Invar - ta type resistance welding power-supply unit

摘要

PURPOSE:To prevent extension of defective welding by operating an inverter circuit when welding electrodes are released and determining conditions of secondary side rectifying devices of a welding transformer based on an output signal of a primary side electric current detection means. CONSTITUTION:When the inverter circuit 14 is operated when the welding electrodes 24A and 24B are released and separated from materials to be welded, a pulse (primary side voltage) of frequency (600-2K Hz) higher than commercial frequency is impressed on a primary coil of the welding transformer 18 from the inverter circuit. When the secondary side rectifying devices 20A and 20B are normal, a secondary side current does not flow and a primary side current also does not flow. The secondary side voltage is detected as the no-load voltage. When either rectifying device is short- circuited and broken down, since it is conducted even when the reverse voltage is impressed on the rectifying device, the secondary current flows on a closed circuit between a secondary side coil and the rectifying device and according to it, the primary side current flows but the secondary side voltage does not appear. Consequently, the condition of each rectifying device is determined and abnormality can be detected from a waveform or a value of the primary side current or the secondary side voltage.