Ever Ready - How Mobile Robots are Lasting Longer through Efficient Battery Management

by Rafael Marengo

In the fast-paced world of automated warehouses and manufacturing facilities, every second counts. Autonomous mobile robots (AMRs) and Automated Guided Vehicles (AGVs) are crucial to this ecosystem, where even a brief downtime can cause significant disruptions. Ensuring the efficient and safe operation of these robots requires meticulous control over their components, especially their batteries.

The Importance of Battery Management Systems

A Battery Management System (BMS) is an electronic system designed to monitor and control various parameters of a battery pack or its individual cells. These systems are essential for maximizing the usable capacity of batteries while ensuring safe and reliable operation. An efficient BMS can provide accurate measurements of cell voltage, state of charge (SoC), depth of discharge (DoD), state of health (SoH), temperature, and current. These parameters are vital for optimizing the performance of mobile robots.

Key Metrics in Battery Management

• State of Charge (SoC): This parameter indicates the current charge level of the battery relative to its total capacity. It is expressed as a percentage, with 0% being empty and 100% being fully charged. Accurate SoC measurements are crucial for planning the operational cycles of mobile robots and preventing unexpected downtimes.
• State of Health (SoH): SoH represents the maximum capacity of the battery compared to its rated capacity. It helps in assessing the aging and overall health of the battery, which is vital for maintenance and longevity.
• Depth of Discharge (DoD): This is the opposite of SoC and indicates the percentage of the battery that has been discharged relative to its rated capacity. Managing DoD is crucial to prevent over-discharging, which can damage the battery and reduce its lifespan.

Why These Metrics Matter for AMRs and AGVs

Different types of batteries, such as Lithium-Ion (Li-Ion) and lead-acid batteries, offer various benefits and challenges. Li-Ion batteries, for instance, have a higher energy density, are lighter, charge faster, and have a longer life cycle compared to lead-acid batteries. However, they are also more expensive and require precise monitoring to realize their full potential.

For example, a typical LiFePo4 battery pack used in an AMR has a specific voltage range that needs to be monitored accurately. Even a minor measurement error can significantly affect performance. If a LiFePo4 battery pack for a 24V system with a capacity of 27.2V has a measurement error, it can lead to underutilization and increased costs. Accurate SoC and DoD measurements are therefore critical for optimizing battery usage and extending its life.

On figure 1 we see a plot of the depth of discharge for two common types of batteries, a Li-Ion battery, and a Lead Acid battery. As it is possible to observe, the voltage variation for the Li-Ion is very small,  while going from 10% to 90% of DoD, from that we can infer that a few mV can have a big impact on a precise measurement thus improving efficiency.

Figure 1: Depth of Discharge for a Li-Ion battery and a Lead Acid battery

Another important topic is the natural degradation of batteries, as we can see on Figure 2, the full range of operation of a battery will decrease within its lifetime so precise voltage measurements and SoC, DoD estimations become paramount.

Figure 2: Battery Range of Operation Natural Degradation

Reducing Waste and Environmental Impact

Efficient battery management is not only about improving performance but also about reducing waste and environmental impact. Citing to the International Energy Agency report of 2023, “Batteries are essential for the clean energy transition”. Proper management can extend battery lifespan, reducing the need for frequent replacements and minimizing environmental damage from battery disposal.

Figure 3 shows some of the most critical degradation factors for batteries, all of them can be controlled and/or monitored with the proper technologies.

Figure 3: Battery Degradation Factors

ADI’s BMS Solutions: Enhancing Efficiency and Safety

ADI’s BMS solutions (ADBMS6948) offer advanced technologies that enhance the performance and safety of mobile robotics applications. These systems provide precise cell measurements, balanced charging, synchronous current and voltage measurements, and fast over-current detection to optimize battery performance, extend battery life, and enhance safety.

For instance, the ADBMS6948 offers several key features, including:

• Low total measurement error (TME) over the battery's lifetime
• Simultaneous and continuous cell voltage measurements
• Built-in isoSPI interface for robust communication
• Hot plug tolerance without external protection
• Passive cell balancing for uniform charge distribution
• Low power cell monitoring and low sleep mode supply current

These features ensure that the batteries are used efficiently and safely, reducing the risk of overcharging, over-discharging, and overheating.

Conclusion

In the evolving landscape of automated manufacturing and warehousing, the efficiency and reliability of mobile robots are paramount. ADI’s Battery Management Solutions play a critical role in enhancing the performance, safety, and longevity of these robots by providing precise monitoring and control of battery parameters. By extending battery life and reducing waste, these solutions not only improve operational efficiency but also contribute to environmental sustainability. As automation continues to advance, the importance of robust and efficient battery management systems cannot be overstated. To learn more visit analog.com/multicell-battery-stack-monitor