There’s something you should know about the lithium-ion batteries powering your electric scooter: they’re not all protected in the same way.
Like other energy sources such as gasoline tanks or hydrogen cells, li-ion battery packs come with risk. It’s how we mitigate that risk that makes all the difference. To do this correctly, system design must be taken seriously.
That’s why Bird developed a state of the art Battery Management System, or BMS, to mitigate failure modes and help keep riders and communities safe. If you’ve got 2 minutes, we’d love to tell you all about it.
Pre-BMS: Cell Selection
The fundamental building block of a battery is the battery cell.
Bird has made the commitment to only use cells from tier 1 suppliers like LG and Panasonic. We do this because these are the same types of cells used in other industries that have the highest requirements for quality and safety. Think automotive and the like.
There are, of course, cheaper alternatives available, but like the weakest link in a chain, the underlying cell in your design is critical. It only takes one to spoil the fun. Failures that originate inside the cell itself as a result of manufacturing quality are the most difficult to prevent.
We seek to avoid them altogether through the use of high quality products.
BMS Technology at Work
To protect these top quality, IP68-rated battery cell packs, Bird developed a highly sophisticated Battery Management System that enables us to monitor and take rapid action in the case of potential safety or sustainability issues. Here’s how it works.
This is where the proverbial magic happens.
Bird BMS uses robust diagnostics to measure the conditions and performance of our batteries in real time. Our internal humidity sensor is designed to disable batteries at the slightest sign of water intrusion. Similarly, sensory inputs for battery temperature, voltage and current help us automatically regulate operating conditions to avoid pushing cells beyond their rated specification envelope. This is critical for safety and pack life.
These diagnostics are run as many as 20 times per second, alerting our system to potential missteps so we can take the appropriate action either in the vehicle or via Bird’s on-the-ground operations.
Beyond the diagnostics, Bird powertrain systems use what are called dynamic limits.
This means the battery continuously calculates a maximum allowable charge and discharge current rate based on real time cell data (temperature and voltage) and other sensor information. The limit is constantly broadcast to the rest of the system so our motor controller can adjust its maximum power levels dynamically. If the motor controller makes a mistake and violates these limits, dead front capability takes over and decouples the battery from the rest of the system.
These kinds of redundant protections are important. In fact, all the safety related controls in our BMS are backed up by analog safety underneath to help ensure no software mistake can lead to an unsafe outcome on its own.
CAN Bus Communication
Bird has made the decision to use Controller Area Network (CAN bus) for our BMS communication network.
This is an extremely reliable and efficient protocol when it comes to data integrity and rapid response, which is why it has become the automotive gold standard for controlling safety functions such as airbag deployment. CAN helps prevent missed or corrupted messages. It is also more robust against electromagnetic interference that can interfere with critical communications.
BMS Is Just the Beginning
The diagnostics, dynamic limits and CAN Bus communication that make up Bird’s BMS (not to mention the tier 1 battery cells) are just the tip of the iceberg when it comes to our overall battery protection.
To get the full picture, we’d have to dive further into things like dead front capability, redundant safety architecture, mechanical design, vibration and shock testing, exceeding the UL2271 standard, our industry-leading IP68-rated dust and waterproofing and much more.
The key takeaway here is this: all energy sources, be they powerful li-ion battery packs or gasoline engines, come with risk, and not all risk mitigation is created equal. Bird engineers have taken the best practices from their backgrounds in aerospace and automotive engineering to create industry-leading battery protections that include our Battery Management System to help keep riders and communities safe.
For more information on all that we’re doing to put safety first, subscribe to the Bird Cities Blog.