I am building a circuit to measure voltages on a 4cell lithium battery. All cells are connected in series and have a nominal voltage of 3.8v per cell.
I'm using a voltage divider to drop the voltage down to 3.8 volts, so they can be read using the analog pins on an arduino.
I'm a self taught hobbbiest and I don't understand why in the simulator and my calculations, I get an output voltage of 3.8 volts. But on a real breadboard The output voltages are closer to 3.5 volts.
- Batteries will have a voltage drop when under load.
My batteries are outputting less than 400 microamps in both the simulator and on the breadboard. Seems unlikely to account for the large difference.
- Account for internal resistance
I do not know the internal resistance, but the battery is brand new and high quality lithium polymer batteries typically have less than 5 milliohms per cell.
Please educate me. Why are the voltages off by almost half a volt? This circuit is the best I can come up with. If there are better ways to design the circuit, I would appreciate that feedback too.
As suggested in the comments, I disconnected the output of the voltage dividers from the arduino. The output of the voltage dividers is now reporting the correct 3.8 volts. I still don't understand why that was the problem, or what the solution would be.