ADC - Voltage measurement on negative voltages

[casemod]

Hi folks,

Im having a problem that I was hoping to get some help with.

I have a 96V solar array, in which the battery is divided in two banks with a center point (+48,0,-48)

I need to measure when an imbalance has occurred and for that I need to measure the individual banks. My CPU ground is connected to the 0V supply. I am not sure how to measure the bottom bank as the voltage is negative in respect to the CPU GND.

Note: Both banks need to be measured at the same time, trough a simultaneous sampling ADC, so that rules out most external SPI ADC's.

Any suggestions on this?

Many thanks

 

[kam1787]

Are I being too simplistic?
After voltage divider, connect to comparator [dual voltage], voltage limiter, then offset, and finally feed to ADC

 

[BradtheRad]

On the chance this might help...

By making the right adjustment to a resistive divider, you shift the negative signal into the positive region.



Ground reference is not shown, but you get the idea.

 

[crutschow]

You could also use an inverting op amp circuit to convert the negative voltage to positive.

 

[andre_luis]

Another option is supply both +Vref and -Vref of A/D converter with external voltages taken from +48v/-48v battery bank ( e.g. -5v/+5v ), so that can determine precisely the drift from GND, which is the half of full scale references of the analog to digital converter.