Siemens SIMATIC S7-400H - Connecting External Backup Current to the “EXT. BATT.” Socket

Installation of a CPU 41x-H
4-5
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
Connecting External Backup Current to the “EXT. BATT.” Socket
You can use one or two backup batteries – depending on the module type – in the
power supply modules of the S7-400 to do the following:
• Provide backup power for the user program you have stored in RAM.
• Ensure memory markers, timers, counters, system data and data in tag data
blocks remain retentive.
• Provide backup power for the internal clock.
You can achieve the same backup if you apply DC voltage between 5 V and 15 V
at the “EXT. BATT.” socket of the CPU.
The “EXT. BATT.” input has the following features:
• Reverse polarity protection
• A short-circuit current limit of 20 mA
To connect external power to the “EXT. BATT” socket, you need a cable with a
2.5 mm ∅ jack, as illustrated in the following figure. Note the polarity of the jack.
Plus pole Minus pole
2.5 mm jack
∅
Note
You will require the external incoming supply at the “EXT. BATT.” socket if you
replace a power supply module and want to provide a backup supply for the user
program stored in RAM and the data mentioned above while the module is being
replaced.