HW-391 20A 2S Balanced Lithium Battery Protection Board

The HW-391 20A 2S Balanced BMS is a battery protection board designed for two-cell-series lithium battery packs. It is listed for 7.4V nominal lithium-ion battery applications and includes a cell-balancing function.

This board is identified as the balanced version of the HW-391 battery protection board. Matching product listings describe protection against overcharge, over-discharge, over-current, and short-circuit conditions.

The HW-391 is listed for lithium batteries with a nominal cell voltage of 3.7V and a full-charge voltage of 4.2V per cell, including 18650, 26650, and polymer lithium batteries.

Key Features

• 2S battery configuration: Designed for two cells connected in series.

• 7.4V nominal battery pack: For 2S lithium-ion battery applications.

• 8.4V full-charge pack voltage: Based on two 4.2V lithium-ion cells in series.

• 20A maximum continuous discharge current: As listed for the HW-391.

• 10A maximum continuous charging current: As listed for the HW-391.

• Cell balancing: Balanced version is identified as supporting equalization charging.

• Overcharge protection: Listed in matching HW-391 descriptions.

• Over-discharge protection: Listed in matching HW-391 descriptions.

• Over-current protection: Listed in matching HW-391 descriptions.

• Short-circuit protection: Listed in matching HW-391 descriptions.

• Compact PCB: Listed dimensions are 48 × 20 × 4mm.

Technical Specifications

Charging-voltage clarification: The seller lists a charging input range of DC 8.4–9V. The battery pack itself is a 2S lithium-ion pack with 7.4V nominal and 8.4V at full charge. Use a suitable 2S lithium-ion charger and follow the supplier's confirmed wiring and charging instructions. The board should not be treated as a standalone charger.

 Protection and Balancing Functions

Cell balancing

The HW-391 is specifically identified as the balanced version. Matching product descriptions explain that the balancing function equalizes charging between the two series cells.

Battery protection

Matching HW-391 listings identify these protection functions:

• Overcharge protection

• Over-discharge protection

• Over-current protection

• Short-circuit protection

Exact protection thresholds are not included in this listing because the sources do not consistently establish them for the exact board revision.

Typical Applications

Potential applications for a properly matched HW-391 battery pack include:

• 2S 18650 lithium-ion battery packs

• 2S 26650 lithium battery packs

• Compatible lithium-polymer battery packs

• Battery-powered DIY electronics

• Suitable power-tool battery projects

• Battery pack protection and balancing projects

Application note: The seller mentions power drills below 50W and resistive loads up to 168W. These are seller-listed application claims, not universal guarantees. Actual suitability depends on battery-cell capability, wiring, cooling, and the load's startup current.

Installation Caution

• Use only a compatible 2S lithium battery pack.

• Confirm the correct battery chemistry and cell voltage.

• Connect the two cells in series according to the supplier's wiring diagram.

• Verify all battery and output terminals before powering the circuit.

• Do not exceed the listed maximum charging or discharging current.

• Reduce load current if the board's heat dissipation is inadequate.

• Use cells capable of supporting the required current.

• Do not confuse the BMS with a battery charger.

• Confirm wiring and polarity before connecting the load.

 Related Products – Electronics Hub

Explore related battery products:

• 18650 Lithium-Ion Cell

• 1000mAh 3.7V 18650 Lithium-Ion Cell

• 3.7V 18650 Battery with Wire, JST Connector and BMS Protection

• Battery Cells Collection

These are related products. Confirm cell current capability, pack configuration, and wiring compatibility before pairing them with the HW-391.