An important element in the particular design of any welding machine is the adjustment of the operating current. Industrial devices carry out this by shunting using chokes of various types, changing the magnetic flux or magnetic shunting, using active ballast rheostats and resistances and rheostats. The disadvantages of such adjustments lie on the surface: the complexity of the design, the massiveness of the resistances, their high heating, inconvenience when switching.
Necessary
- - transistors such as P416, GT308;
- - variable resistor SP-2;
- - MLT resistors;
- - capacitors MBT or MBM 400 V
Instructions
Step 1
Make a secondary winding when winding the welding transformer. Change the current by switching the number of turns. This is the best option. But this method can only be used to adjust the current; it is not used to adjust it over a wide range. It is worth saying that this method is associated with certain problems. First of all, with the fact that a significant current passes through the regulating device, which leads to its bulkiness, and for the secondary circuit it is impossible to choose powerful standard switches that would withstand a current of up to 200 A. 5 times weaker.
Step 2
Assemble the thyristor regulator. The element base is available, it is easy to operate, does not need to be configured and has proven itself well in the process. Power regulation is carried out by periodically switching off the I-th winding of the welding transformer for a specified period of time at each half-cycle of the current. In this case, the average current decreases.
Step 3
Connect the main elements of the regulator (thyristors) in parallel and opposite to each other. They will alternately open with current pulses, which are formed by transistors VT1, VT2. When power is applied to the regulator, both thyristors are closed, capacitors C1 and C2 begin to charge through the variable resistor R7. When one of them reaches the voltage of the avalanche breakdown of the transistor, the latter will open the way for the discharge current of the capacitor connected to it. Then the corresponding thyristor opens, which connects the load to the network. At the beginning of the next half cycle, everything is repeated, but vice versa, in reverse polarity.
Step 4
Adjust the moment of turning on the thyristors by changing the resistance of the variable resistor R7 from the beginning to the end of the half-period. This leads to a change in the total current in the 1st winding of the welding transformer. To decrease or increase the adjustment range, change the resistance of the variable resistor R7 down or up, respectively.
Step 5
Replace the resistors R5, R6, which are included in the base circuits and transistors VT1, VT2, which operate in avalanche mode, with dinistors. Connect the anodes of the dinistors to the extreme terminals of the resistor R7, and connect the cathodes to the resistors R3 and R4. For the current regulator assembled on dinistors, use devices of the KN102A type. Use transistors such as P416, GT308 as VT1, VT2, but you can replace them with modern high-frequency low-power ones with similar parameters. Use a variable resistor of the SP-2 type, others of the MLT type. Capacitors such as MBT or MBM with an operating voltage of 400 V. The regulator does not require adjustment, only make sure that the transistors are stable in avalanche mode.
