The Siemens 6EP1931-2FC21 is a DC uninterruptible power supply (UPS) module from the SITOP family, designed to buffer 24 V DC control voltage when the primary supply dips or fails. It accepts 22 to 29 V DC input and delivers up to 40 A continuously, with a peak of 42 A for short periods. Active power is rated at 960 W typical. In normal operation, a green LED signals OK, and a floating changeover contact confirms the input voltage is above the cut-in threshold. When the input drops, the module switches to buffered mode, drawing from an external battery module — a yellow LED and a separate changeover contact indicate battery-active status. Prewarning at battery voltage below 20.4 V DC triggers a red alarm LED and switches the alarm contact.
The 40 A rated current is the continuous load the module can support in normal operation; the 42 A peak covers motor inrush or capacitive loads during startup. If your control cabinet draws 35 A steady with occasional spikes, this module holds without tripping. Output voltage follows the formula Vin minus approximately 0.5 V, so with a 24 V DC supply you get about 23.5 V at the load. The startup delay is 1 s typical — the module waits before engaging the output to allow the primary supply to stabilize. Storage and transport tolerate -40 to +85 °C.
Snaps onto DIN rail EN 60715 35x7.5/15 — standard 35 mm rail. Enclosure dimensions are 102 mm wide, 125 mm high, 125 mm deep. The top clearance required is 50 mm; left and right clearance is 0 mm, so modules can be butted side-by-side. Bottom clearance is 50 mm for wiring access. Input and output each use two screw terminals accepting 0.33 to 10 mm² (22 to 7 AWG). The signaling contacts are rated for DC 60 V / 1 A or AC 30 V / 1 A — sufficient for driving PLC digital inputs or indicator lamps.
Carries CE marking, cULus listing under UL 508 and CSA C22.2 No. 107.1 (File E197259), plus EAC approval. DNV GL and ABS shipbuilding approvals are on file. Emission limits meet EN 55022 Class B; immunity meets EN 61000-6-2. Protection class is IP20.