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Homemade welding machine (inverter) - design, manufacturing. How to assemble an inverter welding machine at home Homemade welding inverter from available parts

The characteristics of most budget inverters cannot be called outstanding, but at the same time, few will refuse the pleasure of using equipment with a significant margin of reliability. Meanwhile, there are many ways to improve an inexpensive welding inverter.

Typical circuit and principle of operation of the inverter

The more expensive the welding inverter, the more auxiliary units in its circuit that are involved in the implementation of special functions. But the power converter circuit itself remains virtually unchanged even with expensive equipment. The stages of transformation of mains electric current into welding current are quite easy to trace - at each of the main nodes of the circuit a certain part of the overall process occurs.

From the network cable, through a protective switch, voltage is supplied to a rectifying diode bridge coupled with high-capacity filters. In the diagram, this area is easy to notice; there are impressive-sized “banks” of electrolytic capacitors located here. The rectifier has one task - to “turn” the negative part of the sine wave symmetrically upward, while the capacitors smooth out the ripples, bringing the direction of the current almost to a pure “constant”.

Scheme of operation of the welding inverter

Next in the diagram is the inverter itself. This part is also easy to identify; the largest aluminum radiator is located here. The inverter is built on several high-frequency field-effect transistors or IGBT transistors. Quite often, several power elements are combined in a common housing. The inverter again converts direct current into alternating current, but at the same time its frequency is significantly higher - about 50 kHz. This chain of transformations allows the use of a high-frequency transformer, which is several times smaller and lighter than a conventional one.

The output rectifier removes the voltage from the step-down transformer, because we want to weld with direct current. Thanks to the output filter, the nature of the current changes from a high-frequency pulsating current to an almost straight line. Naturally, in the considered chain of transformations there are many intermediate links: sensors, control and control circuits, but their consideration goes far beyond the scope of amateur radio electronics.

Design of the welding inverter: 1 - filter capacitors; 2 - rectifier (diode assembly); 3 - IGBT transistors; 4 - fan; 5 - step-down transformer; 6 — control board; 7 — radiators; 8 - throttle

Units suitable for modernization

The most important parameter of any welding machine is the current-voltage characteristic (CVC), which ensures stable arc burning at different arc lengths. The correct current-voltage characteristic is created by microprocessor control: the small “brain” of the inverter changes the operating mode of the power switches on the fly and instantly adjusts the parameters of the welding current. Unfortunately, it is impossible to reprogram a budget inverter in any way - the control microcircuits in it are analog, and replacement with digital electronics requires extraordinary knowledge of circuit design.

However, the “skills” of the control circuit are quite enough to level out the “crookedness” of a novice welder who has not yet learned to hold the arc stably. It is much more correct to focus on eliminating some “childhood” diseases, the first of which is severe overheating of electronic components, leading to degradation and destruction of power switches.

The second problem is the use of radioelements of questionable reliability. Eliminating this drawback greatly reduces the likelihood of breakdowns after 2-3 years of operation of the device. Finally, even a novice radio engineer will be quite capable of implementing an indication of the actual welding current to be able to work with special brands of electrodes, as well as carry out a number of other minor improvements.

Improved heat dissipation

The first drawback that plagues the vast majority of inexpensive inverter devices is a poor heat removal system from power switches and rectifier diodes. It is better to begin improvements in this direction by increasing the intensity of forced airflow. As a rule, case fans are installed in welding machines, powered by 12 V service circuits. In “compact” models, forced air cooling may be completely absent, which is certainly nonsense for electrical equipment of this class.

It is enough to simply increase the air flow by installing several of these fans in series. The problem is that the “original” cooler will most likely have to be removed. To operate effectively in a sequential assembly, fans must have an identical shape and number of blades, as well as rotation speed. Assembling identical coolers into a “stack” is extremely simple; just tighten them with a pair of long bolts along diametrically opposite corner holes. Also, do not worry about the power of the service power supply; as a rule, it is enough to install 3-4 fans.

If there is not enough space inside the inverter housing to install fans, you can attach one high-performance “duct” to the outside. Its installation is simpler because it does not require connection to internal circuits; power is removed from the power button terminals. The fan, of course, must be installed opposite the ventilation louvers, some of which can be cut out to reduce aerodynamic drag. The optimal direction of air flow is towards the exhaust from the housing.

The second way to improve heat dissipation is to replace standard aluminum radiators with more efficient ones. A new radiator should be selected with the largest number of fins as thin as possible, that is, with the largest area of ​​​​contact with air. It is optimal to use computer CPU cooling radiators for these purposes. The process of replacing radiators is quite simple, just follow a few simple rules:

  1. If the standard radiator is isolated from the flanges of the radio elements with mica or rubber gaskets, they must be preserved when replacing.
  2. To improve thermal contact, you need to use silicone thermal paste.
  3. If the radiator needs to be trimmed to fit into the case, the cut fins must be carefully processed with a file to remove all burrs, otherwise dust will accumulate on them abundantly.
  4. The radiator must be pressed tightly against the microcircuits, so you first need to mark and drill mounting holes on it; you may need to cut a thread in the body of the aluminum base.

Additionally, we note that there is no point in changing the piece heatsinks of separate keys; only the heat sinks of integrated circuits or several high-power transistors installed in a row are replaced.

Welding current indication

Even if a digital current setting indicator is installed on the inverter, it does not show its real value, but a certain service value, scaled for visual display. The deviation from the actual current value can be up to 10%, which is unacceptable when using special brands of electrodes and working with thin parts. You can get the actual value of the welding current by installing an ammeter.

A digital ammeter of the SM3D type will cost around 1 thousand rubles; it can even be neatly built into the inverter housing. The main problem is that measuring such high currents requires a shunt connection. Its cost is in the range of 500-700 rubles for currents of 200-300 A. Please note that the type of shunt must comply with the recommendations of the ammeter manufacturer; as a rule, these are 75 mV inserts with an intrinsic resistance of about 250 μOhm for a measurement limit of 300 A.

The shunt can be installed either on the positive or negative terminal from inside the housing. Typically, the size of the connecting bus is sufficient to connect an insert about 12-14 cm long. The shunt cannot be bent, so if the length of the connecting bus is not enough, it must be replaced with a copper plate, a pigtail of cleaned single-wire cable or a piece of welding conductor.

The ammeter is connected with measuring outputs to the opposite terminals of the shunt. Also, for the digital device to operate, it is necessary to supply a supply voltage in the range of 5-20 V. It can be removed from the fan connection wires or found on the board at points with potential for powering control chips. The ammeter's own consumption is negligible.

Increasing duty cycle

The on-time duration in the context of welding inverters is more reasonably called the load duration. This is the part of the ten-minute interval in which the inverter directly performs work; the remaining time it must idle and cool.

For most inexpensive inverters, the actual PV is 40-45% at 20 °C. Replacing radiators and an intensive airflow device can increase this figure to 50-60%, but this is far from the ceiling. A PN of about 70-75% can be achieved by replacing some radioelements:

  1. The capacitors of the inverter keys need to be replaced with elements of the same capacity and type, but designed for a higher voltage (600-700 V);
  2. Diodes and resistors from the key harness should be replaced with elements with higher power dissipation.
  3. Rectifier diodes (valves), as well as MOSFETs or IGBT transistors, can be replaced with similar, but more reliable ones.

It is worth talking about replacing the power switches themselves separately. First, you should rewrite the markings on the element body and find a detailed datasheet for a specific element. According to the passport data, choosing an element to replace is quite simple; the key parameters are the limits of the frequency range, operating voltage, the presence of a built-in diode, type of housing and current limit at 100 °C. It is better to calculate the latter yourself (for the high-voltage side, taking into account losses on the transformer) and purchase radioelements with a maximum current reserve of about 20%. Of the manufacturers of this type of electronics, International Rectifier (IR) or STMicroelectronics are considered the most reliable. Despite the rather high price, it is highly recommended to purchase parts from these brands.

Winding the output choke

One of the simplest and at the same time most useful additions to a welding inverter will be the winding of an inductive coil that smoothes out the DC ripples that inevitably remain when the pulse transformer is operating. The main specificity of this idea is that the choke is made individually for each individual device, and can also be adjusted over time as electronic components degrade or when the power threshold changes.

To make a choke you will need nothing at all: an insulated copper conductor with a cross-section of up to 20 mm 2 and a core, preferably made of ferrite. Either a ferrite ring or an armored transformer core is optimally suited as a magnetic core. If the magnetic core is made of sheet steel, it needs to be drilled in two places with an indentation of about 20-25 mm and tightened with rivets in order to be able to cut the gap without any problems.

The choke begins to work starting from one full turn, but the real result is visible starting from 4-5 turns. During testing, turns should be added until the arc begins to stretch noticeably strongly, preventing separation. When it becomes difficult to cook with separation, you need to remove one turn from the coil and connect a 24 V incandescent lamp in parallel with the choke.

Fine-tuning the throttle is done using a plumber's screw clamp, which can be used to reduce the gap in the core, or a wooden wedge, which can be used to increase this gap. It is necessary to ensure that the lamp burns as bright as possible when igniting the arc. It is recommended to manufacture several chokes to operate in ranges up to 100 A, from 100 to 200 A and more than 200 A.

Conclusion

It is better to mount all “mounted” additions, such as a choke or an ammeter, with a separate attachment, which is connected to the gap of any of the welding conductors using a bayonet-type plug. This way, enough space for ventilation will remain inside the inverter housing, and additional devices can be easily turned off when not needed.

It must be remembered that it will not be possible to carry out a radical, deep modernization, in other words, “RESANTA” cannot be turned into KEMPPI by reasonable forces and means. However, making fixtures and minor modifications to equipment is a great way to better learn arc welding technology and gain insight into professional intricacies.

The designer and famous scientist Yuri Negulyaev at one time invented an almost irreplaceable device - a welding inverter. We suggest you consider how to make a welding inverter with your own hands using a pulse transformer and powerful MOSFET transistors.

The most important thing when constructing or repairing a purchased or homemade inverter is its circuit diagram. For the manufacture of our inverter, we took it from Negulyaev’s project.

Manufacturing of transformer and choke

To work we will need the following equipment:

  1. Ferrite core.
  2. Frame for transformer.
  3. Copper bar 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 over the full width of the frame; with this design, the transformer becomes more resistant to voltage surges and external influences.

A high-quality pulse transformer is wound with a copper busbar 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 the 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 reach the secondary winding. PTFE heat-resistant insulation is best suited for this.

The transformer can also be made not on a standard core, by using for these purposes 5 transformers from horizontal scanning 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 makes it easier to cool.

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 we wind the 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 attached to the positive power wire; the outputs from this transformer come to the control board to monitor and stabilize the output current.

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

Welding machine design

Let's look at how to construct a fairly powerful pulsed welding inverter at home.

If you repeat the design according to the Negulyaev system, then the transistors are screwed to the radiator with a plate specially cut for this purpose, thus improving the heat transfer from the transistor to the radiator. Between the radiator and the transistors it is necessary to lay a thermally conductive gasket that does not allow current to pass through. This provides short circuit protection between the two transistors.

The rectifier diodes are attached to a 6 mm thick aluminum plate; the fastening is carried out in the same way as the transistors are fastened. Their outputs are connected to each other with a bare wire with a cross-section of 4 mm. Be careful not to let the wires touch.

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

Video: DIY welding inverter

All power conductors inside the inverter housing must be routed in different directions, otherwise there is a possibility of a short circuit. The fan cools several radiators simultaneously, each of which is dedicated to its own part of the circuit. This design allows you to get by with just one fan installed on the rear wall of the case, which significantly saves space.

To cool a homemade welding inverter, you can use a fan from a computer case; it is optimal in both size and power. Since ventilation of the secondary winding plays a large role, this should be taken into account when positioning it.


 Diagram: disassembled welding inverter

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

How to configure the inverter

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

Instructions that make it easier to independently set up a welding inverter:

  1. First, you need to apply mains voltage to the inverter board, after which the unit will begin to emit the characteristic squeak of a pulse transformer. Voltage is also 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 network, 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 producing current in excess of 100 amperes, this value depends on the specific circuit used in the design. 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 amplitude 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 inverter input from any suitable power supply. At idle, the unit consumes a current of about 100 mA, this must be taken into account when carrying out control measurements.
  7. For comparison, you can check the operation of an industrial inverter. Using an oscilloscope, the pulses on both windings are measured; they must correspond to each other.
  8. Now you need to check the operation of the welding inverter with connected power capacitors. We change the supply voltage from 16 volts to 220 volts, connecting the device directly to the electrical network. Using an oscilloscope connected to the output MOSFET transistors, we monitor the waveform; it should correspond to tests at reduced 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 households. In addition, due to the use of a built-in rectifier and current regulator, with the help of such a welding inverter it is possible to achieve better welding results compared to the results that can be achieved when using traditional devices whose transformers are made of electrical steel.

I recently assembled a welding inverter from Barmaley, for a maximum current of 160 amperes, a single-board version. This scheme is named after its author - Barmaley. Here is the electrical diagram and PCB file.

Inverter circuit for welding

Inverter operation: power from a single-phase 220 Volt network is rectified, smoothed by capacitors and supplied to transistor switches, which convert DC voltage into high-frequency alternating voltage supplied to a ferrite transformer. Thanks to the high frequency, we have a reduction in the dimensions of the power trance and, as a result, we use ferrite rather than iron. Next is a step-down transformer, followed by a rectifier and a choke.

Oscillograms for controlling field-effect transistors. I measured it on a ks213b zener diode without power switches, fill factor 43 and frequency 33.

In its version, power keys IRG4PC50U replaced with more modern ones IRGP4063DPBF. I replaced the ks213b zener diode with two 15-volt, 1.3-watt zener diodes connected back-to-back, since the previous ks213b device got a little hot. After replacing the problem immediately disappeared. Everything else remains as in the diagram.

This is an oscillogram of the collector-emitter of the lower switch (according to the diagram). When power is supplied at 310 volts through a 150 watt lamp. The oscilloscope costs 5 volt divisions and 5 µs divisions. through the divisor multiplied by 10.

The power transformer is wound on a core B66371-G-X187, N87, E70/33/32 EPCOS Winding data: first the primary floor, the secondary, and again the remains of the primary. The wire on the primary and on the secondary is 0.6 mm in diameter. Primary - 10 wires 0.6 twisted together 18 turns (total). The first row just fits 9 turns. Next, put the remains of the primary aside, wind 6 turns of 0.6 wire folded into 50 pieces and also twisted. And then again the remains of the primary, that is, 9 turns. Don’t forget the interlayer insulation (I used several layers of cash paper, 5 or 6, we don’t do it any more, otherwise the winding won’t fit into the window). Each layer was impregnated with epoxy.

Then we assemble everything, a gap of 0.1 mm is needed between the halves of the E70 ferrite, and we put a gasket from a regular cash receipt on the outer cores. We pull everything together and glue it together.

I spray painted it with matte black paint, then varnished it. Yes, I almost forgot, when we twist each winding, we wrap it with masking tape - we insulate it, so to speak. Don’t forget to mark the beginning and ends of the windings; this will be useful for further phasing and assembly. If the phasing of the transformer is incorrect, the device will cook at half strength.

When the inverter is connected to the network, charging of the output capacitors begins. The initial charging current is very high, comparable to a short circuit, and can lead to burnout of the diode bridge. Not to mention the fact that for the air conditioners this is also fraught with failure. To avoid such a sharp jump in current at the moment of switching on, capacitor charge limiters are installed. In Barmaley’s circuit, these are 2 resistors of 30 Ohms, with a power of 5 watts each, for a total of 15 Ohms x 10 Watts. The resistor limits the charging current of the capacitors and after charging them, you can supply power directly, bypassing these resistors, which is what the relay does.

In the welding machine according to the Barmaley scheme, the WJ115-1A-12VDC-S relay is used. Relay coil power supply - 12 volt DC, switching load 20 Ampere, 220 Volt AC. In homemade products, the use of 12 Volt, 30 Ampere automotive relays is very common. However, they are not designed for switching currents up to 20 Amps of mains voltage, but, nevertheless, they are cheap, accessible and fully cope with their task.

It is better to use a regular wire-wound resistor as a current-limiting resistor; it will withstand any overload and is cheaper than imported ones. For example, C5-37 V 10 (20 Ohm, 10 Watt, wire). Instead of resistors, you can put current-limiting capacitors in series in the alternating voltage circuit. For example K73-17, 400 Volt, total capacity 5-10 µF. Capacitors are 3 uF, charge a capacitance of 2000 uF in about 5 seconds. The calculation of the capacitor charging current is as follows: 1 µF limits the current at 70 milliamps. It turns out 3 uF at the level of 70x3 = 210 milliamps.

Finally I put everything together and launched it. The current limit was set to 165 amperes, now let’s put the welding inverter in a good case. The cost of a homemade inverter is approximately 2,500 rubles - I ordered the parts on the Internet.

I got the wire from the rewinding shop. You can also remove the wire from the TVs from the demagnetizing circuit from the kinescope (this is almost a ready-made secondary one). The throttle was made from E65, copper strip 5 mm wide and 2 mm thick - 18 turns. The inductance was adjusted to 84 μH by increasing the gap between the halves; it was 4 mm. You can also wind it with 0.6 mm wire instead of a strip, but it will be more difficult to lay it down. The primary on the transformer can be wound with a 1.2 mm wire, a set of 5 pieces of 18 turns, but you can also use 0.4 mm wires to calculate the number of wires for the cross-section you need, that is, for example, 15 pieces of 0.4 mm 18 turns.

After installing and setting up the circuit on the board, I put everything together. Barmaley passed the tests successfully: he pulled the three and four electrodes calmly. The current limit was set to 165 Amps. Assembled and tested the device: Arcee .

Discuss the article WELDING INVERTER BARMALY

Even a home craftsman who does not have deep knowledge of electrical processes can assemble a homemade inverter welding machine. The main requirement is compliance with installation technology, compliance with the diagram and understanding of the operating principle of the device. If you create an inverter with your own hands, then its parameters and performance will not differ significantly from factory models, but the savings can be decent.

A simple homemade inverter-type device will allow you to carry out high-quality welding operations. Even an inverter with a simple circuit allows you to work with an electrode from 3 to 5 mm and an arc up to 1 cm.

Characteristics

A similar welder for home use may have the following parameters:

  • Voltage level – 220 volts.
  • Input current - 32 amperes;
  • Output current - 250 amperes.

An inverter that operates from a 220 V household power supply is suitable for domestic use. If necessary, it is possible to assemble a more powerful device operating from 380 V. It has higher productivity compared to a single-phase inverter welding machine.

Features of operation

First you need to understand how the inverter functions. Essentially, it is a computer power supply. In it you can observe the transformation of electricity in the following sequence:

  • The input AC voltage is transformed into DC.
  • The 50 Hz current consumption is converted to high frequency.
  • The output voltage decreases.
  • The output current is rectified, the required frequency is maintained.

Such transformations are necessary to reduce the weight of equipment and its dimensions.

Transformer welding machines have sensitive weight and dimensions. Due to the significant current strength, arc welding can be carried out in them. To increase the current and lower the voltage, the secondary winding involves the presence of fewer turns, and the cross-section of the wire increases. As a result, the transformer welder is heavy and bulky.

The inverter principle makes it possible to reduce these figures significantly. The circuitry of such a device involves increasing the frequency to 60-80 kHz, which helps reduce its size and weight. To implement such a conversion, power field-effect transistors are used. They communicate with each other precisely at this frequency. They are powered by direct current coming from a rectifying device, which is a diode bridge. The voltage value is equalized by capacitors.

After the transistors, the current is transferred to a step-down transformer. It is a small coil. The small dimensions of the inverter transformer coil are ensured by a frequency that is greatly increased by field-effect transistors. The result is characteristics similar to those of a transformer device, but with less weight and size.

What is needed for assembly

To create such a homemade product, it is necessary to take into account the characteristics of the circuit, i.e., consumed voltage and current. An output current of 250 amps is enough to create a durable seam. To implement the idea you will need the following details:

  • Transformer.
  • Primary winding (100 turns with wire ⌀ 0.3 mm).
  • 3 windings. In the outer: 20 turns, ⌀ 0.35 mm. On average: 15 and ⌀ 0.2. In internal 15 and ⌀ 1 mm.

In addition, before starting to assemble the inverter, it is necessary to prepare tools and elements for developing electronic circuits. You will need:

  • Screwdrivers;
  • Soldering iron;
  • Hacksaw for metal;
  • Fasteners;
  • Electronic elements;
  • Copper wires;
  • Thermal paper;
  • Electrical steel;
  • Fiberglass;
  • Textolite;
  • Mica.

Scheme

The electrical circuit diagram of an inverter is one of the most critical moments when designing or repairing an inverter apparatus. Therefore, we recommend that you first study the options in detail and then begin to implement them.

List of radioelements


Power part

The power supply plays one of the leading roles in the inverter apparatus. It is a transformer wound on ferrite. It provides a stable decrease in voltage and increase in current value. You need 2 cores Ш20х208 2000 nm.

Thermal paper is used to create thermal insulation between the inverter windings. To minimize the negative impact of constant voltage drops in the electrical network, the winding should be carried out across the entire width of the core.

For the winding of the transformer, experts recommend the use of copper sheet having a width of 40 mm and a thickness of 0.3 mm. It needs to be wrapped in 0.05 millimeter thermal paper (cash register tape). Experts explain this by the fact that during welding, high-frequency current is displaced onto the surface of thick wires, while the core is not used and a lot of heat is generated. Therefore, ordinary conductors are not suitable. This effect can be eliminated by using conductors with a significant surface area.

An analogue of copper sheet that can be used is PEV wire with a cross-section of 0.5-0.7 mm. It is multi-core with air gaps between the cores, which reduces heating.

After creating the primary layer, a shielding wire with fiberglass is wound in the same direction. This wire (of similar diameter) must completely cover the fiberglass. It is necessary to proceed in the same way with other windings of the transformer. They must be isolated from each other using the above insulators.

In order for the voltage from the transformer to the relay to be at the level of 20 - 25 volts, it is necessary to select the correct resistors. The main task of the inverter power supply is to change alternating current into direct current. This is implemented by a diode bridge circuit of the “oblique bridge” type.

During operation, the diodes of the inverter device will heat up. Therefore, they must be placed on the radiator. It is allowed to use radiators from computers. Fortunately, they are now widespread and inexpensive. You will need 2 radiators. The upper element of the bridge is fixed on one, and the lower element on the second. In this case, when installing the first one, it is necessary to use a mica gasket, and in the second case, thermal paste.

The output of the diode bridge is in the same direction as the output of the transistors. Use wires no longer than 15 cm. The basis of the inverter unit is transistors. The bridge must be separated from the power supply by a sheet of metal, which is subsequently attached to the case.

Installation of diodes on a radiator

Inverter unit

The main task of this inverter unit is to transform the rectified current into a high-frequency alternating component. Power transistors that open and close at high frequencies are designed to perform this function.

It is better to create a converting unit of an inverter apparatus not with one more powerful transistor, but with the use of several weaker ones. Due to this, the frequency of the current is stabilized and the noise effect during welding is minimized.

The inverter circuit must contain capacitors. Connected in a series circuit. Perform 2 main tasks:

  • Minimize resonant emissions of the power supply.
  • Reduce losses of the transistor unit that occur after switching on. This is explained by the fact that the transistor opens faster. The closing speed is noticeably slower. In this case, a loss of current occurs and the switches in the transistor unit heat up.

Cooling system

The power elements of the converter will heat up significantly during welding. This may cause a breakdown. To eliminate this, in addition to the radiators mentioned above, you should use a fan that eliminates overheating and ensures stable cooling.

One fan of sufficient power may be sufficient. However, when using elements of an old PC, you may need up to 6 pieces, 3 of which must be placed near the transformer.

To completely protect a homemade inverter from overheating, you can use a temperature sensor. It should be mounted on the hottest element with a radiator. The element will be able to turn off the power when a certain temperature is reached, and the indication will signal a critical level.

For efficient and stable operation of the inverter ventilation system, it is necessary to ensure constant correct air intake. To do this, the holes through which air will be taken in should not be blocked by anything. A sufficient number of holes should be provided in the inverter housing. In this case, they need to be placed on opposite surfaces of the body.

Control

When placing the electronic boards of the device, it is possible to use foil-coated PCB with a thickness of 0.5 - 1 millimeter.

To ensure automatic control of inverter welding, you should buy and install a PWM controller. It will stabilize the welding current and voltage level. For convenient control, all controls and connection points are located on the front part.

Frame

After creating the main elements of inverter welding, you can begin preparing the body parts. When planning, you need to take into account the width of the transformer, since it must be placed unobstructed in the housing. Based on this size, approximately 70% of the space should be added for the remaining parts. The protective casing can be made from sheet iron, 0.5-1 millimeters thick. The elements can be connected using welding or bolts. A more sophisticated option would be a one-piece design made from curved raw materials. Handles and belt mounts are required to carry the device.

When designing an inverter, consideration should be given to the possibility of easy disassembly to access internal components for easy repair. The front side must also contain:

  • Current switch;
  • A button that will turn the device on/off;
  • Light indication elements;
  • Connectors for connecting cables.

Factory inverters are powder coated. You can use regular paint at home. It is worth applying a coating to prevent the appearance of rust.

Connection

The assembled welding machine must be connected to the electrical network. When connecting to an outlet, be sure to have a fuse or circuit breaker. For protection, a 25 amp circuit breaker can be installed at the inverter input.

If the connection point is remote, you can use an extension cord.

The device is turned on according to the standard scheme - using the “on/off” button. The indication should light up, usually a green LED is used for this.

The connection to the network must be made with a wire having a cross-section of at least 1.5 mm 2 . However, the optimal cross-section will be a wire of 2.5 mm 2.

Before connecting the device to the electrical network, you should check that all high-voltage elements are insulated from the housing parts.

Functionality check

After all assembly and debugging work has been completed, it is necessary to check the functionality of the created inverter.

According to the recommendations of specialists, it is necessary to check the current and voltage of the device using an oscilloscope. The lower voltage loop should be up to 500 volts, not exceeding 550 V. If all design requirements are met, the voltage level will be 330 - 350 volts. But this method is not always available, because not every home has its own similar measuring device.

Often the inspection is carried out in action directly by the welder. To do this, a test seam is created with complete burnout of the electrode. At the end of the test welding, you need to check the temperature on the transformer. If it goes off scale, then there are some deficiencies in the circuit and everything should be double-checked.

If the temperature of the power unit is normal, then you can carry out another 2-3 test runs. After this, check the temperature of the radiators. They may also overheat. If after two to three minutes they return to normal, then you can safely continue working.

The assembly procedure of the device is not complicated. The most important step is setting up the inverter device. You may need to seek help from a specialist.

1. First you need to connect 15 volts to PWM while simultaneously connecting one convector. This way you can reduce heat and noise during operation.

2. To close the resistor you need to connect a relay. It is connected when the capacitors have finished charging. Due to this, you can significantly reduce voltage fluctuations when connecting to a 220 volt power supply. Without a resistor, an explosion is possible when connected directly.

3. Check the operation of the resistor closure relay a couple of seconds after current is supplied to the PWM board. Check for the presence of a rectangular pulse on the board after the relay has been tested.

4. Supply 15 volt power to the bridge to check its functionality and correct assembly. The current should be no higher than 100 mA at idle.

5. Checking the correct placement of phases. Use an oscilloscope. The bridge circuit is supplied with 200 volts from the capacitors through the lamp with a load of 200 W. The PWM frequency is set to 55 kHz. An oscilloscope is connected, the signal shape and voltage level are checked (no more than 350 volts).

To determine the frequency of the device, you should slowly lower the PWM frequency until a slight turn occurs on the IGBT switch. The resulting frequency value must be divided by 2 and the oversaturation frequency added. The result is an operating frequency oscillation of the transformer.

The transformer of the device should not make any noise. If they are present, the polarity must be checked. The diode bridge can be connected to power for the test through suitable household appliances. For example, a kettle with a power of 3000 W is suitable.

The conductors going to the PWM must be short. They need to be twisted and placed further from the source of interference.

6. The current is gradually increased using a resistor. In this case, you need to listen to the inverter and monitor the values ​​on the oscilloscope. There should be no more than 500 volts on the lower key. The average value is 340. If noise is present, the IGBT may fail.

7. Start welding after 10 seconds. The radiators are checked, if they have not heated up, then extend the work for another 20 seconds. After re-checking, welding can last from one minute or longer.

Safety

All operations performed, with the exception of performance testing, must be carried out exclusively on de-energized equipment. It is recommended to check each element in advance so that after installation it does not fail due to overvoltage. Basic electrical safety rules are also mandatory.

Thus, almost anyone can do homemade inverter welding. The proposed description should help you understand all the nuances. If you study video tutorials and photo materials, then assembling the device will not be difficult.

Inverter welding is a modern device that is widely popular due to the light 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 inverter welding with your own hands. 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 diagrams look like.

Features of the inverter operation

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

2) Current with a constant sinusoid is converted into 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 electrical circuit transformations is necessary in order to be able to reduce the weight of the device and its overall dimensions. After all, as you know, old welding machines, the principle of which is based on reducing the voltage and increasing the current on the secondary winding of the transformer. As a result, due to the high current value, 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, you can notice that a transformer-type welding machine not only has significant dimensions, but also a decent weight.

To solve the problem, an option was proposed for implementing a welding machine using an inverter circuit. The principle of the inverter is based on increasing the frequency of the current 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 thousands of times, which became possible thanks to the use of field-effect transistors.

Transistors provide communication with each other at a frequency of about 60-80 kHz. The transistor power supply circuit receives a constant current value, which is ensured by the use of a rectifier. A diode bridge is used as a rectifier, and capacitors provide voltage equalization.

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

What is needed to assemble an inverter

To assemble inverter welding yourself, you need to know that the circuit is designed, first of all, for a consuming voltage of 220 Volts and a current of 32 Amps. After energy conversion, the output current will increase almost 8 times and reach 250 Amperes. This current is sufficient 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 wire diameter 1 mm;

- medium: 15 turns and diameter 0.2 mm;

— external: 20 turns and diameter 0.35 mm.

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

- copper wires;

- fiberglass;

— textolite;

— electrical steel;

- cotton material.

What does an inverter welding circuit look like?

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

Electrical circuit of inverter welding

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

Inverter welding power supply diagram

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

To control the gates, conductors are used, which must be soldered close to the transistors. These conductors are connected to each other in pairs, and the cross-section of these conductors does not play a special role. The only thing that is important 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 specialist to help you figure it out. For example, below is a diagram of the power part of an inverter welding machine.

Diagram of the power part of inverter welding

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

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

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

2) Assembling the power supply. An important element of the power supply is the transformer. It is recommended to use 7x7 or 8x8 ferrite as the base of the transformer. For the primary winding of the transformer, it is necessary to wind the wire across the entire width of the core. This important feature entails improved operation of the device when voltage surges occur. It is imperative to use PEV-2 copper wires as wire, and if there is no busbar, the wires are connected into one bundle. Fiberglass is used to insulate the primary winding. On top, after the layer of fiberglass, it is necessary to wind turns of shielding wires.

Transformer with primary and secondary windings for creating inverter welding

3) Power part. A step-down transformer acts as a power unit. Two types of cores are used as a core for a step-down transformer: Ш20х208 2000 nm. It is important to provide a gap between both elements, which is solved by placing newsprint. The secondary winding of a transformer is characterized by winding turns in several layers. It is necessary to lay three layers of wires on the secondary winding of the transformer, and fluoroplastic gaskets are installed between them. It is important to place a reinforced insulating layer between the windings, which will avoid voltage breakdown on 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, it is necessary to leave an air gap. A current transformer is assembled on a ferrite core, which is connected to the circuit to the positive line. The core must be wrapped with thermal paper, so it is best to use cash register tape as this paper. Rectifier diodes are attached to the aluminum radiator plate. The outputs of these diodes should be connected with bare wires with a cross-section of 4 mm.

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

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

Aluminum plate inverter

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

Rectifier bridge on the cooling radiator

Photo of the thermostat

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 device body so that they work to extract air.

Fresh air will enter the system thanks to the holes in the device body. The system unit already has these holes, and if you use any other material, do not forget to provide a flow of fresh air.

5) Soldering the board is a key factor since the board is what the entire circuit is based on. It is important to install diodes and transistors on the board in opposite directions 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 arrangement of capacitors with a capacity of 0.15 μF makes it possible to dump excess power back into the circuit. At the output of the transformer there are capacitors and snubbers, with the help of which the overvoltages at the output of the secondary winding are suppressed.

6) Setting up and debugging work. After the inverter welding has been assembled, several more procedures will need to be carried out, in particular, setting up the operation of the unit. To do this, connect a voltage of 15 volts to the PWM (pulse width modulator) and power the cooler. Additionally connected to the relay circuit through resistor R11. The relay is included in the circuit in order to avoid voltage surges in the 220 V network. It is imperative to monitor the relay’s activation, and then apply power to the PWM. As a result, a picture should be observed in which rectangular areas in the PWM diagram should disappear.

The device of a homemade inverter with a description of the elements

You can judge whether the circuit is connected correctly if the relay outputs 150 mA during setup. If a weak signal is observed, this indicates that the board connection is incorrect. There may be a breakdown in one of the windings, so to eliminate interference you will need to shorten all power supply wires.

Inverter welding in a computer system case

Checking the device's functionality

After all the assembly and debugging work has been completed, all that remains is to check the functionality of the resulting welding machine. To do this, the device is powered from a 220 V power supply, then high current values ​​are set and the readings are verified using an oscilloscope. In the lower loop, the voltage should be within 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 this, it is important to monitor the temperature of the transformer. If the transformer simply boils, then the circuit has its shortcomings and it is better not to continue the work process.

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

Checking the welding machine

How to use a homemade device

After connecting a homemade device to the circuit, the controller will automatically set a certain current strength. If the wire voltage is less than 100 Volts, this indicates a malfunction of the device. You will have to disassemble the device and recheck the correct assembly again.

Using this type of welding machine, you can 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.

Inverter welding is an indispensable thing in any owner’s garage, so if you have not yet acquired such a tool, then you can make it yourself.