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Topic: Multiple Volt/Amp Sensors on common + rail (Read 3903 times) previous topic - next topic


From the pdf it has the same ground with arduino, and has library call to read the voltage between the current shunt  lower voltage to ground.

It's simpler but since voltage readings are sufficient for specified application, it's not as simple or cheap as a couple voltage dividers one for battery and one for panel.

And, unfortunately, I now noticed  it is rated for 3.5A, well below the 200watt solar panel output.


The INA219 will not work. At least not the way I wired them. ONE works fine. TWO or more does NOT work because EACH of them has to be connected to the Arduino ground and therefore they all have a common negative and the charger already has a common positive. The Adafruit breakout is rated at 3.5A but that Problem was easily overcome. I provided a second shunt resistor of 0.01 Ohm (off the breaker board) so that theoretically the thing can now measure ten times the current.

The way I have seen voltage dividers connected to Arduinos to measure voltage, that solution has the same Problem. ONE would work fine, TWO or more would not work because they also have a common ground to the Arduino.

Again, I may be missing something here. My electronics training is 35 years old. These days I am more of a keyboard dancer and spend all my time programming.


Did you measured the charger 6 pins (PV, load, battery) ?
They should have common GND


Yes, I measured all the pins.  (Post #9).
With nothing connected, there is no connectivity between any Pins at all so there is no true common ground (as one would have expected) and also no common plus.
When the charger is connected to the battery only, I can read battery voltage directly across the battery, or across the battery terminal of the charger. No surprise there. I didn't test between battery negative and any other plus Pins, probably should have. If I connect the solar Panel as well, the battery starts charging. No surprise. I measure slightly higher voltage across the solar Panel terminals compared to across the battery terminals. That also is to be expected as the battery loads the solar panel and pulls it down.  However, I get the exact same voltages (slightly lower battery voltage) between battery negative and battery positive compared to battery negative and solar plus.  I also get the solar Panel voltage (slightly higher than battery voltage) across solar plus and solar negative and also solar plus and battery negative.  Ergo, my conclusion that at least while charging, the plus terminals (all three of them) are common.

After I scratched my head over this phenomon for a while, I (maybe?) figured out what was going on.  Just like on Arduinos, it is easier/cheaper to have the MOSFET on the negative side of the switching circuit. I think that is what they did with this charger. I own other chargers as well. I measured those and they have a true common positive, even when powered off. I opened them and sure enough, there is a fat copper/solder trace connecting all three terminals.  On the one I am now using, that is not the case but nonetheless, when opeating the plus all seem to be common. (More head Scratching required)



Just wondering if you have any updates on reading multiple V+I sensors off your charge controller? I am facing the exact same problem (with a positive common ground on charge controller) - trying to deploy some remote monitoring Arduino boxes on off-grid solar home systems but can only accurately get 1/3 readings of (panel, battery, load).

The way I see it, if we want to measure multiple voltage values going straight into Arduino analog input:

a) Arduino needs to measure POSITIVE voltages at analog inputs (w/ regards to arduino reference voltage) otherwise pins will get fried.

b) Arduino needs to have the charge controller + rail voltage go into GND (to set the common reference voltage).

c) Arduino needs to have +5V -> +12V differential between Vcc -> GND. So if we're going to power the arduino with the battery itself, and use battery + as GND too, we need to boos battery by +5V to go into Vcc.

I'm really scratching my head here. Not that experienced in electronics so don't want to fry my Arduino. Any way we can use inverting OP amps to solve a). does b) sound right, and then use a buck converter to boost c) for Vcc input?


Maybe you should go back to post #11 and read it...
Electronics and firmware/software design and assistance. No project too small


Thanks Cedar,

Mind if I clarify some things with you because I'm a bit confused still;

a) on arduino GND I input the positive of the charge controller to set reference voltage?
b) how can I create a positive Vcc to power arduino (from the battery connected to charge controller) when I've already put the positive of the charge controller onto the Arduino GND?
c) I use the INA217 amplifier to invert the (relatively negative voltages) off the black lines on panel, bat, load and a voltage divider to get them between 0-> +5V so they can be read by Arduino analog in?

Sorry bit of an electronics n00b.

Thanks so much!



So I decided to try my luck out on stack exchange, and the guys over there have suggested a voltage divider method. It looks like it'll do the job (without amplification). My voltage range is between -17V -> 0V.

I've posted my voltage divider circuit here, to see what you guys think. I'm also curious to get your thoughts on the difference between method A) and method B). Will method A) work without a resistor between GND and & the voltage divider?

Thanks guys.


Hi, any improve in this? I am facing the same problem. Any already checked solution? Thanks

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