Siemens 3RW4037-1BB04 SIRIUS 3RW40 Soft Starter

The Siemens 3RW4037-1BB04 is a compact soft starter from the SIRIUS 3RW40 series. It is designed for three‑phase asynchronous motors rated at 37 A (typical motor power 18.5 kW at 400 V AC). The soft starter reduces inrush current and mechanical shock during motor starting and stopping by controlling the voltage ramp. It features an integrated bypass relay that, after the start-up phase, bridges the thyristor stack, eliminating power dissipation and allowing continuous operation without active cooling. The device includes a torque control function, making it suitable for pumps, fans, compressors, and conveyor systems.

Technical Specifications

Functional Description

The soft starter uses microprocessor‑controlled thyristors to reduce the initial voltage applied to the motor. This minimizes mechanical stress on the drive train and reduces electrical surges. The user can set a start ramp time (0–20 s), a current limit (120–500% of Ie), and a stop ramp time for smooth deceleration. The torque control feature linearises the motor torque during starting, preventing sudden jerks. The integrated bypass closes automatically after the start ramp completes, removing the thyristors from the circuit and eliminating heat loss.

Protection and Diagnostics

The 3RW4037-1BB04 includes motor thermal protection (I²t simulation), phase failure detection, and thermistor (PTC) input for additional motor protection. An alarm output indicates overtemperature, line fault, or electronic overload. The unit features a 2‑line LED display for parameter adjustment and fault indication. The last four errors are stored in memory. The device also has a manual reset button on the front.

Applications

Typical applications include pumps (to reduce water hammer), fans (to reduce belt slippage), compressors (to lower inrush current), and conveyors (to reduce shock loading). The torque control mode is especially useful for high‑inertia loads, such as ball mills and centrifugal separators.

Installation and Wiring

Mount the soft starter on a DIN rail (35 mm) or panel. Connect the mains supply to terminals 1/L1, 3/L2, 5/L3 and the motor to 2/T1, 4/T2, 6/T3. The control inputs are 24 V DC (sink/source). An external 24 V DC supply is required for the control electronics. For remote operation, connect a start/stop pushbutton to the digital inputs. The unit is designed for ambient temperatures up to 60°C, but derating applies above 40°C.

Conclusion

The Siemens 3RW4037-1BB04 soft starter provides reliable, energy‑efficient motor starting with integrated bypass and torque control, suitable for a wide range of industrial machinery.