BMS balancer 4S 40A - 16.8 V Li-Ion 18650 cell charger with protection

BMS 4S 40A module for Li-Ion cells

The circuit is intended for use with devices up to 230 W power and with peak (inrush) current up to 80 A. It works with battery packs in cordless drills - remember to connect a capacitor in parallel to the motor terminals (from 10 uF to 1000 uF).

This module protects the battery against excessive discharge, overcharge, overcurrent overload, and short circuits. It also provides balanced charging and discharging of individual cells, contributing to long-term, reliable battery operation.

Key technical specifications

• Supports 4S batteries: Li-Ion, LiCoO2, LiMn2O4, Li NiCoMn O2
• Supply voltage: 16.8 - 18.1 V
• Maximum peak current: 80 A
• Cell overcharge protection: 4.2 - 4.3 V
• Cell over-discharge protection: 2.4 - 2.6 V
• Maximum continuous charge current: 20 A
• Maximum continuous discharge current: 40 A (if temperature rises, use active cooling)
• Balance current: 100 mA
• Overcurrent protection: 70 A
• Control circuit current draw: 40 uA
• On-resistance: 3 mOhm
• Short-circuit detection time: 100 us
• Overcurrent overload detection time: 500 us
• Short-circuit protection
• Dimensions: 61 x 46 x 4 mm

Example applications

• Rebuilding and building power packs for power tools and cordless drills
• Powering robotics projects and radio-controlled models
• Creating portable power stations and energy storage
• Emergency backup power systems
• Powering high-power mobile lighting systems

Benefits

• Longer battery life thanks to cell balancing
• High safety thanks to built-in overcurrent and short-circuit protection
• Support for high-power devices thanks to inrush current up to 80 A
• Compact dimensions for easy mounting in original battery housings
• Minimal energy losses thanks to low on-resistance of 3 mOhm

Operating recommendations

When using a charger, use cells with the same voltage, capacity, and internal resistance. Do not mix new and used cells.