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Module Overview
This power supply module provides regulated 24V DC to S5 rack components. You can install Siemens 6ES5951-7ND21 directly into the leftmost slot of any S5 chassis. The unit converts AC line voltage into stable DC power for backplane distribution. It supports all CPU and I/O modules within the same rack.
Technical Specifications
| Parameter | Value |
|---|---|
| Dimensions (W x H x D) | 250 mm x 25 mm x 130 mm |
| Weight | 0.72 kg |
| Input voltage range | 85V to 264V AC (universal) |
| Input frequency | 47 Hz to 63 Hz |
| Output voltage | 24V DC (regulated) |
| Output current rating | 5.0 A continuous |
| Output ripple | < 50 mV peak-to-peak |
| Output protection | Overcurrent and short-circuit |
| Efficiency | > 85% at full load |
| Hold-up time | 25 ms at 5A load |
| Status indicators | 1 green LED (output OK) |
| Interface to backplane | S5 rack backplane connector |
| Total onboard components | 178 discrete parts |
| Energy storage type | Large electrolytic capacitors |
| Energy storage rating | 2200 µF at 400V DC (primary) |
| Operating temperature | 0°C to +60°C |
Board Layout and Components
The PCB separates primary and secondary circuits with a safety isolation barrier. Large electrolytic capacitors store 2200 µF of energy on the primary side. Moreover, 178 discrete parts include switching transistors and output regulation circuits. A passive heatsink covers the switching components for cooling. Consequently, the module delivers stable power without external fans.
Installation Process
You can mount Siemens 6ES5951-7ND21 into the leftmost slot of any SIMATIC S5 rack. The backplane connector distributes 24V DC to all other rack modules. Furthermore, the front panel includes a standard AC input terminal block. A green LED confirms output voltage presence at all times.
Performance Advantages
This module operates on any AC voltage from 85V to 264V without jumpers. The 25 ms hold-up time bridges short power interruptions successfully. Therefore, the PLC continues running through momentary dips or brownouts. The built-in short-circuit protection also prevents rack damage from wiring faults.
Safety and Compliance
Siemens 6ES5951-7ND21 meets CE, UL, and RoHS standards. The primary capacitors take 60 seconds to discharge below 50V. Hence, technicians must wait one minute before servicing internal components.