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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Repair and application of network transformers. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies The topic of repair today is not so much popular as it is necessary. Therefore, we continue to talk about how to restore a network transformer (CT) on our own or make the necessary copy of the CT for our needs. About measuring the value of the no-load current (Ixx) CT The widely used digital multimeters of the 830 and 890 series (M830, DT830, M890, DT 890, etc.) are quite suitable for most amateur radio tasks. But they also have their own specific disadvantages. More than a disadvantage is the absence in these meters of the current measurement range within 1 ... 2 A. Say, multimeters of the 890th series have two subranges - 0,2 and 20 A. One can only dream of measuring accuracy at a current of less than 1 A, because instead of, for example, 20 mA, the display will show 10 or 30. It would seem, what are the problems here, because the limit of 0,2 A is almost ideal for measuring the Ixx value of low-power MT? But it was not there. Connecting the primary winding of a fully functional CT to the mains through this milliammeter will cause the regular fuse (0,2 A) located inside the multimeter to blow. To replace the fuse, you have to unscrew the case every time, which is not convenient. The current surge through the primary winding exceeds 200 mA, and installing a fuse in the multimeter for a higher current threatens the device with a possible defect during overloads. In this case, it is easier to put a fixed resistor in series with the primary winding and measure the voltage drop across the primary winding in voltmeter mode. By the way, the 830th series of multimeters is not designed to measure the magnitude of alternating current, which is disappointing. These devices do not have a 20 V range for measuring alternating voltage, which in many cases does not even allow measuring the magnitude of the filament voltage, because the readings are approximate (approximately ± 10% of the true value). A surge of more than 0,2 A almost always occurs, unless, of course, the CT is a little more powerful (more than 10 W is enough to replace the fuse in the multimeter). If there is no LATR at the disposal (and after all, the prices for LATR are already astronomical, even in Kyiv!), To limit the current, use an incandescent network lamp. In the first approximation, the lamp power is approximately equal to the ST power. The power of a ST based on W-iron is approximately equal to the square of its cross section (2×2 cm - 4 W). Most likely, the power of the ST is greater than this value. You should not get carried away with an excess of turns of the 1st winding, and this is not always possible, because. there may not be enough free space for other windings. It will not be possible to "squeeze" the planned power out of the ST, especially when the power of the ST slightly exceeds the load power. The dependence of the no-load current on the mains voltage This question is very important, especially if the mains voltage often exceeds the nominal voltage. It is necessary to measure the no-load current for high voltages as well. the stock here is not an excess, but a necessity. From the parameters of the steel and the number of turns, Ixx varies for different STs, with a change in the value of the mains voltage, in different ways. In pleasant cases, Ixx grows smoothly with an increase in the mains voltage, and it may be that when the voltage increases from 200 V to 220 V, Ixx increases by 1,5 times. In general, it is best to have a network ammeter with one linear scale, several sub-ranges (for example, 0,1-1-10 A) and one low-resistance current sensor. The author of such an ammeter [1] has been using for many years in repair operations with various RES. The value of the current Iхх for ТСА-270А (in this particular case, the primary winding was not winded), measured by an ammeter [1] (as can be seen from the table), varies differently for the same difference ∆Uс.
It all depends on the value of Us, the number of turns (one winding or two windings connected in series), steel parameters and, of course, on the quality of the assembly of the ST magnetic circuit. The fact is that carelessly assembled ST magnetic circuits of types TS-180, TS-200, T-270, etc. are often found. Even (often) the halves of the magnetic circuits are cut inaccurately, and are connected at random. This is bad, because power losses will increase, the hum of the MT will increase, and Ixx will also increase. The halves of the magnetic circuit must be precisely located in their places, as if they were a single product. If one part protrudes above the second in any direction, then the losses increase. We must always remember that the most profitable operation to reduce the magnitude of the current Ixx is precisely in the careful (tight!) connection of the parts of the magnetic circuits. This is especially true for such "bugs" as TS-180, etc. Often, with careful assembly of the ST, its magnetic circuit, it is possible to achieve a decrease in Ixx. Small particles of paraffin, paint, paper or other materials can increase Ixx by tens of milliamps (we are talking about TC-180). The iron surface of the ST magnetic cores from the ends, i.e. at the joints of the halves, it should shine! Having laid one half of the iron on the other, they carefully look at the place of their connection using some kind of bright light source (a fluorescent lamp (LDS) is quite suitable if the iron is brought close to it). So, if the air gap is significant (a large gap between the parts of the iron), then no winding can achieve a small Ixx with a high efficiency of the ST. The author had cases when a single movement was enough to reduce the current Ixx TC type TC-180 or TC-200. The point is that sometimes it is enough to change (turn over) the position of one of the halves of the CT magnetic circuit in order to significantly reduce Ixx. Usually, the air gap between the halves of the ST iron is increased along the outer part of the magnetic circuit (already from the manufacturer). A person, of course, cuts (removes) iron where there are its protrusions. This can reduce Ixx by about 1,5-2 times. But this must be done very carefully, using a vise and a file (needle file) and not being zealous when clamping the iron. Do not forget that you are dealing with numerous plates that make up the magnetic circuit: excessive force contributes to the delamination of the CT core, even without machining with a file. The last operation requires special care and patience. Despite the apparent thoroughness in the work, the process does not take much time. When the surfaces of the ends of the iron are polished, an external examination (on the LDS) should confirm the absence of air gaps between them. Technical aspects of assembly and disassembly ST types TC-180 (200, 270) This question is very important. Even excessive buzz contributes to increased headaches, fatigue and worsening well-being. The author uses ST data everywhere. They are easy to disassemble, quickly restored and reliable in operation. Big Ixx and significant buzz are their disadvantages. Today, an old TV (with one such ST) can be purchased for 10 UAH. And in the bazaar, speculators demand at least 180-10 UAH for one copy of the TS-15. But even that kind of money is worth it (copper alone). If several similar CTs are turned on at the same time (a 42 V power supply for a soldering iron, a device for drilling printed circuit boards, laboratory PSUs, chargers, etc.), which are dishonestly assembled and manufactured, then there is a buzz at the workplace. That is why it is important to take care of a small value of Ixx, even if you do not need to take a lot of power from the ST. Specific losses due to the air gap in the ST gland are well described in [2] on p.17. Continuous (toroidal) magnetic cores have higher magnetic properties: magnetic induction, for example, is 20-30% higher in them than in split ones (such as TS-180, etc.). However, the implementation of windings on a continuous iron is much more complicated and expensive than on a split (traditional, especially for consumer goods). Despite technological difficulties, toroidal CTs are very popular among radio amateurs. The author will try to share his experience with readers on this issue. There is nothing complicated in the manufacture of such STs. A little patience and your work will be rewarded with the quiet operation of these beautiful STs. A ready-made toroidal transformer is quite expensive. Let's return to the TS-180. When testing ST, when it is required from LATR to obtain a voltage exceeding 250 V, you can use the circuit of Fig. 3 from [3]. An additional transformer with one secondary winding connected (via a toggle switch) to the LATR is used here. This achieves the ability to add voltage when needed, with Uc>250 V. When there are two identical CTs, and the mains voltage is increased, a series connection of CTs can be used. Those. the primary windings of both STs are connected in series and connected to a 220 V power supply. The secondary windings are also connected in series. Since there will be only half (110 V) of the mains voltage on each primary winding, the situation is similar on the secondary windings. In other words, two identical MTs can be used for reliable (rather, trouble-free) operation in those situations where there is a risk of prolonged excess of the mains voltage over 300 V or more. Two CTs connected in series are able to work for a long time at a voltage of 440 V! The disadvantage of such an inclusion of the ST is an increase in voltage drops on the secondary windings due to the non-optimal (in terms of efficiency) operation of each ST. You can avoid a fire situation in the "ancient" way: turn on a 220 V incandescent lamp in series with the primary winding of the ST. The power of such a lamp is selected depending on the specific situation. This method has been known for a long time, even from the old Radio magazines (60-70s), although some of the authors are trying to pass it off as their own invention. Incandescent lamps were included in the break in the primary winding of network ST transmitters in series with zener diodes, i.e. in the same way as many radio amateurs do now. The joint operation of the ST and incandescent lamps is checked under a real load of the ST, a change in the mains voltage within the required limits, because the lamps have their own characteristics and features. Consider the process associated with the manufacture and use of ST type TC-180-2 in a powerful PSU. So, TS-180-2, new, was not in use. Before disassembly, it had Ixx = 85 mA at Uc = 220 V. After disassembly with subsequent assembly, Ixx was reached no more than 90 mA (without standard standard fasteners). But this was achieved by a very thorough cleaning of the ends of the iron with a scalpel, and not only because of this. Inside the coil frames, it was necessary to remove the remnants of the adhesive with a scalpel and a file. The winding (on each coil) D1,5 mm had 6,8 V and 23 turns. This is 3,38 turns per volt. According to the method described above, a "reconnaissance" was made to estimate the additional number of turns of the primary winding in order to obtain an Ixx value of approximately 50 mA. After connecting one of the windings 78 (or 7'-8'), Ixx decreased to about 50 mA (even less). Each of the CT coils has one such winding. Those. now the network winding should have 890 turns (744 factory and 155 additional). Unwind all the secondary windings of the ST, not forgetting to count and write down the number of turns of the winding 7-8 or 7'-8'. In order not to waste time later on calculating the number of turns of the required secondary windings, measure the voltage on the existing standard windings, for example, 9 and 10 or 9 'and 10'. Before the series connection of the winding 7-8 with the primary winding, the voltage (Uxx) without load when the windings 9-10 and 9' and 10' were connected in series (so the results will be more accurate) was 13,6 V. With the winding 7-8 in the primary circuit, it became 11 V (5,5 V in each winding of the ST). Check for power, i.e. connect to the 11 V winding a load equal to 1,34 ohms. The voltage is reduced to 10 V, i.e. Uхх−Un=1 V. This is the "drawdown" of the voltage. In such tests, you need to pay attention to voltage drops at the LATR input and, if necessary, re-set (add) the mains voltage so that the value on the primary winding of the ST is not less than 220 V. The author made the resistor of the indicated value on his own, using a D64 mm blank made of electroporcelain. On this frame, 13 turns of nichrome wire with a diameter of more than 1,55 mm are wound (not measured exactly). Yes, and it's not that important. The main thing is to see how the ST will behave at the same time with the required power. The winding came out powerful, because. even with Rн<1 Ohm, the voltage did not decrease to less than 9,8 V. The wire with which this regular winding was made (9-10 and 9'-10') is not designed for such a current. According to the label, the In of these windings is only rated for a current of 4,7 A. About coils TS-180 The difference in the coils lies only in the fact that in the winding 11-12 the wire diameter is approximately 0,85 mm (In≤1,5 A), and in the second coil (11'12') - 0,3 A. On each coil of this The ST author wound (turn to turn) 62 turns of D1 mm wire. One winding (only 62 turns) reduces Ixx from 90 mA to 70 mA, and two windings - up to 50 mA (or less). Caution (rather accuracy) is needed in calculating the free space for the secondary windings. It is easy to count the required number of turns. It is easy to determine the number of turns per each (or specific) layer, the total number of layers and the thickness of the paper. The most unpleasant thing is the appearance of bulges when winding layer after layer, the coil takes on an increasingly convex shape. A layer of paper must be laid between the layers of enamel wire. When removing the secondary windings of the TC-180, there is more special paper than necessary, because many layers of wire are removed, the diameter of which is much smaller than in this case. In order for the coils to bulge less, before laying the wire on the coil, it is bent, i.e. give it a shape approximately opposite to that which it will have in the coil. This needs to be taken care of from the very beginning, ie. from the first layer. The compaction method also helps here. But it is forbidden to strike with metal directly on the wire: the enamel is damaged too easily. To suffer less, you should remember the position of the coils, as it was when the ST was assembled. Then sealing is required only on one side of the coil, i.e. there (inside the magnetic circuit), where both coils will touch ("look" at each other). In one layer, 35 turns of D1,8 mm wire are placed. When the coils are mounted on iron and the complete assembly of the TC-180 is used (with the help of all standard fasteners), the distance between the coils increases slightly (by about 2 mm), i.e. extra space appears. However, don't count on it too much. The windings should be arranged in such a way that the side walls of the coil frames are in contact when they are parallel next to each other. Without much difficulty, three layers of D180 mm wire are placed on each TC-2-1,8 coil. Those. it is possible to have 28 V from each coil separately. There is nothing to fantasize about the options for using such ST. Many amateurs are deprived of the opportunity to both purchase and manufacture such STs. Such STs have been successfully operated for many years in powerful UMZCH, BP, etc. On this ST, two windings (80 turns per coil) of PELSHO wire D0,41 mm (20,3 V) were also made. Now about a very important aspect - testing a specific instance of ST. Uxx (total, i.e. 11,2 V on each coil) was 22,4 V. At Rn = 1,34 Ohm (the above resistor) Un = 19,2 V. In other words, the current in the load is approximately 14 A ! 20 minutes passed, and the CT began to warm up strongly. This point is very important and is not covered at all in the literature. When testing, it is necessary to monitor the process of general heating of the ST. Particular attention should be paid to finding out which parts of the ST are heated first (after heating the entire ST, this will no longer be possible to find out). If the secondary winding is wound without a margin or, worse, with an insufficient copper cross section, then it heats up first and quite strongly. If the ST has a power reserve, and the heated winding is separated from the primary winding by many layers of other secondary windings, which, for example, do not heat up, then the general heating of the ST has little effect on the primary winding. If the heated part of the secondary winding is outside the frame, then there is no need to worry much. After all, not everyone has the opportunity to purchase a thicker enamel wire: it is now sold by speculators at super prices (up to 20 UAH per 1 kg, or even more). Copper is not gold, and demand is gradually being met by supply, as evidenced by a slight decrease in prices for enameled wire in Ukraine, which is encouraging. Along the way, we will also consider the not quite common use of used enameled wire, which is more accessible to all segments of the population. When TS-180 requires a total voltage of no more than 20...30 V at a current of no more than 1...3 A, then windings can be wound in increments exceeding the diameter of the enameled wire. In addition to increasing reliability (in terms of short-circuit turns), the cooling of the windings is also dramatically improved. The method has been tested many times. For example, at D1 mm, up to 3 A and even more were "pulled" out of the winding, which, with a dense standard winding, is considered a violation of the design characteristics for exceeding the maximum allowable current density (see [2], p. 24). When a current of 5 A or more is required, then winding in two or more wires can be used. At the same time, it becomes possible to use substandard wire as a second wire (even with broken insulation). Now the wire becomes a separating element between two adjacent turns. If a person is not oriented in such concepts as current density, then it can be explained differently. The more powerful the transformer, the larger the wire diameter should be. This is due to the fact that a powerful ST has a large enamel wire length. And a long wire already acts as a resistance, on which a lot of heat will be generated. As the temperature rises, the resistance of the winding wire increases. As for our TS-180-2, the reduction of the power consumed from it to 200 W makes it possible to drastically reduce the overheating of the entire ST. Now this ST can be operated for an arbitrarily long time, because. it is warm but not hot. If after a 20-minute warm-up of a powerful ST, only the secondary windings are heated, and the iron is only warm to the touch, then a lot more power can be taken from the ST. If iron also becomes a "stove", then this ST is at the limit of its operational capabilities. It is necessary to distinguish between the possibilities of the primary winding separately from the magnetic circuit. The manufacturer produces winding specifically for their RES. And if you believe the reference book, then iron is used in the TS-180, the limiting parameters of which are about 280 W [2]. Even more impressive are the capabilities of iron from ST type TC-270 - about 600 watts. In order to have a return of 180 W from the TS-200 or TS-250, you need to wind the primary winding with a wire with a diameter of 0,9 ... 1,1 mm. Regarding TS-270: the diameter should be even larger, namely 1,25 ... 1,4 mm. According to [3], at a frequency of 400 Hz, these cores have a "ceiling" of 1220 W and 2600 W. For ST type TS-270-1, the diameter of the primary winding wire is approximately 1 mm, which is why it is able to work for a long time at a power output of about 300 watts. For ST TS-180 or TS-200, it is much thinner, so the results are more modest. Regarding the assembly of the considered ST TC-180 is desirable to assemble "live", i.e. with ST running. When tightening the fastener nuts, you need to carefully monitor the magnitude of the current Ixx and the buzz of the CT. It is very important not to overdo it in the clamp, so as not to strip the thread (it just looks so strong). If the plates of the magnetic circuit are stratified, then it is convenient to use the now popular "superglue". Glue the halves of the magnetic core with this glue should not be for the simple reason that you need to think about the possible repair of the ST. In the mount, the use of two nuts instead of one regular one does not interfere. Many hobbyists are surprised when carefully crafted CTs suddenly start to overheat, for example,with parallel connection of windings. Windings made on different coils can only be connected when their voltages are very close in magnitude. And the digital multimeters used by amateurs lie a lot (for example, 22 V is already measured at the limit of 200 V). This is how it should be done here. The windings that are supposed to be connected in parallel are connected in series-opposite in order to see (measure) the voltage difference between them. A difference of a hundred or two millivolts for the TS-180 will not create overheating, but if it is more, then the difference must be eliminated. Even on the assembled ST, it is possible to wind a round or two of stranded wire of the required cross section without disassembly. In this way, full compensation of the voltage difference can be achieved. From here you can see the advantages of winding in two wires at the same time. There is also such a subtlety: parallel windings should not be located too far along the winding height from one another so that the active resistances of the windings do not differ. It does not hurt to increase the diameter of the wire over the upper winding. When working with transformers, preference should be given not to devices with high input resistance, but to conventional testers (Ts-20, AVO-5M, etc.) of the magnetoelectric system. These testers do not "fuss" in their readings (like digital testers), do not pick up hand pickups. This is especially felt when we are dealing with CTs filled with various compounds and containing many unknown windings. Network transformer type TC-180 A lot of good things can be said about this ST, especially in terms of manufacturability. Consider an example of connecting a 42 V, 65 W soldering iron. In series with the standard primary winding, we turn on the winding 7-8 or 7'-8'. At the same time, 5 V is obtained on winding 6-50, the excess is extinguished by a resistor. At the same time, no disassembly and rewinding of ST. With a series connection of powerful filament windings 9-10 and 9'-10', we get a total of 13,82 V and the current can be removed up to 10 A. You can build a charger for a car battery, connect a 12 V soldering iron, create a powerful (up to several amperes in load) adjustable power supply. Network transformers of types TS-200, TS-250, TS-270 Disassembly of the ST type TS-200, TS-250 and comparison with ST type TS-180 showed that the iron in them has the same size PL20Ch45Ch87, which is clearly more powerful than PL20Ch40Ch80 (280 W). But due to the thin wire of the primary winding, it will not be possible to take more than 180 W from the TS-200. Therefore, if necessary, the primary winding can be rewound with a wire with a diameter of 0,85 ... 1,0 mm. The magnetic circuit in the TS-270 is larger than PL25Ch45Ch105, which allows you to shoot up to 400 watts. But for this, again, you need to rewind the primary winding with a wire with a diameter of at least 1,25 mm. With a cross section of the magnetic circuit in TS-180, TS-200, TS-250 9 cm2, the number of turns per volt according to the standard formula 50/S = 5,55 vit./V. But it turns out that the factory version of the TC-180 has only 3,38 vit./V. Similarly, for the TC-270, with a cross section of 11,25 cm2, it should be 4,4 vit./V, but in fact 2,53 vit./V. TS-200-2 is good because it has a primary winding of 237 V, i.e. has stock for our needs. When connecting the windings 1-2-3 and 1'-2'-3' in series, we have an open circuit current of only 72 mA. With this inclusion, there are voltages on the remaining windings: 5-6 and 5'-6' 111 V each; 7-8 - 17,52 V; 7'-8' - 6,03 V; 9-10 - 6,02 V; 9'-10' - 6,03 V; 11-12 - 6,05 V. After removing all the windings, except for the primary one, a winding with a voltage of 1,1 V was wound with a 26 mm wire. At a load of 4 ohms, the voltage decreased to 22 V. The windings are heated, but the hand can be held. TS-250-2M. The primary winding is wound with approximately the same wire as in the TC-200. The turn / volt ratio in it is not bad at 3,33 vit. / V. Voltages on the windings: 4-4' - 18 V (on each of the coils 9 V); 5-5' - 170 V; 6-6' - 6,4 V; 8-8' - 10 V; 9-9 '- 27 V. Winding on both coils of windings of 25 V with a wire D1 mm and their parallel connection gave a drawdown of up to 5 V at a load of 22,5 ohms. The above types of ST have been in operation for many years with the above modifications. References:
Author: A.G. Zyzyuk
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