As title, I have 3 or 4 batteries connected in series composed by 7 cell each. I have several Arduino nano and I want to use one on each battery to measure all cells voltage.
Since this batteries are connected in series and all Arduino have a common power supply source, I'll get a short between + and - on each battery if I use this common configuration:
Looking again.... It looks like home brew.
What is the difference between Arduino minus and Arduino GND? I will say they are the same and You get a real short circuit.
You might find if you do the sums that you get enough resolution by just taking the input direct from each cell - either switched in or direct to a number of analog inputs .
Eg a 12v battery , where 12v =1024 in an analog read , means you can resolve to 10mv , that might be good enough to check the voltage of a 2v cell making up that battery
7*4 = 28 cells
each (say) 1.2 V = 36V
you would need: 28 voltage dividers - each taking current from the batteries.
You could use analog multiplexers - but cheaper and simpler to use 3 or 4 nanos.
I'd suggest you rethink your requirements - do you REALLY NEED to measure each cell? After all if they are in series you can not use or charge them independently.
Can you explain why?
AFAIK there is NO simple solution to measuring 28 mutually dependent voltages.
Also be aware that the cell voltages will be affected by the current through the cells unless they are off load.
This is funny to me. Around 25 years ago I had to do the same thing: measure cell voltages on large battery packs. We used differential analog multiplexers into a single ADC back then. Weird to realize that it's easier to use multiple microcontrollers these days
I can think of a few reasons that you would want to monitor the voltage of each cell in a series pack. Just ask any Chevrolet Volt owner who is waiting for a BEC module from GM. (Battery Energy Controller). The BEC in a Volt measures individual cell voltages while the car is driving.
I found this circuit which used a linear optoisolator:
Have a look at battery monitoring IC ‘s instead , it might be more fruitful - especially if you want to measure the voltages for charge balancing circuits .
