Read solar panel voltage and battery voltage using 1 arduino nano

[khurramf]

I am trying to build a solar panel powered box for some low power circuitry (using a small solar charge controller) and would like to measure solar panel voltage+current, battery voltage and load current. I am having a real trouble deciphering how to measure the 2 voltages on the same nano. According to what I have read, I have to connect the gnd from the voltage divider circuitry to the nano ground and also to the voltage source negative side.

In my case, I have 2 negative sides: the solar panel and the battery. I dont believe I can connect these 2 together to the arduino ground. Can someone please confirm if this is correct or not. If not, what are my options?

Thanks

[jremington]

The Arduino measures voltage with respect to its own ground, so to measure several voltages, you must connect all the grounds together.

Please post a photo of a hand drawn circuit diagram for your setup (not a Fritzing diagram).

[khurramf]

jremington:
The Arduino measures voltage with respect to its own ground, so to measure several voltages, you must connect all the grounds together.

Please post a photo of a hand drawn circuit diagram for your setup (not a Fritzing diagram).

Please take a look at the attached picture. The problem connection is shown in red. I am not showing full connections (current, controller load, etc) to keep it simple.

Thanks.

[jremington]

What is the "voltage sensor" mystery box?

If you want help with a circuit, post a complete circuit diagram, identifying all the components and their values, and post links to the modules used.

[khurramf]

jremington:
What is the "voltage sensor" mystery box?

If you want help with a circuit, post a complete circuit diagram, identifying all the components and their values, and post links to the modules used.

The voltage sensor is this. Sorry for the omission.

[JCA34F]

That "sensor" is just a 5:1 voltage divider, the V out will be 1 / 5 the voltage in. What is the voltage difference between solar - (ground) and battery - (ground)?

[jremington]

Your photo, posted properly. See image posting guide.

Of course you forgot to post a link to the "solar charger", but if the two "-" connections are common on the charger module, the ground connection in red is already made.

Do yourself a favor and get a decent multimeter, so that you can check voltages, continuity and resistance.

Do not use a lithium based battery in this circuit, if the battery is also loaded. There are no charger modules on the hobby market that can safely charge a lithium battery under load.

[Wawa]

Solar chargers can have a common negative, but more often a common positive.
Measure it.

But why are you interested in solar 'voltage', which is somewhat irrelevant.
I would measure battery voltage (negative to Arduino ground), and solar/charging current (high-side).
That could be done with an INA226 breakout board.
Leo..

[khurramf]

jremington:
Your photo, posted properly. See image posting guide.

Thanks for the info. I will keep this in mind in the future.

Of course you forgot to post a link to the "solar charger", but if the two "-" connections are common on the charger module, the ground connection in red is already made.

Do yourself a favor and get a decent multimeter, so that you can check voltages, continuity and resistance.

It is a small chinese generic charger and does not come with a manual. The positives are connected together as mentioned in Wawa's post below. I don't know which resistances you want me to measure or why but the solar-to-battery resistance is about 17 Kohm and battery-to-load resistance is 24 Kohm. The solar panel rating is 15 Watts, max 18 Volts and the battery is 12 volts.

Do not use a lithium based battery in this circuit, if the battery is also loaded. There are no charger modules on the hobby market that can safely charge a lithium battery under load.

I am aware of this. I am using a small lead acid battery. Thanks for the warning though.

Wawa:
Solar chargers can have a common negative, but more often a common positive.
Measure it.

Yes, you are right in my case; the positives are connected together.

But why are you interested in solar 'voltage', which is somewhat irrelevant.
I would measure battery voltage (negative to Arduino ground), and solar/charging current (high-side).
That could be done with an INA226 breakout board.

I would like to measure solar panel voltage and current so that I can calculate solar radiation as per this.

I would measure battery voltage (negative to Arduino ground), and solar/charging current (high-side).
That could be done with an INA226 breakout board.

Can you please explain what do you mean by "solar/charging current (high-side)"? Do you mean the current from the solar panel?

Thanks for the replies.

[Wawa]

Solar radiation is AFAIK done with a short-circuited solar cell (current only), not by measuring solar voltage.
I wouldn't trust that article.

High-side means in the battery (or panel) + line.
There you can measure/log solar>battery charge current and battery discharge (load) current.
Solar generation is IMHO more practical than knowing solar radiation.
Leo..

[jremington]

As above, to measure solar irradiance, you measure the short circuit PV cell current. The article you linked is simply wrong.

For an Arduino, it is a reasonable approximation to measure the voltage across a low value resistor "short circuiting" a small solar panel (e.g. 6V). Use the 1.1V Arduino reference, and a resistor value that produces about 1V under full sun at noon.

[khurramf]

Wawa:
High-side means in the battery (or panel) + line.
There you can measure/log solar>battery charge current and battery discharge (load) current.
Solar generation is IMHO more practical than knowing solar radiation.

I plan to use an ACS712 to measure the current. The docs say to connect this in series after the load. To measure panel current, should connect ACS72 to solar panel +? To measure load current, I should connect another ACS712 to battery + or load +?

Thanks

[jremington]

To measure load current, you can connect the ACS712 between load and ground. The voltage drop is negligible.