From a simple hand-held trimmer to a super-fast electric car, Lithium batteries have found their way into a lot of applications in recent times. The voltage of a single lithium cell normally varies between 3.2V to 4.2V, and is combined to form a battery pack that can provide higher voltage and capacity. While the process seems to be pretty simple, things get pretty complicated when the number of cells used in a battery pack increases, mainly because each cell used in the battery pack should have the same capacity and similar IR (Internal Resistance).
To filter out defective cells and prevent them from getting into a battery pack, manufacturers do something called “Cell Grading”. Wherein each cell is charged to its maximum voltage and then discharged at a constant current to calculate the actual capacity of the cell. Apart from this some Cell Grading machines will also measure the IR and temperature characteristics of the cell during the charging and discharging process. With this data, cells of similar capacity and IR are combined to gather and cells with lower capacity are rejected.
In this video we are building and demonstrating a basic single-cell Lithium Cell Capacity Tester which will be used to measure the capacity of a single cell.