Introduction:
Proper battery charging is essential for its longevity. Overcharging can reduce the battery's performance and even cause it to deteriorate quickly. In this article, I have shown how to make a 12-volt battery charger with an automatic cutoff using an IRFZ44N MOSFET and a TL431 adjustable shunt regulator. This charger will automatically stop charging once the battery is fully charged, protecting it from overcharging.
With this Smart charger, you can charge a 12V/7AH UPS battery (sealed lead-acid-SLA) or any battery of equivalent size. You can use a 30-watt solar panel or a 13- to 15-volt, minimum 2.5-ampere AC transformer for the input voltage. This project is beneficial for those who are interested in electronics and love DIY projects.
Note: To charge the battery with an AC transformer, the transformer must convert the AC to DC using the necessary rectifier and a 2200µF capacitor. Then, connect the positive from there to the "VIN" of the charger circuit.
DIY 12-Volt Battery Auto Cut Off Charger Schematic Circuit Diagram
Project: Beattery Charger
Here is the tested circuit diagram of a 12V/7AH UPS battery (Sealed Lead-Acid-SLA) charger. This charger can charge any other 12-volt battery within 10A/H. It can be used with a 20-watt solar panel or by inputting the DC voltage of a 14-volt/3A AC transformer into it.
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| 12V Auto Cutoff Battery Charger Schematic Circuit Diagram |
Required components:
Q1- IRFZ44N N-Channel MOSFET
U1- TL431 Shunt Regulator
VR1- 10KΩ Potentiometer
R1- 1KΩ
R2, R3- 2.2KΩ
R4- 1KΩ
LED1- Red LED (Cutoff)
LED2- Green LED (Charging)
A1- 10A Ampere Meter
D1- 6 Ampere Rectifier Diode
How this 12-volt auto cutoff battery charger works
• Q1- IRFZ44N:
IRFZ44N is an N-channel power MOSFET, and it is unique in this circuit for its low temperature even at high current, and excellent auto cutoff. Positive voltage will come to the gate of the MOSFET (via the pull-up resistor), which will turn on the MOSFET and start charging the battery. LED1 will light up (charging indicator). When the gate voltage of the MOSFET drops below the threshold, the MOSFET will turn off, which will cause the battery charging to stop. LED2 will light up (full charge indicator).
• U1- TL431:
TL431 is an adjustable shunt regulator that works like a programmable zener diode. When the battery voltage is low, the voltage at the reference pin of the TL431 will be below its threshold voltage (about 2.5V). Since TL431 is off in this state, the MOSFET gate pin will be positively biased by R1 {Gate Threshold Voltage - Vgs(th)}, and the battery will start charging. As the battery voltage increases, the voltage at the reference pin of the TL431 will also increase through the voltage divider formed by VR1 and R4.
When the voltage at the reference pin reaches about 2.5V, a low-impedance path will be formed between the cathode and anode of the TL431, as soon as the TL431 turns on, the gate voltage of the Q1 MOSFET decreases (negative), cutting off the battery charge, and the negative supply to the cathode of LED 1 will indicate Cutoff.
Note: The TL431 datasheet has all its specifications. It is a widely used component. You can get a TL431 regulator from a working but unused mobile charger if you cannot get one.
Thank you all! For more electronic project building and LED TV repair tutorials, visit our Ornate Pixels channel on YouTube.
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