Multiple voltage sources (PV+Battery)

Hi there

I’m working on measuring current and voltages on my solar system and was hoping someone would be able to point me in the right direction for 1 specific area I needed a hand with.

The attached image shows the current setup in the top half (using a Victron 100/15 charge controller) and this is working fine. I wanted to connect an arduino to measure voltage across PV and Battery and my proposal is in the bottom half of the image.

Question : Does this look like it’ll work (pls ignore resistor values for now) and specifically, am I going to blow this system because, by going through the Arduino ground, I’m essentially connecting the PV ground to battery ground. My concern is that perhaps the charge controller keeps the PV and Battery circuits isolated and I’m now connecting them?

Thanks for any advice at all !

am I going to blow this system because, by going through the Arduino ground,

No.

Looks fine to me.

I would rather use Batt- than PV- as ground reference for the Arduino.
Unless you're sure Batt- is connected to PV- inside the charge controller.

The higher voltage needs the lower resistor value to ground.
With those high resistor values you also need (100n) caps from the analogue inputs to ground.
And a micro-power buck converter to drop that 24volt.
Leo..

Wawa:
I would rather use Batt- than PV- as ground reference for the Arduino.
Unless you're sure Batt- is connected to PV- inside the charge controller.

Thanks
This is exactly my problem - I don't know if they're connected inside the CC but I am connecting both to the GND pin on the Arduino, thus shorting them and that could cause problems in the CC if those circuits are isolated...

In the solar panel charge controller I have (much cheaper than Victron, came with the panels) it is the Positive that is common between input and output. Presumably this is because the electronics for switching the low side is cheaper.

...R

@Robin2
I was expecting that.

Connect Batt- to Arduino ground, and use three analogue inputs to measure...

  1. Batt+

  2. PV+

  3. PV-

Subtract PV- from PV+ to find panel voltage.
Caps on the analogue inputs might be important, to average out the switching frequency of the controller.
Calculate the PV+ voltage divider for total open panel voltage (~85volt).
Read up about using the more stable 1.1volt Aref (or 2.56volt Aref if you're using a Mega).
Please post result and code, so we can all learn.
Leo..