Making a toroidal transformer with your own hands. Making a toroidal transformer with your own hands Rewinding a pulse transformer of a computer power supply

This article does not claim to be a bestseller of popular science literature, but rather a guide for beginners. The article describes the winding process itself, and not its calculation.

Sooner or later, in the practice of every radio amateur, the question arises of how to power a particular device. The most popular ULF power is 2 * 100 or 2 * 200. Therefore, the best option is a “donut” for 150 watts of overall power, in the first case one is needed for 2 channels, in the other a couple for double mono. The toroidal transformer has the best size-to-power ratio, high efficiency, and minimal noise. That is why audiophiles love them so much. Consider the winding process of this type of transformer in more detail.

The main thing that a person who winds a transformer should know and most importantly understand:

• wire length (number of turns) is voltage;
• the cross section of the conductor is the current with which it can be loaded;
• if the number of turns in the primary circuit is small, then this is an extra heating of the wire;
• if the overall power is insufficient (more than possible is consumed), this is again warm;
• overheating of the transformer leads to a decrease in reliability.

So, what is needed for winding:

1. Transformer iron in the form of a torus (hereinafter I will write where to get it);
2. Varnish pipeline (a winding wire is needed for the transformer winding);
3. Masking tape (paper);
4. PVA glue;
5. Fabric tape or kiperka;
6. Pieces of wire in insulation;
7. Last but not least, desire.

TRANSFORMER IRON

I will not talk about how to calculate the power of iron for this, there are already a lot of articles ... Calculating power is difficult from a practical point of view, since the steel grade and the quality of its production are not known. Therefore, two cores with the same overall weight have different parameters. Consider an example of winding a core on an already “used” core. One of the most easily obtained cores, the quality of which is noteworthy. Is the core of the Soviet stabilizer "Ukraine-2" (SN-315). At one time, a lot of them burned down, and on the market you can get such a device for 20 UAH ... We are interested in torus. This donut is wound with an aluminum lacquer pipe, we mercilessly wind it (or bite it), we need a core (carefully so as not to damage the core). Aluminum wire can be used for other purposes (twisting brooms or wires), or as in my case, I melt it for other purposes (making radiators). After winding, a beautiful core is obtained with dimensions of 96-54-32 mm, respectively, the outer, inner diameter and height. Below is an example of such a core ( Fig.1 ). The overall power of such a core is at least 120 watts (tested in practice).

Before winding, it is necessary to prepare the iron for winding. If you look at the corners of the transformer, then take away that they are at an angle of 90 degrees, at these points the wire will bend and the varnish will peel off, so that it would not be necessary to process the corners with a file, rounding them as much as possible (I understand that laziness but necessary). The minimum circle radius is 3mm. Figure 1 shows that the corners have already been processed, and the torus is ready for winding. A little trick, when processing corners with a file, it is necessary to avoid licking the steel so that the layers do not remain closed to each other! To do this, move the file along the direction of the transformer tape. After processing, I recommend looking at the corners for closing the layers and modifying them with a small file.

In order to isolate the core from the winding, it is necessary to isolate it with FABRIC electrical tape (or a kiperka impregnated with paraffin wax). It is better to use electrical tape with a width of about 25 mm (Fig. 2), then there will be a maximum coverage of the metal in one layer, which saves space in the window. We do not seal the end of the winding (read on).

After these operations, the core is ready for winding and we move on to the next step.

lacquer pipe

Lacquering I call an electrical conductor whose insulation is made of varnish (according to cultural winding or winding wire). There are different brands of PEV, PEV-2, PET-155 and others. I recommend using PEV-2, rich orange color. Also, the wire showed itself very well, very dark in appearance (PEL), the color of rotten cherries, this one has a thick layer of insulation, which allows it to be used for high-voltage transformers (more than 500V). For example, a PEV-2 wire with a diameter of 1.6 mm has an insulation thickness of about 0.06-0.07 mm, and a "black" wire 0.1-0.11 mm.

The calculation of the wire cross section is a very interesting process. There is a lot of literature on this topic on the Internet, and I will not write about all sorts of calculations and subtleties (Google to the rescue). Depending on the current density you choose, there will be a different cross-section of the wire. The main thing that is required is the right power ratio. It is necessary that the power of the secondary winding does not exceed the capacity of the primary. As you know, the efficiency of transformers in the form of a torus is very high and equals about 97%, therefore, when winding a torus with a power of 200 watts, 6 watts of loss is a trifle that can be neglected. We assume that the power of the primary winding is greater than or equal to the power of the sum of all secondary windings.

Calculation example. It is necessary to wind the transformer. The primary winding is designed for 220V. There are two secondary windings of 28V each. Primary wire diameter 0.6mm varnished. The thickness of the lacquer is about 0.06mm, and the “clean” diameter of the primary winding wire is about 0.54mm. Substitute in the formula for the area of ​​a circle and get a cross section of 0.228 mm 2 (if you don’t know how I calculated it, then buy an amplifier and don’t bother). And so for the proportion we get 220V / 28V * 2 \u003d 3.92, which means that the secondary winding should have a cross section 3.92 times thicker than the primary winding. As you can see, I did not use power and, accordingly, current density. Everyone takes the current density that he considers correct (for myself, I take 4A / mm 2, and my thoughts confirm the real test of trance, which I will describe further).

For the core described above, it is better to use a primary wire of at least 0.6 mm in diameter. A wire of this cross section and the required length can be found in old tube TVs, in the form of demagnetization loops. There are always people on the market who are engaged in buying old TVs (“hoarders”), they can find the necessary wire. We have two types of loops on the market: small and large, smaller for 20 UAH, large for 50.

Small in diameter, such TVs use 2 pieces each. The diameter of such a half demagnetization loop is about 40-50 cm, the cross section of the conductor is somewhere around 0.6 mm. With high-quality laying, this loop is enough to wind the primary winding of one torus with a margin of a couple of meters.

If you use a large loop, then the length of the wire is literally one and a half times longer than the small one, so it is more profitable to buy small loops. Sometimes a loop comes across from a tube, color TV, the length of the wire in such a loop is similar, but the wire cross section can reach 0.7 mm. If you get one, then you're in luck.

And so you found a demagnetization loop, as a rule, it is wrapped with a keeper cloth (rag strip), and on top with a transparent tape or electrical tape. Near the wire leads there is a joint where you can hook and gently unwind the loop. No need to cut, cut, tear off the insulation, you can damage the wire, in addition, we still need this insulation. After winding, we are left with a beautiful wire that can be used. Some rewind the wire onto the “shuttle”, I personally don’t do this, why bend the wire once again if it is already of the desired shape, besides, if you wind small tori, the shuttle will take up more space and may not climb through the window, and also damage the varnish . Before you start winding it, you need to make twists so that the wire does not move apart. In order to make twists, you need to take pieces of a single-core wire (preferably in PVC insulation) 5-7 cm long. We wrap the loop in a circle from a slightly tight step, then during winding, in order to add (rewind the wires), you just need to scroll this spring and the wire will separate (see photo Fig. 3).

Now our loop has one end from the outside, and the other is somewhere inside, we need the outer one. Next, let's return to the iron that we have already processed and wrapped with electrical tape or kiperka. Remember we didn't seal the edge, that's why (see Fig. 4). On the side where the top of the trance will be (the conclusions go up), at the corner of the torus we make an incision in the center of the electrical tape and thread the varnish pipeline there already in isolation, this will be the tap of the beginning of the winding. Some recommend soldering a piece of flexible stranded wire in the insulation and making such a tap. This option doesn’t suit me because in this way I don’t know which wire is in the primary, and even after ten years I measured it with a micrometer and you know what you can reap from it, and with a tap, who knows what kind of section it is. Although it's up to you.

Let's make leads for the wire. The winding terminals must be "reinforced" with additional insulation. For these things, PVC insulation (Soviet white) is very well suited, but insulation from a wire of the required cross section is even better. You can use heat shrink, but it is better to use PVC or insulation, because the first one tends to bend in one place, which we don’t really need, we are trying to protect ourselves from this so that the wire does not break off. In order to pull off the insulation, I recommend taking a wire that has additional insulation in the form of a thread wrapped around the conductor. In this case, the thread does not give a strong bond between PVC and copper and allows you to pull the insulation. To make it easier to tighten the wire, you need to bend it a little (at 45 degrees). I recommend to “stretch” the insulation at a time and use it. ( Fig.2).

Domestic winding wires

Winding wires in enamel insulation based on high-strength synthetic varnishes with a temperature index (TI) in the range of 105 ... 200 are most widely used. TI is understood as the temperature of the wire at which its useful life is at least 20,000 hours.

Copper enameled wires with insulation based on oil varnishes (PEL) are produced with a core diameter of 0.002 ... 2.5 mm. Such wires have high electrical insulation characteristics, which are practically independent of the external influence of elevated temperatures and humidity.

PEL type wires are characterized by a greater dependence on the external influence of solvents, compared to wires with insulation based on synthetic varnishes. PEL winding wire can be distinguished from others even by its external feature - the enamel coating is close to black in color.

Copper wires of types PEV-1 and PEV-2 (produced with a core diameter of 0.02 ... 2.5 mm) have polyvinyl acetate insulation and are distinguished by a golden color. Copper wires of types PEM-1 and PEM-2 (with the same diameter as PEV) and rectangular copper conductors PEMP (section 1.4 ... 20 mm2) have varnished insulation on polyvinyl-formal varnish. Index "2" in the corresponding designation of PEV and PEM wires characterizes two-layer insulation (increased thickness).

PEVT-1 and PEVT-2 are enameled wires with a temperature index of 120 (diameter 0.05 ... 1.6 mm), they have insulation based on polyurethane varnish. These wires are easy to install. When soldering, it is not necessary to strip the varnished insulation and apply fluxes. Enough ordinary solder brand POS-61 (or similar) and rosin.

Enamelled wires with insulation based on polyesteramide PET-155 have a TI equal to 155. They are produced with conductors not only of a round cross section (diameter), but also of a rectangular (PETP) type with a conductor diameter of 1.6-1 1.2 mm2. In terms of their parameters, PET wires are close to the PEVT type wires discussed above, but have a higher resistance to heat and thermal shock. Therefore, winding wires of types PEVT and PET, PETP can be especially often found in powerful transformers, including transformers for welding.

WINDING PROCESS

To wind a trance, you will need 4-5 evenings and 2 hours of time, why you will understand further why at least 4 days.

We have already launched one end of the wire and pressed it. Then the most dreary winding begins. I recommend winding like this. We take a trance (for now, iron), put on a glove or take some kind of rag made of natural fabric in our hand. We sit down on the sofa or bed, turn on the movie that we have already seen or music (so as not to be too distracted), and start winding. We thread each turn into an iron ring. You need to wind a coil to a coil from the inside (some manage to do it from the outside, I can’t imagine how).

In order to make it easier to count the turns, it is better to group them in 5 or 10 turns. It is necessary to pull the wire not clearly perpendicular (dotted red line) to the tangent (pure red), but slightly inclined towards the winding (yellow), as if the inner part of the winding goes ahead of the outer (Fig. 5). Thus, the winding wire, when stretched, will itself be pressed against other already laid turns. If you have a bent wire, it will not fit perfectly, so it should be as straight as possible, for this, during winding, you need to pull it strongly, thereby straightening it. That's why gloves or rags are needed, if gloves are not used, then the fingers and palm get tired and hurt very quickly. If you wind a wire with a cross section of more than 1.5 mm (very hard), then I recommend that the wire be slightly bent under tension for ease of straightening.

(My friend's father winds welders at 50 hertz, the secondary tavern puts copper 35 squares perfectly evenly with his hands, so he bends 5 kopecks of Ukraine into dumplings with his fingers).

During winding, the wire is inspected for flaws, especially in the places of bending, if the varnish is broken, then we cover it with a carefully insulating cap with varnish or paint (in extreme cases, with ordinary nail polish).

When the layer is wound to the end. Between the layers it is necessary to make interlayer insulation. I was lucky and I have some stash of varnished fabric, and the fabric is such that it stretches and is soaked with something sticky. If such one sticks to each other (formed), then it is very difficult to separate it. Her fingers stick together. Such varnished fabric is an ideal insulator, in addition, the winding does not rattle even when overloaded. But very few people have it. The same functions of an insulator are very well implemented using masking tape.

After the layer has been wound, we take it and isolate it with masking tape. We make stripes about 15mm wide. And with these strips we wrap the trance initially to isolate the inside of the wire winding (from the inside of the donut). Then we isolate the gaps from the outside of the donut. As a result of insulation with adhesive tape, it turns out that from the inside, the insulation by overlaying layers will become twice as thick, from the outside it will be single. After wrapping it is necessary to generously lubricate the torus with PVA glue, this is done so that the adhesive tape does not unwind, and it will also become stronger and seem to be solid. In addition, the glue will hold the windings so that they do not “buzz”. You don’t need to feel sorry for the glue, lubricate it with your finger and rub it lightly. After that, the torus needs to dry. I usually wind the torus in the evening, after winding the layer I impregnate it with glue, and the torus itself, for good air circulation, I put it on a needle radiator. During the night, the torus dries up and can be wound further. That is why a minimum of 4 pm is required for winding (4 pm - 4 layers). If necessary, you can speed up the drying process with a hair dryer. We wind the next layer ... the winding process itself is similar and no different. At the end of the winding, the end of the winding is placed in the same insulation as at the beginning of the winding. Then we fix the end of the winding with masking tape, isolate the winding with masking tape and soak it with glue.

There is another good option for insulation between layers. It will be very good if during the winding you use baking paper (parchment) cut into the same stripes and then wrapped. As a result, the trance will need to be impregnated, but actually boiled on a steam bath with a mixture of 50:50, respectively, paraffin:wax. We take a steam bath in a saucepan, collect water and set it to boil (we need steam). From above we install a container in which a transformer and paraffin wax are placed. We tie the transformer in advance on a wire, leave the end (when the mixture flows over this thread, you need to soak the transformer into it like a tea bag in a cup). When you dip the transformer, you need to be careful so that drops of wax do not fall on the flame, it is very flammable !!! Previously, output transformers for tube ULFs were impregnated with just such a "dissolution", although other high-quality trances were also impregnated. When the mixture is heated, it has a very high fluidity almost like water, causing the paper to become literally soaked in paraffin and wax. However, this option will not be initially effective if the trans is heated (warm) at a temperature of 50 degrees, the wax is already quite soft and will not restrain the wire from 50 Hz vibration, although it will act as a dielectric. (True, it is precisely because of vibration andwires are frayed and a closed loop is obtained, which leads to damage already during exploitation).

For pulse transformers, I recommend using not adhesive tape as an impregnation, but paper + BF-2 glue. This adhesive is primarily used in the manufacture of speaker coils. But in a pulse transformer, he also showed himself very well. With repeated overload, not the slightest squeak at a conversion frequency of 15KHz.Unwinding the windings from the frame, they were removed with a loop Irina at 8 lived.

During winding, we periodically measure the no-load current, for this it is necessary to connect the tester in series with the primary winding in ammeter mode (read the instructions for the tester). Measure current x.x. you need to be very careful because the work from the network! To avoid any emergency, I recommend turning on a 220V light bulb in series with the primary, with a power of about 40W. The light bulb will burn if the number of turns is very small, if the trans is wound correctly, then it should only have a pink tint, which indicates a low current that flows through it. The transformer has large starting currents, at the moment of starting the transformer, overloads can reach 160 times. Therefore, the start of the transformer must be done not directly through the tester, but with the help of a “jumper” which you then open and the current begins to flow through the tester. The jumper can be implemented by simply closing the tester probes, which are then opened. What should be the no-load current, I will write below.

For transformers with low current consumption, it is recommended to use a 10 or 100 ohm (2-5W) resistor that is connected in series with the primary winding. By measuring the voltage drop across the resistor, using Ohm's law, draw the current. This method is more preferable than the first, but at the same time more dangerous at high current consumption - the resistor turns into coal in a fraction of a second !!!

About how to measure the current x.x. I wrote briefly, now about the meanings. Current rate x.x. each determines for each trance individually, but usually the norm is up to 50 mA at 230V, although some say that 0.5A is normal. The lower the current, the better! The lower the quiescent current, the more the shape of the current x.x. similar to sine. If you have current x.x. from 20-50, then this is tolerable, let's say a C grade, from 10-20 it's four, less than 10mA is clearly five. For small torics, the current will be small due to the high resistance of the primary winding, this must be taken into account! Although how to manually wind tori on me less than a hundred watts is an atrocity! The number of turns of the primary winding in them reaches a couple of thousand.

The transformer wound by me according to my method has a current x.x. equal to 11mA (with 4 primary layers).

If you do everything sequentially, you get something similar:

TEST AND MEASUREMENT PROCESS

About how to measure the current x.x. I wrote briefly, now about the meanings. Current rate x.x. each is determined for each trance individually, but usually the norm is up to 50 mA at 230V, although some say that 0.5A is normal. The lower the current, the better! The lower the quiescent current, the more the shape of the current x.x. similar to sine. If you have current x.x. from 20-50, then this is tolerable, let's say a C grade, from 10-20 it's four, less than 10mA is clearly five. For small torics, the current will be small due to the high resistance of the primary winding, this must be taken into account! Although how to manually wind tori on me less than a hundred watts is an atrocity! The number of turns of the primary winding in them reaches a couple of thousand.

It will be very useful to look at the shape of the no-load current in the primary winding using an oscilloscope. BUT!! this must be done under very special conditions! This requires an isolation transformer (220 / 220V), while the induction must be very low so as not to cause additional distortion of the "sine" shape. And also Latr. I recommend doing this test item only to very experienced specialists, the consequences are fraught with burnout of the oscilloscope !!!

Using my winding parameters, I "shot" 150 watts from such a trance for several hours (there was no longer time).

Isolate the primary winding from the secondary.

After winding the required number of layers of the primary winding, we are approaching the moment of winding the secondary. It is necessary to isolate the primary winding from the secondary very carefully.

If the secondary winding suddenly burns out, then the worst consequences are the failure of the ULF. But if at this moment the secondary winding somehow “short-circuits” to the primary, then this is already a danger to life! For the secondary winding of the transformer at the middle point is connected to the body of the ux, imagine that when you turn the volume knob, you are shocked?! It is unpleasant, therefore, grounding in the outlet is not the desired norm, it is a necessity, if your health is dear to you, I recommend that you pay special attention to this ... (This was a small digression).

Based on the fact that REAL grounding is VERY rare in sockets, it is necessary to isolate the primary winding from the secondary as much as possible. For this operation, you can apply the already knurled method and use masking tape. BUT the thickness of the layer must be at least doubled, and preferably tripled. Moreover, impregnation with glue is necessary, the glue will add elasticity and an additional layer. A better option would be to use special electrical varnishes such as TsAPON (color is not important). In this case, we literally soak the torus in varnish, you can even soak it! The varnish will be more fluid if it is heated, the zapon becomes like water when heated, and thus impregnates the windings well, isolating and fixing them. With regard to the primary winding, this is one of the best measures, as for me even better than paraffin. If you are going to use impregnations, then it is logical that using all sorts of “yellow-transformer” adhesive tapes is contraindicated, a layer of adhesive tape simply will not allow it to leak deeper, unlike paper or varnished cloth. Regarding the “fixation” and isolation of the secondary winding with the help of varnishes, it is categorically against (suddenly you need to rewind the secondary, it will not be possible to do this, in addition, the wound wire is only for scrap metal.)

If there is no varnish, and masking tape is not impressive. It would be very nice to isolate the windings with fluoroplastic, this material is a super insulator! In appearance, it looks like a film of white, slightly transparent color (photo below).

The main feature is that it is heat-resistant to heat (from minus -268 to +260 degrees).When I need to increase the temperature of the soldering iron tip, I simply wrap it with fluoroplastic to prevent the “body” of the soldering iron from cooling).Such raisins can only be found in special stores, although there will be J varnished fabric nearby, which is also very good. Not everyone has access to such assortments, but if you want ... In this case, I recommend rummaging through the bins. Fluoroplastic of the shape we need can be obtained in FT-type capacitors. If we carefully dismantle the aluminum case of the capacitor, then we will get the core (the capacitor itself) from the fluoroplast we need tightly wound in such a way. From a 0.022 microfarad capacitor, you can wind two pieces of one meter each. To isolate the primary, we need about 5-6 meters. That is, we are looking for min 3 capacitors. Fluoroplastic capacitors sound very good, so think before you ruin them.

Keep in mind that the fluoroplastic will not allow the trance winding to soak like tape, so if you want to soak with paraffin, do this before the windings are insulated with fluoroplastic.

I will describe the screening of the primary winding from the secondary a little later, this is rather in the section on high matters.

The final finishing of the trance and its fasteners.

I skip the moment of winding the secondary, because it is absolutely similar to the process of winding the primary. As for the final finish, here you need to understand some points.

A toroidal transformer is a closed magnetic circuit, the core tape is wound in a dense roll after annealing in a furnace under vacuum. Winding it is complicated by the need to thread the wire through the window. Its advantage is that the core itself is inside without emitting unnecessary interference, because at the moment they are picked up by the trance secondary. Thus, the core of the trans-coarse piece of iron is inside, and the soft copper wire, opened with a fragile varnish, bravely protects it (a piece of piece of iron). The body of the toroid is very susceptible to damage from the outside. The fall of the torus from a decent height can "kill" it with the help of short circuit windings. Whereas trances such as PL or W-shaped iron, on the contrary, protect the secondary winding. Thus, fixing the TS-nick is much easier because it can and should be very strongly compressed with metal ties in order to reduce the gap in the core, and thereby minimize losses and hum-vibrations of the plates. It is much more difficult to fix the toroid, or rather, at least options. Before doing the final finishing of the trance, you need to clearly understand how the trance will be attached to the body.

And yet, what options for insulation-finishing:

Alternatively, you can use a transparent tape in which the demagnetization loop was packed (by the way, some loops were wrapped with fluoroplastic, check if you are lucky). The result is very beautiful bagels (you can see the winding, and a beautiful wire). But the increased temperature of the transformer will soften the insulation, thereby lowering its strength level. But that's not the point! When you isolate the transformer with a “film”, the heat transfer level drops dramatically, and the torus can heat up more. I think everyone is trying to buy things from natural materials, trying to avoid synthetics, because the body “does not breathe” in it and the person sweats ... so why should Thor endure. For these things, the use of a keeper tape (a sheet cut into strips J) is more suitable. In order for it to be even stronger, I soak it in that PVA glue before winding it. Then I wind the torus, while winding it squeezes out the excess. After drying, a good, harsh rag frame is formed ... If you suddenly need to unwind, just soak it for a while. Treatment options are also allowed (for an already wound transformer) with paint, both alkyd and water-based, or special varnishes.

What mounting options?

One of the obvious ways to fasten the torus is fastening with a bolt threaded through the center of the torus. When fastening in this way, take into account that through the bolt, and then the bottom of the case, after along the walls of the case, the top cover, a coil can form, the section of which is simply crazy (depending on the diameter of the mounting bolt). In no case do not attach the torus to the bottom and top cover, form a closed loop and burn the torus!

In addition, interference will be induced in the gap between the fastener and the top cover, since the bolt is iron (magnetic). The smaller the gap, the higher the level. It is not uncommon to say that without a cover, the ULF plays everything perfectly; there is no background; I cover it with a cover and a crazy background appears. Interference is induced, in order to avoid such interference, it is necessary to use a fixing bolt made of diamagnetic materials, for example, brass has shown itself well ... (but do not forget about the possibility of forming a coil through the case).

Now you need to somehow rest against the winding of the torus, while the contact area should be maximum, to minimize pressure on the wire. For these purposes, I use a rear washer and a core from the magnetic system of the speakers, all that is needed is to drill a hole in the core and cut the threads, after which a very good fastener is obtained (photo below).

You can also cut out a piece of textolite or gitinax with a thickness of 3 mm or more, give it a shape for maximum contact of the "washer" with the surface of the torus. You need to use a gasket between the “washer” and the body of the torus. To do this, use rubber, the thickness of which should be at least twice as thick as the diameter of the secondary winding (guess why), the bed both from below and from above. When making this washer, it is possible to provide for the installation of copper rivets in order to fix the leads on the "terminal block". If someone does not understand, there is a photo of such a design.

The diameter of a stud or bolt threaded through the center of the torus is unlikely to match the diameter of the window. In order for the bagel not to fly on this bolt like a hoop on a ballerina, you must either wrap it with electrical tape (to the desired diameter) or you can use thick cone-shaped rubber. Motorists will find this kind of gum without any problems, for example, gum from a VAZ2107 jet stabilizer or shock absorber, has the right shape and costs a penny.

Not infrequently, in factory versions, the window is filled with a compound by inserting a sleeve there, for which the torus is attached. In practice, radio amateurs do not use this (usually) because, again, it is not possible to disassemble the torus without damaging the wire. At home, such a plug can be implemented using epoxy.

Another option for mounting "spider". In fact, the same cover is made, only a large washer. Its shape is usually a square cover made of iron or textolite, the edges protrude beyond the boundaries of the outer part of the transformer. Holes are drilled in these corners and with the help of bolts it is attracted to the body, so you do not thread the bolt through the center and create an unfinished coil through the ULF body.

It would be VERY good to make an iron “pot with a lid” of thick steel (min 2mm) for the toroid, in which to place the torus and fill it with a compound, for example, paraffin or wax (or the same epoxy), although after epoxy it will not be disassembled. In this way, not only the problem of fasteners is solved, but also shielding from interference. (A photo of a similar design was lying around on a computer, I don’t remember the author, but I think he won’t be offended).

A little about screening.

Between the primary and secondary windings, it will be very good to place a shielding winding. Ideally, this winding should practically cover all visible parts of the toroid, blocking the magnetic fluxes on the way from the core (primary winding) to the secondary. One end of the shielding winding must be "in the air", and the other is connected to the mecca (body) of the amplifier (sometimes through a resistor up to 10 ohms). The first end can be well insulated and left inside the torus. The second, the one that is on the ground of the case, should be brought out using a stranded flexible wire.

In the ideal case, winding should be done with a copper tape about 15-20 mm wide, which is insulated on both sides with varnished cloth, electrical tape or fluoroplastic, you can also use masking tape, but very carefully so as not to tear and not make micro cracks (both in the tape and in the insulator), which will break through the voltage. Shielding in this way takes up a lot of space and makes a lot of voids that impair heat transfer, adding hum and "in vain" move the secondary away from the core. It will be more economical if you wind the screen with a wire with a diameter of about 0.6 mm. But if the core is visible, then be sure the interference will pass through these “windows”, that is, we either wind as it should be very tightly in several layers, or we do not do empty work! If possible, then you can make such a screen, it will definitely be worse!

It is much better to shield the transformer as a result of winding, that is, when the transformer is completely wound (Although, to be honest, it is necessary to divide the interference by class and type, and separately consider methods for dealing with them). Ideally, in this case, it would be to use not a copper tape, but permalloy. Although if they look at you with brick eyes at the word fluoroplast, then you can dream of permalloy;). It is very good to wrap the transformer in several layers of transformer iron; iron from any transformer is suitable for this purpose. (I use steel from an old 2 amp latra core).

Here is a torus shielded with a transformer tape, placed in a metal cover and boiled in paraffin, cold current. 1.5 mA, primary more than 2500 turns, interlayer fluoroplastic, with sequential welding in paraffin. I made it in a mug + transformer steel, it turned out very well (see above)! This torus was used to work in a pre-amplifier.

It is not worth making a pot out of aluminum, it will not protect against anything. You need to make it from thick steel (at least 2mm), and it’s also very good to shield it from the inside with copper (sheet thickness of about 1mm). Although he himself did not do such things (from copper), but authoritative people advised.

In conclusion, about interference from tori, I will say that toroids very rarely generate interference on equipment, while a peculiarity is noticed that the toroids that are not home-wound have a high x.x current. or overestimated induction ... Therefore, if you do not be greedy and wind a toroid from an underestimated magnetic induction (increase the number of turns per volt), then you are unlikely to encounter the problem of interference from the transformer.

It is planned to supplement the article with such "highlights" ... so far very briefly ...

internal resistance.

All transformers and energy sources (power supplies) have such an abstract parameter as internal resistance. What does it mean?! In the case of a transformer, this resistance will be equal to the active resistance of the windings. When you connect a load to the trance, the current flowing and the resistance of the windings create a voltage drop. In order for the voltage drop to be minimal, it is necessary to increase the cross section of the conductor (by reducing its resistance). But at the same time, it is necessary to take into account this fact during operation, that the overall power of the windings will be higher than the overall power of the core, carefully so as not to overload the primary.

Section winding.

Low induction.

Implicit loop.

Shielding and types of interference.

P.S. My first article, and even an unfinished request not to throw tomatoes .. There’s no time to finish, I’m posting what I’ve already done a long time ago ... Now this bagel is successfully working in Natalie 2012EA, you can search for a photo in the corresponding thread, and here

We disassemble the transformer from the microwave oven

Typically, a microwave oven transformer contains three windings. The most numerous, wound with the thinnest wire, is a step-up, secondary, the output of which is 2000-2500 V. We do not need it, we will remove it. The second winding, thicker, with less wire compared to the secondary, is a 220 V network winding. Also, between these two massive windings, there is the smallest one, which consists of several turns of wire. This is a low-voltage winding of about 6-15 V, which outputs voltage to the magnetron glow.

We cut the seams of the magnetic circuit

It is necessary to cut the seams holding together the "W"-shaped plates and the "I"-shaped ones. The seams of the Chinese manufacturer are not as strong as they seem. You can cut them down with a grinder or even split them with a chisel with hammers. I used a grinder, this is a humane way.

Removing coils

Remove all coils. If they are very firmly seated, tap gently with a rubber mallet. We only need a winding for 220 V, we delete the rest. We put back the primary winding at 220 V and place it down the “W”-shaped core.

Calculation of the secondary winding

Now we need to calculate the number of turns of the secondary winding. To do this, you need to know the transformation coefficient. Usually, in such transformers, it is equal to one, therefore, one turn of wire will produce one volt. But this is not always the case and you need to double-check this.
We take any wire and wind 10 turns of wire on the core. Then we collect the core and clamp it with a clamp so that it does not fall apart. Be sure to supply 220 V through the fuse to the primary winding. Meanwhile, we measure the voltage at the output of a 10-turn winding. In theory it should be 10V. If not, then the ratio is not the same as usual and you need to make calculations to calculate the voltage for your winding. All this is not difficult, mathematics is the fifth grade.
I have two transformers. I will do one for 500 V, the other for 36 V. You can do it for any other voltage.

Winding the coil of a transformer for 500 V

The transformation ratio of my copy is one to one. And in order to wind the winding at 500 V, I need to make 500 turns of wire on the coil accordingly. We take a wire.

Of course not like this, but wound on a drum. We estimate the current strength and the volume of the coil. From these values, select the diameter of the wire.

Here is such a simple device I assembled for winding the coil. The core itself is made of wood, the sides are made of plexiglass. You can fix it on a drill or screwdriver.

Wound, assembled, connected. I measure the output voltage, I almost hit it - 513 V, which is acceptable for me.

36V transformer

The 36 V winding can also be wound manually by taking the appropriate wire. To put on and straighten the winding on the core, you can use such wedges, see photo.

After the winding is all stretched, in the holes formed, after removing the wedges, put tightly pressed paper. This is my primitive way. Then I recommend impregnating the winding with epoxy, otherwise it will buzz a lot.

Work on bugs

I rewound the winding to make it denser and more powerful. To do this, I wound it with a double wire, instead of one thick one. At the end I will connect them.

After all the windings are fixed, it's time to assemble the transformer core. To do this, we fix the entire structure with a clamp and arc weld the same places as before. It is not necessary to make a thick seam, everything should look as it was.
Next, for my straightener I will need:

I will load the rectifier at 20 A, of course, the diode bridge must be installed on the radiator.
Also, if you use a metal case like me, don't forget to ground it.

About security

Be careful when connecting the transformer, never rush and double check everything. Connect the transformer only through a fuse to avoid possible short circuits. Do not touch live parts while the transformer is in operation.
Also, when processing metal, be sure to be careful and use eye protection.
Remember that you do all the actions at your own peril and risk!
All the best!

Winding a transformer with your own hands is not so much a complicated process as a lengthy one that requires constant concentration of attention.

For those who start such work for the first time, it can be difficult to figure out what material to use and how to check the finished device. The step-by-step instructions below will give beginners answers to all questions.

Before proceeding directly to winding, it is necessary to stock up on all the necessary tools and tools for the job:

Types and methods, winding directions of the transformer windings are shown in the photo:

Insulation of winding layers

In some cases, it is required to insert spacers between the wires for insulation. Most often, capacitor or cable paper is used for this.

The middle of adjacent transformer windings should be insulated more strongly. For insulating and leveling the surface for the next layer of winding you need a special lacquer to be wrapped on both sides with paper. If there is no varnished fabric, then the problem can be solved with the help of the same paper folded in several layers.

Paper strips for insulation should be 2-4 mm wider than the winding.

To check, first of all, it is necessary to determine the conclusions of all its windings. Useful tips on how to check the transformer with a multimeter for performance, read the following article.

Action algorithm

1. Fix the wire with the coil in the winding device, and the transformer frame - in the winding device. Rotations do soft, moderate, without disruption.
2. Lower the wire from the coil onto the frame.
3. Leave between the table and the wire minimum 20 cm so that you can place your hand on the table and fix the wire. Also on the table should be all related materials: sandpaper, scissors, insulation paper, included soldering tool, pencil or pen.
4. With one hand, smoothly rotate the winding device, and with the other - fix the wire. It is necessary that the wire lay flat, coil to coil.
5. transformer frame insulate, and pass the output end of the wire through the frame hole and briefly fix it on the axis of the winding device.
6. Winding should be started without haste: you need to “fill your hand” so that you can stack turns next to each other.
7. It is necessary to ensure that the angle of the wire and the tension are constant. Winding each subsequent layer "to the stop" should not be, because the wires can slip and fall into the frame "cheeks".
8. Set the counting device (if any) to zero or carefully count the turns orally.
9. Glue the insulating material or press it with a soft rubber ring.
10. Each subsequent turn is 1-2 turns thinner than the previous one.

For winding transformer coils with your own hands, see the video clip:

Wire connection

If a break occurs during winding, then:

• thin wires (thinner than 0.1mm) twist and brew;
• wire ends of medium thickness (less than 0.3mm) should be freed from the insulating material by 1-1.5 cm, twisted and soldered;
• thick wire ends (thicker than 0.3mm) you need to clean a little and solder without twisting;
• insulate the soldering (welding) place.

Important Points

If thin wire is used for winding, then the number of turns must exceed several thousand. From above, the winding must be protected with insulation paper or leatherette.

If the transformer is wound with thick wire, then external protection is not required.

Trial

After winding is finished, it is necessary to test the transformer in action, for this, its primary winding should be connected to the network.

To check the device for short circuits, connect the primary winding and the lamp in series to the power source.

Degree of insulation reliability checked by alternately touching output end of the wire of each output end of the network winding.

The transformer should be tested very carefully and carefully so as not to get under the voltage of the step-up winding.

If religiously follow the suggested instructions and do not neglect any of the points, then manually winding the transformer will not present any difficulties, and even a beginner can handle it.

Welding inverters are inexpensive, buying them today is not a problem. And yet, many home craftsmen are interested in the question of how to make a transformer (welding) with their own hands. How difficult it is, and how a home-made device will work. In principle, it is easy to do it with the right approach. The main thing is the winding of the transformer, because the power of the unit and the quality of its work depend on the correctly selected number of turns, on the cross section of the wire used.

So, before winding the welding transformer, it is necessary to calculate it according to all the required parameters. It should be noted that the calculation carried out does not always correspond to standard rules and schemes, because the welding machine is sometimes assembled from materials other than those used in factory assembly. That is, what was found, then used.

For example, not the best transformer iron or winding wire was used. But even after such winding, the transformers cook perfectly, although they hum and get very hot. We add that when choosing transformer iron, you need to pay attention to such an indicator as the shape of the core. It can be armor or rod. The second type is used in homemade welding transformers more often, because they have a better efficiency. True, the laboriousness of winding a transformer with your own hands is much higher here. But this does not scare the masters.

We add that the transformer can be wound according to several schemes.

• The network winding is when both coils are equal in number of turns and they are connected in series.
• Both windings are connected in anti-parallel fashion.
• The wound wire is located on one side of the core.
• The same as in the previous position, only on two sides connected in series.

The simplest scheme is the last one. It is usually used to assemble a transformer at home. In it, the secondary winding consists of two equal halves. And they are located on opposite arms of the magnetic circuit. The connection, as mentioned above, is serial.

The calculation is based on theoretical parameters, on the basis of which it will be necessary to make a choice of the actual parameters of the magnetic circuit. The main welding parameter is the current that is supplied to the electrode. Since in everyday life electrodes with a diameter of 2 are most often used; 3 or 4 mm, then a current of 120-130 amperes will be sufficient for them. Now you can correctly calculate the power of the welding transformer using this formula:

P=U x I x cos φ / η

U is the open circuit voltage, I is the current strength (120-130 A), cos φ is taken equal to 0.8, η is the efficiency, which is 0.7 for home-made welding machines.

The calculated power value must be checked according to the table with the cross section of the magnetic circuit. The tabular value with these parameters is usually 28 cm², but in fact it is necessary to choose from the range of 25-60 cm². Now, according to other reference tables, the number of turns of wire relative to the core section is selected.

A very important point - the larger the area of ​​\u200b\u200bthe core used for the transformer, the fewer turns in the coil should be. The thing is that a large number of wound turns may not fit in the hole of the magnetic circuit. The calculation of the number of turns is made according to this formula:

N = 4960 × U / (S × I), where U is the power supply voltage on the primary winding, I is the secondary winding current, in fact, this is the same welding current, S is the cross-sectional area of ​​​​the core.

And the number of turns on the secondary winding can be calculated using the ratio:

U1/U2=N1/N2

The open circuit voltage on the secondary winding in homemade welding transformers is 45-50 volts.

How to wind a transformer

So, the calculations have been carried out, the parameters of the used elements of the step-up transformer have been determined, the winding scheme has been determined, you can proceed to the rewinding process itself. But before that, you need to deal with the wires that will be wound on the core.

A copper wire in fiberglass or cotton insulation is wound on the primary winding. No rubber. Based on the current strength on the primary winding, equal to 25 amperes, the cross section of the winding wire is 5-6 mm². The cross section of the wire on the secondary winding should be 30-35 mm², because a high current flows through it (120-130 A). Pay special attention to the insulation of this wire, it must be heat resistant. Now everything is ready, you can proceed to the winding of the teroidal transformer.

Before rewinding the transformer, it is necessary to understand one truth that the primary wires are subjected to greater loads, because a smaller conductor is used here. In addition, the density of the stacked turns is higher here, so they heat up more. That is why the quality of laying in the primary winding must be given special attention.

It happens that a home-made transformer is assembled not from a single piece of wire, but from several segments. There is nothing wrong with this, because the ends of the pieces can be connected. For this, twisting cannot be used, it is better to connect the two ends with a copper wire in several turns, and then solder the joint and insulate it.

It is necessary to wind the turns carefully, pressing them tightly against each other. In this case, the laying of the wire should not be carried out strictly perpendicular to the tangent of the iron, but slightly to the side. But, as it were, the internal winding should go ahead. This will simply make it easy to press the next turn to the previous one. There is no need to trim the wire.

Please note that during the rewinding of the transformer, the wire is fed in a flat state. Kinks and bends will only complicate the process itself. Therefore, it is better to wind the wire around your hand and pull it during installation.

To wind a toroidal transformer, each laid layer must be insulated. To do this, it is better to use a special impregnated brass cloth, which, when in contact, sticks to everything. Or you can use construction tape, which is wound around the transformer with your own hands. It is most convenient if the adhesive tape is cut into strips 15 mm wide. It is easy to cover a layer of wire with them, and at the same time, you need to try to make sure that the inside of the winding is covered with insulating material in two layers, and on the outside in one.

After that, the entire winding must be lubricated with PVA glue. Firstly, it will strengthen the insulation, making it monolithic. Secondly, the winding will not buzz. PVA should not be regretted, it is necessary to treat the entire surface well with it. After that, the device must be dried. And then wind a layer of turns and so on until the welding transformer is ready. Do-it-yourself winding of a toroidal transformer is finished.

Correctly carried out transformer rewinding is a guarantee of high quality and long-term operation. The rewound device will work exactly the same as a practically new one. Of course, it buzzes more strongly, but in all other respects it is still the same necessary device.

Winding materials

As a core, profile plates made of a special alloy are mainly used. They are assembled according to the required thickness, taking into account the calculated cross section of the core. There are several forms of plates, but the W-shaped elements are most often used.

The frame of the transformer is, in principle, an insulator that shields the core from the windings. It also holds the coil. A frame and a dielectric material are made, it must be thin (0.5-2.0 mm) to fit in the core window. If the old transformer is rewound, then cardboard, textolite, and so on can perform the functions of the frame. The dimensions of the frame and its shape are determined by the parameters of the core. But the height of the structure must be greater than the dimensions of the winding.

For toroidal transformers, it is better to use copper wires covered with protective enamel. For welding machines, it is better to use copper or aluminum wires with cellulose, cotton or fiberglass insulation. The last one is not the best. It copes well with loads, especially at high temperatures, but during the vibration process, the fibers delaminate, and this is a violation of the insulating layer. As for the output wires, it is optimal if they are of different colors. This will make it easier to connect.

As you can see, rewinding your own old transformer is not very difficult. This, of course, will take a lot of time, but the device will work well. In any case, it will be cheaper than buying a new one.

Making a homemade transformer is a worthwhile endeavor so as not to spend money on buying transformers.

Selection of materials

We take the Russian wire, it has stronger insulation. From old coils, the wire is used if there is no damage to the insulation. Paper, FUM film is suitable for insulation. For insulation between the windings, it is better to use a lacquer cloth, several layers of insulation. Cable paper, lacquer fabric is suitable for surface outer insulation. You can also wind the transformer using PVC electrical tape.

The frame is made of fiberglass or similar material.

Calculations of the parameters of a homemade transformer

On a simple transformer, the primary has 440 turns for 220 volts. It turns out for every two turns of 1 volt. The formula for counting turns by voltage:

N \u003d 40-60 / S, where S is the cross-sectional area of ​​\u200b\u200bthe core in cm 2.

The constant 40-60 depends on the quality of the core metal.

Let's make a calculation for installing the windings on the magnetic circuit. In our case, the transformer has a window of 53 mm in height and 19 mm in width. The frame will be textolite. Two cheeks at the bottom and at the top 53 - 1.5 x 2 = 50 mm, frame 19 - 1.5 = 17.5 mm, window size 50 x 17.5 mm.

We calculate the required diameter of the wires. Do-it-yourself transformer core power in size 170 watts. On the network winding, the current is 170 / 220 \u003d 0.78 amperes. The current density is 2 amperes per mm 2, the standard wire diameter according to the table is 0.72 mm. Factory winding from wire 0.5, the factory saved on this.

• The winding of a simple high voltage transformer is 2.18 x 450 = 981 turns.
• Low voltage for heating 2.18 x 5 \u003d 11 turns.
• Low voltage filament 2.18 x 6.3 = 14 turns.

Number of turns of the primary winding:

we take a wire of 0.35 mm, 50 / 0.39 x 0.9 \u003d 115 turns per layer. Number of layers 981 / 115 = 8.5. It is not recommended to draw a conclusion from the middle of the layer to ensure reliability.

Calculate the height of the frame with windings. Primary of eight layers with wire 0.74 mm, insulation 0.1 mm: 8 x (0.74 + 0.1) = 6.7 mm. The high voltage winding is best shielded from other windings to prevent high frequency interference. In order to wind the transformer, we make a screen winding from one layer of 0.28 mm wire with two layers of insulation on each side: 0.1 x 2 + 0.28 = 0.1 x 2 = 0.32 mm.

The primary winding will take up space: 0.1 x 2 + 6.7 + 0.32 = 7.22 mm.

Step-up winding of 17 layers, thickness 0.39, insulation 0.1 mm: 17 x (0.39 + 0.1) = 6.8 mm. On top of the winding we make layers of insulation 0.1 mm.

It turns out: 6.8 + 2 x 0.1 = 7 mm. The height of the windings together: 7.22 + 7 = 14.22 mm. 3 mm left for filament windings.

You can calculate the internal resistance of the windings. To do this, the length of the turn is calculated, the length of the wire in the winding is taken, the resistance is determined, knowing the specific resistance from the table for copper.

When calculating the resistance of the primary winding section, a difference of about 6 ohms is obtained. Such resistance will give a voltage drop of 0.84 volts at a nominal current of 140 milliamps. To compensate for this voltage drop, we add two turns. Now, during load, the sections are equal in voltage.

Making a transformer coil frame with your own hands

Angles on parts are important, and accuracy in dimensions will affect the assembly of a simple transformer.

On the cheeks, we allocate places for fastening the output contacts of the windings, we drill holes according to the calculations. When the frame is assembled, now we round off the sharp edges that the winding wire will touch. We use a file for this purpose. The wires should not be sharply bent, as the enamel of the insulation will crack. Now let's check if the plate is inserted into the frame window. It should not hang out or be tight. We put the frame on a special machine or prepare to wind the transformer manually. Thick wires are always wound by hand.

Do-it-yourself transformer winding

We lay the insulation of the first layer. Insert the end of the wire into the hole in the output terminal. We begin to wind the wire, not forgetting about its tension. You can check it like this: the wound coil will not slip from the finger. The wire must not be stretched, as the insulation will be broken. It is recommended to impregnate the finished coil with paraffin so as not to spoil the wire. If the winding hums during the operation of the transformer, then the insulation of the wire is erased, the wire is bent and destroyed. For this reason, the tension of the wire during winding is of great importance.

During winding, we move the turns towards each other, compact them. The first layer is the most important.

There is no need to leave empty space on the layer. The highest voltage on the last turns is for the primary 60 + 60 / 2, 18 + 55 V. The varnish insulation will withstand the voltage, if the wire falls into the void of the layer, then the insulation may be broken. We impregnate the first layer, then the second and so on. Insulation between windings must be treated conscientiously. It must withstand up to 1000 volts. At the top of the insulation, it is recommended to sign the number of turns and the size of the wire, this will come in handy during repairs.

The layers of a homemade transformer must have the correct shape. As it winds, the bobbin will bend at the edges. To do this, the layers must be equalized during winding, without damaging the insulation.

Forced wire joints are better on the edge of the frame behind the core. Connect the wire with a twist with soldering, overlay with soldering. The length of the contact when connecting is made more than 12 wire diameters. The joint must be insulated with paper or lacquer cloth. Soldering should be without sharp corners.

The output ends of the windings are made in different ways. The main thing is to be reliable and quality.

Finishing the manufacture of a transformer with your own hands

We solder the output ends of the windings, isolate the surface of a simple transformer, sign these characteristics on it and assemble the core. After that, you need to check this simple transformer with your own hands.

We measure the current of a home-made transformer idle, it should be minimal. Let's look at heating. If the core is heated, then the iron is incorrectly selected. If the windings are hot, then there is a short circuit. If it is normal, then we close the secondary winding for a short time, there should not be cod and strong buzz.

An example of how to make a homemade transformer

Let's move on to the manufacture of the transformer itself. Based on the finished core, we calculate the power of the transformer, turns and wire, wind the primary and secondary windings, and assemble the transformer completely.

To wind a transformer with a voltage of 220 to 12 volts, we need to pick up a magnetic core. We select a W-shaped magnetic core, and a frame from an old transformer. To determine the power delivered by a simple transformer, it is necessary to make a preliminary calculation.

Calculation of the transformer

We calculate the diameter of the wire of the primary winding. Transformer power P 1 \u003d 108 W:

P 1 \u003d U 1 x I 1

where: I 1 - current in the primary winding;

then the current in the primary winding:

I 1 \u003d P 1 / U 1 \u003d 108 W / 220 V \u003d 0.49 A.

Take I 1 \u003d 0.5 amperes.

From the table, the diameter of the wire, depending on the current, we select the permissible current 0.56 A, diameter 0.6 mm.

A homemade transformer with your own hands can be wound without a machine. It will take two or three hours, no more. Let's prepare strips of paper for laying it between the layers of wire. We cut out a strip with a width equal to the distance between the cheeks of the transformer coil plus a couple more millimeters so that the paper lies tightly, the turns do not climb on top of each other along the edges.

We make the length of the strip with a margin of two centimeters for gluing. Slightly cut along the edges of the strip with scissors so that the paper does not tear when bent.

Then we glue a strip of paper onto the frame, smoothing it tightly.

Primary winding

Now we take the wire from the old coil, which has a wire with good, not cracked insulation. We insert the end of the wire into a flexible tube of insulation from the old used wire of the corresponding suitable diameter. We push the end of the winding into the hole of the coil frame (they are already in the old frame).

The coil is wound tightly, coil to coil. After winding 3-4 turns, you need to press the turns against each other so that the winding of the turns is tight. To wind the transformer after winding the first layer, it is necessary to count the number of turns in the row. We got 73 turns. We make a gasket with a strip of paper. We wind the second layer. During winding, you need to keep the wire taut all the time so that the winding is tight. After the second layer, we also make a paper gasket. If the length of the wire is not enough, then we connect another wire to it by soldering. Ludim varnished wire, heating the end with a soldering iron on an aspirin tablet. At the same time, the varnish is well removed.

When the winding of the primary winding is completed, then we isolate the end of the wire into a tube and bring the coils out. Between the primary and secondary windings we make winding insulation. You can wind the transformer further.

Secondary winding

Calculate the diameter of the wire of the secondary winding of a homemade transformer. We take the power of the secondary winding:

P 2 \u003d 100 watts

P 2 \u003d U 2 x I 2

U 2 \u003d 18 volts;

The allowable current in the secondary winding will be equal to:

I 2 \u003d P 2 / U 2 \u003d 100 W / 18 V \u003d 5.55 A.

From the table, the diameter depending on the current: the diameter for a current of 5.55 A is the nearest value in the table of 6.28 amperes. For such a current, a wire diameter of 2 mm is required.

We take the wire that we received when winding the old transformer. We wind the wire of the secondary winding according to the same principle as the primary winding. The secondary winding wire is much stiffer, therefore, in order for it to lay flat when winding, it must be periodically upset by hammer blows through a wooden block so as not to damage the insulation. We got 3 layers of the secondary winding. It turned out a ready-made wound frame of a simple transformer.

Do-it-yourself transformer assembly

To speed up the assembly, we take two W-shaped plates. We insert them inside the frame alternately from two sides, two pieces each.

We haven't installed the cover plates yet. They will be installed later. If you insert all the plates at once with the whole package, then gaps appear between the plates and the inductance of the entire core drops. After assembling the W-shaped plates of a home-made transformer, we insert the overlapping plates, also two each.

After assembling the core, gently tap its planes with a hammer to align the plates. With the help of racks and studs, we will tighten the core. According to the rules, paper sleeves are put on the studs to reduce core losses.

We clean the ends of the windings and tin. Then solder to the lead strips, which can be attached to the transformer frame. It turned out a ready-made transformer with your own hands.

Write comments, additions to the article, maybe I missed something. Take a look at , I will be glad if you find something else useful on mine.