In this post we will talk about 3 Simple 12V Battery Charger Circuits, which we can use them for charging any lead acid battery.
Circuit take AC power and convert into DC and then, it give proper voltage and current to battery, also it control charging so battery do not overcharge.
Also, these circuits are useful for car battery, backup system and DIY projects and it is easy to make by suing basic electronic parts.
12V Battery Charger Circuit using a DC Power Supply and an Ammeter:
Below are the circuit parts and connections details mentioned:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistor | 1k 0.5W | 1 |
| Capacitor | Electrolytic 100µF 35V | 1 |
| Semiconductors | Transformer 14V / 5A / 230V | 1 |
| Ammeter 0 – 20A | 1 | |
| Diodes 6A4 | 4 | |
| Red LED 5mm 20mA | 1 |
The above circuit diagram show left side as input of transformer, so it connect to main power and make voltage low for charger.
However, on other side of transformer one bridge rectifier connect and then this bridge rectifier change AC current to DC current for battery charging.
After that, filter capacitor C1 connect after bridge rectifier, so this capacitor make DC smooth and remove ripple.
Then, positive side of bridge rectifier connect to positive terminal of 20A ammeter, so ammeter check how much current go in circuit.
Also, for charging lead acid battery, connect negative wire from ammeter to battery positive terminal and then connect battery negative terminal to negative wire from bridge rectifier.
Now, circuit is complete and so current move from rectifier to battery.
Next, talk about Ah formula for battery charge:
First, check battery Ah capacity, say battery is B Ah, then use 20A ammeter and check charging current (I).
Finally, charging time (t) show how many hours we 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
So, be sure battery does not get more current than it can take, because too much charging current can damage the battery.
Therefore, always look battery voltage and condition while charging to keep it safe and to work good.
12V Gel Battery Charger Circuit using LM338 IC:
Also, 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.
Hence, this circuit is good for charging 12V gel type battery in safe and easy way.
Parts List:
| Components | 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.
Here, we set output voltage to 14V for charging 12V battery.
However, one BC547 transistor controls the ADJ pin of the LM338 and changing the voltage at the ADJ pin changes the output voltage of the LM338.
Also, one LED connects between BC547 collector and LM338 ADJ pin and this LED show charging status, if LED is ON and battery is charging, and if LED is OFF and battery is full.
Then, one resistor is put between base and emitter of BC547 and this resistor help to sense current and control charging current.
Formulas:
Here, we calculate the LM338 output voltage (Vout) using the formula from the 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)
Moreover, we can change R2 using one small potentiometer and this helps to set output to exact 14V for battery charging.
Also, current going through BC547 transistor also decide how much battery is charging.
Furthermore, one resistor sits between the base and emitter of the BC547 to sense current and control the charging current, this charging current links to the base current and the BC547 gain 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:
Third, this circuit is a 12V battery charger with an automatic cut-off system, it stops charging when the battery is full, which prevents the battery from overcharging
Hence, this circuit is also for fast charger and it charges battery quickly and safely.
Parts List:
| Components | 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 |
Firstly, 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.
Further, we can use this circuit to give safe and adjustable voltage and input voltage connects to LM338 IC and we can set output voltage how we want.
Also, the LM338 output charges the lead-acid battery.
A 14V Zener diode on the negative side senses the battery voltage and it starts conducting when the battery charges to 14V or higher.
Also, the BC547 transistors collector connects to the LM338 ADJ pin and since the ADJ pin controls the LM338 output voltage, any change in this voltage changes the output
Hence, when battery reaches 14V then Zener diode will ON and then BC547 will also turn ON.
After that, when BC547 is ON and it connect ADJ pin to ground and this make LM338 output connects very low which is almost zero so charging stops.
However, the battery does not take more current and the system automatically cuts off to save the battery from overcharging.
Advantages of 12V Battery Charger Circuit:
- Firstly, circuit is very simple and easy to make.
- Also, cost is low and components are easily available.
- Moreover, it is small in size and easy to carry.
- In addition, it is good for basic charging purpose.
- Furthermore, maintenance is very less.
Disadvantages of 12V Battery Charger Circuit:
- However, it does not control charging automatically.
- Also, battery can overcharge if not monitored.
- Moreover, efficiency is not very high.
- In addition, it is not suitable for all types of batteries.
- Finally, no protection features like short circuit or overload.
Conclusion
Overall, we see different types of 12V battery charger circuits which is from simple capacitor type to more better ones with transistor and voltage regulator.
Also, these circuits gives good way to charge 12V battery safely and nicely.
Therefore, it does not matter if anyone is beginner but want easy charger or hobby person want better charging and these circuits are good for both.
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