MICRO-CONTROLLER BASED LI-ION BATTERY MANAGEMENT SYSTEM

ABSTRACT

This work aims to design and construct a microcontroller-based battery monitoring system for a set of four Lithium-ion batteries connected in series. This device takes advantage of a microcontroller’s ability to read analog voltage signals. The batteries used in this work, a set of four Lithium-ion batteries can give as much as 16.8V when connected in series, voltage dividers are used to prescale the voltages of the individual series connected cells points of the four batteries to achieve voltage values that can never be greater than 5V to enable the microcontroller comfortably read them. The microcontroller reads the prescaled voltages from the voltage divider setup, scales them back internally to their true value using certain calculated multipliers, and then displays them on the LCD screen, these values are also used to monitor the battery and its individual cell voltages during usage. A three-step charging procedure is utilized, First, the fast charging phase where the potential difference battery between the battery’s voltage and the applied charging voltage at 15.5V is relatively large, this is used to charge the battery when the battery is below 30% of its capacity, secondly, the steady charge phase where a constant current at 0.5A is supplied to charge the batteries till its 80% charged, the last charging phase charges the battery with a lower charging voltage such that the potential difference between the battery’s voltage and charging voltage at 17V is small, this ensures the battery will be charged slowly until it is fully charged at 16.8V. The charging voltage is controlled by a DC-DC converter circuit.