The MCU responsible for actually charging the battery must be able to quickly adjust and adapt in real time to the battery’s changing properties, like oxidation on the terminals or cell voltages. During charging, the MCU must be able to respond quickly to overvoltage conditions; otherwise, the battery may overheat and catch on fire.
Advantages of the MCU-controlled charging method include safe charging, time efficiency, and low cost. Battery capacity (C), expressed in milliamp-hours (mAh), is a measure of battery life between charges. Battery current has the units of C-rate.
MCUs can also support multiple power topologies and multiple control loops for voltage and current, plus other system parameters with such high performance that minimizes “missing” changes in battery characteristics.
Complete battery charging applications may be developed quickly using a microcontroller. Add to this the serial communication capability of the microcontrol-ler, real-time data logging and monitoring is possible. Simple battery chargers use all analog components to accomplish their function.
The schematics for the full charger system is shown in Appendix C. This system includes circuits that may be replaced by others at the designer’s option. The PIC16C73A microcontroller is shown in the main schematic. However, a PIC16C72 may be used (for STAND-ALONE mode only) or a PIC16C711 (for STAND-ALONE mode, single battery).
The fast charge (constant current) and constant voltage charging are the most important stages during a recharge process. Most Li-ion batteries have a fully charged voltage of 4.1 V or 4.2 V. The battery is first charged with a constant current of 1C until the battery voltage reaches 4.1 V or 4.2 V.