Here is a simple circuit build around very common electronics components easily available in local market which is used to protect car (automobile) battery from deep discharge and also protect it from getting damaged.
Let’s get some fact about automobile batteries. We all know that battery itself have some self-discharge rate which depends upon battery capacity and the materials used to make it. There are various reasons that discharge battery like electrical installation in a car. When we do not used our automobile for longer period of time the battery becomes fully discharge or also sometimes it gets damaged too.
In order to overcome this problem, we have discharged a circuit which let battery remains always charged.
Circuit Description of Car (Automobile) Battery Maintaining Circuit
The circuit of Car (Automobile) Battery Maintaining Circuit is shown in figure 1. This circuit is basically a power supply unit. The mains supply is given to one input of switch SW1as shown in circuit diagram which is further stepped-down to 21V using stepped-down transformer X1. These voltage is changed to pulsating dc using bridge rectifier comprising diodes D1 trough D4.
From the circuit shown above we conclude that there are basically two channels, each channel contains a voltage regulator IC 7805 (IC1 and IC2). The interesting fact is that, here we are using these IC (7805) as current generator rather than 5V fixed voltage regulator. Resistor R2 is used to maintain minimum output current of 10mA for battery 1 similarly R5 does the same job for battery 2.
Maximum output current of about either 50mA or 100mA can be selected using switch SW2 for channel 1 and switch SW3 for channel 2. At position 1 of switch SW2/SW3 the maximum output will be 50mA similarly at position 2 of switches SW2/SW3 the output will be 100mA.
LED1 with zener diode ZD1 and ZD2 is used to limit the maximum output voltage to 15.5V for channel 1. Similarly, this job is done by LED2 with zener diode ZD3 a ZD4 for channel 2.
In order to prevent the discharging of battery we had used diode D5 for channel 1 and Diode D6 for channel 2. This is done because normal PN diode does not connect in reverse bias. Hence no voltage flow through it.
Construction of Car (Automobile) Battery Maintaining Circuit:-
Actual Size, Solder-Side PCB design of Car (Automobile) Battery Maintaining Circuit is shown in figure 2. Similarly, components side is shown in figure 3. The complete circuit kept in small enclosure box and its input and output can be taken from front and back panel respectively.
Figure 2: Solder side PCB design of Car (Automobile) Battery Maintaining Circuit
Figure 3: Component side PCB design of Car (Automobile) Battery Maintaining Circuit
BEP Note: The two ICs (IC1 and IC2) most mount in individual heat sink. and its ground pin (pin 2) should be connected to heat sink.
PARTS LIST CAR (AUTOMOBILE) BATTERY MAINTAINING CIRCUIT
|Resistor (all ¼-watt, ± 5% Carbon)|
|R1 = 100Ω, 2W
R2, R5 = 510Ω, 0.5W
R3, R6 = 110Ω, 2W
R4, R7 = 51Ω 2W
|C1 = 100nF, 630V (Polyster Capacitor)
C2 = 2200 µF, 40V (Electrolytic Capacitor)
C3, C4 = 330nF (Ceramic disc)
C5 C6 = 1 µF, 35V (Electrolytic Capacitor)
|IC1, IC2 = 7805, 5V voltage regulator
D1 – D6 = 1N4002 rectifier diode
ZD1 – ZD4 = 6.8V zener diode
LED1, LED2 = 5mm any color LED
|X1 = 230V AC primary to 21V, 200mA secondary transformer
SW1 = DPDT Switch
SW2, SW3 = SPDT Switch
F1 = 0.25A fuse with holder
BATT1, BATT2 = 12V battery