2-Pack 2S 20A BMS with Balancing – Advanced Protection for 7.4V Li-Ion Battery Packs
This set of two 2S 20A BMS boards provides a comprehensive solution for managing and protecting Li-Ion battery packs with a nominal voltage of 7.4V (8.4V fully charged). The active balancing function equalises cell voltages during the charging process, significantly extending the lifespan of your battery pack. With a compact footprint of just 48×20×3.4mm, these modules are perfect for DIY projects, portable power tools, and custom power packs.
Note: Upon initial connection, the battery pack must be charged to activate the BMS output. Do not mix cells with significantly different capacities or internal resistances.
Why choose this model? (Key Advantages):
- Integrated active balancing equalises cell voltage during charging, preventing imbalances and extending the overall pack life.
- Comprehensive multi-protection against overcharging (>4.3V), over-discharging (<2.3V), overcurrent (25A), and short-circuits with automatic reset in ~200ms.
- Wide compatibility with 18650 and 26650 Li-Ion cells, as well as standard 3.7V/4.2V Li-Po batteries.
- Compact 48×20×3.4mm design, ideal for integration into small enclosures, portable equipment, and custom builds.
- Economical 2-pack set — double the value for parallel projects or as a handy spare for your applications.
Performance and Specifications
The module is engineered to handle a continuous current of 20A (a heatsink is recommended for high-load applications) and supports peaks of up to 25A. The charging current is automatically limited to 10A, protecting your cells from thermal stress. Wiring is straightforward via clearly marked points: 0V (Cell 1 negative), 4.2V (midpoint between cells), and 8.4V (Cell 2 positive), with the final output available at the + and − terminals on the board. The “430” resistor may warm up during the balancing process — this is normal and indicates that the equalisation circuit is functioning correctly.
| Parameter | Value / Detail |
|---|---|
| Module Type | 2S BMS with active balancing |
| Nominal Voltage | 7.4V (2 × 3.7V) |
| Charging Voltage | 8.4V – 9.0V |
| Overcharge Protection | > 4.3V per cell |
| Over-discharge Protection | < 2.3–2.5V per cell |
| Overcurrent Protection | 25A |
| Recommended Continuous Current | 20A (heatsink required for high loads) |
| Short-circuit Protection | Yes, auto-resetting (~200ms) |
| Limited Charging Current | 10A |
| Compatible Cells | Li-Ion 18650, 26650, Li-Po 3.7V/4.2V |
| Dimensions | 48 × 20 × 3.4 mm |
| Quantity per Set | 2 pieces |
Setup and Usage Instructions
- Prepare your cells: Ensure both Li-Ion batteries have similar voltages (maximum difference of 0.1V) and comparable internal resistances.
- Connect Cell 1: Connect the negative to the 0V point and the positive to the 4.2V point on the board.
- Connect Cell 2: Connect the negative to the 4.2V point (shared with the first cell’s positive) and the positive to the 8.4V point.
- Identify output terminals: The + and − terminals on the board serve as the output for your load and the input for your charger.
- Activate the BMS: Connect a compatible charger (8.4–9.0V) to the output terminals for the first activation — the BMS will automatically unlock the output.
- Test functionality: Verify the output voltage (~8.4V fully charged) before connecting your final load.
- Ensure cooling: For applications drawing currents near 20A, mount a heatsink or ensure adequate ventilation for the board.
Package Contents
- 2 × 2S 20A BMS Module with balancing (48 × 20 × 3.4 mm)
- Wiring diagram included (digital/visual)
Frequently Asked Questions
Can I use this BMS with high-capacity 26650 batteries?
Yes, the module is compatible with 18650, 26650, and standard Li-Po cells, provided the nominal voltage is 3.7V per cell. The recommended continuous current remains 20A regardless of capacity.
Why does the “430” resistor get warm during charging?
This is completely normal. The resistor is part of the active balancing circuit and dissipates the energy required to equalise the voltages between the two cells. Slight warming confirms the balancing function is operating correctly.
What voltage should my charger be?
The recommended charger voltage is 8.4V – 9.0V. The BMS automatically limits the charging current to 10A, so you can safely use power sources with higher current ratings without damaging your batteries.
The output isn’t working on the first connection. What should I do?
This is expected — the BMS enters “sleep” mode until the first charge. Connect the pack to an 8.4V charger to activate the output. Once activated, the module will function normally for all subsequent uses.
Can I connect multiple 2S packs in parallel for higher capacity?
Yes, but each pack must have its own BMS, and all packs must be balanced to the same voltage before connection. Connecting in parallel without individual BMS protection can cause dangerous current flows between packs.
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