Welding - with electronics. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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Those who like to make everything with their own hands are invited to make a compact and reliable device for electric welding of products from structural steels with electrodes with a diameter of 2-5 mm. It is powered from a single-phase alternating current network with a voltage of 220 V, which is quite convenient both when working at home and "on the road". And the presence of a built-in electronic regulator also allows you to smoothly change the welding current from 20 A to 200 A, which, in turn, makes it possible to firmly connect parts of various thicknesses and with great quality.

Rice. 1. Schematic diagram of a welding transformer with electronic current control (click to enlarge)

As follows from the circuit diagram (see Fig. 1), this device is based on a kind of thyristor regulator, which has become widespread recently. It is understandable. After all, such a technical solution makes it possible to use here very affordable materials and details, which is important for repetition both in the "center" and in the conditions of the "outback".

The "welder" consists of the actual power transformer T1, control thyristors VS1 and VS2, included in the power winding circuit II, and an electronic control unit that generates control pulses. Additional winding III stabilizes the burning of the arc and improves the process of seam formation at the initial moment of welding. Well, as for the winding IV, it serves to power the electronic current control unit.

Transformer T1 is made on the basis of a stator core from an asynchronous AC motor with a power of 15 ... 18,5 or 22 kW. According to the methodology, which the magazine has already told its readers more than once (see, for example, Nos. 8'92, 11'95). We only recall that the electric motor is disassembled, and the stator, together with the windings, is removed from the housing. In case of difficulty, the latter can even be broken (of course, with the necessary precautions).

The former windings are cut down with a chisel. The residues are removed without damaging, however, the stator plates themselves. The magnetic core is then wrapped with several layers of fiberglass or keeper tape. Moreover, in the latter case, the insulating material is coated with epoxy glue. Or - with a simple oil varnish (for example, PF-231 brand).

The primary winding of the transformer is carried out with a wire of the PEV-2 (copper) or APSO (aluminum) brands with a diameter of 2,5 mm. It should contain 220 turns, which are wound evenly over the entire cross section of the magnetic circuit.

If there is no wire of the required diameter, then the winding can be done with two wires. It is only important that the total cross section here is 5 mm. For the convenience of winding, a shuttle is used, on which the required amount of wire is preliminarily placed.

The resulting winding I is insulated with 2-3 layers of fiberglass or keeper tape. Then it is useful to check everything for the presence of short-circuited turns. To do this, the winding is connected to a regular network with a voltage of 220 V and make sure that the current in the winding circuit is in the range of 0,3-0,5 A. If the measured value exceeds the specified value, then there is nothing left but to more accurately rewind all 220 turns .

The secondary winding II is already made with a wire with a cross section of 35 mm3. It has fewer turns, only 60. And as a wire, a copper or aluminum bus with reliable insulation is quite suitable here.

Next to winding II, winding III is placed on the magnetic circuit, which also contains 60 turns, but already wires of the PEV-2 brand with a diameter of 2,5 mm. But the winding IV has 40 turns of PEV-2 0,7 mm. Moreover, a withdrawal from the middle is provided.

All secondary windings are insulated as thoroughly as the primary.

After the final winding, the transformer should be tested again at no load. The methodology here is almost the same. The only difference is that at the previously indicated current value, the voltage on the windings II and III should be 220 V, on the winding IV - 40V.

The block of electronic current regulation is based on the scheme of a similar industrial device TC-200. Installation is carried out by printing or hinged method. But in any case, a reliable case is provided for this block.

The T2 transformer is wound on a Sh16 magnetic circuit with a set thickness of 16 mm. Winding I contains 140 turns of PEV-2 wire with a diameter of 0,5 mm. II has only 70 turns of PEV-2 0,1 mm, while III and IV have 90 turns of PEV-2 0,5 mm each.

Rice. 2. Homemade device assembly: 1 - transformer, 2 - radiator (2 pcs.), 3 - thyristor (2 pcs.), 4 - top plate, 5 - bar, 6 - carrying handle, 7 - adjustment block panel, 8 - R-12 potentiometer, 9 - M12 bolt with a nut (2 pcs., for fixing the welding cable), 10 - M12 coupling bolt with a nut and washers, 11 - bottom plate, 12 - power cable fastening bracket, 13 - power cable

Resistors R1 ... R9 - type MLT-0,5. As R10 and R11, MLT-2 is the best fit, and for R12 - SP2-6A. Capacitors C1 and C3 are more appropriate to use type K50-6. As for C2 and C4, K73 is preferable here. Thyristors VS1 and VS2 - TL-200 or the like. They are mounted on heat sinks with a total surface of 1000 mm3 each.

A block assembled from serviceable parts and without errors does not need to be adjusted. Well, if something suddenly goes wrong - check the installation. Pay attention to the correct connection of the windings of the transformer T2 and to the observance of the polarity indicated in the diagram.

The operation of the unit can be easily checked with an oscilloscope. To do this, outputs 4-5 and 6-7 are loaded with resistors with a resistance of 50 ohms and a power of 0,5 watts. By connecting the device first to one output, and then to another, make sure that by moving the slider of the resistor R12 the duty cycle of the pulses changes.

In the absence of an oscilloscope, the performance of the unit can also be checked using an AC voltmeter. Moreover, without connecting the winding III. When the unit is working properly with a change in the resistance of the resistor R12, the voltage at points 9-10 should change smoothly from 0 to 60 V.

A possible design of the "welder" is shown in the illustration. Transformer T1 is fixed, as can be clearly seen, on a round 400 mm base made of 10 mm textolite or 15 mm plywood. Moreover, two bars of hard wood with a section of 30x30 mm and a length of 350 mm should be placed under it for proper air circulation and improved cooling. The transformer is attached to the base using a M12 coupling bolt of the appropriate length and the same plate as the one below. Thyristors are placed on top of the radiators.

The handles for carrying the transformer are made of steel pipe with a diameter of 0,5''. Two textolite plates 5 mm thick are attached to them. One of them is used to install a current control unit, a potentiometer R12, as well as a welding cable connected to the M12 bolts. Two brackets are fixed on the second plate for winding the network cable after work is completed. Here you can also install a circuit breaker, designed for a current of at least 25 A.

However, the design of the welding unit may be different. For example, it is easy to place it in a "holistic" case (providing, accordingly, special ventilation holes or even a small-sized fan for blowing). However, as if the thermal regime did not deteriorate! Indeed, even in the design of a "freely blown" transformer, which is shown in the figure, it is necessary to provide a 10-minute break after each hour of operation.

Welding is carried out with E-5RA UONI-13/55-2,5 UD-1 electrodes. The diameter, as already mentioned, is from 2 to 5 mm. Insert the desired electrode into a reliable and convenient electrode holder, turn on the above devices - and off you go. Naturally, in compliance with safety regulations.

The welding technology can be found in the relevant manuals.

See other articles Section welding equipment.

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