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, repair of inverter welding machines can be carried out independently by examining the device of the inverter, but there are breakdowns that can only be fixed at a 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 possibilities of electrical wiring, then the unit will not work with a sagging network.

So, the device of the inverter welding machine includes the following main modules.

Just like diodes, transistors are mounted on heatsinks for better heat dissipation. To protect the transistor block 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 receives voltage from the household electrical network or from generators, gasoline or diesel. The incoming current is variable, but passing through the diode block, becomes permanent. The rectified current is fed to the inverter, where it is inversely converted 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 current strength. At the next stage, the current again enters the rectifier, where it is converted to direct current, after which it is fed to the output terminals of the unit. All current conversion controlled by a microprocessor control unit.

Video (click to play).

Modern inverters, especially those made on the basis of an IGBT module, are quite demanding on operating rules. This is explained by the fact that during the operation of the unit, its internal modules give off a lot of heat. Although both heatsinks 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, it is necessary to strictly follow the rules that are indicated in the instructions for the device, which imply periodic shutdown of the unit for cooling.

This rule is usually referred to as “Duration On” (DU), which is measured as a percentage. Not observing the PV, the main components of the apparatus overheat and fail. If this happens with a new unit, then this failure is not subject to warranty repair.

Also, if the inverter welding machine is running 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 contaminants.

But more often than not, inverters fail when they work at low temperatures. Breakdowns occur due to the appearance of condensate on a heated control board, resulting in a short circuit between the parts of this electronic module.

A distinctive feature of the inverters is the presence of an electronic control board, so only a qualified specialist can diagnose and fix a malfunction in this unit.. In addition, diode bridges, transistor blocks, transformers and other parts of the electrical circuit of the device may 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 foregoing, 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 the repair of the welding inverter will cost half the cost of a new unit.

As already mentioned, inverters fail due to the impact on the “vital” blocks of the apparatus of external factors. Also, malfunctions of the welding inverter can occur due to improper operation of the equipment or errors in its settings. The following malfunctions or interruptions in the operation of inverters are most often encountered.

Very often this failure is caused network cable failure device. Therefore, you first need to remove the casing from the unit and ring each cable wire 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 supply of the device. The technique for repairing the “duty room” using the example of a Resant brand inverter is shown in this video.

This fault can be caused by incorrect current setting for a certain electrode diameter.

It should also be taken into account welding speed. The smaller it is, the lower the current value must be set on the control panel of the unit. In addition, in order for the current strength to correspond to the diameter of the additive, you can use the table below.

If the welding current is not adjusted, the cause may be regulator failure or violation of the contacts of the wires connected to it. It is necessary to remove the casing 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 it, 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 by a specialist.

Excessive power consumption, even when the machine is unloaded, causes, most often, interturn short circuit 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 network voltage drops. To get rid of the electrode sticking to the parts to be welded, you will need to correctly select and adjust the welding mode (according to the instructions for the machine). Also, the voltage in the network may sag if the device is connected to an extension cord with a small wire section (less than 2.5 mm 2).

It is not uncommon for a voltage drop to cause electrode sticking to occur when using a power extension 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 may spontaneously turn off, which indicates thermal protection trip. So that these interruptions in the operation of the unit do not happen in the future, again, it is required to adhere to the correct duty cycle (PV).For example, if PV = 70%, then the device must operate in the following mode: after 7 minutes of operation, the unit will be given 3 minutes to cool down.

In fact, there can be quite a lot of various breakdowns and causes 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. 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 humoften 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 apparatus “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 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 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.

The existing 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).

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, burnt out conclusions. If this is found, you can start repairing the inverter by replacing it. This is what a broken key looks like.

And this is how it was 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.

control board control. 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.

Every good owner has a small welding machine. It is always useful in the manufacture of greenhouses, garage doors, fences 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 household chores and even earn a living. When such a device breaks, it obviously upsets its owner. Every piece of equipment breaks down from time to time. How to repair welding machines yourself, without outside help? What do you need to know for this? Where to begin?

For successful repair of the welding unit, elementary knowledge of the electronic and mechanical parts of the device is required. In those models where an inert gas is used, one more side is added for research. 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 phased inspection of each node. The identified faults are analyzed and compared with the nodes responsible for this part. And for this it is necessary to understand the purpose of each block well. In the simplest transformers, two windings are used, between which a magnetic field arises, contributing to a decrease in volts and an increase in amperes. The device is also equipped with a mechanical component, in the form of a screw and a movable platform, which changes the distance between the windings, which regulates the current strength.For rotation, a special handle on the lid is used.

The device of inverters exceeds the complexity of a conventional transformer. The equipment scheme has:

• electronic controller that controls the process;
• straightening block;
• a node where the voltage is directly inverted (it 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 that is failing, and more quickly restore its operation. The process is carried out in the following sequence:

1. The current from the outlet 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 node increases the frequency of the current to a large value due to transistors that return the voltage to alternating.
3. The transformer processes the current flowing into it, reducing the volts to safe levels, and raising the amps to values ​​\u200b\u200bthat can melt metal.
4. The electronic board controls the welding processes and regulates important parameters.

By measuring the voltage at different nodes of the structure with a tester, you can identify a section without current, or with insufficient indicators, and proceed with the repair of 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 of an inverter or transformer type, also have traction mechanisms involved in the welding process. Often such units consist of lower rollers on the axle and their clamping pairs, the pressure force of which is regulated by a spring. The rotation of the rollers and the drum with wire is carried out by a small motor and a gearbox that transmits torque.

Semi-automatic 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 the protection of the weld pool. Breakdowns can occur in any part of the device, so understanding its main elements will help you quickly identify the “disease” that has arisen and begin “treatment”.

The complexity of the repair depends on the type of failed part. This is not always due to complex reasons. Often there are cases when the device continues to work, but does not do it naturally, with extraneous sounds, or with poor quality of the weld. 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 device regularly overheated. If the equipment was stored in a damp room, then the dust accumulated inside could serve as a conductor and lead to a short circuit. In dry conditions, such dust serves as an additional "insulation" on the electronic part, preventing it from cooling down, which leads to the burnout of the elements.

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

• transistors with swollen body shapes;
• circuit elements with soot on the legs;
• details with a dark body color;
• objects in the scheme 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 help of the tester.

The tester allows you to check the presence of contact between different sections of the circuit. Sometimes, a break can occur on a diode bridge, inverter module, or other nodes. Step by step testing will help you move forward by elimination to finding the cause.It is worth testing even 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 tested in a similar way.

The complete inoperability of the apparatus could be caused by a short circuit of the turns of the transformer. The tester can detect this breakdown. If detected, 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. A frequency of control signals that 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 you to weld, but the settings are lost. Self-repair of devices involves finding the causes of such a deviation and restoration work.

In welding transformers, over time, the screw thread that regulates the distance between the coils wears out, which affects the current strength. 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 resumes the full operation of the device.

In semi-automatic machines, the filler wire can get stuck, which complicates the conduct of the seam. The jerky feed and "punctures" of the weld pool affect the quality of the connection. The reason is the clogging of the wire feed channel, which is cleaned with a bar with a diameter as close as possible to the inner diameter of the feed path. Slippage of the wire on the rollers may indicate a broken groove that clearly exceeds the width of the filler material being used. 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 manometer 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 won't hurt either. Also, it is necessary to ensure that the hose is not twisted at bends.

Sooner or later, any welding machine will break down and require repair. Applying the above recommendations, and having visually familiarized yourself with the individual processes on 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 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.

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

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 underlying the operation of the inverter that allows such equipment to be compact in size with high efficiency.

Functional diagram of the welding inverter

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.