5S 100A 21V BMS – Robust protection for your high-performance 18650 Li-Ion battery packs
When you’ve put the effort into building a custom battery pack, you need to ensure it’s protected against overcharging or sudden short circuits. A reliable 5S 100A 21V BMS works silently in the background, intervening in microseconds before a minor issue becomes a major failure. It monitors each cell individually, balances them automatically, and cuts the circuit instantly if it detects an anomaly.
Please note: The BMS module does not include 18650 cells. These must be purchased separately. This unit is also compatible with 3S and 4S configurations.
Why choose this model? (Key Advantages):
- 100A Peak Current — Handles sudden power spikes in electric tools and drones without cutting out during high-demand tasks.
- 60mA Passive Balancing — Real-time voltage levelling across all 5 cells ensures your pack lasts longer and delivers maximum capacity during every cycle.
- 4-Way Protection — Integrated safety against overcharging, deep discharge, overcurrent, and short circuits.
- Ultra-Slim 3.4mm Profile — Compact design fits into tight enclosures where standard modules won’t, making it ideal for DIY power banks or space-constrained RC vehicles.
- Versatile 3S/4S/5S Compatibility — One module covers your 11.1V, 14.8V, and 21V projects, giving you flexibility for future builds.
Technical Performance and Details
This circuit utilizes high-grade power MOSFETs rated for 80A continuous discharge and 60A continuous charge, allowing it to handle real-world applications comfortably without overheating under normal conditions. The per-cell cut-off voltage is set to 4.25V for charging and 3.00V for discharging—precise thresholds that prevent premature chemical degradation and preserve the long-term health of your Li-Ion cells.
Passive balancing works by dissipating excess voltage from fully charged cells, ensuring the entire pack reaches the same level before the charge cycle completes. The result is higher usable capacity and fewer cycles lost to cell imbalance. The short-circuit protection triggers in microseconds, reacting faster than any mechanical fuse.
| Parameter | Value / Detail |
|---|---|
| Battery Compatibility | Li-Ion 18650 (5S configuration) |
| Nominal Pack Voltage | 21V (5 x 4.2V) |
| Continuous Charge Current | 60A |
| Continuous Discharge Current | 80A |
| Peak Current | 100A |
| Max Voltage per Cell | 4.25 ± 0.05V |
| Min Voltage per Cell | 3.00 ± 0.025V |
| Balancing Current | 60mA (passive) |
| Short-Circuit Protection | Yes |
| Overcharge Protection | Yes |
| Deep Discharge Protection | Yes |
| 3S / 4S Compatible | Yes |
| Dimensions | 62 x 42 x 3.4 mm |
Package Contents
- 1x 5S 100A 21V BMS Module
Frequently Asked Questions
Can I use this BMS with Li-Po cells instead of 18650 Li-Ion?
Technically, yes—Li-Po cells share the same 3.7V nominal / 4.2V max voltage profile. However, always verify the specific voltage thresholds of your cells before connecting, as some Li-Po batteries have slightly different requirements than standard Li-Ion.
What happens if a short circuit occurs at the output?
The module detects the overcurrent in microseconds and automatically disconnects the discharge circuit, protecting both your battery pack and the connected device. Once the fault is cleared, the module will reset automatically or manually, depending on the specific version.
Does it work with fewer than 5 cells in series?
Yes. The module supports 3S (11.1V) and 4S (14.8V) configurations, providing the same comprehensive protection and balancing. You do not need a separate module for different cell counts.
Do I need a heatsink for high-current applications?
For continuous use under 80A in normal ambient temperatures, the module runs stably without extra cooling. If you are frequently operating near the 100A peak, good ventilation or a small heatsink on the MOSFETs will help extend the module’s lifespan.
Can I charge and discharge simultaneously through the same port?
Yes, this model uses a common port configuration for both charging and discharging. Please refer to the wiring diagram in the technical documentation to ensure the charger and load are connected to the correct terminals.
Photo Gallery
E**** –
High-quality board. Used it to rebuild a cordless drill battery pack and the balancing is perfect. Saved me a lot of money!