Car Battery Charger
OBJECTIVE
Here is a simple battery charger circuit, the one that can be used to charge 12 volt batteries of both the usual automobile type as well as the maintenance free sealed lead-acid type. The charger circuit being described here is quite compact can be placed right on the top of the battery required to be charged. In the event of your car battery misbehaving or having become weak, what not require In addition to this gadget. Is only the |230VACmains.230VAC point is quite conveniently available even if you are stuck somewhere on the roadside or – elsewhere far away from a place where you can get your battery charged. This gadget could be one of the most important tools in your tool-kit and you could make use of this gadget to keep your battery healthy. Another significant point about this charger circuit is that it provides you swell regulated source of constant charging voltage. And that Is what is recommended for charging of lead-acid batteries. The gadget also provides to you metering of both voltage across the battery being charged as well as the charging current being drawn by the battery throughout the charging process. This tells you the status of the battery being charged as the time progresses.
CIRCUIT DESCRIPTION
The circuit is nothing but an AC/DC powersupply that generates a regulated DC voltage of 13.2volts from AC mains. Transformer T-l Diodes D1 and D2 and Capacitor C1 constitute the unregulated power supply portion with D1 and do alongwith transformer providing voltage transformation and rectification and C1 providing the filtering action.IC-l is a three terminal regulator of the type 7812. The common terminal of this regulator has been lifted to a potential of about 1.2 volts by the forward biased diodes D3 and D4 so as to give a regulated output voltage of 13.2volts instead of 12V which would be to: case if the common terminal was grounded. C2, C3 are decoupling capacitors. Diode do provides the charging path for the battery. The charging current flows from the power supply to the battery. The diode D5 also prevents the current to flow in the opposite direction i.e. from battery towards the power supply.Meter M-1, which is a current meter, gives a continuous reading of the charging current. The current reading becomes zero when the battery is fully charged. Meter M-2 gives the reading of the voltage across the battery as it is being charged. A fully charged battery typically has an open circuit voltage of 12.5 volts or so.
CONSTRUCTION GUIDELINES
Refer to Fig.10.2 for PCB layout and Fig.l0.3 for components layout. Lead identification of lC-1 is given in Fig. 10.6.
PARTS LIST
Resistors and Capacitors
R1 : 2.2 K, 1/4 W
C1 : 1000 25V (electrolytic)
C2, C3 : 0.1 (ceramic disc)
Semiconductor Devices and ICs
Diodes D1, D2, do : BY 127
Diodes D3, D4 : 1N4001 or equivalent IC-1 : 78T12 (lt is 7812 in TO-3 package) LED-1 : LED (Any Colour)
Miscellaneous
Meter M-1 : Ammeter 0-3A (Fig.10.4)
Meter M-2 2 DC Voltmeter 0-15VDC (Fig.10.5)
Transformer T-1 : 15-0-15, 2A Fuse F-1 : 1A tubular type with holder Power supply terminals, solder metal, wires, mains power ON/OFF switch
TESTING GUIDELINES
Testing the assembled gadget is straight forward.
Switch on the AC power. Measure the regulated DC output voltage across C3.13.2 to 13.4 volts appearing across C3 shows that the gadget is ready for use. Additionally, the load delivering capability of the charger can be ascertained by temporarily connecting a 6 to 10 ohms (25 watt) resistance across the output in place of the battery. Keep the gadget ON for at least ten minutes and see that there is no change in the regulated DC output voltage and also that there is no excessive heating of the transformer and regulator.
LEAD IDENTIFICATION OF MAJORCOMPONENTS
Fig.10.6 shows the pin connection diagram of IC 78T12.
Note: Photographs shown in Figs. 10.4 any 10.5are only representative ones to give an idea as to how the meters may look like.
Written by David on January 7th, 2010 with
3 comments.
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Prajith
#1. January 7th, 2010, at 10:16 PM.
Thanks for posting this.