Siemens 6ES5951-7NB12 Power Supply

This power supply module provides clean DC voltage for SIMATIC S5 racks. It converts AC line power into regulated 5V and 24V outputs. You can replace it without removing other modules from the rack.

Technical Specifications

Parameter	Details
Brand	Siemens
Model	Siemens 6ES5951-7NB12
Category	Power Supply Module (SIMATIC S5 Series)
Dimensions (H x W x D)	250 mm x 45 mm x 210 mm
Weight	1.25 kg
Input Voltage	85–132 V AC or 170–264 V AC (selectable)
Input Frequency	47–63 Hz
Output Voltages	5 V DC ±2% / 24 V DC ±5%
Output Current (5V)	10 A continuous
Output Current (24V)	1 A continuous
Total Output Power	74 W maximum
Internal Components	1 transformer + 2 rectifiers + 4 filter capacitors + 1 PCB
Number of Filter Capacitors	4 units (2200 µF each for 5V rail)
Total Energy Storage	8800 µF on 5V rail / 1000 µF on 24V rail
Interface Type	Backplane connector + 1x AC input terminal block
Isolation	2500 V AC between input and outputs
Efficiency	Approximately 82% at full load
Overload Protection	Automatic current limiting (110% of rated)
Status Indicators	1 LED (5V OK)
Operating Temperature	0°C to 60°C

Detailed Feature Overview

This module delivers 10 A at 5V for logic circuits and 1 A at 24V for I/O. Four 2200 µF capacitors store energy on the 5V rail. Consequently, brief power dips do not interrupt system operation.

The input accepts either 120V or 230V AC via a selector switch. You must set this switch correctly before applying power. The efficiency reaches 82%, which reduces heat inside the cabinet.

You will find a built-in overload protection feature on both outputs. This protection limits current to 110% of the rated value. The green LED confirms that the 5V output remains within tolerance.

Installation and Compatibility

Siemens 6ES5951-7NB12 occupies the leftmost slot in an S5 rack. Connect the AC input wires to the screw terminal block. Leave 50 mm clearance around the module for proper ventilation.