Transformer is translated from Latin as “converter”, “converter”.
This is a static type electromagnetic device designed to convert alternating voltage or electric current. The basis of any transformer is a closed magnetic circuit, which is sometimes called a core. Windings are wound onto the core, of which there can be 2-3 or more, depending on the type of transformer. When an alternating voltage appears on the primary winding, a magnetic current is excited inside the core. It, in turn, causes an alternating current voltage with exactly the same frequency on the remaining windings. The windings differ from each other in the number of turns, which determines the coefficient of change in voltage. In other words, if the secondary winding has half as many turns, then an alternating voltage appears on it, two times less than on the primary winding. But the current power does not change. This makes it possible to work with high currents at relatively low voltage.
Types of transformers
Depending on the shape of the magnetic circuit, there are three types of transformers:
- Armored. It has a square shape with two side, one central and two transverse rods. In this case, only the central rod is effectively used. It is on this that the winding is put on. Therefore, the efficiency of this device is not very high. Forms two turns of magnetic field. This transformer is designed for heavy loads. This explains its very heavy weight.
- Rod. In some ways similar to the first type. The shape is half of an armored magnetic circuit. It consists of two lateral cores and two transverse ones. The magnetic field is single-turn, and, as a result, it has less power. The efficiency of such a transformer is 40%.
- Toroidal. It got its name due to its original shape. In mathematics there is such a thing as a toroidal surface. To put it simply, it is a voluminous circle or donut shape. Thanks to this shape of the magnetic core, toroidal transformers have the highest level of efficiency, approaching 100%. Therefore, such transformers are always smaller in size with the same power compared to other types. Due to the fact that the windings are evenly distributed over the entire area of the core, more efficient cooling of the turns occurs. Which, in turn, allows such devices to be loaded to the maximum without the risk of overheating.
Price overview
You can buy a toroidal transformer HBL-200 in any city in the Russian Federation and CIS countries. It is used for various audio equipment. Let's look at how much the converter costs.
Transformer is translated from Latin as “converter”, “converter”. This is a static type electromagnetic device designed to convert alternating voltage or electric current. The basis of any transformer is a closed magnetic circuit, which is sometimes called a core. Windings are wound onto the core, of which there can be 2-3 or more, depending on the type of transformer. When an alternating voltage appears on the primary winding, a magnetic current is excited inside the core. It, in turn, causes an alternating current voltage with exactly the same frequency on the remaining windings.
The windings differ from each other in the number of turns, which determines the coefficient of change in voltage. In other words, if the secondary winding has half as many turns, then an alternating voltage appears on it, two times less than on the primary winding. But the current power does not change. This makes it possible to work with high currents at relatively low voltage.
Plate materials
Transformer cores are made of either metal or ferrite. Ferrite, or ferromagnetic, is iron with a special crystal lattice structure. The use of ferrite increases the efficiency of the transformer. Therefore, most often the transformer core is made of ferrite. There are several ways to make a core:
- Made from stacked metal plates.
- Made from wound metal tape.
- In the form of a monolith cast from metal.
Any transformer can operate in both step-up and step-down modes. Therefore, all transformers are conditionally divided into two large groups. Boost: The output voltage is greater than the input. For example, it was 12 V, it became 220 V. Step-down: the output voltage is lower than the input. It was 220, but became 12 volts. But depending on which winding the primary voltage is supplied to, you can turn the step-down transformer into a step-up transformer, which will turn 10 A into 100 A.
DIY toroidal transformer
A toroidal transformer, or simply a torus, is most often made at home as the main part for a home welding machine and more. In fact, this is the most common type of transformer, first manufactured by Faraday in 1831.
Advantages and disadvantages of the torus
Thor has undoubted advantages compared to other types:
- Relatively small in size.
- Very strong output signal.
- The windings are short and, as a result, these devices are characterized by low resistance and very high efficiency.
- Thanks to their shape, they are easy to install and also easy to dismantle if necessary.
The simplest torus consists of two windings on its ring-shaped core. The primary winding is connected to the source of electric current, the secondary winding goes to the electricity consumer. By means of a magnetic circuit, the windings are combined and their induction is enhanced. When the power is turned on, an alternating magnetic flux appears in the primary winding. Connecting to the secondary winding, this flux generates electromagnetic force in it. The magnitude of this force depends on the number of wound turns. By changing the number of turns, you can convert any voltage.
Calculation of the power of a toroidal transformer
Making a welding toroidal transformer at home begins with calculating its power. The main parameter of the future torus is the current that will be supplied to the welding electrodes. Most often, electrodes with a diameter of 2–5 mm are sufficient for domestic needs. Accordingly, for such electrodes the current power should be in the range of 110–140 A.
The power of the future transformer is calculated using the following formula:
U - open circuit voltage
cos f - power factor equal to 0.8
n - efficiency equal to 0.7
Next, the calculated power value is compared with the cross-sectional area of the core using the appropriate table. For home welding transformers, this value is usually 20−70 kV. cm depending on the specific model.
After this, using the following table, the number of turns of the wire is selected in relation to the cross-sectional area of the core. The pattern is simple: the larger the cross-sectional area of the magnetic circuit, the fewer turns are wound on the coil. The direct number of turns is calculated using the following formula:
U is the current voltage on the primary winding.
I - secondary winding current, or welding current.
S is the cross-sectional area of the magnetic circuit.
The number of turns on the secondary winding is calculated using the following formula:
Toroidal core
Toroidal transformers have a rather complex core. It is best made from special transformer steel (an alloy of iron and silicon) in the form of a steel strip. The tape is pre-rolled into a dimensional roll. Such a roll, in fact, already has the shape of a torus.
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Where can I get a ready-made core? A good toroidal core can be found on an old laboratory autotransformer. In this case, it will be necessary to unwind the old windings and wind new ones onto a ready-made core. Rewinding a transformer with your own hands is no different from winding a new transformer.
Features of torus winding
The primary winding is made of copper wire in glass cloth or cotton insulation. Under no circumstances should rubber-insulated wires be used. For a current on the primary winding of 25 A, the wound wire must have a cross-section of 5-7 mm. On the secondary, it is necessary to use a wire of a much larger cross-section - 30-40 mm. This is necessary due to the fact that a much higher current will flow on the secondary winding - 120-150 A. In both cases, the wire insulation must be heat-resistant.
In order to properly rewind and assemble a homemade transformer, you need to understand some details of the process of its operation. It is necessary to correctly wind the wires. The primary winding is made using a wire of a smaller cross-section, and the number of turns themselves is much larger, this leads to the fact that the primary winding experiences very heavy loads and, as a result, can get very hot during operation. Therefore, the installation of the primary winding must be done especially carefully.
During the winding process, each wound layer must be insulated. To do this, use either a special varnished cloth or construction tape. The insulating material is pre-cut into strips 1-2 cm wide. The insulation is laid in such a way that the inner part of the winding is covered with a double layer, and the outer part, respectively, with one layer. After this, the entire insulating layer is coated with a thick layer of PVA glue. The glue in this case has a dual function. It strengthens the insulation, turning it into a single monolith, and also significantly reduces the humming sound of the transformer during operation.
How to do
Even young electricians can make a toroidal transformer. Winding and calculation are not complicated. We suggest considering how to properly wind a toroidal magnetic circuit for a semi-automatic machine:
- A special machine can be used to wind a transformer on a ferrite core. It will help significantly speed up work and reduce the likelihood of iron jumping off. It can be made as a clamp for wrapping wires;
- It should be noted that the latres that are needed for winding must be the same size. When winding, make sure that there are no gaps between the sheets. If your power transformer has small gaps in the magnetic circuit, then they can be filled with iron sheets from any other transformer, cut to a certain size;
Photo - calculation - After winding of the iron is completed, its terminals are secured by welding. This will prevent the winding from unwinding. Literally two or three weld points are enough;
- After this, the ends of the magnetic circuit are coated with epoxy glue. The edges are first slightly rounded;
- Insulation is wound over the side of the amplifier - it can even be a sheet of cardboard. It can be attached using masking tape. We repeat the action on all surfaces of the magnetic circuit;
- Now you need to wrap textile tape around the cardboard insulation. It is sold in special electrical stores. On top of this layer of insulation you can wrap an additional layer of masking tape;
- Now a wire of the selected cross-section is screwed onto the ring; a special program will help you calculate the size of the wires and the required characteristics. After finishing the winding, everything is covered with NC varnish, one terminal of the winding should remain free;
Photo - winding the winding - Then you need to make insulation from varnished fabric or textile tape, on top of which the second winding is wound. It is also varnished. All that remains is to screw on the last insulation and protect it. Continue actions until the required number of windings is obtained;
Photo - tape wrapping - The secondary winding is wound from a larger wire cross-section. If a network transformer is needed for arc welding, then it is necessary to add a certain number of turns at the end, in addition to the calculated winding ones.
