For welding, special equipment is used, the schemes of individual models are very different from each other. The most commonly used is an inverter. This equipment is accurate, working with it is extremely simple. The scheme of this device is not too complicated, many craftsmen prefer to assemble such devices with their own hands.
Scheme of the device welding inverter.
This work is laborious, requires certain skills and attention. Before starting the assembly, it is necessary to draw up a future scheme of the welding machine, to determine which elements and components are needed. After assembly, it is imperative to check the equipment performance, safety of its use. When welding, be sure to use special protective gloves and a mask.
Welding machine diagram
Figure 1. Functional diagram of the power source of an inverter welding machine.
The welding inverter has a maximum supply current of 32 A, 220 V. Welding is 250 A. This ensures high quality operation with an arc length of 1 cm. The efficiency of the inverter is not lower than the factory versions. The power supply circuit used for such a welding machine includes:
- transformer based on ferrite 7 * 7 or 8 * 8;
- the primary winding should have 100 turns of wire with a cross section of 0.3 mm;
- the first layer of the secondary winding is made of 15 turns, the wire cross-section is 1 mm;
- the second layer of the secondary winding also includes 15 turns, the wire cross-section is 0.2 mm;
- the third layer of the secondary winding is made of 20 turns, the cross-section of the wire is 0.35 mm.
When performing the winding, it is necessary to ensure that the wire fills all the space, this will give a stable voltage. An example of the scheme is shown in Fig.1. The general scheme of the welding machine includes 2 transformers at 41 kHz, but it can also be used at 55 kHz. After that there is a gasket and a choke type L2, a special current transformer. Additional fans for cooling are used.Back to table of contents
Throttle circuit welding inverter.
The assembly scheme provides winding of the transformer, it is done using copper. Its width is 40 mm, and its thickness is 0.3 mm. It will take thermal paper to wrap. A regular cash register will suit, its thickness should be 0.05 mm. Such paper has the necessary quality, it is durable, it does not tear when wound. The usual wire is not suitable for work, as it will overheat, all currents will be forced out to the surface part, the lower layers will not be involved.
The secondary winding consists of 3 copper tapes, they are divided among themselves by a special fluoroplastic film, which darkens when heated. It is not recommended to use conventional semiconductor wires with a cross section of 0.5-0.7 mm for winding. Such wires are round; during winding they leave a large number of air gaps, i.e. heat transfer slows down. The scheme necessarily provides for the presence of a 0.13 A 220 V fan, and other values can be used.Back to table of contents
Welding inverter assembly
Connection diagram of the inverter to the battery.
For the assembly of inverters, it is recommended to try on fans and radiators that are in computer units. Buy them is not difficult, the cost of such equipment is democratic. Oblique bridge will be assembled from 2 radiators, with the upper part of the bridge being installed on one radiator, and the lower one placed on the other. Diodes are mounted on radiators using a special gasket of mica. If the bridge used is IRG4PC50W, then instead of mica, you need a special heat-conducting paste.
All pins of transistors, diodes should be installed in such a way that they meet one for one. A board is placed between the radiators, it is designed to connect all the power supply circuits of the future equipment with the individual parts of the bridge. It should be remembered that the power circuit is 300 V. In order for the emissions of the transformer to go into the circuit, the circuit provides for solder on the board, capacitors of 0.15 microns All other parts are interconnected by conductors. Snubber with capacitors are used, they help suppress all the emissions of the resonant type transformer, reduce IGBT losses.Back to table of contents
Winding scheme of the welding transformer.
Setup of the inverter welding machine is carried out after the end of the assembly. The PWM is powered at 15 V, it is also recommended to supply power to the fan. Relay K1 is connected through resistor R11. This allows you to eliminate strong surges during the supply of a working voltage of 220 V. The accuracy of the relay is checked, after which after 2-10 seconds a working voltage is applied to the PWM. There should be no rectangular pulses, especially after the relay has tripped.
After that, the bridge is supplied with power equal to 15 V. This makes it possible to make sure that its circuit is assembled correctly. At idle current consumption will be up to 100 mA. Plus, you need to make sure that the phasing of the windings is carried out correctly.
On PWM, the clock frequency decreases until a bend appears on the lower key, that is, until the node becomes oversaturated. The resulting value is divided by 2, the number is added to the frequency value, which is the operating frequency for the PWM board and the welding transformer itself. If during the adjustment the relay lamp is lit at a current of 150 mA, then the circuit is assembled correctly. If it glows too bright, the assembly is carried out incorrectly or there is a breakdown of the windings. To reduce the level of interference, you need to twist all the supply wires, they should be as short as possible.Back to table of contents
Checking the unit in action
After the inverter welding machine is fully prepared, it is necessary to check its performance. To do this, the equipment should be turned on, gradually add current and check the voltage with an oscilloscope. The values of the voltage of the lower key should not exceed 500 V, the maximum allowed is 550 V, subject to overshoot. If the scheme is properly followed, then the value does not exceed 350 V.
During the test, it is necessary to take into account that when the bus makes the maximum noise, no current should be applied.
The next stage of the test will be directly welding. The first 10 seconds of the welding machine do not need to do anything, then you should check the radiators. For the next 20 seconds it is necessary to observe the cold mode, for 60 seconds - warm. Then you need to take 2 long electrodes for the selected type of welding, completely expend them. The condition of the transformer is checked, it should be hot, but not much, since the high level of heating indicates that the assembly circuit has been broken. Usually, after 3 electrodes burned in a row, the radiators heat up quite strongly. A small cooler cools them to an acceptable state within 2 minutes, after which you can continue to work with a high level of quality.
The welding inverter circuit is labor intensive. To assemble an inverter, you will have to have some experience. It is first necessary to determine which materials and tools will be required for the work, and then proceed to assembly. After its completion, the equipment must be checked to ensure its operability and correct construction.