Convert an AC welder to a DC one. We make a semi-automatic welding machine from an inverter. Electronic control module

Inverters are widely used by home and garage craftsmen. However, welding with such a machine requires certain skills from the operator. The ability to “hold the arc” is required.

In addition, arc resistance is not a constant value, so the quality of the weld directly depends on the qualifications of the welder.

All these problems fade into the background if you work with a semi-automatic welding machine.

Design features and operating principle of the semi-automatic device

A distinctive feature of this welder is that instead of replaceable electrodes, wire is continuously fed into the welding zone.

She provides constant contact and has lower resistance compared to arc welding.

Due to this, a zone of molten metal is instantly formed at the point of contact with the workpiece. The liquid mass glues the surfaces together, forming a high-quality and durable seam.

Using a semi-automatic machine, any metals can be easily welded, including non-ferrous and stainless steel. You can master welding techniques on your own; there is no need to enroll in courses. The device is very easy to operate, even for a novice welder.

In addition to the electrical part - a high-power current source, the semi-automatic device has a continuous feeding mechanism in its design welding wire and a burner equipped with a nozzle for creating a gaseous environment.

They work with ordinary copper-plated wire in a protective inert gas environment (usually carbon dioxide). To do this, the cylinder with a reducer is connected to a special inlet fitting on the body of the semi-automatic device.

In addition, semi-automatic welding can be done in a self-protective environment, which is created using a special coating on the welding wire. In this case, no inert gas is used.

It is the ease of operation and versatility of the semi-automatic machine that makes the unit so popular among amateur welders.

Many kits feature a two-in-one function - and a semi-automatic device in a common body. An additional outlet is made from the inverter - a terminal for connecting the holder of replaceable electrodes.


The only serious drawback is that a high-quality semi-automatic machine costs significantly more. simple inverter. With similar characteristics, the cost differs by 3-4 times.

A semi-automatic welding machine is a functional device that can be purchased ready-made or made from. It should be noted that making a semi-automatic device from an inverter device is not an easy task, but it can be solved if desired. Those who set such a goal should thoroughly study the principle of operation of a semi-automatic device, look at thematic photos and videos, and prepare everything necessary equipment and components.

What is needed to convert an inverter into a semi-automatic machine?

To convert an inverter into a functional semi-automatic welding machine, you must find the following equipment and additional components:

• inverter device capable of generating welding current power 150 A;
• a mechanism that will be responsible for feeding the welding wire;
• the main working element is the burner;
• a hose through which the welding wire will be fed;
• hose for supplying shielding gas to the welding area;
• a coil of welding wire (such a coil will need to undergo some modifications);
• an electronic unit that controls the operation of your homemade semi-automatic machine.

Special attention should be devoted to redesigning the feeder, through which welding wire is supplied to the welding zone, moving along a flexible hose. In order for the weld to be high-quality, reliable and accurate, the wire feed speed through the flexible hose must correspond to the speed of its melting.

Since when welding using a semi-automatic machine, wire made from different materials And various diameters, its feed speed must be adjusted. It is precisely this function – regulation of the welding wire feed speed – that the feed mechanism of a semi-automatic device should perform.

Internal layout Wire spool Wire feeder (view 1)
Wire feed mechanism (type 2) Attaching the welding sleeve to the feed mechanism Design of a homemade torch

The most common wire diameters used in semi-automatic welding are 0.8; 1; 1.2 and 1.6 mm. Before welding, the wire is wound onto special reels, which are attachments of semi-automatic devices, secured to them using simple structural elements. During the welding process, the wire is fed automatically, which significantly reduces the time spent on such a technological operation, simplifies it and makes it more efficient.

The main element of the electronic circuit of the semi-automatic control unit is a microcontroller, which is responsible for regulating and stabilizing the welding current. Exactly from of this element The electronic circuit of a semi-automatic welding machine depends on the parameters of the operating current and the possibility of their regulation.

How to convert an inverter transformer

In order for the inverter to be used for a homemade semi-automatic device, its transformer must be subjected to some modifications. It’s not difficult to do this kind of alteration yourself, you just need to follow certain rules.

To bring the characteristics of the inverter transformer into line with those required for a semi-automatic device, you should wrap it with a copper strip on which a thermal paper winding is applied. It must be borne in mind that for these purposes you cannot use ordinary thick wire, which will become very hot.

The secondary winding of the inverter transformer also needs to be redone. To do this, you need to do the following: wind a winding consisting of three layers of sheet metal, each of which must be insulated with fluoroplastic tape; Solder the ends of the existing winding and the one you made yourself together, which will increase the conductivity of currents.

The design used to include it in a semi-automatic welding machine must necessarily provide for the presence of a fan, which is necessary for effective cooling of the device.

Setting up an inverter used for semi-automatic welding

If you decide to make a semi-automatic welding machine with your own hands using an inverter, you must first turn off the power to this equipment. To prevent such a device from overheating, its rectifiers (input and output) and power switches should be placed on radiators.

In addition, in the part of the inverter housing where the radiator is located, which heats up more, it is best to mount a temperature sensor, which will be responsible for turning off the device if it overheats.

After all of the above procedures have been completed, you can connect the power part of the device to its control unit and connect it to the electrical network. When the network connection indicator lights up, an oscilloscope should be connected to the inverter outputs. Using this device, you need to find electrical pulses with a frequency of 40–50 kHz. The time between the formation of such pulses should be 1.5 μs, which is regulated by changing the voltage value supplied to the device input.

It is also necessary to check that the pulses reflected on the oscilloscope screen have rectangular shape, and their front was no more than 500 ns. If all the checked parameters correspond to the required values, then you can connect the inverter to the electrical network. The current coming from the output of the semi-automatic device must have a force of at least 120 A. If the current value is less, this may mean that voltage is supplied to the equipment wires, the value of which does not exceed 100 V. If such a situation occurs, you must do the following: test the equipment by changing the current (in this case, the voltage on the capacitor must be constantly monitored). In addition, the temperature inside the device should be constantly monitored.

After the semi-automatic machine has been tested, it is necessary to test it under load. To make such a check, a rheostat is connected to the welding wires, the resistance of which is at least 0.5 Ohm. Such a rheostat must withstand a current of 60 A. The strength of the current that in such a situation flows to the welding torch is controlled using an ammeter. If the current strength when using a load rheostat does not meet the required parameters, then the resistance value of this device is selected empirically.

How to use a welding inverter

After starting the semi-automatic device that you assembled with your own hands, the inverter indicator should display a current value of 120 A. If everything is done correctly, then this will happen. However, the inverter indicator may display a figure of eight. The reason for this is most often insufficient voltage in the welding wires. It is better to immediately find the cause of such a malfunction and quickly eliminate it.

If everything is done correctly, the indicator will correctly show the strength of the welding current, which is adjusted using special buttons. The operating current adjustment interval, which is provided, is in the range of 20–160 A.

How to monitor the correct operation of equipment

So that the semi-automatic welding machine that you assembled with your own hands serves you long time, it is better to constantly monitor temperature regime inverter operation. To carry out such control, you need to press two buttons simultaneously, after which the temperature of the hottest inverter radiator will be displayed on the indicator. Normal operating temperature is considered to be one whose value does not exceed 75 degrees Celsius.

If this value is exceeded, then, in addition to the information displayed on the indicator, the inverter will begin to emit an intermittent sound signal, which should be noted immediately. In this case (as well as if the temperature sensor breaks or shorts) electronic circuit The device will automatically reduce the operating current to 20A, and a sound signal will be emitted until the equipment returns to normal. In addition, a malfunction of self-made equipment may be indicated by an error code (Err) displayed on the inverter indicator.

The advantages of DC welding machines over their “AC counterparts” are well known. This includes soft arc ignition, the ability to connect thin-walled parts, less metal spattering, and the absence of unwelded areas. There is not even the annoying (and, as it turned out, harmful effect on people) crackling sound. And all because the main thing inherent in welding machines is missing AC feature - intermittent arc burning when the supply voltage sinusoid flows through zero

Rice. 1. Graphs explaining the welding process on alternating (a) and direct (b) current.

Moving from the graphs to real structures, it is also impossible not to note: in AC machines, to improve and facilitate welding, powerful transformers are used (the magnetic core is made of special electrical iron with a steeply falling characteristic) and a deliberately high voltage in the secondary winding, reaching up to 80 V, although for 25-36 V is sufficient to support arc combustion and metal deposition in the welding zone. You have to put up with the prohibitively large mass and dimensions of the apparatus, and increased energy consumption. By reducing the voltage transformed into the secondary circuit to 36 V, you can lighten the weight of the “welder” by 5-6 times, bring its dimensions to the size of a portable TV while simultaneously improving other performance characteristics.

But how to light an arc with a low-voltage winding?

The solution was to introduce a diode bridge with a capacitor into the secondary circuit. As a result, the voltage at the output of the modernized “welder” was increased by almost 1.5 times. The opinion of experts has been confirmed in practice: when the 40-volt DC barrier is exceeded, the arc easily ignites and burns steadily, allowing you to weld even thin body metal.

Rice. 2. Fundamental electrical diagram DC welding machine.

The latter, however, is easily explained. With the introduction of a large capacity into the circuit, the characteristics of the welding machine also turn out to be steep (Fig. 3). The initial increased voltage created by the capacitor facilitates ignition of the arc. And when the potential on the welding electrode drops to U2 of the transformer (operating point “A”), a process of stable arc burning will occur with metal deposition in the welding zone.

Fig.3. Volt-ampere characteristics of a DC welding machine.

The “welder” recommended by the author can be assembled even at home, using an industrial one as a basis. power transformer 220-36/42 V (these are usually used in systems safe lighting and power supply of low-voltage plant equipment). After making sure that the primary winding, which usually contains 250 turns, is intact insulated wire with a cross section of 1.5 mm2, check the secondary ones. If their condition is unimportant, everything (with the exception of a serviceable network winding) is removed without regret. And in the freed space a new secondary winding is wound (until the “window” is filled). For a recommended transformer with a power of 1.5 kVA, this is 46 turns of a copper or aluminum bus with a cross-section of 20 mm2 with good insulation. Moreover, a cable (or several insulated single-core wires twisted into a bundle) with a total cross-section of 20 mm2 is quite suitable as a bus.

Selection of electrode cross-section depending on the power of the transformer.

The rectifier bridge can be assembled from semiconductor diodes with an operating current of 120-160 A, installing them on 100x100 mm heat sinks. It is most convenient to place such a bridge in the same housing with a transformer and a capacitor, bringing to the front textolite panel a 16-amp switch, an “On” signal light eye, as well as “plus” and “minus” terminals (Fig. 4). And to connect to the electrode holder and the ground, use a piece of single-core cable of the appropriate length with a copper cross-section of 20-25 mm2. As for themselves welding electrodes, then their diameter depends on the power of the transformer used.

Rice. 4. Homemade welding machine for DC welding.

And one more thing. When testing, it is recommended to disconnect the machine (10 minutes after welding) from the network and check thermal conditions transformer, diode bridge and capacitor. Only after making sure that everything is normal can you continue working. After all, an overheated “welder” is a source of increased danger!

Among other requirements, it is worth noting, I think, that the welding machine must be equipped with a spark-protective mask, gloves and rubber mat. The place where welding work is performed is equipped taking into account fire safety requirements. In addition, you need to make sure that there are no rags or other flammable materials nearby, and connect the “welder” to the network in compliance with electrical safety rules through the powerful plug connector of the electrical panel at the entrance to the building.

V. Konovalov, Irkutsk
Mk 04 1998

A unit designed for welding products is considered to be a semi-automatic welding machine. Such devices can be various types and forms. But the most important thing is the inverter mechanism. It is necessary that it be of high quality, multifunctional and safe for the consumer. Most professional welders do not trust Chinese products, making devices themselves. The manufacturing scheme for homemade inverters is quite simple. It is important to consider for what purposes the device will be manufactured.

• Welding using flux-cored wire;
• Welding with various gases;
• Welding under a thick layer of flux;

Sometimes, to achieve a high-quality result and obtain an even weld, the interaction of two devices is necessary.

Inverter devices are also divided into:

• Single-hull;
• Double-hull;
• Pushing;
• Pulling;
• Stationary;
• Mobile, which includes a trolley;
• Portable;
• Designed for beginner welders;
• Designed for semi-professional welders;
• Designed for professional craftsmen;

What will you need?

A homemade device, the circuit of which is very simple, includes several main elements:

• A mechanism with the main function responsible for controlling the welding current;
• Mains power supply;
• Special burners;
• Convenient clamps;
• Sleeves;
• Cart;

Scheme of welding using a semi-automatic device in a protective gas environment:

The master will also need:

• A mechanism that provides wire feeding;
• A flexible hose through which wire or powder will be supplied to the weld under pressure;
• Bobbin with wire;
• Special control device;

Operating principle

The operating principle of the inverter includes:

• Adjusting and moving the burner;
• Control and monitoring of the welding process;

When the unit is connected to the electrical network, a conversion of alternating current to direct current is observed. For this procedure you will need an electronic module, special rectifiers and a high-frequency transformer. For high-quality welding, it is necessary that the future unit has parameters such as the feed speed of the special wire, current strength and voltage in identical balance. For these characteristics, you will need an arc power source that has current-voltage readings. The length of the arc must be determined by the given voltage. The wire feed speed directly depends on the welding current.