Charger Device for NiCd and NiMH Battery Cells

Overview

The project illustrates a constant current and automatic charge termination when the total voltage for all cells reach the setting voltage as it produces a NiCd/NiMH charger.

Explanation

There are four NiCd/NiMH cells only used in the design of this project. The voltage regulator VR1 is adjusted after all components are assembled into the PCB, in order to get the voltage at Pin 5 of LM555 which is about 5.8V to 5.9V or around 1.45V per cell. This would result to 5.8V from the product of 1.45 multiplied by 4. The device charges the battery at about 270mAh or 10% of the battery cell. The charge current can be changed with the replacement of R2.

When the voltage at Pin 6 of LM555 for the total voltage cells reach to the voltage of Pin 5 of LM555, the charge termination will occur. When the charging is complete, the relay1 will turn OFF causing no power consumption. This is due to the opening of the main AC power supply. Since the circuit takes a long time a long time to complete the charging, the project is behaving like a general night charger.