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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Welding - without schemes and formulas. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / welding equipment I have been doing homemade welding machines for more than a year. I started with "Welding Baby", using LATR with a ready-made primary winding. For the secondary one, I did not find the recommended bus duct. I ventured to wind the required number of turns with a flexible stranded wire with a cross section of 6 mm2 in vinyl insulation. And what? Of course, such a device quickly overheated even when welding with a three-millimeter electrode. In order to somehow solve the problem associated with cooling, I decided to lower the "welder" ... into the water. I proceeded from the fact that the secondary winding has excellent insulation. Yes, and the primary one, on which the runner used to walk, was also not bare, since it was possible to cover it in several layers with a protective varnish in advance. The apparatus was lowered into a polyethylene bucket filled with water with a capacity of 20 l (metal is more dangerous) and gave 140 A at the outlet during welding. , bay once again with cold water and "cut" into the network, continue welding. The following devices I had were "dry" - made on the basis of a stator from an electric motor. I was convinced that it is best to use the appropriate magnetic circuit from an asynchronous three-phase machine with a power of 4-5 kW. It is easiest to release such a stator from the housing shell with a sledgehammer or a heavy hammer, hitting the weakest points. Next, the winding is removed. And - in two steps. First, they remove it from one side, using a hacksaw for metal. Although it is quite possible to use a hammer with a chisel for the same purpose, directing the impact force tangentially to the stator diameter. Well, then, having already entered from the opposite side, they begin to pull out segments of "half-disarranged" wires from the grooves with pliers. The magnetic core released from the winding will become the toroidal core of the welding transformer. As practice shows, when choosing an "iron package" for it, one should strive to ensure that the size "a" of the stator-blank would be within 30 ... 40 mm. Then, in order to obtain an optimal cross section of 20...25 cm2, we will have to divide our original torus into 2-3 parts so that the size "c" is equal to 50...80 mm. It is better to do this with a hacksaw, cutting through the outer cast ties in the grooves (usually there are 8 of them). Then, having removed the "spoiled" 3...4 sheets of "stator iron", the ties are riveted, thereby fastening each of the future toroidal cores. But arc cutting-welding should not be carried away here, since the Foucault eddy currents arising in these places lead to heating of the magnetic circuit and significantly reduce the efficiency of the transformer. The internal teeth - the stator poles - are selected with a cross-cut chisel with a special sharpening (see Fig.). Naturally, one should not neglect the safety rules. Be sure to use goggles and gloves. The chisel is best held with pliers, not hands.
In no case should you cut the teeth with electric or gas welding. After all, Foucault currents will again arise in the magnetic circuit during the operation of the transformer. Therefore, it is best to use the "old-fashioned method" here with a chisel and a hammer weighing 1 kg. And it is advisable to remove the irregularities remaining after cutting out the teeth by grinding with an abrasive wheel. The finished magnetic conductor is wrapped with a keeper or other fabric-based insulating tape. Now it's up to the primary winding. The number of turns in it with an accuracy acceptable for practice can be found by multiplying the value of the voltage in the network by the quotient of dividing "40" by the cross-sectional area (in cm2) of the transformer core. In our case, this coefficient characterizing the calculated number of turns per 1 V is equal to two. Thus, for the network (primary) winding of the "welder" I propose, only 440 turns are required. And it is best to use here a copper wire with a cross section of 2 ... 3 mm2 (diameter 1,6 ... 2 mm) in fiberglass insulation. The layers of the primary winding are carefully isolated from each other. As, however, the layers of the secondary, the number of turns in which, based on the required voltage (56 V) and the above coefficient (2), should be equal to 112, and the cross section should be 10 ... 30 mm2. Winding wires can be taken from old electric motors with a phase rotor with a power of 3 ... 6 kW. For example, I used a wire with fiberglass insulation from them (section - 3 mm2) for the primary winding. By the way, from the same electric motors, you can also borrow a busbar with a cross section of 18 mm2 for the secondary winding of a welding transformer. Moreover, all this is made of the purest copper. Naturally, for winding the "welder" you can be content with aluminum. But then the size of the section of each of the windings increases by 1,65 times. For example, for the primary, a wire of at least 3,3 ... 5 mm2 is required. With this in mind, in one of the options for welding transformers, I was forced to use a two-core aluminum wire - "noodles" with a cross section of 2x2,5 mm2 (the diameter of one core is almost 1,9 mm). How much wire should be taken for a particular winding? Determining this, as they say, is easy. Having measured the wire consumption per 1 turn of the winding (see Fig.), This value must be multiplied by the estimated number of turns of the winding. But take (taking into account the thickness of the insulation, etc.) with a three percent margin (for the primary) or six percent (for the secondary winding). In my "welders" I provide 5 steps of adjustment (up to a maximum of 56 V), making taps in the secondary winding, designed for voltages of 32 V, 38 V, 44 V and 50 V. When switching to turns, these will, respectively, be 64, 76 , 88 and 100. I prefer to make taps by winding pieces of flexible wire with a cross section of at least 10 mm2. The easiest way to find the exact places of the conclusions in the secondary winding is experimentally, by the "trial and error" method. Especially if its winding is "loose", and even carried out with a flexible wire. Then they boldly turn on the transformer in the network and conditionally, taking the first output of the secondary winding as "common", they pierce the insulation with a probe-needle in one place or another. And having thus found voltages of 32 V, 38 V, 44 V, 50 V, they mark them. If the secondary winding is wound with a busbar, then you will have to limit yourself to the "calculated" method. That is, to determine in advance on which turn this or that tap will be performed, multiplying the above coefficient (2) by the required number of volts. The finished transformer is given a convenient and reliable form from the point of view of users. To do this, cut out two squares of 10 mm plywood. And even better - from fiberglass or other heat-resistant insulator. In the middle, a 30-mm circle is drilled for ventilation (see Fig.), And symmetrically to it and in the corners - seven 8-mm holes for the passage of tie-rods and a network wire. The body is essentially ready. Well, the rest, I think, is clear from the illustrations that are given here. I am convinced that anyone can make a solid welding transformer according to the above method. In the proposed welding in the secondary winding, conclusions are made in increments of 6 V. Using the principle of an autotransformer, you can have a whole range of voltages at the output: from 6 to 56 V. In particular, using 56 V and 50 V conclusions, it is easy to obtain a difference voltage 6 V. The 44 V and 56 V outputs allow you to have 12 V at the output. By connecting, for example, a 200 A rectifier to such a transformer, you can safely start the engine starter. Yes, the "welder" really gives out up to 200 A in the secondary winding. And this means that you can already use electrodes with a diameter of 2 ... 5 mm! Being made according to the proposed technology, the welding transformer has small dimensions (within 350x350x200 mm) and a truly minimal weight (up to 25 kg). Author: O.Lavrov
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