DIY welding transformer repair

In detail: do-it-yourself repair of a welding transformer from a real master for the site my.housecope.com.

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).

Video (click to play).

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.

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

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

A sign of a burnt out resistor may be a small carbon deposit on the board, which is difficult to distinguish with an inexperienced eye.

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

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

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

associated with the wrong choice of welding mode;

caused by the failure of parts of the device or their incorrect operation.

The technique for detecting an inverter malfunction for subsequent repair is reduced to the sequential execution of technological operations, from the simplest to the most complex. The modes in which such checks are performed and what their essence is, is usually specified in the equipment instructions.Common inverter malfunctions, their causes and remediesIf the recommended actions did not lead to the desired results and the operation of the device has not been restored, most often this means that the cause of the malfunction should be looked for in the electronic circuit. The reasons for the failure of its blocks and individual elements may be different. Let's list the most common ones.

Moisture has penetrated into the interior of the device, which can happen if precipitation falls on the body of the device.

Dust has accumulated on the elements of the electronic circuit, which leads to a violation of their full cooling. The maximum amount of dust gets into inverters when they are used in highly dusty rooms or on construction sites. In order not to bring the equipment to such a state, its interior must be regularly cleaned.

Overheating of the elements of the electronic circuit of the inverter and, as a consequence, their failure can lead to non-observance of the duration of the switch (DC). This parameter, which must be strictly observed, is indicated in the technical passport of the equipment.

Liquid traces inside the inverter housingThe most common problems encountered when operating inverters are as follows.Unstable arc burning or active metal spatter This situation may indicate that the wrong amperage has been selected for welding. As you know, this parameter is selected depending on the type and diameter of the electrode, as well as on the speed of welding. If the packaging of the electrodes that you are using does not contain recommendations on the optimal value of the current strength, you can calculate it using a simple formula: 1 mm of the electrode diameter should account for 20–40 A of welding current. It should also be borne in mind that the lower the welding speed, the lower the current should be.

Dependence of the diameter of the electrodes on the strength of the welding currentThis problem can be associated with a number of reasons, and most of them are based on undervoltage. Modern models of inverter devices also operate at reduced voltage, but when its value drops below the minimum value for which the equipment is designed, the electrode begins to stick. A drop in the voltage value at the output of the equipment can occur if the device blocks do not contact the panel sockets poorly.This reason can be eliminated very simply: by cleaning the contact sockets and fixing the electronic boards in them more tightly. If the wire through which the inverter is connected to the mains has a cross-section of less than 2.5 mm2, this can also lead to a voltage drop at the input of the device. This is guaranteed to happen even if such a wire is too long.If the length of the supply wire exceeds 40 meters, it is practically impossible to use an inverter for welding, which will be connected with its help. The voltage in the supply circuit can also drop if its contacts are burnt or oxidized. A frequent cause of electrode sticking is insufficiently high-quality preparation of the surfaces of the parts to be welded, which must be thoroughly cleaned not only from the existing contaminants, but also from the oxide film.Selection of the cross-section of the welding cableThis situation often occurs in the event of overheating of the inverter device. At the same time, the control indicator on the panel of the device should light up. If the glow of the latter is hardly noticeable, and the inverter does not have a sound alert function, then the welder may simply not be aware of overheating. This state of the welding inverter is also typical when the welding wires are broken or spontaneously disconnected.Spontaneous shutdown of the inverter during welding Most often, this situation occurs when the supply of the supply voltage is turned off by circuit breakers whose operating parameters are incorrectly selected. When working with an inverter device, automatic machines designed for a current of at least 25 A must be installed in the electrical panel.

Cables and various connecting components on it can overheat due to improper use of technology (for example, with prolonged use of the device at the highest current value) and due to the presence of poor contact.

Under such conditions, the insulation of the wires begins to melt, which leads to a short circuit of the electrical circuit. You can cope with the voiced problem with your own hands, it is enough to thoroughly strip the cables and the places of their contact with the equipment, and then dock them together as tightly as possible.

The presence of any malfunction in the device is usually signaled by the following symptoms:

the welding current is difficult to adjust;
there is a spontaneous shutdown of the unit;
the welding arc is interrupted periodically;
starting the equipment causes certain difficulties (it does not turn on the first time, it turns on and immediately turns off, and so on);
During welding, the unit becomes very hot and hums.

Next, we will talk about what malfunctions are inherent in welding inverters, rectifiers and transformers, and give advice on how to fix them yourself.

Now welding inverters are used both in industrial enterprises and individuals. These units provide real comfort for the welder and guarantee a high quality of the welding process. This is achieved due to the complication of their design, which, naturally, in most cases reduces the reliability of inverters.It is not always possible to repair inverter equipment with your own hands, since it is an electronic technique, and not a simpler electrical device (like a transformer or rectifier for welding). And this means that the diagnosis of unit breakdowns and their elimination require a person to have special knowledge.To successfully restore the operability of such installations with their own hands, the user must “be on your toes” with a variety of measurement equipment, from multimeters to oscilloscopes. These devices make it possible to carry out accurate diagnostics of inverters and their electronic "stuffing" (zener diodes, diodes, all kinds of transistors, etc.), thereby establishing all existing faults. Image - DIY welding transformer repair

The difficulty of repairing inverter welding machines is that a person must consistently check the electrical circuit of the unit and find the failed component. Otherwise, nothing will work, since by the nature of the malfunction it is almost impossible to find the “dead” element of the welding equipment.

Thus, if you have never dealt with electronics, there is no point in doing inverter repairs with your own hands. You will simply waste energy and waste a lot of time, but you will not achieve anything. Moreover, there is a danger that during such a "repair" you will only aggravate the problem by disrupting the electrical circuit.

In the same cases, when a person has experience with microcircuits and electrical components, he may well cope with simple breakdowns of welding inverter equipment. Usually, its malfunctions are revealed during the following checks:

Analysis of the performance of diode bridges (output and input rectifiers), which are mounted on a radiator. They should be dismantled from the board by disconnecting the wiring, and then look for a punched rectifier using the elementary ringing method. After identifying a non-functioning component, it is replaced with a new one. Experts advise to use a special soldering iron equipped with a suction mechanism to perform such an operation.
Checking the components of the driver. Carried out with an ohmmeter. When a failed driver is found, it is soldered off, a suitable analog is selected from the device datasheet and replaced by the old component.
Inspection of transistors. In most inverter devices, it is the transistors that most often fail. Finding such an element is not difficult at all, it betrays itself with burnt leads, the presence of small cracks on the case. If there are no indicated visible defects, you can ring each transistor with a multimeter, determining the faulty one.

Welding inverters today can have a different arrangement of elements. But at the same time, their design does not differ much, therefore, do-it-yourself repair of inverter equipment from different manufacturers cannot cause difficulties for a person who has an idea of \ u200b \ u200bthe principles of constructing electrical circuits.

Restoring normal operation of such devices is easier. Self-repairing welding transformers can be done by almost any amateur welder. Usually he has to deal with the following malfunctions of welding equipment: Image - DIY welding transformer repair

The rewinding of the coil, which we talked about, may also be required when there is no load on the equipment, and the device takes a high current from the network. The reason for such a breakdown is the same - the winding is closed.

All other malfunctions of the welding transformer are caused by the breakdown of its individual units and components. For example, the current control device and its coils (secondary and choke) often fail, into which foreign objects fall during operation. Finding such a malfunction is easy due to the simplicity of the design of the transformer for welding.

Welding rectifiers are structurally similar to transformers, but they are additionally equipped with mechanisms that are inherent in inverter equipment (control module and diode rectifier). This state of affairs determines the peculiarities of their repair. Image - DIY welding transformer repair

If the nodes of the power unit fail, they are repaired in the same way as welding transformers (rewinding coils, restoring insulation between cables, changing regulators and capacitors, etc.). But in case of breakdowns of the control unit and the diode rectifier, the state of the electrical circuit of the apparatus should be analyzed.

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The electronics fail due to ignoring the manufacturer's recommended operating rules for the device. Read the instructions carefully and follow the rules.

Before starting to disassemble the device, check the correctness of all settings and read the instructions. There are indicated not only recommendations for the correct operation of the device, but also problems that are quickly eliminated on their own.

Unscrew the screws on the case and remove all parts. Diagnostics begins with a superficial examination of all elements and boards. There may be several of them:

Power transistor board.

Rectifier diode board.

Mains voltage rectification board.

You need to carefully look for burnt tracks and damaged elements. If no damage is found, then diagnose with a multimeter:

If the inverter does not turn on, put the multimeter in Continuous Mode and ring the power cord and power button pins. Check the charging resistor. If it is in a cliff, then the device will not work. The resistor is responsible for charging the capacitors.

Check power transistors.On the board, put the black probe on the left leg, and the red one on the right, then swap the probes. The ringing should go one way.

Place the black probe on the middle leg, and the red one on the left, then on the right. Ringing should be in both positions.

Transistors have a small resistance in hundredths of an Ohm. But they pass through themselves a current of several tens of amperes. To avoid overheating, they are installed on aluminum radiators. A badly damaged transistor is usually visible.

To replace the transistor, you first need to unscrew it from the radiator, and then dismantle the radiator itself from the board.
To solder the transistor from the board, you need to warm it up with a hairdryer. During dismantling, the tracks must not break.
The surface of the radiator for the new transistor must be well cleaned with alcohol and polished. The surface on the transistor should be smooth. Any blotch or grain of sand will create a gap between the transistor and the heatsink. It is unacceptable. Apply a very thin layer of heat-conducting paste to the surface of the transistor that will be in contact with the heatsink. When tightening the transistor, the paste should come out slightly from under the case. The thick layer will not come out and the transistor will deform. The component must be applied to the surface of the radiator and rub in in a circular motion so that it lies over the entire area. It should stick.
Screw the adhered transistor to the heatsink and insert into the board. Solder the legs.

If the transistor is out of order, it means that the elements of the driver board are damaged, which shakes the transistors.

All components of the board are called with a multimeter. The damaged ones are fed and changed.

Input and output rectifiers are made in the form of diode bridges. To prevent overheating, they are installed on radiators.

For diagnostics, it is unsoldered from the wires and dismantled from the board so as not to be mistaken in case of a short circuit in the circuit. Defective elements are replaced.

If the capacitor is discharged and we connect power to it, its resistance increases from zero. When fully charged, its resistance is equal to infinity.

Set the resistance mode in the multimeter to 20 kOhm.
If the device has recently been turned on, the capacitor has retained its charge. To determine if it is working properly, discharge the capacitor before testing. Connect the capacitor leads with a multimeter probe.
Connect the test leads of the multimeter to the capacitor leads. If the resistance was zero, then as the capacitor was charged from the multimeter, it increased to infinity, the capacitor was functioning.
But you still need to measure the voltage. Set the multimeter to DC voltage measurement in the 2000 mV range. Connect the test leads of the device to the capacitor leads. The device should show voltage. Short-circuit the capacitor leads and measure the voltage again. If it drops to zero, your capacitor is functional.

All elements of the welding machine depend on the control board.

This is the hardest block. It is diagnosed with an oscilloscope. Control signals are checked. If they do not arrive, all the elements are called with a multimeter and the damaged ones change.

If you learn how to independently identify and troubleshoot the welding inverter, you can avoid unnecessary repair costs at the service center.Hello everyone! So, another report on the repair of electrical equipment. Today we have welding KAISER AC WELDER TURBO - 250M. This is not an inverter, which means the simplicity of design and reliability of such welding transformers ensure long-term operation in harsh conditions.What are the symptoms: there is no spark, but the cooler works, and at first glance there is nothing else to complain about. Immediately he began to sin on the wires and almost guessed. I took a tester-multimeter, it has a function, dials, which is what we need.To see the insides of the welding, you need to remove the cover - it's not so easy, the handle holds the transformer on two bolts, first unscrew them, then unscrew the rest of the bolts. And two bolts hid behind the wheels.Remove the cover and retaining ring from the wheel.Then everything goes according to plan - the nickname of the wire and, to my surprise, everything is also in order. It turns out that the tire winding burned out. To believe, I cleaned the tire itself at the ends and rang the bell again - and again there is a resistance of 6 ohms, yes, either the tester is broken or I have toilets from fatigue.Yes, the weak point 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, from which a short circuit occurs.I clean the bus and bring it out of the case with aluminum wires, since the bus is aluminum, and the copper wires are not very good contact and always burn out at their docking. Galvanic steam. So I found the problem. I know from experience that the bus is connected to the cable with a clamp. But I couldn't just twist it, but I can twist it with bolts. But I thought of replacing the wires for a long time with a longer one, the standard ones are 1 meter, agree a little, but this 5 meters is already something.

In a private house or garage, many users have a welding machine. It is needed in the household to repair inventory and create new products. High quality and tastefully made metal structures in skilled hands look like works of art.What does a welding machine look likeWelding machines are used in industry and are irreplaceable where there is work with metal.The operational reasons for the failure of the welding machine are as follows:

hit of precipitation, high humidity, violation of the temperature regime;

too low or high welding current;

ingress of contaminants inside: dust, oil, debris, metal particles;

deviation from the operating rules specified in the instructions.

Proper maintenance of the inverter is especially important.The devices are the simplest of all used for welding. The main advantages of this type of welder are simplicity, unpretentiousness, reliability and relatively low price. The main disadvantages are large dimensions and weight.Welding transformer - the easiest welding machineMost of the device is occupied by a transformer. Its important parts are the contacts on the terminal block, to which the cables for welding are connected. At high currents, the reliability of the joints is important, since with their deterioration, intensive heating of the parts occurs.Repair of welding transformers consists in disassembling joints, replacing burnt parts, stripping contacts and creating reliable insulation. Other malfunctions and solutions are as follows:The welding machine must be equipped with a safety device that is triggered when the cooling system does not cope with prolonged operation.In this case, the apparatus must "rest" for at least 30-40 minutes. If there is no protection, the machine is installed in the electrical panel. It must be correctly selected.For each model, the instructions indicate the operating mode, for example, for the Interskol inverter, a break of 3-4 minutes is required. after 7-8 minutes. welding.The simplest diagram of a welder with a rectifier is shown in the figure below, where a diode bridge and a capacitor are connected after the transformer. The device can be made by hand.DC welding machine diagramPower is supplied from a 220 V network. A 10 A fuse is connected to the primary winding. When it burns out, this is one of the faults that is easiest to fix by making a replacement. The SA1 machine for 16 A is also connected there.The power section fails for the same reasons as the transformer. The electronic part, which includes the rectifier and the control unit, brings the device closer to the inverter. The diode bridge or other parts may fail.A careful study of the causes and their elimination with your own hands will save significant money.Inverter-type devices provide the highest welding quality, but are less reliable due to the high complexity of the electronic device. The figure below shows the device without a cover.Inner part of inverter for weldingDuring the repair, radio components and the correct passage of signals through the modules are checked using an oscilloscope, multimeter and other measuring instruments.A feature of finding a malfunction of electronic parts is the difficulty of identifying defects in appearance. Successful repairs can be done with experience with electrical wiring.The welding inverter consists of modules, the main of which are the input and output rectifier, as well as the control board.Principle of operation:

rectification of the supply alternating current;

converting direct current into alternating current with high frequency;

decrease in voltage to operating value;

rectification of current into direct current.

Inverter control board schematicThe modules are located in series one after the other, with the exception of the control system connected to the frequency converter.Inverters often burn out transistors, and the inspection begins with them. Malfunctions can be seen by the burnt casing or leads (Fig. 5).Damaged transistor in the welding machineAll transistors are called with a multimeter. The discovered keys change. To improve heat dissipation, installation is carried out with thermal grease. Finding the right element can be tricky. Therefore, instead of faulty electronic parts, analogues are selected.Transistors have sufficient power, and the reason for their destruction is the failure of other elements. They also need to be found and replaced. Rectifier diodes can be punctured. Before dialing, you must first unsolder the wires from them.The most complex module of the device is the control board, which is repaired by specialists. The passage of signals through the circuits is checked.If repairs can be made, a significant amount of money will be saved.