here is a 12V, 7Ah smart battery charging circuit which is also referred as smart charger uses three stage of charging i.e. bulk stage, absorption stage and float stage.
Normal battery charger technology uses single stage battery charging technology i.e. only charge the battery up to maximum charging voltage preset by charging circuit. Now here is a 12V, 7Ah smart battery charging circuit which is also referred as smart charger uses three stage of charging i.e. bulk stage, absorption stage and float stage.
80% of the charge is done in bulk stage where current is constant but voltage is increases. Similarly, rest 20% of charge is done in absorption stage (14.1VDC to 14.8VDC, depending upon voltage set for sealed-lead-acid (SLA) 12V, 7Ah battery). Whereas float stage is occurred when charge voltage is reduced to between 13.0 VDC to 13.6 VDC and current does not drop, also this stage is used to maintain a fully charged indefinably.
Circuit Description 12v, 7Ah Smart Battery Charger with PCB Diagram
The circuit diagram of charger is shown in figure 1. It utilizes a step-down transformer, adjustable voltage regulator IC (LM317), op-amp comparator, zener diode and few other active and passive components.
The input 220 Volt AC is step-down to 15V-0-15V using center-tapped transformer. The stepdown voltage is changed to pulsating DC with the help of full wave rectifier (D1 and D2) and is smoothed by capacitor C1. This voltage is further given to input pin (pin 3) of adjustable voltage regulator (IC1).
The output voltage obtained from adjustable voltage regulator is determined or controlled by changing resistance at pin 1 of IC1.
Here, we had used dual operation amplifier LM358 (IC2) as comparator which compare output voltage with reference voltage and control overcharge of battery. The LED1 is used to indicate power where as LED2 and LED3 are used to indicate charging and full charged of battery respectively.
Calibration of 12v, 7Ah Smart Battery Charger with PCB Diagram
For calibration or setup, remove jumper and reconnect it back after calibration.
- Adjust potentiometer VR2 to get 13.6V at cathode of diode D5 or at Vcc (pin 8) of IC2.
- Adjust VR1 to get 0.5V (difference of output i.e. 14.1V-13.6V = 0.5V) at collector of transistor T1.
- Adjust VR3, so that charging LED (LED2) start to glow.
- Again adjust VR2 to get 14.1V at cathode of diode D5 or Vcc (IC2) of IC2.
- The voltage at jumper should be either 14.1 V or 13.6V depends upon voltage at cathode at D5. If voltage at jumper is 14.1V then the volte at cathode must be 13.6V and vice-versa.
BEP NOTE: –
- Must use good heat for adjustable voltage regulator IC LM317 (IC1) and it’s must not be connected to ground.
- Capacitor C4 should be kept near as far as possible to pin 1 of IC2.
- For calibration jumper JU1 must be removed and put it back after calibration.
- Battery must be connected with right polarity to the connector CON1.
If you are wish to design your own battery charge indicator there here a circuit for you.
PARTS LIST OF 12v, 7Ah Smart Battery Charger with PCB Diagram
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1 = 270 Ω
R2 = 2.2 KΩ
R3, R6 = 10 KΩ
R4, R5 = 22 KΩ
R7 = 0.2Ω, 5W
R8, R9 = 4.7 KΩ
VR1 = 2 KΩ
VR2 = 5 KΩ
VR3 = 20 KΩ
|C1 = 2200 µF/40V
C2, C3 = 10 µF/25V
C4 = 0.1 µF
|IC1 = LM317
IC2 = LM358
ZD1 = 6.8V Zener Diode
T1 = BC547
D1 – D5 = 1N4007
LED1 – LED3 = 5mm LED
|X1 = 230V AC primary to 15V-0-15V, 1A secondary transformer
CON1 = 2-pin connector terminal
JU1 = 2-pin connector for jumper
SW1 = On/Off Switch
Heat sink for LM317