The SITOP DC UPS 6EP1931-2DC21 is Siemens' entry-level uninterruptible power supply module for 24VDC industrial circuits. It buffers connected loads against mains failures and voltage dips by seamlessly switching to an external battery module, making it suitable for protecting PLCs, HMIs, sensors, and small automation controllers from data loss and unplanned downtime.

How It Works

In normal operation, the module passes 24VDC from the upstream power supply through to the load while trickle-charging the connected battery. When input voltage drops below the DIP-switch-configurable threshold (22-25.5V), the unit switches to battery power in under a millisecond. Output during buffering is approximately input voltage minus 0.5V. Once mains returns, the module reverts to normal mode and recharges the battery.

Protection and Signaling

The module includes reverse polarity protection on both input and battery terminals, short-circuit-proof output with dynamic current limiting, and LED indicators for normal operation (green), buffering mode (yellow), and alarm conditions (red). Three floating signal contacts — OK/Bat, Alarm/Bat, and Battery >85% — allow remote status monitoring via a PLC or supervisory system. A red flashing LED warns when battery replacement is needed.

Installation and Configuration

Snap-on DIN rail mounting (EN 60715 35mm) with side-by-side installation capability. All connections use screw terminals accepting 1-4mm² wire. A 10-position DIP switch configures the cut-in threshold, buffering time (5-315s or continuous), charging current (0.2A/0.4A), and end-of-charge voltage. The module occupies 50mm of rail width and requires 50mm clearance above and below for convection cooling.

Key Decision Parameters

Compatible battery modules from the SITOP BAT series are ordered separately. For applications requiring PC-based monitoring and remote control, consider the 6EP1931-2DC31 (RS-232) or 6EP1931-2DC42 (USB) variants of this module.