Siemens 6ES5551-3UA11 – Mass Storage Module for SIMATIC S5 Programs

The Siemens 6ES5551-3UA11 stores backup copies of PLC programs and system data. This storage module measures 250 mm in depth and 25 mm in width. It fits standard SIMATIC S5 rack slots without any modifications. The unit weighs 0.41 kg, making installation quick and straightforward.

Storage Capacity and Memory Technology

This mass storage module holds 64 kB of program data in non-volatile memory. The Siemens 6ES5551-3UA11 uses battery-backed RAM to retain data during power loss. A long-life lithium battery maintains stored content for up to three years. The module stores complete program blocks, data blocks, and system parameters. It supports both read and write operations from the central processing unit.

Internal Architecture and Component Layout

The module contains two separate circuit boards inside its plastic housing. One board holds the RAM chips, while the other manages memory control logic. The Siemens 6ES5551-3UA11 includes a dedicated controller for memory access arbitration. A 48-pin edge connector interfaces with the S5 backplane for power and data. The module stores 100 µF of capacitance for power supply filtering only.

Battery Monitoring and Data Protection

The Siemens 6ES5551-3UA11 includes a battery voltage monitoring circuit on its main board. This circuit triggers a warning LED when battery voltage drops below acceptable levels. A write-protect switch prevents accidental overwriting of stored program data. The module retains data even when you remove it from the rack. You can replace the lithium battery without losing stored information.

Power Requirements and Environmental Tolerance

The Siemens 6ES5551-3UA11 draws 120 mA at 5V DC from the backplane supply. It also draws 10 µA from the backup battery during power-off conditions. The module operates reliably from 0°C to 60°C ambient temperature. It tolerates humidity levels up to 95 percent without any condensation issues. The unit withstands vibration up to 2g from 10 to 500 Hz.

Below is a complete summary of its technical specifications.

The Siemens 6ES5551-3UA11 replaces older EPROM-based storage modules in S5 systems. You do not need any special programmer or UV eraser for this module. This unit also supports online backup without stopping the PLC program. Consequently, it provides reliable program storage for critical industrial processes.