Electric Scooter Battery Management System (BMS): A Technological Breakthrough from Safety Protection to Life Enhancement

Keywords: electric scooter BMS、 Lithium batteries, balanced charging, thermal management

abstract

The battery management system is the key to the safety and lifespan of electric scooters. This article analyzes the technical solutions and engineering practices of battery selection, balancing technology, and thermal runaway protection.

2.1 Comparison of lithium battery types

18650 cylindrical battery:

Energy density of 250Wh/kg (such as Samsung INR18650-35E), cycle life of 500 times (80% capacity retention rate), low cost ($0.5/Wh).

More than 10 sections need to be connected in series (such as a 36V system), which increases the complexity of BMS.

21700 cylindrical battery:

The energy density is 300Wh/kg (such as LG M50LT), with a cycle life of 800 times, but the increase in diameter poses a risk of vibration fatigue (requiring optimization of the support structure).

Soft pack polymer battery:

The energy density is 350Wh/kg (such as ATL 50Ah), and the shape can be customized, but additional packaging is required (cost increases by 30%).

2.2 BMS Core Functions

Active balancing technology:

Implemented through the TI BQ76940 chip, the balanced current is 100mA, the balancing time is less than 4 hours (traditional passive balancing requires 24 hours), and the efficiency is improved by 80%.

SOC estimation algorithm:

Combining the ampere hour integration method with Kalman filtering, with an error of less than 3% (as implemented by NXP S32K144 MCU), to avoid overcharging/overdischarging.

2.3 Thermal Management Strategy

Air cooling heat dissipation:

Add aluminum heat sinks (with a surface area of 0.1m 2) at the bottom of the battery pack, coupled with a 5V/0.2A fan, to achieve a temperature rise of less than 15 ℃ in a 40 ℃ environment.

Phase change materials (PCM):

Using paraffin based PCM (melting point 45 ℃) with a heat absorption capacity of 200J/g, it suppresses the propagation of thermal runaway (such as when a single battery experiences thermal runaway, the temperature rise of adjacent batteries is less than 20 ℃).

2.4 Security Protection Mechanism

Overcharge protection:

By using the BQ77915 monitoring chip, the charging circuit is cut off when the voltage is greater than 4.25V (response time<10 μ s).

Short circuit protection:

PTC self recovery fuse (B59120C0100A060) is used, with a resistance of less than 10m Ω and triggering protection when the short-circuit current is greater than 50A.

2.5 Aging Testing and Certification

Cycle life test:

According to the IEC 62660-2 standard, the capacity retention rate is greater than 80% after 800 cycles of charging and discharging at a 1C rate at 25 ℃.

UL 2272 certification:

Require the battery pack to pass tests such as compression (100kN), impact (150g acceleration), overcharging (150% SOC), etc. to ensure no risk of fire/explosion.

conclusion

BMS needs to shift from "passive protection" to "active management". By actively balancing, thermal management, and multi-level protection, battery safety and lifespan can be improved.