The most complex element of the inverter is the key control board, the operability of which depends on the operability of the entire device. Such a board for the presence of control signals that are fed to the gate buses of the key block is checked using an oscilloscope. The final stage in testing and repairing the electronic circuits of the inverter device should be to check the contacts of all existing connectors and clean them with a regular eraser.
Self-repair of an electronic device such as an inverter is quite difficult. It is almost impossible to learn how to repair this equipment just by watching a training video, for this you need to have certain knowledge and skills. If you have such knowledge and skills, then watching such a video will give you the opportunity to make up for the lack of experience.
VIDEO The design of a welding inverter is rather complex, therefore, the least safe to operate. The great advantage is the high quality of the work performed by the device. At the same time, any structure wears out and breaks down over time. Therefore, there are two solutions to this problem. In the first case, the apparatus is repaired by hand, and the second case is associated with contacting specialists for the repair of welding inverters.
Diagram of a welding inverter semiautomatic device.
A complex device requires appropriate knowledge and the correct approach to repair. It is important to understand electronics here, that is, diodes, transistors, resistors and stabilizers.
What devices will be needed for this:
Multimeter connection diagram.
Other special instruments will be required to measure various indicators. It can be too difficult to detect a malfunction, therefore, it will be necessary to check all the elements more than once, their certain sequence, in which they should be contained in the general scheme.
The operation of the inverter is based on a scheme associated with a step-by-step signal conversion. Initially, the current is rectified due to the input rectifier, after which it begins to be converted into variable frequency current due to the inverter module. Then, a power transformer is involved in the conversion process, therefore, the frequency current is converted into a welding one. After the transformer, the variable frequency current is converted into a welding form due to the output rectifier. Before inspecting the inverter, refer to its microcircuit and drawings.
It is necessary to emphasize that the main features of welding inverters is the accuracy of work. If even the highest quality inverter is out of order, then among the main reasons for this are the following:
Incorrect use of the device.
Lack of accurate connection of the device.
Changes in mains voltage.
Changes in current strength.
Figure 1. List of possible malfunctions of the welding inverter.
The causes of breakdowns can also be bad weather conditions, if they are observed during the operation of the device on the street. These may be too dirty rooms, high levels of humidity, rain, snow, etc. The most vulnerable point of the inverter is the terminal block, the cable is connected to it. The lack of normal contact and at the same time a significant indicator of the current strength will be a prerequisite associated with overheating of all elements and connections.
Melting of the insulation is also a malfunction, which can cause a short circuit. The list of possible malfunctions is presented in the table (Fig. 1).At the same time, do-it-yourself repair of the welding inverter is carried out by stripping the contacts and tightly joining the connection, which heats up during operation.
There are the following main stages associated with the diagnosis of inverter malfunctions:
The equipment does not turn on.
The inverter shuts down by itself.
The appliance makes a lot of noise.
Strong overheating of the structure occurs.
An interruption of the electric arc is observed during welding.
Poor current regulation.
Electricity consumption is over-limit.
If the device does not turn on, then the main reason for this is:
Lack of mains voltage.
Operation of the machine on the dashboard.
The equipment stops working.
Before starting the repair of the inverter for welding with their own hands, they check the transistors, which often fail in the first place.
Diagram of an electronic oscilloscope device.
A thorough inspection will be required here. The appearance of the faulty part speaks for itself, featuring a warped body. If a burned-out transistor is found, it must be replaced with a new one. If there are no external defects, then with the help of a multimeter it is necessary to ring the transistor, after which you should select a new element and make it a high-quality installation in place of the previous transistor.
Power transistors have driver elements that should be checked second. This type of parts is more resistant to damage, since this can happen to the elements that power the drivers themselves. An ohmmeter allows you to check the performance of the power transistors, after which the part can be evaporated and replaced with an analog.
If there are difficulties in detecting defects, then it is very important to check the rectifiers connected by diode bridges mounted on the basis of a radiator. These elements of the inverter have significant durability, as breakdown inside the mechanism can occur. Diagnostics of the diode bridge requires first to release it from any wires with a soldering iron, removing it from the control board, respectively. The work with the inverter is greatly facilitated by the lack of dependence of the circuit on a short circuit. A soldering iron equipped with a suction helps to evaporate the faulty diode.
Finishing the diagnostics, they inspect the board that allows you to manage the keys. This detail is a complex and important element of the apparatus. Finishing the repair of the inverter, they check the operation of the control signals, which should go to the busbars of the gates of the key module.
Diagram of the front panel of the inverter.
Monitoring this control signal is not difficult as an oscilloscope can be used. If the case is unclear, expert intervention will be required.
Long and trouble-free operation of the inverter can be ensured by observing special rules:
Carrying out a technical inspection of the welding inverter before starting work with it and preparing the workplace.
Installation of the device in a horizontal position, which will prepare the workplace.
Connecting welding cables to the power connectors of the device: to the electrode holder with a "+" sign, and to ground - with a "-" sign.
Checking the fixation of the cable glands in the soldering sockets by turning them clockwise.
Connect the appliance to the power supply by plugging it into a power outlet.
Switch the switch to the "ON" position to turn on the fan.
Trial arc ignition.
The current regulator knob sets the required mode for welding.
If you follow the recommendations related to the correct maintenance of the device, then it will serve for a long time:
Block diagram of a digital voltmeter with a time-to-pulse converter.
It is strictly forbidden to use the device with the cover removed for a long time.
Inspection of the internal components of the device should be carried out more often, which is determined by the frequency of use of the device and the degree of contamination of the working space.
The dust accumulated in the device must be removed by using compressed air at low pressure, i.e. less than 10 bar.
Cleaning of electronic boards is not done with a jet of compressed air, but only with a small brush.
Before carrying out work, a safety check should be carried out when fixing the power connectors in the corresponding sockets of the device, check the power plug, the socket and the insulation of the electronic cable.
The device must be transported and stored in accordance with the weather conditions.
When transporting the device by transport, it can also be placed in an upright position.
Store the device only in a dry room where the relative humidity is 80%.
The inverter is kept disconnected from the mains.
Welding inverter circuit.
To repair a faulty inverter, you should find out all the principles of its operation. At the first stage of work with a welding inverter, the mains voltage is rectified by the devices, and then it is converted into a variable frequency voltage. After that, it is reduced to a level that allows safe welding. The last stage is associated with the presence of constant welding voltage.
The listed processes are regulated by the control unit, which has a rather complex design. Starting the repair of the welding inverter, it must be visually inspected in order to clean out all the places that do not have normal contact.
These zones are traditionally rectifier diodes. It is possible to mount the diodes using threaded connections, and all special tools are not needed.
Pre-check the diodes, examining their "throughput" or "breakdown", which is associated with the possibility of free passage of current through the diode in the same direction. This is done with a multimeter. With a constant resistance, in the case of measurements from plus to minus, the diode should be replaced.
VIDEO Even a faulty diode will allow welding with an inverter, and the ability to turn on the device is not associated with ensuring normal operation. If the device cannot be turned on or off normally, an urgent repair will be required. Any inverter model has a fuse on the control board. If you dismantle it, then you can get to this device.
Removing the control board requires marking all connectors, of which there can be more than three, and they themselves are similar to each other. If the fuse is defective, then it is not difficult to assemble and install it, only patience and accuracy are required.
Welding inverter power circuit.
Often the reason for the failure of the transistors of welding inverters is insufficient cooling. The element contact must have thermal grease and a heat sink plate. It is not difficult to unsolder and install the part, but it is imperative to control the possibility of its overheating, since a sufficiently hard-melting solder is used for soldering.
If the power transistor fails, then this leads to breakdown of the drivers adjacent to this part. Diodes and zener diodes can often fail. The transistors are first inspected from the outside and then replaced.
If the transistors have already been inspected and checked, followed by replacement, since the cause of their breakdown has been found, then the presence of a "swinging" driver is considered as a prerequisite. Similarly, using the tester, you can call any elements of the board, replacing them with serviceable ones.
It is imperative to check the printed conductors of the board, which will reveal the presence of burn. Existing burnt-on areas can be removed and the other jumpers can be re-soldered. All soldering points are covered with a special varnish.First, check and clean each pin of the connectors with a white drawing eraser.
Diagram of the internal device of the welding inverter.
Rectifiers are output and input full-wave diode bridges that are equipped with silicon valves. They are considered reliable parts, but they can also wear out. Controlling them is not a difficult task. Soldering bridges from electronic circuits is associated with dismantling the brackets. If the bridge is ringing only in one of the directions, then it is serviceable, and if in both directions at once, then this bridge is broken. The check is carried out when the bridge is already assembled and in place.
Checking the board that allows the control of the device is associated with a continuity tester, which allows you to control the gate control signal using the key module. You can check it using an instrument called an oscilloscope. In a normal test, all signals will be correct, otherwise it will turn out that something has been missed.
VIDEO If a semiautomatic welding machine is used, then only mechanical malfunctions can occur in it. For example, if a wire feed delay is detected, this may be due to the following two reasons:
The wire feeder has a low clamping force that needs to be adjusted correctly.
A strong process of friction is observed between the wire and the channel in the sleeve.
VIDEO
Change the channel in one pull. For this purpose, the old one is removed and a new channel is placed, allowing to unite the beginning and the end.
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.
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.
VIDEO
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.
When buying an inverter welding machine for working in a garage or in the country, the first thought is - wow, now I’ll cook everything! No need for a welder's diploma, the device is designed for a user without special education. Welding is now easier and more comfortable to handle. The main thing is to understand the principle of work and first aid in case of difficulties and breakdowns.
Since the early 2000s, inverter welders have become cheaper and more affordable. To carry out welding at home, it is enough to have this small and easy-to-use device and good electrodes.
Inverter machines are lightweight, compact, and their scope of use and welding quality are higher than those of heavy and bulky welding transformers. They fulfill their task in full: they cook cars, gates, pipe structures (for example, greenhouses or gazebos). Working with them is mobile - throwing a sliding belt over your shoulder, welding is carried out in any hard-to-reach places.
With vertical, horizontal or top welding, the current is reduced by 10–20%, and when welding at an angle, it is increased by the same amount compared to the normal position.
There are also no problems with the connection, the welding machine works from a normal electrical network. It is great that it will not stop when the mains voltage drops. If the deviation is within +/- 15%, the device will continue to work normally. The current value can be adjusted by selecting the power depending on the type and thickness of the metal. All this makes inverters ideal for beginners and professionals alike.
VIDEO
The inverter machine connects parts with direct current using electric arc welding with a coated electrode. A big plus is that at the very beginning of the process there are no power surges in the network to which the device is connected. The storage capacitor ensures the continuity of the electrical circuit and soft ignition of the arc with its further automatic maintenance. When connected to an electrical outlet, the 50 Hz AC mains voltage is converted first into a DC voltage and then into a high-frequency modulated voltage. Then, with the help of a high-frequency transformer, the current increases, the voltage decreases, and the output current is rectified. The device provides for the adjustment of the welding current and protection against overheating.
The basic operating mode of inverter welding machines is MMA. This is manual arc welding with stick electrodes.For welding steel and cast iron products on direct or alternating current, a diameter of 1.6–5.0 mm is used.
Devices differ in power and duration of the working cycle ... The second indicator is the period during which it is allowed to cook at the maximum permissible power in order to prevent the device from overheating. It is denoted by the letters PV (on period) and is determined as a percentage relative to a unit of time of 10 minutes. For example, if the PV of 60% is indicated on the device, this means that it can be cooked for 6 minutes, and then turned off for 4 minutes. Sometimes the welding cycle is set to 5 minutes. Then the value of the PV indicator of 60% indicates the period of work in 3, and rest in 2 minutes. Indicators of PV and duty cycle are indicated in the instructions for each device.
In order not to look for a repair specialist at the first difficulties in the operation of the device, it is advisable to have at least a basic understanding of its design.
Craftsmen with knowledge of electrical engineering assemble the welding machine themselves. Not only for the sake of economy, but also at the behest of the creative soul. Circuit diagrams of inverters, drawings and instructions of those who made the inverter themselves are posted on the Internet. The main thing is to get stability of the welding arc. Most often, the "oblique bridge" scheme ("Barmaley's circuit") is used using two key transistors: bipolar or field-effect. They are placed on a radiator to dissipate heat, they open and close synchronously.
The electrical design of the circuit eliminates high-voltage emissions and allows the use of relatively low-level switches. The scheme is used because of its simplicity, reliability and not very expensive consumables.
VIDEO
The apparatus is assembled from the following blocks:
power supply for stabilization of input signals. A metal partition is placed between it and other elements and blocks. The multiwinding inductor is controlled by transistors and a stored energy capacitor. Diodes are used in the throttle control system;
a power unit, with the participation of which a complete current conversion cycle takes place. Collected from a primary rectifier, an inverter transistor converter, a high-frequency step-down transformer and an output rectifier;
Control block. It is based on a master oscillator with a special microcircuit or a pulse-width modulator. They put a resonant choke and 6-10 resonant capacitors;
protective block. Most often they are assembled on a power unit, installing thermal switches for thermal protection of its elements. To avoid overloads, they put a board based on the 561LA7 microcircuit. Snubbers with resistors and capacitors K78-2 protect the converter and rectifiers.
VIDEO
The design of inverter welding machines is more complicated than transformer ones and, unfortunately, less reliable. This often leads to the failure of various nodes for the following reasons:
low protection against dust. When it accumulates inside, a thermal protection signal is triggered, the device turns off. Disassembly is required at least twice a year to clean the internal parts with a jet of compressed air or a soft brush;
ingress of moisture inside, causing a short circuit, dangerous for the unit;
low quality of the cooling system in cheap devices. Because of this, the plastic parts of the structure melt, the emergency shutdown does not work. In models with tunnel ventilation, the radiator is located along the case, and the main components are located inside it. Such devices are much more expensive;
voltage surges, especially a drop to 190 V or more;
overload when cutting thick metal and work for which the specific device is not designed. Then the IGBT power module fails;
poor-quality fastening in the contacts of the pads, which provokes overheating of these places and sparking;
sensitivity to shocks and falls due to the presence of plastic parts;
poor quality of spare parts that are used for repairs;
violation of the permissible temperature regime. Electronic microprocessors melt and degrade when overheated. It is recommended to adhere to the range from -10 to +40 o C.
Malfunctions are both mechanical and associated with the failure of electronics. The welding machine is a complex device, problems can arise anywhere:
A short circuit or breakdown in any important node of the electrical circuit makes it impossible to operate the welding machine:
a malfunction of the control board does not give a stable welding current and does not allow a normal arc to be obtained;
damage to the transistor of the upper printed circuit board leads to the shutdown of the device;
failure of the overheating protection system is determined by the smell of burnt insulation, smoke comes from inside the case.
When starting to repair a faulty unit, it is worth considering some points.
The poor quality of the device does not always mean an internal breakdown. Wet or poor quality electrodes are often the culprit. If drying or replacing does not produce a beautiful seam, consider other possible reasons:
It is important to select the correct size of the electrodes for the correct operation of the welding machine.
To be able to repair the welding machine yourself, you first need to deal with its internal structure. On the front panel there are sockets for working cables, a knob for the current regulator and a power indicator. If the design provides for additional functions, the operating indicators are located here.
The check begins with an external examination of the device. The first step is to check for mechanical damage. If there are black spots on the case, most likely a short circuit has occurred. The tester checks the fuses, replace them if necessary, inspect the insulation of the welding cables, the connections in the sockets. If necessary, tighten the bolts, clean the contacts.
After unscrewing the screws and removing the cover, the inside of the machine opens, where the following components are located:
power transistor board;
control board;
rectifier diode board;
mains voltage rectification board;
fan;
controls - knob and switches.
The following tools are required for repairs.
Multimeter with multiple modes:
ringing the chain;
ringing diodes;
voltage measurement;
resistance test.
Oscilloscope. It is used to test diodes, zener diodes, transistors, capacitors and other elements of an electrical circuit. Repairing a welding machine is much more difficult without an oscilloscope.
The filling of the welding machine is understandable for those who work with radio electronics. If the necessary skills are not available in this area, the intervention will only harm. Without knowing the rules for handling the board and the technology of such delicate work, you can cause much more damage than the initial one. It is cheaper and safer to entrust the repair to a professional.
If it is difficult to find a specialized workshop, you have to restore the welding inverter yourself. Important check in sequence what stopped the operation of the device.
If difficulties arise, read the operating instructions for the welding machine first. It necessarily contains a section on possible problems during welding, causes of malfunctions and recommendations for their elimination.
After removing the cover of the device, there is often a noticeable violation of the soldering of parts, swelling of capacitors, breakage of contacts. In such cases, the damaged parts are replaced with similar ones. Torn off and burnt areas are removed and re-soldered. If it is not possible to quickly determine the cause of the breakdown, check each element of the electrical circuit. Diodes, transistors, zener diodes, resistors and other parts are tested.
A detailed check is carried out sequentially: from the parts that most often fail to the most resistant ones.
Unplug the device from the socket before checking the power supply!
For self-repair, craftsmen use phosphoric acid. If you need to solder something to the diode cases (for example, broken off racks), they are pre-tinned. When repairing a broken-off rack, take into account the perpendicularity. It is important to install it by clearly aligning the holes. If you solder, even with a minimal skew, the post will break again when you tighten the fastener again.
If there is no technical hair dryer, a 100–150 W soldering iron is used for desoldering. This will not damage the connectors and tracks. Experts recommend, for a better result, before soldering, heat the block to 160–170 ° C, while the plastic parts of the fan should not be heated. When working with a soldering iron or other heating elements, care must be taken not to touch the fusible parts of the apparatus.
VIDEO
Video (click to play).
The inverter welding machine is confidently registered in home workshops. Before buying, it is worth taking the time to learn the basics of welding and electrical engineering. This will help you navigate the characteristics of the device and, if necessary, repair it yourself. It is better to entrust difficult cases to specialists.
