This Simple Constant Voltage, Constant Current Battery Charger Circuit talks about how to make smart 12V battery charger!
It uses one common chip named LM317 IC.
This charger give two thing always same: voltage and current.
Voltage help stop too much load on battery.
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.
Because of this two way working battery charge safe and stays good and also makes charging better.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | 240Ω, RC (as given in description) (all 1/4 W CFR) | 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 |
The 12V AC coming from transformer changes to DC using four diodes 1N5402 in bridge shape.
Then one big capacitor 1000uF is used to make the DC smooth and clean.
This smooth DC around 16V connects to LM317 IC.
LM317 is set to work in constant voltage and constant current mode.
The ADJ pin of LM317 connect to 240 ohm resistor and other side of resistor connects to OUT pin.
One small transistor BC547 is used to control current and give steady current to battery.
BC547 collector connects to ADJ pin through one LED and this LED show charging is happening.
One resistor called RC is connected between base and emitter of BC547 and is also connected in ground line of 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 battery take charging current the LED stays ON which means battery is charging.
When battery is full and no more current is needed BC547 stop working and LED goes OFF, this mean battery is full.
One potentiometer is added between ADJ pin and ground which help to set correct full voltage around 14V for 12V battery.
How it work:
The potentiometer control voltage for battery and IS LM317 keep this voltage same.
BC547 keep current same during charging.
It changes current in LM317 IC as battery needs.
LED with BC547 show charging status , ON means charging OFF means full.
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.
LED make easy to know if battery is charging or full.
How to Build:
To build a Simple Constant Voltage, Constant Current Battery Charger Circuit follow the below mentioned steps for connections.
Bridge Rectifier:
- Take 12V 1A transformer and connect its AC wires to AC side of bridge rectifier.
- Now connect 1000uF capacitor to DC side of rectifier.
- Positive and negative of capacitor should connect to PCBs positive and GND.
LM317 Setup:
- Connect DC output from bridge rectifier to IN pin of LM317.
- Take ADJ pin of LM317 and connect to one side of 240 ohm resistor.
- Other side of resistor connect to OUT pin of LM317.
- Also connect ADJ pin to middle pin of potentiometer.
- One side pin of potentiometer connects to PCB ground.
BC547 Transistor for Current Control:
- BC547 collector connect to LM317s ADJ pin through one LED.
- BC547 emitter connects to ground.
- RC resistor connect BC547 base to ground also.
Charging LED:
- LED positive leg anode connect to BC547s collector.
- LED negative leg cathode connects to ground.
Final Connections:
- Batteries positive wire connect to circuits positive output.
- Batteries negative wire connects to circuits negative output.
Testing:
- After connecting transformer to mains power use multimeter to check LM317 output voltage.
- Be sure it is in correct range.
Charging LED:
Note:
- Before switching ON check PCB for short circuits.
- Check e all parts are fitted correctly.
- Adjust potentiometer properly to stop battery from overcharging.
- 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 Simple Constant Voltage, Constant Current Battery Charger Circuit give proper and safe charging to battery.
The voltage can be changed so it work with different type of batteries and their needs.
References:
Using constant current and constant voltage charging to fully charge a battery
Hello, I have been attempting to construct a battery charger for my 18650 4s battery packs (5 of them).
Your post here seems to be a do-able project for me (enthusiast electronics amature).
Already have modified a salveged microwave oven transformer to give me ~19VAC. Not sure of the amp output yet. Have constructed a rectfier bridge using 4 diodes, 2 Caps, and a choke.
I am undecided from here how to proceed. I have reviewed your post, and find it interesting. One would think it possible to adjust the design to accomodate 16v 8a CV/CC.
However, my expertise is not to that level yet. Might you have some direction on this?
Thank you.
Hello Bill, the above circuit is perfectly suitable for your application, since it is 100% a CC/CV based design.
You can go ahead and build this circuit to charge your 4S5P 18650 battery bank safely.
16V is the correct optimization for the voltage setting, since it enable around 4.1V for each, instead of the full 4.2V allowing the cells to charge under safe conditions and never over-charge.
For the resistor RC, you can use the following formula:
Rc = 0.6 / 50% of Battery Ah
I would recommend removing the LED network, since it might hamper with the proper cut-off of the LM317 IC.
And yes, LM317 might not be able to provide sufficient current for the charging. so please consider using the LM338 equivalent, for optimal current to the batteries.