# 150V voltage follower

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?

• You could increase the resistors by a factor of 10 and then buffer the divider outputs with a cheap quad amp. The loading would be pretty minimal. – Peter Smith Sep 12 at 10:42
• High voltage starts from 1000$V_{DC}$. I hope you don't mind I removed "high voltage" from the title, as this title would give incorrect search results. – Huisman Sep 12 at 19:35
• @Huisman, that definition varies with the context. In power engineering, for example, 10 to 20 kV would be considered medium voltage whereas in, say, a valve amplifier the "high tension" supply could be considered high voltage - and certainly is in relation to the audio signal - especially if you touch it. The edit to the title is fine though. – Transistor Sep 12 at 20:10