2S 8.4V 20A BMS Lithium Battery Protection Board Standard & Balance Version, Overcharge Over‑Discharge Short Circuit Protection Module For 18650 Li‑ion Battery Pack DIY Power Project

HW‑391 2‑Series Lithium Battery Charging Protection Board 20A With Balanced Charge

📌 Product Overview

✅ This 2‑series lithium battery protection board is designed for 2S 7.4V lithium battery pack, compatible with 18650, 26650 and polymer lithium‑ion batteries. It integrates over‑charge, over‑discharge, over‑current and short‑circuit protection functions, and comes with active balance charging function to balance voltage difference between series cells. Lithium rechargeable batteries require protection due to their inherent chemical characteristics. They cannot be overcharged, over‑discharged, over‑current loaded, short‑circuited, or operated under excessive high‑temperature charge‑discharge conditions. This protection board monitors battery status in real‑time: stop charging at approx 4.2V per cell, cut‑off discharge when cell voltage drops below 2.75V, limit max output current up to 20A, trigger discharge stop for output short‑circuit with delayed self‑recovery. Intelligent current control prevents battery damage and greatly extends battery service life. Balanced charging (equalizing charge) solves cell voltage imbalance caused by individual cell difference and temperature drift during long‑term usage. It raises pack charging voltage and activates each cell to align cell characteristics, serving as effective maintenance to prolong whole pack lifespan.

📋 Product Specifications

Item	Parameter
Product Name	2‑Series 7.4‑8.4V 20A Battery Protection Board
Model	HW‑391
Charging Voltage	DC 8.4‑9V
Max Continuous Discharge Current	20A (Reduce load current under poor heat dissipation)
Max Continuous Charging Current	10A
Dimension	48 * 18 * 3.5mm
Weight	3.7g
Applicable Battery	3.7V nominal / 4.2V full‑charge lithium cells (18650,26650,polymer battery)
Startup Current	25A
Max Resistive Load Power	168W

⚡ 2S20A Electrical Parameters

Project	Min.	Typ.	Max.	Unit	Remark
Self‑consumption Current	12	18	24	uA
Overcharge Protection Voltage	4.2	4.25	4.3	V
Balance Start Voltage	4.17	4.2	4.23	V	Balanced version
Balance Current	95	100	105	mA	Balanced version
Balance Heating Power	0.78	0.86	0.95	W	Balanced version
Overcharge recovery voltage	4.1	4.15	4.2	V
Over‑discharge Protevery Voltage	2.4	2.5	2.6	V
Voltage recovery after over discharge protection	2.8	3	3.2	V	1C discharge
Voltage recovery after over discharge protection	3.2	3.5	3.8	V	2C discharge
Over‑discharge Recovery Voltage	2.5	2.6	2.7	V
On‑resistance	5	6	7	mΩ
Over‑discharge Protection Current	19	22	25	A
Overcurrent delay time	50	100	150	ms
Continuous working current	0	20	20	A	Resistive load
Continuous Output Power	0	168	168	W	Resistive load
Ambient Temperature	-40	25	85	℃

🔧 Core Features

1. Built‑in balance charging circuit for 2S battery pack, correct cell voltage deviation.
2. Adopt high‑current power MOS tube, low internal resistance, large current carrying capacity.
3. Mature stable main control IC solution, complete multiple protection mechanisms.
4. Support 2S battery pack, suitable for power drill, small power equipment, DIY power supply projects.
5. Delayed self‑recovery after short‑circuit protection, no frequent manual reset operation.

📝 Wiring & Usage Tips

• This board is for 2 series lithium‑ion battery pack. Connected battery cell must support 20A discharge, you can use parallel‑combined high‑rate cells.
• Charging input voltage range DC 8.4‑9V, max charging current ≤10A.
• For electric drill application: 2pcs 10C‑20A power cells or 4pcs 5C‑10C power cells are recommended. Use ≥2mm² copper wire for 0V /8.4V connection, nickel‑plated wire is not suggested.
• After first battery soldering, you need to finish charging to get normal output. Strictly follow wiring diagram for 0V,4.2V,8.4V terminals. Do not short‑circuit components during soldering.
• When single cell voltage exceed 4.2V during charging, the 430 balance resistor will heat for balance discharge. If resistor gets extremely hot, double‑check wiring mistake.

⚠ Important Usage Notice

Kind reminder: If there are version differences or images not been updated, please refer to the actual product.

• Do not mix old and new batteries or cells of different capacity.
• Good heat dissipation environment is required under large‑current working status.
• Wrong wiring will cause permanent damage to this board, man‑made damage is not covered by warranty.
• Working ambient temperature: -40℃ ~ +85℃.