DIY welding transformer repair

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

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. In order to believe, I cleaned the tire itself at the ends and rang again - and again there is a resistance of 6 ohms, yes, either the tester is broken or I have latches 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.

Video (click to play).

Modern equipment for welding various alloys and metals is distinguished by a relatively simple design and high operational reliability. Despite this, the repair of welding machines is periodically required even by the most "sophisticated" units.

Malfunctions of welding machines are most often caused by their incorrect use, non-compliance by consumers with the recommendations of the manufacturer of the equipment, as well as natural wear and tear of its individual units. Also, repairs may be required in the following cases:

inconsistency of the current in the power supply and voltage with those indicators that are required for the stable operation of the welding installation;
illiterate connection of equipment to a power source and incorrect completion of work;
welding in dirty or very humid rooms, in open areas during rain or snow.

As practice shows, most often in welding units, the terminal node fails, to which the wires are connected, which are necessary to perform the work.

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 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 the hook” 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.

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 looking 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 analogue 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 not difficult 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.

Semi-automatic welding equipment can be designed on the basis of rectifiers or inverters. As you yourself understand, it is necessary to repair such units according to the principles described above - the breakdowns will be identical. Note that during the operation of semiautomatic devices, mechanical breakdowns are often recorded, which are caused by wear of the wire feed device to the welding zone.

In the specified device, with the active use of welding equipment, increased friction between the channel and the supplied wire can be observed. This problem is solved by installing a new channel. It is better not to use other methods of restoring the normal functioning of the apparatus due to their low efficiency.

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. Metallic structures made with high quality and tasteful look like works of art in skilled hands.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, a 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.

The principle of operation of the step-down transformer. East. https://my.housecope.com/wp-content/uploads/ext/1220/svarochnyj/raschet-svarochnogo-transformatora.html.

The appearance of the welder is shown in the figure "Welding transformer".

Welding transformer. East. https://my.housecope.com/wp-content/uploads/ext/1220/svarochnyj/svarochnyi-transformator-svoimi-rukami.html

The most common faults in welding transformers and methods for their elimination are summarized in the table.

ATTENTION! When carrying out any repairs, be sure to disconnect the device from the mains.

short circuit in high-voltage or low-voltage circuits:
- between the lead wires and the body. IMPORTANT. To exclude the injury of the maintenance personnel by electric shock, it is mandatory to ground the welder's body of good quality;
- wires between themselves;
- turn-to-turn circuit in coils;
- shorting of wires (lead or coils) to the magnetic circuit;
- electrical breakdown of capacitors;
- failure of other components of the welding gadget.
- replacement of wires and restoration of damaged insulation;
- replacement of capacitors and other failed parts and assemblies with air-conditioned ones.
- overload:
  - long-term operation without technological breaks for cooling;
  - the welding electrode is incorrectly selected (brand, excessively large diameter, etc.);
  - the welding mode is incorrectly selected (high value of the welding current, etc.);
  - loosening of fasteners of equipment assemblies:
    - hairpins tightening the "iron";
    - malfunctions in the fastening of the magnetic circuit;
    - the adjustment of the mechanism for moving the coils is broken;
    - short circuit between welding cables;
    - the insulation between the sheets of the magnetic circuit is broken.
    - check electrical insulation and eliminate all defects;
    - tighten all fasteners;
    - eliminate violations in the mechanism of moving the coils
    - welding current is higher than the permissible value for this equipment model;
    - welding electrodes are used, the model and diameter of which do not correspond to this type of welding;
    - work takes place without a sufficient number of technological breaks (for cooling).
    Excessive heating of the welding machine can lead to the complete destruction of the electrical insulation of the windings and the need for a major overhaul of the entire machine. Therefore, this defect must be eliminated immediately upon detection.
    - the mechanical connection is destroyed;
    - the insulation at the ends of the wires burns out;
    - the electrical connection is destroyed.
    - go over and check the status of contacts;
    - if necessary, clean them or replace them with conditioned ones;
    - ensure tight clamping of all elements
    - undervoltage in the power supply network;
    - malfunction of the regulator of the magnitude of the welding current.
    - overvoltage of the power supply;
    - malfunction of the regulator of the magnitude of the welding current.
    Power supply overvoltage occurs most commonly when powered by mobile generators. In power grids, this parameter is regulated centrally. A sharp increase is possible only in the event of an accident (breakage of the "neutral wire" at the KTP).
    
    IMPORTANT. In the event of an increase in the voltage in the mains, it is necessary to urgently turn off all consumers of electricity at the main switchgear (otherwise they will fail - "burn out").
    - malfunction in the lead screw mechanism of the current regulator;
    - short circuit between the contacts on the regulator terminals;
    - the mobility of the secondary winding coils is limited;
    - short circuit in the choke coil.
    - violation of the insulation of the high voltage winding (primary) and its short circuit to the welding circuit (secondary winding and everything that follows it);
    - short circuit between welding wires;
    - the connection of the welding wires to the terminals of the machine has been loosened.
    - conduct an external examination and establish the cause;
    - in case of violation of the insulation of the windings, the latter should be replaced (rewind the transformer);
    - restore insulation on welding wires or replace them;
    - restore the connection of the welding wires to the terminals of the device.
    The thinnest point of the welder is the terminal block.
    
    Equipment malfunctions, the elimination of which will require rewinding the coils of the primary and secondary windings, are indicated in the table. Repair should begin with the preparation of materials:
    - wire for the primary and secondary windings (the brand and quantity can only be found after disassembling the burnt-out apparatus);
    - shellac (can be replaced with tsaponlak or PF paint);
    - a mandrel (bar) for winding the secondary winding (according to the dimensions of the coil frame). It is recommended to make it from wedges. Otherwise, after winding from a solid bar, it will be very problematic to remove. Dimensions are removed after disassembly;
    - varnished cloth.
    We disassemble the transformer, unwind the windings and count the turns and layers (be sure to write them down).
    
    We calculate the length of the wire by:
    - the length of the "middle turn". This is the arithmetic mean between: the maximum length - the turn of the outer layer and the minimum - the inner one;
    - the number of layers and turns.
    Wire length is defined as the product of the "average turn" length, the number of turns in a layer and the number of layers.
    
    On the unburned part of the winding, we visually determine the brand of the wire and, having measured the diameter, calculate its cross section. Now we know: what and how much wire we need.
    
    We wind new coils: the primary winding from a thin wire can be directly on the frame, the secondary from a wire of large cross-section - on the mandrel. We pre-roll one layer of varnished cloth. We wind the turns tightly "one to one", repeating the burned-out winding and strictly adhering to the number of turns. We carefully coat each layer of winding with shellac or its substitute and lay a layer of varnished cloth. After drying, the shellac will prevent the wires from moving, caused by their expansion when heated (a large electric current flows through the windings), and the destruction of the insulation. Together with varnished cloth, this will prevent an inter-turn short circuit and the need for repeated repairs.
    
    After winding, we collect the coils of the welding transformer and dry them (at home, you can use the oven for this). The temperature and duration depends on the materials used.
    
    We make the final assembly of the transformer. With a tester or any other ohmmeter, we "ring" (check the integrity) of the windings. The primary must have an electrical resistance of about 20 ohms, the secondary - "0", between the windings - "infinity".
    
    We check the operability of the transformer by measuring the voltage XX (open circuit - it is indicated in the "Passport of the welding machine". Usually 50 ... 60 V). Primary winding through an electric machine (IMPORTANT! The machine must be included in the power circuit) we connect it to the electrical network, and with a tester (or any other AC voltmeter) we measure the voltage of the secondary winding. If everything is done correctly, then the value of this electrical voltage corresponds to the voltage XX indicated in the "Passport".
    
    We install the welding transformer in its rightful place in the welder and try to cook.
    
    Before repairing a welding machine that suddenly “stopped cooking”, check the following:
    - whether the selected polarity and the magnitude of the welding current correspond to the workpiece and the electrode used (material and diameter);
    - is there sufficient contact between the clamp of the welding cable and the workpiece to be welded;
    - whether the time of continuous operation of the welding machine has been exceeded or a trivial cable break.
    Often, the elimination of these defects will "revive" your device, and the repair will be completed at this point.
    
    If none of the above is found, then you need to identify the problem and start fixing it. We remove the equipment case and conduct an external inspection. Often failed units can be identified visually: a contact block that has changed its appearance, a violation of the insulation of the lead wires, weakened contact fasteners, etc. Replacement of these parts and assemblies does not cause difficulties and can be done independently.
    
    If there is no voltage XX on the secondary winding of the welding transformer, then it must be rewound. The technology for this process is described above. If you do not have the skills for similar repairs, and you have never rewound even a low-power transformer, then we recommend contacting a service center.
    
    Overhaul of a welding transformer is the largest type of scheduled repair in terms of volume, in which:
    - disassembly of the unit;
    - replacement of all worn out units and parts.
    - primary and secondary coils;
    - choke, capacitors, etc.
    - all contact nodes: clamps, pads, etc.
    - movable units and mechanisms.
    After the overhaul, the technical parameters of the welding transformer must correspond to the new device. In many cases, as agreed with the Customer, during the overhaul, the welder is modernized.
    
    The repair price consists of two main components:
    - the cost of parts and assemblies to be replaced;
    - cost of work.
    When repairing in the "Service Center" (or any other workshop), overhead costs will also be added.
    
    It should be borne in mind that every repair, no matter how carefully it is done, does not make the equipment "completely new". Therefore, determine the cost of failed units and parts, find out how much the repair will cost and compare the amount received with the cost of new equipment. In most cases, it makes sense for a welder who has “survived” several repairs to scrap metal (copper windings are expensive) and purchase a really new, and maybe more modern and convenient inverter.
    
    It is well known that the repair of welding machines in the overwhelming majority of cases can be organized and carried out independently. The only exception is the restoration of the efficiency of the electronic inverter, the complexity of the circuit of which does not allow for full repairs at home.
    
    Even an electrical engineer can be confused by just trying to turn off the protection of an inverter. So in this case, it is best to seek help from a specialized workshop.
    
    The main manifestations of malfunctions in electric arc welding machines are:
    - the device does not turn on when connected to the mains and started;
    - sticking of the electrode with a simultaneous hum in the area of the converter;
    - spontaneous shutdown of the welding machine in case of overheating.
    Repair always begins with an inspection of the welding machine, checking the supply voltage. It is not difficult to repair transformer welding machines, moreover, they are not picky to maintain. In inverter devices, it is more difficult to determine the breakdown, and repair at home is often impossible.
    
    However, if handled correctly, inverters will last a long time and will not break down. Protect from dust, high humidity, frost, store in a dry place. There are the most typical malfunctions of welding machines, which can be eliminated by hand.
    
    In this case, first of all, you need to make sure that there is voltage in the network and the integrity of the fuses installed in the transformer windings.If they are working properly, use the tester to ring the current windings and each of the rectifier diodes, thereby checking their performance.
    
    If one of the current windings breaks, it will need to be rewound, and in the event of a failure of both, it is easier to replace the entire transformer. A damaged or "suspicious" diode is replaced with a new one. After repair, the welding machine is turned on again and checked for serviceability.
    Sometimes the filter capacitor fails. In this case, the repair will consist in checking it and replacing it with a new part.
    
    If all the elements of the circuit are working properly, it is necessary to deal with the mains voltage, which can be greatly underestimated and is simply not enough for the normal functioning of the welding machine.
    
    Electrode sticking and arc interruption can be caused by a voltage drop due to a short circuit in the transformer windings, diode failure, or loose connection contacts. A breakdown of the capacitor filter or short circuiting of individual parts to the body of the welding machine is also possible.
    
    For reasons of an organizational nature, due to which the device does not cook as it should, it is possible to attribute the excessive length of the welding wires (more than 30 meters).
    If sticking is accompanied by a strong hum of the transformer, this also indicates an overload in the load circuits of the device or a short circuit in the welding wires.
    
    One of the repair options with the elimination of these effects can be the restoration of the insulation of the connecting cables, as well as the tightening of loose contacts and terminal blocks.
    
    In some cases, repairs can be carried out independently if the device starts to shut down spontaneously. Most models of welding machines are equipped with a protective circuit (automatic) that is triggered in a critical situation, accompanied by a deviation from normal operation. One of the options for such protection involves blocking the operation of the device when the ventilation module is turned off.
    
    After spontaneous shutdown of the welding machine, first of all, you should check the state of protection and try to return this element to working condition..
    
    If the protective unit re-operates, it is necessary to proceed to troubleshooting according to one of the methods described above, associated with short circuits or malfunction of individual parts.
    
    In this situation, first of all, you should make sure that the cooling unit of the unit is working properly, and that overheating of the internal spaces is excluded.
    
    It also happens that the cooling unit does not cope with its functions due to the fact that the welding machine has been under a load exceeding the permissible norm for a long time. The only correct decision in this case is to give it a "rest" for about 30-40 minutes, and then try to turn it on again.
    In the absence of internal protection, the circuit breaker can be installed in the electrical panel. To maintain the normal functioning of the welding unit, its settings must correspond to the selected modes.
    
    So, some models of such machines (welding inverter, in particular), in accordance with the instructions, should work according to a schedule that assumes a break for 3-4 minutes after 7-8 minutes of continuous welding.
    
    Before repairing an inverter welding machine with your own hands, it is advisable to familiarize yourself with the principle of operation, as well as with its electronic circuit. Their knowledge will allow you to quickly identify the causes of breakdowns and try to eliminate them in a timely manner.
    
    The operation of this device is based on the principle of double conversion of the input voltage and obtaining a constant welding current at the output by rectifying a high-frequency signal.
    The use of an intermediate high-frequency signal makes it possible to obtain a compact impulse device that has the ability to effectively adjust the value of the output current.
    
    Breakdowns of all welding inverters can be conditionally divided into the following types:
    - malfunctions associated with errors in the choice of the welding mode;
    - failures in operation due to the failure of the electronic (conversion) module or other parts of the device.
    The method for detecting inverter malfunctions associated with malfunctions of the circuit involves the sequential execution of operations performed according to the principle "from simple damage to more complex breakdown." The nature and cause of breakdowns, as well as repair methods, can be found in more detail in the summary table.
    
    It also contains data on the main parameters of welding, providing a trouble-free (without turning off the inverter) operation of the device.
    
    To do this, you will need an oscilloscope and a multimeter, which you should start working with only if you have full confidence in your abilities. If you have any doubts about your qualifications, the only correct solution would be to take (carry) the device to a specialized workshop.
    
    Specialists in the repair of complex impulse devices will quickly find and eliminate the malfunction that has arisen, and at the same time will carry out maintenance of this unit.
    
    If you decide to repair the board yourself, we recommend using the following advice from experienced specialists.
    
    If burnt wires and parts are found during a visual inspection, they should be replaced with new ones, and at the same time all connectors should be plugged in, which will eliminate the option of losing contact in them.
    
    If such a repair did not lead to the desired result, you will have to start a block-by-block inspection of the electronic signal conversion circuits.
    To do this, it is necessary to find sources in which the diagrams of voltages and currents are given, intended for a more complete understanding of the operation of this unit.
    
    Based on these diagrams using an oscilloscope, you can sequentially check all the electronic circuits and identify the node in which the normal picture of the signal conversion is disturbed.
    
    One of the most complex components of an inverter welding machine is considered to be an electronic key control board, which can be checked for serviceability using the same oscilloscope.
    
    If you have doubts about the performance of this board, you can try to replace it with a serviceable one (from another working inverter) and try to start the welding machine again.
    
    In case of a favorable outcome, it remains only to give your board for repair or replace it with a purchased new one. The same should be done when there is a suspicion that all other modules or blocks of the welding machine are in good working order.