The Siemens 6ES5 951-7LD21 (PS 951) is a robust power supply module engineered for the legacy SIMATIC S5-115U and S5-115H PLC systems. This unit converts 120-230 VAC input power into a stabilized 5 VDC output, supplying either 7 A or 15 A to the backplane bus to support central processing units and I/O modules. It is designed to maintain system stability in demanding industrial environments, such as automotive manufacturing, power generation, and metal processing, by protecting sensitive logic circuits from AC line fluctuations and voltage instability.
Features
Designed specifically for SIMATIC S5-115U and S5-115H rack systems.
Provides reliable 5 VDC output for backplane bus distribution.
Integrated short-circuit and overvoltage protection for rack safety.
Passive convection cooling design for operation in enclosed industrial cabinets.
Front-panel status indicators for real-time monitoring of input and output voltage health.
Applications
This power supply module is a critical component for maintaining uptime in legacy Siemens S5-115 series PLC installations. It is typically deployed in large-scale automation systems where consistent DC power is required for CPU operation and extensive I/O configurations.
Technical Specifications
Model
6ES5 951-7LD21
Brand
Siemens
System Series
SIMATIC S5-115U / S5-115H
Module Type
Power Supply Module (PS 951)
Input Voltage
120 VAC to 230 VAC
Output Voltage
5 VDC
Output Current
7 A / 15 A
Operating Temperature
0 to 60 deg C
Status
Discontinued
Installation Guidelines
Ensure the PLC rack is powered down before inserting or removing the power supply module.
The module relies on passive convection cooling; ensure adequate clearance above and below the unit in the control cabinet to maintain airflow.
Verify that the input voltage matches the module rating before applying power.
Ensure the module is fully seated in the subrack to guarantee proper contact with the backplane bus pins.
Handle with care to avoid damage to the connector pins; use standard ESD protection practices during installation.
FAQ
Is this module compatible with S5-135U or S5-155U systems?
No, the 6ES5 951-7LD21 is specifically designed for the mechanical and electrical requirements of the S5-115U and S5-115H series. It is not intended for use in the larger S5-135U or S5-155U rack architectures.
Does this unit include a backup battery?
No, this specific version does not include an integrated backup battery. It relies on internal capacitors for short-term ride-through capability during minor power interruptions.
