Welding inverter circuit - schematic diagram of inverter welding

The circuit of a welding inverter is fundamentally different from the design of its predecessor, the welding transformer. The basis of the design of previous welding machines was a step-down transformer, which made them large and heavy. Modern welding inverters, thanks to the use of advanced developments in their production, are lightweight and compact devices characterized by wide functionality.

Welding inverter without cover

The main element of the electrical circuit of any welding inverter is a pulse converter that generates high-frequency current. It is thanks to this that the use of an inverter makes it possible to easily ignite the welding arc and maintain it in a stable state throughout the welding process. The welding inverter circuit, depending on the model, may have certain features, but the principle of its operation, which will be discussed below, remains unchanged.

What types of inverters are available on the modern market?

For a certain type of welding, you should choose the right inverter equipment, each type of which has a specific electrical circuit and, accordingly, special technical characteristics and functionality.

Inverters produced by modern manufacturers can be used equally successfully both in industrial enterprises and in everyday life. Developers are constantly improving the electrical circuit diagrams of inverter devices, which allows them to be equipped with new functions and improve their technical characteristics.

The number of connectors and controls on the front panel speaks volumes about the capabilities of the welding inverter

Inverter devices as the main equipment are widely used to perform the following technological operations:

electric arc welding with consumable and non-consumable electrodes;
welding using semi-automatic and automatic technologies;
plasma cutting, etc.

In addition, inverter machines are the most efficient type of equipment used for welding aluminum, stainless steel and other difficult-to-weld metals. Welding inverters, regardless of the features of their electrical circuit, allow you to obtain high-quality, reliable and neat welds made using any technology. At the same time, what is important is that the compact and not too heavy inverter machine, if necessary, can be easily moved at any time to the place where welding work will be performed.

Mobility is one of the advantages of inverter devices

What does the design of a welding inverter include?

The welding inverter circuit, which determines its technical characteristics and functionality, includes such mandatory elements as:

a unit that provides electrical power to the power part of the device (it consists of a rectifier, a capacitive filter and a nonlinear charging circuit);
power part, made on the basis of a single-cycle converter (this part of the electrical circuit also includes a power transformer, a secondary rectifier and an output choke);
power supply unit for elements of the low-current part of the electrical circuit of the inverter apparatus;
PWM controller, which includes a current transformer and a load current sensor;
a block responsible for thermal protection and control of cooling fans (this block of the circuit diagram includes inverter fans and temperature sensors);
controls and indications.

Bottom line

For some specialists, a welding diagram provides an additional hint when assembling units for welding metals, which allows them to quickly complete the desired job. It is quite important to have basic knowledge of electrical engineering.

The availability of welding inverter circuits is determined by their principles, in other words, any master will need either instructions or drawings for assembly. It is worth noting that the electrical circuit diagrams place emphasis on achieving a high level of stability in the welding arc.

How does a welding inverter work?

The formation of a high current, with the help of which an electric arc is created to melt the edges of the parts being joined and the filler material, is what any welding machine is designed for. For the same purposes, an inverter apparatus is also needed, which allows the generation of welding current with a wide range of characteristics.

In its simplest form, the principle of operation of the inverter looks like this.

Alternating current with a frequency of 50 Hz from a regular electrical network is supplied to the rectifier, where it is converted into direct current.
After the rectifier, the direct current is smoothed using a special filter.
From the filter, direct current flows directly to the inverter, whose task is to convert it again into alternating current, but at a higher frequency.
After this, using a transformer, the voltage of the alternating high-frequency current is reduced, which makes it possible to increase its strength.

Block diagram of an inverter type welding machine

In order to understand the importance of each element of the electrical circuit diagram of an inverter device, it is worth considering its operation in more detail.

Device repair

Repair of these devices to convert one type of voltage to another is best done in service centers, where the personnel are highly qualified and will subsequently provide guarantees for the work performed. Most often, any modern high-quality converters consist of several hundred electronic parts, and if there are no obvious burnt elements, then it will be very difficult to find a breakdown and fix it.

It will be interesting➡ Why do you need a frequency converter

Some Chinese inexpensive devices of this type, in general, are in principle deprived of the possibility of repairing them, which cannot be said about domestic manufacturers. Yes, they may be a little bulky and not compact, but they can be repaired, since many of their parts can be replaced with similar ones.

Processes occurring in the electrical circuit of a welding inverter

The circuit of an inverter-type welding machine allows you to increase the current frequency from the standard 50 Hz to 60–80 kHz. Due to the fact that high-frequency current is subject to regulation at the output of such a device, compact transformers can be effectively used for this. An increase in the frequency of the current occurs in that part of the inverter electrical circuit where the circuit with powerful power transistors is located. As you know, only direct current is supplied to transistors, which is why a rectifier is needed at the input of the device.

Schematic diagram of the factory welding inverter "Resanta" (click to enlarge)

Inverter circuit from the German manufacturer FUBAG with a number of additional functions (click to enlarge)

An example of a circuit diagram of a welding inverter for self-production (click to enlarge)

The electrical circuit diagram of the inverter device consists of two main parts: the power section and the control circuit. The first element of the power section of the circuit is a diode bridge. The task of such a bridge is precisely to convert alternating current into direct current.

In the direct current converted from alternating current in the diode bridge, pulses may occur that need to be smoothed out. To do this, a filter consisting of capacitors of predominantly electrolytic type is installed after the diode bridge. It is important to know that the voltage that comes out of the diode bridge is approximately 1.4 times greater than its value at the input. When converting AC to DC, rectifier diodes become very hot, which can seriously affect their performance.

Components of a welding inverter using the example of a homemade machine

To protect them, as well as other elements of the rectifier from overheating, radiators are used in this part of the electrical circuit. In addition, a thermal fuse is installed on the diode bridge itself, the task of which is to turn off the power supply if the diode bridge has heated up to a temperature exceeding 80–90 degrees.

High-frequency interference generated during operation of the inverter device can enter the electrical network through its input. To prevent this from happening, an electromagnetic compatibility filter is installed in front of the rectifier block of the circuit. Such a filter consists of a choke and several capacitors.

Inverter power supply

The inverter itself, which converts direct current into alternating current, but with a much higher frequency, is assembled from transistors using an “oblique bridge” circuit. The switching frequency of transistors, due to which the alternating current is generated, can be tens or hundreds of kilohertz. The high-frequency alternating current thus obtained has a rectangular amplitude.

A voltage-reducing transformer installed behind the inverter unit allows you to obtain a current of sufficient strength at the output of the device so that you can effectively perform welding work with its help. In order to obtain direct current using an inverter apparatus, a powerful rectifier, also assembled on a diode bridge, is connected after the step-down transformer.

Transistors for the power module of the welding inverter

Methods of application

Current converters from 12 to 220 V are especially widely used in places where there is no electricity supply. Any car battery can be used to supply 220 V to supply electricity to a country house. It should be remembered that voltage inverters from 12 V to 220 V convert a form of electrical current that limits its use. That is, not all electrical devices are able to perceive voltage supplied graphically in an almost rectangular shape. Structurally, inverters are:

If we consider the output power, then car batteries produce a maximum of 500 W, and stationary ones - up to 10 thousand W. If, when leaving the city on vacation or at a summer cottage, it is necessary to illuminate a room or overnight stay in the evening, then the easiest way is to connect an LED lamp to the converter.

Energy consumption of a car battery is a very unprofitable process, since the efficiency of the battery decreases with increasing load.

Stationary voltage converters 12-220 volts are mainly used to transform electrical energy from solar panels and wind structures. Mobile inverter converters are connected to a network from 12 to 50 V and are considered unpretentious in choosing a power source. For car maintenance, this device is a charger with a socket.

Inverter protection and control elements

Several elements in its circuit diagram allow you to avoid the influence of negative factors on the operation of the inverter.

To ensure that transistors that convert direct current into alternating current do not burn out during their operation, special damping (RC) circuits are used. All electrical circuit blocks that operate under heavy load and become very hot are not only provided with forced cooling, but are also connected to temperature sensors that turn off their power if their heating temperature exceeds a critical value.

Radiators and cooling fans take up significant space inside the inverter

Due to the fact that the filter capacitors, after being charged, can produce a high current, which can burn the inverter transistors, the device must be provided with a smooth start. For this purpose, stabilizers are used.

The circuit of any inverter has a PWM controller, which is responsible for controlling all elements of its electrical circuit. From the PWM controller, electrical signals are sent to a field-effect transistor, and from it to an isolation transformer, which simultaneously has two output windings. The PWM controller, through other elements of the electrical circuit, also supplies control signals to the power diodes and power transistors of the inverter unit. In order for the controller to effectively control all elements of the inverter's electrical circuit, it is also necessary to supply electrical signals to it.

To generate such signals, an operational amplifier is used, the input of which is supplied with the output current generated in the inverter. If the values of the latter diverge from the specified parameters, the operational amplifier generates a control signal to the controller. In addition, the operational amplifier receives signals from all protective circuits. This is necessary so that he can disconnect the inverter from the power supply at the moment when a critical situation arises in its electrical circuit.

Where is it used?

The scope of application of three-phase inverters is quite large, and in some cases it is simply impossible to do without them. Motor control will be much more efficient when modified modern three-phase inverter devices are used. They are included in the general circuit with single- and three-phase asynchronous motors, commutator units, as well as three-phase DC motors.

To control different types of engines, their own modes are used, supported by appropriate software. This makes it possible to connect almost any motors whose windings have from 1 to 3 phases. As an exception, we can note the design of bipolar two-phase stepper motors equipped with two independent windings.

The components of such an inverter include the main control board, power inputs and outputs, as well as an interface for entering the necessary data and displaying current readings on a display or scoreboard. Quite often, control is carried out using a computer. The inverter is connected through a special connector installed on the board.

Modern control inverters have a demonstration mode, in which the main functions are shown one by one - start and stop, speed change and reverse. To switch between functions there are 4 buttons located on the board.

Advantages and disadvantages of inverter-type welding machines

Inverter welding machines, which replaced the usual transformers, have a number of significant advantages.

Thanks to a completely different approach to the formation and regulation of welding current, the weight of such devices is only 5–12 kg, while welding transformers weigh 18–35 kg.
Inverters have very high efficiency (about 90%). This is explained by the fact that they spend significantly less excess energy on heating the components. Welding transformers, unlike inverter devices, get very hot.
Due to such high efficiency, inverters consume 2 times less electrical energy than conventional transformers for welding.
The high versatility of inverter machines is explained by the ability to regulate the welding current over a wide range with their help. Thanks to this, the same device can be used for welding parts made of different metals, as well as for welding using different technologies.
Most modern inverter models are equipped with options that minimize the impact of welder errors on the technological process. Such options, in particular, include “Anti-stick” and “Arc Force” (fast ignition).
Exceptional stability of the voltage supplied to the welding arc is ensured by the automatic elements of the inverter electrical circuit. In this case, automation not only takes into account and smoothes out differences in input voltage, but also corrects even such interference as the attenuation of the welding arc due to strong wind.
Welding using inverter equipment can be performed with any type of electrode.
Some models of modern welding inverters have a programming function, which allows you to accurately and quickly configure their modes when performing a certain type of work.

Like any complex technical devices, welding inverters have a number of disadvantages that you also need to be aware of.

Inverters are highly expensive, 20–50% higher than the cost of conventional welding transformers.
The most vulnerable and often failing elements of inverter devices are transistors, the cost of which can be up to 60% of the price of the entire device. Accordingly, repairing a welding inverter is quite an expensive undertaking.
Due to the complexity of their electrical circuitry, inverters are not recommended for use in bad weather conditions and at low temperatures, which seriously limits their scope of application. In order to use such a device in field conditions, it is necessary to prepare a special closed and heated area.

When welding work performed using an inverter, long wires cannot be used, as they induce interference that negatively affects the operation of the device. For this reason, the wires for inverters are made quite short (about 2 meters), which makes welding work somewhat inconvenient.

Popular models

A lot of inverter models are produced in our country. They can be used both in industrial production and in domestic conditions. The following are considered popular:

AIRLINE API-150−01 - the permissible power threshold of the device is 150 W. The case is made of durable plastic that can withstand high temperatures. The car inverter is connected from the cigarette lighter, which is located in the passenger compartment. You can connect several electrical appliances to this device, the total power of which is no more than 150 W. The device is protected against short circuits and surges in incoming voltage.
Jet A JA-P11 - if there is no electrical power network nearby, then this device will help out in any situation. The maximum power of the device is about 300 W. There is protection against low supply voltage, overheating and overload.
Titan HW-150E1 150 W - makes it possible to use electrical appliances up to 150 W. It is connected from the car cigarette lighter and the output voltage is 220-240 V. The weight of the device does not exceed 0.5 kg, which makes it very convenient on long trips.