It is unlikely that anyone will be surprised at the presence of a welding transformer in the house. This device is actively used in everyday life, so every owner is simply obliged to have it. Electric welding, drill and grinder are essential elements of the standard "gentleman's" set of this master. If the last two points can be found only in specialized outlets, then the welding machine can be made independently, because it is not as difficult as it may seem.
A welding transformer is an apparatus that converts the AC mains voltage to AC voltage for welding.
Preparation of materials for work
There are several types of designs of welding machines that you can build yourself:
- AC or DC;
- impulse and many others.
The device of the welding transformer.
The most popular are transformer devices, so consider the simplest welding transformer that operates on alternating current. Such a device is enough for simple household work, and if necessary, it is possible to make an additional set-top box so that there is an opportunity to cook thin metal more accurately.
First of all, to make a home-made welding transformer, it is worth preparing a transformer iron for the core. It is desirable that it has a high level of magnetic permeability. You also need to get a thick wire, preferably copper. You can search for it with friends or in special locations that accept scrap metal. It is most convenient to make a transformer with a U-shaped core core, but this is not necessary, because the core can be round, toroidal, for example, from a littor or a stator with an electric motor.Back to table of contents
The method of manufacturing a transformer for welding
Consider a method of manufacturing a classic welding transformer with a core having a U-shape. It will be much easier to wind the winding on such a device, rather than on a toroidal one, because it is easier to disassemble it if you need to remove or put new coils.
In order to be able to use a transformer for domestic needs, it is necessary that it be able to “boil” the metal with the help of electrodes, whose diameter is 3-4 millimeters. All calculations must be made with these requirements in mind.
Top view of a welding transformer.
First of all, you need to dial the core. Moreover, its cross-section should be 25-35 square centimeters, although it is better if it is equal to 45 or 55 centimeters. It is no longer necessary, because the apparatus will turn out too heavy, but there will still be no effect from such weighting. If the area will be 45-55 square centimeters, then the transformer will receive the necessary power reserve, but will not overheat. To calculate the area of the transverse core, you need to use the following formula:
S = a * b, cm²
Then you need to choose a type of wire, calculating its cross section and the length of both windings. For the primary, it is desirable to use a specialized winding heat-resistant wire made of copper with cotton or glass cloth insulation, having a square cross-section.
Special attention should be paid to the primary winding, because it is very difficult to rewind (it is known that during the welding process it can heat up to 100 degrees or even more). That is why it is absolutely impossible to use wires with conventional PVC insulation. In the worst case, you can take the wires with rubber or rubber insulation. It is necessary that the device normally withstand medium welding, without overheating too much during the combustion of the seven electrodes.
The principle of operation of the welding transformer.
If there is no wire with the necessary insulation, however there is a wire with the desired cross section, then you can make the insulation yourself, removing the unnecessary one. To do this, you must prepare a few strips of cotton cloth or fiberglass width of 2 centimeters, and then wrap the wire with them. Then it is necessary to soak everything with the help of electrotechnical varnish.
In order for the welding transformer to “cook” well, it is necessary to ensure the correct level of output voltage without load (when idling). It should be 60-65V. During the welding process, the voltage should be 18-24V, depending on the diameter of the electrode.Back to table of contents
Features of the calculations
Making home-made welding transformers, you need to calculate the cross-sectional area of the wire of the secondary and primary windings. In this case, it is necessary to take into account the maximum power that the transformer will have. It turns out that during welding with an electrode whose diameter is 4 millimeters, and the current Is = 130-160 A. This can be subtracted using the formula P2 = Ic * Uc, therefore, the power of the secondary winding is P2 = 160 * 24 = 3.5.4 kw. Given all the losses, it turns out that the primary winding consumes about 5 kW, so the current can reach 25 A.
Calculation of the cross-sectional area of the wire of the secondary and primary windings.
It is necessary that the current density reaches no more than 5 A / mm², therefore the cross-sectional area of the primary winding wire is 25/5 = 5 mm². Of course, it is better to take with a small margin - 6-7 mm². In the secondary, the cross-sectional area should be about 30 mm², not taking into account the insulation.
It is necessary to determine the number of turns, as well as the length of the wire. In the primary winding should be less voltage than in the entire network - 210V. It will decrease under load. First you need to determine the number of turns for 1 volt, using the formula:
n = 48 / Sm
Sm is the cross-sectional area of the core in square centimeters. It should be within 55 cm².
If the magnetic circuit is good enough, then n will be 0.9-1.
Then it is necessary to determine the number of turns W1 = U1 / n, divide 210 / 0.9 and as a result you will get 200-300 turns depending on the cross section of the magnetic cores. The secondary winding must be calculated by a similar principle: W2 = U2 / n. The length of the wire for the secondary and primary windings is measured in this way: you must first measure the length of the coil on the coil frame, and then multiply by the number of turns, leaving a small margin.Back to table of contents
Coil winding procedure
Winding scheme of the welding transformer: 1 - primary, 2 - secondary.
Having finished with all the calculations, you must begin to wind the coils. It is necessary to make the frame of the coil according to the size of the magnetic core, so that it can be easily put on the core made of PCB or electrical cardboard. First you need to wind 50% of the primary winding, and then 50% of the secondary. The next coil is wound with a similar principle. It is desirable to lay electrotechnical cardboard, fiberglass, paper or special cardboard strips between the layers, this is necessary in order to provide better insulation.
Before starting to wind the coil, it is recommended to insert a pair of wedges of wood, which will have the shape of a core. Such a coil will not be cut, in addition, it will be easier to put on the magnetic core.
Doing a transformer with your own hands must take into account that all calculations are approximate. To get more accurate numbers, you need to take into account a huge number of different things. In practice, it turns out that most of the calculations differ from these figures. That is why homemade transformers always have to adjust after their assembly.
Welding transformer for arc welding.
It is necessary to turn on the device, and then measure the voltage that is on the secondary winding. It is necessary that it be within 65V. Then it is necessary to wind or wind the winding to achieve such a value.
What about the primary winding, it is necessary to provide several branches for different voltage networks. This is useful if you have to use the transformer in different places. Practice shows that the mains voltage can vary greatly, starting with 210V (this is often observed in villages) and ending with 240V.
If the calculations are wrong, for example, the magnetic permeability is incorrectly determined, then you just need to rewind the winding or switch to more turns. It is easy to fix, because the transformer is not in-store, you need to follow the counter disk, because in this case it will spin much faster than from a 2-kilowatt apparatus. Therefore, while the transformers will not be configured, do not bite off the extra winding.
Back to table of contents
If there is no necessary wire cross-section, you can simply wind two wires in parallel on the coil (for an aluminum wire, you need to increase the cross-section by one and a half times).
Features of work with the device
All materials from which make welding transformers, you can buy in a regular store. If a person is at least a little familiar with the features of electrical engineering, he can easily make such a device.
To avoid burns when making a transformer, it is necessary to use a fiber protective shield with an E-2 or E-2 light filter. Also considered to be mandatory clothing, gloves and a hat. Welding transformers should be stored away from moisture, preventing them from overheating. The device must be periodically turned off from the network for a few minutes.
We must not forget that such transformers are suitable only for the execution of small amounts of work. That is why, using up to 15 electrodes, whose diameter is about 3 millimeters, it is necessary to allow it to cool slightly.
Accordingly, if the diameter of the electrodes is 4 millimeters, then the time for continuous operation of the device should be further reduced. But having put 2-millimeter electrodes into a transformer, you can work with it for a long time without mandatory breaks, because the heating temperature of the device will not exceed 70 degrees.
A simple transformer will most quickly heat up in cutting mode, so you need to give it more rest. The device can be used for cutting virtually any metal used in everyday life. It is necessary to turn off the power switch, switching to another welding mode.