Calculation of the welding transformer is performed using specific formulas. This is due to the fact that standard transformer diagrams, as well as calculation methods, cannot be used for welding tools. In the manufacture of welding must be repelled by what is available. The most important thing is iron. What is, is and usually put, the whole calculation is just for a particular magnetic circuit. Of course, it is not always good, so heat and vibrations occur. Well, if you have available iron, the parameters of which are very close to industrial. Then you can safely use the techniques for calculating typical devices. To make a welding machine, you need to know its basic parameters and device.
Scheme of the device of the welding transformer.
Transformer power for welding machine
Before starting the calculation, especially the fabrication, you need to find out for yourself what the welding current should be. Since in everyday life electrodes are most often used, the diameter of which is 3-4 mm, it is worth relying in the calculations on them. Three millimeters is enough for housework and housekeeping. Even body work in the car can be carried out without fear of poor-quality welds that can be done by welding. So, if you chose three, you need to choose a current of about 115 A. It is at this current that these electrodes work perfectly. If you decide to use a two, the current at the output of the device should be about 70 A, and for the four - twice as much.
The scheme of the transformer with the primary and secondary winding.
Note that the welding transformer power should not be very large. The current consumption is a maximum of 200 A. And even then, there will be excessive heating not only of the winding wires, but also of the power cables. Consequently, the load on the network increases, and the electrical fuses may not withstand. So, if you decide to use electrodes with a thickness of 3 mm, repel the current of no more than 130 A. In order to calculate the power of the welding transformer, you will need the product of the current in the secondary winding when the arc ignites, phase angle, voltage in rest mode divided by efficiency. In this case, it can be considered a constant value, it is equal to 0.7.Back to table of contents
The most important thing in cores is form. It can be pivotal (U-shaped) or armored type (W-shaped). If we compare them, it turns out that the efficiency is higher for the first type of welding equipment. Winding density can also be quite high. Of course, they are most often used for the manufacture of electric welding. A self-made metal welding machine can have windings of the following types:
- cylindrical (secondary winding is wound over the network);
- disk (both windings are located at some distance from each other).
Cylindrical windings: a - single-layer, b - double-layer, c - multi-layer of round wire, 1 - rounds of rectangular wire, 2 - split leveling rings, 3 - paper bakelite cylinder, 4 - end of the first layer of winding, 5 - vertical slats 6 - internal branch winding.
It is worth looking at each type of winding in more detail. As for the cylindrical winding, it has very hard current-voltage characteristics. But it will not be suitable for use in manual welding machines. You can get out of the situation by using chokes and rheostats in the design of the device. But they only complicate the whole scheme, which is impractical in most cases.
When using disk-type winding, the network is remote from a secondary one. Most of the magnetic flux arising in the device (or more precisely, it arises in the mains winding) cannot be connected (even inductively) with the secondary winding. This type of winding is best used in cases where there is a need for frequent adjustment of the welding current. The external characteristic of such devices is available in the required quantity. And the leakage inductance of the welding transformer directly depends on the location of the network winding relative to the secondary one. But it also depends on the type of magnetic circuit, even on whether there are metal objects near the welding machine. Calculate the exact inductance is not possible. When calculating apply approximate calculations.
The current required for welding operation is regulated by changing the gap between the primary and secondary windings. Of course, they should be made so that they can be easily moved along the magnetic circuit. That's only in the conditions of home production is quite difficult to do, but you can make a certain number of fixed values of the welding current. When using welding in the future, if you need to slightly reduce the current, you need to lay the cable in rings. Consider only that it will warm up from this.
Transformer windings separated on different shoulders: 1 - primary, 2 - secondary.
Welding machines that are equipped with U-shaped cores will have a very strong dispersion. And they have a network winding must be located on one shoulder, and the secondary - on the second. This is due to the fact that the distance from one winding to another is quite large. The main indicator of the welding transformer is the transformation ratio. It can be calculated by dividing the number of turns of the secondary winding by the number of turns of the primary. You will get the same value by dividing the output current or voltage by the corresponding input characteristic (current or voltage).Back to table of contents
Standard calculation of welding transformer
The following method is used exclusively for calculating conversion devices using magnetic cores of only U-shaped form. Both windings are wound on the same frame, located on different shoulders. It should be borne in mind that it is necessary to connect half of both windings in series with each other. For example, a converter is calculated for operation with 4 mm electrodes. This requires a current in the secondary winding of approximately 160 A. The output voltage should be 50 V. At the same time, the mains (supply) voltage should be taken 220 or 240 V. Let the duration of work be 20%.
For the calculation, it is necessary to enter a power parameter that takes into account the duration of work. This power will be equal to: Rdl = I2 x U2 x (PR / 100) 1/2 x 0.001.
For the parameters of the welding machine, which were taken as a starting point, the power value is equal to 3.58 kW. Now it is necessary to calculate the number of turns of the windings. For this: E = 0.55 + 0.095 × Pdl.
The location of the windings on the rods in the transformers: 1 - rod, 2 - HV winding, 3 - HV winding, 4,5- groups of coils.
In this formula, E is the electromotive force of a single turn. For the calculated device, this value will be equal to 0.89 Volts / turn. That is, it is possible to remove 0.89 V from each turn of the converter. Therefore, the ratio 220 / 0.89 is the number of turns of the primary winding. And the ratio of 50 / 0.89 is the number of turns of the secondary winding of the welding transformer.
In the primary winding there will be a current equal to the ratio of the product of the current of the secondary winding and the coefficient k = 1.1 to the transformation ratio. In the example, a current equal to 40 A is obtained. To determine the cross section of the welding transformer core, use the formula: S = U2 × 10,000 / (4.44 × f × N2 × Bm).
For the calculation in the example, the area will be 27 cm². In this case, f is assumed to be 50 Hertz, and Bm is the field induction (magnetic) in the core of the device. Its value is assumed to be 1.5 Tesla.
For a welding transformer that will work with electrodes 4 mm thick, the following characteristics have been obtained:
Types of magnetic cores: a - armor, b - rod.
- welding current - 160 A;
- core section area - 28.5 cm²;
- primary winding contains 250 turns.
But these characteristics are valid for the welding transformer. Only in the manufacture of its used scheme, which applied an increased value of magnetic scattering. To reproduce at home such a device is unlikely to succeed, therefore, it will be easier to manufacture a transformer with secondary winding directly on top of the network. Even if we take into account the condition that the use of chokes is inevitable, deterioration of characteristics, then the magnetic flux of such a simple device will be concentrated in a certain point and around it. And all the energy in it can be transmitted rationally.Back to table of contents
Simple calculation of transformer for welding
Standard methods for calculating transformers are unacceptable in most cases, as non-standard forms of iron are used, and a wire with an unknown cross section, calculated approximately. When calculating, such characteristics of a welding transformer as the sectional area of the magnetic circuit and the number of turns were obtained. It is worth noting that by doubling the cross-sectional area, the characteristics of the transformer itself will not deteriorate. You only have to change the number of turns of the primary winding in order to achieve the required power.
The larger the section of the magnetic circuit, the fewer turns will have to wind. Use this quality if you have trouble winding wire. To calculate the number of turns of the primary winding, you can use simple formulas:
Current dependencies in the primary winding of the transformer on the supply voltage, in the idling mode.
- N1 = 7440 × U1 / (S of × I2);
- N1 = 4960 × U1 / (S of × I2).
The first is used in the calculation of welding machines, in which both windings are located on the same shoulder. For separated windings, the second formula should be applied. In these formulas, Siz is the section of the magnetic circuit, measured before the calculations. Note that when you separate the windings on different shoulders, you will not receive a current of more than 140 A at the output of the welding machine. And for any type of device, it is also impossible to take into account the current value that is more than 200 A. And do not forget that you have many unknowns:
- grade of transformer iron;
- mains voltage and its change;
- resistance in power lines.
To exclude the possibility of the influence of such minor factors on the operation of the welding transformer, it is necessary to make a tap every 40 turns. You can change the operating mode of the transformer at any time by applying a supply voltage for fewer or more turns.Back to table of contents
The cross section of the magnetic circuit and the selection of turns of the transformer
Package of transformer iron (magnetic core).
Knowing the cross section of the magnetic circuit, you can find the number of turns of the windings of the welding transformer. The main thing that you have to decide is what exactly the section should be. Ideally, a value of 28 cm² was obtained. But it can not always be used in a welding transformer, if you look at the structural and economic components. You need to think carefully about how you will wind the wire. For one power, you can choose two schemes:
- 30 cm² and 250 turns;
- 60 cm² and 125 turns.
It is also possible to use an intermediate option. If the window is small, it is better to simply increase the cross-sectional area. But then the weight of the welding transformer will increase. Therefore, it can be freely moved only on a special trolley.
There are cases when you have to judge the useful power of a transformer for a welding machine, best by current, which is measured in the primary winding of the device in idle mode. And to be more precise, you have to talk more about the value of power during the formation of the arc, but only about adjusting the welding transformer to the highest power. Squeeze the maximum out of your design. And the main thing in the process of calculating the transformer is to prevent an insufficient number of turns of the primary winding. The following devices are required:
- LATR (linear autotransformer);
Even for transformers of the same type, current can be different. Therefore, it is impossible to judge about the power of electric welding. But dependence in the primary winding current can tell a lot. Some special properties of a welding transformer can be identified. To do this, it is necessary to apply voltage from the output of the LATR to the primary winding of the welding. Thanks to the linear autotransformer, you can change the voltage value from 0 to 240 V. A voltmeter is connected in parallel with the winding, and an ammeter is inserted into the break of one wire.
First, there is a linear increase in current, which takes a small value.
After the rate of increase becomes larger, the current increases rapidly and rapidly. With an insufficient number of turns in the primary, the current curve will tend to an infinite value until the threshold of 240 V. Therefore, you need to add a certain number of turns to the winding of the welding machine. And do not forget to take into account the fact that when you turn on the network without LATR, your device will consume at least a third more current from it. In this way, it is not easy to theoretically calculate the welding transformer, in practice, everything is much simpler.