DIY welding inverter

DIY welding inverter

The method of welding metals today has many methods and most of them are based on the use of electricity. Electric welding, in turn, is also divided into several types, including the inverter method.

The latter became popular relatively recently, and before small-sized and easy-to-carry devices appeared on store shelves, home welding was the lot of a few. After the massive introduction of welding inverters, it turned out that the principle of the device and operation of this device is quite simple and, if desired, you can assemble the same one yourself.

Description

An inverter is a device that converts direct electric current into alternating current, and in an inverter-type welding machine, a double conversion occurs:

1. An alternating current with a force not exceeding 5 amperes, with a voltage of 220/380 volts and a frequency of 50 Hz is converted into direct current with the same values.
2. The resulting direct current is converted into alternating current with a voltage of several tens of volts and a current strength of up to several hundred amperes.

This transformation is more beneficial, since the resulting characteristics of the welding current have high stability and easily controlled, which makes it possible to adjust the optimal welding mode for different sizes of welded details.

Welding inverters are monoblock devices, and their main advantage is ergonomics. Unlike welding transformers, including those emitting direct current, inverters can be carried one person, and those with low power, have a weight of only a few kilograms and are easily hung on shoulder.

The transformation takes place at the expense of a transformer and electronic microcircuits that require high-quality cooling, therefore a powerful fan is also placed in the case. Despite the apparent complexity, the welding inverter can be assembled with your own hands. Such a device will be able to provide welding no worse than its factory counterparts.

Principle of operation

The main element of the system is a power transformer with a rectifier. Its secondary winding is very hot, therefore, when assembling the device, it is very important to place it in the path of the outgoing air flow from the fan.

The rectified current is passed through a triode filter with a high switching frequency, as a result, the frequency of the secondary alternating current can reach 50 kHz. The inverse dependence of the frequency and dimensions of electrical equipment has been known for a long time, which made it possible to give inverters such a modest size. The same principle is successfully used wherever space saving is required, for example, in the on-board network of an aircraft or a submarine, the frequency of the electric current is also measured in thousands of hertz.

In the welding transformer, the electromotive force is converted, while in the inverter, high-frequency currents, which made it possible to significantly reduce the weight of the transformer and reduce the consumption of material for its manufacturing. For overload protection, a fuse is installed on the secondary side, which can be replaced from the front panel. The user can adjust the strength of the current supplied to the electrode using the regulator, the current value is displayed on a digital display.

Application area

It is difficult to imagine construction work that does not involve welding. Welding inverters have significantly expanded the scope of its application, since they have a fairly large share of mobility, in contrast to bulky transformer devices. Today, inverter welding is used:

• For welding ferrous metal parts.
• For welding non-ferrous metal parts.
• When welding is required in difficult-to-pass places, for example, in underground pipelines.
• For welding fittings in production.
• For domestic welding.

In industry, for welding, inverters with automatic and semi-automatic welding wire feed are used, which allows unifying the process and reducing the proportion of manual labor.

Advantages and disadvantages

The main advantage of inverter welding machines is their size, since before that, they had to cook either on stationary post, or else, move a heavy welding transformer using improvised means to the place of welding works.

Thanks to the double conversion, the welding current of the inverter does not depend on the mains and therefore always remains at constant values, which made it possible to avoid such unpleasant phenomena during welding as:

• Sticking electrode.
• No arc at undervoltage in the network.
• Burnt or underburned metal.

The inverter is versatile and suitable for welding cast iron or non-ferrous metals with appropriate electrodes, as well as for TIG welding with non-consumable electrodes. The operator has the ability to adjust the current over a wide range.

The disadvantage of inverters is a relatively high cost compared to transformers, but given the existing advantages, it is completely eliminated. Like any electronics, the microcircuits of the device require careful handling, therefore it is recommended to periodically clean the interior of the dust.

Also, electronics can fail in conditions of low temperatures or high humidity, so the surrounding conditions must be consistent with the passport data of the device.

How to do it yourself?

Although inverter welding machines are widely available in modern design, they have become available relatively recently, they are nothing new. In fact, only convenient digital control and more modern electronic components have been added.

The principle of operation, like the device itself, was developed several decades ago, and even today, many assembly schemes are relevant. You can assemble the inverter yourself by having old electrical parts, based on modern electronic components. Such a device will come out much cheaper than the factory counterpart.

Required materials and tools

To assemble the device you will need:

• Ferrite core for power transformer.
• Copper bar or wire to create windings.
• Fixing bracket for connecting the halves of the core.
• Heat-resistant electrical tape.
• Computer fan.
• Transistors.
• Soldering iron, pliers, wire cutters.

Schemes

To date, all welding inverter circuits are unified and built on the basis of the use of a pulse transformer and powerful MOSFET transistors.

Each of the manufacturers makes minor changes in the form of proprietary developments, however, in general, the functionality of the device does not undergo any significant changes.

The schematic diagram of Yuri Negulyaev, a scientist and developer of a domestic inverter-type welding machine, can also be taken as a basis.

Step by step guide

1. To accommodate all the elements, you must select the case. It is recommended to use an old system computer unit, as there are already provided ventilation holes.
2. It is necessary to increase the strength of the case, since the weight of the unit can reach up to ten kilograms. For this, metal corners are installed in the corners with threaded fasteners.
3. Primary winding of the transformer - the wire is wound over the entire width of the frame, this contributes to the stable operation of the transformer with a voltage drop. For winding, only copper wires are used, in the absence of a bus, several wires are connected in a bundle.
4. The secondary winding of the transformer is wound in several layers, for this they use several wires with a cross section of 2 mm, connected in a bundle.
5. A reinforced layer of insulation is required between the windings to prevent mains voltage from reaching the secondary winding.
6. An air gap is provided between the transformer core and the windings to ensure air circulation.
7. Separately, a current transformer is made on the ferrite core, which is fixed on the plus line during assembly and connected to the control panel.
8. Transistors must be attached to the radiator, but always through a thermally conductive dielectric gasket. This will provide efficient heat dissipation and short circuit protection.
9. The rectifying circuit diodes are attached in the same way to the aluminum plate. The diode outputs are connected with a bare wire with a cross section of 4 mm.
10. The power conductors inside the housing are routed in such a way as to prevent short circuits.
11. The fan is installed on the rear wall, which will save space and allow blowing several radiators at once.

Setting up the machine

After assembling the machine, additional adjustment is required to obtain the correct values ​​of the welding current and voltage:

1. The mains voltage is supplied to the board and the fan drive.
2. It is necessary to wait until the power capacitors are fully charged, then check the operation of the relay, making sure that there is no voltage across the current-limiting resistor installed in the capacitor circuit, after which close it.
3. With the help of an oscilloscope, the value of the current generated by the inverter is determined, for which the frequency of the pulses arriving at the transformer winding is measured.
4. The welding mode is checked on the control unit, for which a voltmeter is connected to the output of the oscilloscope amplifier. In low-power inverters, the voltage reaches about 15 volts.
5. The operation of the output bridge is checked by supplying a voltage of 16 volts from the power supply. It should be remembered that in idle mode, the unit consumption is about 100 mA and this must be taken into account when making measurements.
6. Work with power capacitors is being tested. The voltage is changed from 16 volts to 220 volts. The oscilloscope is connected to the output transistors and the amplitude of the signal is monitored; it must be identical with that which was tested with reduced voltage.

Maintenance and repair

For assembly, maintenance and repair of inverter type welding machine you must have a sufficient level of electrical engineering knowledge. In the absence of such and the need for repair, the user can only perform routine maintenance:

• Cleaning the device from dust - done with a vacuum cleaner with an open case. If the device is used constantly in construction work, then regular cleaning is necessary.
• Replacing the fuse - protects the circuitry of the device from damage due to overload and short circuits.
• Repair of switching parts on welding cables.

Semiautomatic welding machine from inverter

In technological processes, welding of template parts is required and the highest quality can be achieve using automatic and semi-automatic welding machines with wire feed for welding. You can get such a device from a home-made or industrial inverter only if you have the appropriate knowledge and correct reconfiguration of the control unit.

The fact is that power supplies for manual and semi-automatic welding are designed with different volt-ampere characteristics, and the inverter to which only the wire feeder is added will end up with an uneven seam with torn edges.

Tips & Tricks

1. It should be remembered that power capacitors and transistors in the inverter circuit require additional safety measures, in particular, the mandatory presence of a current-limiting resistor. Applying current without it can cause an explosion.
2. Do not lengthen the welding cables, their length cannot exceed 2.5 meters.