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

24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 is a very useful project, it helps battery work good and last long.

This charger is designed specifically for a 24V, 7Ah lead-acid battery.

Also, it uses an LM317 IC to regulate both voltage and current, ensuring safe and proper charging of the battery.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors	100Ω 1/4 watt	1
	0.85Ω 2W	1
	220Ω 1/4 watt	1
	Preset 10k	1
Semiconductors	IC LM317	1
	Transistor BC547	1
Capacitors	Electrolytic 2200μF 50V	1
	Electrolytic 100μF 50V	1
	Diodes 1N5402	1
	Bridge Rectifier 1N5402	4
	Fuse 2A	1
	Transformer 0V-24V 1AH, 230V primary, 35V/3A secondary step-down	1

230V AC change to 35V AC using step-down transformer and then 35V AC change to DC using bridge rectifier D1.

C1, a 2200µF capacitor, smooths the DC supply and removes voltage ripples and then the LM317 IC controls the voltage and provides the correct charging voltage.

After that, output voltage depend on resistors R3 and VR1 setting and transistor Q1 BC547 and resistor R2 limit charging current and protect from too much current.

Now diode D2 stop reverse current from battery to circuit and R2 is 0.85 ohm which is not common so make it using 6.2 ohm and 1 ohm in parallel.

Finally, we connect the battery through fuse F1 and this fuse protects the circuit from overcurrent and short-circuit conditions.

Formulas with Calculations:

1. Output Voltage Vout of LM317:

Formula:

Vout = Vref × (1 + VR1 / R3)

where,

• Vref is 1.25V for LM317 reference voltage

Example:

R3 = 220 ohms and VR1 = 10k ohms

Vout = 1.25 × (1 + 10000 / 220)

Vout = 24.1V

2. Current Limiting Resistor R2:

Formula:

R2 = 0.6 / Imax

Example:

Imax is 0.85A

R2 = 0.6 / 0.85 = 0.85 ohms

3. Capacitor Selection C1 & C2:

Formula:

C = I / (2 × f × ΔV)

where:

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

Example:

C1, a 2200µF capacitor, works well in the actual circuit, as these formulas help set the output voltage, limit the charging current, and smooth the DC voltage.

How to Build:

To build a 24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 follow the below steps for connections:

• First, place all parts as shown in circuit diagram.
• Next, connect input pin of LM317 IC1 to positive of C1 and negative of C1 to GND, ADJ pin of IC1 connect to collector of Q1 transistor and then output pin of IC1 connect to one end of R3 and other end of R3 go to middle leg of VR1 and 2nd leg of VR1 to GND.
• Then C2 positive side go to IC1 output and negative side go to GND.
• After that, D2 diode anode go to IC1 output and cathode go to one side of fuse F1 and other side of fuse go to positive of battery.
• Lastly, negative of battery go to GND.

Bridge Rectifier D1:

• One pin goes to input of IC1, two pins go to wires from transformer and then last pin to GND

Q1 Transistor:

• Now collector pin to ADJ pin go of IC1, base pin go to GND through R1 and emitter pin go to GND
• Then R2 0.85Ω resistor connects to GND which works as current limiter.

Conclusion:

Overall, this 24V Battery Charger Circuit for Lead Acid Batteries with IC LM317 is safe and good for charging small lead acid batteries.

Furthermore, it controls voltage and current and has reverse current protection and fuse for safety.

Therefore, follow the wiring and values, through this we can build this charger easily.