Powerful power supply from a microwave transformer. Contact welding from an old microwave How many turns in the primary winding of a microwave transformer

Designed to form the voltage required to power the magnetron. The choice of a transformer by parameters depends on the characteristics of the magnetron installed in a particular furnace. The more powerful the magnetron, the more power the transformer feeding it must develop. Thus, a high-voltage transformer and a magnetron form an inseparable pair. The basis of the transformer is the core, which is a package recruited from W - shaped plates made of electrical steel and fastened together by welding (welds in the figure). A flange is welded to the bottom of the package, in the form of a rectangle made of steel sheet, through which the transformer is attached to the bottom of the microwave oven. The transformer contains three windings: primary (network), and two secondary. The secondary windings include: the filament winding and the step-up (anode) winding. The network winding is wound (as a rule) with enameled aluminum wire. The ends of the winding are brought out under the terminals. The filament winding is 2 - 3 turns of the mounting wire and is designed to power the magnetron filament. The winding leads, in the form of conductors, are equipped with connectors for easy connection to the magnetron terminals. The filament winding produces a voltage of about 3.3V., At a current of 10A. The exact values ​​​​of current and voltage depend on the specific pair, magnetron - transformer. The step-up winding generates the high voltage required to power the magnetron. About 2000 volts are removed from this winding at a current of 0.3A., The exact values ​​\u200b\u200balso depend on the specific magnetron-transformer pair. The winding is wound with enameled wire. One end is brought out under the terminal, the second is connected to the core of the transformer (and through the core and to the furnace body) by soldering. The entire design of the transformer, for reliable insulation of the windings and to eliminate chatter during operation, is impregnated with a special impregnating varnish.

The main malfunctions of a high-voltage transformer include an interturn short circuit in the windings. Such a malfunction occurs as a result of a violation of the insulation between the turns of the winding (destruction of the wire enamel). It is accompanied by an increased hum during transformer operation (even without load) and a significant increase in temperature, both of the windings and the core. Visually noticeable darkening of the enamel of the winding wire and impregnating material. When used for a long time, there is a pungent odor.

Since all the windings of the transformer are made with a rather thick wire, the breakage of the windings occurs very rarely (if only as a result of external mechanical action). More often, as a result of poor soldering, there is a loss of contact between one of the ends of the winding and the terminal (in the figure, the place of soldering). The transformer terminals are made of a copper alloy, which is well soldered, but the winding is wound with aluminum wire, and it is practically impossible to solder aluminum and copper without a special flux. Contact can be checked with an ohmmeter. The filament winding should ring almost shortly, the network winding has a resistance in the region of 4 ohms, and the boost winding is approximately 150 - 200 ohms. Winding resistance depends on the parameters of a particular transformer.

The most common malfunction of the magnetron power circuits is the loss of contact between the terminals of the transformer windings and the connectors of the external circuits of the furnace. This happens as a result of poor crimping of the connectors. The place of poor contact starts to spark, the contact surface of the connector gets very hot and burns out, as a result, the contact disappears altogether. The consequences of poor crimping of the connectors are shown in the figure.

Almost every motorist or just a person who likes to spend time repairing or creating something wants to see a welding machine. There is a wide variety of types and models on the market. “What to do if there is not enough money to purchase a welding machine?” is a question that always arises when thinking about buying. If you have a broken microwave at home, do not rush to throw it away. With a little effort and time, a completely working welding machine can be made from a breakdown. Let's talk today about how a microwave transformer is used for welding.

An important part is the transformer

In a microwave oven, there is only one important detail that can be useful in creating an apparatus - a transformer. A microwave transformer is basically two coils of copper wire wound around a core. There are two windings - primary and secondary. Coils with windings have a different number of turns of wire: in order to connect voltage to the primary winding, a current with a lower voltage arose in the second coil due to induction, and the current strength increased.

extraction

To remove the transformer from the microwave oven, it is necessary to carefully disconnect the fasteners on the microwave housing without damaging the transformer winding. With a sharp or very rough extraction, a break in the circuit may occur, and then there will be unnecessary problems in rewinding the coil with the winding. Next, you need to clean the coils and the core from small chips or debris that got during disassembly. For cleaning, you can use a regular paint brush, the main one so that it is dry and clean, as in the photo.

Training

Every welder knows that if the welding machine produces a small amount of current, then this can affect the quality of the weld. It is worth noting that with an increase in amperage during the welding process, burning of the metal by the electrode may occur. Simply, the parts will not be welded together, but cut. A voltage of 2 thousand volts appears on the secondary winding of the microwave transformer, which is quite a lot. This requires rewinding the secondary winding with a larger wire. For this, a PV-3 type rein with a cross section of 4 squares is well suited, it has good flexibility and you do not have to bend the wire around the coil for a long time. Rewinding is required very carefully, in order to avoid damage to the primary winding. First you need to bite the winding in several places and remove it from the coil. Then, carefully wind each turn of the new wire. The number of turns directly depends on the power of the transformer, since microwave ovens exist with different technical characteristics, respectively, transformers are mounted according to the parameters of the microwave oven. When the rewinding is completed, electrical insulation varnish should be applied to the surface of the new winding.

Mounting

We take into account that if the power of the transformer is 600–800 watts, then the future welding machine will be able to weld metal no more than one millimeter thick. If you plan to weld a thicker metal, you can resort to connecting two transformers together, which will significantly increase the power of the welding machine. When the rewinding process is completed, and the varnish has dried well on the new winding, we proceed to the connection, given that we have two transformers - the primary windings should be connected in parallel, the secondary windings, respectively, in series. It is necessary to correctly connect the terminals of the winding contacts to each other, otherwise a short circuit is possible.

Electrodes for the device

The welding machine, like the spotter from a microwave oven, works under the means of the electrode. For reliable operation, the rods must be carefully processed, slightly sharpened, otherwise they will easily lose their shape. The cable to the electrodes should be as short as possible and have as few connections as possible so that there is no power loss. Copper lugs should be attached to each end of the wire. During the welding process, oxidation of copper is possible, unsoldered areas will give excess resistance, which will lead to a loss of power.

Chassis Mounting

For safety, the future welding machine should be placed in a sturdy case, having previously made a number of holes around the perimeter (the more, the better) to ensure proper cooling of the machine during welding. For greater effect, two fans can be attached to the ends of the case. For this, cooling coolers from the system unit of a personal computer are perfect. Also very often such transformers are used to create a Tesla coil and a tube amplifier.

Alexey () Dear, tell me if anyone has come across ... There is a bare iron from an LG microwave. And there is a desire to rewind to a current of 7-10A, the secondary needs 20 volts. Feb 8, 2017 at 8:33 am

Eduard (Alvena)  Aleksey, why wouldn't it work, of course it will! Throw in the dimensions, I'll tell you how much power can be removed from it, and I'll calculate it.

Yes, still, take a photo from the end, I want to look at the set of plates, otherwise it’s not clear from this photo.

Alexey

Alexey (Rimona)  it is interesting for a long-term operation as it is, otherwise opinions are divided ....

Eduard (Alvena)  Damn, is it welded on the side? This is bullshit. Perhaps it will be heated, but not fatally, it should work. Well, measure the dimensions of the window and the section of the rod.

Eduard

Alexey (Rimona)  yes it’s cooked. I measured it.

Alexey (Rimona)

Alexey (Rimona)  As far as I know, microwave trances are still designed exclusively for short-term operation.

Eduard (Alvena)  So, the area of ​​the window is small, the cooling of the windings is poor, and it is very difficult to fit all the coils there.

And plus welding, the no-load current will be large. And so. Primary 490 turns of wire 0.55-0.6mm. Approximately 100 meters of wire. Secondary 46 turns with a diameter of 1.8 mm, approximately 11-12 meters. Overall power 130W, losses in the windings 5W, excluding idling. Well, about 120 watts. As a result, we have 20v at a current of up to 6A.

Alexey (Rimona)   Alexey, yes, I have such information. Thank you.

Alexey (Rimona)  Eduard, thank you for your work. my doubts are justified, they haven’t come up with anything better than Soviet iron, but it’s becoming less and less common.

Eduard (Alvena)  Aleksey, it's not like that! Imported iron is better, as it allows you to work at a higher induction, due to this we get more power with smaller dimensions! And the short-term mode of operation is only because they are trying to squeeze out more from this trance than it can give. I gave calculations for long-term operation, with a margin for power, current, induction and voltage. It can run for hours at full load.

Alexey (Rimona)  Eduard, thank you very much for the work done and for the capacious, practical information, it remains only to lay the coils, especially the primary, well, 6 A is just for 55 batteries, and then with a margin !!!

Eduard (Alvena)  Aleksey, and everything fits there, the main thing is to find the wire 0.55-0.6 no thicker and no thinner. The primary is about 7 layers, taking into account the frame and interlayer insulation, it will take somewhere around 7-8mm. The secondary 2 layers of wire 1, 8-2mm, will take 4mm, respectively, and that 12-13mm in the window, and the window is 15, so everything fits.

Alexey (Rimona)  Eduard, well, that's great, it's a pity there is no winding machine so that you can count the turns, you will have to do it on your hands, but not for the first time!

Eduard (Alvena)  Aleksey, don't count everything! What for? We count the first layer, for example 75 turns, and then we just add layers! After all, the turns will be approximately the same, well, there are +/-2-3 turns, this is nothing. This is winding a donut, yes, there are less and less turns with each layer, we must count.

Ilya (Tobikuma) winding machine is made of a wooden bar, a 30 cm stud, a pair of nuts, a magnet, a reed switch, a calculator...

Tags: Where can I rewind a microwave oven transformer

In this video, I show in detail how to easily and quickly disassemble a transformer from a microwave oven, just ...

Where can I get a powerful transformer? What can you get out of? | Topic Author: Egor

We need transformers from 400W and above, but where can you find treasures like that? Old TVs, tape recorders? My uncle pulled out an armored trans with a power of 600-650W from an old Soviet TV set, quite heavy. Do not tell me where are the same? I saw a non-working Rubin in the village with a neighbor standing in the garage, what's interesting there? Business transformers.

Dmitry   in old soviet tube color TVs - 380 watts. .Ruslan
you can peel off the entire secondary and wind your own. .

easier to walk through the flea markets ..

Pavel  there were no such TVs pi.. your uncle!

Vladislav  An old color tube TV, a transformer car charger, a microwave oven, wire broadcasting linear transformers.

Grigoriy  If "Rubin" has a switching power supply, you won't find anything in it for yourself. Walk around the markets, they often sell junk there. You are sure to find something.

Ilya  In the old COLOR tube TVs, there were 250-270W, a maximum of 315W.

Alexey  Microwaves. But keep in mind that there transformers operate with an excess of overall power, in core saturation mode.

Valery   Any transformers from 250 W to 5 KW can be made from old color tube TVs. It remains to peel off all the windings from the iron, put the iron into the necessary packages, of course, you will need more than one such trance, make a new frame and rewind the windings according to the calculation. Even a welding transformer can be built from 4 of these transformers.

Igor  Industrial companies have different capacities. Factories should be interested

microwave transformer - Metal forum

microwave transformer: 01072011754.jpg microwave transformer: .... you can rewind, the main thing is that it is needed.

Application of transformers from a microwave oven [Archive] - AUDIO PORTAL Forums

He got hold of two transformers from the Lena microwave oven. Type - AVU ... Tell me - can they be used as a weekend? (With rewinding ... advise .... And if you use only iron, and rewind the coils?

Microwave ovens heat food. The transformer is an important element of the beam-generating chain. This device converts the normal household voltage supplied to its primary winding to the secondary output values ​​necessary for operation. Often it is he who causes a malfunction of the equipment, so special attention is paid to checking the microwave transformer. When working independently, it is desirable to use a safe method of examining the device.

A microwave oven high-voltage transformer is a device consisting of a magnetic circuit, a frame, one primary winding and two secondary windings. The latter feed magnetron circuit: filament and anode line. The first is made from a thick wire, and the voltage at its output is a few volts (about three). The second (anodic) secondary winding creates an alternating voltage of up to 4 kV at the output. The primary winding is supplied with 220 V from the network.

Microwave oven transformers manufactured by various manufacturers differ not only in their appearance: in size, mounting options. They are produced in different capacities and classes. The output voltage of the secondary windings, the number of turns and the thickness of the wire in them (hence the resistance) are also different.

The secondary high-voltage winding is closed to the case, as is one of the magnetron outputs.

AT microwave wiring diagram in addition to the high-voltage transformer, the following elements are included:

• high voltage capacitor and diode;
• magnetron;
• Limit switches;
• fuse;
• electric motors: platform (turns it inside the microwave cabinet) and fan;
• control block.

In expensive models of furnaces, they are used instead of transformers impulse blocks having a more complex device, but less weight.

Possible transformer malfunctions and their symptoms

Checking the microwave transformer should be arranged when this household appliance is not working well, or when it does not function at all. Symptoms transforming device are:

• a fairly strong hum (noise) begins to emanate from the equipment after switching on;
• dishes placed on the platform are not warmed up at all or are slightly heated;
• during operation, the smell of burning insulation appears.

If such signs appear, it is better not to use the device until it is repaired. In the latter case, it is necessary to disconnect it from the network immediately in order to avoid even greater damage.

It must be remembered that breakdowns with electrical appliances happen during power surges supply network. If this was the case, then when the slightest hint of a malfunction appears, repairs should be started, during which a manufacturing defect may also be detected.

The above manifestations in most cases are caused by a number of reasons:

• breakage of the wire of the primary or secondary (step-up) windings, in both at the same time (rare case);
• a short circuit between the turns in one of them, or in two at once;
• breakage or short circuit in the winding of the filament circuit of the magnetron.

The transformer magnetic circuit consists of sheets of electrical steel. Noise during oven operation can also appear as a result of their delamination from each other - then it is necessary to change the transformer completely. But this happens very rarely and is easily determined visually.

The vast majority of problems during the operation of the transformer are associated with its windings.

The procedure for working on a secure check

Starting an independent check, you need to stock up on a multimeter (in extreme cases, a two-pole indicator with a built-in power source), screwdrivers with various tips, an ohmmeter, and pliers.

The general scheme of safe work looks like this:

• disconnect the device from the power supply;
• unscrewing the screws, remove the casing;
• discharge the capacitor;
• carefully remove the terminals from the transformer;
• check its windings: if the parameters are normal, put them in place and look for other reasons;
• when an open or short circuit is found in them, the device is replaced;
• the furnace is assembled and its performance is checked.

If, after assembly, the microwave does not function, then you should look for more reasons or resort to checking with the voltage connected.

If, after removing the transformer, traces of insulation melting are visible on its windings, a strong burnt smell emanates from it, then it is no longer suitable for use, and it makes no sense to check. In this case, only device replacement.

Before proceeding with the examination of the transforming device, it is necessary to make sure that it is receiving power. To do this, check with a multimeter the presence (after plugging the device into the network and starting the heating program) at the connection points of the primary winding of an alternating voltage of 220 V. This work is done with extreme caution to avoid electric shock.

Since it will be necessary to disassemble the microwave oven to check the transformer, this can only be done after disconnecting it from the mains.

The presence of a high-voltage capacitor capable of storing an electric charge leads to the need for its discharge before testing. This is done by simply closing its contacts to each other (with a screwdriver, pliers) or to the case when the voltage is off.

Methods for diagnosing device health

The simplest way to test the performance of a transformer is to replace an existing device with a known good one.

Safe verification method

The safest way to diagnose is to check the integrity of the transformer windings with a multimeter. The whole process is carried out sequentially. The resistance of the primary winding and two secondary, dismantled and disconnected transformers is determined by a measuring device (set to certain limits). If there is a break, 1 will be displayed on the display. If the circuit is closed, the readings for the primary winding (the device is set to 200 Ohms) should be in the range of 2 - 4.5 Ohms, the filament - 3.5 - 8 Ohms, and for the high-voltage secondary (switch set to 2000 ohms) their range is already 140 - 350 ohms.

The output of the resistance beyond the specified limits indicates the presence of an interturn circuit.

When performing measurements, it is required to take into account the value of its own multimeter errors. It is determined by short-circuiting its probes in the limit used. The output value will be an error that should be taken into account.

You can either check the transformer in the microwave with the device yourself, or entrust this matter to professionals from the workshop. The first case will require knowledge of the elementary basics of electrical engineering and the presence of some working skills.

Voltage tests

When the measurement results correspond to the normative indicators, but the furnace is not working, in order to make sure that the transformer is working, it is necessary to check its performance.

A dangerous option is to measure the output voltages of the secondary windings. Actions are performed in the following sequence:

• the furnace is powered by 220 V;
• the tester checks the voltage at the output of each winding: for high-voltage it will be about 2 kV, and its value on the filament will be around 3 V.

In addition to observing safety precautions, this method requires equipment capable of measuring alternating voltages greater than 2000 V.

It is safer to use the following methods.

1. Reverse verification method it is carried out by supplying 220 V to the boosting secondary winding, and about 24 V should be obtained at the primary output (the average transformation ratio is assumed to be 9.1).
2. You can power the primary coil with 12 V (from a low voltage transformer or power supply), then the secondary should be approximately 109 V.
3. Also, a short circuit between the turns is present if the transformer device is heated at idle.
4. If it heats up when there is a load in the secondary circuits, and stops after it is turned off, then the cause should be sought further according to the diagram.

The choice of a method for testing a microwave transformer at home depends on personal qualifications, knowledge and skills, and available tools. The safest option is the usual continuity test to detect the integrity of the circuits or the presence of breaks. The use of 220 V voltage during the determination of the operability of the device requires strict compliance with electrical safety measures. When there is uncertainty in one's own abilities, it is better to resort to the help of professionals.

Resistance welding is increasingly used not only in manufacturing plants, but also in home workshops and garages, where it can be successfully used for various metal-related jobs. Serial equipment for performing such a technological operation is quite expensive, but a resistance welding device can be made with your own hands from an old microwave oven.

One of the variants of the apparatus for resistance welding from a microwave oven

For the manufacture of resistance welding equipment at home, the following components, accessories and tools will be required:

• a transformer that can be dismantled from an old microwave oven (if a high-power apparatus is needed, then two such transformers will be needed);
• thick copper wire or small diameter wire harness;
• levers to be used as clamps;
• lever of the required length;
• a reliable base on which the welding machine will be installed;
• clamping clamps;
• Screwdriver Set;
• cables and winding materials;
• copper electrodes, due to which welding will be performed.

Transformer Assembly

The main element of any resistance welding machine is a transformer, which can be taken from an old but working microwave. In order for a home-made welding device to be able to connect steel sheets up to 1 mm thick, a transformer with a power of at least 1 kW is required. If you need a more powerful resistance welding machine, you will need two transformers.

microwave step-up transformer

To make equipment for resistance welding with your own hands, you do not need to take the entire transformer from the microwave oven, but only its magnetic circuit and primary winding. The secondary winding is carefully dismantled from the transformer, and shunts are also removed from it, which are located on its two sides.

We cut off the secondary winding with a chisel (chisel) or cut it with a hacksaw

Shunts are removed

A new winding for a microwave transformer is made of stranded wire with a cross section of at least 100 mm 2 (or more than 1 cm in diameter). It will be enough to make 2-3 turns. If the wire has too thick insulation, then it is allowed to remove it and replace it with fabric insulating tape. If two transformers are used at once, then the secondary winding is made common for them, but it is very important to correctly connect the leads from their primary windings.

The next steps in making resistance welding from a microwave with your own hands are the installation of controls, the manufacture and connection of electrodes, the installation of the inside of the equipment in a reliable case, which can also be taken from failed household appliances.

Another great video on the topic:

Choice of electrodes

The electrodes of equipment for spot welding perform several functions simultaneously: compression of the sheets to be joined, current supply to the welding zone, and subsequent heat removal. Important parameters when choosing an electrode are its shape, dimensions, etc. It is on these parameters that the quality of the welded joint directly depends. The geometric shape of the electrodes can be straight or figured, but straight models are preferred, as they provide better access to the welding area.

When choosing electrodes for a microwave welding machine, you can simply refer to the corresponding GOST (14111-90), which already specifies all possible diameters of these elements (10, 13, 16, 20, 25, 32, 40 mm).

The diameter of the copper bars that will be used as electrodes must be greater than or equal to the diameter of the working wires. To avoid active oxidation of the electrodes during operation, they are connected to the working wires by soldering. The electrodes of a resistance welding device (including those made from a microwave oven) actively wear out during operation, so they must be regularly sharpened, giving them the shape of a sharpened pencil with a file.

Bottom electrode installed

How to operate a homemade welding machine

Despite the fact that resistance welding is a fairly simple technological operation, it must be properly controlled to achieve the required quality of the joint being performed. It is for these purposes that a home-made apparatus from a microwave oven should be equipped with the appropriate controls. The main ones are a switch and a lever, with the help of which the required compressive force of the electrodes and the parts to be connected is provided.

The quality of the resulting joint directly depends on the compression force, so it is advisable to make the lever for the welding machine longer. It is very important that the equipment for resistance welding from the microwave is securely fixed to the surface of the desktop. Clamps are used for these purposes.

It is possible to increase the force transmitted by the electrodes not only with the help of a lever, but also by means of a lever-screw mechanism, which can also be equipped with a do-it-yourself device. It is most convenient to fix such a mechanism directly on the lever so that manipulations with it do not take additional time. In addition, such an arrangement of controls will free up the second hand of the operator, which can hold the parts to be connected.

A feature of working on a contact welding machine is that it is possible to supply current to the electrodes only when they are in a compressed state. If you turn on the current supply before compressing them, then they will spark at the moment of contact with the parts, and this will lead to their burning and rapid failure.

A switch, also related to resistance welding controls (including those made from a microwave oven), must be installed in the primary circuit. If you ignore this recommendation and install it in the secondary winding circuit, through which a significant current flows, the switch will create additional resistance, which will lead to welding of the electrodes together.

For a home-made welding machine with a microwave transformer, it is necessary to provide for the simplest cooling system, also made by hand. An ordinary fan can be used as such a system. With this device it will be possible to cool the transformer itself, electrodes and other conductive elements. Of course, such cooling will not be very effective, and you still have to take regular breaks in work, necessary for self-cooling of all heating elements of the equipment.

The welding process performed on a do-it-yourself apparatus is practically no different from a similar technological operation carried out on serial equipment. The first stage of such a process is the compression of parts, during which their plastic deformation occurs at the place of the future connection. At the second stage, a current is supplied to the welding zone, passing through the copper electrodes.

This stage is characterized by the formation of a liquid welding core, expansion of the weld pool and plastic deformation and precipitation of the metal of the parts at the junction point. At this point, molten metal begins to splash out of the weld pool. After the cessation of the current supply to the connection zone, it begins to cool, which is accompanied by crystallization of the molten metal.

Finished welding machine (top view)

As a result of the processes described above, a cast core is formed in the joint zone, which is characterized by high strength. The resulting connection zone is characterized by significant residual stresses, which can be minimized if the electrodes are not immediately opened after the current supply is stopped, but rather wait for a while. It is even possible to slightly increase the force on the connection zone after the current is cut off, which will also reduce residual stresses and allow for a forging effect.

By the way, using a transformer from an old microwave oven and the simplest components, you can independently assemble a welding machine for arc welding. Of course, such a device can hardly be called a full-fledged one, but for some types of small work it is quite applicable. An example of creating such a mini-welder can be seen in the video below.

A spot welding machine can be bought today at any store, but its cost is sometimes high. What to do if the welding machine is required only for a certain type of work?

As a basis for manufacturing, you can use a transformer from an unnecessary microwave oven. Such spot welding from a trance from a microwave oven will be not only simple, but also of high quality. Simple tools are used for assembly, only the transformer itself is an expensive part. If there is no relevant experience in assembling such equipment, then it is best to prefer the finished version. But if you have the skills, you can easily avoid unnecessary expenses by assembling the device with your own hands.

To make a do-it-yourself welding contact machine for point-to-point connection of steel sheets, you will need the following tools and materials:

• transformer from an old microwave oven (or 2 if welding with high power is required);
• copper wire or bundle of wires;
• clamping levers;
• convenient lever with the required length;
• base for the welding machine;
• clamps;
• screwdriver;
• cables and winding for connecting individual elements;
• copper electrodes of the required diameter and length.

The main element is the transformer. The case for such equipment may not be used, there is no great need for it. It is important to make levers of the required length, at the ends of which the electrodes will be strengthened. With the help of a special lever, the electrodes will close, when turned on, a current will pass through them, which ensures spot welding.

Transformer Assembly

The main part of the contact welding machine is a transformer from an old microwave oven (Fig. 1). In this case, its power must be at least 1 kW. Such a transformer allows welding sheets of steel, the thickness of which is 1 mm. If more powerful equipment is needed, then 2 such transformers will be required.

Figure 1. Microwave transformer diagram.

From the transformer, a magnetic circuit is used, the primary winding. The secondary winding must be carefully cut down, and then selected with a rod. The shunts located on both sides are also removed. Next, you need to make a secondary winding, for this a stranded wire with a diameter of 10 cm² is used. If 2 transformers are used, it is necessary to combine them into one when creating the secondary winding. The conclusions of the windings are interconnected, it is impossible to make mistakes here. Next, you should provide for the installation of controls and the connection of electrodes. You will also need a durable case, you can borrow it from old household appliances. Pay attention to the approximate assembly diagram (Fig. 2).

Manufacturing of electrodes

For work, special electrodes are used that provide current to the welding point. They perform the function of a compressive element, serve to further remove heat. It is important to choose the right electrode type, shape, dimensions and other parameters. Today, curly or straight electrodes can be used. The latter are used most often, as they provide direct access to the welding point. The parameters of such electrodes fully comply with GOST 14111-90, which regulates the diameters for working rods: 10 mm, 13, 16, 20, 25, 32, 40 mm.

Figure 2. Scheme of assembly of the apparatus for welding.

When spot welding is planned, it is best to use copper rods, while their diameter should be equal to or greater than the diameter of the working wire. As you use the electrodes, you need to undermine, giving them the shape of a pencil tip, since during operation they grind down a lot. Over time, the electrode needs to be replaced, this should not be forgotten. Before starting work, the tips must be soldered to the wires, otherwise they will oxidize.

Management and process of welding

Resistance welding is a relatively simple process, although it is not always possible to obtain a sealed seam. The quality won't be that bad. However, in order for welding to be done correctly, you must first take care of the controls. This device, made on the basis of a microwave oven transformer, uses such simple controls as a switch and a lever. In this case, it is necessary to ensure the maximum compression force, since the quality of welding depends on it. The lever is best made longer, its quality must be high in order to ensure all working conditions. The base of the welding machine must be fixed to the work surface with clamps.

The force during welding is given not only by a lever, but also by a special lever-screw mechanism. There are other methods, but it is best to use these on your own. The control switch must be installed directly in the primary winding circuit, since a large current is observed in the secondary circuit, and the installed switch creates additional resistance. In such a situation, the contacts can be welded to each other tightly.

The clamping lever mechanism is mounted directly on the lever, in this case it turns out to be convenient to turn on the current and press the lever, without wasting time when welding.

The second hand can hold the details. A feature of using a welding machine is that it is possible to turn on the current only if the electrodes are compressed. If this condition is not met, then sparks appear. And this leads to the fact that the electrodes burn out, become unusable.

If a microwave oven, or rather its transformer, is used for the manufacture of a welding machine, then it is necessary to provide a method of cooling. For this, a fan is used, which makes it possible to control the temperature of the installed transformer, electrodes, and conductive elements. You will have to take breaks during work so that the work items can cool down on their own.

The resistance welding process itself includes 2 main stages (first, the parts are compressed to induce plastic deformation at the point that will be welded):

A pulse is turned on, after which a current is applied to the point, a liquid core is formed. The passing current creates the conditions for the expansion of the weld pool to the required parameters, plastic precipitation begins in the contact zone. Metal splashes out of the weld zone.
The current is turned off, cooling occurs, the crystallization of the metal at the junction.

A cast strong core is formed, but one of the undesirable consequences of welding is residual stresses, which can be dealt with by various methods. One of them is the delay in removing force from the lever after the current is turned off. Some experts even recommend slightly increasing the force after the current is turned off, i.e., the so-called metal forging is performed.

A transformer from an old microwave oven can be used for a variety of purposes. It can be applied to the manufacture of resistance welding machine. Such equipment is assembled from simple parts, but for this and welding itself, it is necessary to have at least a minimum work experience, to follow safety rules.

To power the magnetron of a microwave oven, a rectified high voltage is traditionally used, obtained from the mains using a step-up transformer, which is called “MOT” (an abbreviation for the English “Microwave Oven Tranformer” - a microwave oven transformer).

At the output of the MOTA (or rather, on its anode winding), an alternating voltage in the region of 2200 volts is added to the voltage on the doubler pass-through capacitor (capacity 1 microfarad), and is fed to the magnetron anode already in the form of a pulsating voltage with a frequency of 50 Hz, a value of about 4000-4500 volt - this is just enough, which is a very powerful electronic device. The magnetron here is connected in parallel with a high-voltage diode, which serves as a valve in the voltage doubler circuit.

The incandescence of the magnetron is also provided by the MOT, for this purpose there is an additional secondary winding (filament), consisting of 3 turns, and giving out from 2.5 to 4.6 volts at a current of up to 20 amperes. For each magnetron, the MOT is selected individually, and therefore the parameters of the windings of MOTs from different microwave ovens will differ slightly from model to model, up or down. One way or another, it is the MOT that remains the heaviest element of any microwave oven, and it depends on it how much power the magnetron can provide in this microwave oven.

Many of those who have seen the ILO or even been lucky enough to hold it in their hands must have paid attention to the peculiarity that the dimensions of the ILO are very modest, despite the power of the microwave in which it was installed.

For example, if we proceed from the usual guidelines regarding the overall power of the mains transformer, it turns out that the MOT has 2 times less volume than it should be used with such a significant operating power of the microwave. This means that under its normal load, a transformer of this type operates in an unusual mode.

Let's look at what distinguishes the ILO.

Indeed, the microwave transformer does not work all the time for a purely resistive load. The AC magnetron circuit is by and large a capacitive load. It is for this reason that additional structural elements of the magnetic circuit - shunts - are installed between the windings of the microwave transformer.

Due to the presence of shunts, the working magnetic flux has the ability to partially close outside the secondary winding, which is equivalent to including a ballast choke in the working circuit. For this reason, it is this particular ILO, it is with this particular magnetron that it will work perfectly in pairs, and will not fail. However, the ILO will still work at the limit of its capabilities, although without flying into a dangerous saturation. Statistics show that most often magnetrons fail, but not MOTs.

Fans of spark-gap coils often use MOTs as high-voltage mains transformers. To do this, several MOTs are connected with anode windings in series, and the primary windings are connected in parallel. Often, to get more power from MOTs, Tesla builders knock shunts out of MOTs, and even immerse transformers in oil.

Of course, even without shunts, the ILO is able to work even with a powerful active load, but such work will last no more than a few minutes, and strong overheating will not take long. Therefore, if the ILO is not used for its intended purpose, and even without shunts, it makes sense to use its forced cooling.

Attention! The voltage of the secondary winding of the MOTA is deadly and must be handled with extreme care.