Simple Lead Acid Battery Charger Circuit using IC LM350

A Simple Lead Acid Battery Charger Circuit made just for lead acid batteries is really important for keeping them charged properly and helping them last longer.

These batteries are used in many places like backup power systems, cars and renewable energy storage.

In this article, we will explore how a battery charger circuit works that uses the IC LM350 voltage regulator.

This regulator is special because it can provide a steady and adjustable voltage making it perfect for charging 12V lead acid batteries effectively.

Circuit Working:

Parts List:

The circuit diagram for the lead acid battery charger using LM350 shown here is a really useful adjustable voltage regulator that can provide up to 3A of current.

It can output a voltage anywhere from 1.25V to 33V.

This circuit is carefully designed to give the battery a steady voltage and current which helps prevent overcharging and makes the battery last longer.

It works with a 20V DC input.

To protect the circuit from mistakes like connecting the battery the wrong way a diode called D1 1N5401 is used.

The main part of the regulation is done by IC1 LM350 which controls the output voltage and current.

The reference voltage is set using resistors R1 120Ω and R2 82Ω.

Capacitor C1 10µF helps keep the voltage stable and reduces any ripples.

Transistor Q1 BC557 is in charge of controlling the charging current.

Additionally, Q2 BC547 acts as a switch that stops the charging when the battery is fully charged.

Resistors R3 10k, R4 33k and preset R6 2.2k help manage the transistors functions.

An LED1 lights up to show that the battery is charging.

When the battery reaches the right voltage Q2 BC547 kicks in reducing the charging current and indicating that the battery is fully charged.

This whole system makes sure the battery is charged safely and efficiently with a controlled voltage and current.

Formulas with Calculations:

Below mentioned are the formulas with calculations for Simple Lead Acid Battery Charger Circuit using IC LM350:

Output Voltage Calculation:

Vout = Vref * (1 + (R2 / R1)) + Iadj * R2

where,

Vref = 1.25V Reference voltage of LM350

Iadj = 50µA Negligible

R1 = 120Ω

R2 = 82Ω

Substituting values:

Vout = 1.25 * (1 + (82 / 120))

Vout = 1.25 * (1 + 0.683)

Vout = 1.25 * 1.683

Vout = 2.1V

To set the output voltage to 14.4V for charging a 12V lead acid battery, R2 needs to be adjusted accordingly.

Current Limiting Calculation:

I = Vref / R1

Substituting values:

I = 1.25V / 120Ω

I = 10.4mA

With transistor amplification, the circuit can provide a charging current that goes as high as 2A to 3A.

How to Build:

To build a Simple Lead Acid Battery Charger Circuit using IC LM350 following steps need to be followed:

• Assemble all the components mentioned in the above circuit diagram
• Connect pin 1 ADJ of IC1 LM350 to one end of resistor R2 and the other end of resistor R2 to emitter of transistor Q1.
• Connect pin 2 OUTPUT of IC1 to one end of resistor R1 and other end of resistor R1 between ADJ pin of IC1 and resistor R2.
• Connect pin 3 INPUT pin of IC1 to one end of resistor R5 and other end of resistor R5 to base of transistor Q2.
• Connect positive of capacitor C1 to INPUT pin of IC1 and connect negative of capacitor C1 to GND.
• Connect positive of capacitor C2 to OUPUT pin of IC1 and connect the negative of capacitor C2 to GND.
• Connect cathode of diode D1 to input of IC1 and anode of D1 to +20V DC.
• Connect collector of transistor Q1 to positive of LED1 and negative of LED1 to collector of transistor Q2.
• Connect the base of transistor Q1 between resistor R3 and R4 .
• Connect one end of resistor R3 from output pin of IC1 and other end of resistor R1 to base of transistor Q1, connect resistor R4 from base of transistor Q1 and the other end of resistor R4 to center leg of VR1 preset, connect the other leg of VR1 preset to GND.
• Connect transistor Q2 collector to negative of LED1.
• Connect the transistor Q2 base to one end of resistor R5 and other end of resistor R5 to INPUT pin of IC1.
• Connect the emitter of transistor Q2 to GND.

Conclusion:

This Simple Lead Acid Battery Charger Circuit using IC LM350 made with the IC LM350 is a easy and effective design that keeps the voltage and current in check for safe charging.

When the battery is fully charged the circuit automatically lowers the charging current to avoid overcharging.

With transistors like the BC557 and BC547 along with the IC LM350 it offers dependable and adjustable voltage control making it a great option for anyone looking to create their own battery charger.

References:

Lead-Acid Battery charger using LM350 and LM301