This article first appeared in the November 2020 edition of the Australian Automotive Aftermarket Association Magazine.

What is a battery management system?

I’m sure you are familiar with engine management systems, or engine control units, that electronically adjust engine actuators to ensure optimal engine performance. However, coming from the electric vehicle industry, there is a small challenge with writing a feature on engine management systems; because electric vehicles don’t actually have them.

So today we will be taking a look at a battery management system (BMS), and how its role compares to that of an engine management system in helping the vehicle operate at its full potential.

A battery management system is similar to an engine management system in that it works by having a wide array of sensors all throughout the vehicle, enabling it to monitor and control the electrical output in the car. The actual unit itself is usually a small circuit board with several controllers and inputs on it, and typically closely resembles an engine control unit in both appearance and size.

BMS features and benefits

One of the most important features of a BMS is its ability to monitor the state of the battery, keeping tabs on many different characteristics such as the state of charge, temperature, current, voltage and the flow of coolant. All essential things to help keep an EV running smoothly. Much like how an engine management system can control the engine to keep it healthy, a BMS is able to protect EVs from things like overcurrent and undervoltage. 

The BMS plays a critical role in keeping the batteries of the car cool. Much like when an engine is running, EV batteries heat up through use, and by being able to monitor the temperature of the battery cells, the BMS is able to adjust the cooling system to keep the battery pack as close to its optimal temperature as possible. Batteries are particularly sensitive to temperature, and as such, being able to keep them from overheating, or from getting too cold has a significant impact on the overall driving range of the vehicle. (Image courtesy of Japan Aviation Electronics)

EV specific features

Additionally, the BMS helps to manage many EV-specific features such as regenerative braking and charging the vehicle. As the vehicle slows down, the BMS is able to allocate power generated from the electric motor running in reverse back to the battery to increase driving range. Moreover, the BMS has to negotiate with the onboard charger to manage the rate at which the vehicle can be recharged and help to preserve the battery over the vehicle's life.

While there may not be complex calculations about optimal fuel to oxygen ratios being performed during operation like there is in an engine management system, a battery management system plays a similarly significant role in communicating between all the different parts that come together to make an EV run.