In recent years, the market share of light electric vehicles has continued to rise, accompanied by a surge in various electrical safety failures. Data from after-sales services and field tests across multiple regions show that low-voltage electric scooters and simple e-bikes often experience sudden power loss and communication failures due to short circuits and ESD interference. For high-power electric motorcycles, electric tricycles, and logistics vehicles with voltages exceeding 60V, the failure risks are even more severe — insulation aging in high-voltage circuits causes chassis leakage, arcing from high-current switching ablates components, and transient surges damage sampling and communication chips. At best, these issues leave the vehicle stranded or trigger ECU fault codes; at worst, they can lead to battery thermal runaway or electric shock hazards.

At the same time, 60V is also a critical threshold for EMC compliance in light electric vehicles: for high-voltage motor vehicle-type models, vehicle-level EMC is a mandatory market access requirement, while low-voltage non-motorized vehicles focus primarily on component-level immunity design. These differences in compliance directly affect the barriers to market entry.

At the root, most failures point to a mismatch between BMS protection design and the voltage class. Many designs overlook the 60V critical threshold, using the same protection components across high-voltage and low-voltage models or simplifying dedicated high-voltage protection modules, ultimately creating safety risks. How to implement differentiated BMS protection design based on voltage class has become a core challenge for engineers in the industry.

I. Introduction: The rapid development of light electric vehicles, with voltage classification determining BMS safety design

Currently, light electric vehicles (LEVs) such as e-bikes, e-scooters, e-trikes, high-end electric motorcycles, and in-plant logistics vehicles are experiencing large-scale adoption. With their compact design, low-carbon footprint, flexibility, and efficiency, these vehicles have become a mainstream choice for urban commuting, short-haul freight, and leisure travel.

The battery system is the core power source of LEVs, and battery safety has always been a top priority in industry design. The industry widely adopts 60V as the key voltage threshold, dividing LEV battery systems into two main categories: Class A (voltage < 60V) and Class B (voltage > 60V). The electrical risks, wiring requirements, and protection standards for these two voltage platforms differ significantly, directly determining the overall BMS architecture, protection component selection, and safety design logic, and serving as the core basis for the overall vehicle electrical safety design.

Overview of power, voltage, current, and application scenarios for full-category LEV models

II. Core Architecture Comparison: Overall BMS Architecture Differences Between <60V and >60V Systems

Based on the differences in BMS architectures between the two voltage platforms, Leiditech has compiled a complete comparison table of functions, hardware configurations, and electrical parameters for the seven key protection nodes across both platforms, as follows:

From the perspective of EMC compliance, the mandatory requirements for the two platforms also differ fundamentally:

· Class A (<60V): Represented by e-bikes, subject to GB 17761-2024 Safety Technical Specification for Electric Bicycles. There is no mandatory radio disturbance assessment at the vehicle level; EMC requirements focus on the immunity performance of components such as the BMS, controller, and charger.

· Class B (>60V): Classified as motor vehicles and must comply with GB 14023-2022 Vehicles, Boats and Internal Combustion Engines — Radio Disturbance Characteristics — Limits and Methods of Measurement for the Protection of Off-Board Receivers, and GB 24155-2020 Safety Requirements for Electric Motorcycles and Electric Mopeds. It is generally required to refer to GB/T 36282-2018 Electric Motorcycles and Electric Mopeds — Electromagnetic Compatibility Requirements for full vehicle-level emission and immunity testing. Starting in 2027, the new mandatory standard GB 34660-2026 Road Vehicles — Electromagnetic Compatibility Requirements and Test Methods will take effect, further upgrading the compliance requirements.

From an electrical safety perspective, high-voltage circuits above 60V are more prone to arcing, transient surges, and leakage hazards, imposing higher requirements on protection components in terms of voltage tolerance, surge current capability, and noise immunity. In response to the various electrical risks in high-voltage scenarios, Leiditech has built deep expertise in the automotive-grade circuit protection field, with mature technical capabilities in transient suppression, overcurrent protection, high-voltage isolation, and ESD protection devices. It can comprehensively match the protection requirements of both high-voltage and low-voltage LEV battery systems.

III. In-depth analysis of the seven key protection nodes

Based on the seven core protection nodes listed in the table above, Leiditech provides a breakdown of each node, analyzing the operating condition risks and protection requirements, along with the corresponding protection solutions.

1. Main circuit fuse: Short circuits generate extremely high currents that can burn out components and wiring harnesses. Select fuses with appropriate voltage ratings and breaking capacity based on requirements; in high-voltage scenarios, prioritize higher-spec products.

2. Battery disconnect unit:

· Function: Enables controlled connection and disconnection between the battery pack and the vehicle load, coordinating with the BMS to complete power-on, power-off, and fault shutdown logic.

· Operating conditions and threats: The high-current switching process is prone to arcing and voltage spikes, which can cause component aging and misoperation over long-term use.

· <60V platform: Uses multiple MOSFETs in parallel to achieve circuit connection and disconnection.

· >60V platform: Uses MOSFETs in combination with high-voltage DC contactors to handle higher voltage and current.

Protection solution: Use Leiditech's automotive-grade TVS from the S-SMDJ (3KW) or 5.0SMDJ (5KW) series to absorb voltage spikes generated during switching and suppress arc interference. Select low-RDS(on) MOSFETs and high-voltage DC contactors to improve loop stability. This design meets the immunity requirements for power line transients and load dump specified in GB/T 21437.2-2021 Road vehicles — Electrical disturbances from conduction and coupling — Part 2: Electrical transient conduction along supply lines only.

3. Insulation monitoring device (IMD): Only configured in high-voltage systems (>60V). Cable aging and moisture can easily cause leakage. Solid-state relays are used to achieve high-voltage to low-voltage isolation, ensuring accurate and reliable monitoring signals. This module is an essential unit for high-voltage motor vehicles to meet vehicle-level electrical safety and EMC compliance, conforming to GB 24155-2020 Safety Requirements for Electric Motorcycles and Electric Mopeds.

4. Analog front-end & cell balancing circuit (AFE sampling lines):

Function: Collects voltage of each cell and performs active/passive balancing. This is the core circuit for precise cell state management by the BMS.

Operating conditions and threats: Sampling leads are susceptible to short circuits, overcurrent, and transient overvoltage faults, which can directly damage the AFE sampling chip and wiring harness.

Protection solution: Use resettable fuses (PPTC) for overcurrent protection on sampling lines, paired with Leiditech's 600W S-SMBJ series automotive-grade TVS to suppress line overvoltage and surges. This dual protection ensures stable sampling circuit operation. The solution can pass the industry-standard test levels of GB/T 17626.5-2019 Surge (Impact) Immunity Test, and complies with the immunity requirements for sampling circuits specified in GB/T 38661-2020 Technical Specifications for Battery Management Systems for Electric Vehicles.

5. Battery pack secondary protection: Cell overcharging and overvoltage can cause thermal runaway. Select three-terminal fuses of the appropriate specifications based on the voltage class to permanently disconnect the circuit in case of faults. This is the ultimate hardware protection for the BMS and is a mandatory safety configuration for batteries as explicitly required by GB/T 38661-2020.

6. Temperature monitoring loop: Abnormal heating of cells and power devices can trigger safety incidents. NTC thermistors are used for multi-point temperature measurement, working with the BMS to achieve

CAN interface ESD and filtering protection solution: Leiditech recommends using the multi-channel integrated device SMC24Q or the single-channel SD24CQ for protection, with capacitance <50pF. This solution ensures signal integrity while passing ESD testing, meeting the requirements of GB/T 17626.2-2018 (equivalent to IEC 61000-4-2) ESD immunity Level 4, achieving contact discharge of 30kV and air discharge of 30kV. It also complies with GB/T 19951-2019 Road vehicles — Test methods for electrical disturbances from electrostatic discharge (equivalent to ISO 10605), the dedicated automotive ESD test specification. The SMC24Q is certified to automotive-grade AEC-Q101.

LIN bus ESD protection solution: Leiditech recommends using the integrated device PESD1LIN for protection, with capacitance <20pF, ensuring signal integrity while passing ESD testing. It complies with GB/T 17626.2-2018 (equivalent to IEC 61000-4-2) Level 4, achieving contact discharge of 30kV and air discharge of 25kV.

LEV model - voltage - protection device - standard quick reference table

IV. Component Selection Pitfall Avoidance Guide

1. CAN/LIN selection taboos: For signal channels, priority must be given to low-capacitance TVS/ESD devices, with junction capacitance ≤50pF recommended. High-power power-class TVS devices are prohibited, as high parasitic capacitance can cause signal drift and communication anomalies.

2. High and low temperature environment adaptation: All automotive protection components should be AEC-Q101 qualified products, meeting the -40°C to 125°C wide-temperature operating requirements to ensure stable EMC performance under wide-temperature conditions.

3. PCB layout precautions: Protection devices such as ESD and TVS must be placed as close as possible to the connector/sampling terminal to shorten trace lengths and avoid interference coupling. High-voltage loops and low-voltage signal loops should be laid out in separate zones to reduce crosstalk risk — this is also a core layout principle for EMC rectification.

4. IMD supporting component requirements: High-voltage IMD loops must be equipped with contactless solid-state relays; conventional mechanical relays are prohibited to prevent arcing and leakage hazards and to ensure the insulation performance of high-voltage systems.

5. Graded compliance design principle: For <60V low-voltage models, component-level immunity must be ensured; for >60V motor vehicle-class models, system-level design must comply with mandatory vehicle-level EMC and electrical safety standards. Protection component selection must simultaneously match automotive-grade test standards to avoid subsequent certification failures.

Conclusion

60V, as the voltage threshold for LEV battery systems, defines two distinct BMS safety design frameworks: low-voltage platforms focus on basic overcurrent and temperature protection, while high-voltage platforms require additional advanced protection measures such as insulation monitoring, high-voltage isolation, and arc suppression. At the same time, 60V also serves as the boundary for EMC compliance — low-voltage models emphasize component-level reliability, while high-voltage models must meet mandatory vehicle-level EMC market access requirements. A well-designed protection strategy is the dual safeguard for product safety and regulatory compliance.

Battery safety is the bottom line for the development of the LEV industry, and professional circuit protection components are the core enabler of BMS safety design. With years of expertise in automotive-grade protection technology and a deep alignment with the high-voltage and low-voltage architectural needs of the LEV sector, Leiditech provides stable, reliable, and compliant one-stop battery system protection solutions for all categories of LEV customers, including electric two-wheelers, three-wheelers, leisure vehicles, and in-plant logistics vehicles.