24V Battery Charger Circuit for Lead Acid Batteries with IC LM317

A lead acid battery charger is really important for keeping lead acid batteries working well and lasting a long time.

This type of charger is specially designed to safely and effectively charge a 24V, 7AH lead acid battery.

It uses a special part called an IC LM317 voltage regulator to control the charging voltage and it also has a system to manage the current making sure the battery gets charged just right.

Circuit Working:

Parts List:

A 230V alternating current AC is changed to a lower voltage of 35V AC using a step down transformer.

This lower AC voltage is then turned into direct current DC with a bridge rectifier called D1.

To make the DC smoother and reduce any bumps in the voltage a capacitor C1 which has a capacitance of 2200µF is used.

The LM317 integrated circuit regulates the voltage to make sure the battery gets the right charging voltage.

The exact output voltage depends on how resistors R3 and VR1 are set up.

The transistor Q1 BC547 along with resistor R2 that helps limit the current protecting against too much current during charging.

To keep the circuit safe diode D2 is added to stop any reverse current from the battery from going back into the circuit.

R2 is 0.85 ohm is not a common resistor value.

You can get this by putting a 6.2 ohm resistor and a 1 ohm resistor together in parallel.

Lastly, the output connects to the battery through a fuse F1, which helps protect against overcurrent or short circuits.

Formulas with Calculations:

Formulas with calculations for 24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 is mentioned below for better understanding:

Output Voltage (Vout) from LM317:

Vout = Vref * (1 + VR1 / R3)

where,

Vref =1.25V reference voltage of LM317
Example: If R3 = 220 ohms and VR1 = 10k ohms:
Vout = 1.25 * (1 + 10000 / 220)
Vout = 24.1V

Current Limiting Resistor (R2):

R2 = 0.6 / Imax
For a maximum charging current of 0.85A:
R2 = 0.6 / 0.85
R2 = 0.85 ohms

Capacitor Selection (C1 and C2):

C = I / (2 * f * ΔV)

where,

• I is the load current
• f is the frequency 50Hz
• ΔV is the ripple voltage

A C1 2200µF capacitor is selected because it meets the practical needs.

How to Build:

To build a 24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 following steps for connections are mentioned below:

• Assemble all the components as mentioned in the above circuit diagram.
• Connect the input pin of IC1 LM317 to positive of capacitor C1 and negative of capacitor C1 to GND.
• Connect the ADJ pin of IC1 LM317 to collector of transistor Q1.
• Connect the Output pin of IC1 LM317 to one end of resistor R3 and the other end of resistor R3 to center leg of VR1 and 2nd leg of VR1 preset to GND.
• Connect positive of capacitor C2 to output supply of IC1, and the negative of capacitor C2 to GND.
• Connect a anode of diode D2 from output pin of IC1 and cathode of diode D2 to one end of fuse and the other end of fuse to positive supply of 24V lead acid battery.
• Connect the negative of 24V lead acid battery to GND.
• Connect the bridge rectifier D2 didoes one pin to input of IC1, other pin to one wire of transformer, third pin to other wire of transformer and fourth pin to GND.
• Connect the collector of transistor Q1 to ADJ pin of IC1, connect the base of transistor Q1 to GND through resistor R1, and emitter of transistor Q1 to GND.
• Connect a resistor R2 at GND for current limiting resistor.

Conclusion:

This 24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 is a dependable and effective way to charge small lead acid batteries.

Its design makes sure that the voltage and current are controlled correctly and it includes safety features such as reverse current protection and a fuse.

If you follow the steps and calculations provided you can build and use this circuit successfully.

References:

BATTERY charger circuit