WELDER FROM LETRASure: from a compact and yet sufficiently reliable, cheap and simple to manufacture “svarochnik” no workman, Thrifty, the owner will not refuse. Especially if he knew that at the heart of this machine is easily upgradable 9-ampere (familiar to almost everyone from school physics lessons) laboratory autotransformer ЛАТР2 Yes homemade mineralwater with thyristor rectifier bridge. They allow not only to safely connect to domestic lighting AC voltage of 220 V. but to change u on the electrode, and means to select the desired value of welding current.

Modes of operation set with the potentiometer. Joint capacitors C2 and C3, it forms a phase-shifting chains, each of which actuating during a half period. opens the corresponding thyristor for a certain period of time. As a result, the primary winding of the welding T1 are adjustable 20-215 V. Transformed in the secondary winding, the required -u make it easy to strike the arc for welding on AC (terminals x2, X3) or straightened (X4, X5) current.
Resistors R2 and RZ shunt control circuit of the thyristors VS1 and VS2. The Capacitors C1. C2 reduce to an acceptable level of interference accompanying the arc discharge. In the role of a light detector НL1, signaling the start of the machine in household electricity used nonova light bulb with a current limiting resistor R1.
To connect “svarochnik” for residential wiring applies the usual plug X1. But it is better to use a more powerful electric connector, which is vulgarly called “Euro plug the Euro plug” . And as the switch SB1 is suitable for “batch file” ВП25 designed for the current 25 and allowing a break both wires at once.
As practice shows, set on the welding machine any fuses (Pro-Levoberezhnye machines) does not make sense. Here we have to deal with such currents, under exceeding of which will certainly work protection on input in apartment.
For the manufacture of the secondary winding with the base ЛАТР2 remove the cover-fencing, choosemy the slider and the fastening fittings. Then the winding 250 (taps 127 and 220 remain unclaimed) impose isolation (for example, of varnished cloth), over which is placed a secondary (lower) winding. And it is 70 turns of insulated copper or aluminium busbars with 25 mm2 diameter. Acceptable execution of the secondary winding of several parallel wires with the same total cross section.
The winding is more convenient than two. While single, taking care not to damage the insulation of neighboring turns, gently reaches out and places the wire, the other holds the free end of the next coil, preventing it from twisting.
Upgraded ЛАТР2 placed in a protective metal casing with vent holes, on which a circuit Board of 10 mm of Micarta or fiberglass with packet switch SV1, the thyristor voltage regulator (resistor R6), the operation indicator lamp HL1 incorporating the device into the network and output terminals for welding on AC (x2, X3) or permanent (X4, X5) current.
In the absence of basic ЛАТР2 you can substitute homemade “SVA-rocznika” with the magnetic core of transformer steel (cross-section of the core is 45-50 cm2). Its primary winding should contain 250 turns of wire ПЭВ2 with a diameter of 1.5 mm. the Secondary is no different from that used in the modernized ЛАТР2.
The output of the low-voltage winding set block rectifiers with power diodes VD3 – VD10 for welding on direct current. In addition to these valves is acceptable and more powerful counterparts, for example, D122-32-1 (rectified current up to 32 A).
Power diodes and thyristors mounted on heat sinks-heat sinks, each with an area not less than 25 cm2 . The outside of the housing of the output axis of the adjusting resistor R6. Under arm is placed a scale with divisions corresponding to specific values of DC and AC voltage. And next — a table of dependence of welding current on the voltage in the secondary winding of the transformer and the diameter of the welding electrode (0.8—1.5 mm).
Welding transformer on the basis of widespread ЛАТР2
Welding transformer on the basis of widespread ЛАТР2 (a) and its connection to the circuit diagram homemade adjustable welding on AC or DC (b) stress plot (b), explaining the operation of resistor control mode of burning of an electrical arc.
Of course, acceptable, and homemade electrodes made from carbon steel “rod” with a diameter of 0.5—1.2 mm. Workpiece length 250-350 mm is coated with a liquid glass silicate with a mixture of glue and powdered chalk, leaving unprotected the 40 mm ends needed to connect the welding machine. The plaster is thoroughly dry, otherwise when you weld it will “intermittently”.
Although welding can be used as an AC (terminals x2, X3) and continuous (X4, X5) current, the second option, for reviews of welders, preferably the first. Moreover, the polarity plays an important role. In particular, when submitting a “plus” to “weight” (the base object) and, therefore, the connection electrode to the terminal with the sign “minus” so-called straight polarity. It is characterized by the release of more heat than when you reverse polarity when the electrode is connected to the positive terminal of the rectifier and ground to negative. Reverse polarity is applied if necessary to reduce heat generation, for example, when welding thin sheets of metal. Almost all of the allocated spectrology energy goes to the formation of the weld, and therefore the depth of penetration by 40-50 percent more than when the current of the same magnitude but a polarity.
And a few very significant features. The increase in the arc current at a constant welding speed leads to increase the depth of penetration. And if the work is carried out on alternating current, the latter of these options become 15-20 percent less than when using DC reverse polarity. The same welding voltage has little effect on the penetration depth. But from the WIS depends on joint width: with increasing voltage it increases.
Hence an important conclusion for those involved in, say, welding in the repair of the car body of sheet steel: the best results will weld DC reverse polarity with a minimum (but sufficient for stable burning of arc) voltage.
The arc is necessary to maintain the shortest, the electrode is then spent evenly, and the depth of penetration of the weld metal, the maximum. The seam is clean and durable, virtually devoid of inclusions. And the few splashes of melt, difficult to remove after cooling the product, can be protected, rubbed with chalk the weld surface (the drops will slide, not sticking to the metal).
Excitation of the arc produced (after submitting the electrode and ground the appropriate Ucв) in two ways. The essence of the first light touch of the electrode to the welded parts and then discharge it to 2-4 mm to the side. The second method resembles cercana a match on the box: sliding electrode on the welding surface, it is immediately withdrawn for a short distance. In any case, you need to capture the moment of the arc and then, smoothly moving the electrode over the formed seam immediately to maintain her calm burning.
Depending on the type and thickness of the weld metal choose one or the other electrode. In the presence of, for example, a standard assortment for sheet St3 1 mm thick, with suitable electrodes with a diameter of 0,8—1 mm (it is basically a calculated and considered design). For welding on 2 mm steel rolled, it is desirable to have and “SVA-rocnik” more powerful, and the electrode is thicker (2-3 mm).
For welding jewelry made of gold, silver, Nickel silver is better to use a refractory electrode (e.g., tungsten). Can be welded and less oxidation-resistant metals, using protection with carbon dioxide.
In any case, the operation can be performed vertically positioned electrode and tilted forward or backward. But sophisticated professionals say: when welding a corner ahead (refers to the acute angle between the electrode and the finished seam) provided a more complete penetration and a smaller width of the weld. Welding corner back is recommended only to connect the lap especially when you have to deal with line rental (by area, I-beam and channel).
The important thing is welding cable. For the considered device is the best fit stranded copper (total cross section of about 20 mm2) in the rubber insulation. The required amount of two half meter cut, each of which should be equipped thoroughly compressed and soldered a terminal lug for connecting to the “svarochnik”. For direct connection to ground using a powerful clamp type “crocodile” and the electrode — holder, resembling drills the plug. You can use automotive “cigarette lighter”.
Care must be taken also about personal safety. When the electrode-traction weld to try to protect themselves from the sparks, and even more — from splashes of molten metal. It is advisable to wear canvas clothes casual, protective gloves and use a mask to protect eyes from the hard radiation of the electric arc (the sunglasses here).
Of course, we cannot forget about the “safety Regulations when performing work on electrical networks with voltage up to 1 kV”. Electricity is not forgiving of carelessness!
M. WIEWIOROWSKI, Moscow region

Recommend to read

    In the construction of models of domestic aircraft such as TB-1, TB-3 and other required shirred casing, which is coated frame model. To make this trim easy. For this is the "rolling...
    Juice — Jack" was the name of the material published in the "Modeller-designer", No. 4, 1998. I liked the simplicity and originality of the proposed technical solutions.   ...