Nowadays, Ni-Cd cells are commonly used in household goods. Depending on their use, these need to be changed quite often. Hence a good Ni-Cd charger has become a necessity. Now, here is a versatile circuit diagram of a verified Ni-Cd battery charger.
The commonly used Ni-Cd batteries, which are rated at 500mA/hour, need to be charged at a 50mA constant current. The circuit presented here will charge at a time seven Ni-Cd pencil cells connected in series or a 9V Ni-Cd battery. It will indicate faults such as reverse polarity, a shorted battery, a high resistance battery, or a low voltage battery through just two LEDs. After a normal charging time of 14 hours, it will disconnect the battery but shall start trickle charging it, thus ensuring that the battery does not lose its charge. Also, after the battery has been charged fully, it will give an aural indication.
Circuit Description of Ni-Cd Battery Charger Circuit
Despite performing all these functions, the circuit is very simple. It comprises a constant current source of 50mA, a 14-hour timer, and a comparator.
LM317 (IC2) provides a very stable current source. Output current at terminal Vout of IC2 is given by I = 1.2V/R14. For the given value of resistor R14, the output is 50mA, irrespective of the battery voltage. Diode D1 and D2 prevent the battery discharge during mains failure. Resistor R7 along with diode D2 provides trickle charging, in case the battery remains unattended after a lapse of 14 hours.
IC1 CD4060 is a 14- stage counter with an on-chip oscillator. The oscillator frequency is given as F=1/2.2RC, where R=R11 + R12 and C=C2+C3+C4. With the value of R and C shown in the circuit, the oscillator is at about 1/6 Hz, and the output at pin 3 goes high after 14 hours.
The Darlington drive is built around transistor T1 and T2 switches on relay RL1 which disconnects the batteries from the current source. At the same time, the buzzer starts ringing, indicating that the battery is fully charged. The C1-R1 combination automatically resets IC1 at power-on.
IC3 forms a simple comparator. The voltage at its pin 2 is set to 0.4V with VR1. Its pin 3 is connected across the battery, but in normal conditions, it remains tied to +Vcc through resistor R3. R10 provides some hysteresis.
Check out other various battery charger circuits posted on bestengineeringprojects.com
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The table shows the conditions when different faults are detected.
|
Condition |
RED LED |
Yellow LED |
Indication |
|
1. |
ON |
OFF |
Normal battery charging |
|
2. |
ON |
ON |
There may be a reverse connection of the battery. Check whether the battery is connected correctly. If it is connected properly then the battery is short and is not usable. |
|
3. |
ON |
Remains “ON” for some time and then goes “OFF” |
Low voltage battery. Charging may be continued. |
|
4. |
Remains “ON” for some time and then goes “OFF” |
OFF |
High resistance battery. This indicates that the battery is not usable |
If you wish to charge a 6V lead-acid battery (for the bike) reduce R14 to 2.2Ω, 2 watts, and mount IC2 on a heatsink.
PARTS LIST OF NI-CD BATTERY CHARGER CIRCUIT
|
Resistor (all ¼-watt, ± 5% Carbon) |
|
R1 – R4, R6, R7 = 100 KΩ R5 = 1 KΩ R8, R9 = 1.5 KΩ R10, R11 = 1 MΩ R12, R13 = 3.3 MΩ R14 = 22 Ω/0.5W R15 = 33 Ω/0.5W VR1 = 100 KΩ linear |
|
Capacitors |
|
C1 = 0.01 µF (Ceramic Disc) C2 – C4 = 0.22 µF (Ceramic Disc) C5 = 220 µF, 25V (Electrolytic capacitor) C6 = 0.1 µF (Ceramic Disc) |
|
Semiconductors |
|
IC1 = CD4060 (Counter IC) IC2 = LM317T (Adjustable positive voltage regulator) IC3 = µA741CN (Operational Amplifier) T1, T2 = BC547 (NPN Silicon Transistor) D1 = 1N4001 (Rectifier Diode) D2 = 1N4148 (Signal Diode) LED1 = Red LED2 = Yellow |
|
Miscellaneous |
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PZ1 = piezo buzzer PEC 27IH RL1 = 12V, 150Ω SPDT, relay |