There are several ways to create a seamless connection metal elements, but among all of them, capacitor welding occupies a special place. The technology has become popular since about the 30s of the last century. Docking is carried out by supplying electric current to the desired location. A short circuit is created, which allows the metal to melt.
Advantages and disadvantages of technology
The most interesting thing is that capacitor welding can be used not only in industrial conditions, but also in everyday life. It involves the use of a small-sized device that has a constant voltage charge. Such a device can easily move around the work area.
Among the advantages of the technology, it should be noted:
- high work productivity;
- durability of the equipment used;
- the ability to connect various metals;
- low level of heat generation;
- lack of additional consumables;
- accuracy of connection of elements.
However, there are situations when it is impossible to use capacitor welding to connect parts. This is primarily due to the short duration of the power of the process itself and the limitation on the cross-section of combined elements. In addition, pulsed load can create various interferences in the network.
Features and specifics of application
The process of joining workpieces itself involves contact welding, for which a certain amount of energy is consumed in special capacitors. Its release occurs almost instantly (within 1 - 3 ms), due to which the thermal impact zone is reduced.
It is quite convenient to carry out capacitor welding with your own hands, since the process is economical. The device used can be connected to a regular electrical network. There are special high-power devices for industrial use.
The technology has gained particular popularity in workshops designed to repair vehicle bodies. During the work they are not burned or subjected to deformation. There is no need for additional straightening.
Basic process requirements
In order for capacitor welding to be performed at a high quality level, certain conditions must be adhered to.
- The pressure of the contact elements on the workpieces immediately at the moment of the impulse must be sufficient to ensure reliable connection. The opening of the electrodes should be done with a slight delay, thereby achieving a better crystallization of metal parts.
- The surface of the workpieces to be joined must be free of contaminants so that oxide films and rust do not cause too much resistance when electric current is applied directly to the part. The presence of foreign particles significantly reduces the efficiency of the technology.
- Copper rods are required as electrodes. The diameter of the point in the contact zone must be at least 2-3 times the thickness of the element being welded.
Technological techniques
There are three options for influencing workpieces:
- Capacitor spot welding is mainly used to join parts with different thickness ratios. It is successfully used in the field of electronics and instrument making.
- Roller welding is a certain number of spot connections made in the form of a continuous seam. The electrodes resemble rotating coils.
- Impact capacitor welding allows you to create elements with a small cross-section. Before the collision of the workpieces, an arc discharge is formed, melting the ends. After the parts come into contact, welding is carried out.
As for the classification according to the equipment used, the technology can be divided according to the presence of a transformer. In its absence, the design of the main device is simplified, and the bulk of the heat is released in the direct contact zone. The main advantage of transformer welding is the ability to provide a large amount of energy.
Do-it-yourself capacitor spot welding: diagram of a simple device
To connect thin sheets up to 0.5 mm or small parts, you can use a simple design made at home. In it, the impulse is supplied through a transformer. One of the ends of the secondary winding is connected to the array of the main part, and the other to the electrode.
In the manufacture of such a device, a circuit can be used in which the primary winding is connected to the electrical network. One of its ends is output through the diagonal of the converter in the form of a diode bridge. On the other hand, a signal is supplied directly from the thyristor, which is controlled by the start button.
The pulse in this case is generated using a capacitor having a capacity of 1000 - 2000 μF. To manufacture a transformer, a Sh-40 core with a thickness of 70 mm can be used. The primary winding of three hundred turns can be easily made from wire with a cross-section of 0.8 mm marked PEV. A thyristor with the designation KU200 or PTL-50 is suitable for control. The secondary winding with ten turns can be made of a copper busbar.
More powerful capacitor welding: diagram and description of a homemade device
To increase power indicators, the design of the manufactured device will have to be changed. With the right approach, it will be possible to connect wires with a cross-section of up to 5 mm, as well as thin sheets no more than 1 mm thick. To control the signal, a contactless starter marked MTT4K, designed for electricity 80 A.
Typically, the control unit includes thyristors connected in parallel, diodes and a resistor. The response interval is adjusted using a relay located in the main circuit of the input transformer.
The energy is heated in electrolytic capacitors, combined into a single battery using the table. You can see the necessary parameters and the number of elements.
The main transformer winding is made of wire with a cross-section of 1.5 mm, and the secondary winding is made of a copper busbar.
The homemade device operates according to the following scheme. When you press the start button, the installed relay is activated, which, using thyristor contacts, turns on the transformer of the welding unit. The shutdown occurs immediately after the capacitors are discharged. The pulse effect is adjusted using a variable resistor.
Contact block device
The manufactured device for capacitor welding must have a convenient welding module that provides the ability to fix and freely move the electrodes. The simplest design involves manually holding contact elements. In a more complex version, the lower electrode is fixed in a stationary position.
To do this, it is fixed on a suitable base with a length of 10 to 20 mm and a cross-section of more than 8 mm. The upper part of the contact is rounded. The second electrode is attached to a platform that can move. In any case, adjustment screws must be installed, with the help of which additional pressure will be applied to create additional pressure.
It is imperative to isolate the base from the moving platform to the contact of the electrodes.
Work order
Before doing capacitor spot welding with your own hands, you need to familiarize yourself with the main steps.
- At the initial stage, the elements to be connected are prepared properly. Contaminants in the form of dust particles, rust and other substances are removed from their surface. The presence of foreign inclusions will not allow achieving high-quality joining of the workpieces.
- The parts are connected to each other in the required position. They should be located between two electrodes. After squeezing, an impulse is applied to the contact elements by pressing the start button.
- When the electrical influence on the workpiece stops, the electrodes can be moved apart. The finished part is removed. If there is a need, then it is installed at a different point. By the amount of the gap direct influence depends on the thickness of the welded element.
Application of ready-made devices
Work can be carried out using special equipment. This kit usually includes:
- apparatus for creating an impulse;
- device for welding and clamping fasteners;
- return cable equipped with two clamps;
- collet set;
- instructions for use;
- wires for connecting to the electrical network.
Final part
The described technology for connecting metal elements allows not only to weld steel products. With its help, you can easily join parts made of non-ferrous metals. However, when performing welding work, it is necessary to take into account all the features of the materials used.
slonik wrote:
after the rectifier bridge there is a set of condensers (7 pieces in parallel) and then a choke. So these condensers are designed so that you can connect them with jumpers or the rectifier field, or after the choke, or even turn them off. So why is this necessary? And where is the best place to install these condensers? And what are they worth?
Tribune wrote:
To ensure the conditions for stabilizing the arc gap, the source for semi-automatic welding must have a rigid load characteristic and a high rate of current rise during a short circuit. These requirements are especially relevant when welding with thin wire D0.6...0.8mm. As the wire diameter increases, the load characteristic becomes more decreasing and the required rate of current rise decreases. To correct the rate of current rise, on classical sources, the choke is even made with taps (BC300).
Judging by the stated current of 140A, the source is designed for welding with thin wire and most likely the capacitor should be turned on before the choke. In this case, the inductance of the inductor should be about 0.2 mH. Turning on a capacitor after the inductor almost always leads to an excessively high rate of current rise, which is not good (spattering increases sharply).
valvol.ru
Electrolytic capacitors in welding inverters
Bugaev Victor, Vitaly Diduk, Maxim Musienko
Aluminum electrolytic capacitors are one of the main elements that ensure stable operation of high-frequency inverters of welding machines. Reliable high-quality capacitors for this type of application are produced by Hitachi, Samwha, Yageo.
In the first devices using the electromechanical method arc welding, adjustable AC transformers were used. Transformer welding machines are the most popular and are still used today. They are reliable, easy to maintain, but have a number of disadvantages: heavy weight, high content of non-ferrous metals in the transformer windings, low degree of automation of the welding process. It is possible to overcome these disadvantages by moving to higher current frequencies and reducing the size of the output transformer. The idea of reducing the size of the transformer by moving from a power supply frequency of 50 Hz to a higher one was born back in the 40s of the 20th century. Then this was done using electromagnetic transducers-vibrators. In 1950, vacuum tubes - thyratrons - began to be used for these purposes. However, it was undesirable to use them in welding technology due to low efficiency and low reliability. The widespread introduction of semiconductor devices in the early 60s led to the active development of welding inverters, first on a thyristor basis, and then on a transistor one. Insulated gate bipolar transistors (IGBTs) developed at the beginning of the 21st century gave new impetus to the development of inverter devices. They can operate at ultrasonic frequencies, which can significantly reduce the size of the transformer and the weight of the device as a whole.
A simplified block diagram of the inverter can be represented as three blocks (Figure 1). At the input there is a transformerless rectifier with a parallel-connected capacitance, which allows you to increase the DC voltage to 300 V. The inverter unit converts DC into high-frequency alternating current. The conversion frequency reaches tens of kilohertz. The unit includes a high-frequency pulse transformer, in which the voltage decreases. This block can be manufactured in two versions - using single-cycle or push-pull pulses. In both cases, the transistor unit operates in a key mode with the ability to adjust the on-time, which allows you to regulate the load current. The output rectifier unit converts alternating current after the inverter into D.C. welding
Rice. 1. Simplified block diagram of a welding inverter
The principle of operation of the welding inverter is the gradual conversion of the mains voltage. First, the AC mains voltage is increased and rectified in the preliminary rectification unit. A constant voltage powers a high-frequency generator using IGBT transistors in the inverter unit. The high-frequency alternating voltage is converted to a lower one using a transformer and supplied to the output rectifier unit. From the output of the rectifier, current can already be supplied to the welding electrode. The electrode current is regulated by circuitry by controlling the depth of negative feedback. With the development of microprocessor technology, the production of inverter semi-automatic machines began, capable of independently selecting the operating mode and performing such functions as “anti-sticking”, high-frequency arc excitation, arc retention and others.
Aluminum electrolytic capacitors in welding inverters
The main components of welding inverters are semiconductor components, a step-down transformer and capacitors. Today, the quality of semiconductor components is so high that if they are used correctly, no problems arise. Due to the fact that the device operates at high frequencies and fairly high currents, special attention should be paid to the stability of the device - the quality of the welding work directly depends on it. The most critical components in this context are electrolytic capacitors, the quality of which greatly affects the reliability of the device and the level of interference introduced into the electrical network.
The most common are aluminum electrolytic capacitors. They are best suited for use in the primary network IP source. Electrolytic capacitors have high capacitance, high rated voltage, small dimensions, and are capable of operating at audio frequencies. Such characteristics are among the undoubted advantages of aluminum electrolytes.
All aluminum electrolytic capacitors are composed of sequential layers of aluminum foil (the anode of the capacitor), a paper spacer, another layer of aluminum foil (the cathode of the capacitor) and another layer of paper. All this is rolled up and placed in an airtight container. Conductors are brought out from the anode and cathode layers for inclusion in the circuit. Also, the aluminum layers are additionally etched in order to increase their surface area and, accordingly, the capacitance of the capacitor. At the same time, the capacity of high-voltage capacitors increases by about 20 times, and low-voltage ones by 100. In addition, this entire structure is treated with chemicals to achieve the required parameters.
Electrolytic capacitors have a rather complex structure, which makes them difficult to manufacture and operate. The characteristics of capacitors can vary greatly under different operating modes and operating climatic conditions. With increasing frequency and temperature, the capacitance of the capacitor and ESR decreases. As the temperature decreases, the capacitance also drops, and the ESR can increase up to 100 times, which, in turn, reduces the maximum permissible ripple current of the capacitor. The reliability of pulse and input network filter capacitors, first of all, depends on their maximum permissible ripple current. Flowing ripple currents can heat up the capacitor, which causes its early failure.
In inverters, the main purposes of electrolytic capacitors are to increase the voltage in the input rectifier and smooth out possible ripples.
Significant problems in the operation of inverters are created by large currents through transistors, high requirements for the shape of control pulses, which implies the use of powerful drivers to control power switches, high requirements for the installation of power circuits, and large pulse currents. All this largely depends on the quality factor of the input filter capacitors, so for inverter welding machines you need to carefully select the parameters of electrolytic capacitors. Thus, in the preliminary rectification unit of a welding inverter, the most critical element is the filtering electrolytic capacitor installed after the diode bridge. It is recommended to install the capacitor in close proximity to the IGBT and diodes, which eliminates the influence of the inductance of the wires connecting the device to the power source on the operation of the inverter. Also, installing capacitors near consumers reduces the internal resistance to alternating current of the power supply, which prevents excitation of the amplifier stages.
Typically, the filter capacitor in full-wave converters is chosen so that the ripple of the rectified voltage does not exceed 5...10 V. It should also be taken into account that the voltage on the filter capacitors will be 1.41 times greater than at the output of the diode bridge. Thus, if after the diode bridge we get 220 V pulsating voltage, then the capacitors will already have 310 V DC voltage. Typically, the operating voltage in the network is limited to 250 V, therefore, the voltage at the filter output will be 350 V. In rare cases, the mains voltage can rise even higher, so capacitors should be selected for an operating voltage of at least 400 V. Capacitors can have additional heating due to high operating currents. The recommended upper temperature range is at least 85...105°C. Input capacitors for smoothing out rectified voltage ripples are selected with a capacity of 470...2500 µF, depending on the power of the device. With a constant gap in the resonant choke, increasing the capacitance of the input capacitor proportionally increases the power supplied to the arc.
There are capacitors on sale, for example, of 1500 and 2200 µF, but, as a rule, instead of one, a bank of capacitors is used - several components of the same capacity connected in parallel. Thanks to parallel connection, internal resistance and inductance are reduced, which improves voltage filtering. Also, at the beginning of the charge, a very large charging current flows through the capacitors, close to the short circuit current. Parallel connection allows you to reduce the current flowing through each capacitor individually, which increases the service life.
Choice of electrolytes from Hitachi, Samwha, Yageo
On the electronics market today you can find a large number of suitable capacitors from well-known and little-known manufacturers. When choosing equipment, one should not forget that with similar parameters, capacitors differ greatly in quality and reliability. The most well-proven products are from such world-famous manufacturers of high-quality aluminum capacitors as Hitachi, Samwha and Yageo. Companies are actively developing new technologies for the production of capacitors, so their products have best characteristics compared to competitors' products.
Aluminum electrolytic capacitors are available in several form factors:
- for mounting on a printed circuit board;
- with reinforced snap-in pins (Snap-In);
- with bolted terminals (Screw Terminal).
Tables 1, 2 and 3 present the series of the above manufacturers that are most optimal for use in the pre-rectification unit, and their appearance is shown in Figures 2, 3 and 4, respectively. The given series have a maximum service life (within the family of a particular manufacturer) and an extended temperature range.
Table 1. Electrolytic capacitors manufactured by Yageo
Table 2. Electrolytic capacitors manufactured by Samwha
Table 3. Electrolytic capacitors manufactured by Hitachi
| Name | Capacity, µF | Voltage, V | Ripple current, A | Dimensions, mm | Form factor | Service life, h/°C |
| HP3 | 470…2100 | 400, 420, 450, 500 | 2,75…9,58 | 30×40, 35×35…40×110 | Snap-In | 6000/85 |
| HU3 | 470…1500 | 400, 420, 450, 500 | 2,17…4,32 | 35×45, 40×41…40×101 | Snap-In | 6000/105 |
| HL2 | 470…1000 | 400, 420, 450, 500 | 1,92…3,48 | 35×40, 30×50…35×80 | Snap-In | 12000/105 |
| GXA | 1000…12000 | 400, 450 | 4,5…29,7 | 51×75…90×236 | Screw Terminal | 12000/105 |
| GXR | 2700…11000 | 400, 450 | 8,3…34,2 | 64×100…90×178 | Screw Terminal | 12000/105 |
As can be seen from Tables 1, 2 and 3, the product range is quite wide, and the user has the opportunity to assemble a capacitor bank, the parameters of which will fully meet the requirements of the future welding inverter. The most reliable are Hitachi capacitors with a guaranteed service life of up to 12,000 hours, while competitors have this parameter up to 10,000 hours in Samwha JY series capacitors and up to 5,000 hours in Yageo LC, NF, NH series capacitors. True, this parameter does not indicate a guaranteed failure of the capacitor after the specified line. Here we mean only the time of use at maximum load and temperature. When used in a smaller temperature range, the service life will increase accordingly. After the specified period, it is also possible to reduce the capacity by 10% and increase losses by 10...13% when operating at maximum temperature.
Rice. 2. Yageo electrolytic capacitors
Rice. 3. Samwha electrolytic capacitors
Rice. 4. Hitachi electrolytic capacitors
It is noteworthy that in each series you can find a different configuration of capacitor leads - with reinforced snap-in terminals or bolted terminals. Bolted terminals provide guaranteed reliability of the assembly, and capacitors with latched terminals add to the reliability and ease of installation on a printed circuit board.
Conclusion
The considered high-quality aluminum electrolytic capacitors manufactured by Hitachi, Samwha and Yageo can solve almost any problem in the development of a high-frequency inverter welding machine. A distinctive feature of the presented capacitors is their development in accordance with the requirements of RoHS (Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment) and other environmental standards. For advice on application, as well as on the purchase of capacitors produced by all three companies, you can contact their distributor - the COMPEL company.
Literature
Obtaining technical information, ordering samples, ordering and delivery.
www.compel.ru
Simple semi-automatic do-it-yourself welding machine
How to do it yourself semi-automatic welding. This question worries many, since the cost of a semi-automatic welding machine for domestic purposes ranges from $300 to $800. Industrial semi-automatic welding machines are even more expensive. There is only one option left - to assemble the semi-automatic machine yourself, with your own hands. Let's consider what main components and parts a semi-automatic welding machine consists of. The basis of the semi-automatic welding machine is a welding power transformer. It is advisable to have a ready-made transformer, but you can make it yourself. The main requirements for the transformer are that with an output voltage of 10 - 20V, ensuring a rated output current of up to 60A. To adjust the output voltage, when winding the primary winding, it is necessary to make taps and provide a switching option.
Of course, the most difficult component to make at home is the wire feed mechanism. The quality of the weld and the uniformity of the wire feed will directly depend on its operation. The most suitable option for manufacturing a feed mechanism is a gearbox from a car windshield wiper complete with an electric motor.
Because Semi-automatic welding is performed with direct current, it is necessary to use a rectifier. The type of rectifier depends on the method of winding the welding transformer. For our version, with two windings, two DL161-200 rectifier diodes are used. For a bridge rectifier circuit, four rectifier diodes are used. The 30000x63V capacitor is designed to smooth out voltage ripples after the rectifier.
In the DC circuit, after the rectifier diodes, to improve the stability of the arc, a choke is installed, wound on a transformer core with a cross-section of at least 35 mm x 35 mm, about 20 turns of wire, the diameter of which is not less than the diameter of the wire on the secondary winding of the welding transformer.
The electric motor of the wire feed drive mechanism is powered from a power supply with an output voltage of 12 - 15V and a current of about 5A.
The semi-automatic welding machine also has:
gas solenoid valve;
electromagnetic starter for switching on a semi-automatic welding machine;
wire feeding sleeve
and other little things.
The diagram of the semi-automatic welding machine is shown below:
A variable resistor is used to adjust the wire feed speed during operation of the semiautomatic machine. When you press the start button, the gas supply valve is synchronously turned on and the welding transformer is turned on using relay K1.
This semi-automatic welding circuit is just an example. At self-production The semi-automatic circuit can be changed based on the available components.
Technical data of our semi-automatic welding machine:
Supply voltage: 220 V
Power consumption: no more than 3 kVA
Operating mode: intermittent
Operating voltage regulation: stepwise from 19 V to 26 V
Welding wire feed speed: 0-7 m/min
Wire diameter: 0.8mm
Welding current value: PV 40% - 160 A, PV 100% - 80 A
Welding current control limit: 30 A - 160 A
A total of six such devices have been made since 2003. The device shown in the photo below has been in service since 2003 in a car service center and has never been repaired.
Appearance of semi-automatic welding machine
At all
Front view
Back view
Left view
The welding wire used is standard
5kg coil of wire with a diameter of 0.8mm
Welding torch 180 A with Euro connector
was purchased at a welding equipment store.
Welder diagram and details
Due to the fact that the semi-automatic circuit was analyzed from such devices as PDG-125, PDG-160, PDG-201 and MIG-180, circuit diagram differs from a circuit board because the circuit was drawn up on the fly during the assembly process. Therefore, it is better to stick to the wiring diagram. On printed circuit board all points and details are marked (open in Sprint and hover your mouse).
Installation view
Control board
A single-phase 16A type AE circuit breaker is used as a power and protection switch. SA1 - welding mode switch type PKU-3-12-2037 for 5 positions.
Resistors R3, R4 are PEV-25, but they don’t have to be installed (I don’t have them). They are designed to quickly discharge choke capacitors.
Now for capacitor C7. Paired with a choke, it ensures combustion stabilization and arc maintenance. Its minimum capacity should be at least 20,000 microfarads, optimal 30,000 microfarads. Several types of capacitors with smaller dimensions and higher capacity were tried, for example CapXon, Misuda, but they did not prove to be reliable and burned out.
As a result, Soviet capacitors were used, which still work to this day, K50-18 at 10,000 uF x 50V, three in parallel. 
Power thyristors for 200A are taken with a good margin. You can install it at 160 A, but they will work at the limit, and you will need to use good radiators and fans. The used B200s stand on a small aluminum plate.
Relay K1 type RP21 for 24V, variable resistor R10 wirewound type PPB.
When you press the SB1 button on the burner, voltage is supplied to the control circuit. Relay K1 is activated, thereby, through contacts K1-1, voltage is supplied to the electromagnetic valve EM1 for acid supply, and K1-2 - to the power supply circuit of the wire drawing motor, and K1-3 - to open the power thyristors.
Switch SA1 sets the operating voltage in the range from 19 to 26 Volts (taking into account the addition of 3 turns per arm up to 30 Volts). Resistor R10 regulates the supply of welding wire and changes the welding current from 30A to 160A.
When setting up, resistor R12 is selected in such a way that when R10 is turned to minimum speed, the engine still continues to rotate and does not stand still.
When you release the SB1 button on the torch, the relay releases, the motor stops and the thyristors close, the solenoid valve, due to the charge of capacitor C2, still remains open, supplying acid to the welding zone.
When the thyristors are closed, the arc voltage disappears, but due to the inductor and capacitors C7, the voltage is removed smoothly, preventing the welding wire from sticking in the welding zone.
Winding up a welding transformer
We take the OSM-1 transformer (1 kW), disassemble it, put the iron aside, having previously marked it. We make a new coil frame from PCB 2 mm thick (the original frame is too weak). Cheek size 147×106mm. Size of other parts: 2 pcs. 130×70mm and 2 pcs. 87x89mm. We cut out a window measuring 87x51.5 mm in the cheeks.
The coil frame is ready.
We are looking for a winding wire with a diameter of 1.8 mm, preferably in reinforced fiberglass insulation. I took such a wire from the stator coils of a diesel generator). You can also use ordinary enamel wire such as PETV, PEV, etc.
Fiberglass - in my opinion, the best insulation is obtained
We begin winding - the primary. The primary contains 164 + 15 + 15 + 15 + 15 turns. Between the layers we make insulation from thin fiberglass. Lay the wire as tightly as possible, otherwise it won’t fit, but I usually didn’t have any problems with this. I took fiberglass from the remains of the same diesel generator. That's it, the primary is ready.
We continue to wind - the secondary. We take an aluminum busbar in glass insulation measuring 2.8x4.75 mm (can be purchased from wrappers). You need about 8 m, but it is better to have a small margin. We begin to wind, laying it as tightly as possible, we wind 19 turns, then we make a loop for the M6 bolt, and again 19 turns. We make the beginnings and ends 30 cm each, for further installation.
Here small retreat, personally, for me to weld large parts at such a voltage, the current was not enough; during operation, I rewound the secondary winding, adding 3 turns per arm, in total I got 22+22.
The winding fits snugly, so if you wind it carefully, everything should work out.
If you use an enamel wire as a primary material, then you must impregnate it with varnish; I kept the coil in the varnish for 6 hours.
We assemble the transformer, plug it into an outlet and measure the no-load current of about 0.5 A, the voltage on the secondary is from 19 to 26 Volts. If everything is so, then the transformer can be put aside; we no longer need it for now.
Instead of OSM-1 for a power transformer, you can take 4 pieces of TS-270, although there are slightly different sizes, and I only made 1 on it welding machine, then I don’t remember the data for winding, but it can be calculated.
We'll roll the throttle
We take an OSM-0.4 transformer (400W), take an enamel wire with a diameter of at least 1.5 mm (I have 1.8). We wind 2 layers with insulation between the layers, lay them tightly. Next we take an aluminum tire 2.8x4.75 mm. and wind 24 turns, making the free ends of the bus 30 cm long. We assemble the core with a gap of 1 mm (lay in pieces of PCB).The inductor can also be wound on iron from a color tube TV like TS-270. Only one coil is placed on it.
We still have one more transformer to power the control circuit (I took a ready-made one). It should produce 24 volts at a current of about 6A.
Housing and mechanics
We've sorted out the trances, let's move on to the body. The drawings do not show 20 mm flanges. We weld the corners, all iron is 1.5 mm. The base of the mechanism is made of stainless steel.
Motor M is used from a VAZ-2101 windshield wiper.
The limit switch for returning to the extreme position has been removed.
In the bobbin holder, a spring is used to create braking force, the first one that comes to hand. The braking effect is increased by compressing the spring (i.e. tightening the nut).
I came across a Chinese Vita semi-automatic welding machine (from now on I will simply call it PA), in which the power transformer burned out; my friends just asked me to repair it.
They complained that when they were still working, it was impossible for them to cook anything, there were strong splashes, crackling, etc. So I decided to bring it to a conclusion, and at the same time share my experience, maybe it will be useful to someone. Upon first inspection, I realized that the transformer for the PA was wound incorrectly, since the primary and secondary windings were wound separately; the photo shows that only the secondary remained, and the primary was wound next to it (that’s how the transformer was brought to me).
This means that such a transformer has a steeply falling current-voltage characteristic (volts ampere characteristic) and is suitable for arc welding, but not for PA. For Pa, you need a transformer with a rigid current-voltage characteristic, and for this, the secondary winding of the transformer must be wound on top of the primary winding.
In order to start rewinding the transformer, you need to carefully unwind the secondary winding without damaging the insulation, and cut off the partition separating the two windings.
For the primary winding I will use copper enamel wire 2 mm thick; for complete rewinding we will need 3.1 kg copper wire, or 115 meters. We wind turn to turn from one side to the other and back. We need to wind 234 turns - that's 7 layers, after winding we make a tap.
We insulate the primary winding and taps with fabric tape. Next we wind the secondary winding with the same wire that we wound earlier. We wind tightly 36 turns, with a shank of 20 mm2, approximately 17 meters.
The transformer is ready, now let's work on the choke. The throttle is an equally important part in the PA, without which it will not work normally. It was made incorrectly because there is no gap between the two parts of the magnetic circuit. I will wind the choke on iron from the TS-270 transformer. We disassemble the transformer and take only the magnetic circuit from it. We wind a wire of the same cross-section as on the secondary winding of the transformer on one bend of the magnetic circuit, or on two, connecting the ends in series, as you like. The most important thing in the inductor is the non-magnetic gap, which should be between the two halves of the magnetic circuit; this is achieved by PCB inserts. The thickness of the gasket ranges from 1.5 to 2 mm, and is determined experimentally for each case separately.
For a more stable arc burning, capacitors with a capacity of 20,000 to 40,000 μF must be placed in the circuit and the capacitor voltage should be from 50 volts. Schematically it all looks like this.
In order for your PA to work normally, it will be enough to do the above steps.
And for those who are annoyed by the direct current on the burner, you need to install a 160-200 ampere thyristor in the circuit, see how to do this in the video.
Thank you all for your attention -)
I once bought my own semi-automatic transformer. Well, I thought it would last me a long time, since I planned it for welding and repairing car bodies. In the end, I was disappointed that it simply burned the thin metal the moment the welding wire touched the surface to be welded. And it simply didn’t boil the thick metal, about 4 mm thick, properly.
As a result of this, I wanted to just throw it away. You can’t take it back to the store, since a lot of time has passed, and I have more than one job. So it was decided to assemble an inverter for my device in order to get rid of the transformer, which was not clear how it worked.
The figure shows the actual circuit itself. This circuit was taken from the basis of a 250 ampere welding inverter, which was developed by Evgeny Rodikov. For which I thank him.
True, I had to tinker quite a bit with this circuit so that an ordinary welding inverter, which has a soft current-voltage characteristic (volt-ampere characteristic), would become hard and so that there would be voltage feedback and could be adjusted from 7 volts to 25 volts. Since on a semi-automatic device there is no need to regulate the current, it needs to change the voltage. Which is what I did.
First, we need to assemble a power supply that will power the PWM generator and key drivers.
Here is the actual circuit of the power supply, it is not complicated and I don’t think I will go into details and everything is clear.
Operating principle of the inverter
The operation of the inverter is as follows. From the network, 220 volts are supplied to the diode bridge and rectified, then the high-capacity capacitors are charged through the current-limiting resistor R11. If it were not for the resistor, a strong bang would occur, which would cause the diode bridge to fail. When the capacitors are charged, the timer on VT1, C6, R9, VD7 turns on relay K1, thereby bypassing the current-limiting resistor R11 and the voltage at this time on the capacitors increases to 310 volts. and at the same time, relay K2 is turned on, which opens the circuit of resistor R10, which blocks the operation of the PWM generator assembled on the UC3845 chip. The signal from the 6th leg of the PWM generator is supplied to the optocouplers through resistors R12, R13. Next, passing through the HCPL3120 optocouplers to the drivers for controlling power IGBT transistors that trigger the power transformer. After the transformer, a large high-frequency current comes out and goes to the diodes, thereby rectifying it. Voltage and current control are performed using a PC817 optocoupler and a current sensor built on a ferrite ring through which the power transformer wire is passed.
Starting to assemble the inverter
The assembly itself can be started however you like. I personally started assembling from the power supply itself, which should power the PWM generator and key drivers. After checking the functionality of the power supply, it worked for me without any modifications or settings. The next step was to assemble a timer that should block the PWM generator and bypass the current-limiting resistor R11, making sure that it works, it should turn on relays K1 and K2 for a period of time from 5 seconds to 15 seconds. If the timer operates faster than necessary, then you need to increase the capacitance of capacitor C6. After which I began assembling a PWM generator and a power switch driver. The PWM generator has one drawback with resistors R7, it should have a resistance of 680 Ohms R8 1.8 Ohms and a capacitor C5 510p C3 2200p, also making sure the assembly was correct, set the initial frequency to 50 kHz using a resistor R1. In this case, the signal generated by the PWM generator must be strictly rectangular 50/50 and not have any bursts or emissions from the edges of the rectangles shown on the oscilloscope waveform. Afterwards, I assembled the power switches and applied a voltage of minus 310 volts to the lower power switches. plus the upper power switches, I supplied power plus 310 volts through a light bulb 220 volts 200 watts is not shown on the diagram itself, but it is necessary to add capacitors 0.15 μF x 1000 volts 14 pieces to the power supply of the power switches plus and minus 310 volts. this is necessary so that the emissions that the transformer will create go into the power supply circuit of the power switches, eliminating interference in the 220 volt network. After which I started assembling a power transformer and it all started like this for me. I don’t know what kind of ferrite material I wound the test winding, for example 12 turns of copper wire 0.7 mm in diameter coated with varnish, turned it on between the arms of the power switches and started the circuit, made sure that the light bulb was on, waited a little for about 5 or 10 minutes, turned off the circuit from the socket Letting the filter capacitors discharge so that no electric shock occurs, check the power trance core itself; it should not heat up. If it got hot, I increased the number of windings and thus I reached 18 turns. And so I wound the transformer with the calculation of the sections that are written on the diagram.
Setting up and first startup of the inverter
Before setting up and starting for the first time, we check once again that it is correctly assembled. We make sure that the power transformer and the current sensor on the small ring are correctly phased. The current sensor is usually selected by the number of turns of the wire; the more turns, the greater the output current, but you should not neglect it because you can overload the power switches and they can easily fail. In this case, if you do not know the ferrite material, it is best to start with 67 turns and gradually increase the number of turns until the arc is sufficiently rigid when welding. For example, I got 80 turns, while my network does not load, the power switches do not heat up and, of course, there is no noise from the power transformer and the output inductor.
And so we begin the first start-up and setup with the light bulb turned on as described above, while a bunch of capacitors of 14 pieces of 0.15 μF each must be turned on to power the keys plus and minus 310 volts. We turn on the oscilloscope to the emitter and collector of the lower arm of the power switches. Before this, we do not hook up the voltage feedback optocoupler, temporarily leave it hanging in the air; on the oscilloscope there should be a rectangular frequency signal; we take a screwdriver and twist the resistor R1 until a small bend appears on the lower corner of the rectangle. Turn in the direction of decreasing frequency. This will indicate oversaturation of the power transformer core. When bending at the resulting frequency, write it down and calculate the operating frequency of the power transformer core. For example, the oversaturation frequency is 30 kHz, we calculate 30, divide by 2, we get 15, the resulting number is added to the oversaturation frequency of 30 plus 15, we get 45. 45 kHz is our operating frequency. In this case, the light bulb should glow almost imperceptibly dimly. The current consumption should not exceed 300 mA at full idle, usually 150 mA. watch an oscilloscope to ensure there are no voltage surges above 400 volts, usually 320 volts. Once everything is ready, we attach a kettle or a heater or a 2000-watt iron to the light bulb. We connect a wire of a decent cross-section to the output, for example from 5 squares of 2 meters, we make a short circuit, while the light bulb should not burn at full brightness; it should glow a little more than half the incandescence. If it glows at full brightness, then you need to check the current sensor again in phasing, just pass the wire on the other side. As a last resort, reduce the number of turns on the current sensor. After everything is ready, now plus 310 volt power supply, run directly without a light bulb and a 2000 watt heater. Don’t forget about cooling the power switches, a radiator with a fan is best suited to a radiator from an old-style computer, Intel Pentium or AMD Atom. Power switches must be screwed onto the radiator without a mica gasket and through a thin layer of KPT8 thermal conductive paste to ensure maximum cooling efficiency. The radiator must be made separately from the upper and lower arms of the half-bridge. Snubber diodes and diodes connected between the power supply and the transformer should be placed on the same radiators as the keys, but through a mica gasket to avoid short circuits. All capacitors on our generator should be film capacitors with the inscription NPF, this will help you avoid unpleasant moments in weather conditions. The capacitors on the snubbers and on the output diodes should strictly only be of the K78-2 or SVV81 type; do not put any debris in there, since snubbers play an important role in this system and they absorb all the negative energy that the power transformer creates.
The start button of the semi-automatic machine, which is located on the burner sleeve, must be placed in the gap of the overheating temperature sensor. And I almost forgot at the output of the power transformer when setting up the entire system without a feedback optocoupler, the 220 μF capacitor must also be temporarily removed so as not to exceed the output voltage and at the same time at the output in this situation, the voltage should be no more than 55 volts; if it reaches 100 volts or more, it is advisable to reduce the number of turns, for example, rewind 2 turns to get the voltage we need, after which we can install a capacitor and feedback optocoupler. Resistor R55 is a voltage regulator. R56 is a maximum voltage limiting resistor; it is better to solder it on the board next to the optocoupler to avoid a jump when the regulator breaks and select it in the direction of increasing the resistance to the required maximum current; for example, I did it up to 27 volts. Resistor R57 is a tuning resistor for a screwdriver to adjust the minimum voltage, for example 7 volts.