The procedure for assembling homemade welding inverters with your own hands, diagrams and description of testing

Inverter welding machines are widely used in the construction industry due to their high performance and low weight. However, not everyone can afford yourself such a tool. The only way out is to make a do-it-yourself welding inverter. There are many schemes of such devices on the Internet. Many of them are complex and expensive, but there are also budget models.

General information about the welding inverter

Traditional welding machines have a fairly low price, easy maintainability, however, a very significant drawback is not only their weight, but also their dependence on voltage. The electronic meter input is limited to a power of 4 to 5 kW. For welding thick metal, the device consumes significant power and often it becomes impossible to perform work. They were replaced by inverter welding machines.

Purpose and features of functioning

It is used for welding at home, as well as at enterprises, aboutprovides stable combustion and maintaining the welding arc using a high frequency current (other than 50 Hz).

The welding inverter is an ordinary switching power supply, the operation of which is based on the following principles:

1. The input voltage (AC 220V AC inverter mains supply) is converted to DC.
2. The direct current is converted to high frequency alternating current.
3. There is a process of converting the voltage by reducing it.
4. Current rectification and conversion for frequency-safe welding.

Thanks to these moments, the weight and dimensions of the apparatus are reduced. In order to assemble inverter welding with your own hands, you need to know the principle of operation of this apparatus.

The principle of operation of the equipment

In previous models, the main element was a huge powerful power transformer, which makes it possible to receive powerful currents in the secondary winding, necessary for welding. To obtain such a current, it is necessary to use a wire with a large diameter, which affects the weight of the welding machine.

With the invention of a switching power supply, it turned out to be easier to solve the problem with mass and dimensions, because the dimensions and weight of the transformer itself are reduced by several tens or hundreds of times. For example, if you increase the frequency by 6 times, you can reduce dimensions of the transformerbut 3 times. This results in significant material savings.

Thanks to the powerful key transistors used in the inverter circuit, switching occurs with a frequency of 50 to 80 kHz. These transistors only operate on constant voltage.

As you know from the physics course, to obtain a constant voltage, the simplest semiconductor device is used - a diode. The diode passes current in one direction, cutting off negative sinusoidal voltages. But the use of one diode leads to large losses, therefore, a group consisting of powerful diodes is used, which is called a diode bridge.

At the output of the diode bridge, a constant ripple voltage is obtained. A capacitor filter is used to obtain a normal DC voltage. After these transformations, a DC voltage above 220 V appears at the filter output.

A block consisting of a rectifier bridge and filter elements is called a power supply unit (PSU).

The PSU serves as a power source for the inverter circuit. The transistors are connected to a step-down transformer, which is pulsed and operates at frequencies in the range from 50 to 90 kHz. The power of such a transformer is about the same as that of its huge brother - a welding power transformer.

Modernization of such a device becomes lighter, because thanks to its size and weight, there are additional opportunities to increase the stability of the welding machine.

There is a huge number of homemade welding inverters manufacturing, the circuits of which are diverse in functionality and installation methods. Let's analyze each of the homemade models in detail.

Making a resonant inverter

As a basis, you need to use an AT form factor computer power supply, from which you will need a cooler and radiators. Parts are taken from the elementary base of monitors and televisions, otherwise, if they are not there, they are bought on the market. All components are low cost.

Manufacturing recommendations:

1. To simplify the PWM circuit, completely exclude it, since a stabilized voltage obtained by the master oscillator is required.
2. Use zener diodes KC213 to prevent damage to transistors.
3. To reduce pickup and interference, it is necessary to mount high-frequency power transistors near the transformer.
4. The tracks for the power bridge and the power unit on a board made of thick PCB (at least 4 mm) must be made wider (currents up to 30 A flow) and tinned with refractory solder (at least 2 mm).
5. TOpower cable use at least 3 squares.
6. Use double insulation (non-combustible mica or fiberglass sleeves) for high voltage circuits.
7. The choke must be without a metal cover.
8. Good constant ventilation.
9. The power diodes (output) must be protected against breakdown by means of an RC circuit.

Then you need to decide on the parameters of inverter welding with your own hands. It is also possible to use the following characteristics:

1. Output load current: 5 to 120 A.
2. Voltage (no-load): 90 V.
3. The duration of the load may vary. It all depends on the diameter of the electrode: 2 mm = 100%, 3 mm = 80%. The effect of high temperature must be taken into account.
4. Input current: about 10A.
5. Approximate weight: about 3 kg.
6. There must be a regulator for amperage when welding.
7. Type of volt-ampere characteristic providing operation in semi-automatic mode: falling.

Equipment diagram

The main part - the master oscillator is assembled on the SG3524 microcircuit, which is used in all uninterruptible power supplies. The inverter has a low power consumption of about 2.5 kW, which makes it possible to use it in an apartment.

The transformer must be assembledand cores of the E42 type, which is used in old lamp monitors. For the manufacture, you need about 5 pieces of such transformers.

Another transformer should be used for the choke. The rest of the inductance elements are assembled from a 2000HM core. Diodes and transistors must be installed on radiators with KTP-8 or other type of thermal grease. The open circuit voltage is approximately 36 V with an arc length of 4 to 5 mm, which allows novice builders to work with it. Output cables should be placed in ferrite tubes or ferrite rings of the power supply.

The design feature of the circuit is the occurrence of a maximum current in the I winding during resonance.

Scheme 1 - Scheme of welding resonant inverter

Due to its low weight and dimensions, it becomes possible to upgrade the device.

Prevent electrode sticking

For this case, an IRF510 transistor is used, which is a field effect. In addition, it also provides a soft start and input interruption on the SG3524 microcircuit:

1. At high temperatures, the thermal sensor is triggered.
2. Shutdown with a toggle switch.
3. Blocking at short circuit (short circuit).

Simple welding device

This model is designed for a voltage of 220 V and a current of 32A, after conversion, its value will reach 280A. This value is quite enough for a strong seam at a distance of up to 1.5 centimeters.

Scheme and accessories

The main element is the transformer, which is quite difficult to make, but quite realistic.

Basic data:

1. Consists of a ferrite core (7 × 7 or 8 × 8).
2. The primary winding is approximately 100 turns and its diameter is 0.3 mm.
3. Secondary windings - 3 pieces: 15 turns and wire diameter 1 mm; 15 turns - 0.2 mm; 20 turns - 0.35 mm.
4. Materials for the transformer: copper wires of the appropriate diameter, fiberglass, textolite, electrical steel (for iron ore), cotton material.

For a clear understanding of the principle of operation, it is necessary to carefully study the diagram of the main units.

Figure 1 - Block diagram of an inverter welding machine

Explanation of the diagram:

1. AC-to-DC mains rectifier.
2. The surge protector smooths out the ripple.
3. The frequency converter is based on transistors.
4. High frequency welding transformer participates in the transformation of voltage.
5. The power rectifier rectifies the current to a constant of a given frequency.
6. The frequency converter is controlled as a regulator for setting the operating mode.

Power supply unit and power section

The block, consisting of a transformer, rectifier and filter (or filter system), is performed separately from the power section.

Scheme 2 - Schematic diagram of the power supply unit

Conductors (no more than 15 cm long) to control the gates of transistors must be soldered closer to the latter, and the conductors are connected in pairs to each other, their cross section does not matter.

The basis of the power unit is a step-down transformer with a core Ш20 × 208 2000 nm, and the II winding is wound in several layers of wire, the insulation of which is not damaged. It is necessary to wind on the secondary in the following way, isolating the layers: 3 layers, and then a fluoroplastic gasket, then again 3 layers and again a fluoroplastic gasket. This is done to increase overload resistance. Then put a capacitor of at least 1000 V on the II winding.

To ensure air circulation between the layers of the windings, it is necessary to assemble on a ferrite core current transformer connected to positive, and its core should be wrapped in thermal paper (cash register ribbon). Attach the rectifier diodes to the radiator.

Scheme 3 - Power section of the inverter

Inverter unit and cooling

The main purpose of the inverter unit is the process of converting DC to AC high-frequency current. Powerful transistors are used for this, although in some cases it is possible to replace a more powerful one with 2 or more medium power transistors.

Quite good cooling is an important element of the whole device. To do this, you should use a cooler from computer technology, but you should not be limited to one, because you need provide sufficient cooling for the power circuit, the radiators of which are used to remove heat, but this heat is necessary dissipate. For complete protection, it is necessary to mount a temperature sensor (installed on the heating element), thanks to which the power supply from the mains will be disconnected.

Soldering, adjustment and functional check

Soldering is key, because when the parts are positioned correctly, the size of the entire product and the possibility of optimal cooling depend on it. Diodes and transistors are installed in the opposite direction to each other. The input circuit is calculated with a margin of about 300 V.

To configure the function, you need connect the pulse width modulator to 15 V to power the cooler. The relay turns on together with the resistor R11 and should provide 150mA.

After the performed manipulations, it is necessary to proceed directly to checking the operability of the device:

1. Power up the device from the mains.
2. Set high current values.
3. Check the readings on the oscilloscope: in the lower loop, the voltage is about 500 V, but not more than 550. With proper assembly, this voltage will be at least 350 V.
4. Disconnect the oscilloscope and turn off the inverter. Prepare electrodes.
5. Start welding and monitor the transformer, if it boils, then go over the circuit again.
6. After 3-4 seams, the radiators heat up. For cooling, it is necessary to let the device cool down without disconnecting it from the mains (cooling will perform its function).

If this scheme seemed very complicated, then consider the diagram of a very simple device.

The simplest inverter welding device

The model of this unit is very simple and budgetary. It is easy to assemble thanks to its simple circuit diagram.

The entire assembly process can be divided into stages, in addition, it is necessary to collect all the parts, materials:

1. The winding of the transformer includes: winding of copper sheet 4 cm and a diameter of 0.3 mm, paper spacers for a cash register or varnished cloth, using 3 strips when rewinding, and you need to insulate their. Instead of copper tin, you can use a wire consisting of several conductors up to 0.7 mm in diameter (I - 100 turns, II - 15, II - 15 II - 20).
2. A cooler is mounted.
3. The base of the welding machine is connected to a transformer, consisting of diodes, transistors.
4. Capacitors are required to eliminate resonant surges.
5. You must use snubbers for power dissipation (svv-81 and k78−2).
6. Install all elements on the getinax board, based on the configuration dimensions.
7. Bring the LEDs and variable resistor (knob) to the setting and indication panel.
8. Put it all in the case.

Diagram 4 - Diagram of the simplest do-it-yourself welding inverter

After assembly, the device must be configured and diagnosed at the first start to identify operating errors.

Inverter setting:

1. Connect 15V to PWM.
2. Connect the relay after charging the capacitors to close the resistor. Risk of explosion if used directly!
3. At no load, the bridge current should be less than 100mA.
4. Checking the correctness of the installation of the phases of the transformer, using an oscilloscope in 2-a beam. Set the PWM frequency to 55 kHz and in this case the voltage should not exceed 330 V.
5. To determine the frequency of the device itself, it is worth lowering the PWM frequency gradually until a volvulus appears on the IGBT, fixing this indicator (divide by 2 and add the saturation frequency). This is the operating frequency of the transformer.
6. Consumption of the bridge is 150mA.
7. The transformer should not make much noise, if there are noise effects, then pay attention to the polarity.
8. Increase smoothly the inverter current nvariable resistor. In this case, the oscilloscope readings do not exceed 550 V. The optimum is 340 V.
9. Start welding at 5 seconds and gradually increase the time. Cook for no more than 3 minutes, letting the apparatus cool down.

Thus, you can assemble an inverter for welding with your own hands. It is not necessary to use complex schemes, because radio amateurs have found the best solution in a budget option. And the level of complexity of the schemes varies from fairly complex to simple. To assemble a welding inverter with your own hands, it is not necessary to buy expensive parts, but you can use improvised means.