1. Product Overview

The TDT-9141 is an 8S common-port battery-management and protection board designed for NMC lithium-ion battery packs containing eight cells or parallel cell groups connected in series.

An 8S NMC battery pack has a nominal voltage of approximately 29.6V and reaches 33.6V when fully charged.

The product label specifies a 20A charging-current rating and a 20A discharging-current rating. Its common-port design allows the charger and load to share the P− negative connection.

The PCB is protected by a metal cover that helps shield the electronic components and distribute heat. A multi-pin connector is provided for the cell-group voltage-sensing wires.

2. Technical Specifications

Protection thresholds, delay times, balancing capability and recovery behaviour should be confirmed from the manufacturer’s specification for the exact model.

3. Typical Connection Points

The exact balance-wire sequence must be confirmed using the supplied wiring diagram. Do not identify the connections only by wire colour or physical position.

4. Protection Functions

The TDT-9141 BMS is intended to provide essential protection for compatible 8S NMC lithium-ion battery packs, including:

• Individual cell-group voltage monitoring
• Overcharge protection
• Over-discharge protection
• Charge-overcurrent protection
• Discharge-overcurrent protection
• Short-circuit protection
• Charge and discharge switching through onboard MOSFETs
• Recovery after supported protection events

Cell balancing and temperature protection are not confirmed by the visible product markings and should be verified before advertising these functions.

5. Suitable Applications

This BMS may be suitable for compatible 8S NMC lithium-ion battery packs used in:

• Electric bicycles
• Electric scooters
• Robotics projects
• Portable power equipment
• Rechargeable tools
• Battery-powered instruments
• Backup-power equipment
• DIY battery packs
• Custom 29.6V lithium-ion batteries
• Battery repair and replacement projects

The continuous operating current and startup current of the connected equipment must remain within the verified capabilities of the BMS, cells, wiring and connectors.

6. Battery and Charger Compatibility

Use this BMS only when:

• The battery contains exactly eight series-connected NMC lithium-ion cell groups.
• Each cell group has a nominal voltage of approximately 3.6V or 3.7V.
• Each cell group has a maximum charging voltage of 4.2V.
• The pack has a nominal voltage of approximately 28.8V–29.6V.
• The charger is designed specifically for an 8S lithium-ion battery.
• The charger’s maximum output voltage does not exceed 33.6V.
• All eight cell groups are at closely matched voltages before installation.
• The battery cells can safely provide the required current.
• The charger output remains within the verified charging-current limit.
• The connected load remains within the verified continuous and peak-current limits.

Do not use this BMS with 8S LiFePO₄ cells. LiFePO₄ batteries require different charging and protection-voltage thresholds.

7. Installation Guidance

• Measure the voltage of all eight cell groups before installation.
• Confirm that the cell-group voltages are closely matched.
• Connect B− to the battery pack’s main negative terminal.
• Connect each sensing wire sequentially to the appropriate cell-group junction.
• Connect the final positive sensing wire to the battery pack’s positive terminal.
• Connect the charger and load negative to P−.
• Connect the charger and load positive directly to battery positive unless the supplied diagram states otherwise.
• Verify the voltage between every consecutive balance wire before inserting the connector.
• Use appropriately sized power cables and connectors for the expected current.
• Install a suitable fuse close to the battery’s positive terminal.
• Keep soldering or terminal-heating time as short as possible.
• Insulate every exposed terminal and conductive surface.
• Mount the BMS where it cannot contact nickel strips, busbars or a metal enclosure.
• Provide adequate space for heat dissipation.

Incorrect connection of even one sensing wire can permanently damage the BMS.

8. Important Current-Rating Note

The 20A BMS rating does not increase the current capability of the battery cells.

The safe current of the complete battery system is determined by its lowest-rated component, including:

• Battery cells
• BMS
• Nickel strips or busbars
• Power cables
• Connectors
• Fuse
• Charger
• Connected load

Motors and other inductive equipment may draw startup current considerably higher than their normal operating current. Confirm both continuous and peak-current requirements before using this BMS.

The label specifies 20A charging and 20A discharging. Avoid operating continuously at the maximum rating without adequate cooling and verification under actual load conditions.

9. Safety Information

• Use only with a compatible 8S NMC lithium-ion battery pack.
• Use only an 8S lithium-ion charger with a maximum output of 33.6V.
• Never reverse the battery polarity.
• Never short B−, P−, B+ or the battery terminals.
• Do not connect the balance wires in the wrong order.
• Verify every sensing voltage before inserting the balance connector.
• Do not exceed the verified charging or discharging current.
• Use correctly rated cables, connectors and a suitable fuse.
• Keep the BMS away from water, conductive dust and loose metal objects.
• Do not use a damaged, burnt, corroded or unusually hot board.
• Stop using the battery if any cell becomes swollen, overheated or abnormally unbalanced.
• Installation should be performed by someone familiar with lithium-ion battery wiring and safety.