Newer technological devices require battery cells to provide higher levels of power while being lightweight and small. When seeking higher levels of energy and power in battery packs, these circumstances create an environment that leads to potentially unstable battery chemistries, elevated temperatures, short circuits, cell swelling, loss of capacity, and overcharging/over-discharging.
Battery management systems (BMS) equipped with smart sensors and monitoring systems control these potential issues and improve the state of health (SoH) and state of charge (SoC) of the battery pack.
Smart sensors and monitoring systems are programmed with set parameters to ensure the working components of the battery do not exceed the required temperatures, voltage, and current levels. These sensors also provide safety protection by providing electrolyte leak detection, water penetration, and gas detection. Monitoring systems allow for improvements to battery performance, capacity, and longevity.
Types of Sensor Monitoring
The type of sensor to design will depend on its required function. While some sensors can detect one factor, others are designed to monitor multiple functions.
Battery management systems (BMS) with various sensors.
Some detection factors can include the following:
- Temperature
- Voltage
- Current
- Pressure
- Humidity
- Isolation resistance
- Gas detection
- Deformation
Evaluating the needs of the device as well as the environment can determine the appropriate components to install to improve the health, safety, and efficiency of the battery pack. Most battery pack sensors will detect temperature, current, and voltage. When requiring additional functions, the sensors may need additional components. This design aspect can increase both the size and the weight of the battery pack, along with increasing the price.
Temperature Sensors
Temperature sensors can range from thermocouples, resistors, and thermistors. Thermistors and temperature-sensitive resistors will change in resistance based on the rising and falling temperatures in the pack. Thermocouples will check the temperature based on voltage differences. Sensors can be used to check internal temperatures as well as surface temperatures and hotspots.
These sensors provide real-time data continuously. Many sensors are used during the assembly and testing of the battery pack to determine potential issues.
Current Sensors
Current sensors monitor the flow of the current to ensure that it is at an optimal level. They help with overseeing charging and discharging cycles. These ICs collect data that helps with determining the SoH and SoC of the battery pack.
If the sensor's measurements encounter instances where the current exceeds charging or discharging parameters, the battery management system activates internal controls to disconnect the battery pack from the load or charger. By activating this electronic switch, both the battery pack and the device are protected from overcharging and over-discharging.
In addition, current sensors also detect faults with the circuits or cells in the pack. These faults may lead to short circuits. The sensor can prevent damage while improving the lifespan and efficiency of the battery pack.
Current sensors come in the form of Hall effect sensors and shunt resistors. Hall effect sensors perform measurements based on the generated magnetic field. Shunt resistors measure voltage drops along the current path of the batteries.
Voltage Sensors
Voltage sensors are designed within a battery pack to monitor the SoH and SoC to detect overcharging and deep discharging issues. Overcharging and over-discharging can damage the battery cells as well as cause a loss in capacity. These sensors can be designed to monitor all the cells within the battery pack or a single battery.
Much like current sensors, voltage sensors are also available as shunt resistors. They also come as high voltage sensors for applications that require higher voltages, as well as battery voltage sensors (BVS) designed to measure the voltage to charge controllers.
Smart Sensor Types
Newer technologies have led to developments in smart sensor types. These smart sensors are able to give more accurate readings for better data generation and improved control of internal battery components. They may also provide additional monitoring functions, such as pressure and mechanical stress.
- Electrochemical Impedance Spectrography: Electrochemical Impedance Spectrography (EIS) is designed to monitor the performance of cells. They are used to determine the aging and degradation rates of batteries when undergoing charging and discharging cycles.
- Intelligent Battery Sensor: Intelligent battery sensors (IBS) gather measurements regarding the temperature, voltage, and current of the battery. They are commonly found on electric vehicle battery packs yet may also be used for energy storage devices and emergency lighting. The IBS helps extend the battery's life to avoid excessive discharge rates that could cause device failures.
- Wireless monitoring: Wireless monitoring will allow battery packs to communicate with external data collection and monitoring devices. With the advent of wireless connections, it can remove the need for additional communication components. It may also provide weight and size benefits to the battery pack.
Sensor Testing
To ensure sensors work as expected, independent test validation protocols are used during BMS assembly as well as when battery packs are in operation for devices. The use of data acquisition systems (DAQ) can measure sensors such as thermistors, thermocouples, and resistance temperature devices. The DAQ ensures that the BMS is working as expected and can check to see if the BMS is monitoring its full range throughout the battery pack and device.
Summary
While many sensors are found in BMS for lithium-based battery packs, they can also be employed with other battery chemistries. These sensors prevent damage and improve performance for the entire lifecycle of the battery pack and the device.
Key Takeaways
- Smart sensors improve safety & performance: Sensors within a BMS monitor critical parameters like temperature, voltage, current, pressure, and gas detection to prevent overheating, short circuits, electrolyte leaks, and overcharging/discharging.
- Temperature, current, and voltage monitoring are essential: These core sensors ensure optimal charging and discharging, track state of health (SoH) and state of charge (SoC), and trigger protective actions when thresholds are exceeded.
- Advanced smart sensors enhance data accuracy: Technologies like Electrochemical Impedance Spectrography (EIS) assess battery aging, Intelligent Battery Sensors (IBS) integrate multi-parameter monitoring, and wireless monitoring reduces pack weight and simplifies communication.
- Sensor selection impacts size, cost, and functionality: Adding multi-function sensors can increase battery pack size, weight, and cost, making it important to balance monitoring needs with design constraints.
- Testing ensures reliability: Independent validation protocols using data acquisition systems (DAQ) verify that sensors and the BMS perform correctly across the full range of operations, improving overall safety and lifecycle performance.
