12V Lead-Acid Battery Charger Circuit with LM350

12V Lead-Acid Battery Charger Circuit Using LM350

Charging a 12V lead-acid battery efficiently requires a constant voltage source with temperature compensation to prevent overcharging. This battery charger circuit is designed around the LM350 voltage regulator, providing an adjustable output voltage between 13V and 15V.

How This Circuit Works

This charger operates as a constant voltage source with negative temperature coefficient adjustment to enhance battery life and prevent overheating.

Key Components & Their Roles:

🔹 LM350 Voltage Regulator: Maintains a stable charging voltage.
🔹 Q1 (BD140 Transistor): Acts as a temperature sensor, adjusting output voltage based on temperature variations.
🔹 Q2 Transistor: Prevents battery discharge through R1 when mains power is unavailable.
🔹 R6 (Potentiometer): Allows adjustment of output voltage between 13V to 15V.
🔹 Power Supply: Requires 20V-30V DC at 3A for proper operation.

Circuit Operation Explained

1️⃣ The LM350 regulator maintains a fixed 1.25V voltage drop between its input and output terminals, ensuring constant current flow through R1.

2️⃣ Q1 (BD140) acts as a temperature sensor. With R6/R3/R4, it controls the base current of Q1, adjusting the output voltage based on temperature.

3️⃣ The negative temperature coefficient (-8mV/°C) ensures that as the battery temperature rises, the charging voltage decreases, preventing overcharging and thermal runaway.

4️⃣ Q2 Transistor prevents the battery from discharging through R1 when the main power supply is off.

5️⃣ LED Indicator glows when the circuit is powered, showing that charging is active.

Circuit Diagram & Implementation

🛠 Assembly Tips:

Place Q1 (BD140) close to the battery for accurate temperature sensing.
Use a heat sink with LM350 to prevent overheating.
Ensure your power supply is 20V-30V at 3A for reliable performance.

⚠️ Note: This circuit is not suitable for gel-type batteries, as they draw high current that could damage the charger.

Conclusion

This 12V lead-acid battery charger using LM350 provides a safe, efficient, and temperature-controlled charging process. By incorporating Q1 for temperature sensing and Q2 for protection, this circuit enhances battery lifespan while preventing overheating.

🔧 Start building your own charger today and optimize your battery’s performance! 🔧