This AA, AAA, medium and large battery charger is very useful for those who use this type of batteries. The circuit is transistorized and very easy to assemble.
We describe the assembly of a simple constant current source that serves as the basis for a Nicad battery charger.
The charging time depends on each model and should be consulted because it is recorded on the battery itself.
In figure 1 we have the complete diagram of the loader.
The assembly is based on a small terminal strip, as shown in figure 2.
In this figure we have a support for two small batteries, but can be recharged up to 4 batteries, using appropriate support.
The Rx resistor has its value determined by the type of battery being recharged as follows:
• Large batteries - 150 mA load - 10 ohms
• Medium batteries - 100 mA load - 15 ohms
• AA batteries (small) - 50 mA - 33 ohms
• AAA batteries (stick) - 15 mA - 100 ohms
The circuit is connected to an unregulated or regulated 12 V supply with at least 200 mA of current supply capacity.
The transistor Q2 must be mounted on a heat radiator and the resistor Rx is 2 W. R1 is 1/8 W.
On the assembly observe the positions of the transistors, diode polarity and battery holder.
Material list
Q1 - BC548 - NPN general purpose transistor
Q2 - TIP31 - NPN power transistor
D1 to D4 - 1N4148 - silicon diodes
R1 - 2k7 ohms - resistor - red, violet, red
Rx - see text
Several:
Terminal strip, heatsink for transistor, support for batteries in charge, wires, etc.
