The SITOP DC UPS 6EP1931-2DC31 is the RS-232-equipped variant of Siemens' 6A 24VDC uninterruptible power supply module. It provides the same seamless battery backup for PLCs, HMIs, and small automation loads while adding a galvanically isolated serial port for real-time PC monitoring of UPS status, input/output voltages, load current, and battery charge level.

Serial Communication

The RS-232 interface operates at 9600 baud (8N1) via a 9-pin SUB-D connector, using only three active pins (RxD, TxD, RTS). It outputs 5-character plain-text status strings — BUFRD (battery ready), ALARM (fault), *BAT* (normal), BA>85 or BA<85 (charge level) — every 84ms. No proprietary driver is required; any terminal or COM port application can read the data. The free SITOP DC UPS Software tool from Siemens provides graphical monitoring, data logging, and remote timer-start control.

Core UPS Functionality

Identical in power performance to the base 2DC21 model: 22-29VDC input range, 24VDC output at up to 6A (144W), 95% normal-mode efficiency, and seamless sub-millisecond transition to battery. Ten DIP switches configure the cut-in threshold, buffering duration, charging current, and end-of-charge voltage. Three floating signal contacts provide relay-based status outputs independent of the serial link.

Key Decision Parameters

Compatible battery modules are ordered separately. For modern USB connectivity, see the 6EP1931-2DC42 variant.