Replacing the IGBT module in the welding machine. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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Today, inverter sources of welding current are widely used. Their advantages are known: direct current welding and its easy adjustment, high efficiency, low weight. There is probably only one drawback - the high cost.

Unfortunately, like any other electronic devices, welding sources sometimes fail. The most common reason is the "burning" of the powerful output transistors of the inverter. this is exactly what happened with the ETALON ZX7-180R inverter, which I bought already faulty, but very cheap.

An IGBT module was pierced in it (Fig. 1). This, according to the seller, is a typical malfunction of such devices, and the price of a new module reaches half the cost of the entire inverter, and there is no guarantee that the newly installed module will not be broken after some time.

Fig. 1

As a result of checking the device, it turned out that when the voltage in the network is below 190 V, the shape of the signals applied to the IGBT gates begins to be distorted. Therefore, a drawdown of the mains voltage can lead to incomplete opening of these transistors and, as a result, their overheating and breakdown. In addition, RC circuits (15 ohms, 0,015 uF) between the windings of the output transformer of the control unit and the IGBT gates strongly tighten the rise and fall of the control pulses. The result is the same - excessive heating of the IGBT module.

There is no blocking capacitor in the power circuit of this module, and without it, reactive currents created by the leakage inductance of the output transformer, the capacitance of its windings and mounting, circulate through the power circuits. This also worsens the thermal regime of the IGBT and the device as a whole.

It was decided to replace the module with several separate IGBTs, which cost several times cheaper than buying a new module, and at the same time try to eliminate the noted shortcomings. The refinement scheme is shown in fig. 2. Here T1 is the output transformer of the welding source control unit, T2 is the current transformer in the output circuit of the inverter, T3 is its powerful output transformer. Removed and replaced with jumpers, as shown in the diagram, RC circuits R24C12 and R25C13. Capacitors C2, C3 (conditional numbers) and C11 were already in the source.

Rice. 2 (click to enlarge)

The pin numbers of the new node (in the diagram, it is circled by a dash-dotted line) that replaces the IGBT module match the pin numbers of the latter. The node is assembled on a printed circuit board, shown in fig. 3. The IGBT VT3-VT6 leads are inserted into the holes of the corresponding pads of the board and soldered to them.

Fig. 3

The transistors themselves are located on the reverse side of the board. they are pressed to the heat sink with M3 screws, passed through the holes on the board with a diameter of 3,3 mm. Threaded holes must be made in the heat sink for these screws. they are drilled using the board itself as a template. Do not forget to grind the heat sink at the transistor installation sites, lubricate these places and the heat-removing surfaces of the transistors with KPT paste and insulate them with mica gaskets.

The conclusions of the protective diodes VD5 and VD6 are soldered according to the scheme to the printed conductors 1-3. On these conductors, through which a large current flows, it is necessary to solder segments of the shielded wire braid along the paths of its flow. The terminals of the capacitor C1 are also reinforced by wrapping them with a layer of tinned wire or by putting a braid on them and carefully soldering them.

Among other improvements, it should be noted the replacement of the power transformer of the control unit and the full-wave rectifier connected to it with a charger for a cell phone with an output voltage of 15. V at a current of 200.300 mA. In the open circuit of the common wire (pin 2) installed in the inverter of the integral stabilizer 7812, any diode should be included (with the anode to pin 2). This will increase the stabilized voltage (up to 12,7 V) and the amplitude of the pulses at the IGBT gates. After such an alteration, the welding source remains operational even when the mains voltage drops to 80 V.

When it is turned on for the first time after modification, it is advisable to apply a voltage of 310 V to the IGBT through a 220 V, 75 W incandescent lamp. By setting the welding current regulator to the maximum and gradually increasing the voltage supplied to the welding source from the mains from 80 to 250 V with the help of LATR, we make sure that it works. If there is no voltage at the output terminals, connect the same incandescent lamp to them. This should start the generator.

The lamp in the 310 V circuit should light up slightly.

Use the inverter operating frequency regulator (it is located on the control unit board closer to its edge) to achieve a minimum glow. Now, having removed the pumps and restoring the 310 V circuit, you can finally assemble the welding source and start working with it.

The maximum welding current should not exceed 180 A at a voltage of 24 ... 25 V, and the short circuit current - 190 ... 200 A. It is even better to make the maximum current smaller (about 170 A) with the regulator available in the source, which will increase the allowable duration continuous operation of the source under load. Perform this operation only when the source is switched off! Rotating the trimmer slider clockwise reduces the maximum current, and counterclockwise increases it.

Welding machines modified in this way (a total of seven pieces passed through my hands) can also work from a weak network (in my garage, for example, the voltage does not exceed 180 V), their thermal regime is facilitated and maintainability is ensured.

Author: Chesnokov S.

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