7S 25.9V 29.4V 4.2V Li-ion 18650 Battery Passive Equalizer Balancer Board

7S 25.9V 29.4V 4.2V Li-ion 18650 Battery Passive Equalizer Balancer Board is an auxiliary 7-series (7S 24V/25.9V nominal, 29.4V full charge) cell voltage equalization module designed for 7-cell 18650, 21700, and LiPo battery packs used in 24V e-bikes, scooters, and solar energy storage. Equipped with 7 independent 4.20V voltage-detection and 66mA bleed-resistor channels (`B1` through `B7`), it equalizes all 7 series cell groups during charging when paired with a non-balanced 7S BMS.

Key Features:

• 7-Series (25.9V / 29.4V) E-Bike & 24V Pack Balancing: Monitors and equalizes all 7 series cell groups in standard 24V (7S) lithium-ion battery packs.
• 66mA Per-Cell Shunt Balancing at 4.20V: As soon as any single cell group reaches 4.20V during charging, its dedicated 66mA bleed channel shunts excess current so the remaining 6 cells can finish charging to 4.20V.
• Prevents Premature 7S BMS Charge Cut-Off: Stops a single slightly higher cell from hitting 4.25V and tripping the main BMS before the rest of the 29.4V pack is fully charged.
• Zero Drain During Discharge & Storage: Remains completely inactive below 4.18V/cell so it never drains your 24V battery pack while parked.
• Compact 8-Pad Strip Layout: Clearly labeled `B-` through `B7+` solder pads make parallel wiring to existing 7S cell taps straightforward.

Technical Specifications:

• Supported Pack Configuration: 7S (7 Series 3.7V Li-ion / 18650 / 21700 / LiPo Cells — 25.9V Nominal / 29.4V Full)
• Single-Cell Balance Trigger Voltage: 4.20V DC per cell
• Single-Cell Balance Current: 66 mA per channel
• Recommended BMS Cut-Off Pairing: Pair with a 7S BMS whose overcharge cutoff is ≥ 4.25V/cell
• Recommended Cell Matching: Internal resistance difference ≤ 5 mΩ, voltage within 0.03V, capacity within 50 mAh

Mechanical Specifications:

• PCB Material: FR-4 Fiberglass Strip PCB with 7 × Precision Shunt Channels
• Terminals: 8 × Tinned Solder Pads (`B-`, `B1+`, `B2+`, `B3+`, `B4+`, `B5+`, `B6+`, `B7+`)

Dimensions:

• Length: ~48 mm
• Width: ~26 mm
• Thickness: ~2.5 mm
• Weight: ~5.5 g

Pinout and Wiring:

• B- (0V): Connect to Cell 1 Negative (Pack Negative).
• B1+ to B6+: Connect sequentially to the positive terminals of Cell 1 (`3.7V`), Cell 2 (`7.4V`), Cell 3 (`11.1V`), Cell 4 (`14.8V`), Cell 5 (`18.5V`), and Cell 6 (`22.2V`).
• B7+ (25.9V/29.4V): Connect to Cell 7 Positive (Pack Positive).
• Important Note: Must be used alongside a 7S BMS (`PID 63730` 7S 25A BMS or similar) that provides over-discharge and overcurrent protection.

Datasheet Reference:

• Circuit Architecture: 7 × Independent 4.20V Voltage Detectors + MOSFET Switches + $6262 Ω SMD Bleed Resistors (66mA)

Commonly Used in:

• 24V (7S 25.9V / 29.4V) Electric Bicycle, Scooter, and Wheelchair Packs
• 24V Solar Off-Grid & Telecom Backup Battery Banks
• 24V Industrial AGVs, Lawn Mowers, and Mobility Scooters
• Upgrading Non-Balanced 7S 18650 BMS Packs

Applications:

• Pairs with our `7S 25A 10 MOS BMS Lithium 18650 Battery Charge Board` (`PID 63730`) to add 66mA per-cell top balancing across all 7 cell strings.
• Extends the service life and range of 24V e-bike and mobility scooter battery packs.
• Keeps 7 series cell groups tightly matched within 30mV at full charge.

Equivalent Models:

• 6S 4.2V Li-ion Balancer Board: 6-series (22.2V/25.2V) 66mA passive balancer board (`PID 3362`).
• 8S 29.6V 18650 Lithium Battery Equalizer Board: 8-series (29.6V/33.6V) passive balancer board (`PID 3364`).

Package Includes:

• 1 × 7S 25.9V 29.4V 4.2V Li-ion 18650 Battery Passive Equalizer Balancer Board