18650ma Battery charger Voltage Protector Circuit
Build a 18650 battery charger with voltage protection using TL431. Ensures safe charging, prevents overcharge, and extends battery life.
TL431 voltage protector for 18650
The battery charger will have a 18650 battery with TL431 voltage protection to ensure safe charging that will terminate at 4.2 V and prevent overcharging to prolong the battery life.
overcharge protection using TL431
The 18650 Lithium-ion battery has a safe charging voltage of 4.2V/cell. The overcharging may destroy a cell or even become dangerous. To avoid this, a TL431-based voltage protection circuit can be developed. TL431 is a programmable shunt voltage reference IC that behaves as an adjustable Zener diode. TL431 used as a circuit watch in this circuit is set to sense the battery voltage. A TL431 is activated once the voltage across the battery has reached 4.2 V and forces the flow of charge across a transistor or a relay to avoid overcharging. The IC has its reference voltage based on a network of resistor dividers. It can also be supplemented with an LED indication to indicate charging (charging or cutoff). This is a simple but useful charger protection circuit, which is extensively utilized in DIY lithium-ion charging, battery banks, power banks, and small UPS systems. It also guarantees a long battery life, overheating is avoided, and it is safer and comfortable when charging batteries of 18650.
Work / Installation (Inputs → Outputs)
This circuit has a DC input (5V12V), then through a regulator (LM317 or 7805), and then to the battery (18650). The TL431 maintains a constant check on the output voltage. When battery voltage goes to 4.2 V, TL431 is activated, turning off a transistor/relay and breaking the charger circuit. This offers an auto-cutoff system, which is safe.
Testing & Final Adjustments
Once assembled, a discharged 18650 cell should be connected. DC supply to the regulator (5 V or 12 V). Charge with a multimeter to measure battery voltage. Tilt the resistor divider network to fine-tune the cutoff at 4.2V. Check whether it will automatically cease charging when the voltage is 4.2V or not. When the cutoff point is wrong, adjust the values of the resistors. Heat check TL431, and transistor install heatsinks where necessary. Include a charging/full indicator. In the case of a battery using multiple cells, a battery management system (BMS) should be used rather than a single TL431. The charger would guarantee long-lasting battery life and safety with proper adjustment.
