Scheme. The welding inverter does not turn on. DIY repair. Scheme Features of maintenance and repair of inverter devices

Inverter welding has found wide application today. Despite the reliability of inverters, there are frequent cases of their failure for various reasons. At such moments, the question arises of how to make repairs.

itself is not a big problem. To carry it out, you need to know the design of the apparatus and the basic principles of repairing equipment of this type. When repairing, elementary knowledge of the basics of electrical engineering and radio engineering in terms of installing simple circuits will be required.

General information about inverters

The inverter is a direct current source for ignition and maintenance of an electric arc when welding metals. The principle of operation of welding inverters is based on the fact that a welding current of significant strength is obtained by high-frequency transformation, which makes it possible to significantly reduce the dimensions of the transformer, as well as increase the stability and controllability of the output current.

The whole process of obtaining the required current includes the following steps: primary rectification of the current received from the mains; transformation of primary direct current into high frequency current; increase in current strength with a corresponding decrease in the magnitude of the voltage in the high-frequency transformer; secondary rectification of the output power current.

Current rectification is carried out using diode bridges of appropriate power. The frequency change is carried out by powerful transistors. The required output current is provided by a high-frequency transformer.

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Design of inverters

Welding inverters consist of several main blocks. The power supply provides input signal stabilization. The block diagram is based on a multi-winding choke controlled by transistors and energy storage in a capacitor. In addition, diodes are used in the throttle control system. The power supply unit is located separately from other units and, as a rule, is separated from them by a metal partition.

The basis of the welding inverter is the power unit, which provides all the transformations from the primary current coming from the power supply to the output welding current. The power block consists of the following boards: primary rectifier, inverter converter, high frequency transformer and secondary rectifier.

The primary rectifier is a diode bridge, which is supplied with an electric current of no more than 40 A (the most common is 25-32 A) with a voltage of 200-250 V with a frequency of 50 Hz. The inverter converter is a power transistor with a power of at least 8 kW (at a current of 32 A) with an operating voltage of up to 400 V. The signal from the converter comes out with a frequency of up to 100 kHz (most often 50-55 kHz).

The high-frequency transformer has tape windings and increases the current up to 200-250A at a voltage in the secondary winding of not more than 40 V. The secondary rectifier is assembled on the basis of powerful diodes with an operating current of at least 250 A for an operating voltage of up to 100 V. Obligatory cooling is provided using radiators, as well as installed fans. To stabilize the output signal, a choke is installed on the output plateau.

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Control and protection units

The control unit is assembled on the basis of a master oscillator or a wide pulse modulator. If the circuit is assembled on the basis of a generator, then a microcircuit is used as it. In addition to it, a resonant choke and resonant capacitors in the amount of 6 or 10 pieces are placed on the control plateau. The cascade control circuit is provided by a transformer.

Protection circuits are usually assembled on the plateau of the power block to protect the corresponding element. To protect against overloads, a circuit based on the 561LA7 microcircuit is used. In the rectifier and converter protection system, snubbers based on K78-2 capacitors and resistors are used. Thermal protection of the elements of the power unit is provided by the installation of thermal switches.

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Causes of failure of inverters

Most breakdowns of welding inverters are caused by violations of the operation of the devices. Moisture is a common cause of short circuits in electrical circuits. Unpredictable consequences can be caused by the concentration of dust inside the inverter.

Often the reason for repairing the device is an attempt to perform work for which the inverter is not designed. For example, a small-sized apparatus is not capable of cutting a railway rail - this will cause unplanned overloads.

Of the domestic reasons, a strong decrease in the voltage in the network should be especially noted. This can be observed everywhere, but is especially true for suburban work and in rural areas. Reducing the electrical voltage to 190 V can have an extremely negative effect on the performance of the inverter.

Quite often, the failure of the inverter is caused by poor-quality fastening of the inlet or outgoing cable in the terminal blocks (terminals). When the contact is weakened at the junction, an overheating zone is observed, and sometimes sparking.

Repair of welding inverters due to failure of circuit elements most often occurs when low-quality parts are used. In addition, damage in electrical circuits can occur due to overheating of power elements, i.e. if their cooling is not enough.

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The main types of faults

Among the many possible malfunctions, the main types should be distinguished. First of all, these are cases when, in the presence of input voltage, there is no current at the output of the inverter. Such a malfunction is due to blown fuses or a violation of the integrity of the electrical circuit, which can occur in any zone of the inverter.

Another type of malfunction: the output welding current does not reach the desired values ​​even at maximum settings. This inverter fault can be caused either by insufficient input voltage and terminal losses, or by faults in the power unit.

Frequent spontaneous shutdowns of the inverter indicate that there is a short circuit in the electrical circuit or that there is excessive overheating of the elements of the power unit. At the same time, the protection system works normally and provides an emergency shutdown.

The instability of the welding arc and the lack of adjustment of the welding current indicates a malfunction in the power unit or control unit. The increased noise emitted by the inverter indicates the presence of overloads and may subsequently lead to its failure. The inverter protection system is malfunctioning. The same can be said in the case when the heating of the apparatus itself is felt. In the latter case, weak fixing of the cable in the terminal block is added to the possible reasons.

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General repair procedure for welding inverters

Any repair of the inverter for welding work should begin with an external inspection. The presence of mechanical damage to the case and traces of a short circuit (blackening, burns) is visually determined. Then the quality of fastening the cables in the terminal blocks (at the input and output of the inverter) is checked.

Regardless of the results of the check, tighten the clamping elements with a screwdriver or wrench. The integrity of the fuses should be checked with a tester and, if necessary, replaced.

If the cause of the malfunction has not been eliminated, then the cover of the inverter housing is removed. After removing the cover, a visual inspection is carried out in order to detect breaks in the electrical circuit or traces of a short circuit. The input voltage and input current are measured, as well as their values ​​​​at the output of the welding inverter using a tester or multimeter.

In the absence of obvious malfunctions, a block-by-block check of the integrity of the electrical circuit is carried out. The test starts with the power supply and moves gradually to other units.

Simplicity of design and reliability of welding transformers are among their main advantages. However, the most reliable mechanisms sometimes fail, especially when the welding machines are operated in violation of the rules. Read about the device of welding transformers.

The weakest element of welding transformers is the terminal block to which the welding cables are connected. A bad contact, together with a high welding current, leads to a strong heating of the connection and the wires connected to it. As a result, the connection itself is destroyed, the insulation at the ends of the windings burns out, as a result of which a short circuit occurs.

Repair of the welding transformer in this case comes down to sorting out the heating joint, cleaning the contact surfaces and clamping them to ensure tight contact of all elements.

Among others, the following malfunctions occur.

Spontaneous shutdown of the welding machine. When the transformer is connected to the network, its protection is triggered, as a result of which the device is turned off. This may be due to short circuits in the high voltage circuit - between the wires and the case or the wires between themselves. A short circuit between the turns of the coils or sheets of the magnetic circuit, as well as a breakdown of capacitors, can also lead to the operation of the protection. When repairing, it is necessary to disconnect the transformer from the network, find the defective place and eliminate the malfunction - restore the insulation, replace the capacitor, etc.

Strong transformer hum often accompanied by overheating. The reason may be loosening of the bolts tightening the sheet elements of the magnetic circuit, malfunctions in the fastening of the core or the mechanism for moving the coils, transformer overload (excessively long operation, high welding current, large electrode diameter). A short circuit between the welding cables or sheets of the magnetic circuit also leads to a strong hum. It is necessary to check and tighten all screws and bolts, eliminate violations in the mechanisms for attaching the core and moving the coils, check and restore the insulation in the welding cables.

Excessive heating of the welding machine. The most common reasons for this include a violation of the operating rules in the form of setting the welding current above the permissible value, using a large diameter electrode or working too long without interruption. It is necessary to observe the standard mode of operation - set moderate current values, use electrodes of small diameters, take breaks in work to cool the device.

Strong heating can lead to a short circuit between the turns of the coil winding due to the combustion of the insulation, usually accompanied by smoke. This is the most serious case, about which they say that the device "burned out." If this happens, then the repair of the welding machine will require, at best, local restoration of the insulation of the coil wire, at worst, its complete rewinding. In the latter version, in order to preserve the characteristics of the device, it is necessary to rewind with a wire of the original section - with the same number of turns as it was.

Low welding current. The phenomenon can be observed with a low voltage in the supply network or a malfunction of the welding current regulator.

Poor welding current regulation. This can be caused by various malfunctions in the current control mechanisms, which differ in different designs of welding transformers. Namely, malfunctions in the current regulator screw, a short circuit between the regulator terminals, a violation of the mobility of the secondary coils due to the ingress of foreign objects or other reasons, a short circuit in the choke coil, etc. It is necessary to remove the casing from the apparatus and examine the specific current control mechanism for a malfunction. The simplicity of the device of the welding machine and the availability of all its components for inspection facilitate troubleshooting.

Sudden interruption of the welding arc and the inability to re-ignite it. Instead of an arc, only small sparks are observed. This can be caused by a breakdown of the high voltage winding on the welding circuit, a short circuit between the welding wires, or a violation of their connection to the terminals of the device.

High current consumption from the network in the absence of load. This can be caused by a short circuit of the turns of the winding, which is eliminated by local restoration of the insulation or by a complete rewinding of the coil.

Repair of welding rectifiers

Structurally, the rectifier occupies an intermediate position between the welding transformer and the inverter. From the first one, he inherited a power transformer with all its shortcomings, in particular, a large mass, heating and the potential for closing the windings or sheets of the magnetic circuit. Therefore, the causes of failure and repair methods of the welding machine in the part of the power transformer are the same as those of the welding transformer. In the case shown in the photo below, the winding of the power transformer burned out, and in this case it is no longer possible to do without rewinding.

The available electronic part - a diode rectifier and a control module - makes the welding rectifier related to the inverter. Therefore, troubleshooting involves checking the diode bridge and control board elements. The diode bridge is a reliable component of electronic circuits, but sometimes it fails. In general, the causes of a malfunction can be very different: the tracks on the boards burn out, the transformers of the control circuit fail. The photo below shows a case where do-it-yourself repair of a welding machine, which consisted in replacing a non-working part of the control board with a Russian counterpart, allowed the user to save a considerable amount on repairs (70% of the cost of the welding machine).

Repair of welding inverters

Welding inverters provide excellent welding quality and maximum comfort for the welder. However, these advantages are acquired at the price of a more complex design and - no matter what inverter manufacturers say - less reliability compared to their predecessors - transformers and rectifiers.

Unlike a welding transformer, which is more of an electrical product, a welding inverter is an electronic device. This means that the diagnostics and repair of welding inverters involves checking the performance of transistors, diodes, resistors, zener diodes and other elements that make up electronic circuits. You need to be able to work with an oscilloscope, not to mention multimeters, voltmeters and other ordinary measuring equipment.

A feature of the repair of inverters is that in many cases it is difficult or even impossible to determine the failed component by the nature of the malfunction, you have to check all the elements of the circuit in sequence.

From the foregoing, it follows that a successful repair of a welding inverter with your own hands is possible only if you have at least basic knowledge in electronics and little experience in working with electrical circuits. Otherwise, self-repair can only result in a waste of time and effort.

As you know, the principle of operation of a welding inverter is to gradually convert an electrical signal:

• Rectification of the mains current - using the input rectifier.
• Converting rectified current to high-frequency alternating current - in the inverter module.
• Lowering the high-frequency voltage to welding - by a power transformer (having a very small size due to the high voltage frequency).
• Rectification of alternating high-frequency current into direct welding - by an output rectifier.

In accordance with the operations performed, the inverter structurally consists of several electronic modules, the main of which are the input rectifier module, the output rectifier module and the control board with keys (transistors).

Although the main components in inverters of various designs remain unchanged, their layout in devices from different manufacturers can vary greatly.

Checking transistors. The weakest point of inverters are transistors, so the repair of inverter welding machines usually begins with their inspection. A faulty transistor is usually immediately visible - a hacked or cracked case, burned-out terminals. If this is found, you can start repairing the inverter by replacing it. This is what a broken key looks like.

And here it is - installed instead of the burnt one. The transistor is mounted on thermal grease (KPT-8), which provides good heat dissipation to the aluminum radiator.

Sometimes there are no external signs of a malfunction, all keys look intact. Then, to determine the faulty transistor, a multimeter is used to check them.

Identifying faulty elements is very good, but far from everything. Repair of inverter welding machines also involves looking for, instead of burned out elements, suitable analogues. To do this, the characteristics of the failed elements are determined (according to the datasheet) and, based on it, analogues are selected for replacement.

Checking Driver Elements. Power transistors usually do not fail on their own, most often this is preceded by the failure of the elements of the driver that "swings" them. Below is a photo of the board with elements of the Telwin Tecnica 164 inverter driver. The check is carried out using an ohmmeter. All defective parts are soldered and replaced with suitable counterparts.

Checking rectifiers. Input and output rectifiers, which are diode bridges mounted on a radiator, are considered reliable elements of inverters. However, sometimes they fail too. This does not apply to those shown in the photo below, they are serviceable.

It is most convenient to check the diode bridge by unsoldering the wires from it and removing it from the board. This makes work easier and does not mislead in the presence of a short circuit in the circuit. The verification algorithm is simple, if the whole group rings shortly, you need to look for a faulty (broken) diode.

For soldering parts, it is convenient to use a soldering iron with suction.

The key control board is the most complex module of the welding inverter; the reliability of the functioning of all components of the device depends on its operation. A qualified repair of welding inverters should end with a check for the presence of control signals coming to the gate busbars of the key module. This check is carried out using an oscilloscope.

Control board control (in the photo is not an inverter, but a rectifier, but the essence of this does not change)

semi-automatic

In semiautomatic devices, regardless of whether they are based on inverters or rectifiers, purely mechanical problems can be added to the malfunctions of the electronic and electrical parts. In particular, wire feed delay caused by low clamping force in the feed mechanism or high friction between the wire and the channel in the sleeve. In the latter case, the most effective way to repair the welding machine is to replace the channel. Moreover, it is recommended to change it by combining the removal of the old one with the installation of a new one - in one pull, connecting the end of the old channel with the beginning of the new one.

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Hello!!! The other day, a welding inverter was brought in for repair, perhaps my note about this repair will be useful to someone.

This is not the first welding machine that had to be done, but if in one case the malfunction manifested itself as follows: I turned on the inverter in the network ... and boom, the circuit breakers in the electrical panel were knocked out. As the autopsy showed in the welder, the output transistors broke through, after the replacement everything worked.

But in this case, everything was somewhat different, according to the owner, the device sometimes stopped cooking, although the power indicator was on. These guys opened the case themselves - they tried to determine the malfunction and noticed that the inverter reacted to the bending of the board, i.e. when it was bent, it could earn. But when the welding inverter came to me, it no longer turned on at all, even the power indicator did not light up.

Welding inverter does not turn on

"Titan - BIS - 2300" - it was this inverter model that went into repair, the circuitry repeats the Resant welding machine of similar power and, as I assume, many other inverters. You can view and download the diagram

In this welding machine, a switching power supply is used to power low-voltage circuits, and it was just it that was faulty. The UPS is made on the PWM controller UC 3842BN. Analogues - domestic 1114EU7, Imported UC3842AN differs from BN only in lower current consumption, and KA3842BN (AN). The UPS schematic is below. (Click on it to enlarge) Red marks the voltages that the working UPS was already producing. Please note that you need to measure voltages of 25V not relative to a common minus, but from points V1+, V1- and also V2+, V2- they are not connected to a common bus.

The UPS key is made on a transistor, field worker 4N90C. In my case, the transistor remained intact, but the microcircuit required replacement. There was also a break in the resistor R 010 - 22 Om / 1Wt. After that, the power supply worked.

However, it was too early to rejoice, having measured the voltage at the output of the welder, it turned out that it was not there, and in idle mode it should be about 85 volts. I tried to move the board, remember from the words of the owner it affected, but nothing.

Further searches revealed the absence of one of the voltages of 25 volts at points V2-, V2 +. The reason is a break in the winding transformer 1-2. I had to solder the trance, used a medical needle to release the findings.

In the transformer, one of the ends of the winding was cut off from the output.

We carefully restore the connection using a suitable wiring, it will not be superfluous to fix the restored connection with a drop of glue or sealant. I had polyurethane glue at hand and used it, we make an audit of other conclusions, if necessary, we solder it.

Before installing the transformer, you should prepare the board so that it effortlessly enters its place. To do this, you need to clean the holes from the remnants of the solder, you can also do this with a needle from a syringe of a suitable diameter.

After installing the transformer, the welding inverter started working.

How to check the microchip

How to check the microcircuit without soldering it from the board and what else to look for.

You can partially check the microcircuit with a voltmeter and an adjustable stabilized constant voltage source. A complete test requires a signal generator and an oscilloscope.

Let's talk about what's easier. Before checking, be sure to turn off the power supply to the inverter. Next - from an external regulated power supply to pin 7 of the microcircuit, we apply a voltage of 16 - 17 volts, this is the startup voltage of the MS. At the same time, pin 8 should be 5 V. This is the reference voltage from the internal stabilizer of the microcircuit.

It should remain stable when the voltage at pin 7 changes. If this is not the case, the MS is faulty.

When changing the voltage on the microcircuit, keep in mind that below 10 V the microcircuit turns off and turns on at 15-17 volts. You should not increase the supply voltage of the MS above 34 V. There is a protective zener diode inside the microcircuit and, if the voltage is too high, it will simply break through.

Below is the block diagram of UC3842.

Addition to this article: After some time, they brought another device. Failed due to falling on its side. This happened because during operation, the screws securing the case became loose, and some simply got lost, so when it fell, the board played and touched the case with the mounting side. As a result of the short circuit, all 4 output transistors K 30N60HS failed. After replacing everything worked.

That's all! If you found this article useful, leave your comments, share with friends by clicking on the social network buttons.

Repair, despite its complexity, in most cases you can do it yourself. And if you have a good understanding of the design of such devices and have an idea of ​​\u200b\u200bwhat is more likely to fail in them, you can successfully optimize the cost of professional service.

Purpose of equipment and features of its design

The main purpose of any inverter is the formation of a direct welding current, which is obtained by rectifying a high-frequency alternating current. The use of high-frequency alternating current, converted by a special inverter module from a rectified network, is due to the fact that the strength of such a current can be effectively increased to the required value using a compact transformer. It is this principle put into operation that allows such equipment to have compact dimensions with high efficiency.

The scheme of the welding inverter, which determines its technical characteristics, includes the following main elements:

• primary rectifier unit, which is based on a diode bridge (the task of such a unit is to rectify alternating current coming from a standard electrical network);
• an inverter unit, the main element of which is a transistor assembly (it is with the help of this unit that the direct current supplied to its input is converted into an alternating current, the frequency of which is 50–100 kHz);
• a high-frequency step-down transformer, on which, by lowering the input voltage, the strength of the output current increases significantly (due to the principle of high-frequency transformation, a current can be generated at the output of such a device, the strength of which reaches 200–250 A);
• output rectifier assembled on the basis of power diodes (the task of this inverter unit is to rectify high-frequency alternating current, which is necessary for welding).

The welding inverter circuit contains a number of other elements that improve its operation and functionality, but the main ones are those listed above.

Features of maintenance and repair of inverter devices

Repair of an inverter-type welding machine has a number of features, which is explained by the complexity of the design of such a device. Any inverter, unlike other types of welding machines, is electronic, which requires specialists involved in its maintenance and repair to have at least basic radio engineering knowledge, as well as skills in handling various measuring instruments - a voltmeter, digital multimeter, oscilloscope, etc. .

In the process of maintenance and repair, the elements that make up are checked. This includes transistors, diodes, resistors, zener diodes, transformer and choke devices. The design feature of the inverter is that very often during its repair it is impossible or very difficult to determine the failure of which element caused the malfunction.

In such situations, all details are sequentially checked. To successfully solve such a problem, it is necessary not only to be able to use measuring instruments, but also to understand electronic circuits well enough. If you don’t have such skills and knowledge at least at the initial level, then repairing a welding inverter with your own hands can lead to even more serious damage.

Really evaluating your strengths, knowledge and experience and deciding to undertake an independent repair of inverter-type equipment, it is important not only to watch a training video on this topic, but also to carefully study the instructions in which manufacturers list the most typical malfunctions of welding inverters, as well as ways to eliminate them.

Factors leading to the failure of the welding inverter

Situations that can cause the inverter to fail or lead to malfunctions can be divided into two main types:

• associated with the wrong choice of welding mode;
• caused by the failure of parts of the device or their incorrect operation.

The method for identifying an inverter malfunction for subsequent repair is reduced to the sequential execution of technological operations, from the simplest to the most complex. The modes in which such checks are performed and what their essence is is usually specified in the instructions for the equipment.

If the recommended actions did not lead to the desired results and the operation of the device was not restored, most often this means that the cause of the malfunction should be sought in the electronic circuit. The reasons for the failure of its blocks and individual elements may be different. We list the most common.

• Moisture has penetrated the inside of the unit, which may occur if the unit is exposed to precipitation.
• Dust has accumulated on the elements of the electronic circuit, which leads to a violation of their full cooling. The maximum amount of dust gets into the inverters when they are operated in very dusty rooms or on construction sites. In order to prevent the equipment from getting into such a state, its interior must be cleaned regularly.
• Overheating of the elements of the electronic circuit of the inverter and, as a result, their failure can be caused by non-compliance with the duty cycle (DU). This parameter, which must be strictly observed, is indicated in the technical data sheet of the equipment.

Common faults

The most common faults encountered in the operation of inverters are as follows.

Unstable burning of the welding arc or active spatter of metal

This situation may indicate that the current strength is incorrectly selected for welding. As you know, this parameter is selected depending on the type and diameter of the electrode, as well as on the speed of welding. If the packaging of the electrodes you are using does not contain recommendations on the optimal current strength, you can calculate it using a simple formula: 20–40 A of welding current should fall on 1 mm of electrode diameter. It should also be borne in mind that the lower the welding speed, the lower the current strength should be.

Sticking of the electrode to the surface of the parts to be joined

This problem can be due to a number of reasons, most of which are based on low supply voltage. Modern models of inverter devices also operate at reduced voltage, but when its value drops below the minimum value for which the equipment is designed, the electrode begins to stick. A voltage drop at the output of the equipment can occur if the device blocks do not make good contact with the panel jacks.

This reason is eliminated very simply: by cleaning the contact sockets and fixing the electronic boards in them more tightly. If the wire with which the inverter is connected to the mains has a cross section of less than 2.5 mm2, this may also lead to a voltage drop at the input of the device. This is guaranteed to happen even if such a wire is too long.

If the length of the supply wire exceeds 40 meters, it is almost impossible to use an inverter for welding, which will be connected with it. The voltage in the supply circuit may also drop if its contacts are burnt or oxidized. A frequent cause of sticking of the electrode is insufficient preparation of the surfaces of the parts to be welded, which must be thoroughly cleaned not only from existing contaminants, but also from the oxide film.

Inability to start the welding process when the machine is turned on

This situation often occurs in case of overheating of the inverter apparatus. At the same time, the control indicator on the device panel should light up. If the glow of the latter is hardly noticeable, and the inverter does not have an audible warning function, then the welder may simply not be aware of overheating. This state of the welding inverter is also characteristic of a break or spontaneous disconnection of the welding wires.

Spontaneous shutdown of the inverter during welding

Most often, this situation occurs if the supply voltage is turned off by circuit breakers whose operating parameters are incorrectly selected. When working using an inverter apparatus, circuit breakers rated for a current of at least 25 A must be installed in the electrical panel.

Inability to turn on the inverter when turning the toggle switch

Most likely, this situation indicates that the voltage in the supply network is too low.

Automatic shutdown of the inverter during continuous welding

Most modern inverter devices are equipped with temperature sensors that automatically turn off the equipment when the temperature in its internal part rises to a critical level. There is only one way out of this situation: give the welding machine a rest for 20-30 minutes, during which it will cool down.

How to repair an inverter device yourself

If after testing it becomes clear that the cause of malfunctions in the operation of the inverter device lies in its internal part, you should disassemble the case and proceed to inspect the electronic filling. It is possible that the reason is poor-quality soldering of device parts or poorly connected wires.

Careful inspection of electronic circuits will reveal faulty parts that may be darkened, cracked, with a swollen case, or have burnt contacts.

During repair, such parts must be removed from the boards (it is advisable to use a soldering iron with suction for this), and then replaced with similar ones. If the marking on the faulty elements is not readable, then special tables can be used to select them. After replacing faulty parts, it is advisable to test the electronic boards using a tester. This is especially necessary if the inspection did not reveal the elements to be repaired.

A visual check of the electronic circuits of the inverter and their analysis with a tester should begin with a power unit with transistors, since it is he who is the most vulnerable. If the transistors are faulty, then, most likely, the circuit (driver) that swings them has also failed. The elements that make up such a circuit also need to be checked first.