Simple Ni-Cd Battery Charger

Ni-Cd Battery Charger Circuit

This Ni-Cd battery charger is a circuit based on the regulator IC lm317.This circuit is very simple and uses minimum components. By varying value of resistor R1 from 1 ohm to 120 ohms, charging current can be varied from 10 mA to 1.25 A. This circuit functions as a constant current generator.

PARTS LIST
R1	from 1 ohm to 120 ohms (see text)
D1	1N4002
D2	1N4002
C1	1000µF 40V
IC1	LM317
Ammeter	250mA Ammeter
BT1	4×Ni-Cd cell under charge
X1	12V-0-12V (250 mA) SEC
S1	ON/OFF Switch

To see LM 317 pin configuration

Construction is fairly simple and it can be constructed on a veroboard or tag board. As a general rulle all Ni-Cd batteries should be charged at the maximum charging current of 1/10 ampere-hour rating of the battery. This should never be exceeded. Exact charging current can be set by using a potentiometer or a preset in place of R1 and putting an ammeter or multimeter in series with the load. As the maximum input voltage to IC is 40V, input voltage should always remain less. Proposed circuit is suitable for charging four cells in series. But the maxmum number that can be charged  will depend on input DC voltage o regulator.

This circuit is vary rugged and reliable. Output current is virtually independent of load and can be controlled very precisely. Almost any type of Ni-Cd battery can be charged. IC should be fitted with heatsink (LM317T is plastic package of LM317K with same rating but costs only half as much). Typical specifications for a Ni-Cd cell are as follow:

• Nominal 1.2V Full charge 1.4V.
• Charging time max. 12 hrs.
• Discharge rate on storage is 0.014V/24 hrs.
• Totally discharged cell recovers fully on 12hrs charging
• Electrolyte seepage does not affect performance.Wipe cell with dry cloth.

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