Repair welding inverters with your own hands: we repair the welding machine
Repair of welding inverters, despite its complexity, in most cases you can do it yourself. And if you understand the design of such devices and have an idea about it, that they are more likely to fail, you can successfully optimize the cost of professional service.
Replacement of radio parts in the process of repairing the welding inverter
Purpose of equipment and features of its design
The main purpose of any inverter is the formation of direct welding current, which is obtained by rectifying a high-frequency variable. The use of high-frequency alternating current, converted using a special rectified inverter module, due to the fact, that the strength of such current can be effectively increased to the required value by means of a compact transformer. It is this principle, put into operation of the inverter, allows such equipment to have a compact size with high efficiency.
Functional diagram of the welding inverter
Scheme of welding inverter, which determines its technical characteristics, includes the following basic elements:
- primary rectifier unit, the basis of which is a diode bridge (the task of such a unit is the rectification of alternating current, coming from the standard electrical network);
- inverter unit, the main element of which is the transistor assembly (it is with the help of this unit DC, coming to his entrance, turns into a variable, whose frequency is 50-100 kHz);
- high speed lowering transformer, on which due to the reduction of the input voltage significantly increases the strength of the output current (due to the principle of high-frequency transformation at the output of such a device can be generated current, whose strength comes to 200-250 A);
- output rectifier, assembled on the basis of power diodes (the task of this inverter unit is the rectification of alternating high-frequency current, what is needed to perform welding work).
The circuit of the welding inverter contains a number of other elements, which improve its performance and functionality, but the main ones are listed above.
Features of maintenance and repair of inverter devices
Repair of the welding machine, relating to the inverter type, has a number of features, due to the complexity of the design of such a device. Any inverter, unlike welding machines of other types, is electronic, which requires specialists, engaged in its maintenance and repair, availability of at least basic radio engineering knowledge, as well as skills in handling various measuring devices - voltmeters, digital multimeter, oscilloscope and others .
In the process of maintenance and repair, the elements are checked, of which the welding inverter circuit consists. These include transistors, diodes, resistors, zener diodes, transformer and choke devices. The peculiarity of the inverter design is, which is often impossible or very difficult to determine during its repair, failure of which element was the cause of the fault.
A sign of a burnt resistor may be a small deposit on the board, difficult to distinguish with the untrained eye
In such situations all details are consistently checked. To successfully solve this problem, it is necessary not only to be able to use measuring instruments, but also quite well versed in electronic circuits. If you do not have such skills and knowledge at least at the initial level, then repairing the welding inverter with your own hands can lead to even more serious damage.
Really appreciating your strengths, knowledge and experience and deciding to undertake self-repair of inverter equipment, it is important not only to watch a training video on this topic, but also carefully study the instructions, in which manufacturers list the most typical faults of welding inverters, as well as ways to eliminate them.
Factors, leading to failure of the welding inverter
Situations, which 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;
- due to failure of parts of the device or their malfunction.
The method of detecting the inverter malfunction for further repair is reduced to the sequential execution of technological operations, from the simplest to the most complex. They, on what modes such checks are performed and what is their essence, usually agreed in the instructions for the equipment.
Common inverter faults, their causes and ways to eliminate
If the recommended actions did not lead to the desired results and the device is not restored, most often it means, that the cause of the fault should be sought in the electronic circuit. The reasons for the failure of its blocks and individual elements may be different. List the most common.
- Moisture has penetrated into the inside of the device, what can happen, if precipitation falls on the body of the device.
- On the elements of the electronic circuit of dust accumulation, which leads to a violation of their full cooling. The maximum amount of dust in the inverters falls in those cases, when they are operated in very dusty rooms or on construction sites. In order not to bring the equipment to such a state, its inner part must be cleaned regularly.
- Before overheating the elements of the electronic circuit of the inverter and, Consequently, failure to observe the duration of inclusion may lead to their failure (PV). This parameter, which must be strictly adhered to, specified in the technical data sheet of the equipment.
Traces of liquid entering the inverter housing
common faults
The most common faults, encountered in the operation of inverters, there are the following.
Unstable combustion of the welding arc or active spraying of metal
This situation may indicate that, 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 the speed of welding. If on the packaging of the electrodes, which you use, does not contain recommendations for the optimal amount of current, it can be calculated by a simple formula: on 1 mm of electrode diameter should be 20-40 A welding current. It should also be considered, that the lower the speed of welding, the lower the current should be.
Dependence of the diameter of the electrodes on the strength of the welding current
Adhesion of the electrode to the surface of the parts, connecting
There are a number of reasons for this problem, while most of them are based on low supply voltage. Modern models of inverter devices work at low voltage, but, when its value falls below the minimum value, on which the equipment is intended, the electrode begins to stick. The drop in voltage at the output of the equipment may occur in that case, if the unit blocks are in poor contact with the panel sockets.
This reason is eliminated very simply: cleaning of contact sockets and more dense fixing in them of electronic boards. If the wire, by which the inverter is connected to the mains, has a smaller cross section 2,5 mm 2, then it may also cause a voltage drop at the input of the device. This is guaranteed to happen in that case as well, if such a wire is too long.
If the length of the supply wire exceeds 40 meters, use an inverter for welding, which will be connected with it, practically impossible. The mains voltage of the circuit may drop in that case, if its contacts are burned or oxidized. Insufficient preparation of surfaces of details becomes the frequent reason of sticking of an electrode, welded, which must be thoroughly cleaned not only of existing contaminants, but also from the oxide film.
Choice of welding cable cross section
Impossibility to start welding process when the device is switched on
This situation often occurs in case of overheating of the inverter device. The control indicator on the device panel should light up. If the glow of the latter is inconspicuous, and the inverter does not have an audible alert function, then the welder may simply not know about the overheating. This state of the welding inverter is typical in case of breakage or involuntary disconnection of welding wires.
Spontaneous shutdown of the inverter during welding
Most often such a situation arises in that case, if the supply voltage is switched off by circuit breakers, whose operating parameters are incorrectly selected. When working with the inverter device in the electrical panel must be installed machines, designed for current not less 25 A.
Impossibility to turn on the inverter when turning the toggle switch
Probably, this situation indicates, that the mains voltage is too low.
Automatic shutdown of the inverter during prolonged welding
Most modern inverter devices are equipped with temperature sensors, which automatically turn off the equipment when the temperature in its interior rises to a critical level. There is only one way out of this situation: give the welding machine a rest on 20-30 minutes, during which it cools.
How to perform self-repair of the inverter device
If after testing it becomes clear, that the cause of the malfunction of the inverter device lies in its inner part, you should disassemble the case and start inspecting the electronic filling. It is possible, that the reason is poor soldering of parts of the device or poorly connected wires.
Careful inspection of electronic circuits will reveal faulty details, which may be darkened, cracked, with a swollen body or have burnt contacts.
Burned parts on the Fubac IN-160 inverter board (AC-DC regulator, transistor 2NK90, resistor 47 Ohm)
Such details at repair need to be soldered from boards (it is desirable to use a soldering iron with suction), and then replace with similar ones. If the markings on the defective elements are not readable, then you can use special tables for their selection. After replacing defective parts, it is advisable to test electronic boards with a tester. The more it needs to be done, if the inspection did not reveal elements, subject to repair.
Visual inspection of electronic inverter circuits and their analysis with a tester should start with the power unit with transistors, since he is the most vulnerable. If the transistors are faulty, then, probably, failed and swing their contour (driver). Elements, of which such a contour consists, it is also necessary to check first.
Inverter power unit
After checking the transistor unit, all other units are tested, for which a tester is also used. The surface of the printed circuit board must be carefully inspected, to determine the presence of burnt areas and cliffs. If any, then such places should be carefully cleaned and jumpers soldered to them.
If burnt or broken wires are found in the inverter filling, then at repair they need to be replaced with similar on section. Although diode bridges of inverter rectifiers are quite reliable elements, they should also be called by a tester.
The most complex element of the inverter is the key management board, on serviceability of which working capacity of all device depends. Such a fee for the presence of control signals, which are fed to the shutter bus keys, check with an oscilloscope. The final stage of testing and repair of 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 such electronic device, as an inverter, quite complex. Learn how to repair this equipment, just watching the training video, practically impossible, this requires certain knowledge and skills. If you have such knowledge and skills, then watching such a video will give you the opportunity to fill the lack of experience.
