EXT. BATT. connector - connecting 12V battery with charger

Hi all

We would like to use the EXT.BATT. connection on the CPU in our rack, because we find that the battery that we put in the PS405 doesn't keep the memory on for long enough.

My idea was to use a car battery (or a small 12V battery that is used in alarm systems), connect that to the CPU, and also connect the 12V battery to a trickle charger to extend its lifespan.

Will this work?

Hi,

To connect an external battery to an S7-400, you must take into account the requirements indicated in the manual: https://support.industry.siemens.com/cs/us/en/view/109818285/86223983371

in the section "Power Input...." come the requirements: The "EXT.-BATT." input has the following features:

Polarity reverse protection

Short-circuit current limiting to 20 mA

Hello,

The life of the battery (6ES7 971-0BA00) is based on the modules and CPU installed on the rack itself.

It can be calculated using the backup current of each item.

1. Details on how to calculate the duration can be found here: 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?
2. If you would like not to use batteries anymore, you can avail a stabilized source and connect it to EXT. BATT jack on the CPU itself. That supply should be 5..15VDC. Please refer to sec. 2.1 of this manual : SIMATIC S7-400 S7-400 Automation System, CPU Specifications