Schematic diagram of the welding inverter nikkei mma 250. Schematic diagram of the welding inverter. Advantages and disadvantages of inverter-type welding machines

The circuit is fundamentally different from the device of its predecessor - a welding transformer. The basis of the design of the former welding machines was a step-down transformer, which made them bulky and heavy. Due to the use of advanced developments in their production, modern welding inverters are lightweight and compact devices with wide functionality.

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 entire 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 on the market today

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

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

  • consumable and non-consumable electrodes;
  • welding by 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 metals that are difficult to weld. Welding inverters, regardless of the features of their electrical circuit, make it possible to obtain high-quality, reliable and accurate welds performed using any technology. At the same time, what is important, a compact and not too heavy inverter machine, if necessary, can be easily transferred at any time to the place where welding work will be performed.

What does the design of the welding inverter include

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

  • a block that provides power to the power part of the device (it consists of a rectifier, a capacitive filter and a non-linear charging circuit);
  • the 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.

How a welding inverter works

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

In its simplest form, the principle looks like this.

  • Alternating current with a frequency of 50 Hz from a conventional electrical network enters the rectifier, where it is converted to direct current.
  • After the rectifier, the direct current is smoothed out 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 that, using a transformer, the voltage of an alternating high-frequency current is lowered, which makes it possible to increase its strength.

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

The processes occurring in the electrical circuit of the welding inverter

The circuit allows you to increase the frequency of the current from the standard 50 Hz to 60–80 kHz. Due to the fact that high-frequency current is regulated 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 electrical circuit of the inverter, where the circuit with powerful power transistors is located. As you know, only direct current is supplied to the transistors, for which 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 features (click to enlarge)

An example of a circuit diagram of a do-it-yourself welding inverter (click to enlarge)

The 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 purpose of such a bridge is precisely to convert alternating current into direct current.

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

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 is heated to a temperature exceeding 80–90 degrees.

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

The inverter itself, which converts already direct current into alternating current, but with a much higher frequency, is assembled from transistors according to the “oblique bridge” scheme. The switching frequency of transistors, due to which the alternating current is formed, can be tens or hundreds of kilohertz. The resulting high-frequency alternating current has a rectangular amplitude.

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

Inverter protection and control elements

To avoid the influence of negative factors on the operation of the inverter, several elements in its circuit diagram allow.

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

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

In the circuit of any inverter, there is a PWM controller that is responsible for controlling all elements of its electrical circuit. From the PWM controller, electrical signals are sent to the 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 manage all the elements of the electrical circuit of the inverter, it is also necessary to apply electrical signals to it.

To generate such signals, an operational amplifier is used, to the input of which the output current generated in the inverter is supplied. When the values ​​of the latter differ from the given 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 his electrical circuit.

Advantages and disadvantages of inverter-type welding machines

The devices that have replaced the usual transformers have a number of significant advantages.

  • Thanks to a completely different approach to the formation and regulation of the welding current, the mass of such devices is only 5–12 kg, while welding transformers weigh 18–35 kg.
  • Inverters have a very high efficiency (about 90%). This is due to the fact that they consume much less excess energy for heating the components. Welding transformers, unlike inverter devices, get very hot.
  • Inverters due to such high efficiency consume 2 times less electrical energy than conventional welding transformers.
  • The high versatility of inverter devices is explained by the ability to regulate welding current over a wide range with their help. Due to this, the same device can be used for welding parts from different metals, as well as for its implementation using different technologies.
  • Most modern inverter models are endowed with options that minimize the impact of welder errors on the process. These options include, in particular, "Anti-stick" and "Arc forcing" (quick ignition).
  • The exceptional stability of the voltage applied to the welding arc is ensured by the automatic elements of the electrical circuit of the inverter. In this case, automation not only takes into account and smooths out fluctuations in the 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 adjust their modes when performing certain types of work.

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Modern welding work is carried out using special inverters. Previously, conventional transformers were used for such metal processing, which are characterized by lower efficiency. The circuit diagram of the welding inverter may differ slightly, but they are all characterized by lightness and compactness. Only when taking into account the design features, it is possible to repair the welding inverter and fine-tune it.

Elements of the electrical circuit of welding inverters

The circuit diagram of an inverter welding machine provides for a combination of several elements that are interconnected. The main ones are:

  1. The block responsible for supplying energy to the power unit. This element is represented by a combination of several devices that are capable of changing the current parameters to the required values. As a rule, a capacitive filter and a rectifier are switched on.
  2. The device includes a power transformer. Also, the 4n90 transistor is included in the power supply of the welding inverter.
  3. A separate element is responsible for powering the low-current part of the structure.
  4. To control the main parameters, a PWM controller is installed. It is represented by a combination of a load current sensor and a transformer.
  5. A separate block is responsible for protecting the structure from heat. When an electric current passes, some elements can become seriously heated. Therefore, an additional cooling module is installed, represented by a fan and a temperature sensor.
  6. Control units that allow you to set the main parameters, as well as display elements.

The equipment of the diode bridge for the welding machine is manufactured and installed taking into account the power of the device and some other points. Each device has its own characteristics, which we will consider in more detail below.

Schemes of devices Svaris

The welding machine Svaris 200 is characterized by ease of use and low cost. Already the Svaris 160 models were characterized by high performance, and the new version was improved. The scheme of the inverter welding machine determines the following performance characteristics:

  1. The maximum consumption rate is 5 kW.
  2. Welding current can vary from 20-200 A.
  3. Open circuit voltage indicator 62 V.
  4. Efficiency index 85%.
  5. Recommended electrodes 1.6-5.0.

In general, we can say that the inverter is made according to the classical scheme, which was discussed above.

Schematics Inverter 3200 and 4000

For manual arc welding, either the Inverter 4000 or 3200 can be used. Both machines have an almost identical design, which provides the following features:

  1. Protection against electrode sticking effect.
  2. Protection of the main elements from a serious voltage drop.
  3. Control of the main parameters of the arc.
  4. Built-in cooling element with control sensors.

In the manufacture of inverters, protection class IP21 was provided. The power of the device is 5.3 kW, it is powered by a standard power supply network. A detailed diagram of the inverter 3200 pro determines the very attractive properties of these models, due to which they are widely used.

Diagrams of other models

As previously noted, almost all inverters operate on a similar principle, and the circuits created may differ slightly. All welding machines are divided into several main groups:

  1. For electric arc welding when using electrodes coated with a special composition, equipment of the MMA type is used. Such a scheme is characterized by high efficiency, and the design is light in weight.
  2. For the use of refractory electrodes, welding equipment of the MMA + TIG type is used. They can work in an inert gas environment.
  3. On production lines there are units with semi-automatic bar feed. In this case, work is usually carried out in an inert gas environment or in special baths.
  4. When forging or other repairs, spot welding is used.

Model ARC 160, the scheme of which is quite complex, can be used for a wide variety of jobs. Unlike arc 140, the scheme of the new model is devoid of major drawbacks.

Torus 250 version consists of the following elements:

  1. A clock-type generator built on a TL chip It should be borne in mind that the powerful inverter circuit does not provide for the use of PWM, but the microcircuit has two comparators with thermal protection sensors.
  2. The protection system and the control module are made on the basis of LM. The sensor that determines the current parameters is placed on a ferrite ring with a winding.
  3. The circuit also includes two output drivers built on IR

Repair of Torus 250 should be carried out from the opening of the structure and visual inspection of the main elements. In this case, they are:

  1. The output type rectifier is represented by a separate board, which houses two radiators. They serve as a base for placing diode assemblies. The module also includes one transformer and a choke. The number of elements in the output rectifier largely depends on the specific assembly.
  2. The key module is represented by four transistors in each of the four groups. In order to reduce the degree of heating, they are all placed on separate radiators, which are insulated with special gaskets.
  3. A powerful diode bridge is used as the output rectifier. In this case, it is located at the bottom of the structure. An extremely reliable and practical bridge is installed on this model, which is difficult to burn if the cooling system is working properly.
  4. The control chip is the main design element. As a rule, the durability of the entire apparatus depends on the correctness of its operation. You can check the block yourself only if you have a special oscilloscope and the appropriate skills to work with it.
  5. Chassis with cooling fan. As a rule, the cooling block fails only in the event of mechanical impact.

To diagnose many elements, they have to be dismantled. That is why it is best to entrust the work to professionals, as improper assembly can lead to significant problems.

Welding inverter SAI 200, the scheme of which does not differ significantly from devices of a similar type, is used for manual arc welding and surfacing when using stick electrodes. RDMMA 200 is a new type of equipment that is built without the use of transformers. Due to this, a more accurate and smooth adjustment of current indicators is possible, no strong noise appears during operation.


Schematic diagram of the welding inverter SAI 200

In conclusion, we note that the above information determines the complexity of the design of welding inverters. At the same time, manufacturers do not distribute detailed diagrams of devices, which complicates maintenance and repair. Despite the use of a similar circuit in the creation of almost all inverters, they differ significantly from each other. That is why, before carrying out any work, you need to familiarize yourself in detail with the design features of the device.

The device is made using IGBT technology or (half-bridge).

With a complaint from the owner that the electrode is sticking and does not want to weld. After networking
and attempts to weld the part, nothing worked. And after changing the welding current to a higher one, the welding began to smoke and heard an electric crackle. The owner said that the cause of the breakdown was not the correct choice of welding current for the electrode.

Attention: all work on the repair and restoration of the welding inverter, you perform at your own peril and risk.

After disassembly, it was decided to unscrew and check the PSU.

A burnt 150 ohm resistor at 10W was found.

The diode bridge for 100V 35A and the relay for 24 35A turned out to be working.

And in the PSU, a swollen capacitor 470 microfarads x 450 V was found, which was replaced.

This board has:

  1. Power key driver. (everything that is possible on this scarf is checked, the resistance should be no more than 10 ohms).
  2. Power keys.
  3. Power supply 24 V. (the K2611 transistor or its analogue is checked and its body kit, see photo).
  4. master generator. (all field-effect transistors are checked, you can check by turning on welding, when turning it on and off, a generator squeak should appear).

How to check power keys

Keys IRG4PC50UD or its analogues are installed here. With a multimeter in the diode test mode, you need to ring the legs of the transistor "E" and "C" in one direction, they should ring, and in the other direction they should not ring, the transistor must be discharged (close all legs). On legs "G" and "E" the resistance should be infinite, regardless of polarity.

Next, you need to apply to the leg "G" - "+" and to "E" "-" 12 volts DC. and ring the legs "C" and "E" they should ring. Next, you need to remove the charge from the transistor (close the legs). Legs "C" and "E" should have infinite resistance. If all these conditions are met, then the transistor works, and so you need to check all transistors.

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