This ATmega8-based device can be used to measure the internal resistance of Lithium Polymer (LiPo) batteries used in electric RC models. By measure the internal resistance you can estimate your battery age and condition, whether the lipo is still good enough to power your RC model or you need to find new battery. New LiPo cell has Rin below 5mohm and becomes above 20mohms when the cell at the end of their life. It also depends on the original quality.
This project measure internal resistance using this approach, first, it measure V lipo without load. Then connect battery with resistor load 1 ohm, and measure the voltage (V load) and current (I). By using these parameter, it calculate internal resistance value with formula,
Rin = (V no load – V load)/I load
The project comes with self calibration feature and is equipped with 7segment LED to display the result. You can use it to measure Rin up to 8 cell LiPo battery. Accuracy of Rin measurement estimated 6% due to the accuracy of the load resistance and voltage measurement accuracy is 1%.