JK-BD4AxxS-12P 120A Active Balancing BMS | Full Technical Guide

Product Overview

This BMS is an all-in-one management system built for large-capacity series-connected lithium battery packs. It integrates voltage acquisition, high-current active balancing, full-spectrum protection, coulomb counting, Bluetooth communication and optional GPS remote monitoring. It is fully compatible with ternary lithium, lithium iron phosphate and lithium titanate battery chemistries.

Its core advantage lies in the energy-transfer active balancing architecture, which transfers energy directly from higher-voltage cells to lower-voltage cells without resistive heat loss. With a continuous balancing current of 0.4A, it maximizes battery pack consistency, extends usable range and slows down cell aging effectively.

The board works with the dedicated JK BMS mobile APP for both Android and iOS systems. Via Bluetooth connection, users can monitor real-time battery status, adjust all protection parameters, and control charge/discharge switches remotely. With compact dimensions, straightforward wiring and complete functions, it fits a wide range of scenarios including low-speed sightseeing vehicles, mobility scooters, shared vehicles, high-power energy storage systems, base station backup power and solar power stations.

Core Features & Functions

1. Bidirectional Active Balancing

The board adopts non-destructive energy transfer balancing technology. When the voltage difference between any two cells exceeds the set threshold, balancing activates automatically, and stops once the difference falls below the setting. The default balancing current is 0.4A at maximum, and the trigger threshold is adjustable via APP. It is recommended to keep the balancing current below 0.2C of the total battery capacity. Users can also turn off the balancing function completely in the APP control panel if not needed.

2. Full-Range Protection Mechanisms

All protection parameters are adjustable through the mobile APP to match different battery types. The standard protection functions include:

• Charge protection: overvoltage protection, overcurrent protection, over-temperature protection and low-temperature protection, each with independent recovery settings
• Discharge protection: undervoltage protection, overcurrent protection and over-temperature protection, plus automatic shutdown voltage for deep discharge prevention
• Short circuit protection: hardware-level short circuit detection with adjustable delay and recovery time, suitable for capacitive loads and high inrush current chargers
• MOS over-temperature protection: independent temperature monitoring for power MOSFETs to prevent thermal runaway

3. Extended Optional Functions

The board reserves hardware interfaces for multiple expandable functions, which can be selected per project requirements:

• Heating function: supports external heating film with 10A heating current, controllable via APP. It is recommended to add an external 45℃-65℃ normally closed temperature switch as secondary protection.
• Alarm function: works with external buzzer to alert users when over-temperature, overcharge or over-discharge faults occur.
• Battery parallel function: works with dedicated parallel modules for multi-pack parallel operation, suitable for large-capacity energy storage systems.
• Communication options: optional CAN and RS485 communication for host computer integration and industrial control scenarios.
• GPS function: reserved UART interface for external GPS module, enabling remote location and fleet management.

4. Practical Auxiliary Functions

• Emergency switch: when faults occur during use, activating the emergency switch will force both charge and discharge on for 30 minutes, providing emergency power to avoid breakdown situations. It remains active even if cells reach the auto-shutdown voltage.
• Intelligent sleep: when charge/discharge current stays below 1A for 26 consecutive hours, the board enters sleep mode automatically to cut standby power consumption. It can be reactivated by charger, external button or display screen.
• High precision sampling: single cell voltage detection covers 1V to 5V with ±3mV accuracy, paired with high-precision current sampling and accurate coulomb counting for reliable SOC calculation.
• Display support: standard display interface compatible with Jikong LCD screens for local status viewing without mobile phones.

Model Selection & Battery Compatibility

The BD4AxxS-12P series includes two base models for different cell counts, with multiple function suffix versions for flexible configuration.

Base Models by String Count

JK-BD4A20S-12P supports 7~20 strings of ternary lithium, 8~20 strings of lithium iron phosphate, and 14~20 strings of lithium titanate batteries, working within 20V to 100V pack voltage.

JK-BD4A24S-12P supports 7~24 strings of ternary lithium, 8~24 strings of lithium iron phosphate, and 14~24 strings of lithium titanate batteries, covering wider high-voltage pack applications within the same 20V to 100V operating range.

Function Suffix Configuration

Users can select extended functions by model suffixes based on actual needs: H for heating function, C for CAN communication, R for RS485 communication. Suffixes can be combined, for example, BD4A24S-12PHCR represents the 24-string version with heating, CAN and RS485 functions all enabled.

Key Technical Specifications

Basic Electrical Parameters

• Supply voltage range: 20V to 100V DC
• Operating power consumption: ≤800mW
• Operating temperature range: -30℃ to 70℃
• Maximum cell sampling count: 24 strings
• Maximum active balancing current: 0.4A
• Maximum continuous charge / discharge current: 120A
• Maximum instantaneous discharge current: 240A
• Maximum main loop internal resistance: 0.9mΩ
• Board dimensions: 146.8mm × 103mm × 17.6mm
• Net weight: 230g
• Temperature sensors: 1 built-in, 2 external standard, expandable to 4 external

Default Protection Parameters

All parameters are factory preset for three mainstream battery types and can be adjusted freely via APP.

For ternary lithium batteries: overcharge protection at 4.2V per cell, undervoltage protection at 2.82V per cell, balancing trigger at 10mV differential, charge overcurrent delay 30s, discharge overcurrent delay 300s, short circuit delay 5μs, charge over-temperature protection at 70℃, charge low-temperature protection at -20℃.

For lithium iron phosphate batteries: overcharge protection at 3.6V per cell, undervoltage protection at 2.6V per cell, with the same balancing current, timing and temperature thresholds as ternary preset.

For lithium titanate batteries: overcharge protection at 2.7V per cell, undervoltage protection at 1.8V per cell, matching the low-voltage characteristics of LTO chemistry.

Interface Definition & Installation Notes

The board integrates multiple dedicated connectors for clear wiring and reliable connection.

• Balancing & sampling ports: 15-pin and 11-pin HY2.0 connectors for cell voltage sampling and balancing, covering B- to B24+ in sequence
• Temperature ports: two 4-pin HY2.0 connectors for external NTC temperature sensors
• GPS port: 4-pin 1.25T connector with power output and UART communication for external GPS module
• Buzzer port: 2-pin connector for optional alarm buzzer
• Communication port: 4-pin connector with integrated CAN and RS485 signals
• Display port: 6-pin connector with activation pins, power output and RS485 signals for matching display screens
• Parallel port: 3-pin connector for parallel module status and enable control
• Power terminals: M6 screw terminals for battery B-, B+ and load P- connection

Installation Precautions

Before powering on the board, double check that all balancing wires are connected correctly and that B- and P- polarities are not reversed. The board adopts charge activation design: it will power on automatically when a charger with 2V higher voltage than the pack is connected. It also supports button activation and display activation for models with matching accessories. Wrong wiring may cause abnormal operation or permanent damage to the board, so wiring must follow the official wiring diagram strictly.

APP Operation & Parameter Setup

All settings and monitoring are operated through the official JK BMS mobile APP, which can be downloaded by scanning the QR code on the product or from the official download center.

After Bluetooth connection, users can view real-time total voltage, single cell voltages, current, SOC, temperature and operating status on the homepage. In the parameter setting page, users can modify battery type, cell count, total capacity, all protection thresholds, balancing trigger voltage difference and timing parameters. In the control page, users can manually turn charge and discharge on/off, enable or disable balancing, activate emergency mode, control heating function and switch communication port modes.

For first-time use, it is recommended to set battery type and cell count first, then perform voltage and current calibration to ensure sampling accuracy. For detailed parameter adjustment instructions, please refer to the official parameter setting guide.

Typical Application Scenarios

• Low-speed electric vehicles, electric tricycles and electric sightseeing buses
• Electric motorcycles and two-wheeler battery packs
• Small and medium-sized off-grid solar energy storage systems
• RV and caravan house battery systems
• Base station backup power and industrial UPS battery packs
• Shared mobility and small fleet battery management