Thursday, October 2, 2014
Simple Ni Cd Battery Charger Circuit
This Ni-Cd cell charger can charge upto eight cells at 21 time and has facilities of standard and fast charging and full-charge indicator. The auto shut-off chargers arc unsuccessful in r India due to frequent interruptions in the mains supply.
The transformer has two separate windings of 0-12V on the secondary side the first being for the charging circuit and the second for the monitor- ing circuit. lC LM3l7T variable volt- age regulator is the heart of the circuit which selects between the standard and U the quick charging modes. Diode D10 blocks the reverse flow of current during mains off while R5 to Rl2 limit the ` current. The current is constant due to the constant voltage. Comparator IC2 uA7 41 compares the reference voltage with the monitoring voltage. When these are equal LED2 starts glowing, indicating full-charge condition. The monitoring circuit monitors only one cell at a time. A multi-way switch can be used to monitor the other cells.
This circuit can be used for charging more than eight cells by using a transformer and semiconductors of higher current capacity. IC LM317T should be used with a suitable heatsink. For the adjustment of VR2, adjust VRl to read 3V and then connect a fully charged Ni-Cd cell in the test cum charge terminal. Adjust VR2 till LED l0 starts glowing.
The transformer has two separate windings of 0-12V on the secondary side the first being for the charging circuit and the second for the monitor- ing circuit. lC LM3l7T variable volt- age regulator is the heart of the circuit which selects between the standard and U the quick charging modes. Diode D10 blocks the reverse flow of current during mains off while R5 to Rl2 limit the ` current. The current is constant due to the constant voltage. Comparator IC2 uA7 41 compares the reference voltage with the monitoring voltage. When these are equal LED2 starts glowing, indicating full-charge condition. The monitoring circuit monitors only one cell at a time. A multi-way switch can be used to monitor the other cells.
This circuit can be used for charging more than eight cells by using a transformer and semiconductors of higher current capacity. IC LM317T should be used with a suitable heatsink. For the adjustment of VR2, adjust VRl to read 3V and then connect a fully charged Ni-Cd cell in the test cum charge terminal. Adjust VR2 till LED l0 starts glowing.
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