Hi,
I want to use Arduino Mega's differential ADC feature to monitor the cell voltages of a LiFePO4 battery and I am wondering about the best option to supply the Arduino with power. I see three options (see attachments), i.e. power from
Are there any reasons to favor one option over the other? Are all of the three options feasible?
Thanks,
Willy
All three will vaporize your Mega. If you apply a voltage outside the range 0V to 5V to any pin you'll burn it out.
You need to bring the voltages down into the safe range, say by a set of voltage dividers or an opamp
differential amplifier configuration.
MarkT,
thank you for your prompt reply, and best regards from my Mega, saying "Thank you for keeping that dump i**** from blasting me!" 
I fully trust your expertise. I just want to reflect what you wrote in my own words to make sure that I understand the problem. So, ...
Voltage differences of more than 5 V are applied to some pins of the ADCs, which is out of spec. For example, AD2 has to carry 10.8 V compared to AD7. Even though there is no (external) connection to GND in option 3, the pin-to-pin voltage difference of AD2-to-AD7 is producing harmful conditions inside the controller. The other cell's voltages (VB1C1 + VB1C2 = 7.2 V ) are not able bring VDIFF of AD2-to-AD3 to safe 3.6 V.
Got it?
Happy easter,
Willy
willyzzzz:
Voltage differences of more than 5 V are applied to some pins of the ADCs, which is out of spec. For example, AD2 has to carry 10.8 V compared to AD7. Even though there is no (external) connection to GND in option 3, the pin-to-pin voltage difference of AD2-to-AD7 is producing harmful conditions inside the controller. The other cell's voltages (VB1C1 + VB1C2 = 7.2 V ) are not able bring VDIFF of AD2-to-AD3 to safe 3.6 V.
Got it?
This made my head spin.
The A/D, single-ended or differential, can only accept voltages within supply/ground of the chip.
Leo..