In this DIY Project, I will show you how to build a simple Lead Acid Battery Charger Circuit using easily available components. This circuit can be used to charge Rechargeable 12V Lead Acid Batteries with a rating 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
Introduction
Lead Acid Batteries are one of the oldest types of rechargeable batteries on the market. Lead Acid Batteries are still the favoured choice of batteries in almost all vehicles due to their inexpensive cost (for the capacity) compared to newer battery technologies and their ability to generate large surge currents (an important element in automobiles).
The fundamental issue with any battery is that it will deplete with time and will need to be recharged in order to supply the required voltage and current.
Different batteries have different strategies of charging and in this project, I will show you how to recharge a lead acid battery using a simple Lead Acid Battery Charger Circuit.
Warning: Before proceeding further, I want you to know that this circuit is tested in a specific test conditions and we do not guarantee that it will be 100% successful. Try this circuit at your own risk. Take all the necessary precautions as you might be handling Mains Voltage and high potential DC.
How to Recharge a Lead Acid Battery?
A step down transformer, a rectifier, a filtering circuit, and a regulator to maintain a constant voltage are required to charge a battery from AC. The battery can then be charged with the regulated voltage. If you only have DC voltage and want to charge a lead acid battery, you can accomplish so by sending the DC voltage through a DC-DC voltage regulator and some additional circuitry before sending it to the battery. A lead acid battery is also used in automobiles.
As seen in the above block diagram, a DC voltage is given to the DC voltage regulator. The voltage regulator used here is 7815, which is a 15V regulator. The regulated DC out voltage is given to battery. There is also a trickle charge mode circuitry which will help to reduce the current when the battery is fully charged.
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
7815
The 7815 is a part of the 78XX series of linear voltage regulators. You might have used 7805 and 7812 which produce a regulated voltage of 5V and 12V respectively. Similarly, the 7815 Voltage regulator produces a constant regulated voltage of 15V.
Lead Acid Battery
Lead Acid Battery is a rechargeable battery developed in 1859 by Gaston Plante. The main advantages of Lead battery is it will dissipate very little energy (if energy dissipation is less it can work for long time with high efficiency), it can deliver high surge currents and available at a very low cost.
Calibrate the Circuit
Before seeing the working, let me show you how to calibrate the circuit. For calibrating the circuit, you need a variable DC Power Supply (a bench power supply). Set the voltage in your bench power supply to 14.5V and connect it to CB+ and CB- of the Circuit.
Initially, set the jumper between positions 2 and 3 for calibrating. Now slowly turn the 50KΩ Potentiometer until the “Charged” LED turns ON. Now disconnect the power supply and connect the jumper between 1 and 2. Your circuit is ready as all you need is a DC (or AC) supply of 18V.
NOTE
- 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
NOTE:
- The battery should be charged with 1/10th it’s charging current.so 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.
