In this post we will talk about 3 Simple 12V Battery Charger Circuits.
We can use them for charging any lead acid battery.
12V Battery Charger Circuit using a DC Power Supply and an Ammeter:
Below are the circuit parts and connections details mentioned:
Parts List:
| Component | Description | Quantity |
|---|---|---|
| Resistor | 1k 0.5W | 1 |
| Capacitor | 100µF 35V | 1 |
| Semiconductors | ||
| Transformer 14V / 5A / 230V | 1 | |
| Ammeter 0 – 20A | 1 | |
| Diodes 6A4 | 4 | |
| Red LED 5mm 20mA | 1 |
This is input side of transformer.
To make voltage low for charger it connect to main power.
On other side of transformer one bridge rectifier is connected.
Bridge rectifier change the transformers AC alternating current to DC direct current for charging battery.
One filter capacitor is connected after bridge rectifier.
This capacitor help to make DC smooth and remove ripple from voltage.
Positive side of bridge rectifier connects to positive terminal of 20A ammeter.
Ammeter check how much current is going in the circuit.
To charge lead acid battery connect negative wire from ammeter to batteries positive terminal.
Then connect batteries negative terminal to negative wire from bridge rectifier.
Now circuit is complete and current can move from rectifier to battery.
Now talk about Ah formula for battery charge:
First check battery Ah (ampere-hour) capacity.
Say the battery is B Ah.
Use 20A ammeter to see how much charging current (I) is coming.
Charging time (t) is how many hours we can charge the battery.
Use this formula:
Ah = I × t
where:
- Ah is battery charge
- I is current in amperes
- t is time in hours
For example: If ammeter show 5A for 5 hours then battery gets:
5A × 5 hours = 25 Ah
Be sure battery does not get more current than it can take.
Too much charging current can damage the battery.
Always look battery voltage and condition while charging to keep it safe and to work good.
12V Gel Battery Charger Circuit using LM338 IC:
This second battery charger uses LM338 IC it gives steady current and voltage to battery.
Because of this battery charge very well and stay healthy for long time.
This circuit is good for charging 12V gel type battery in safe and easy way.
Parts List:
| Component | Quantity |
|---|---|
| Resistors (all 1/4 watt unless specified) | |
| 1k | 1 |
| 1Ω 2W | 1 |
| 470Ω | 1 |
| 10k | 1 |
| 2.2k | 1 |
| Capacitors | |
| Ceramic 0.1µF | 2 |
| Semiconductors | |
| Voltage Regulator IC LM338 | 1 |
| Transistor BC547 | 1 |
| DC Source 15V | 1 |
| Red LED 5mm 20mA | 1 |
| Green LED 5mm 20mA | 1 |
Circuit Working:
This circuit start with input voltage source.
LM338 is voltage regulator and it makes output voltage stable.
We set output voltage to 14V for charging 12V battery.
One BC547 transistor is used to control ADJ pin of LM338.
By changing voltage at ADJ pin we can change output voltage of LM338.
One LED connects between BC547 collector and LM338 ADJ pin.
This LED show charging status.
If LED is ON and battery is charging.
And if LED is OFF, battery is full.
One resistor is put between base and emitter of BC547.
This resistor help to sense current and control charging current.
Formulas:
LM338 output voltage (Vout) is calculated using formula from LM338 datasheet:
Vout = Vref × (1 + R2/R1) + Iadj × R2
where:
- Vref is inside voltage around 1.25V
- R1 is resistor between ADJ pin and Vout pin
- R2 is resistor between ADJ pin and ground
- Iadj is very small current going into ADJ pin which is very tiny in microampere
To make Vout = 14V we can change formula and solve for R2:
R2 = R1 × (Vout / Vref – 1)
We can change R2 using one small potentiometer and this helps to set output to exact 14V for battery charging.
Current going through BC547 transistor also decide how much battery is charging.
One resistor between base and emitter of BC547 is for current sensing and it control charging current.
Charging current is linked to base current and BC547 gain which is called hfe.
To keep charging current safe and not too high then we can adjust this resistor properly.
12V Battery Charger Circuit with Auto Cut Off:
This is third circuit and it is 12V battery charger with auto cut off system.
It stop charging when battery is full and so battery does not get overcharged.
This circuit is also for fast charger and it charges battery quickly and safely.
Parts List:
| Component | Quantity |
|---|---|
| Resistors (all 1/4 watt unless specified)) | |
| 240Ω | 1 |
| 0.5Ω 5W | 1 |
| 1k | 2 |
| Potentiometer 10k | 1 |
| Capacitors | |
| Electrolytic 1000µF 25V | 1 |
| Ceramic 0.1µF | 1 |
| Semiconductors | |
| Voltage Regulator IC LM338 | 1 |
| Transistor BC547 | 1 |
| Transformer 0 – 12V 5A | 1 |
| Diodes 6A4 | 5 |
| Zener Diode 14V 1W | 1 |
| Red LED 5mm 20mA | 1 |
| Green LED 5mm 20mA | 1 |
This circuit start with 15V DC power supply and it goes to input of LM338 voltage regulator.
LM338 is 3-pin adjustable voltage regulator which gives steady output voltage for charging battery.
We can use this circuit to give safe and adjustable voltage.
Input voltage connects to LM338 IC and we can set output voltage how we want.
LM338 output is connected to lead acid battery for charging.
One Zener diode is used in negative side and it helps to sense battery voltage.
Zener diode is 14V type, when battery charges up to 14V or more the Zener diode start to conduct.
BC547 transistors collector pin is connected to ADJ pin of LM338.
ADJ pin control the output voltage of LM338 and if voltage change here then output also will change.
When battery reaches 14V then Zener diode will ON and then BC547 will also turn ON.
When BC547 is ON and it connect ADJ pin to ground.
This make LM338 output connects very low which is almost zero so charging stops.
Battery does not take more current and this is auto cut off.
It save battery from overcharging.
Conclusion
We see different types of 12V battery charger circuits which is from simple capacitor type to more better ones with transistor and voltage regulator.
These circuits gives good way to charge 12V battery safely and nicely.
Does not matter if anyone is beginner but want easy charger or hobby person want better charging and these circuits are good for both.