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Product Description
The 7S 20A 24V Lithium Battery Management System (BMS) is a high-performance protection module engineered to monitor, balance, and safe-guard a 7-cell serial lithium-ion or lithium polymer battery pack. Operating at a nominal pack voltage of 24V (25.2V to 29.4V fully charged), this board acts as the central safety hub for your custom battery builds, managing a continuous discharge current of up to 20A.
This BMS provides critical industrial-grade protection mechanisms, including over-charge, over-discharge, over-current, and short-circuit prevention. It features an onboard passive cell-balancing circuit with precision resistors. As cells near full charge, the board automatically bleeds off excess voltage from higher-capacity cells, ensuring every single cell in the 7S configuration reaches its peak state evenly. This balancing action significantly maximizes your pack’s overall lifespan, runtime, and safety profile.
⚠️ Wiring Precaution Sequence: To prevent burning out the sensitive balancing IC, always follow the exact wiring sequence. Solder the balancing cable harness to your battery cells first while it is completely disconnected from the BMS board. Use a multimeter to verify that the voltage increases sequentially from B1 up to B7 on the connector plug. Only plug the cable harness into the BMS socket after verifying the wiring is 100% correct.
Connection Interface & Wiring Map
The board utilizes clear heavy-duty solder pads for high-current paths alongside a dedicated multi-pin balancing port:
High-Current Power Pads:
B- (Battery Negative): Connect to the absolute negative terminal of the first battery cell (Cell 1 Negative).
P- (Pack Output / Charge Negative): Connect to your load’s negative wire AND your charger’s negative wire (Common port configuration).
Pack Positive (+): The positive wire of your load and charger bypasses the BMS board entirely and connects directly to the absolute positive terminal of the 7th battery cell (B7+).
7S Balancing Port Pinout (From right to left / lowest to highest voltage):
B-: Connects to Cell 1 Negative (shared reference).
B1: Connects to the junction between Cell 1 Positive and Cell 2 Negative.
B2: Connects to the junction between Cell 2 Positive and Cell 3 Negative.
B3: Connects to the junction between Cell 3 Positive and Cell 4 Negative.
B4: Connects to the junction between Cell 4 Positive and Cell 5 Negative.
B5: Connects to the junction between Cell 5 Positive and Cell 6 Negative.
B6: Connects to the junction between Cell 6 Positive and Cell 7 Negative.
B7: Connects to the absolute positive terminal of Cell 7.
Applications
Electric Bikes & Scooters: Building or rebuilding 24V lightweight battery packs for e-mobility vehicles and electric skateboards.
Solar Power Storage: Designing reliable 24V battery banks for off-grid solar LED streetlights, agricultural telemetry systems, and remote sensory nodes.
DIY Power Walls: Constructing medium-scale backup power stations using salvaged or brand-new high-drain lithium-ion cells.
Technical Specifications
| Parameter | Value / Specification |
| Battery Configuration | 7 Cells in Series (7S Lithium-Ion / LiPo) |
| Nominal Voltage | 24V / 25.2V |
| Fully Charged Cut-off Voltage | 29.4V (4.2V per cell) |
| Continuous Discharge Current | 20A Maximum |
| Instantaneous Over-Current Limit | 30A to 40A |
| Cell Balancing Current | 40mA to 60mA per cell (Passive bleed style) |
| Over-Charge Protection Voltage | 4.25V +/- 0.05V per cell |
| Over-Discharge Protection Voltage | 2.50V +/- 0.08V per cell |
| Short-Circuit Protection | Automatic disconnect with self-recovery after load removal |
| Internal Resistance | Less than 20 milliohms |
| Dimensions | Approx. 60mm x 35mm x 8mm |
What’s in the Box
1 x 7S 20A 24V Lithium Battery Protection BMS Board.
