This Constant Voltage, Constant Current Battery Charger Circuit teaches about how to make smart 12V battery charger! also, it uses one common chip named LM317 IC.
Further, this charger give two thing always same: voltage and current.
Voltage help stop too much load on battery and current ensures battery charges slowly and safely.
What is a Constant Voltage, Constant Current Battery Charger:
This battery charging circuit call CVCC charger keeps voltage same on battery when charging.
Also, it control charging current so battery gets steady current all time during charging and because of this two way working battery charge safe and stays good and also makes charging better.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 W CFR) | 240Ω, RC (as given in description) | 1 each |
| Potentiometer 10k | 1 | |
| Capacitor | Electrolytic 1000µF 25V | 1 |
| Semiconductors | Transistor BC547 | 1 |
| IC LM317 | 1 | |
| Diodes 1N5402 | 4 | |
| LED red 20mA 5mm | 1 | |
| Transformer 12V 1 Amp | 1 | |
| Battery 12V 7 Ah | 1 |
First, the 12V AC coming from transformer changes to DC using four diodes 1N5402 in bridge shape.
Then, a large 1000µF capacitor smooths and cleans the DC supply and this smooth DC of around 16V feeds into the LM317 IC, as a result, the LM317 operates in constant voltage and constant current mode.
Next, the ADJ pin of LM317 connect to 240 ohm resistor and other side of resistor connects to OUT pin.
Furthermore, a small transistor BC547 controls the current and provides a steady current to the battery, also in this setup, its collector connects to the ADJ pin through an LED and this LED indicates that charging is taking place.
One resistor, called RC, connects between the base and emitter of the BC547 and also connects to the ground line of the LM317.
To find RC value use this formula:
RC = 0.6 / (10% of battery Ah)
For Li-ion battery use this formula:
RC = 0.6 / (50% of battery Ah)
When the battery draws charging current, the LED stays ON, which means the battery is charging.
However, when the battery becomes full and no longer needs current, then BC547 stops working and the LED turns OFF and this means the battery is fully charged.
Additionally, a potentiometer between the ADJ pin and ground helps set the correct full voltage, around 14V for a 12V battery.
How it work:
The potentiometer control voltage for battery and LM317 keep this voltage same.
BC547 keep current same during charging and it changes current in LM317 IC as battery needs.
LED with BC547 show charging status , ON means charging OFF means full and also we can set exact voltage for 12V battery using potentiometer.
This charger circuit is strong and useful and it gives constant voltage and current while charging and LED make easy to know if battery is charging or full.
How to Build:
To build a Constant Voltage, Constant Current Battery Charger Circuit follow the below mentioned steps for connections.
Bridge Rectifier:
- First, take 12V 1A transformer and connect its AC wires to AC side of bridge rectifier.
- Now connect 1000uF capacitor to DC side of rectifier.
- Also, positive and negative of capacitor should connect to PCBs positive and GND.
LM317 Setup:
- Then connect DC output from bridge rectifier to IN pin of LM317.
- After that, take ADJ pin of LM317 and connect to one side of 240 ohm resistor and other side of resistor connect to OUT pin of LM317.
- Also, connect ADJ pin to middle pin of potentiometer and one side pin of potentiometer connects to PCB ground.
BC547 Transistor for Current Control:
- BC547 collector connect to LM317s ADJ pin through one LED, emitter connects to ground and also RC resistor connect BC547 base to ground.
Charging LED:
- Next, LED positive leg anode connect to BC547s collector and LED negative leg cathode connects to ground.
Final Connections:
- Batteries positive wire connect to circuits positive output and batteries negative wire connects to circuits negative output.
Testing:
- Also, after connecting transformer to mains power use multimeter to check LM317 output voltage and be sure it is in correct range.
Charging LED:
Note:
- Before switching ON, check the PCB for short circuits and verify that all parts are fitted correctly.
- Adjust potentiometer properly to stop battery from overcharging and check all component values and wires again if something is not working.
- Always be careful when working with electricity and follow safety rules.
Conclusion:
To conclude, the LED show if 12V battery is charging or full.
This constant voltage, constant current battery charger circuit provides proper and safe charging to the battery.
Additionally, we can adjust the voltage, so it works with different types of batteries and their requirements.