Titel: wie das Sichern s7 400 mit zwei Akku
Title: backing-up a S7 400 with two batteries

Hello Friend;

I have a doubt regarding the backup battery in our S7 400.

We have option for two backup batteries, our real problem is that we are planning activities for a month-long shutdown of the switchgear after the pre commissioning, it is possible for us to keep the logic fed to the S7 400 with the ram of backup batteries?

There are 2 batteries so it is possible to replace them to prevent the backup batteries in sequence in order (to limit) battery consumption and thus save the RAM memory. Tto my knowledge we only make use of one backup battery at a time and the second one acts as reserve battery. so my idea is to switch to a backup battery every two or three days. Even when changing the battery, the other battery will be active and maintenance of RAM.

I expect a concrete answer from the experts.

Thank you

How great is the power requirement (from the backup battery) of the modules to be backed up at "Power Off" and what is the relationship between the backup current and the length of the backup time?

Backup time = Total battery power / Total load;
Total battery power = 2 * 2.3 Ah * 0.63 = 2.9 Ah;
Total load = 100 μA + 125 μA = 225 μA;
Backup time = 2.9 Ah / 225 μA = 12888 h = 537 d = 18 m = 1.5 y;

The constellation above therefore results in a backup time of approx. 1.5 years.

Depending on the backup current and the required buffer time, it may make sense

• to use two batteries in the power supply;
• or, alternatively, to use an external backup, e.g. via a 9V monobloc battery, connected to the CPU (manual "S7-400 CPU Data, sect. 1.1, Entry ID 14016796). Furthermore, a battery box is available that permits you to use a standard lithium battery of the D type (mono). More information is available from your Siemens sales partner.

And:

Where can you find information about the S7-300/400 backup batteries?

So basically, you can backup yourCPU RAMfor the shutdown period with a pair of new batteries or by using the power jack on the CPU in order to connect an external power source (we use a 9V DC battery connected to an audio jack to supply power to the RAM whenever we have to remove or maintain the power supply module on our S7-400 PLC).

Hope this helps,
Daniel Chartier