverter. This device has less power, compact dimensions and low weight.

The cost of such a machine is higher than a conventional transformer. Therefore, many home "kulibins" make a welding inverter with their own hands.

Unlike a transformer, in which you struggle with a large secondary winding weight and thickness, the inverter offers a different solution.

The welding inverter circuit can shock even an experienced radio amateur, not to mention a home master whose knowledge comes down to replacing a fuse.


Don't be afraid. Following the assembly instructions, any radio amateur who knows how to handle a soldering iron will assemble this block in a few free evenings.

Important! The welding inverter uses high frequency currents during operation, so some elements get very hot.

Any inverter. even low power, requires forced cooling. To this we add a competent arrangement of components inside the case.

Of course, the case itself must be equipped with flow holes for ventilation. Otherwise, the thermal protection (a necessary piece of equipment) will constantly work.

We offer for consideration options on how to make welding with your own hands.

Resonance inverter in factory case

As a shell, you can use the usual power supply for your computer. The older the age, the better. 20 years ago, no metal was spared on the walls, and the dimensions of the AT format power supplies were larger.

From the power supply itself, you only need a fan (if it is in good condition) and cooling radiators. Therefore, the health of the donor's electrical filling does not interest us. So it will be cheaper to buy it.

The inverter is built on a used element base from old monitors and TVs. If there is no access to such "repositories" - the purchase of radio elements on the market will not greatly burden the wallet.
A detailed story on how to make a welding inverter with your own hands - video

Important! Currents up to 25A flow through these tracks, the thin copper of the printed circuit board will burn out from high temperature.

Any circuits related to power blocks must be carefully soldered with refractory solder. Otherwise, parts may ignite from sparks.

The network cable is made with a cross section of at least 2.5 squares

The input machine must be designed for the load current plus 50%. In our case - 16A

High-voltage circuits are made in double insulation: fireproof cambrics based on mica or fiberglass are put on the conductors

The resonant choke must not have a metal casing. Fastening only on the terminals - no metal brackets. Otherwise, pickups will violate its parameters

Flow forced ventilation is a must

Output power diodes must be protected from voltage breakdown. Usually RC chains are used.

Important! Failure to comply with safety requirements when installing power electronics will result in damage to the equipment, and in the worst case, personal injury.

We set for ourselves the parameters of the future welding machine:

• Output load current: 5 - 120A
• Open circuit voltage 90V
• The duration of the load for electrodes 2 mm - 100%, for electrodes 3 mm - 80%. (when the air temperature is high, the cooling time is extended by 20%-50%)
• Input current consumption: no more than 10A
• Weight without power cables 2 kg
• current regulator
• The current-voltage characteristic is falling. Therefore, it is possible to work in semi-automatic mode with CO2.

This is a fairly simple welding inverter, despite the fact that the circuit is saturated:


All denominations of the element base are indicated on the diagram; it makes no sense to duplicate them in a separate list. The heart of the master oscillator is assembled on the popular SG3524 chip.

It is used in computer power supplies. You can remove the part from the burned UPS.

The peculiarity of the inverter is the extremely low power consumption (by the standards of a welder, of course) - no more than 2.5 watts. This allows you to use it not only in the garage, but also in an apartment with a 16A input machine.

The power transformer is assembled on E42 cores. Installation is vertical, otherwise it will not fit into the case. Such cores are abundant in old tube monitors, and are not in short supply in principle. For the manufacture of one transformer, you will need to “gut” 6 monitors.

From the same parts (which will remain from the disassembled transformers) we make a choke. The cores for the rest of the components are made from standard 2000 NM ferrite.


The basis of the power block is powerful diodes and transistors that need heat dissipation. They can be installed on radiators from the power supply (in which the inverter is assembled), or dialed from the same old computer monitors.


Before switching on the voltage boost, the idle speed is maintained at 35V. Due to this low voltage, the power section is not overloaded. The length of the grasping arc is 3-4 mm. This is a comfortable value that allows even novice welders to work confidently.

The rectified voltage is in the form of a sine (this is a feature of resonant inverters). For the final smoothing of half-waves, it is necessary to lay the output cables in ferrite tubes with an inductance of 3-4mkH. You can use filter rings from the same power supply for the computer, and lay the wire in 2 turns.


The additional winding of the transformer adds voltage, so when starting work, the arc ignites instantly, regardless of atmospheric conditions. The main thing is the high-quality coating of the electrodes.

Current transformers are connected in the secondary winding. This is a design feature of the circuit - in the primary winding, the maximum current is possible only during the formation of resonance.

Inverter Protection

Sticking of the electrode prevents the field effect transistor IRF510. This area is clearly visible on the diagram. They also provide a soft start. Note that such a device adds comfort for an inexperienced welder.

On the SG3524 chip, the shutdown input is interrupted in three cases:

1. Thermal sensor operation
2. Blocking by transistor circuit in case of short circuit
3. Shutdown by toggle switch.

Important! A homemade welding inverter does not have a factory safety certificate. Therefore, the protection of the operator is the responsibility of the manufacturer of the device.

The scheme provides for the main points of safety, they should not be excluded from the design. The case should not have extra holes (except for ventilation) and open cavities. Power output terminals are mounted on heat-resistant durable insulators.


Outcome:
It is possible to assemble an inverter with your own hands. Do not be afraid of the many details in the circuit - this is the concern of the developer. You do not have to adjust the finished product, the welder is immediately ready for work. Provided that you solder everything correctly and arrange the modules in the case.

Step by step assembly of inverter welding

Do-it-yourself inverter welding is very simple

Inverter welding is a modern device that is widely popular due to the low weight of the device and its dimensions. The inverter mechanism is based on the use of field effect transistors and power switches. To become the owner of a welding machine, you can visit any tool store and acquire such a useful thing. But there is a much more economical way, which is due to the creation of do-it-yourself inverter welding. It is the second method that we will pay attention to in this material and consider how to do welding at home, what is needed for this and what the circuits look like.

Features of the operation of the inverter

An inverter-type welding machine is nothing more than a power supply, the one that is now used in modern computers. What is the basis of the work of the inverter? In the inverter, the following picture of the conversion of electrical energy is observed:

2) The current with a constant sinusoid is converted into an alternating current with a high frequency.

3) The voltage value decreases.

4) The current is rectified while maintaining the required frequency.

A list of such transformations of the electrical circuit is necessary in order to be able to reduce the weight of the apparatus and its overall dimensions. After all, as you know, old welding machines, the principle of which is based on a decrease in the magnitude of the voltage and an increase in the current strength on the secondary winding of the transformer. As a result, due to the high value of the current strength, the possibility of arc welding of metals is observed. In order for the current to increase and the voltage to decrease, the number of turns on the secondary winding decreases, but the cross section of the conductor increases. As a result, it can be seen that the transformer-type welding machine not only has significant dimensions, but also a decent weight.

To solve the problem, a variant of the implementation of the welding machine by means of an inverter circuit was proposed. The principle of the inverter is based on increasing the current frequency to 60 or even 80 kHz, thereby reducing the weight and dimensions of the device itself. All that was required to implement an inverter welding machine was to increase the frequency by a thousand times, which was made possible thanks to the use of field-effect transistors.

Transistors provide communication between themselves with a frequency of about 60-80 kHz. A constant current value comes to the power circuit of the transistors, which is ensured by the use of a rectifier. A diode bridge is used as a rectifier, and capacitors provide voltage equalization.

Alternating current, which is transmitted after passing through the transistors to the step-down transformer. But at the same time, a hundreds of times smaller coil is used as a transformer. Why a coil is used, because the frequency of the current that is fed to the transformer is already increased 1000 times thanks to field effect transistors. As a result, we obtain similar data as in the case of transformer welding, only with a big difference in weight and dimensions.

What you need to build an inverter

To assemble inverter welding on your own, you need to know that the circuit is designed, first of all, for a consuming voltage of 220 volts and a current of 32 amperes. Already after the conversion of energy at the output, the current will be increased by almost 8 times and will reach 250 amperes. This current is enough to create a strong seam with an electrode at a distance of up to 1 cm. To implement an inverter-type power supply, you will need to use the following components:

1) A transformer consisting of a ferrite core.

2) Winding of the primary transformer with 100 turns of wire with a diameter of 0.3 mm.

3) Three secondary windings:

- internal: 15 turns and a wire diameter of 1 mm;

- medium: 15 turns and a diameter of 0.2 mm;

- outer: 20 turns and a diameter of 0.35 mm.

In addition, to assemble the transformer, you will need the following items:

- copper wires;

- electrical steel;

- cotton material.

What does an inverter welding circuit look like?

In order to understand what an inverter welding machine is in general, it is necessary to consider the diagram below.

Electrical diagram of inverter welding

All these components must be combined and thereby obtain a welding machine, which will be an indispensable assistant in the performance of plumbing work. Below is a schematic diagram of inverter welding.

Inverter welding power supply circuit

The board, on which the device's power supply is located, is mounted separately from the power section. The separator between the power unit and the power supply is a metal sheet, electrically connected to the body of the unit.

To control the gates, conductors are used, which must be soldered near the transistors. These conductors are interconnected in pairs, and the cross section of these conductors does not play a special role. The only important thing to consider is the length of the conductors, which should not exceed 15 cm.

For a person who is not familiar with the basics of electronics, reading this kind of circuit is problematic, not to mention the purpose of each element. Therefore, if you do not have skills in working with electronics, then it is better to ask a familiar master to help you figure it out. Here, for example, below is a diagram of the power section of an inverter welding machine.

Scheme of the power part of inverter welding

How to assemble inverter welding: a step-by-step description + (Video)

To assemble the inverter welding machine, you must perform the following work steps:

1) Frame. As a body for welding, it is recommended to use an old system unit from a computer. It fits best, as it has the required number of holes for ventilation. You can use an old 10-liter canister that you can cut holes in and place the cooler. To increase the structural strength of the system housing, it is necessary to place metal corners, which are fixed with bolted connections.

2) Assembly of the power supply. An important element of the power supply is the transformer. It is recommended to use 7x7 or 8x8 ferrite as the basis of the transformer. For the primary winding of the transformer, it is necessary to wind the wire across the entire width of the core. Such an important feature entails an improvement in the operation of the device when voltage drops occur. As a wire, it is imperative to use copper wires of the PEV-2 brand, and in the absence of a bus, the wires are connected into one bundle. Fiberglass is used to insulate the primary winding. From above, after a layer of fiberglass, it is necessary to wind the turns of shielding wires.

Transformer with primary and secondary windings to create inverter welding

3) Power part. The step-down transformer acts as a power unit. Two types of cores are used as a core for a step-down transformer: W20x208 2000 nm. It is important to provide a gap between both elements, which is solved by placing newsprint. The secondary winding of the transformer is characterized by winding turns in several layers. Three layers of wires must be laid on the secondary winding of the transformer, and PTFE gaskets are installed between them. Between the windings, it is important to place a reinforced insulating layer, which will avoid voltage breakdown to the secondary winding. It is necessary to install a capacitor with a voltage of at least 1000 volts.

Transformers for the secondary winding from old TVs

To ensure air circulation between the windings, an air gap must be left. A current transformer is assembled on the ferrite core, which is connected to the positive line in the circuit. The core must be wrapped with thermal paper, so it is best to use a cash register tape as this paper. The rectifier diodes are attached to the aluminum heatsink plate. The outputs of these diodes should be connected with bare wires, the cross section of which is 4 mm.

3) inverter unit. The main purpose of the inverter system is the conversion of direct current into alternating current with a high frequency. To ensure the increase in frequency, special field-effect transistors are used. After all, it is transistors that work to open and close at a high frequency.

It is recommended to use more than one powerful transistor, but it is best to implement the circuit based on 2 less powerful ones. This is necessary in order to be able to stabilize the frequency of the current. The circuit cannot do without capacitors, which are connected in series and make it possible to solve such problems:

Inverter on aluminum plate

4) Cooling system. Cooling fans should be installed on the case wall, and for this you can use computer coolers. They are necessary in order to ensure the cooling of the working elements. The more fans you use, the better. In particular, it is mandatory to install two fans to blow the secondary transformer. One cooler will blow over the radiator, thereby preventing overheating of working elements - rectifier diodes. Diodes are mounted on the radiator as follows, as shown in the photo below.

Rectifier bridge on the cooling radiator

It is recommended to install it on the heating element itself. This sensor will be triggered when the critical heating temperature of the working element is reached. When it is triggered, the power to the inverter device will be turned off.

Powerful fan for cooling the inverter device

During operation, inverter welding heats up very quickly, so the presence of two powerful coolers is a prerequisite. These coolers or fans are located on the body of the device so that they work to extract air.

Fresh air will enter the system through the holes in the device case. The system unit already has these holes, and if you use any other material, then do not forget to provide fresh air.

5) Board soldering is a key factor, since the entire circuit is based on the board. It is important to install diodes and transistors on the board in the opposite direction to each other. The board is mounted directly between the cooling radiators, with the help of which the entire circuit of electrical appliances is connected. The supply circuit is designed for a voltage of 300 V. The additional location of 0.15 μF capacitors makes it possible to dump excess power back into the circuit. At the output of the transformer, capacitors and snubbers are located, with the help of which overvoltages are damped at the output of the secondary winding.

6) Setting up and debugging work. After the inverter welding is assembled, it will be necessary to carry out a few more procedures, in particular, to set up the functioning of the unit. To do this, connect a voltage of 15 volts to the PWM (pulse width modulator) and power the cooler. Additionally included in the relay circuit through the resistor R11. The relay is included in the circuit in order to avoid power surges in the 220 V network. It is imperative to control the switching on of the relay, and then apply power to the PWM. As a result, a picture should be observed in which rectangular sections on the PWM diagram should disappear.

Homemade inverter device with a description of the elements

You can judge the correct connection of the circuit if, during setup, the relay outputs 150 mA. In the case when a weak signal is observed, this indicates an incorrect connection of the board. It is possible that there is a breakdown in one of the windings, therefore, to eliminate interference, it will be necessary to shorten all the supply wires.

Inverter welding in the case of the system unit from the computer

Device health check

After carrying out all the assembly and debugging work, it remains only to check the performance of the resulting welding machine. To do this, the device is powered from the mains 220 V, then high current strength is set and the readings are verified using the oscilloscope. In the lower loop, the voltage should be in the range of 500 V, but not more than 550 V. If everything is done correctly with a strict selection of electronics, then the voltage indicator will not exceed 350 V.

So, now you can check the welding in action, for which we use the necessary electrodes and cut the seam until the electrode burns out completely. After that, it is important to control the temperature of the transformer. If the transformer simply boils, then the circuit has its drawbacks and it is better not to continue the workflow.

After cutting 2-3 seams, the radiators will heat up to a high temperature, so after that it is important to allow them to cool down. For this, a 2-3 minute pause is enough, as a result of which the temperature will drop to the optimum value.

Checking the welding machine

How to use a homemade device

After the home-made device is included in the circuit, the controller will automatically set a certain current strength. If the wire voltage is less than 100 volts, then this indicates a malfunction of the device. You will have to disassemble the device and again re-check the correctness of the assembly.

Using this type of welding machine, it is possible to solder not only ferrous, but also non-ferrous metals. In order to assemble a welding machine, you will need not only knowledge of the basics of electrical engineering, but also free time to implement the idea.

(1 ratings, average: 5,00 out of 5)

Scheme of a simple welding inverter

Good day gentlemen radio amateurs. Every radio amateur, and not only in his practice, is faced with the problem of connecting metal, and such a thickness that a soldering iron is no longer needed. So I had such a problem, so I will tell you about how I assembled the welding inverter. But I warn you right away, the device is not easy. If you have never worked with converters, you should not take on such a complex circuit.

Inverter circuit for welding

I have long been involved in power electronics, ranging from automotive inverters to 160 amp welding machines! Since the student himself and not so much money, he chose a circuit with good repeatability and a few details!

I took power capacitors on the robot, I also took a couple of fans from coolers, they are well suited because they are high-speed and provide good air flow, I took one big fan, but not so fast, it stands for blowing warm air.

UC3842 master oscillator chip, UC3843 can also be used. UC3845, I used a complementary pair of KT972-KT973 to pump the power transistor, the irg4pf50w power switch burned one, but nothing, there are a lot of them on the radio market 🙂

The power tracks were reinforced with copper wire. I didn’t take a picture of the process of winding the transformer, I can only say that the primary is 32 turns with a 1.5 mm wire, the secondary is a loop from the kinescope, it just fit well! Read about transformers on ferrite rings here.

The aparatik will turn out to be small, in general, just what you need for country work. Very satisfied with the result. Sincerely, Coloner.

Today, a widely demanded welding machine is a welding inverter. Its advantages are functionality and performance. You can make a mini welding machine with your own hands without much financial investment (spending only on consumables), if you have an understanding of how electronics are arranged and work. Today, good inverters are expensive, and cheap ones can disappoint with poor welding quality. Before constructing such a tool on your own, you need to carefully study the circuit.

All components of the device must be installed on the base. For its production, a getinax plate ½ cm thick is suitable. Cut a round hole for the fan in the center of the plate, which will need to be protected with a grill.

There must be air space between the wires.

On the front of the base, you need to bring out the LEDs, resistor and toggle switch knobs, cable clamps. This entire mechanism must be equipped with a “casing” from above, for the manufacture of which vinyl plastic or textolite (at least 4 mm thick) is suitable. A button is mounted on the electrode holder, which, together with the connected cable, must be well insulated.

The assembly process itself is not that complicated. The most important step is setting up the welding inverter. Sometimes this requires the help of a wizard.

1. First, the inverter must connect 15V power to PWM, simultaneously connect one convector to the power supply to reduce the heating of the device and make its operation quieter.
2. To close the resistor connect relay. It is connected when the charging of the capacitors is over. This procedure significantly reduces voltage fluctuations when the inverter is connected to a 220V network. If you do not use a resistor when connecting directly, an explosion may occur.
3. Then check how the relays work closing the resistor a few seconds after connecting the current to the PWM board. Diagnose the board itself for the presence of rectangular pulses after the relays work.
4. Then 15V power is supplied to the bridge to check its serviceability and correct installation. The current strength should not be higher than 100mA. Move set to idle.
5. Check the correct installation of the transformer phases. To do this, you can use a 2-beam oscilloscope. Connect power to the bridge from capacitors through a 220V 200W lamp, before that set the PWM frequency to 55kHz, connect an oscilloscope, look at the signal form, make sure that the voltage does not rise more than 330V.

In order to determine the frequency of the device, you need to gradually reduce the PWM frequency until a slight inversion appears on the lower IGBT key. Fix this indicator, divide it by two, add the value of the oversaturation frequency to the resulting sum. The final sum will be the working frequency oscillation of the transformer.


The bridge should consume current in the region of 150mA. The light from the bulb should not be bright, a very bright light may indicate a breakdown in the winding or errors in the design of the bridge.

The transformer should not produce any noise effects. If they are present, then it is worth checking the polarity. You can connect test power to the bridge through some household appliance. You can use a kettle with a power of 2200 watts.

The conductors that come from the PWM should be short, twisted and placed away from sources of interference.

6. Gradually increase current inverter with a resistor. Be sure to listen to the device and observe the oscilloscope readings. The lower key should not rise more than 500V. The standard indicator is 340V. In the presence of noise, IGBTs may fail to work.
7. Start welding from 10 seconds. Check radiators, if cold, extend welding to 20 seconds. Then you can increase the welding time to 1 minute or more.
   After using several electrodes, the transformer heats up. After 2 minutes, the fan cools it and you can start working again.

Assembling a homemade welding inverter with your own hands on video

Many in the household would need an apparatus for electric welding of parts made of ferrous metals. Since mass-produced welding machines are quite expensive, many radio amateurs are trying to make a welding inverter with their own hands.

We already had an article about that, but this time I offer an even simpler version of a home-made welding inverter from available do-it-yourself parts.

Of the two main options for the design of the apparatus - with a welding transformer or based on a converter - the second one was chosen.

Indeed, a welding transformer is a large and heavy magnetic circuit and a lot of copper wire for windings, which is inaccessible to many. Electronic components for the converter, with their correct choice, are not scarce and relatively cheap.

How I made a welding machine with my own hands

From the very beginning of my work, I set myself the task of creating the most simple and cheap welding machine using widely used parts and assemblies in it.

As a result of rather lengthy experiments with various types of converters based on transistors and trinistors, the circuit shown in Fig. one.

Simple transistor converters turned out to be extremely capricious and unreliable, and trinistor converters withstand the output shorting without damage until the fuse blows. In addition, trinistors heat up much less than transistors.

As you can easily see, the circuit design is not original - it is an ordinary single-cycle converter, its advantage is in the simplicity of design and the absence of scarce components, the device uses a lot of radio components from old TVs.

And, finally, it practically does not require adjustment.

The scheme of the inverter welding machine is presented below:

Kind of welding current - constant, regulation - smooth. In my opinion, this is the simplest welding inverter that you can assemble with your own hands.

When butt-welding steel sheets 3 mm thick with an electrode 3 mm in diameter, the steady current consumed by the machine from the mains does not exceed 10 A. The welding voltage is switched on by a button located on the electrode holder, which allows, on the one hand, to use an increased arc ignition voltage and increase electrical safety, on the other hand, since when the electrode holder is released, the voltage on the electrode is automatically turned off. The increased voltage facilitates the ignition of the arc and ensures the stability of its burning.

A little trick: a do-it-yourself welding inverter circuit allows you to connect thin sheet metal. To do this, you need to change the polarity of the welding current.

Mains voltage rectifies the diode bridge VD1-VD4. The rectified current, flowing through the lamp HL1, begins to charge the capacitor C5. The lamp serves as a charging current limiter and an indicator of this process.

Welding should be started only after the HL1 lamp goes out. At the same time, battery capacitors C6-C17 are charged through the inductor L1. The glow of the HL2 LED indicates that the device is connected to the network. Trinistor VS1 is still closed.

When you press the SB1 button, a pulse generator is started at a frequency of 25 kHz, assembled on a unijunction transistor VT1. The generator pulses open the VS2 trinistor, which, in turn, opens the VS3-VS7 trinistors connected in parallel. Capacitors C6-C17 are discharged through the inductor L2 and the primary winding of the transformer T1. Circuit choke L2 - primary winding of transformer T1 - capacitors C6-C17 is an oscillatory circuit.

When the direction of the current in the circuit changes to the opposite, the current begins to flow through the diodes VD8, VD9, and the trinistors VS3-VS7 close until the next pulse of the generator on the transistor VT1.

The pulses that appear on the winding III of the transformer T1 open the trinistor VS1. which directly connects the mains diode rectifier VD1 - VD4 with a trinistor converter.

The HL3 LED serves to indicate the process of generating a pulsed voltage. Diodes VD11-VD34 rectify the welding voltage, and capacitors C19 - C24 smooth it out, thereby facilitating the ignition of the welding arc.

Switch SA1 is a packet or other switch for a current of at least 16 A. Section SA1.3 closes capacitor C5 to resistor R6 when turned off and quickly discharges this capacitor, which allows, without fear of electric shock, to inspect and repair the device.

The VN-2 fan (with an M1 electric motor according to the scheme) provides forced cooling of the device components. Less powerful fans are not recommended, or you will have to install several of them. Capacitor C1 - any designed to operate at an alternating voltage of 220 V.

Rectifier diodes VD1-VD4 must be rated for a current of at least 16 A and a reverse voltage of at least 400 V. They must be installed on plate-shaped corner heat sinks 60x15 mm in size, 2 mm thick, made of aluminum alloy.

Instead of a single capacitor C5, you can use a battery of several connected in parallel for a voltage of at least 400 V each, while the battery capacity may be greater than that indicated in the diagram.

Choke L1 is made on a steel magnetic core PL 12.5x25-50. Any other magnetic circuit of the same or larger cross section is also suitable, provided that the winding is placed in its window. The winding consists of 175 turns of wire PEV-2 1.32 (a wire of smaller diameter cannot be used!). The magnetic circuit must have a non-magnetic gap of 0.3 ... 0.5 mm. Choke inductance - 40±10 μH.

Capacitors C6-C24 should have a small dielectric loss tangent, and C6-C17 should also have an operating voltage of at least 1000 V. The best capacitors I have tested are K78-2, used in TVs. You can use more widespread capacitors of this type of a different capacity, bringing the total capacitance to that indicated in the diagram, as well as imported film ones.

Attempts to use paper or other capacitors designed for operation in low-frequency circuits, as a rule, lead to their failure after a while.

SCRs KU221 (VS2-VS7) should preferably be used with the letter index A or, in extreme cases, B or G. As practice has shown, during the operation of the device, the cathode terminals of the SCRs noticeably heat up, which can lead to the destruction of solder joints on the board and even failure trinistors.

Reliability will be higher if either piston tubes made of tinned copper foil with a thickness of 0.1 ... along the entire length. The piston (bandage) should cover the entire length of the lead almost to the base. It is necessary to solder quickly so as not to overheat the trinistor.

You will probably have a question: is it possible to install one powerful one instead of several relatively low-power trinistors? Yes, this is possible when using a device that is superior (or at least comparable) in its frequency characteristics to the KU221A trinistors. But among those available, for example, from the PM or TL series, there are none.

The transition to low-frequency devices will force the operating frequency to be lowered from 25 to 4 ... 6 kHz, and this will lead to a deterioration in many of the most important characteristics of the device and a loud shrill squeak during welding.

When mounting diodes and trinistors, the use of heat-conducting paste is mandatory.

In addition, it has been found that one powerful trinistor is less reliable than several connected in parallel, since it is easier for them to provide better conditions for heat removal. It is enough to install a group of trinistors on one heat-removing plate with a thickness of at least 3 mm.

Since the current equalizing resistors R14-R18 (C5-16 V) can get very hot during welding, they must be freed from the plastic shell before installation by firing or heating with a current, the value of which must be selected experimentally.

Diodes VD8 and VD9 are installed on a common heat sink with trinistors, and the VD9 diode is isolated from the heat sink with a mica gasket. Instead of KD213A, KD213B and KD213V, as well as KD2999B, KD2997A, KD2997B, are suitable.

Inductor L2 is a frameless spiral of 11 turns of wire with a cross section of at least 4 mm2 in heat-resistant insulation, wound on a mandrel with a diameter of 12...14 mm.

The throttle during welding is very hot, therefore, when winding the spiral, a gap of 1 ... 1.5 mm should be provided between the turns, and the throttle must be positioned so that it is in the air flow from the fan. Rice. 2 Transformer core

T1 is made up of three PK30x16 magnetic circuits made of 3000NMS-1 ferrite stacked together (they used horizontal transformers of old TVs).

The primary and secondary windings are divided into two sections each (see Fig. 2), wound with wire PSD1.68x10.4 in fiberglass insulation and connected in series according to. The primary winding contains 2x4 turns, the secondary - 2x2 turns.

Sections are wound on a specially made wooden mandrel. The sections are protected from unwinding by two bandages made of tinned copper wire with a diameter of 0.8 ... 1 mm. Bandage width - 10...11 mm. A strip of electric cardboard is placed under each bandage or several turns of fiberglass tape are wound.

After winding, the bandages are soldered.

One of the bandages of each section serves as the output of its beginning. To do this, the insulation under the shroud is made so that from the inside it is in direct contact with the beginning of the section winding. After winding, the bandage is soldered to the beginning of the section, for which the insulation is removed from this section of the coil in advance and it is tinned.

It should be borne in mind that winding I operates in the most severe thermal conditions. For this reason, when winding its sections and during assembly, it is necessary to provide air gaps between the outer parts of the turns by inserting between the turns short, lubricated with heat-resistant glue, fiberglass inserts.

In general, when making transformers for inverter welding with your own hands, always leave air gaps in the winding. The more of them, the more efficient the removal of heat from the transformer and the lower the probability of burning the device.

It is also appropriate to note here that winding sections made with the mentioned inserts and gaskets with wire of the same section 1.68x10.4 mm 2 without insulation will be cooled better under the same conditions.

The bandages in contact are connected by soldering, and it is advisable to solder a copper pad in the form of a short piece of wire from which the section is made to the front ones, which serve as the leads of the sections.

The result is a rigid one-piece primary winding of the transformer.

The secondary is made in the same way. The difference is only in the number of turns in the sections and in the fact that it is necessary to provide an output from the midpoint. The windings are installed on the magnetic circuit in a strictly defined way - this is necessary for the correct operation of the VD11 - VD32 rectifier.

The winding direction of the upper winding section I (when looking at the transformer from above) must be counterclockwise, starting from the upper terminal, which must be connected to the L2 choke.

The winding direction of the upper winding section II, on the contrary, is clockwise, starting from the upper output, it is connected to the VD21-VD32 diode block.

Winding III is a coil of any wire with a diameter of 0.35 ... 0.5 mm in heat-resistant insulation that can withstand a voltage of at least 500 V. It can be placed last in any place of the magnetic circuit from the side of the primary winding.

To ensure the electrical safety of the welding machine and effective cooling of all elements of the transformer with air flow, it is very important to maintain the necessary gaps between the windings and the magnetic circuit. When assembling a do-it-yourself welding inverter, most do-it-yourselfers make the same mistake: they underestimate the importance of cooling the trance. This cannot be done.

This task is performed by four fixing plates laid in the windings during the final assembly of the assembly. The plates are made of fiberglass with a thickness of 1.5 mm in accordance with the drawing in the figure.

After the final adjustment of the plate, it is advisable to fix it with heat-resistant glue. The transformer is attached to the base of the apparatus with three brackets bent from brass or copper wire with a diameter of 3 mm. The same brackets fix the mutual position of all elements of the magnetic circuit.

Before mounting the transformer on the base, between the halves of each of the three sets of the magnetic circuit, it is necessary to insert non-magnetic gaskets made of electric cardboard, getinaks or textolite with a thickness of 0.2 ... 0.3 mm.

For the manufacture of a transformer, you can use magnetic cores and other sizes with a cross section of at least 5.6 cm 2. Suitable, for example, W20x28 or two sets of W 16x20 from ferrite 2000NM1.

Winding I for the armored magnetic circuit is made in the form of a single section of eight turns, winding II - similarly to that described above, from two sections of two turns. The welding rectifier on diodes VD11-VD34 is structurally a separate unit, made in the form of a bookcase:

It is assembled in such a way that each pair of diodes is placed between two heat-removing plates 44x42 mm in size and 1 mm thick, made of aluminum alloy sheet.

The whole package is pulled together by four steel threaded studs with a diameter of 3 mm between two flanges 2 mm thick (of the same material as the plates), to which two boards are screwed on both sides, forming the rectifier leads.

All diodes in the block are oriented in the same way - with the cathode leads to the right according to the figure - and the leads are soldered into the holes of the board, which serves as a common positive lead of the rectifier and the device as a whole. The anode terminals of the diodes are soldered into the holes of the second board. Two groups of conclusions are formed on it, connected to the extreme conclusions of the winding II of the transformer according to the scheme.

Given the large total current flowing through the rectifier, each of its three leads is made of several pieces of wire 50 mm long, each soldered into its own hole and connected by soldering at the opposite end. A group of ten diodes is connected in five segments, of fourteen - in six, the second board with a common point of all diodes - in six.

It is better to use a flexible wire, with a cross section of at least 4 mm.

In the same way, high-current group outputs from the main printed circuit board of the device are made.

The rectifier boards are made of foil fiberglass 0.5 mm thick and tinned. Four narrow slots in each board help to reduce the stress on the diode leads during thermal deformations. For the same purpose, the diode leads must be molded as shown in the figure above.

In the welding rectifier, you can also use more powerful diodes KD2999B, 2D2999B, KD2997A, KD2997B, 2D2997A, 2D2997B. Their number may be less. So, in one of the variants of the apparatus, a rectifier of nine 2D2997A diodes successfully worked (five in one arm, four in the other).

The area of ​​the heat sink plates remained the same, it was possible to increase their thickness up to 2 mm. The diodes were placed not in pairs, but one in each compartment.

All resistors (except R1 and R6), capacitors C2-C4, C6-C18, transistor VT1, trinistors VS2 - VS7, zener diodes VD5-VD7, diodes VD8-VD10 are mounted on the main printed circuit board, and the trinistors and diodes VD8, VD9 are installed on heat sink screwed to a board made of foil textolite 1.5 mm thick:
Rice. 5. Board drawing

The scale of the board drawing is 1:2, however, the board is easy to mark, even without using photo enlargement tools, since the centers of almost all holes and the borders of almost all foil areas are located on a grid with a 2.5 mm step.

The board does not require great accuracy in marking and drilling holes, however, it should be remembered that the holes in it must match the corresponding holes in the heat sink plate.

The jumper in the circuit of diodes VD8, VD9 is made of copper wire with a diameter of 0.8 ... 1 mm. It is better to solder it from the printing side. The second jumper from the wire PEV-2 0.3 can also be placed on the side of the parts.

The group output of the board, indicated in fig. 5 letters B, connected to the throttle L2. Conductors from the anodes of the trinistors are soldered into the holes of group B. The conclusions G are connected to the bottom terminal of the transformer T1 according to the diagram, and D - to the inductor L1.

The pieces of wire in each group must be of the same length and the same cross section (at least 2.5 mm2).
Rice. 6 heat sink

The heat sink is a 3 mm thick plate with a bent edge (see Fig. 6).

The best heat sink material is copper (or brass). In extreme cases, in the absence of copper, an aluminum alloy plate can be used.

The surface on the installation side of the parts must be flat, without nicks and dents. Threaded holes are drilled in the plate to assemble it with a printed circuit board and fasten the elements. Leads of parts and connecting wires are passed through holes without thread. The anode leads of the trinistors are passed through the holes in the bent edge. Three holes M4 in the heat sink are designed for its electrical connection with the printed circuit board. Three brass screws with brass nuts were used for this. Fig. 1. 8. Placement of knots

The unijunction transistor VT1 usually does not cause problems, however, in the presence of generation, some instances do not provide the pulse amplitude necessary for the stable opening of the trinistor VS2.

All components and parts of the welding machine are installed on a base plate made of getinaks 4 mm thick (textolite 4 ... 5 mm thick is also suitable) on one side of it. A round window is cut in the center of the base for mounting the fan; it is installed on the same side.

Diodes VD1-VD4, trinistor VS1 and lamp HL1 are mounted on angle brackets. When installing the T1 transformer between adjacent magnetic circuits, an air gap of 2 mm should be provided. Each of the clamps for connecting welding cables is a M10 copper bolt with copper nuts and washers.

From the inside, a copper square is pressed against the base by the head of the bolt, additionally fixed from turning with an M4 screw with a nut. The thickness of the square shelf is 3 mm. An internal connecting wire is connected to the second shelf with a bolt or soldering.

The printed circuit board-heat sink assembly is installed with parts to the base on six steel racks bent from a strip 12 wide and 2 mm thick.

The handle of the toggle switch SA1, the fuse holder cover, the LEDs HL2, HL3, the handle of the variable resistor R1, the clamps for welding cables and the cable to the SB1 button are displayed on the front side of the base.

In addition, four stand-sleeves with a diameter of 12 mm with M5 internal thread, machined from textolite, are attached to the front side. A false panel with holes for the controls of the apparatus and a protective grille of the fan is attached to the racks.

The false panel can be made of sheet metal or dielectric with a thickness of 1 ... 1.5 mm. I cut it out of fiberglass. Outside, six racks with a diameter of 10 mm are screwed to the false panel, on which network and welding cables are wound after welding is completed.

Holes with a diameter of 10 mm are drilled in the free areas of the false panel to facilitate the circulation of cooling air. Rice. 9. Appearance of the inverter welding machine with cables laid.

The assembled base is placed in a casing with a lid made of sheet textolite (you can use getinaks, fiberglass, vinyl plastic) 3 ... 4 mm thick. Cooling air outlets are located on the side walls.

The shape of the holes does not matter, but for safety it is better if they are narrow and long.

The total area of ​​the outlet holes should not be less than the area of ​​the inlet. The casing is equipped with a handle and a shoulder strap for carrying.

The electrode holder can be of any design, as long as it provides convenience and easy replacement of the electrode.

On the handle of the electrode holder, you need to mount the button (SB1 according to the diagram) in such a place that the welder can easily hold it pressed even with a hand in a mitten. Since the button is under mains voltage, it is necessary to ensure reliable insulation of both the button itself and the cable connected to it.

P.S. The description of the assembly process took up a lot of space, but in fact everything is much simpler than it seems. Anyone who has ever held a soldering iron and a multimeter in their hands will be able to assemble this welding inverter with their own hands without any problems.