Voltage addition in the welding machine. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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Home-made small-sized welding machines with alternating welding current and power from a household power supply are easy to manufacture and inexpensive, but it is difficult to work with them - the arc stability is insufficient. You can improve the operation of the device if you transfer it to a constant welding current [1].

As practice shows, at a constant welding current, a voltage of 30 ... 40 V is quite enough to burn the arc. But it is still not easy to ignite it. For a low-power welding machine, this is the most difficult mode, since the secondary winding closes for a short time until the electrode is removed from the workpiece.

The process of ignition of the arc can be facilitated by increasing the open circuit voltage of the welding machine. However, the increase in this voltage is limited by the requirements of electrical safety - it should not exceed 80 V according to GOST95-77E [2]. In addition, as already mentioned, the optimum for arcing conditions is, on the contrary, in the zone of lower voltage values.

Therefore, I set myself the task of developing a welding machine, in which the open-circuit voltage is increased by a "voltage boost", and after ignition of the arc, it decreases to the optimal 30 ... 40 V. The circuit of such an apparatus is shown in fig. 1.

The welding transformer T1 with a diode rectifier VD1-VD4 is supplemented with another winding III, a rectifier VD5-VD8, a choke L1 and a switching diode VD9. Winding III is wound on a separate frame and is located next to the coil containing the network and main windings I and II, respectively.

The main secondary winding II is designed for a voltage of 30 ... 40 V and a current of 100 ... 120 A. It provides a working welding current in the arc. Additional secondary winding III is designed for a voltage of 12 ... 14 V at a current of 10 A. It generates a "voltage boost" voltage.

Until the electrode touches the parts to be welded, the voltage on it is equal to the sum of the rectified voltage values ​​of both windings, since the switching diode VD9 turns out to be the closed output voltage of the VD5-VD8 bridge, and both bridges are connected in series. The voltage at the electrode is 42...54 V.

When the electrode touches the workpiece, the VD9 diode opens, the voltage across it decreases to 1,5 V, providing the welding current through the ignited arc. Since the welding current does not flow through the VD5-VD8 diodes and the L1 choke, ten-ampere diodes are enough for this bridge, and the choke can be wound on any magnetic circuit with a cross section of 10 ... 12 cm2. The winding is carried out with a PEV-2 wire with a diameter of 1,6 ... 1,8 mm until the window is filled. When assembling the magnetic circuit, it is necessary to provide a non-magnetic gap between its parts by inserting a gasket made of pressboard with a thickness of 0,5 ... 1 mm.

Instead of KD242B, you can use diodes D305, D214, KD213A, KD213V, KD2999A-KD2999V. They must be installed on plate heat sinks 100x100x5 mm in size. Instead of VK2-200, diodes D161-250, D161-320 are suitable. These diodes are best mounted on factory-made heat sinks. The recommendations given in [2] can be useful here.

Structurally, the "voltage addition" device can also be made in the form of an attachment to a household welding machine, switched to direct welding current. The scheme of such a prefix is ​​shown in Fig. 2. The magnetic circuit of the transformer T1 and its mains winding are from the mains transformer TS-270, used in old tube color TVs. The secondary winding for 12 V at a current of up to 15 A must be wound independently. It is advisable to provide this winding with leads for 13, 14 and 15 V so that the attachment can be used for other purposes, in particular for charging batteries.

Switching diode VD5 is included in the set-top box. Choke L1 is the same as above.

If we slightly change the diagram in Fig. 2, you can reduce the number of required diodes, and hence the bulky heat sinks for them, as shown in Fig. 3.

The operation of this node is similar to that described above, the only difference is that the role of switching is performed by two diodes VD1, VD3 of the rectifier bridge of the device. They open alternately for half a period of mains voltage when the arc is not yet ignited, and closed when the arc is lit.

In conclusion, it should be noted that in the manufacture of a welding machine it is advisable to use the information presented in [2].

Literature

1. Klabukov A., Babintsev S. Refinement of the welding machine. - Radio, 2002, No. 4, p. 42.
2. Volodin V. Welding transformer: calculation and production. - Radio, 2002, No. 11, p. 35, 36; No. 12, p. 38, 39.

Author: L.Stepanov, Istra, Moscow Region

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