Multi-Chemistry Battery Charger

Overview

The project produces a battery charger that may be used to charge NiMH, Li-Ion, NiCad, sealed lead acid, and rechargeable alkaline batteries.

Explanation

There are two channels that the charger imposes which can charge two different batteries at a time at up to 2A each while channel A can be used as a discharger alternatively. All necessary parameters are allowed to be set by a 2x16 LCD display with a 5-key keypad while displaying charging/discharging values including mAH when complete. A fixed voltage, current limited output, fixed current, voltage limited output, and a variable PWM output are provided as a bonus. The brain of the circuit is performed by an ATmega32 microcontroller that runs at 16MHz.

In the charging circuit, the inductor/capacitor pair are optimized for a 16kHz pulse width modulated signal and provide and provide a smooth DC output. The raw signal is compensated in software for the drop across the current measurement resistor and lead wires while and the voltage input needs to be accurate at least 1%. The Fast 10-bit PWM mode is used by the PWM signal and the thermistor is linearized in the software to provide a °F temperature output.