3S 40A 18650 Lithium Battery Protection Board

3S 40A 18650 Lithium Battery Protection Board (BMS) is an indispensable module for managing and protecting lithium-ion battery packs configured in a 3-series (3S) arrangement. This high-current Battery Management System (BMS) actively safeguards your 18650 cells against the most common threats to battery life and safety: overcharge, over-discharge, over-current, and short circuits. Therefore, using this board significantly extends the lifespan of your battery pack while preventing catastrophic failures like fire or explosion. Furthermore, its robust 40A continuous discharge capability makes it ideal for high-power applications, including power tools and electric vehicles, requiring a stable and safe 12.6V nominal output. Easily integrate this compact board to ensure maximum performance and reliable operation of your lithium-ion power source.

Key Features:

• High Current Rating: Supports a continuous discharge current of up to 40A and a peak current of 70A, enabling use in high-demand power applications.
• 3S Cell Configuration: Specifically designed for three series-connected 18650 cells, providing a nominal output voltage of 10.8 V to 11.1 V (charging up to 12.6 V).
• Comprehensive Protection: Actively manages over-charge protection, over-discharge protection, short-circuit protection, and over-current protection for superior battery longevity and safety.
• Accurate Cell Balancing: The board often includes a cell balancing function, ensuring that all three cells maintain an equal state of charge, consequently maximizing pack capacity and minimizing degradation.
• Low Self-Consumption: Operates with minimal power draw from the battery pack, preserving energy during long periods of storage or standby.

Technical Specifications:

• Nominal Voltage: 10.8 V / 11.1 V
• Maximum Charging Voltage: 12.6 V (3 × 4.2 V)
• Continuous Discharge Current (I_D): 40 A maximum
• Instantaneous Peak Discharge Current (I_Peak): 70 A
• Overcharge Detection Voltage (V_OCD): 4.25 V ± 0.05 V (Per Cell)
• Over-discharge Detection Voltage (V_ODD): 2.8 V ± 0.08 V (Per Cell)
• Short Circuit Protection: Delay ≈ 100 μs
• Internal Resistance (R_DS(on)): ≤ 20 mΩ

Mechanical Specifications:

• Component Type: Integrated Circuit Board (PCB)
• Heat Dissipation: Uses high-power low-resistance MOSFETs for effective thermal management under load.
• Connectivity: Solder pads (B-, B1, B2, B+, P-, P+) for secure wiring to the battery pack and load/charger.
• Operating Temperature Range: −40°C to +85°C

Dimensions:

• Board Length: ≈ 56 mm
• Board Width: ≈ 45 mm
• Board Thickness: ≈ 4.0 mm
• Mounting Holes: Typically includes four corner holes for secure fixture within a device enclosure.
• Weight: ≈ 10 g

Pinout and Wiring:

• B- (GND): Connect the common negative terminal of the entire 3S battery pack (0 V).
• B1: Connect the junction between Cell 1 positive and Cell 2 negative (≈ 3.7 V / 4.2 V).
• B2: Connect the junction between Cell 2 positive and Cell 3 negative (≈ 7.4 V / 8.4 V).
• B+ (V_TOTAL): Connect the positive terminal of Cell 3, which serves as the main pack positive (Max 12.6 V).
• P- (Load/Charge Negative): Connect the common negative terminal for both the charger and the load.
• P+ (Load/Charge Positive): Connect the common positive terminal for both the charger and the load (connects internally to B+).
• Wiring Note: Always connect B- and P- last to avoid damage from instantaneous current surges.

Datasheet Reference:

• Download 3S BMS 40A Protection Board Reference Datasheet

Commonly Used in:

• Power Tools: Used frequently in high-drain battery packs for drills, angle grinders, and electric screwdrivers.
• Electric Bicycles/Scooters: Providing management for smaller 3S power packs used in light mobility devices.
• RC Hobbies: Essential for safe charging and discharging of high-current Li-ion batteries in remote-controlled vehicles and drones.

Applications:

• DIY Battery Packs: Enables the safe construction of custom 18650 power banks and portable power stations.
• Medical Devices: Used in portable medical equipment requiring reliable, high-energy-density power sources.
• Uninterruptible Power Supplies (UPS): Providing a secure, managed backup power system for critical low-voltage electronics.

Equivalent Models:

• HW-391 or HW-392 BMS: These are common reference models for 3S 40A protection circuits, therefore they offer identical core functionality and protection levels.
• Li-ion BMS 3S 25A: A lower-current alternative suitable for less demanding applications, but with the same voltage configuration.
• Various Unbranded 3S 40A Modules: Due to the simple design, many suppliers offer functionally equivalent boards utilizing the same control ICs.

Package Includes:

• 1 x 3S 40A 18650 Lithium Battery Protection Board (BMS)