Product Description:

The PST6250.680-L is a thyristor power unit delivered by Bosch Rexroth Indramat within the PST Thyristor Power Units series. This solid-state module is intended for industrial resistance welding equipment where precise regulation of transformer primary current is required. By firing its thyristors in two phases, it converts line voltage into controlled pulses that match the duty cycles demanded by automated welding controllers.

The firing electronics use an isolated 24 V DC control supply, while the main line stays on a two-phase path that the unit commutates with zero-cross firing. Heat from conduction losses is removed by forced-draft air cooling; under rated conditions, the cabinet dissipates 70 W and the cooling air may not exceed 45 °C. An internal 2.2 kΩ de-excitation resistor suppresses transformer magnetizing energy when conduction ends, and a MOV limits voltage surges. Continuous operation is allowed up to a maximum ambient temperature of 55 °C, but built-in logic enforces a duty cycle of 50% to keep junction temperatures within limits. For installations using large weld transformers, the permissible transformer rating extends to 250 kVA. The module exchanges timing and diagnostic data through a DeviceNet timer interface, and it must be mounted with at least 100 mm clearance in cabinets installed below 2000 m altitude.

For field wiring, the power terminals accept copper conductors up to 95 mm², allowing short leads to weld transformers without excessive voltage drop. During each conduction window, the silicon path carries a nominal system current of 200 A, giving predictable secondary current when combined with the transformer turns ratio. The enclosure is rated IP20, so it requires placement inside a protected control cabinet while allowing direct touch-safe access for service tools.