How to Power my Arduino

[metrologist]

I have my Arduino project ready to connect to a solar panel and take voltage and current readings. I thought it would be easy to use the solar charge controller USB output to power the micro, but the solar panel negative and controller grounds are isolated - connecting them can cause 6 amps to run through that ground connection.

The current sensor is a hall effect so is isolated, but the voltage measurement is via a 100k/10k divider to an analog pin and needs to have a ground reference to the solar panel, so I think I am looking for an isolated DC/DC converter.

What would be good to power from 12V SLA battery that will have good voltage regulation, good enough for a reference voltage. I know I have a few of the ebay buck modules.

[Cyberdragon]

Buck converters aren't isolated, you'd need a transformer based converter.

[ez24]

Is this a real DC - DC isolator?

https://www.aliexpress.com/item/power-module-dc-12v-to-5v-2a-single-output-isolated-dc-power-supplies-dc-dc-buck/32234023692.html

Before this topic, I did not know about DC-DC isolators 

[macboy]

If your charge controller connects the positive output directly, then put the voltage divider the other way around. If the panel voltage was zero you'd measure full scale (panel gnd = VCC ) and when in full sun you'd measure closer to zero. Is just a little extra math on the Arduino to convert.

[metrologist]

If your charge controller connects the positive output directly, then put the voltage divider the other way around. If the panel voltage was zero you'd measure full scale (panel gnd = VCC ) and when in full sun you'd measure closer to zero. Is just a little extra math on the Arduino to convert.

So you are thinking the negative lead is pulse modulated and positives are connected, and bridging the negatives is about the same as connecting the solar panel direct to the battery.

Also, I was thinking a B1205S might work out.

[metrologist]

Well, I am using a meanwell isolated DC-DC converter brick that has good line regulation, from LA battery to 5V arduino pin.

I had not noticed it right away, but it sunk in later, that after connecting power to Arduino all 3 LEDs were on and one was blinking (probably signaling data write to an SD card).

Now, why would all the lights be on? I recall when powering through USB that there was just a red LED, and another green/red (or yellow) LED would flash when programming. 5V should be the right pin since the voltage is regulated.

Oh, it is working as there is an OLED display.

[metrologist]

Well, now there is one revelation and a disturbing observation.

I forgot to connect Arduino ground to the solar panel, so just the positive wire is connected. That wont cause a problem as the panel and circuit will just be a floating mass connected to an analog pin, through a 10k/100k resistor divider.

The image below is with minimal light on the panel (morning overcast), and the top line display has expected results. Usually the system draws 60mA.
I cannot explain the -31.14AHr.

The next line shows watts and max watts, and it should show 0.12W at least. The code was working but maybe I changed something at the last minute.

[metrologist]

This Arduino is a bit finicky. Sometimes when it reboots because I either hit the reset or re-apply power, it will boot up with both RX/TX leds stuck on. It seems to be running, but some of my calculated values are corrupted on boot most of the time. I do initialize them with a value. There might be some reason in the code, so I'll go revisit that thread. Powering the device is otherwise not a problem now.