Thursday, January 27, 2022

12 Volts Automatic Lead Acid Battery Charger Using LM350 IC with PCB

Fig, 1 - 12 Volts Automatic Lead Acid Battery Charger Circuit + PCB

This is a 12V Automatic Lead Acid Battery Charger Circuit, of the type used in nobreaks, with loads ranging from 1A to 9 Amps.

The main advantage of this battery charger circuit is its charging mode, since it has a charge control, so that the battery does not receive voltage when it is not needed, giving more autonomy to the battery and protecting it from overvoltage.

What is Lead Acid Battery

The lead acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté

It is the first type of rechargeable battery ever created. Compared to modern rechargeable batteries, lead-acid batteries have relatively low energy density. 

Despite this, their ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. 

These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by starter motors.

Lead Acid Battery Charger Method

There are several features related to the charging process of various battery segments and classes. 
The charging method for lead-acid batteries differs from NiCd batteries in the voltage limit, rather than the current limit to be used.

The charging time for lead-acid (sealed) batteries is 8 to 16 hours, depending on the capacity of the battery and the method used. 

With higher charging currents and multi-stage charging methods, the charging time can be reduced to 8 hours or less. 

For a multi-stage charger, three stages of charging application are required: 
  •  Constant current
  •  Peak charge
  •  Float charge

The Circuit

In Figure 2 below, we have the schematic diagram of the lead-acid battery charger circuit. It is a very simple circuit, with few external components, easy to assemble, yet even with its simplicity it works very well.
Fig. 2 - Schematic Circuit 12 Volts Automatic Lead Acid Battery Charger Circuit


The voltage regulation for charging the battery is done by the LM350 IC voltage regulator. 
The charging current control is done using the BC548B NPN transistor, it controls the demand current from the battery, causing the circuit to activate or deactivate the voltage required for charging the battery.

The potentiometer RP1 1K is used for fine tuning the battery charging voltage, which should be adjusted by using a multimeter to measure the output voltage, which should be at most 20% of the nominal battery voltage.

If you cannot find the description of the battery charging voltage on the battery itself, you can adjust the average charging voltage, which ranges from 13.8V to 14.4V.

It is necessary to use a heat sink in the voltage regulator, since the initial current to charge the battery is high. 
As the circuit charges the battery, it lowers the charging current until it reaches zero voltage, when the battery is fully charged.

Components List

  • Semiconductors
    • U1 .......... LM350 Voltage Regulator Circuit
    • Q1 .......... BC548B NPN Transistor
    • D1 .......... 1N5408 Silico Diode

  • Resistor
    • R1 .......... 100Ω Resistor (brown, black, brown, gold)
    • R2 .......... 0.5Ω 5W Resistor (green, black, silver, gold
    • R3 .......... 470Ω Resistor (yellow, violet, brown, gold)
    • R4 .......... 120Ω Resistor (brown, red, brown, gold)
    • RP1 ........ 1KΩ Potentiometer

  • Capacitor
    • C1 .......... 2.2uF / 25V Electrolytic Capacitor
    • C2 .......... 0.33uF / 25V Electrolytic Capacitor
  • Other
    • P1, P2 .... 2-pin PCB soldering terminal blocks
    • Others .... Printed Circuit Board, Heat Sink, tin, wires, etc.

Printed Circuit Board

In Figure 3, we provide the PCB - Printed Circuit Board, in GERBER, PDF and PNG files. These files are available for free download, on the MEGA server, in a direct link, without any bypass. 

All to make it easier for you to do a more optimized assembly, either at home, or with a company that prints the board. You can download the files in the Download option below.

Fig. 3 - PCB - 12 Volts Automatic Lead Acid Battery Charger Circuit

Files to Download, Direct Link:

Click on the link beside: GERBER, PDF and PNG files

If you have any questions, suggestions or corrections, please leave them in the comments and we will answer them soon.

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