Toroidal Welding Transformer

Encyclopedia of radio electronics and electrical engineering / welding equipment

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The weight and size characteristics of toroidal transformers are much better than those of W- and U-shaped ones. With the same characteristics, the toroid is 1,3...1,5 times smaller. This is very handy when the welding machine now and then has to be dragged from place to place.

In the proposed design, the toroidal transformer is made from a used industrial welding transformer. To do this, it is disassembled, and a "donut" is assembled from plates measuring 90x450 mm. The required core area depends on the number of plates.

In principle, plates can also be used from old tube color TVs. The transformer TC270 or TCA310 is disassembled, the U-shaped cores are broken into plates with a hammer blow, which are straightened on the anvil. To make a "donut" it is necessary to rivet a hoop from plates with an outer diameter of 260 mm. The first plate is inserted inside the hoop, holding it with your hand so that it does not unwind, butt to it - the second, etc. until the inner diameter of the "donut" is 120 mm (Fig. 1).

Ris.1.

If the "donut" is made from TS270 transformers, then its diameter must be recalculated to obtain the required cross-sectional area.

It can be recommended to make two "donuts" and fold them in half, in this case the outer and inner diameters can be left unchanged.

The edges of the toroid are processed with a file. Two rings with an outer diameter of 270 and an inner diameter of 110 mm are made from electric cardboard, as well as a strip 90 mm wide. Cardboard blanks are applied to the "donut" and wrapped with fabric-based electrical tape. You can wrap it with tape from the kinescope degaussing loop.

The primary winding of the transformer is wound with PEV-2 wire d = 2,0 mm, the number of turns for a 220 V network is approximately 170. It largely depends on the assembly density of the plates. The exact number of turns can be determined experimentally. We connect in series with the primary winding of the transformer an alternating current ammeter for 10 ... 20 A and plug it into the network. If the no-load current is more than 1 ... 2 A, it is necessary to wind the turns, if less, you can unwind. The secondary winding is wound with a PVZ wire with a cross section of 15 ... 20 mm² and contains 30 turns. The third winding also contains 30 turns and is wound with 0,35 mm MGTF wire. Tape insulation is laid between the layers.

After testing the transformer, you can begin to manufacture the control circuit (Fig. 2). It is a phase current regulator. The alternating voltage from the winding III of the transformer is rectified by a bridge on diodes VD5 ... VD8. The positive half-wave of this voltage through the resistors R1, R2 charges the capacitor C1. When the voltage reaches about 6 V, a breakdown of the analog of the low-voltage dinistor occurs on the zener diode VD6 and the thyristor VS3, and the thyristor VS3 opens through the diode VD1, while the capacitor C1 is discharged. The same thing happens with a negative half-wave, only the VD4 diode and the VS2 thyristor open. Resistor R3 serves to limit the current through the analogue of the dinistor.

Fig.2. Control scheme

The adjustment of the device consists in setting the required welding current control zone with the resistor R1.

As SA1, you can use any machine for a trip current of 25 A. VD3 ... VD8 - diodes KD202V ... KD202M or any diodes designed for a current of more than 0,7 A and a voltage of 70 V are suitable. Instead of a thyristor KU101A, you can use KU201, KU202 . Resistors R1, R2 - for a power of at least 10 watts. Capacitor C1 - type K50-6. Diodes VD1, VD2 and thyristors VS1, VS2 - for current 160...250 A with any voltage group. They must be installed on radiators with an area of ​​at least 100 cm². Winding III of the transformer is designed for a voltage of 40 V. The secondary winding can be rewound if it is necessary to increase the welding current.

Author: S. Abramov, Orenburg, asmoren@mail.ru; Publication: radioradar.net

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