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 sealed lead-acid-SLA battery (UPS Battery) 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 Battery Charger Schematic Circuit Diagram
Project: Battery Charger
Here is the tested circuit diagram of a 12V/7AH sealed lead-acid-SLA 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.
12V Auto Cutoff Battery Charger Schematic Circuit Diagram
Required components:
| Component ID | Description / Specification | Quantity |
|---|---|---|
| Q1 | IRFZ44N N-Channel MOSFET | 1 |
| U1 | TL431 Shunt Regulator | 1 |
| VR1 | 10KΩ Potentiometer | 1 |
| R1 | 1KΩ - 1/4W Resistor | 1 |
| R2, R3 | 2.2KΩ - 1/4W Resistor | 2 |
| R4 | 1KΩ - 1/4W Resistor | 1 |
| LED1 | Red LED (Cutoff Indicator) | 1 |
| LED2 | Green LED (Charging Indicator) | 1 |
| A1 | Ampere Meter (10A Panel Meter) | 1 |
| D1 | 1N5400 - 6 Ampere Diode | 1 |
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. A 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. If you cannot get one, you can get a TL431 regulator from a working but unused mobile charger.
More Electronic Project: 555 IC Adjustable Delay Timer
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Frequently Asked Questions (FAQ)
1. Can I use another MOSFET instead of IRFZ44N in this circuit?
Yes, you can use equivalent N-channel power MOSFETs like IRF3205 or IRFZ48N. However, ensure that the pin configuration matches and it can handle the required battery charging current without excessive heating.
2. How do I accurately adjust the auto cutoff voltage using VR1?
Connect a fully charged battery (approx 14.2V to 14.4V) or a variable DC power supply set to 14.4V to the output terminal. Then, slowly turn the 10KΩ potentiometer (VR1) until LED1 turns off and LED2 lights up. This sets the perfect full-charge threshold.
3. Why are both LEDs glowing at the same time or flickering?
This usually happens when the battery voltage is right at the cutoff threshold, or if there is excessive voltage ripple from the input supply. Adding a 100µF capacitor parallel to the battery output or slightly adjusting VR1 will stabilize the circuit.
4. Can I charge a 12V Car or Motorcycle battery with this charger?
Yes, you can charge small motorcycle batteries easily. For larger car batteries (above 35AH), the circuit will work, but you will need a higher current transformer, a proper bridge rectifier, and a large heatsink for the IRFZ44N MOSFET to handle the continuous load.
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