Wednesday, August 4, 2010

Austere Ni-Cad Cell Charger

This simple,low cost ni-cad cell charger can charger up to two AA or C sized cells at one time at the standard rate of 40 mA.The unique feature of this charger is its extremely compact size and transformer less design(unlike others),hence ending up in the form of a neat and compact little module.There is provision for mounting the cells to be charged within the PCB (hence no external wiring is needed ,thus eliminating chance of failures due to snapping of wires etc).This enhances the utility all the more as the charger can then be used as a rechargeable power pack that can be used to replace the original battery holders in equipment such ac pocket radio make them rechargeable.The circuit employs the PCR (periodic current reversal) method of charging which increases cell life
R1 is used as a surge protector.C1 works as a series dropper.The dropped voltage is rectified and converted into DC by diodes D1 through D4.C2 provides the necessary filtration.The final voltage is applied to the cells for charging.R4 through R7 generate the PCR effect by allowing current in direction opposite to the diodes to pass in minute proportion,it may create the effect just the opposite that desired,These resistors may be simply left out if the normal charging procedure is to adopted.

 The Schematic Austere Ni-Cad Cell Charger

As C1 may be charged to fatally high voltage, an 820 kohm shunt resistor is used to discharge it when the power is turned off.The LED D5 along with R2 provide pilot indication as well as a"don't touch warning indication.

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