3S 20A BMS Protection Board for 11.1V Li-ion and Li-Po Batteries

12.6V Battery Protection Module with Auto Recovery, Overcharge, Over-Discharge and Short Circuit Protection

The 3S 20A BMS Protection Board is designed to protect and manage battery packs consisting of three lithium-ion or lithium-polymer cells connected in series (Li-ion / Li-Po). It is compatible with cells featuring a nominal voltage of 3.6V–3.7V, including popular 18650 and 26650 formats, as well as lithium-polymer battery packs.

The module supports battery packs with a nominal voltage of 11.1V and a maximum fully charged voltage of 12.6V. Its integrated electronics monitor the voltage and operating conditions of the three series-connected battery groups and provide protection against overcharging, excessive discharging, overcurrent and short circuits.

One of the main advantages of this model is its Automatic Recovery (Auto Recovery) function. After a protection event, such as an overload, the board can automatically restore normal operation once the cause of the fault has been removed, without requiring additional activation through a charger.

With a maximum continuous discharge current of up to 20A and a charging current of up to 10A, this module is suitable for building higher-power battery packs and supplying various electrical devices. It uses low-resistance power MOSFET transistors to control the charging and discharging processes.

It is particularly suitable for DIY battery packs, cordless screwdrivers, electric drills, portable power supplies and other applications requiring reliable protection for 3S lithium battery systems.

Key Features:

• Designed for 3S Li-ion and Li-Po battery packs.

• 11.1V nominal battery voltage.

• 12.6V maximum fully charged voltage.

• Continuous discharge current up to 20A.

• Continuous charging current up to 10A.

• Automatic recovery after the protection trigger condition is removed.

• Overcharge protection.

• Over-discharge protection.

• Overcurrent protection.

• Short-circuit protection.

• Low-resistance power MOSFET transistors.

• Compact dimensions and extremely lightweight design.

• Suitable for battery packs with high peak current demands.

Suitable Applications:

• Cordless screwdrivers and electric drills.

• DIY battery packs using 18650 and 26650 cells.

• 3S Li-Po rechargeable battery systems.

• Portable power supplies and autonomous electronic devices.

• Power tools and brushed DC motor applications.

• Electronic projects requiring a 12V battery supply.

• Various rechargeable battery systems and custom power solutions.

Technical Specifications:

• Type: BMS Battery Protection Board

• Configuration: 3S (3 battery groups connected in series)

• Compatible Batteries: Li-ion / Li-Po

• Nominal Cell Voltage: 3.6V–3.7V

• Nominal Pack Voltage: 11.1V

• Maximum Pack Voltage: 12.6V

• Charging Voltage: 12.6V DC (CC/CV)

• Maximum Continuous Discharge Current: 20A

• Maximum Continuous Charging Current: 10A

• Overcharge Protection: Yes

• Over-discharge Protection: Yes

• Overcurrent Protection: Yes

• Short Circuit Protection: Yes

• Automatic Recovery: Yes

• Power Components: MOSFET transistors

• Dimensions: 59 × 20 × 3.4mm

• Weight: 4.3g

• Battery Connections: 0V, 4.2V, 8.4V, 12.6V

• Load and Charging Terminals: Positive (+) and Negative (-)

Board Connection Guide:

The correct wiring sequence must be followed when connecting the three battery groups:

• 0V – negative terminal of the first battery and the common negative connection of the complete pack.

• 4.2V – connection point between the first and second battery.

• 8.4V – connection point between the second and third battery.

• 12.6V – positive terminal of the third battery and the common positive connection of the complete pack.

• + / - – output terminals for connecting the load and charger.

Important Usage Instructions:

1. Charging: Use a dedicated CC/CV charger with a final charging voltage of 12.6V, designed for 3S Li-ion/Li-Po batteries. The maximum charging current supported by the board is 10A, but the actual charging current must also comply with the specifications of the battery cells.

2. Cordless Drill Applications: Electric tools can generate high starting currents. High-discharge battery cells are required for reliable operation. According to the recommendations for this model, use 3 high-drain cells rated at 15C–20C or 6 cells rated at 10C–15C in a 3S2P configuration. Standard 18650 cells with insufficient discharge capability may not provide the required starting current.

3. Brushed Motor Applications: When powering brushed motors, the manufacturer recommends connecting a non-polar capacitor rated above 25V with a capacitance of 10–100µF in parallel across the motor terminals. This helps suppress reverse voltage spikes that could damage the MOSFET transistors.

4. Battery Cell Matching: Use three identical battery cells or three matched parallel cell groups with similar capacity, internal resistance and voltage before connection. Do not mix new and worn cells or batteries with different specifications.

Note: This BMS board is a protection module, not a standalone battery charger. The maximum 20A current depends on cooling, connecting wires, contacts and the capabilities of the battery cells themselves. Active cell balancing is not specified for this model.