3S 4S BMS 40A Li-ion Battery Protection Board for Drill

3S / 4S BMS Li-ion Battery Protection Board – 40A / 60A for Drill Motors & 18650 Packs

Keep your lithium battery packs safe, balanced, and performing at their best with this high-current Battery Management System (BMS) protection board. Designed for 3S (11.1V / 12.6V) and 4S (14.8V / 16.8V) configurations, this board is ideal for power drills, DIY battery packs, and motor-driven tools using 18650, 26650, or polymer lithium cells.

Key Specifications

• Compatible Configurations: 3S (3-cell) & 4S (4-cell) Li-ion packs
• Continuous Discharge Current: 40A maximum (reduce load in poor heat-dissipation environments)
• Continuous Charging Current: Up to 20A
• 3S Charging Voltage: DC 12.6V – 13.6V
• Cell Compatibility: 3.7V nominal / 4.2V fully charged Li-ion cells (18650, 26650, polymer)
• Balance Version Board Size: 41 × 61 × 4 mm
• Enhanced Version Board Size: 41 × 55 × 4 mm
• Drill Capacity: Supports drills rated up to 170W

Features & Benefits

• ✅ Overcharge & Over-discharge Protection – Automatically cuts off to protect your cells
• ✅ Balance Charging – The onboard balancing circuit ensures all cells charge evenly for longer pack life
• ✅ High Current Handling – 40A continuous discharge handles demanding drill motor loads
• ✅ Short Circuit Protection – Built-in safeguard against accidental shorts
• ✅ Compact & Lightweight – Slim 4mm profile fits neatly into custom battery housings
• ✅ Broad Cell Compatibility – Works with 18650, 26650, and polymer Li-ion cells

Important Installation Notes

1. Battery Selection: To successfully drive a drill, use high-drain power cells (e.g., Sony VTC4, VTC4A, VTC5A, or VTC6). Use copper wire of 3 mm² cross-section or larger for the 0V and 12.6V leads — do NOT use nickel strips for high-current connections.
2. Wiring Sequence: Strictly follow the wiring diagram and connect 0V → 4.2V → 8.4V → 12.6V in the correct order. Do not touch any components on the board while soldering wires. Never intentionally short circuit the board.
3. Balancing Resistor Heat: During first-time battery installation or while charging, if any single cell exceeds 4.2V the onboard "430" balancing resistor will warm up and discharge the cell back to approximately 4.19V. Excessive resistor heat indicates a wiring error — check your connections immediately.

Made in Mainland China.

Compatible & Related Products

• Need a gauge for your DIY projects? Check out the Air Compressor Pressure Gauge 0–25 Bar | DIY Tool.
• Looking for another electronics tool? Explore the Electromagnetic Induction Tester – Coil & Circuit Fault Detector.

Learn more: ENERGY STAR product efficiency guidance

Frequently Asked Questions

Q: What cell types are compatible with this BMS protection board?

A: This BMS board is compatible with any 3.7V nominal lithium-ion cells that charge to 4.2V fully — including 18650, 26650, and polymer lithium cells. High-drain power cells such as the Sony VTC4A, VTC5A, and VTC6 are strongly recommended when powering a drill motor.

Q: Can I use this board for both 3S and 4S battery configurations?

A: Yes. The board supports both 3-string (3S) configurations at 11.1V / 12.6V and 4-string (4S) configurations at 14.8V / 16.8V, making it versatile for a range of DIY lithium battery pack builds.

Q: What wire gauge should I use when wiring this BMS board?

A: For the main power leads (0V and 12.6V / pack voltage), always use copper wire with a cross-section of at least 3 mm² (approximately 12 AWG). Nickel strips are not suitable for high-current connections and must not be used.

Q: Why is the balancing resistor getting hot during charging?

A: Mild warming of the "430" balancing resistor is normal when a cell exceeds 4.2V — it discharges the cell back to ~4.19V. If the resistor becomes severely hot, this is a signal to immediately check your wiring diagram and ensure all connections (0V, 4.2V, 8.4V, 12.6V) are correctly sequenced.