I am working on a datalogger to measure the voltage of a series of solar modules. I have 4 solar modules in series, let say 35V each. I am using an ADS1115 for the measurements. First I wanted to do differential measurements, but this is not possible as the voltage between the some of the pins of the ADS will exceed the max.
Now I will something simple, reference the series solar modules to the the measurement circuit and measure the voltage from the divider as in the drawing:
I want to add a voltage follower before the the voltage divider in order to not load the sources in a different way. The problem is I cannot find a (cheap) op amp to do this, that is rated above 150V. Is there a reason for this? I there another way to achieve a nice way to measure the voltage in series? how is it done on high voltage battery packs for example?