Battery Voltage Monitor Problem

[wastevenson]

Hey guys. I'm having an issue with getting the battery voltage monitor working. I'll explain the two setups that I have tried, and tested with two batteries.

2x 11.1V, rated 3S batteries. Metered at (12.4v, and 11.3v).

I power my arduino Multiwii flight controller with a UBEC off of the battery terminal. I have tried both an Atmega328p (Arduino Nano on A3 pin) and the Atmega2560 (Arduino Mega 2560 on A0 pin).

I am getting for-instance 4.4V off of the end of my monitor cable when using my multimeter.

My monitor cable was made with a 51k and 33k resistor. And is soldered directly onto the positive and ground pads on my battery terminal distributor.

V+ ------ 51k\\\
>>>>>>>>>> A3 / A0
V- ------33k///

I removed the comment marker from " #define VBAT " in the config.h script.

In my GUI, no matter what battery I have, it is showing 12.4 (or whatever voltage it calculates based on my scale value). Regardless of whether I use a Nano, or Mega controller.

Can anyone give me some guidance on what I am doing wrong please? Or whatever information I may need to provide to help troubleshoot this?

[wastevenson]

Just to update everyone, my problem seems to be with ground? Ideas?

If I power my board direct from the LIPO, it works as expected.

Using BEC, DC adapter, UBEC doesn't seem to work. Which was kind of what I had suspected when I had decided to go with a UBEC to power my board. Am I missing something? Is there a way to power my board with BEC and still be able to use the voltage divider properly?

And for whatever reason, USB power will work if I ground the Arduino board to BAT-.

Power by USB 5V, Arduino GND to BAT GND, everything works.
Power by LIPO BAT+ to Arduino VIN, everything works.
Power by LIPO 5.25V UBEC from BAT+/BAT-, shows 4S 12.9V.
Power by LIPO from 5V BEC on ESC, shows 4S 12.9V.
Power by DC adapter 5.31V, Arduino GND to BAT GND, shows 4S 12.9V