When designing, assembling or repairing something, you often have to connect parts. The types and methods of connections are different. For example, when connecting metal products, a threaded connection (screw or bolt with a nut), riveting, gluing, soldering and welding are used.
And if for the first three you only need mechanical tools, then soldering irons are needed for soldering, and for welding some craftsmen make homemade DC and AC welding machines. Many of these units have been operating without failures for decades.
Homemade AC devices
When assembling, repairing or designing household appliances or any equipment, it becomes necessary to weld several parts together. AC welding machines are expensive and not easy to buy. But it is perfectly acceptable to make them yourself. The circuits of such devices are very different.
One of original designs made on the basis of the LATR transformer (laboratory autotransformer). This device operates from a regular network using alternating current. Its electrical characteristics are very high due to the special design of the magnetic circuit.
It is made of transformer strip iron (rolled) and has the shape of a ring or torus, although the usual welding machine AC is assembled from plates similar to the letter “W”. The characteristics of a toroidal product are 4.7 times higher, and losses are almost minimal compared to an W-shaped core.
But such transformer strip iron is now in short supply, so it is easier to get a ready-made 9-amp laboratory autotransformer (LATR) or a toroidal magnetic circuit from a burnt product. It needs to be rewound - remove the old or burnt secondary winding and wind a new one with a thicker wire. Using all this, you will assemble a 75-155 Amp AC unit in about 1-2 hours.
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Rewind LATR
To replace the windings proceed as follows:
- Remove the casing (if there is one).
- Reinforcement made of non-magnetic material (plastic, aluminum) is removed along with the mechanical part.
- Get rid of old or burnt windings:
- if the windings are not damaged, then the secondary is simply wound onto a special shuttle for use in other developments and designs. A shuttle measuring 4-5x10-20 cm can be cut from plywood;
- if the windings are burned out, then the wire is removed by any method: cut off, torn off.
- The core is electrically insulated from the future winding by wrapping the iron in two layers of varnished cloth or making overlays from special electrical cardboard.
- New windings are wound, isolating them from each other;
- Assembly is carried out.
Devices made on the basis of the LATR transformer are wound with only two windings.
If the transformer burns out completely, you have to wind both windings.
The primary is performed with a 1.2 mm wire of the PEV-2 type. The approximate length of this piece is 170 m. A shuttle is used for winding. The wire is wound completely around it.
And then, having secured the end, they begin to perform translational movements with their hand inside the toroid, wrapping the insulated core with wire. Winding is done turn to turn. After winding, the primary winding is covered with insulation (the same varnished fabric).
For more reliable insulation and efficient cooling of the device, you can use the air gap method between the windings. In this case, the primary winding does not need to be insulated from above - its own coating will suffice.
The method is:
- two rings are made of thick (3-5 mm) PCB with an external gauge 3-5 mm (on each side) larger than the diameter of the core with a wound “primary”;
- the edges are chamfered (they are rounded) to avoid damage to the insulation;
- the rings are secured at the top and bottom of the core with double-sided tape;
- the secondary winding is wound.
The secondary one - 45 turns - is performed with several wires twisted together, or a busbar, which must be in glassy or CB insulation. The cross section is calculated depending on the required welding current and is 5-7 A per 1 sq. mm. For a current of 170 A you will need a busbar or twist with a cross section of 35 mm or larger. The secondary winding (for cooling) is distributed over the toroid with a gap, trying to distribute it evenly.
If you have a working autotransformer or have purchased a new one, then the work comes down to only rewinding one (secondary) winding, since the primary is already wound with wire of the required cross-section and length.
It moves in the following sequence:
- First, unscrew the metal or plastic casing (if there is one);
- remove the slider with the graphite current collector;
- remove reinforcement from non-magnetic material (plastic, aluminum);
- identify (call the tester) and mark all network outputs;
- the remaining wires are wrapped with insulation or PVC tubes are put on them and laid on the side of the LATR perpendicular to the windings;
- then the secondary winding is mounted; the turns, diameter and brand of copper wires are similar to the option described above (completely burnt).
Welding machines, or rather their transformers, are recommended to be installed by two people. The first person pulls the wire and lays it down, trying not to spoil the insulation and maintain a distance between the turns. The second holds the end of the wire, preventing it from twisting.
If the insulation is broken and the ends of at least one turn touch, an interturn short circuit will occur, the transformer will overheat and the device will fail.
Welding machines with such a transformer operate at currents of 55-180 A.
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Wiring diagram
Any design that operates from the network has its own circuit. The welding machine described above also has it.
The rewound transformer is covered with an old casing (if it fits), a new one is prepared or dispensed with without a fence. It's not that dangerous. After all, the device has an output potential of no more than 50 V. And it is much easier to cool a transformer without a casing.
The terminals of the transformer windings are connected to your device as follows:
- Primary (I) - connected to 220 V with a 2-4 mm flexible copper wire (VRP or ShRPS). An automatic switch (Q1) is required - an automatic switch like those found in houses.
- Carefully insulated, but also flexible PRG wires of the appropriate cross-section are attached to the secondary (multi-ampere) one.
One end is attached to the workpiece and grounded (for electrical safety). On the other, a ballast resistor is mounted (to regulate the output current) and a homemade or standard electrode holder for the device.
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Current regulators
The regulator is a 3 mm caliber coiled wire made of constantan or nichrome wire approximately 5 m long. This is a kind of ballast connected in series to the electrical holder circuit.
The spiral is fixed separately on a sheet of asbestos cement. The welding current of the machine can be changed in three ways:
- Selection method. A large alligator clip is attached to the regulating end. The current is changed by moving the clamp in a spiral. If you strengthen the spiral only at the ends (or straighten), the adjustment will be smooth.
- Switching method. Take the switch. Its common terminal is connected to the control wire. The remaining terminals are connected to spiral turns. The current is controlled by discrete movement of the slider.
- Replacement method. The current is changed by selecting electrodes (thick and thin, long and short). Regulation occurs within small limits. This method is almost never used.
These machines change the welding current by adjusting the secondary winding. A large current is removed from it, so changing the current electronically is unprofitable. It is necessary to install powerful parts, huge radiators and appropriate cooling.
A common material for the manufacture of homemade welding transformers has long been burnt LATRs (laboratory autotransformers). Inside the LATR housing there is a toroidal autotransformer made on a magnetic core of large cross-section. It is this magnetic circuit that will be needed from LATR for the manufacture of a welding transformer. A transformer usually requires two identical magnetic core rings from large LATRs.
LATRs are produced in different types, with maximum currents from 2 to 10A, not all of them are suitable for the manufacture of transformers for welding, only those whose magnetic core sizes allow for laying required amount turns. The most common among them is probably the LATR-1M autotransformer. Depending on the winding wire, it is designed for currents of 6.7-9A, although this does not change the dimensions of the autotransformer itself. The LATR-1M magnetic core has the following dimensions: outer diameter D=127 mm, inner diameter d=70 mm, ring height h=95 mm, cross-section S=27 cm 2, weight about 6 kg. From two rings from LATR-1M you can make a good welding transformer, however, due to the small internal volume of the window, you cannot use too thick wires and you will have to save every millimeter of window space. A significant disadvantage of a transformer made from LATRs, compared to the U-shaped transformer circuit, is also that it is impossible to manufacture the coils separately from the magnetic circuit. This means that you will have to wind, pulling each turn through the window of the magnetic circuit, which, of course, greatly complicates the manufacturing process.
There are LATRs with larger magnetic conductor rings. They are much better suited for making welding transformers, but are less common. For other autotransformers, similar in parameters to LATR-1M, for example AOSN-8-220, the magnetic circuit has different dimensions: the outer diameter of the ring is larger, but the height and diameter of the window d = 65 mm are smaller. In this case, the window diameter must be expanded to 70 mm.
The magnetic circuit ring consists of pieces of iron tape wound on each other, fastened at the edges spot welding. In order to increase the inner diameter of the window, it is necessary to disconnect the end of the tape from the inside and unwind the required amount. But don’t try to rewind everything at once. It is better to unwind one turn at a time, cutting off the excess each time. Sometimes the windows of larger LATRs are expanded in this way, although this inevitably reduces the cross-sectional area of the magnetic circuit.
In principle, the cross-sectional area and one ring would be sufficient for a welding transformer. But the problem is that smaller magnetic cores inevitably require more turns, which increases the volume of the coils and requires more window space.
Transformer with spaced arms
At the beginning of transformer manufacturing, it is necessary to insulate both rings. Special attention In this case, you should pay attention to the corners of the edges of the rings - they are sharp, they can easily cut the applied insulation, and then short-circuit the winding wire. It is better to first smooth out the corners somewhat with a file, and then apply some kind of strong and elastic tape along it, for example, a thick keeper tape or a cambric tube cut lengthwise. On top of the rings, each separately, is wrapped with a thin layer of fabric insulation.Next, the isolated rings are connected together. The rings are tightly pulled together with strong tape, and fixed on the sides with wooden pegs, also then tied with tape - the core magnetic circuit for the transformer is ready.
The next step is the most important - laying the primary winding. The windings of this welding transformer are wound according to the scheme: primary in the middle, two sections of secondary on the side arms.
The primary winding takes about 70-80 m of wire, which will have to be pulled through both windows of the magnetic circuit with each turn. In this case, there is no way to do without a simple device.
First, the wire is wound on a wooden reel and in this form is pulled through the windows of the rings without any problems.
The primary winding wire can have a diameter of 1.6-2.2 mm. For magnetic cores made up of rings with a window diameter of 70 mm, you can use a wire with a diameter of no more than 2 mm, otherwise there will be little space left for the secondary winding. The primary winding contains, as a rule, 180-200 turns at normal mains voltage, which is sufficient for efficient work 3 mm electrode.
A cambric is put on the end of the wire, which is attracted by cotton tape to the beginning of the first layer. The surface of the magnetic circuit has a rounded shape, so the first layers will contain fewer turns than subsequent layers to level the surface.
The wire is laid turn to turn, in no case allowing wire to overlap wire. The layers of wire must be insulated from each other. Again, to save space, the winding should be placed as compactly as possible. On a magnetic circuit made of small rings, the interlayer insulation should be used thinner. You should not try to wind the primary winding quickly. This process is slow, and after laying the hard wires, your fingers begin to hurt. It’s better to do this in 2-3 approaches - after all, quality is more important than speed.
If the primary winding is made, most of the work is done, leaving the secondary. But first you need to determine the number of turns of the secondary winding for a given voltage. To begin, connect the ready-made primary to the network. Current idle move This version of the transformer is small - only 70-150 mA, the hum of the transformer should be barely audible. We wind 10 turns of any wire onto one of the side arms and measure the output voltage on them. Each of the side arms accounts for half of the magnetic flux created on the central arm, so here each turn of the secondary winding accounts for 0.6-0.7V. Based on the result obtained, the number of turns of the secondary winding is calculated, focusing on a voltage of 50V (about 75-80 turns).
The choice of secondary winding material is limited by the remaining space of the magnetic circuit windows. Moreover, each turn of a thick wire will have to be pulled along its entire length into a narrow window. The easiest way is to wind it with ordinary stranded wire 16 mm 2 in synthetic insulation - it is soft, flexible, well insulated, and will only heat up slightly during operation. You can make a secondary winding from several strands of copper wire.
Half of the turns of the secondary winding are wound on one arm, half on the other. If there are no wires of sufficient length, you can connect them from pieces - no problem. Having wound the windings on both arms, you need to measure the voltage on each of them, it can differ by 2-3V - the slightly different properties of the magnetic cores of different LATRs affect it, which does not particularly affect the properties of the arc during welding. Then the windings on the arms are connected in series, but care must be taken that they are not out of phase, otherwise the output voltage will be close to zero (see the article Winding of a welding transformer). With a network voltage of 220-230V, a welding transformer of this design should develop a current of 100-130A in arc mode. Short circuit current secondary circuit- up to 180A.
It may turn out that it was not possible to fit all the calculated turns of the secondary winding into the windows, and the output voltage turned out to be lower than desired. This will not decrease the operating current much. To a greater extent, a decrease in open circuit voltage affects the arc ignition process. The arc ignites easily at voltages close to 50V and higher. Although the arc can be ignited without any problems at lower voltages. So if the manufactured transformer has an output of about 40V, then it can be used for work. It's another matter if you come across electrodes designed for high voltages - some brands of electrodes operate from 70-80V.
Toroidal transformer
Using rings from LATRs, you can also make a welding transformer using a different - toroidal scheme. For this you also need two rings, preferably from large LATRs. The rings are connected and insulated: one ring-magnetic core with a significant cross-sectional area is obtained.
The primary winding contains the same number of turns as in the previous circuit, but is wound along the length of the entire ring and, as a rule, lies in two layers. The problem of the lack of internal space in the magnetic circuit window of such a transformer circuit is even more acute than for the previous design. Therefore, you need to isolate here as much as possible thin layers and materials. Thick winding wires cannot be used here. Although in some installations LATRs are used especially large sizes, only on one ring of this can a toroidal welding transformer be made.
The advantageous difference between the toroidal circuit for a welding transformer is its higher efficiency. Each turn of the secondary winding will now have more than one volt of voltage, therefore, the “secondary” will have fewer turns, and the output power will be higher than in the previous circuit. However, the length of the turn is toroidal magnetic circuit there will be more, and it’s unlikely that you’ll be able to save on wires here. The disadvantages of this scheme include: the complexity of winding, the limited volume of the window, the inability to use large-section wire, and also the high heating intensity. If in the previous version all windings were located separately and at least partially had contact with air, now the primary winding is completely under the secondary, and their heating is mutually reinforcing.
It is difficult to use rigid wires for the secondary winding. It is easier to wind it with soft stranded or multi-core wire. If you select all the wires correctly and carefully lay them out, then the required number of turns of the secondary winding will fit into the space of the magnetic circuit window and the required voltage will be obtained at the transformer output.
Sometimes a toroidal welding transformer is made from several rings of LATRs in a different way, they are not placed on top of each other, but the iron strips of the tape are rewinded from one to another. To do this, first the inner turns of strips are selected from one ring to widen the window. The rings of other LATRs unravel completely into strips of tape, which are then wound as tightly as possible onto outside diameter first ring. After this, the assembled single magnetic circuit is wrapped very tightly with insulating tape. Thus, a ring-magnetic core with a larger volume is obtained internal space than all the previous ones. This one can accommodate a wire of significant cross-section. The required number of turns is calculated based on the cross-sectional area of the assembled ring.
The disadvantages of this design include the complexity of manufacturing the magnetic circuit. Moreover, no matter how hard you try, you still won’t be able to manually wind the iron strips around each other as tightly as before. As a result, the magnetic circuit turns out to be flimsy. When working in welding mode, the iron in it vibrates strongly, producing a powerful hum.
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I am sure that not a single craftsman or homely owner will refuse a compact and at the same time quite reliable, cheap and easy-to-manufacture “welder”. Especially if he finds out that this device is based on an easily upgradeable 9-ampere (familiar to almost everyone with school lessons physics) laboratory autotransformer LATR2 and a homemade thyristor mini-regulator with a rectifier bridge. They allow you not only to safely connect to a household AC lighting network with a voltage of 220 V, but also to change u on the electrode, and therefore select the desired value of welding current.
Operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which operates during its own half-period. opens the corresponding thyristor for a certain period of time. As a result, an adjustable 20-215 V appears on the primary winding of the welding T1. Transforming in the secondary winding, the required -u allows you to easily ignite the arc for welding on alternating (terminals X2, X3) or rectified (X4, X5) current.
Resistors R2 and RЗ bypass the control circuits of thyristors VS1 and VS2. Capacitors C1. C2 is reduced to permissible level radio interference accompanying an arc discharge. A new light bulb with a current-limiting resistor R1 is used as a light indicator HL1, signaling that the device is connected to the household power supply.
To connect the “welder” to the apartment electrical wiring, a regular X1 plug is used. But it is better to use a more powerful electrical connector, which is commonly called a “Euro plug-Euro socket”. And as a switch SB1, a “packet” VP25, designed for a current of 25 A and allowing you to open both wires at once, is suitable.
As practice shows, it makes no sense to install any kind of fuses (anti-overload circuit breakers) on the welding machine. Here you have to deal with such currents, if exceeded, the protection at the network input to the apartment will definitely work.
To manufacture the secondary winding, the casing-guard, current collector slider and mounting hardware are removed from the base LATR2. Then, reliable insulation (for example, made of varnished fabric) is applied to the existing 250 V winding (the 127 and 220 V taps remain unclaimed), on top of which a secondary (step-down) winding is placed. And this is 70 turns of an insulated copper or aluminum busbar with a diameter of 25 mm2. It is acceptable to make the secondary winding from several parallel wires with the same general cross-section.
It is more convenient to carry out winding together. While one, trying not to damage the insulation of adjacent turns, carefully pulls and lays the wire, the other holds the free end of the future winding, protecting it from twisting.
The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which there is a mounting plate made of 10-mm getinax or fiberglass with a packet switch SB1, a thyristor voltage regulator (with resistor R6), an HL1 light indicator for connecting the device to the network and output terminals for welding on AC (X2, X3) or direct (X4, X5) current.
In the absence of a basic LATR2, it can be replaced with a homemade “welder” with a magnetic core made of transformer steel (core cross-section 45-50 cm2). Its primary winding should contain 250 turns of PEV2 wire with a diameter of 1.5 mm. The secondary one is no different from the one used in the modernized LATR2.
At the output of the low-voltage winding, a rectifier block with power diodes VD3 - VD10 is installed for DC welding. In addition to these valves, more powerful analogs are also quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).
Power diodes and thyristors are installed on heat sinks, the area of each of which is at least 25 cm2. The axis of the adjusting resistor R6 is brought out from the casing. A scale with divisions corresponding to specific values of direct and alternating voltage is placed under the handle. And next to it is a table of the dependence of the welding current on the voltage on the secondary winding of the transformer and on the diameter of the welding electrode (0.8-1.5 mm).
Welding transformer based on the widely used LATR2 (a), its connection to the principle electrical diagram a homemade adjustable welding machine for alternating or direct current (b) and a voltage diagram (c) explaining the operation of a resistor regulator of the electric arc combustion mode.
Of course, homemade electrodes made from carbon steel “wire rod” with a diameter of 0.5-1.2 mm are also acceptable. Blanks 250-350 mm long are coated liquid glass- a mixture of silicate glue and crushed chalk, leaving the 40 mm ends required for connection to the welding machine unprotected. The coating must be thoroughly dried, otherwise it will start to “shoot” during welding.
Although both alternating (terminals X2, X3) and direct (X4, X5) current can be used for welding, the second option, according to reviews from welders, is preferable to the first. Moreover, polarity plays a very important role. In particular, when applying “plus” to “ground” (the object being welded) and, accordingly, connecting the electrode to the terminal with the “minus” sign, the so-called direct polarity occurs. It is characterized by the release of more heat than with reverse polarity, when the electrode is connected to the positive terminal of the rectifier, and the “ground” to the negative. Reverse polarity is used when it is necessary to reduce heat generation, for example, when welding thin sheets of metal. Almost all the energy released by the electric arc goes to the formation of a weld, and therefore the depth of penetration is 40-50 percent greater than with a current of the same magnitude, but of straight polarity.
And a few more very significant features. An increase in the arc current at a constant welding speed leads to an increase in the depth of penetration. Moreover, if the work is carried out on alternating current, then the last of these parameters becomes 15-20 percent less than when using direct current of reverse polarity. The welding voltage has little effect on the penetration depth. But the width of the seam depends on uw: it increases with increasing voltage.
Hence an important conclusion for those involved in, say, welding work during body repairs passenger car from thin sheet steel: best results welding will give DC reverse polarity at a minimum (but sufficient for stable arcing) voltage.
The arc must be kept as short as possible, then the electrode is consumed evenly, and the depth of penetration of the metal being welded is maximum. The seam itself is clean and durable, practically free of slag inclusions. And you can protect yourself from rare splashes of the melt, which are difficult to remove after the product has cooled, by rubbing the heat-affected surface with chalk (the drops will roll off without sticking to the metal).
The arc is excited (after applying the corresponding Ucb to the electrode and the ground) in two ways. The essence of the first is to lightly touch the electrode to the parts being welded and then move it 2-4 mm to the side. The second method is reminiscent of striking a match on a box: sliding the electrode along the surface to be welded, it is immediately withdrawn a short distance. In any case, you need to catch the moment the arc occurs and only then, smoothly moving the electrode over the seam that forms immediately, maintain its quiet combustion.
Depending on the type and thickness of the metal being welded, one or another electrode is selected. If, for example, there is a standard assortment for a St3 sheet with a thickness of 1 mm, electrodes with a diameter of 0.8-1 mm are suitable (this is what the design in question is mainly designed for). For welding work on 2-mm rolled steel, it is advisable to have both a more powerful “welder” and a thicker electrode (2-3 mm).
For welding jewelry made of gold, silver, cupronickel, it is better to use a refractory electrode (for example, tungsten). You can also weld metals that are less resistant to oxidation using carbon dioxide protection.
In any case, the work can be done either with a vertically positioned electrode or tilted forward or backward. But experienced professionals claim: when welding with a forward angle (meaning an acute angle between the electrode and the finished seam), more complete penetration and a smaller width of the seam itself are ensured. Backward angle welding is recommended only for lap joints, especially when dealing with rolled profiles (angles, I-beams and channels).
An important thing is the welding cable. For the device in question, it’s impossible would be better suited stranded copper (total cross-section about 20 mm2) in rubber insulation. The required quantity is two one and a half meter sections, each of which should be equipped with a carefully crimped and soldered terminal lug for connection to the “welder”. For direct connection to ground, a powerful alligator clip is used, and with the electrode, a holder resembling a three-pronged fork is used. You can also use a car cigarette lighter.
The homemade welding machine from LATR 2 built on the basis of a nine-amp LATR 2 (laboratory adjustable autotransformer) and its design provides for adjustment of the welding current. The presence of a diode bridge in the design of the welding machine allows welding with direct current.
Current regulator circuit for a welding machine
The operating mode of the welding machine is regulated by variable resistor R5. Thyristors VS1 and VS2 each open in their own half-cycle alternately for a certain period of time thanks to a phase-shifting circuit built on elements R5, C1 and C2.
As a result, it becomes possible to change the input voltage on the primary winding of the transformer from 20 to 215 volts. As a result of the transformation, a reduced voltage appears on the secondary winding, allowing you to easily ignite the welding arc at terminals X1 and X2 during welding alternating current and at terminals X3 and X4 when welding with direct current.
The welding machine is connected to the electrical network using the usual plug. A paired 25A circuit breaker can be used as switch SA1.
Conversion of LATR 2 into a homemade welding machine
First, remove from the autotransformer protective cover, electrical removable contact and fastening. Next, good electrical insulation is wound onto the existing 250 volt winding, for example, fiberglass, on top of which 70 turns of the secondary winding are laid. For the secondary winding, it is advisable to choose a copper wire with a cross-sectional area of about 20 square meters. mm.
If there is no wire of a suitable cross-section, you can wind it from several wires with a total cross-sectional area of 20 sq. mm. The modified LATR2 is mounted in a suitable homemade housing with ventilation holes. There you also need to install a regulator board, a packet switch, as well as terminals for X1, X2 and X3, X4.
In the absence of LATR 2, the transformer can be made homemade by winding the primary and secondary windings on a transformer steel core. The core cross-section should be approximately 50 square meters. cm. The primary winding is wound with PEV2 wire with a diameter of 1.5 mm and contains 250 turns, the secondary winding is the same as that wound on LATR 2.
At the output of the secondary winding, a diode bridge consisting of powerful rectifier diodes is connected. Instead of the diodes indicated in the diagram, you can use D122-32-1 diodes or 4 VL200 diodes (electric locomotive). Diodes for cooling must be installed on homemade radiators with an area of at least 30 square meters. cm.
Another important point is the choice of cable for the welding machine. For this welder, it is necessary to use a copper stranded cable in rubber insulation with a cross-section of at least 20 sq. mm. You need two pieces of cable 2 meters long. Each must be tightly crimped with terminal lugs to connect to the welding machine.
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An excellent welding machine can be made based on laboratory autotransformer LATR and a homemade thyristor mini-regulator with a rectifier bridge. They make it possible not only to safely connect to a standard 220 V network, but also to change the voltage on the electrode, and therefore select the required amount of welding current.
Inside the housing there is a toroidal autotransformer (ATR), made on a large cross-section magnetic core. It is this magnetic core that will be needed from LATR for the manufacture of a new welding transformer (ST).
We will need two identical magnetic core rings from large LATRs. LATRs were produced in the USSR different types with a maximum current of 2 to 10 A. Welding transformers for its manufacture are suitable for those whose magnetic core dimensions will make it possible to place the required number of turns. The most common among them is the ATR type LATR 1M.
The magnetic core from LATR 1M has the following dimensions: outer diameter 127 mm; internal 70 mm; ring height 95 mm; cross section 27 cm2 and mass 6 kg. You can make an excellent welding transformer from two rings from this LATR.
In many ATRs, the magnetic core has a larger outer diameter of the ring, but a smaller height and diameter of the window. In this case, it must be increased to 70 mm. The magnetic circuit ring is made of pieces of iron tape wound on each other, welded at the edges.
In order to adjust the inner diameter of the window, it is necessary to disconnect the end of the tape from the inside and unwind required quantity. Don't try to do it all in one go.
The welding transformer begins the manufacturing operation, firstly it is necessary to insulate both rings. Paying attention to the corners of the edges of the rings, if they are sharp, they can easily damage the applied insulation and then short-circuit the winding wire. It is better to glue some elastic tape or cambric cut lengthwise to the corners. The top of the ring is wrapped with a small layer of insulation. Next, the insulated rings are fastened together.
The rings are tightly twisted with thick tape, and secured on the sides with pegs secured with electrical tape. Now the core for ST is ready.
Let's move on to the next point manufacturing a welding transformer, namely laying the primary winding.
Welding transformer windings - wound as shown in figure three - the primary winding is in the middle, both sections of the secondary are placed on the side arms. The primary winding requires about 70-80 meters of wire, which will have to be pulled with each turn through both windows of the magnetic circuit. In this case, I can recommend using the device shown in Figure 4. First, the wire is wound on it and in this form is easily pulled through the windows of the rings. The winding wire can be in pieces, ten meters long, but it is better to use a whole one.
IN in this case it is wound in parts, and the ends are fastened without twisting and soldered together, and then insulated. The diameter of the wire used in the primary winding is 1.6-2.2 mm. in the amount of 180-200 turns.
Let's start winding the ST. We attach the cambric to the end of the wire using electrical tape to the beginning of the first layer. The surface of the magnetic circuit is rounded, so the first layers will have fewer turns than each subsequent layer, to level the surface, see Figure 5. The wire must be laid turn to turn, in no case should the wire overlap the wire.
The layers of wire must be insulated from each other. To save space, the winding should be laid as compactly as possible. On a magnetic circuit made of small rings, the interlayer insulation must be used thinner, for example using regular tape. Do not rush to wind the primary winding once. It's easier to do this in 2-3 approaches.
Let us determine the number of turns of the secondary winding of the CT for the required voltage. First, let's connect the already wound primary winding to an alternating voltage of 220 volts. The no-load current of this version of the ST is low - only 70-150 mA, the hum of the ST should be quiet. Wind 10 turns of wire around one of the side arms and measure the output voltage on it with a voltmeter. Each of the side arms receives only half of the magnetic flux generated on the central arm, so here for each turn of the secondary winding there will be 0.6-0.7 V. Based on the result obtained, we calculate the required number of turns in the secondary winding, focusing on the voltage level at 50 volts, this is usually about 75 turns. The easiest way is to wind it with 10 mm2 stranded wire in synthetic insulation. You can assemble a secondary winding from several strands of copper wire. Half the turns should be wound on one arm, half on the other.
Having wound the windings on both arms of the CT, you need to check the voltage on each of them; a difference of 2-3 volts is allowed, but no more. Then the windings on the arms are connected in series, but so that they are not in antiphase, otherwise the output will be near zero.
At standard mains voltage, a welding transformer on a magnetic core made of LATR can produce a current in arc mode of up to 100-130 A; during a short circuit, the secondary circuit current reaches 180 A.
The arc starts very easily at XX voltage, about 50 V or higher, although the arc can be started at lower voltages without any problems. On rings from LATRs, you can also assemble ST in a toroidal pattern.
For this you will also need two rings, preferably from large LATRs. The rings are connected and insulated: one large ring-magnetic circuit is obtained. The primary winding contains the same number of turns as described above, but it is wound around the entire ring and usually in two layers. The layers need to be insulated with as thin materials as possible. Thick winding wires should not be used.
The advantage of the toroidal CT circuit is its high efficiency. For each turn of the secondary winding there is 1 V of voltage, therefore, the secondary winding will contain fewer turns, and the output power will be higher than in the previous case.
Obvious disadvantages include the problem with winding, the limited volume of the window and the inability to use large-diameter wire.
Using hard wires for secondary use is problematic. It is better to use soft stranded
The arc burning characteristic of the toroidal CT is an order of magnitude higher than that of the previous version.
Diagram of a welding machine based on ST on a magnetic core from Latrov |
Operating modes are set by potentiometers. Together with capacitors C2 and C3, it forms classic phase-shifting chains, each of which will operate in its own half-cycle and open its thyristor for a given period of time. As a result, an adjustable 20 - 215 V will appear on the primary winding of the CT. Transforming in the secondary winding, they easily ignite the arc for welding on alternating or rectified current to the desired voltage.
To make a welding transformer, you can use a stator from an asynchronous motor. The size of the core is determined in this case by the area cross section stator, which must be at least 20 cm 2.
Domestic color TVs used large, heavy network transformers, for example, TS-270, TS-310, ST-270. They have U-shaped magnetic cores, they are easy to disassemble by unscrewing just two nuts on the tightening pins, and the magnetic core breaks up into two halves. For older transformers TS-270, TS-310, the cross-section of the magnetic core has dimensions of 2x5 cm, S = 10 cm2, and for newer ones - TS-270, the cross-section of the magnetic core has S = 11.25 cm2 with dimensions of 2.5x4.5 cm. This means that the window width of old transformers is several millimeters larger. Older transformers are wound with copper wire; wire from their primary windings may be useful.
Welding transformer other possible types and design options |
In addition to special production, ST can be obtained by converting ready-made transformers for various purposes. Powerful transformers of a suitable type are used to create networks with a voltage of 36, 40 V, usually in places with increased fire hazard, humidity and for other needs. For these purposes they use different types transformers: different powers, connected to 220, 380 V according to a single or three-phase circuit.
