A car battery charger is an important tool that helps keep a car running smoothly by maintaining the batteries charge.
The circuit design shown here is a simple but very effective car battery charger that uses the MC78T12ABT integrated circuit.
This voltage regulator is strong enough to handle a lot of current.
Made by Freescale this IC is similar to a 7812 and comes in a TO-3 package with a maximum capacity of 3A.
This circuit is specifically designed to charge 12V lead acid batteries and has features that let you check the current and voltage levels.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistors | ||
| Resistor | 2.2k | 1 |
| Capacitors | ||
| Ceramic Capacitor | 0.01µF | 2 |
| Electrolytic Capacitor | 1000µF, 25V | 1 |
| Semiconductors | ||
| IC | MC78T12ABT | 1 |
| IC ground diode | 1N4001 | 3 |
| Output Diode | 6A4 | 1 |
| Bridge rectifier diode | 6A4 | 4 |
| LED | Any 5mm, 20mA | 1 |
| Meters | ||
| Ammeter | 3A FSD | 1 |
| Voltmeter | 20V FSD | 1 |
| Other Components | ||
| Transformer | 0-12V primary, 230V and 3A secondary step-down transformer | 1 |
| Battery | 12V | 1 |
The above circuit diagram shows alternating current AC from the wall outlet which operates at 230V goes through a process where its voltage is lowered to a safer level using a transformer.
This transformer has a secondary winding that outputs 15V and can handle a current of 3A.
This lower voltage is then ready for further processing.
Next, the AC is changed into direct current DC using a bridge rectifier BR1.
The result of this conversion is a pulsating DC which is then smoothed out by a large electrolytic capacitor C1 that has a capacitance of 1000µF and a voltage rating of 25V.
This smoothing helps to stabilize the DC voltage.
The voltage is regulated by ICI MC78T12ABT integrated circuit keeping it steady at 14.1V.
To do this the ground pin of the regulator is raised to 2.1V with the help of diodes D1, D2 and D3.
This adjustment brings the output voltage to the needed 14.1V which is the total of 12V and 2.1V.
The regulated output is sent to the battery through diode D4 which prevents any current from flowing back into the circuit if the mains power is off.
Additionally resistor R1 and LED1 work together to show if the battery is charging.
M1 acts as an ammeter to show the charging current while M2 is a voltmeter that displays the batteries voltage during charging.
Formulas with Calculations:
To design you own circuit for Car Battery Charger Circuit using IC MC78T12ABT follow the below mentioned formulas with calculations:
Filter Capacitor (C1):
Ripple voltage (∆V) is given by:
∆V = I / (f × C)
where,
- I is the load current, 2A is required for a car battery charger)
- f is the mains frequency for avout 50Hz
- C is the capacitance for 1000µF
Substituting the values:
∆V = 2 / (50 × 1000µ10^-6) = 0.04V
The ripple voltage is within acceptable limits for the circuit.
Current Limiting Resistor for LED (R1):
Voltage across LED = 2V for red LED
Current through LED = 10mA
R1 = (14.1V – 2V) / 10mA = 2.2kΩ
How to Build:
To build a Car Battery Charger Circuit using IC MC78T12ABT follow the below mentioned steps for connections and assembling:
- Assemble all the components as required in the above circuit diagram.
- Connect capacitor C2 from the input pin of IC1 MC78T12ABT to GND.
- Connect the positive of capacitor C2 from input pin of IC1 MC78T12ABT and the negative of capacitor C2 to GND.
- Connect the bridge rectifier BR1 one wire of 0V-12V transformer, other pin of BR1 to input pin of IC1 MC78T12ABT, third pin GND, and fourth pin to second wire of 0V-12V transformer.
- Connect a fuse F1 to 230V AC.
- Connect GND pin of IC1 MC78T12ABT to GND through diodes D1, D2 and D3 in series.
- Connect the output pin of IC1 MC78T12ABT to capacitor C3 and GND.
- Connect the diode D4 from output pin of IC1 MC78T12ABT.
- Connect resistor R1 and LED1 in series from output pin of IC1 MC78T12ABT and GND.
- Connect meter M1 from output pin of IC1 MC78T12ABT.
- Connect meter M2 from output pin of IC1 MC78T12ABT to GND.
- Connect the output pin of IC1 MC78T12ABT to positive supply of +12V battery and negative of battery to GND.
Conclusion:
This Car Battery Charger Circuit using IC MC78T12ABT is a dependable and budget friendly way to keep 12V lead acid batteries charged.
It offers steady charging and has built in safety features to prevent reverse currents.
The addition of monitoring tools like an ammeter and voltmeter makes it even more useful for users.
With its easy design and common parts this circuit is perfect for people who love DIY electronics.