First, the principle of ring transformer
There are many ways to fix the toroidal transformer, and the most common method is to use the central hole of the toroidal transformer to fix it. It should be noted that the top and bottom plates of the transformer cannot be grounded at the same time by fixing pieces such as screws, so as not to form a short circuit ring.
The principle of transformer is transformation? The principle of diagram, when a positive? String communication? Voltage U 1? To the primary level? When the coil is at both ends, there is an alternating current I 1 in the conductor and an alternating magnetic flux Ф1is generated, and the magnetic flux runs along the iron core. A closed magnetic circuit is formed by the primary coil and the secondary coil. In the secondary coil? Inductive mutual inductance potential U2, and Ф1? Will it be induced on the primary coil? What should be the square of self-induced potentials E 1 and E 1? The direction is opposite to the applied voltage U 1 and the amplitude is similar, thus limiting the size of I 1. In order to maintain the existence of magnetic flux Ф1,what is needed? Have a certain amount of electricity? It can be consumed, and the transformer itself has a certain loss. Although the secondary is not connected to the load at this time, there is still a certain current in the primary coil, which we call "no-load current".
If the secondary is connected to a load, the secondary coil will generate current I2, thus generating magnetic flux Ф 2. The direction of Ф 2 is opposite to Ф1,and they cancel each other out, reducing the total magnetic flux in the core, thus reducing the primary self-inductance voltage E 1, resulting in an increase in I 1. It can be seen that the primary current is closely related to the secondary load. When the secondary load current increases, I 1 increases, so does Ф1,and the increased part of Ф1just supplements the flux offset of Ф 2 to keep the total flux in the core unchanged. If the loss of transformer is not considered, it can be considered that the power consumed by the secondary load of an ideal transformer is also the electric power obtained by the primary from the power supply.
Second, the winding skills of ring transformer
1. Remove the old winding.
After cutting the insulating paper with scissors, the secondary winding of the transformer is exposed. The wire diameter of secondary winding is usually thick, and it is rarely burned out in actual maintenance. Because there are not many laps, you can take them down one by one and count them. Multiple secondary windings can be disassembled and counted in a similar way. The primary winding has small wire diameter and common burning loss. Because the number of turns in the primary winding is more than 1000 turns, and the insulating material is attached to the turns after melting, it is obviously troublesome to count the number of turns with the above method. The quick processing method is: use scissors to cut off the primary coil layer by layer along the center line of the circumference, then peel off the cut coil from the iron core and count it to get the total number of turns.
2. Insulated annular iron core.
The iron core of toroidal transformer is usually made of silicon steel sheet with high quality and high permeability. When the primary coil is burnt out, the insulating layer of the annular iron core impregnated with insulating paint will be damaged to varying degrees at the same time, so it should be dipped in paint before rewinding the coil. The method is: soak the annular iron core in insulating paint, take it out for a few minutes to dry, and then put it in an oven to dry. Then stick a layer of adhesive tape on the inner and outer circumferences, cut cellophane into strips about 2cm wide, wrap a layer on the iron core, and stick the joint with double-sided tape.
Step 3 make a thread shuttle
In order to facilitate manual operation, special winding edges must be made. I designed an I-shaped thread shuttle, as shown in Figure 2. It can be made of plastic sheet or stainless steel sheet, which can be about 8 times the circumference of a single turn, and its width is about 2cm smaller than the inner diameter of the annular core. This kind of wire core is not only convenient to thread, but also can reduce the number of threads. Obviously, the length of the enameled wire wound on the bobbin is 8×2= 16 times of the circumference of a single wire turn. If double-stranded winding is adopted, each winding of enameled wire on the bobbin can be wound on the annular iron core for 32 times. Taking Emperor AV-228 professional power amplifier as an example, the primary winding of its ring transformer is 1068T. Double parallel winding of 534T, winding of 534÷I6≈34 turns of enameled wire on the bobbin is enough.
4. Winding coil
First, wind the winding once, take high-quality and high-strength enamelled wire with a diameter similar to the original wire, and wind the double-stranded wire in parallel on the I-beam, and cut it after the number of turns meets the requirements. Stick the end of the double thread on the outer circumference of the annular core with double-sided tape, so that the thread shuttle can be wound in the inner hole of the annular core, as shown in Figure 3. After winding the first layer of coil, brush a layer of insulating paint (which is beneficial to the positioning and insulation of turns), wrap a layer with cellophane, and then wind the second layer of coil. After winding, the head and tail of the two coils are connected in series, and the other two ends are welded and insulated with soft leather wires. Before winding the secondary winding, a layer of interlayer insulating paper is added to the primary system, and the winding method is similar to that of the primary winding.
When all windings are wound, put the ring transformer into a constant temperature box and bake for a period of time to dry the insulating paint. Then wrap a thick layer of insulating paper on the outermost layer, and the toroidal transformer is completed.
There are many choices of ring transformers in the market, and it will be difficult for consumers who buy for the first time to choose the one that really suits them. Therefore, from the professional point of view, the above small series suggests that you can spend more time on the study of professional basic knowledge, because as long as the principle of the product is clear, you can draw a reliable product by analogy in the later stage, and you can also make accurate judgments and gain satisfactory results.