In welding works, devices specially adapted for specific purposes are used. Schemes of individual devices are very different in structure. Among the most practical and widespread, you can select the inverter circuit. The device, assembled according to this scheme, is smoothly and precisely adjusted, compact, for masters who work on the road, it is simply irreplaceable.
Scheme of the device welding inverter.
The circuit of the inverter unit is one of the simplest, all the necessary circuit board elements and transistors can easily be found in the shops of radio components, and the assembly schemes are available from the masters. The task to assemble such a welding machine with their own hands is quite within the power of people who can work with a soldering iron.
The principle of operation of the inverter welding machine
By itself, this device is the similarity of a powerful power supply, similar to the impulse units such as AT and ATX, which are installed in personal computers. The order of changes in the initial parameters of the electric current in these two devices is identical. In the inverter, electrical energy passes through a series of transformations:
- AC household voltage is converted to DC.
- DC current is converted to AC with high frequency.
- The voltage value decreases.
- The current with reduced voltage is rectified with preservation of the set frequency.
All of these transformations are explained by the need to reduce the weight and dimensions of the power transformers of welding machines.
The scheme of the welding inverter.
The principle of operation of old devices was reduced to reducing the voltage from the mains and increasing the value of the current strength on the secondary winding to several dozen, or even hundreds of amperes - the values required for arc welding. In order to provide the desired ratio for reducing the voltage and increasing the magnitude of the current, the secondary winding asked fewer turns and a larger cross-section of the wire. Because the old welding transformers were with large dimensions and weight. The production of transformer winding required large costs of copper wire, which is why the welding machines were not cheap at all.
Inverter circuits allowed to correct the situation. By increasing the frequency of the current on the working winding to 60-80 kHz and above, it was possible to reduce the size and weight of the whole structure. Due to the 4-fold increase in the working frequency of the conversion, the dimensions of the apparatus were halved. And in our case we are talking about a thousandfold increase in frequency.
Such high values of the AC frequency are achieved by switching transistors installed in the inverter circuit, which communicate with each other at a frequency of 60-80 kHz. The current to the transistors comes constant from the rectifier. AC voltage is rectified by a bridge circuit of the diodes and is equalized by capacitors. At the output of the rectifier and capacitor, a constant voltage of 220 V. is supplied. This is the first step of the circuit.
Inverter circuit high-frequency transistors transmit alternating high-frequency current to a step-down transformer. Since the operating frequency is already 1000 times lower than the power supply frequency, the transformer is a very compact coil.Back to table of contents
Components of the circuit welding machine
Electric circuit welding inverter.
The inverter circuit is designed for the value of the supply current up to 32 A and voltage 220-230 V. The current value at the output of the converter reaches 250 A. This value ensures a strong weld when welding with an electrode up to 1 cm away. The power supply unit of the inverter unit includes such components :
- Transformer with 7x7 or 8x8 base of ferritic core.
- The primary winding has 100 rings of wire with a diameter of 0.3 mm.
- Internal secondary winding at 15 turns with a wire of 1 mm thickness.
- Average secondary winding at the same number of turns with a wire of smaller thickness (0.2 mm).
- External entry of the secondary winding for 20 turns of wire with a thickness of 0.35 mm.
The scheme of the transformer winding.
Before winding the wires on the transformer core, it is wrapped in copper. The width of the strips is 40 mm, the height of the tape is 0.3 mm. Together with the copper tape, the core is wrapped with thermal paper. For this purpose, good cash tape and any other thin and durable paper, which is convenient to fit around the core. A round wire is not suitable for the primary winding, because it is easily overheated. Because of this, the currents are redirected to the outer side of the winding, and the inner layers remain unloaded.
The secondary winding is placed in 3 layers of wires, between which insert a strip of fluoroplastic. For these purposes, standard wires with a diameter of 0.5-0.7 mm are not suitable. Because of the circular cross section in the winding, they do not adhere well to each other, leaving gaps, thereby impairing heat transfer.
While winding the winding, pay attention to the wire curling without gaps around the core. Only in this way the voltage will be stable. A typical inverter device design implies the presence of two transformers with a frequency of 41 kHz, but they are also suitable for 55 kHz. Then install an insulating gasket and a choke marked L2. On the side of the board, an additional blower is installed, its electrical characteristics are 0.13 A and 220 V.Back to table of contents
Inverter board soldering
On the mapping of the welding machine of the inverter type are coolers and radiators, which are found in computer power supplies. They can be extracted from the old technology or contact the store of radio components for new ones.
Radiators are placed at the top and bottom of the ends of the oblique bridge.
Diodes are attached to the radiator on a pre-prepared layer of mica.
To build the inverter will need a cooler.
When the IRG4PC50W bridge is used for flow distribution, use thermal grease instead of mica.
The direction of the outputs of the transistors and diodes is set to meet each other. In between the radiators, a board is mounted, which will connect all parts of the welding appliance power circuit with the intermediate elements of the bridge. Keep in mind that the rated voltage of the power supply circuit is 300 V. The powers discharged by the transformer must go to the circuit, for which solders with 0.15 μF capacitors are soldered to the board. Installation after the transformer snubber and capacitors extinguishes unwanted surge from surges at the exit of the secondary winding.Back to table of contents
Setup and debugging of the inverter
Scheme of the internal device of the inverter.
After completing the assembly, it is imperative to customize the operation of the inverter module. Connect a 15 V to PWM and power the fan. Then through the resistor R11 connect the relay K1. All this is done in order to prevent jumps when connected to the 220 V network. Check the timely activation of the relay and after 10 seconds, apply working power to the PWM. After the relay is triggered, the rectangular areas in the PWM diagram should not be observed.
Then the bridge is connected to a voltage source of 15 V. When idling, the inverter consumes current within 100 mA. If the metering shows the permissible value, then the circuit is assembled correctly. Additionally, you must ensure that the phasing of the windings is not confused.
On PWM, the frequency setting is reduced until a bend appears on the bottom of the graph, which will indicate a node oversaturation. We divide this frequency value by 2 and add it to the operating frequency of the PWM board and directly to the transformer. The circuit is connected correctly if the relay outputs a signal at 150 mA when tuning. If the light signal is fuzzy and weak, then the board is connected incorrectly or one of the windings punches. Remove unnecessary interference will, if you shorten all the power wires.Back to table of contents
Device Health Check
After assembling the welding inverter, it is necessary to check it for operability.
So, the inverter welding machine is assembled and ready for use, it now remains to make sure that it is operational. Turn on the device in the mains, smoothly set a large amperage and check the voltage on the oscilloscope. The voltage in the lower loop of the oscillogram is acceptable in the range of 500 V, in conditions of overshoot, an excess of up to 550 V is allowed. In a correctly compiled scheme, this figure will not exceed 350 V.
When checking the performance of the device, make sure that the hum from the tire does not increase with increasing load. To apply the maximum current, the background noise must remain unchanged.
Then proceed to the very welding. After starting, you must wait 10 seconds and check the temperature of the coolers. For the first 20 seconds, they should remain cold, for the next minute - slightly warm.
After that, we take 2 electrodes for the desired type of welding and cut the seam on the test material until they completely burn out. When finished, we control the temperature of the transformer: by that time it will have time to warm up, but do not become white-hot. Excessive heat will indicate a flaw in the assembly.
Radiators have time to seriously warm up after continuous operation at 3 electrodes. Therefore, you need to let them cool for 2 minutes. This is enough for the cooler to lower the temperature to a normal level and to continue working without loss of quality.
The process of assembling the welding machine with your own hands, very laborious, show as much concentration and attention to it as possible. Carefully study your chosen scheme, sort out the sequence of connecting parts in it, count the exact number of components and wires. At the end of the assembly, the invention must be checked for health and safety. Organize welding work with all the necessary conditions for safe labor: wear tight gloves on your hands, cover your face with a welding shield.