The life of lithium-ion batteries depends on how each cell is managed throughout its life. This is the job of the battery management system (BMS).
If a cell is discharged to an extreme end of its state of charge, especially below 2.5V, its life will be severely shortened. An EV battery pack combines hundreds of 3.7V cells in series to achieve pack voltages of 400-800V. Several series arrangements are connected in parallel to achieve the required capacity.
The BMS must monitor all of the cells in the battery pack and balance charging and discharging between them to ensure that extreme C-rate, temperature, or discharge conditions are not encountered by any individual cells.
Modern distributed battery management systems require complex communications systems to relay voltages, temperatures, and other information from individual cells. In a wired BMS, sensors are daisy-chained using twisted-pair cabling. Additional isolation components are required to ensure reliable communications within the noisy electromagnetic interference environment seen within vehicles. It can also be challenging to time-synchronize measurements as the signals propagate through the network.
A wireless BMS avoids the need for this complex cabling. The advantages of a wireless BMS include:
- Reduced weight and complexity
- Smaller packaging footprint
- Easier servicing
- More synchronized sensor measurements
Disadvantages include overcoming the noisy electromagnetic environment and the potential for security breaches. Established wired BMS systems have proven reliability, enhanced by ring architecture providing redundant cabling. Wireless BMS can use various communication protocols, including a wireless universal asynchronous receiver transmitter (UART) and Bluetooth Low Energy and SmartMesh.
The UART sends data one bit at a time, starting with the least significant and ending with the most significant bit. The data is framed by start and stop bits. This is one of the oldest digital communication protocols in the world, which was first used by teletypewriters.
At the other end of the spectrum, SmartMesh is a blockchain-based Internet of Things protocol that uses blockchain technology. It allows agile self-repairing networks with path and frequency diversity to route messages around obstacles and deal with interference.
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Filed Under: Batteries, FAQ