The Siemens 6EP1931-2DC21 is a DC uninterruptible power supply (UPS) module designed to buffer 24 V DC control circuits when the primary supply drops. It sits between a standard 24 V DC power supply and the load, providing seamless battery-backed ride-through for PLCs, HMIs, and field I/O during line sags or short interruptions. Rated for 6 A continuous output (0...6 A in normal operation) with a peak of 6.3 A, it delivers up to 144 W of buffered power. The output voltage follows the input minus roughly 0.5 V, so the load sees nearly the same rail voltage during normal operation. The module accepts 22...29 V DC input and includes a 1 s startup delay typical, preventing nuisance battery drain during initial power-up. It uses external batteries (not included) as the energy storage medium.
Snaps onto standard 35 mm DIN rail per EN 60715 (35x7.5/15). The enclosure measures 50 mm wide, 125 mm deep, and 125 mm high — a compact footprint that fits a single DIN-rail slot, leaving room for adjacent power supplies or breakers. Input uses two screw terminals accepting 1...4 mm² (17...11 AWG); output uses four screw terminals for the same wire range. All connections are at the front, so wiring doesn't require side clearance — the 0 mm left and right clearance spec means it can be mounted flush against other modules. IP20 rated — suitable for clean, dry control cabinets only. Not for washdown or outdoor use without an enclosure.
Status signals and alarm contacts
Contact rating is DC 60 V / 1 A or AC 30 V / 1 A. LED indicators on the front panel show operating state: green for normal, yellow for buffered mode, red for alarm (low battery or battery replacement needed). The alarm LED flashes at roughly 0.25 Hz when battery replacement is required. The prewarning threshold is set at battery voltage below 20.4 V DC, giving the control system time to execute an orderly shutdown before the battery is fully depleted.
Carries cULus listing per UL 508 and CSA C22.2 No. 107.1 (File E197259), CE marking, and EAC approval. Also holds shipbuilding approvals from ABS and DNV GL, making it suitable for marine and offshore applications. EMC compliance: emitted interference per EN 55022 Class B (residential/commercial limits), immunity per EN 61000-6-2 (industrial environment). MTBF at 40 °C is rated at 1,085,776 hours — over 120 years mean time between failures under continuous operation at that temperature, reflecting solid-state design with no moving parts.