Thx

 Test program

Good question!! thanks for asking (and reminding me)

Assuming there is no method to read 'system voltage' in a LOGO? 

Anyways:

I have the same requirement of checking battery voltage, but my Ohms law application sucks (i just remember P = I x V and V = I x R) But I do not know what resistance figure do you use in this situation?

About half of my installations will be Solar with either 12 or 24V power supply, i need to know too.

My thoughts:

So I know we must reduce voltage to 0-6 volts as both 12V and 24V units with AI's are 0-10V. 

The analogue amp will then be 0 to 600 (zero to 6.00 volts), and then multiplied by 2 for a 12V System or by 4 for a 24V system? 

What fixed resistors must i use in case of 12 and 24V systems to get 0-6V?

Let the comments flow...

Example of the setup.

Adjustment Potmeter (voltage divider): 15V measured value corresponds to 10V on analog input.
The maximum voltage will never exceed 15V so that the maximum analog input value remains below 10V.
Charger is permanently connected to battery and charges when required (CTEK microprocessor controlled). Max. charging voltage is 14.2V (cycle load).