Siemens 6ES5951-4LB11 Power Supply | 5V 20A, 24V 1A, 124W

This power supply unit energizes SIMATIC S5 backplanes and I/O modules. The Siemens 6ES5951-4LB11 mounts directly into the S5 rack’s leftmost slot. You can rely on this unit for continuous operation in factory environments. Its robust design provides stable DC power to all connected modules.

Physical Dimensions and Hardware Layout

The Siemens 6ES5951-4LB11 measures 25.0 cm in overall width. Its total height reaches 28.0 cm including the front panel. This power supply unit weighs approximately 2.80 kg. A metal enclosure provides excellent heat dissipation and shielding. Three LEDs display input power, output status, and overload conditions. The unit fits standard S5 6U height racks exclusively.

Input and Output Specifications

This unit accepts 85 to 132V or 170 to 264V AC input voltage. A manual selector switch sets the correct input range. The Siemens 6ES5951-4LB11 delivers 5V DC at 20A for the backplane. It also provides 24V DC at 1A for external field devices. Built‑in overload protection shuts down outputs during short circuits.

Parameter	Specification
Product Type	Rack-mounted power supply
Input Voltage (Selectable)	85‑132V AC or 170‑264V AC
Input Frequency	47 to 63 Hz
Inrush Current	30A max at 230V AC
Output Voltage (Backplane)	5V DC ±2%
Output Current (Backplane)	20A continuous
Output Voltage (External)	24V DC ±5%
Output Current (External)	1A continuous
Output Power (Total)	124W
Ripple and Noise (5V)	< 20 mV peak‑to‑peak
Efficiency	82% typical
Hold‑Up Time	30 ms at full load
Dimensions (W x H x D)	250 mm x 280 mm x 210 mm
Weight	2.80 kg (6.17 lbs)
Terminal Type	Screw terminals (input, external output)
Backplane Connection	48‑pin DIN connector
Number of Components	1 main board, 1 heatsink, 1 fan
Internal Energy Storage	2200 µF capacitor bank
Protection Features	Overload, short circuit, overvoltage
LED Indicators	Power (green), output (green), overload (red)
Cooling Method	Forced air with internal fan
Operating Temperature	0°C to +55°C

Energy Storage and Hold‑Up Performance

A 2200 µF capacitor bank stores energy for brief power interruptions. The Siemens 6ES5951-4LB11 provides 30 ms of hold‑up time at full load. This storage allows the CPU to complete critical operations safely. Consequently, system shutdowns occur gracefully rather than abruptly.

Protection Circuits and Diagnostic Features

Overload protection activates when backplane current exceeds 22A. Short circuit protection responds within 50 µs of fault detection. The Siemens 6ES5951-4LB11 latches off during overvoltage events. A red overload LED illuminates when any protection trips. Cycle the input power to reset the unit after fault removal.

Installation and Wiring Guidelines

Insert the unit into the leftmost slot of the S5 rack. The Siemens 6ES5951-4LB11 connects to the backplane via a 48‑pin DIN connector. Set the input voltage selector before applying power. Connect external field devices to the 24V output screw terminals. Use wire sizes from 0.5 to 2.5 mm² for all connections.