For some household chores and for repairing motor vehicles and vehicles, a reliable welding inverter circuit is needed. Many inverter circuits are unreliable and have drawbacks (overheating of control elements, low power, weak welding, etc.). The presented apparatus is free from them.
The scheme of the welding inverter.
Characteristics and circuit of the inverter
Technical data of the device are as follows:
- consumption current (max) - 32 A;
- welding voltage - 220 V;
- welding current - 250 A;
- working arc (length) - 1 cm (more than 1 cm - low temperature plasma);
- electrode - 5 mm or less;
- Efficiency - better than many purchased (inverter).
The inverter circuit consists of two parts:
Figure 1. Diagram of an inverter power supply.
- Power supply (Figure 1). All winding data is shown in the image. Transformer - W-shaped ferrite (W8x8 or 7Х7). According to the instructions, the windings should fill the entire width of the opening for better stabilization of current and voltage.
- Inverter (Figure 2). The frequency conversion of this unit - 41 kHz. The parameters of the windings with increasing frequency up to 55 kHz and other data are shown in the image.
- isolation "primary" - paper tape from the cash register;
- isolation "secondary" - fluoroplastic (to increase the conductivity of high-frequency currents);
- the output contacts of the second winding are twisted together or soldered;
- L2 (choke) is made on a W-shaped ferrite (W20x28 conductivity not exceeding 2000 nm).
Current sensor is made according to the following principle:
Figure 2. Scheme of the welding source.
- on two folded rings K30x18x7, 85 turns of 0.5 mm of the secondary wire are wound;
- 1 wire is passed through the rings - this is the “primary”.
The high-frequency transformer is wound with copper tape (40 mm and 0.3 mm long and 40 mm thick, respectively) or a tin of the same material. Insulation of the layers is carried out by tape from the cash register apparatus (due to high strength).
It is impossible to wind the high-frequency transformer with a normal wire (as stated in the instructions). High-frequency currents always go not on the full cross-section of the wire, but on its surface. A large current is applied to a small surface area, and not to the volume of the wire. Because of this, the wire heats up (skin effect).
To eliminate this effect, a large area of conductor, such as copper tape, is needed. Many people make a mistake and wind up with a lot of thin wires, but the presence of air gaps between them reduces heat transfer. Such a winding does not always fit into the openings of the core.Back to table of contents
Figure 3. For forced blowing of the device, it is necessary to insert a fan and a thermal sensor mounted on an RF transformer or radiator into the circuit.
According to the instructions, the source of the RF current and any device operating in the inverter mode (Figure 3) requires forced airflow. To do this, you can insert a fan and a thermal sensor attached to an RF transformer or radiator in the circuit.
It is also necessary to install all the powerful elements on the radiators, for example, from the CPU coolers.
The components of an oblique bridge (diodes HFA25 and HFA30) are put on one radiator through a mica pad, and the diodes IRG4PC50W are smeared with a paste (conductive) and screwed onto the second.
The conclusions of the details of the first radiator are installed to meet the counter elements of the second, and between them (guided by the scheme) they solder the power board of 300 V.
The instruction indicates that 10-14 capacitors with a nominal value of 0.15 microfarads - 630 V should be inserted into this circuit (to smooth out surge currents and key voltages).
C15 and C16 must be installed brand SVV-81 or K78-2. They play a special role:
- suppress resonant bursts of the high-frequency transformer;
- when turned off, IGBT loss is reduced.
IGBT opening time is significantly less than their closure. During locking, the C16 and C15 are recharged through the VD31 and VD32 for much longer closure. This node takes power and, accordingly, reduces the risk of overheating of the elements by almost 3 times with an unequal IGBT switching time. When opening, the IGBT node is smoothly discharged through R24 R25, and all power is allocated to them.
Materials and tools:
- copper tape wires;
- electronic parts;
- soldering iron with tin and rosin;
- screwdriver, pliers, awl.
After every 2-3 electrodes, you must wait 2-3 minutes to avoid overheating of the elements of the apparatus.