Battery Circuit Diagrams

Lead Acid Battery Charger Circuit

In this DIY Project, I will demonstrate how to construct a straightforward Lead Acid Battery Charger Circuit using readily available components. You can use this circuit to charge Rechargeable 12V Lead Acid Batteries rated in the range of 1Ah to 7Ah.


  • Introduction
  • How to Recharge a Lead Acid Battery?
  • Circuit Diagram
    • Components of Lead Acid Battery Charger Circuit
    • Component Description
  • Calibrate the Circuit
  • Circuit Explanation


Lead Acid Batteries represent one of the longest-standing categories of rechargeable batteries available. They continue to be the preferred battery type for most vehicles due to their cost-effectiveness (in terms of capacity) when compared to more recent battery technologies and their capacity to produce significant surge currents, a crucial aspect in automobiles.

The inherent challenge with any battery lies in its gradual discharge over time, necessitating recharging to ensure it can deliver the necessary voltage and current.

Various types of batteries employ distinct charging techniques, and within this project, I will illustrate the process of recharging a lead-acid battery using a straightforward Lead Acid Battery Charger Circuit.

Caution: Before advancing further, it’s essential to note that this circuit has been tested under specific test conditions, and we cannot assure a 100% success rate. Experiment with this circuit at your own risk. Exercise all necessary precautions, as you will be working with Mains Voltage and high DC potential.

How to Recharge a Lead Acid Battery?

To charge a battery from an AC power source, you’ll need a step-down transformer, a rectifier, a filtering circuit, and a voltage regulator to ensure a consistent voltage. Once these components are in place, you can charge the battery using the regulated voltage.

If you have only a DC voltage source and need to charge a lead-acid battery, you can achieve this by directing the DC voltage through a DC-DC voltage regulator and incorporating supplementary circuitry before delivering it to the battery. It’s worth noting that lead-acid batteries are commonly employed in automobiles as well.


As depicted in the block diagram above, a DC voltage is supplied to the DC voltage regulator. In this setup, we utilize a 7815 regulator, which provides a steady 15V output. This regulated DC voltage is then supplied to the battery. Additionally, there is a trickle charge mode circuitry implemented to diminish the current flow once the battery reaches a full charge.

Circuit Diagram

The circuit diagram of the Lead Acid Battery Charger is given below.

Components of Lead Acid Battery Charger Circuit

  • 7815
  • Bridge Rectifier
  • Resistors – 1Ω (5W), 1KΩ x 2, 1.2KΩ, 1.5KΩ x 2, 10KΩ
  • Diodes – 1N4007, x 3, 1N4732A (Zener)
  • 2SD882 NPN Transistor
  • LEDs x 4
  • 50KΩ Potentiometer
  • 12V Relay

Component Description


The 7815 belongs to the family of linear voltage regulators known as the 78XX series. You may be familiar with the 7805 and 7812 regulators, which generate regulated voltages of 5V and 12V, respectively. Likewise, the 7815 Voltage regulator maintains a steady regulated voltage output of 15V.

Lead Acid Battery

The Lead Acid Battery, invented by Gaston Plante in 1859, possesses several key benefits. Notably, it exhibits minimal energy dissipation, enabling extended operational periods with high efficiency. Additionally, it can supply substantial surge currents, all while remaining highly cost-effective.

Calibrate the Circuit

Before delving into its operation, let me guide you through the calibration process of the circuit. To calibrate the circuit effectively, you’ll require a variable DC Power Supply, such as a bench power supply. Set the voltage on your bench power supply to 14.5V and establish a connection to the CB+ and CB- terminals of the circuit.

Lead Acid Battery Charger Circuit

To begin, configure the jumper between positions 2 and 3 for the initial calibration. Gradually adjust the 50KΩ Potentiometer until the “Charged” LED illuminates. Next, disconnect the power supply and switch the jumper to positions 1 and 2. Your circuit is now prepared, requiring only an 18V DC (or AC) power source.


  • The 14.5V we set in the calibration is called the Tripping Point. When the Tripping point is set to 14.5V, the battery will charge for about 75% of its capacity.
  • If you want to charge 100%, then set the tripping point to ≈16V by removing the 7815 regulator and directly supplying 18V DC, but this is not recommended.

Circuit Explanation


  • The battery should be charged with 1/10th it’s charging the voltage regulator must generate 1/10th of the charging current produced by the battery
  • Heat sink should be attached to the 7815 Regulator to the get the better efficiency.

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