SPECIFICATIONS

3S 4S 40A 60A Li-ion Battery Protection Board BMS – with Balance / Enhanced, Overcharge Overdischarge Protection for Drill DIY

Key Features & Benefits

⚡ High Current Support: 40A/60A continuous discharge (80A peak for 60A version) – perfect for drills, saws, angle grinders.

🔋 Multiple Configurations: Choose 3S (11.1V/12.6V) or 4S (14.8V/16.8V) to match your battery pack voltage.

⚖️ Balance Version: Cell voltage balancing prevents overcharge/overdischarge of individual cells, extending pack life – ideal for long-term use.

🛡️ Enhanced Version: Optimized MOSFET cooling for lower temperature rise under high current – better stability for heavy loads.

🛑 Full Protection: Overcharge (4.25V±0.05), overdischarge (2.5V±0.1), overcurrent (80A±10), short circuit (<200ms).

📏 Compact Size: As small as 41×55×4mm (enhanced), with mounting holes for easy installation.

Product Description

This series of Li-ion battery protection boards (BMS) is designed for 3S or 4S battery packs made of 18650/26650/polymer cells, supporting 40A/60A continuous discharge. Whether you're building a DIY power tool (drill, saw), sprayer, LED light, or small inverter, these boards keep your batteries safe. Choose "Enhanced" for better heat dissipation and high-current stability, or "With Balance" to ensure all cells stay at the same voltage, extending pack lifespan. Built-in overcharge, overdischarge, overcurrent, and short circuit protection make your projects safer and more reliable.

⚡ Quick Start Guide & Important Tips

What It Does & What You Need

✅ This BMS does:

🔹Prevents overcharge (cuts off at >4.25V per cell)

🔹Prevents overdischarge (cuts off at <2.5V per cell)

🔹Cuts off output during overcurrent or short circuit

🔹(Balance version) Balances cell voltages automatically

❌ This BMS is NOT:

🔹For LiFePO4 batteries (3.2V nominal)

🔹For single cell use (must be 3S or 4S)

🔹A charger (you need an external charging power supply)

⚠️ Critical prerequisites (MUST READ!):

🔹Battery requirement: For drill startup, use 3S 10C-20C high-drain cells (e.g., Sony VTC4/VTC5A/VTC6) or 6S 5C-10C cells. Standard capacity cells cannot deliver 40A continuously!

🔹Wiring: Strictly follow the diagram: B- → pack negative, B1 → between cell1&2, B2 → between cell2&3, B+ → pack positive. Do NOT touch any components on the board while soldering. Do NOT short circuit.

🔹Wire gauge: Use copper wire at least 3mm² (do NOT use nickel strips). Keep wires short.

Cooling: When running ≥40A continuously, if the board gets very hot, add a heatsink or reduce load.

🔹First use note: When charging for the first time, if any cell exceeds 3.6V (3S) or 4.2V (4S), the balancing resistor (labeled "360" or "430") will heat up to discharge that cell. This is normal. If it gets extremely hot, check for wiring errors.

🔧 You will need:

🔹3 or 4 identical, same-batch, same-capacity high-drain 18650/26650 cells

🔹3mm² copper wire, soldering iron, multimeter

🔹12.6V (for 3S) or 16.8V (for 4S) dedicated charger

Wiring Diagram (Example for 3S)

B- ←→ Negative terminal of cell 1
B1 ←→ Positive of cell1 / Negative of cell2
B2 ←→ Positive of cell2 / Negative of cell3
B+ ←→ Positive of cell3

Load/Charger: Connect P- to negative, P+ to positive (common port)

⚠️ Polarity warning! Reversing any wire will instantly burn the board. Use a multimeter to confirm polarity of each cell before soldering!

Common Questions & Tips

❓ Why does the balancing resistor get hot?

This is normal. When one cell has a higher voltage than others, the balancing circuit discharges it through the resistor to equalize voltages. Heat dissipation is about 1-2W. If it's extremely hot, check for wiring errors.

❓ My drill won't start – no output from BMS?

🔹Check if you are using high-drain cells (at least 10C). Standard cells cannot provide 40A surge.

🔹Wires may be too thin or too long (voltage drop).

🔹Battery may be overdischarged – charge first.

❓ Can I get both Enhanced and Balance in one board?

Each SKU offers either Enhanced OR Balance. If you need both, choose the Balance version (slightly less cooling) or contact us for custom options.

❓ Can I use a 4S board with a 3S pack?

No. The number of cells must match, otherwise protection voltages will be wrong. Buy the correct S count for your pack.

❓ How to recover from short circuit protection?

Disconnect the load, and the BMS will automatically restore output. If it doesn't, briefly connect a charger to reactivate.

Package Includes

Single Board (1 PC): 1 × Selected BMS model