4S 40A BMS with Active Balancing – Complete Protection for 14.8V 18650 Li-Ion Packs
Is your battery pack failing prematurely? It is rarely the cells themselves, but rather a lack of proper voltage balancing. This 4S 40A BMS module monitors each cell independently and automatically redistributes energy where needed, ensuring your pack stays healthy without any manual intervention.
Note: Exclusively compatible with 4S Li-Ion configurations (14.8V nominal). Not suitable for LiFePO4 or NiMH cells.
Why choose this model? (Key Advantages):
- Cell-to-cell active balancing — When voltage differences exceed 0.1V, current is automatically diverted rather than wasted as heat, ensuring cells reach 4.2V ± 0.03V simultaneously.
- 40A continuous, 70A peak current — Easily handles the high power demands of cordless drills, drones, and robotic vacuums without cutting out.
- 10 Power MOSFETs — Features low internal resistance and superior thermal dissipation compared to standard 6-MOSFET modules.
- Instant short-circuit protection — MOSFETs trigger in microseconds to protect your cells; the module resets automatically once the fault is cleared.
- Ultra-slim profile: 60 × 45 × 3.4 mm — Designed to fit into almost any DIY or commercial battery casing without requiring modifications.
Technical Specifications and Performance
Each cell is managed by a dedicated controller. When one cell charges faster than the others, a 100 mA current at 4.2V is diverted through a balancing resistor. During discharge, the BMS prevents any cell from dropping below 3.2V ± 0.1V, the critical threshold where Li-Ion chemistry begins to degrade irreversibly. The module supports a continuous charging current of up to 20A, with an input voltage between 16.8V and 18.1V DC.
| Parameter | Value / Detail |
|---|---|
| Input Voltage (Charging) | 16.8V – 18.1V DC |
| Max Charging Current | 20A (continuous) |
| Max Discharge Current | 40A (continuous), 70A (peak) |
| Max Voltage per Cell | 4.2V ± 0.03V |
| Min Voltage per Cell | 3.2V ± 0.1V |
| Number of MOSFETs | 10 |
| Balancing Current | 100 mA at 4.2V |
| Integrated Protections | Overcharge, over-discharge, short-circuit, over-current, balancing |
| Dimensions | 60 × 45 × 3.4 mm |
| Compatible Configuration | 4S Li-Ion 18650 (14.8V nominal) |
Package Contents
- 1× 4S 40A BMS Module with Active Balancing
Frequently Asked Questions
Can I use this BMS with LiFePO4 cells?
No. This module is calibrated for Li-Ion batteries with a maximum voltage of 4.2V per cell. LiFePO4 cells have a different voltage profile (max 3.6V) and require a dedicated BMS to prevent overcharging and damage.
What charger should I use?
Use a CC/CV charger with an output of exactly 16.8V and a current of up to 20A. Any standard charger designed for 4S Li-Ion packs with a 16.8V output is directly compatible.
Is this suitable for power tools or drones?
Yes. The 40A continuous and 70A peak current rating is designed to handle the high-drain, impulsive loads of cordless power tools and drone motors without triggering the protection circuit.
What happens during a short-circuit?
The MOSFETs will cut the output instantly to protect your cells. Once the short-circuit is removed and the battery is reconnected, the module automatically resets to normal operation without needing manual intervention.
Can I connect cells in parallel (e.g., 4S2P)?
Yes. You can increase capacity using 4S2P or 4S3P configurations, provided the total discharge current does not exceed the 40A continuous limit. The balancing function works correctly regardless of the number of parallel cells.
Photo Gallery
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Great for 14.8V battery packs. Provides solid protection and doesn’t get too hot during discharge.