Product Description:

The PST6250.100-L thyristor power unit is produced by Bosch Rexroth Indramat and belongs to the PST Thyristor Power Units series. As a two-phase supply with an integrated weld timer, it delivers controlled current pulses to resistance-welding transformers used in automated assembly lines. The device links plant mains to the welding electrodes, coordinating timing, amplitude, and duty so each weld seam receives identical energy. Because the timer and power semiconductors are combined in one housing, cabinet wiring is simplified and cycle accuracy improves.

On the line side, the unit draws up to 200 A from a grounded TN or TT system. Conductors terminate on lugs rated for 95 mm², which helps keep conductor temperature within limits during peak pulses. The enclosure has an IP20 rating, so it must be installed inside an IP54 cabinet with either vertical or rear mounting and at least 100 mm of clearance above and below for airflow. An integrated auxiliary supply provides 24 V DC to power contactors, sensors, and the battery-buffered RAM without a separate supply module. Weld sequences can run at up to a 50 % duty cycle; above this value, heat dissipation could exceed the allowed 360 W of cooling losses.

The thyristor stack can energize a matching welding transformer rated at 224 kVA when application duty is limited to 20%, or 141 kVA at the 50% setting. Internal firing circuits address up to 256 electrodes, allowing a single power unit to cycle through multiple welding heads under one controller. During continuous production, the switch cabinet adds 170 W of thermal load on top of the basic 69 W losses in quiescent operation, and onboard temperature sensors monitor these conditions relative to the 2000 m operating altitude limit. The auxiliary supply delivers 2 A, which provides enough capacity for external I/O and for logic protected by metal-oxide varistors during overvoltage events.