Do-it-yourself arc welding machine repair

Inverter welding machines are gaining more and more popularity among master welders due to their compact size, low weight and reasonable prices. Like any other equipment, these devices can fail due to improper operation or due to design flaws. In some cases, the repair of inverter welding machines can be carried out independently by examining the inverter device, but there are breakdowns that are eliminated only at the service center.

Welding inverters, depending on the models, operate both from a household electrical network (220 V) and from a three-phase (380 V). The only thing to consider when connecting the device to a household network is its power consumption. If it exceeds the capabilities of the wiring, then the unit will not work with a sagging network.

So, the following main modules are included in the device of an inverter welding machine.

Just like diodes, transistors are installed on radiators for better heat dissipation from them. To protect the transistor unit from voltage surges, an RC filter is installed in front of it.

Below is a diagram that clearly shows the principle of operation of the welding inverter.

So, the principle of operation of this module of the welding machine is as follows. The primary rectifier of the inverter is supplied with voltage from the household electrical network or from generators, gasoline or diesel. The incoming current is alternating, but passing through the diode block, becomes permanent... The rectified current is fed to the inverter, where it is converted back to alternating current, but with changed frequency characteristics, that is, it becomes high-frequency. Further, the high-frequency voltage is reduced by a transformer to 60-70 V with a simultaneous increase in the current strength. At the next stage, the current again enters the rectifier, where it is converted to DC, after which it is supplied to the output terminals of the unit. All current conversions controlled by a microprocessor control unit.

Video (click to play).

Modern inverters, especially those based on the IGBT module, are quite demanding on the rules of operation. This is explained by the fact that when the unit is operating, its internal modules give off a lot of heat... Although both radiators and a fan are used to remove heat from power units and electronic boards, these measures are sometimes not enough, especially in inexpensive units. Therefore, you need to strictly follow the rules that are indicated in the instructions for the device, implying periodic shutdown of the installation for cooling.

This rule is usually referred to as the “Duty Cycle” (Duty Cycle), which is measured as a percentage. Not observing the PV, overheating of the main units of the apparatus occurs and their failure occurs. If this happens with a new unit, then this breakdown is not subject to warranty repair.

Also, if the inverter welding machine is working in dusty rooms, dust settles on its radiators and interferes with normal heat transfer, which inevitably leads to overheating and breakdown of electrical components. If it is impossible to get rid of the presence of dust in the air, it is necessary to open the inverter case more often and clean all the components of the device from accumulated dirt.

But most often inverters fail when they work at low temperatures. Breakdowns occur due to the appearance of condensation on the heated control board, as a result of which a short circuit occurs between the parts of this electronic module.

A distinctive feature of inverters is the presence of an electronic control board, therefore, only a qualified specialist can diagnose and eliminate a malfunction in this unit.... In addition, diode bridges, transistor blocks, transformers and other parts of the electrical circuit of the apparatus can fail. To carry out diagnostics with your own hands, you need to have certain knowledge and skills in working with measuring instruments such as an oscilloscope and a multimeter.

From the above, it becomes clear that, without the necessary skills and knowledge, it is not recommended to start repairing the device, especially electronics. Otherwise, it can be completely disabled, and repairing the welding inverter will cost half the cost of a new unit.

As already mentioned, inverters fail due to external factors affecting the “vital” units of the apparatus. Also, malfunctions of the welding inverter can occur due to improper operation of the equipment or errors in its settings. The most common malfunctions or interruptions in inverter operation are as follows.

Very often, this breakdown is caused by faulty network cable apparatus. Therefore, first you need to remove the cover from the unit and ring each wire of the cable with a tester. But if everything is in order with the cable, then more serious diagnostics of the inverter will be required. Perhaps the problem lies in the standby power source of the device. The repair technique for the “duty room” using the example of a Resant brand inverter is shown in this video.

This malfunction can be caused by an incorrect setting of the amperage for a certain diameter of the electrode.

You should also consider and welding speed... The smaller it is, the lower the current value must be set on the control panel of the unit. In addition, to match the current strength to the diameter of the additive, you can use the table below.

If the welding current is not regulated, the cause may be breakdown of the regulator or violation of the contacts of the wires connected to it. It is necessary to remove the cover of the unit and check the reliability of the connection of the conductors, and, if necessary, ring the regulator with a multimeter. If everything is in order with him, then this breakdown can be caused by a short circuit in the inductor or a malfunction of the secondary transformer, which will need to be checked with a multimeter. If a malfunction is found in these modules, they must be replaced or rewound to a specialist.

Excessive power consumption, even when the device is not loaded, most often causes turn-to-turn closure in one of the transformers. In this case, you will not be able to repair them yourself. It is necessary to take the transformer to the master for rewinding.

This happens if the voltage drops in the network... To get rid of the sticking of the electrode to the parts to be welded, you will need to correctly select and set up the welding mode (according to the instructions for the device). Also, the voltage in the network may sag if the device is connected to an extension cord with a small wire cross-section (less than 2.5 mm 2).

It is not uncommon for a voltage drop that causes the electrode to stick when using a power strip that is too long. In this case, the problem is solved by connecting the inverter to the generator.

If the indicator is on, this indicates overheating of the main modules of the unit. Also, the device can turn off spontaneously, which indicates tripping of thermal protection... So that these interruptions in the operation of the unit do not occur in the future, again, it is necessary to adhere to the correct mode of the duration of the on (DC).For example, if duty cycle = 70%, then the device should work in the following mode: after 7 minutes of operation, the unit will have 3 minutes to cool down.

In fact, there can be a lot of various breakdowns and the reasons that cause them, and it is difficult to list them all. Therefore, it is better to immediately understand what algorithm is used to diagnose the welding inverter in search of faults. You can find out how the device is diagnosed by watching the following training video.

The weakest element of welding transformers is the terminal block to which the welding cables are connected. Poor contact together with a high welding current leads to 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 a welding transformer in this case is reduced to sorting out the heating joint, cleaning the contact surfaces and clamping them, ensuring 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 can occur due to short circuits in the high voltage circuit - between the wires and the case, or wires between themselves. A short circuit between the turns of the coils or sheets of the magnetic circuit, as well as the breakdown of capacitors, can also trigger 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 hum of the transformer, 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, overloading of the transformer (excessively long operation, high value of the welding current, large diameter of the electrode). A short circuit between welding cables or sheets of a magnetic circuit also leads to a strong hum. It is necessary to check and tighten all screws and bolts, eliminate irregularities in the mechanisms for fixing 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 too long work without interruption. It is necessary to observe the standard operating mode - 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 combustion of the insulation, usually accompanied by smoke. This is the most serious case, about which they say that the apparatus "burned out". If this happened, then the repair of the welding machine will require, at best, a local restoration of the coil wire insulation, at worst - its complete rewinding. In the latter version, in order to preserve the characteristics of the apparatus, 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 undervoltage in the supply network or a malfunction of the welding current regulator.

Poor welding current adjustment... This can be caused by various faults in the current control mechanisms, which differ in different designs of welding transformers.Namely, malfunctions in the screw of the current regulator, a short circuit between the terminals of the regulator, 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 investigate the specific current control mechanism in order to detect a malfunction. The simplicity of the device of the welding machine and the accessibility of all its components for inspection make it easier to troubleshoot.

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

Consumption of large current from the network at no load... This can be caused by a short circuit of the winding turns, which is eliminated by a local restoration of insulation or a complete rewinding of the coil.

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

Unlike a welding transformer, which is more of an electrical product, a welding inverter is an electronic device. This means that 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 the fact that in many cases it is difficult or even impossible to determine by the nature of the malfunction a failed component, you have to check all the elements of the circuit sequentially.

From the foregoing, it follows that the successful repair of a welding inverter with your own hands is possible only if you have at least initial 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 a step-by-step conversion of an electrical signal:

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

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

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

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

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

It is very good to identify faulty items, but not all. Repair of inverter welding machines also involves the search, instead of burnt out elements, suitable analogues. For this, the characteristic of the failed elements is determined (according to the datasheet) and, based on it, analogues are selected for replacement.

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

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

The diode bridge is most conveniently checked by unsoldering the wires from it and removing it from the board. This makes work easier and does not deceive when there is a short circuit in the circuit. The verification algorithm is simple, if the entire group is short-circuited, you need to look for a faulty (punctured) diode.

It is convenient to use a soldering iron with a suction for desoldering parts.

Control board monitoring... 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 busbars of the gates of the key module. This check is carried out using an oscilloscope.

Every good owner has a small welding machine. It will always come in handy when making a greenhouse, garage door, fence or other needs. Some were able to acquire not just an inverter or a transformer, but more sophisticated types of welding equipment, which allows them to solve matters in the yard and even make a living. When such a device breaks down, it clearly upsets its owner. Any equipment periodically fails. How to repair welding machines yourself, without outside help? What do you need to know for this? Where to begin?

To successfully repair a welding unit, basic knowledge of the electronic and mechanical parts of the device is required. In those models where inert gas is used, another side to be examined is added. A breakdown of an inverter or other equipment can be compared to a disease. Then the visible and audible faulty factors will be “symptoms”, analyzing which it is necessary to determine the “disease” itself, and establish a “diagnosis”.

Repair of the welding machine begins with a step-by-step inspection of each unit. The identified faults are analyzed and compared with the nodes responsible for this part. And for this it is necessary to understand well the purpose of each block. In the simplest transformers, two windings are used, between which a magnetic field arises, which helps to lower volts and increase amperes.The device is equipped with a mechanical component, in the form of a screw and a movable platform, which changes the distance between the windings, thereby regulating the current strength. A special handle on the lid is used for rotation.

The inverter design is superior in complexity to a conventional transformer. The equipment diagram has:

• an electronic regulator that controls the process;
• straightening unit;
• a node where the voltage is directly inverted (returns to alternating, but with a high frequency);
• a step-down transformer.

Understanding the operation of the inverter will allow you to more accurately determine the place of failure and restore its operation sooner. The process is carried out in the following sequence:

1. The current from the socket is fed to the rectifier unit, which consists of a series of diodes connected by a bridge. The alternating voltage becomes constant.
2. The inverter unit increases the frequency of the current to a large value due to transistors that return the voltage to AC.
3. The transformer processes the current flowing to it, reducing volts to safe values, and raising amperes to values ​​that can melt metal.
4. The electronic board controls the welding processes and regulates important parameters.

By measuring the voltage at different structural nodes with a tester, you can identify a section without current, or with insufficient indicators, and start repairing the welding machine with your own hands. Models that automatically feed the wire into the welding zone, in addition to the electronic part, which can be inverter or transformer type, also have traction mechanisms involved in the welding process. Often such assemblies consist of lower rollers on the axle and their pressure pairs, the pressure force of which is regulated by a spring. The rotation of the rollers and the wire drum is carried out by a small motor and a gearbox that transmits torque.

Semi-automatic machines and argon devices are equipped with a gas valve, hoses and a cylinder with a reducer, which interact with the control circuit and participate in protecting the weld pool. Breakdowns can occur in any part of the apparatus, therefore, understanding its basic elements will help to quickly identify the "disease" that has arisen and start "treatment".

The complexity of the repair depends on the type of the failed part. This is not always due to complex reasons. There are often cases when the device continues to work, but it does not do it naturally, with extraneous sounds, or with poor weld quality. The most common reasons for not working correctly are as follows:

How to repair welding machines with your own hands is shown in some videos. There you can also see the principles of equipment inspection. If the unit does not work at all, then the electrical part may have broken. This could happen due to the wrong choice of welding modes, when the work was carried out for too long, and the machine regularly overheated. If the equipment was stored in a damp room, dust accumulated inside could serve as a conductor and cause a short. In dry conditions, such dust serves as an additional "insulation" on the electronic part, preventing it from cooling, which leads to burnout of the elements.

To find a failed part, you can visually inspect the equipment. On the board you should look for:

• transistors with swollen body shapes;
• circuit elements with carbon deposits on the legs;
• parts with a dark body color;
• items in a pattern with cracks.

If a damaged element is found, it must be removed from the board by unsoldering the legs. The replaced part must be identical to the previous one in terms of voltage and resistance. After soldering, it is worth checking the device for operability. If its functions are not restored, then the search continues with the tester.

The tester allows you to check the presence of contact between different parts of the circuit. Sometimes, an open circuit can occur on a diode bridge, inverter module or other nodes.A step-by-step check will help you move forward to find the cause by elimination. It is even worth testing short wires leading from the circuit to the buttons, because a break could occur anywhere. Most often, contact loss occurs in transistors. "Ringing" each of them, and the entire circuit, solves the problem in 50% of cases. Diodes are checked in a similar way.

The complete inoperability of the apparatus could be caused by the short circuit of the turns of the transformer. The tester can detect this breakdown. If found, you will need to remove the old winding and wind a new one in the exact number of turns and cable cross-section. The key control board is checked last due to the complexity of its design and the need for an oscilloscope. The frequency of control signals, which does not correspond to the required one, will be detected only by this equipment.

Breakdowns of welding machines can also be associated with a malfunction of mechanical parts. Sometimes, this allows welding, but the customization options are lost. Self-repair of devices implies finding the reasons for such a deviation and restoration work.

In welding transformers, over time, the screw thread wears out, which regulates the distance between the coils, which affects the amperage. Loses the edges and the axis to which the handle is attached to rotate the screw. This makes it impossible to adjust the welding voltage. Replacing the screw or handle restores the full operation of the device.

In semiautomatic machines, filler wire can get stuck, making it difficult to guide the weld. The jerky feed and "punctures" of the weld pool affect the quality of the joint. The reason is a clogged wire feed channel, which is cleaned with a bar with a diameter that is as close as possible to the inside diameter of the feed path. Slippage of the wire on the rolls can mean breakage of the groove, clearly exceeding the width of the filler material used. The rollers need to be replaced.

In the gas equipment of devices where argon and its mixtures are used, there is nothing to break apart from the pressure gauge membrane, which is responsible for stable pressure in the hoses. Replacing this rubber part restores the operation of the device. Checking the gas solenoid valve doesn't hurt either. Also, care must be taken to ensure that the hose does not kink at bends.

Sooner or later, any welding machine will break down and require repair. Applying the above recommendations, and having visually familiarized themselves with the individual processes in the video, most will be able to carry out repairs with their own hands.

Repair of welding inverters, despite its complexity, in most cases can be done independently. And if you are well versed in the design of such devices and have an idea of ​​what is more likely to fail in them, you can successfully optimize the costs of professional service.

Replacement of radio components in the process of repairing a welding inverter

The main purpose of any inverter is to generate a constant welding current, which is obtained by rectifying a high-frequency alternating current. The use of a high-frequency alternating current, converted by means of a special inverter module from a rectified mains supply, 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 underlying the operation of the inverter that allows such equipment to have compact dimensions with high efficiency.

Functional diagram of the welding inverter

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

• a primary rectifier unit, the basis of which is a diode bridge (the task of such a unit is to rectify an alternating current supplied 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, due to a decrease in the input voltage, the output current is significantly increased (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 block of the inverter includes rectifying an alternating high-frequency current, which is necessary for performing welding work).

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