Backup Battery (Option) - Siemens SIMATIC S7-400 Reference Manual

3.3

Backup battery (option)

Introduction
The power supply modules of the S7-400 have a battery compartment for one or two backup
batteries. Use of these batteries is optional.
Function of the backup batteries
If backup batteries have been installed, the parameters set and the memory contents (RAM)
will be backed up via the backplane bus in CPUs and programmable modules if the power
supply module is turned off or the supply voltage fails. The battery voltage must be within the
tolerance range.
In addition, the backup battery enables you to carry out a restart of the CPU after power-on.
Both the power supply module and the backed up modules monitor the battery voltage.
Insert backup battery
Activate battery monitoring once you have installed one or two backup batteries. Make sure
that neither the respective LED BATT1F or BATT2F nor the LED BAF are illuminated. Only
then is the backup battery working properly and backup guaranteed as described above.
Note
Insert the power supply module in the rack and switch it on before you insert the backup battery
for the first time. This will increase the service life of the backup battery.
Power supply modules with two backup batteries:
Some power supply modules contain a battery compartment for two batteries. If you use two
batteries and set the switch to 2BATT, the power supply module defines one of the two batteries
as the backup battery. This assignment remains in force until the battery is empty. When the
backup battery is completely discharged, the system switches to the reserve battery which is
then in turn used as the backup battery for the duration of its life. The status "backup battery"
is also stored in the event of a power failure.
Battery type
You may only use batteries certified by Siemens! (see Appendix C: Spare parts (Page 429)).
The batteries can form a passivation layer. Depassivation takes place when the batteries are
inserted in the power supply module.
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
Power supply modules
3.3 Backup battery (option)
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