Testing and acquiring test data are necessary to verify EV batteries’ safety, performance, and reliability. Various types of testing are needed for battery cell development, battery pack design and verification, and active testing of completed EV battery packs.
This FAQ reviews the basic elements of a test and data acquisition (DAC) system, examines the specific testing and DAC needs related to battery cells and modules, and concludes by considering the utility of regenerative battery pack test systems.
A DAC system consists of a collection of dedicated hardware and software. It begins with signal conditioning and is connected to various sensors and transducers to capture performance data from the tested system. The sensor data is digitized, sampled, and sent for analysis (Figure 1).
The system may include a multiplexer to combine numerous data streams. The analysis can occur on a separate personal computer or within the DAC system. Some DAC systems for EV battery testing have accessories like a digital multimeter (DMM), a dedicated power analyzer, or other specialized measurement and analysis equipment.
DAC performance characteristics
DACs and related testing and analysis equipment for EV batteries must provide high-performance levels. Some examples include:
- Megahertz (MHz) DACs with sample rates of up to 20 Mega samples (MS) per second are needed to provide highly granular measurements and supply the data required to identify even minor anomalies in performance.
- High sample rates are not useful without a low noise floor that can provide high-resolution measurements like ±10 μV or ±10 μA to support accurate analysis.
- High-density system designs that support the hundreds of sensors and measurement points required for EV battery performance testing.
Cell testing
Resistance, temperature, and open circuit voltage (OCV) are critical parameters for testing battery cells. Resistance measurements are highly versatile. Welding is a common assembly technique for connecting the cell tabs to the electrodes and several cells into a module by welding them to a busbar. Good welds will have a resistance of a few μΩ, while a poor weld can rise to several mΩ. With the proper testing platform, the difference is easy to spot. It can reduce the potential for excessive heat generation, reducing cell performance or leading to thermal runaway.
Temperature measurements are a vital part of the safety qualification for EV batteries. Effective thermal testing for a completed EV battery pack can involve hundreds of thermocouples installed at test points. Embedded sensors monitor the internal temperature of cells or modules, whereas external sensors monitor the ambient temperature and gain insights into how the pack interacts thermally with the environment. Excessive temperatures can identify sub-standard cells or poor assemblies like bad welds.
OCV testing measures a cell’s self-discharge performance. Cells with defects like pinholes or micro shorts in the separator or contaminants in the active materials will have higher self-discharge rates than high-quality cells. Unacceptably high changes in OCV may be only tens or hundreds of μV over an extended period, depending on the cell design and chemistry. Identifying those changes requires the use of stable and high-resolution DACs.
Regenerative testing of packs
Testing EV battery modules or packs takes a lot of energy for repeated charge and discharge cycles. Regenerative testing systems can recycle the energy back to the source or the testing channels for reuse. Electricity consumption is a significant cost when testing EV batteries, and using regenerative test systems reduces energy consumption and results in a greener solution. The systems have various channels for different testing environments (Figure 2).
These systems include basic functions like battery polarity checks and protection from overvoltage, overcurrent, and over-temperature conditions. They are also available with software packages to implement complex testing cycles like rapid (50 ms) transition from maximum charging rate to maximum discharge to simulate actual operating conditions. They can also simulate complex drive cycles and include thermal chamber control to create dynamic thermal testing conditions.
Summary
DAC systems are essential in designing, developing, and testing EV battery cells, modules, and packs. They must deliver high-performance levels, including high sample rates and high-resolution measurements with high system densities. Key performance capabilities include measuring resistances, temperatures, and OCVs. Regenerative testing of EV battery packs can significantly reduce the environmental impact.
References
- Electric vehicle & battery testing, Gantner Instruments
- EV Battery Testing, Tektronix
- Module/Pack Battery Testing, Arbin Instruments
- Regenerative battery pack test system, Chroma Systems
- Test Electric Vehicle Battery Packs and Modules, NI
- Use Cases for Data Acquisition Systems in Automotive Applications, Keysight
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Filed Under: Batteries, FAQs