Product Description

4S 40A Enhanced BMS Lithium Battery Protection Board

= HighPerformance Battery Management System for 4Cell Li-ion Packs =

The 4S 40A Enhanced BMS is a robust battery management system designed to protect and balance 4series lithiumion battery packs. Featuring 40A continuous discharge current and 100mA balancing current, this board provides comprehensive protection against overcharge, overdischarge, overcurrent, and short circuits. Perfect for power tools, electric drills, ebikes, and portable power supplies.

Designed for 3.6V/3.7V Liion and LiPo battery cells (18650, 26650, polymer)

Supports 4S configuration with 16.8V full charge voltage

Not suitable for LiFePO4 batteries Liion/Li-Po only

= Technical Specifications =

Parameter	Value
Battery Configuration	4S (4 cells in series)
Supported Battery Types	Liion / LiPo (3.6-3.7V cells)
Full Charge Voltage	16.8V
Continuous Discharge Current	40A (enhanced version)
Continuous Charge Current	Up to 20A
Peak Discharge Current	80-120A (depending on version)
Balancing Current	100mA (passive balancing)
Overcharge Protection	4.25-4.35V per cell
Over-discharge Protection	2.3-3.0V per cell
Short Circuit Protection	Yes (auto recovery)
Static Current	< 30-40uA
Board Dimensions	~60 x 45 x 4mm
Mounting	Through-hole pads

= Key Features =

Enhanced Current Capacity - 40A continuous discharge with peak support up to 120A for demanding applications

Passive Cell Balancing - 100mA balance current ensures cells remain at equal voltage for extended battery life and performance

Comprehensive Protection Overcharge, overdischarge, overcurrent, and short circuit protection with auto recovery

Low SelfConsumption Only 30-40uA static current minimizes battery drain during idle periods

Wide Application Range Supports electric drills, ebikes, power tools, LED lights, and low-power inverters

Auto Recovery - After short circuit or overcurrent protection, automatically recovers when load is removed

== Applications ==

Power tools (electric drills, screwdrivers, sprayers)
E-bikes and electric scooters
Portable power supplies and generators
LED lighting systems
Low-power inverters and solar systems
DIY battery pack builds
Power banks and backup systems
Industrial and automation equipment

= Wiring Guide =

Connection	Description
B+ (Battery Positive)	Positive terminal of cell 4
B1	Positive terminal of cell 1 (balance wire)
B2	Positive terminal of cell 2 (balance wire)
B3	Positive terminal of cell 3 (balance wire)
B- (Battery Negative)	Negative terminal of cell 1
P+ (Load/Charger Positive)	Positive output/charge input
P- (Load/Charger Negative)	Negative output/charge input

Connect in series: Cell 1: B- to B1, Cell 2: B1 to B2, Cell 3: B2 to B3, Cell 4: B3 to B+

Use appropriate gauge wire for 40A current (minimum 8-10 AWG)

Connect balance wires in strict order: B- then B1 then B2 then B3 then B+

= How It Works =

The 4S 40A BMS protects your battery pack through multiple mechanisms:

1. **Overcharge Protection**

Detects when any cell exceeds 4.25-4.35V and disconnects charging

2. **Over-discharge Protection**

Disconnects the load when any cell drops below 2.3-3.0V to prevent cell damage

3. **Overcurrent Protection**

Monitors current flow and disconnects during short circuits or excessive loads

4. **Cell Balancing**

Equalizes cell voltages during charging to maintain pack health and maximize capacity

5. **Auto Recovery**

After a fault condition is resolved, the BMS automatically reconnects the circuit

The BMS uses passive balancing discharges highervoltage cells through resistors to match lower-voltage cells

For optimal performance, use matched cells with similar internal resistance and capacity

The board will not function if balance wires are connected incorrectly - follow wiring order carefully

= Installation Tips =

1. Cell Matching	Use cells from the same batch with similar voltage before assembly
2. Balance First	Connect all balance wires in correct order before connecting main leads
3. Awaken BMS	After wiring, connect a charger to activate the BMS before first use
4. Heat Management	For continuous high-current operation, ensure adequate cooling and airflow
5. Wire Gauge	Use thick wires for main power connections to handle 40A current

Before assembly, ensure all cells have similar voltage (within 0.1V) for optimal balancing

Mount the BMS on a flat, non-conductive surface away from heat sources

Improper wiring can damage the BMS and connected batteries

= Why Choose Enhanced 4S 40A BMS? =

High 40A discharge capacity for demanding power tool applications

Active balancing extends battery pack lifespan

Auto recovery after fault conditions reduces maintenance

Low standby current preserves battery charge

Comprehensive protection ensures safe operation

Compact design fits standard battery pack configurations

√ Compatible with all 3.6V/3.7V Liion and LiPo cells

√ Supports 18650, 26650, and polymer battery formats

√ Direct replacement for standard battery management systems

√ Easy installation with clear wiring labels

√ Proven reliability for DIY and professional use

√ Excellent value for battery protection and management

= Safety Precautions =

Do not use with LiFePO4 batteries only Liion/LiPo (3.63.7V per cell)

Do not exceed 40A continuous discharge current

Ensure correct polarity and wiring order

Keep away from moisture and flammable materials

Use only with appropriate charger (16.8-18.1V for 4S)

Do not short circuit output terminals

Ensure adequate ventilation for heat dissipation

The BMS should be mounted in a protected area away from physical damage

For applications exceeding 40A continuous, consider a higher-current BMS model

= What's Included =

4S 40A Enhanced BMS Protection Board

The 4S 40A Enhanced BMS provides reliable battery protection and management for your 4series Liion battery packs. With comprehensive protection features, passive balancing, and auto recovery, it is the ideal solution for power tools, e-bikes, portable devices, and DIY battery projects.