Description
The 4S 20A 14.8V 18650 Li-ion BMS Board is a compact Battery Management System designed for 4-cell series lithium-ion battery packs. It helps protect Li-ion cells from overcharging and over-discharging during normal battery operation.
With a 16.8V charging voltage, up to 10A working current, and a 20A maximum instantaneous current, this BMS is suitable for a range of low-power battery projects, backup power systems, electronic devices, and DIY 4S Li-ion battery packs.
The board features a compact 35 × 35 × 3.6mm design, simple wiring, and support for custom battery-pack installations.
Key Features
- Designed for 4S Li-ion battery packs
- Suitable for 18650 lithium-ion cells
- 14.8V nominal battery pack configuration
- 16.8V–17V charging voltage
- Maximum working current: 10A
- Maximum instantaneous/peak current: 20A
- Overcharge protection
- Over-discharge protection
- Short-circuit protection
- Charge recovery function
- Low static current consumption
- Compact PCB for custom installations
- Simple wiring configuration
- Controller: S-8254AA
- Model: HX-4S-D20
4S Battery Configuration
This BMS is designed for four Li-ion cells connected in series (4S).
A typical 4S pack uses four 3.7V nominal Li-ion cells:
3.7V × 4 = 14.8V nominal
The fully charged pack voltage is approximately:
4.2V × 4 = 16.8V
For proper operation, the individual cells should have similar voltage, capacity, and internal resistance.
BMS Wiring
Follow the specified wiring sequence carefully:
- 0V / B−
- 3.7V / B1
- 7.4V / B2
- 11.1V / B3
- 14.8V / B+
The source specifies that B+ and B− are the battery connections, while P+ and P− are used for output/input.
Do not intentionally short-circuit the board.
Protection Functions
The 4S BMS provides protection functions intended to help protect the battery pack during charging and discharging.
Overcharge Protection
The stated overcharge voltage range is:
4.25–4.35V ± 0.05V per cell
This protection helps prevent individual cells from being charged beyond the specified voltage range.
Over-Discharge Protection
The stated over-discharge voltage range is:
2.3–3.0V ± 0.05V per cell
This helps protect the cells from excessive discharge.
Short-Circuit Protection
The board includes short-circuit protection with charge recovery according to the supplied specifications.
Current Ratings
The supplied product specifications list:
- Maximum working current: 10A
- Maximum instantaneous/peak current: 20A
- Static current: less than 30µA
- Additional specification lists small current as approximately 6µA
Because the source provides different static-current figures, buyers should treat the exact quiescent-current value as specification-dependent.
Battery Cell Matching
For a reliable 4S battery pack, use cells with similar:
- Voltage
- Capacity
- Internal resistance
- Overall condition
Do not mix significantly different or damaged cells.
If the voltage of individual batteries is different before assembly, the supplied instructions recommend charging them separately and bringing them to a similar voltage before connecting them in series.
Battery C-Rate Consideration
For products requiring 3A or higher discharge current, the supplied specifications recommend using batteries with a discharge rate above 3C.
For example:
- 1C battery: 2000mAh = 2Ah × 1 = 2A
- 3C battery: 2000mAh = 2Ah × 3 = 6A
If the battery becomes excessively hot during use, the source indicates that the battery’s discharge rate may not be suitable for the application and continued operation may damage the cells.
Technical Specifications
| Specification | Details |
|---|---|
| Product Type | 4S Li-ion BMS Protection Board |
| Model | HX-4S-D20 |
| Controller | S-8254AA |
| Battery Type | Li-ion / Lithium-ion |
| Battery Configuration | 4S |
| Nominal Pack Voltage | 14.8V |
| Charging Voltage | 16.8V–17V |
| Overcharge Voltage | 4.25–4.35V ± 0.05V |
| Over-Discharge Voltage | 2.3–3.0V ± 0.05V |
| Maximum Working Current | 10A |
| Maximum Peak/Instantaneous Current | 20A |
| Static Current | Less than 30µA |
| Additional Small Current Specification | Approx. 6µA |
| Internal Resistance | Less than 100mΩ |
| Working Temperature | -40°C to +50°C |
| Storage Temperature | -40°C to +80°C |
| Service Life | More than 50,000 hours |
| Board Size | 35 × 35 × 3.6mm |
| Short-Circuit Protection | Yes |
| Short-Circuit Recovery | Charge recovery |
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