The area of ​​the core of a microwave oven transformer. How to make a spot welder from a conventional microwave

Many home craftsmen want to have a personal welding machine. But it does not always have to be bulky equipment, since household operations involve the use of a more popular option - spot welding. The modern market offers a lot of options - from the most budgetary to the most expensive. However, the purchase is not always advisable due to the possibility self-manufacturing. Next, we will consider how spot welding from a microwave is created, its features and sequence of actions. Naturally, it will not work to weld serious structures, but it is quite a suitable option for minor repairs.

How does a spot welding machine work?

It takes a lot of current to melt a metal. The voltage level in this case is not important. Often a level of up to 3 volts is used.

Experimenting with different current levels is not worth it. Each considered option of a welding machine from a transformer from a microwave oven has been repeatedly tested. The power of the transformer used must be selected from the planned thickness of the workpieces to be joined. For example:

• Thickness up to 1 mm - enough power of 1000 W;
• Up to 2 mm - enough 2000 W;
• Up to 3 mm - 5000 W level.

The primary winding is selected based on the total power of the assembled device. Since it is very problematic to create a transformer on your own, it is better to use a ready-made version using a microwave transformer. This option works great with the following features:

• The radiating elements of the furnace require a voltage of several thousand volts. However, the level of current does not play any role;
• The power on the windings is the same. By increasing the number of turns on the secondary winding, the magnitude of the voltage will also increase, losing current;
• Transforming elements in microwave ovens have a power of up to 3000 watts. This is enough to create contact welding with your own hands.

The required parts can be easily found on the radio markets or seized in your old furnace. The failure of old microwaves is characterized by burnout secondary winding because it has a smaller diameter.

The generated current level of 1 kA will allow you to easily melt the metal at the contact points, ensuring reliable welding. This can be achieved from a 3 kW transformer.

The principle of welding can clearly explain the video lesson.

Removal and assembly of a transformer from a microwave oven

Every microwave has a magnetron. He, as was said, needs increased tension. The built-in transformer has fewer turns in the primary winding and more in the secondary, on which voltages up to 2000 volts are induced. In the presence of a doubler, this value increases by another 2 times. This property is used when creating do-it-yourself spot welding from a microwave.

It is necessary to carry out the extraction of the transformer with care. Do not use heavy tools to avoid damage to the device. To begin with, the body and all fasteners are removed. The transforming element is removed from the fixation point. This device will require a magnetic circuit and a primary winding with a thicker wire and fewer turns.

The secondary winding is not needed in the design and must be removed. This can be done with a hammer and chisel. How to make a cutting is probably not worth learning. However, this must be done carefully so as not to harm the primary winding. It is possible that during operation you will find shunt devices that are used in some types of furnaces. They also need to be removed.

If there is a magnetic core not on an adhesive basis, but on the basis of welding, then it will be more convenient to remove the winding from it with a chisel or a hacksaw. The winding can be quite tightly planted in the magnetic circuit. In this case, drilling or removal by improvised means will be required. It must also be done carefully to avoid damage to the magnetic circuit.

Further, assembling resistance welding from a microwave oven with your own hands involves the creation of a new secondary winding. To create it, you will need a whole wire with a diameter of at least 100 mm2, which corresponds to 1 cm. It is even possible to use a bundle of wires providing a suitable diameter. When you create a new winding in your transformer, it will be possible to create a current of up to 1 kA.

If there is a desire to assemble arc welding from a more powerful microwave, then one transforming element may not be enough. In this case, it will be necessary to combine two elements from two microwaves.

It will be enough to create two or three turns. If there is too thick insulation, you can remove it and replace it with a thinner one, for example, fabric. When using two transformers at once, the secondary winding must be made common. However, in this case, it is necessary to correctly connect the outputs from the primary ones.

How to connect two transformers

Do-it-yourself microwave welding of the two transformers, it is possible to achieve a significant increase in the power of the device. In this case, you can achieve an increase of up to two times.

In a similar proportion, the welding current will increase. However, there will be significant losses, since the resistance of the circuit will also be large. In this case, the ends of the secondary winding must be connected to the electrodes.

If you have 2 transformers, but their voltage is not enough to make a welder, then you can connect their output windings in series. But you need an equal number of turns on each element. This is also done in cases where it is not possible to wind the required number of turns on the magnetic circuit.

Also, when a similar apparatus is assembled with your own hands, it is necessary to control the direction of the turns and their coordination with each other. Otherwise, it is possible to create an antiphase and obtain an almost zero final voltage. As an experiment, when determining the correct connection, you can use small wires.

Creating electrodes

When doing spot welding from a microwave transformer, you need to create suitable electrodes. At the same time, they must correspond in diameter to the diameter of the wires with which they will be connected. For this, copper bars are suitable, and at low power, you can use a tip from a professional soldering iron.

While working, homemade spot welding actively wears out the electrodes. To adjust the geometric dimensions, they need constant undercutting. Accordingly, over time, they will have to be replaced.

To connect the apparatus to the electrodes wires should be kept as short as possible.
Otherwise, there will be significant power losses. They will also take place subject to availability. a large number connections.

To increase the efficiency of a device created on your own, you can create copper tips on the wires connecting the electrodes. In this way, power losses occurring at the contact points can be avoided.

Wires are required to select a fairly large diameter. Tin-plated ferrules can be used to facilitate soldering. Since the electrodes are of a removable type, soldering should not be done at the fixation points with a tip. Naturally, oxidation and subsequent power losses will occur at these points. However, they are much easier to clean than with crimped lugs.

The tips are fixed to the electrodes by a simple bolted connection. It must be created reliable so that there is no increase in transient resistance, which contributes to the loss of power of the spotter. It is advisable to create holes of equal diameter in both parts.

Connecting elements are better to choose copper or alloy, which has a minimum electrical resistance.

Controls

Self-made resistance welding is not a complex apparatus. However, when creating spot welding from a microwave oven with your own hands, you need to provide controls. The main ones are a switch and a lever element, with the help of which the necessary force will be created on the electrodes and workpieces to be welded.

The level of quality of the connections created will depend on the degree of pressing.
That is why it is worth considering as long a lever as possible. It is also necessary to take into account that microwave welding must be securely installed on work surface. It may even be worth fixing it, for example, with a clamp.

It is possible to increase the applied efforts with the help of levers or lever-screw mechanisms, with which it is allowed to equip your structure. It is advisable to fix such a mechanism on the lever. In this case, it will not take much time during operations with it. In addition, there is freedom for the other hand, which can hold the elements to be welded.

An important feature is that current can only be supplied to the electrodes in a closed position. If this is done before compression, then sparking will occur during contact with the part. This also contributes to the burnout of the electrodes and the breakdown of the device.

The switch should be installed in the primary winding circuit. If you mount it in the secondary, then it will create additional resistance, leading to welding between the electrode parts. It should also be noted that a significant current flows in the secondary winding, which not every machine is able to withstand.

Also, welding from a microwave transformer should be equipped with an elementary cooling system. It is possible to use an ordinary cooler from a computer. Thus, it is possible to cool the transformer itself, electrodes and current-carrying elements. Naturally, it will not be possible to effectively cool the device and you will have to take regular breaks in work to cool all the parts.
A home-made machine welds parts no worse than factory models. Therefore, it is worth studying the assembly process in more detail on the video and trying to assemble it yourself.

A microwave transformer is an important link in a circuit that generates microwave radiation. This is a voltage converter of the mains to the value supplied to the input of the magnetron. The high-voltage converter often causes damage to the microwave oven.

Checking the transformer for operability is a mandatory item in the list of measures for technical diagnostics to find out the causes of the malfunction. Since we are talking about high voltages, self-intervention is possible only if all safety measures are observed.

Where can I get high voltage?

Food in microwave ovens is heated by the work of microwaves. A special emitter, the magnetron, generates microwaves. To work in the given characteristics, it needs high voltage- 2,000 V. This is almost an order of magnitude higher than what the household power supply (220 V) gives.

Where do kilovolts come from? They are created at the output of the secondary winding of the high-voltage converter.

Important! A microwave oven, even disconnected from the mains, can be electrocuted (U up to 5,000 V).

Types of high voltage converters

Elements of the converter installed in the microwave oven:

• magnetic core;
• frame;
• primary winding;
• two secondary windings.

On the primary winding U = 220 V is supplied. The filament is fed from the secondary. The first of the two secondary windings is made of heavy gauge wire. U at the output is approximately 3 V. At the output of the second winding - variable high U = 4 kV.

In microwave ovens of different brands, converting devices of various manufactures are used. The transducers do not look the same and have different characteristics. They differ:

• power;
• output voltage of the secondary windings;
• the number of turns in the coils and the cross section of the wire;
• dimensions;
• fastening method.

The secondary coil, like one of the outputs of the emitter, is closed to the housing.

Electrical circuit diagram

In the electrical circuit of the microwave oven, in addition to the converter, there are:

• diode;
• high voltage capacitor;
• magnetron;
• fuse;
• electric motor - one or two (for rotating the pallet, if it is provided for by the design, and for the fan);
• Control block.

In expensive microwave ovens, instead of a converter, a pulse unit is used, which has a more complex device, but weighs less.

What are the faults?

You need to check the transformer in two cases: when the stove does not work well and when it does not work at all. You can suspect a malfunction of this particular element by the following signs:

• the microwave oven is unusually loud;
• food placed in the chamber is not heated or heated slightly;
• when working, it smells of burnt insulation, the equipment smokes.

If at least one of the listed symptoms appears, it is better not to turn on the device - until the problem is fixed. Turning on a faulty stove can lead to an aggravation of the breakdown.

One of the most common causes of electrical equipment failure is power surges. If there is a suspicion that the device is faulty due to power outages, it is necessary to urgent repair. However, it is possible that during the repair work a factory defect will be found.

Causes of malfunctions

The converter fails most often due to:

• Wire break. The wire of one of the windings may break.
• Short circuit in windings. This can happen in one coil or both.
• Open or short circuit in the magnetron coil.

The magnetic circuit of the converter is assembled from steel plates. If the plates peel off, the machine will make noise. It is necessary to find out the power of the transformer and replace it. Such global breakdowns can be easily identified by eye, but they do not happen often. The vast majority of problems are still provoked by coils.

Checking procedure

To check the health of the high-voltage converter, you need to arm yourself with a multimeter, you will also need:

• screwdrivers with different tips;
• pliers;
• ohmmeter.

Sequencing:

• turn off the device - remove the plug from the socket;
• unscrew the screws and remove the casing;
• discharge the capacitor;
• remove the terminals from the transformer;
• check with a coil tester - if there are no deviations, put back;
• if damage is detected - the wire breaks or a short circuit occurs, the device is changed;
• assemble the oven and check its operation.

If the device still does not work after the measures taken, continue troubleshooting or check the device under voltage.

The transformer, with traces of melted insulation and a burning smell, does not need further examination: it is broken and beyond repair.

Important! To check the transformer, you have to disassemble the microwave oven - this can only be done when it is disconnected from the mains.

A high-voltage capacitor easily stores a huge electric charge, so it must be discharged before measurements. How to achieve this? Just close its contacts with each other - this can be done, for example, with pliers.

Diagnostic options

Consider common options for finding the causes of a breakdown.

Secure check

The safest examination is carried out by a tester and consists in examining the coils for damage. Procedure:

• The multimeter is adjusted to the required limits and with its help the resistance of all windings is determined - the primary and two secondary. The study is done on a removed transformer.
• If the unit is displayed on the tester, then a break has occurred.
• At closed circuit a value in the range of 2–4.5 ohms will appear on the primary coil (the tester is set to 200 ohms). On the incandescent - 3.5–8 ohms, on the high-voltage secondary (2,000 ohms) - 140–350 ohms.

If the resistance value is outside the specified ranges, an interturn short circuit has probably occurred.

When measuring, it is necessary to take into account the own error of the multimeter. You can determine it by short-circuiting the probes within the specified limit. The resulting value is an error.

You can perform a secure check yourself or invite a specialist from the service. To ring the windings, the user only needs to know the basics of electrical engineering and have the skills to work with a tester.

Voltage test

If the measurements are taken, the measurements are correct, but the stove still does not work, it is necessary to investigate a number of characteristics. Measuring the output voltage on the secondary windings is a rather dangerous business. Procedure:

• 220 V is supplied to the microwave.
• The tester measures U at the outputs of both secondary windings. High voltage - 2 kV, incandescent - 3 V.

This method requires equipment that can measure AC voltages greater than 2 kV.

This option is less problematic. 220 V is supplied to the secondary winding, about 24 V is removed from the primary winding. The coefficient is 9.1. If 12 V is applied to the primary winding, the secondary will be about 109 V.

If the transformer heats up during idling, an inter-turn short circuit has probably occurred. If the device heats up under load, and when it is turned off, it stops heating, you should continue to look for a problem.

How to choose a verification method

It is important to choose the converter study option based on your qualifications, knowledge and skills. The safest thing is to just ring the circuit for integrity. If 220 V is connected during measurements, special precautions must be taken.

If you are not sure of your knowledge, it is better to contact a professional.

Which microwave ovens have problems

Most often, problems with the converter occur in microwave ovens of the brands "",.

Considering the famous brands, it is difficult to assume that they all neglect the quality of the components used in the electrical circuits. Most likely, this trend is associated with the popularity of these brands. They are bought more, and therefore the breakdown statistics are higher. But when calculating the number of breakdowns per number of units sold, it becomes clear that they break no more often than other well-known brands.

Precautionary measures

Damage may occur when measuring under voltage. electric shock up to and including death. Two rules will help to avoid danger:

• It is strictly forbidden to touch the internal parts of the microwave oven during its operation. To perform measurements, it is necessary to put on the tester clamps the “crocodile” probes - with them and connect to the sections of the circuit.
• If you need to touch high-voltage parts with your hands, you should not only disconnect the stove from the mains: you can prevent electric shock by shorting the magnetron leads to the housing. With this precaution, you will protect yourself from discharging the capacitor. AT electrical circuit microwave oven has a resistor to discharge the capacitor, but it does not eliminate the danger by 100%. The resistor may burn out or they forgot to install it at all, and such a mistake can cost the life of a self-repair lover.

Repair of any electrical equipment is associated with the danger of electric shock. When testing a transformer in a microwave, you need to be especially careful due to the high voltage and capacitor. Use safe measurement methods and follow safety regulations.

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 quite 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.

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. And the characteristics of this iron are also interesting, is it suitable for charging auto batteries? 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?

Almost every motorist or just a person who loves 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, you can make a completely working welding machine out of a breakdown. Let's talk today about how a microwave transformer is used for welding.

An important part is the transformer

There is only one important detail in a microwave oven 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. The rods for reliable operation should be carefully processed, slightly undermined, in otherwise they 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 durable 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. Cooling coolers from system block personal computer. Also very often such transformers are used to create a Tesla coil and a tube amplifier.

The high-voltage microwave oven transformer is designed to generate the voltages necessary 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.

If the microwave oven hums strongly, emits a sweetish smell of burnt winding, does not heat. All these signs indicate that the high-voltage (step-up) transformer may be faulty.
In this case, it must be checked and, if necessary, repair the microwave.

In this article, we will diagnose the high-voltage microwave oven transformer and also consider the reasons for the failure of this component.

Attention!
A microwave oven can give you an electric shock
(voltage up to 5 kilovolts) even if it is disconnected from the network

We strongly recommend that you seek professional help if you are unsure of your knowledge of electrical safety precautions.

Transformers in microwave ovens can differ in: the configuration of attachment to the chassis, dimensions, power, class, output voltage and winding resistance.

The failure of this component can be facilitated by power surges of the 220V network, huge pressure, short circuit of the magnetron feed-through capacitor, manufacturing defect.

Scheme of a high-voltage microwave oven transformer

So let's get started.

We take a microwave oven with a suspicion of a transformer malfunction (the oven hums a lot, smokes, does not heat food).

We unscrew the screws, remove the casing.

We find a high-voltage transformer.

It is important to remember that a high-voltage capacitor in a microwave oven can hold about 4000 volts for several minutes, and if a 10 MΩ resistor (which serves to discharge) is cut off in it, then a dangerous charge can last for quite a long time. Therefore, before starting the test, it is advisable to discharge the capacitor, for example, with a screwdriver on the case or by closing the contacts with each other with pliers.

We got to the transformer, we will check, for this we need a multimeter and pliers.

So, we check the primary winding.
Carefully remove the terminals from the terminals of the primary winding of the transformer.

We set the measurement limit on the multimeter to 200 ohms.

We make measurements.
Winding resistance usually varies from 2 ohms to 4.5 ohms (depending on the class of the transformer and on the section of the winding wire). If less than two or more than four and a half ohms, the problem is most likely in the primary winding. Also, when measuring, do not forget about the error of the multimeter. In order to find out the error, close the multimeter probes for a few seconds at the limit of 200 ohms.

In our case, everything is in order with the primary winding.

Let's move on to the next phase of measurements.
We measure the secondary winding, the device limit is 2 kOhm

We remove the terminals from one terminal of the secondary winding, the second terminal is the transformer housing (since the housing is bolted to the microwave oven chassis, you can call the furnace housing). The resistance of the secondary winding can vary from 140 ohms to 350 ohms (again, as mentioned earlier, this depends on the class and section of the winding) if the readings exceed 350 ohms or less than 140 ohms, this indicates that there is most likely an interturn short circuit of the secondary winding.

Now let's check the filament winding, the measurement limit is 200 ohms.
We disconnect the terminals from the magnetron, and measure the conclusions with the device. The resistance of the filament winding ranges from 3.5 to 8 ohms.

It happens that the device shows the resistance of all windings within the normal range and the transformer still works poorly, this happens when the winding burns only slightly and manifests itself only under load, in which case it is best to throw in a known good high-voltage transformer.

You should also check whether the transformer is receiving 220 volts.
To do this, connect the multimeter to the terminals that fit the primary winding of the high-voltage transformer, turn on the microwave oven in the 220V network and start the microwave heating program.

Good luck with the repair!

If you are not sure of your knowledge in the field of electrical engineering, you can contact us to call a microwave oven repairman in Kyiv. Acceptable prices and quality are guaranteed.