.C. S C D I I E W V D
12V BATTERY CHARGER-CHARGER Cum VA V ARIABLE POWER SUPPLY
DO-IT-YOURSELF
4 3 * N R S O P O C F V
Y L P P U S R E W O P E L B A I R A V = * S P V
Y E T S I R R E A V L E O R P 5 D E L
7 D E L
7 0 0 1 4 1 N D 1
5 P T
T
Circuit and working Circuit of the 12V battery charger-cum-variable power supply is shown in Fig. 1. It is built around two LM138 variable voltage regulators (IC1 and IC2), dual op-amp LM358 (IC3), 12V voltage regulator 7812 (IC4), two relays (with normal 12V, 12V, 1C/O PCB-mounted and 12V, 1C/O, 10A contact-current rating) and a couple of transistors. LM138 is a 3-pin, 5A positive-voltage regulator available in TO-220 TO-220 or TO-3 package. But continuous current flow of 5A generates a high temperature, which shuts down output of LM138 automatically due to its internal thermal protection. 94
NOVEMBER 2016 | ELECTRONICS FOR YOU
6
3
− 1 N I
c c V 8
7 0 0 0 4 1 N D 1
R E P M 2 U J J
S S N O N I O T I T C E C N N N U O J E C R L A A N 6 R E H T X G E U R O O R F H B T C 1 P N S I T D N E I O S P U
+ 1 N I
− 2 N
+ 2 N I
T U O
T U O
D N G
8 I 3 5 3 C M I L 2 1 7
1
4
K 7 3 . R 3 6 P T K 6 3 . R 3
Y R E 6 D T D A T E E A L D B
K 4 3 . R 3 2
1
E 4 L G D L R E U A L F H C
2 R K V 5
O / C 1 2 1 , / O C 2 V / N N L R 2 1
2 O / N W 5 , E 3 1 . R 0
7 4 5 1 C T B
O 1 / C C 1 / , N 1 V L 2 R 1 2 2 2 2 2 N T 2
4 3 A D 6 2 P T
3 P T
3
4 2 C 1 8 I 7
3 K R 7 V 4
1 P
4 5 A D 6
7 0 8 0 4 3 N 2 1 1 C I
M L
8 D
7 0 0 4 9 N D 1 1
V 5 3 , u 3 0 0 C 1
E 1 0 7 R 2
V 5 2 , u 7 2 0 0 C 1 2 0 4 7 N 8 D 1
7 0 0 4 1 3 N C 1 1 1 I M 6 D
3
2
7 P T
K 5 3 . R 3
7 0 0 2 4 1 N D 1
4 P G T N I 2 L N R O N O O O A C F C F
R E P M 3 U J J
L
3
1
, V 5 R 1 E − M 0 R − V O 5 F 1 S O N A T R Y T R Y A R M I A R D P N O C C A E V 0 S 3 A 2 5 = 1 X
D N 0 G P T
1 P T 1 4 A D 6
u 0 V 1 0 7 0 C 4 4 2 4 A D 6 K 2 3 . R 3
1 X F H F C T O I / 1 N W S O S
C , T 1 A z V U N R 0 H P O O 3 0 N C F 2 5 I L
N
G N I G R A H C R E D N U Y R E T T A B = # C U B
R E P M 1 U J J
1 R K V 5
2
3 1 D
Y H T 2 L D A E E L H
2 P
u V 4 0 5 C 1 2
7 0 0 4 N 1
1 V D 7 . Z 4
5
3 4 4 A D 6
he circuit presented here can charge a 12V lead-acid battery of 50Ah to 80Ah (even up to 100Ah) capacity and can even be used as up to 18V DC variable power supply of maximum 5A capacity, capacity, which is useful for a test bench. The circuit can automatically detect the presence of a battery connection and start charging. At that time, it disconnects the output provided as variable power supply. It also detects the wrong/reverse wrong/reverse polarity connection of the battery terminals and raises an alarm. The charger initially charges the battery at a higher voltage (about 14.2V), and once it is fully charged, it maintains the battery charge at a constant voltage (about 13.4V).
4 R K V 5
2
G N I G R A H C 3 D E L
K 9 3 . R 3
FAYAZ HASSAN
5 R K V 5 K 8 0 R 1
E 0 0 1 0 K 1 1 3 1 . R R 3
6
u 5 1 . C 0
R E V 5 Z 2 Z 1 U 4 # B N R C O O U O C F B 1 Z E Z I P P
R E 1 W D O E L P
y l p p u s r e w o p e l b a i r a v m u c r e g r a h c y r e t t a b V 2 1 e h t f o t i u c r i C : 1 . g i F
WWW.EFYMAG.COM
Fig. 2: Actual-size PCB pattern of the battery charger-cum-variable power supply
Fig. 3: Component layout of the PCB
This circuit simplifies higher current handling of LM138 by using IC1 and IC2 in parallel, but still output voltage can be regulated by a single variable resistance. Care should be taken for handling the lines carrying 5A current. Two separate relays (RL1 and RL2) are used to reduce the cost of the project. Transformer X1 steps down 230V AC to 15V-0-15V AC that is then rectified by diodes D1 and D2 and smoothened by capacitor C1. This voltage, which is around 20V DC, WWW.EFYMAG.COM
is fed to IC1 and IC2 that are wired in parallel. Their output voltage is regulated either by VR1 (in case of variable power supply) or VR2 (in case of battery charger), which is selected by relay RL2. Output so obtained is available for the variable power supply or battery charger through RL1. Dual op-amp LM358 (IC3) is used to control the relays and select the type of output, that is, whether for battery charger or variable power supply. When no battery is connect-
ed for charging, no power is given to IC3. RL1 and RL2 are in non-energised state, and potmeter VR1 can be used to get variable voltage output across CON3 fitted on the cabinet. When a 12V battery under charging (BUC#) is connected properly to terminal CON4 for charging, IC3 gets power supply from the battery through diode D10. If battery voltage is below ‘dead’ voltage (say, 6-9V and at least above 6V), pin 7 of IC3 pulls low and LED6 glows. If the battery is healthy (say, more than 9V), ELECTRONICS FOR YOU | NOVEMBER 2016
95
DO-IT-YOURSELF
pin 7 of IC3 goes high and switches on LED2 and conducts transistor T2, and RL1 and RL2 energise. Output voltages of IC1 and IC2 are regulated by VR2 and are available for charging at CON4. Once the battery under charging attains its full charging voltage, pin 1 of IC3 goes high, as indicated by the glowing of LED4, and T1 conducts, which reduces the voltage at pin 1 of IC1 and IC2. When a 12V battery is connected in reverse polarity, D11 conducts, which, in turn, switches on the piezo buzzer and LED5 glows. This protection is important while charging batteries externally.
Construction and testing An actual-size, single-side PCB for the 12V battery charger-cum-variable power supply is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on the PCB, place it in a suitable cabinet. Fit CON3 and CON4 on the front side of the cabinet. CON3 is for variable power supply (VPS*) and CON4 for battery under charging (BUC#). Connect CON3 between N/C2 terminal of relay RL2 and point 4 given on the PCB. Connect CON4 between points 3 and 5 given on the PCB. Fix VR1 through VR5 and all LEDs on front side of the cabinet, and label these as shown in the circuit diagram. Place transformer X1 inside the cabinet. Fix CON1 and switch S1 on the rear side of the cabinet. Use proper heat-sinks for IC1, IC2 and IC4, and connect a 12V cooling fan at CON2 for fast cooling. The circuit works off 230V mains power supply. Refer the test points table for checking the voltages at various points before using the circuit.
PARTS LIST
Semiconductors: IC1, IC2 - LM138, variable voltage regulator IC3 - LM358 dual op-amp IC4 - 7812, 12V voltage regulator T1 - BC547 npn transistor T2 - 2N2222 npn transistor LED1-LED7 - 5mm LED D1-D5
- 6A4 rectifer diode
D6-D13
- 1N4007 rectifer diode
ZD1 - 4.7V zener diode Resistors (all 1/4-watt, ±5% carbon, unless stated otherwise): R1 - 270-ohm R2, R4-R7, R9, R11 - 3.3-kilo-ohm R3 - 0.1-ohm, 5watt R8 - 10-kilo-ohm R10 - 100-ohm VR1, VR2, VR4, VR5 - 5-kilo-ohm potmeter VR3 - 47-kilo-ohm potmeter Capacitors: C1 - 4700µF, 40V electrolytic C2, C4 - 10µF, 25V electrolytic C3 - 100µF, 35V electrolytic C5 - 0.1µF ceramic disk Miscellaneous: X1 - 230V AC primary to 15V-0-15V, 5A secondary transformer RL1 - 12V, 1C/O PCB-mounted relay RL2 - 12V, 1C/O, 10A contactcurrent rating relay CON1, CON2 - 2-pin connector CON3, CON4 - 2-pin connector terminal for 10A S1 - On/off switch (6A) PZ1 - Piezo buzzer J1-J3 - 2-pin shorting jumper connector - Heat-sink for IC1, IC2, IC4 - 12V cooling fan
3.
4.
5.
6.
Initial setup and testing 1. Remove jumper J1 and J3, connect J2 and switch on S1. 2. Adjust VR1 and VR2 to get 9V DC (as battery dead voltage or as 96
NOVEMBER 2016 | ELECTRONICS FOR YOU
7.
required) with respect to ground at TP6. Adjust VR4 such that you can turn on and off status LED2 and LED6 alternately. RL1 and RL2 also change their states (energise/de-energise). Adjust VR2 to get the full battery voltage (say, 13.4V DC with respect to ground) at TP6. Adjust VR5 to turn on LED4, if TP7 is connected to ground through J3. Once LED4 is set, adjust VR2 to get battery charging voltage (say, 14.2V DC with respect to ground) at TP6. Connect J1 (J2 still connected) and adjust VR3 to get battery standby voltage (say, 13.4V DC
Test Points Test point
Details
TP0
0V (GND)
TP1
Around 20V DC when S1 is closed
TP2
1.2V to 18V
TP3
1.2V to 18V
TP4
0.5V to 18V
TP5
0.5V to 18V
TP6
Around battery voltage
TP7
0 when J3 is grounded or 12V when J1 is not grounded
with respect to ground) at TP6. 8. Once the required voltages are set, remove J2. The circuit is ready to use. 9. If no battery is connected at CON4, variable voltage is obtained at CON3 by using VR1. Brightness of LED7 is proportional to the output voltage at CON3. 10. If 12V (≥50Ah) battery is connected at CON4 in reverse polarity, buzzer PZ1 gives an alarm sound and LED5 glows. 11. If the same battery is connected in correct polarity at CON4, status of the battery is indicated by LED2 (healthy) or LED6 (dead). RL1 and RL2 will get energised in case the battery is healthy and the battery will get charging voltage. Once the battery is fully charged, LED4 glows, which indicates that the battery is fully charged and the charger is at standby voltage. 12. Use proper crocodile clips for connecting the battery terminals. EFY note. 1. Charging voltage, standby voltage and battery dead voltage may vary as per the manufacturer of the battery. The values indicated here are safe voltage values. 2. Heat-sink with mica insulation must be provided for IC1 and IC2. Fayaz Hassan is a manager at Visakhapatnam Steel Plant, Visakhapatnam, Andhra Pradesh. He is interested in microcontroller projects, mechatronics and robotics
WWW.EFYMAG.COM