Intro: Simple Ni-Cd Battery Charger
The charger has the following specs and characteristic:
1. Simple and minimal parts thus good for beginners and hobbyist.
2. Can be used to charge Ni-Cd of different voltages (2.4V, 3.6V, 7.2V, and other battery voltage)
3. Automatic with battery over-voltage protection . Current limited and voltage controlled.
4. Visual led indicator . Charging (red) and full-charge (yellow) indicator.
R1 - 1.2 kilo ohms 1/4W
R2 - see R2 vs Charging current below
R3 - 2 kilo ohms 1/4W
Q1 - TIP41C or any NPN transistor min 1A current and 3W power
Q2 - 2N2222, CS9013, or similar NPN transistor
LED1 - Red or any LED with forward voltage around 2V (see LED)
LED2 - yellow or any LED color except Red
D1 - 1N4001 or similar diode
D2 - see D2 vs Battery voltage below
DC supply - 12V to 15V DC supply or battery
project originally from http://www.simple-electronics.com/2011/10/simple-ni-cd-charger-automatic.html