Security, performance and system management
The scope of "battery testing" is very broad, ranging from the characterization of the smallest batteries in portable devices to large vehicle batteries operating at 1,000 V or even higher. Battery systems are crucial for electric transportation. Today, lithium-ion batteries are one of the most commonly used battery types in electric vehicles due to their high energy and power density. Depending on the market context, "battery" has different nomenclature. For example, in the automotive sector, depending on the vehicle's integration status, the electric vehicle battery under test and the associated testing procedures may differ based on battery manufacturing, module manufacturing, or battery pack manufacturing.
A battery is typically a single electrochemical device, with the voltage of a single storage cell usually not exceeding 5 V. A module consists of multiple interconnected batteries and some electronic equipment for controlling the entire system. Modules are packaged in a certain way, so testing is usually performed on the entire module as a single element. A battery pack is a larger element composed of multiple modules, also connected by some wiring, and equipped with more complex control and communication electronics to communicate with other processing units (such as vehicles).
As mentioned above, testing a battery differs from testing a module or battery pack, and the testing setup can vary at each stage of the manufacturing value chain. Ultimately, testing may differ depending on the testing methods employed, such as impedance measurements.
TechgiScience provides test system designers with solutions covering electrical testing, focusing on areas where potential voltages, currents, and resistances in complex ATEs need to be measured in system integration testing in battery manufacturing (e.g., battery, module, and battery pack assembly lines) and end-application integration (e.g., automotive battery management systems [BMS] and battery pack integration).
Testing typically involves three main areas: safety testing, which is crucial for systems composed of multiple batteries arranged in series/parallel topologies to provide higher power density; performance testing of battery cells/modules/groups, which is closely related to charge/discharge cycle count, operating time, and temperature; and management testing, where performance optimization and end-of-life (EOL) testing verification are key.
Example 1: Busbar weld impedance safety testing workstation in battery pack manufacturing
Multiple cells that make up a battery module are connected in parallel or series to achieve the required voltage output. All cells are laser-welded to a busbar, a long conductor isolated from ground, responsible for carrying large currents to distribute the battery's power. VSH busbar weld impedance testing characterizes the weld's impedance. Small resistance in the weld can generate enough heat to degrade battery performance and lead to premature failure or unsafe operating conditions. By measuring the resistance before testing battery operation, defective modules can be quickly removed from the line.
Measuring weld impedance involves introducing a current into the weld and measuring the voltage to calculate the resistance. Test execution speed and measurement accuracy are the two most important considerations when measuring weld impedance. This can be accomplished using a source measurement unit (SMU) (such as the Keithley model 2460 or 2461) with a model 3706A system switch and multimeter, or a model DAQ6510 data acquisition and recording multimeter system.
The 2460 and 2461 SMUs can deliver up to 7 A of current to battery systems requiring high current. The impedance of the solder joints can be as low as a few milliohms. Therefore, it is crucial to use a sufficiently sensitive instrument to measure very small voltages. The 3706A model features a 7.5-digit digital multimeter (DMM) capable of measuring tens of nanovolts in the 100 mV range. Since a battery pack may have nearly 80 solder joints on a single busbar, we support a main unit with configurable slots for multi-channel plug-in modules, eliminating the need for rewiring. To further enhance speed and efficiency, the process of shutting down each channel for measurement is obviously automated.
Example 2: Internal resistance measurement and open circuit voltage in battery performance testing
The performance and efficiency of a battery during charging and discharging can be evaluated using several different methods and metrics. One such metric is the battery's internal resistance, which essentially means accurately characterizing its changes under several charging/discharging current rates, state of charge, temperature, and other aging parameters.
Open-circuit voltage (OCV) is the voltage measured at the battery terminals after a sufficient rest period (sometimes called "relaxation"), and it is a key measurement for lithium-ion battery cells.
OCV also varies primarily based on the battery's state of charge, and to a lesser extent based on temperature. It can be used not only to evaluate/assess battery specifications and condition, but also to create equivalent battery models for BMS design.
Battery internal resistance refers to the change in voltage drop between battery terminals when a load is connected, compared to the no-load voltage, and can be obtained from OCV measurement.
OCV is typically not just a single measurement, but a set of measurements. In fact, we call it the "OCV characteristics of a battery," and we trace a detailed analysis from the curves of state of charge versus the OCV plane.
To track this curve, you need to place the battery in a specific charging state, typically by using a smart source/load to charge or discharge current in a pulse manner, wait for a period of time, and then measure the open circuit potential at the electrodes.
A Keithley SMU like the 2460 or 2461 (with 10-A pulse capability and a digitizer) is the perfect solution for performing this test. In fact, it can supply or draw battery current in a controlled manner while simultaneously measuring battery current and voltage using a four-wire (Kelvin) connection with contact checks. All of this can be easily automated and controlled via a programmable embedded microprocessor.
The accuracy of OCV voltage measurements is a decisive factor in instrument selection. In some cases, typical 6.5-bit measurement resolution and thermal stability are desirable, but in most cases, the accuracy of an SMU may be considered insufficient.
Therefore, some test setups require the use of a special digital multimeter, the Keithley DMM7510, which has become the standard for lithium-ion battery cell testing. Its low-noise 32-bit A/D converter enables 7.5-bit resolution and metrological-grade accuracy.
Example 3: Special Cases of BMS Testing and Collision Switch Detection
The Battery Management System (BMS) is a specific component responsible for performing critical battery functions such as battery monitoring, battery balancing, charge and discharge control, safety control, and communication with external cells. Some ATE designers strive to cram all the necessary test cells into a compact and reliable platform to control the interaction between the BMS and the battery.
These ATEs used for verification are typically modular elements, combining products from multiple vendors to operate as a single system. This system needs to track and log multiple input signals from the battery and BMS. The sensing units and I/O communication phases are indeed crucial and must be implemented for proper screening. In some cases, the selection of individual instruments that make up the system is partly driven by the test management software environment, but generally, system integrators prefer to design custom solutions based on OEM requirements. These solutions are environment-independent, allowing multiple automated verification test systems to run in parallel, interchangeably, and rapidly.
To validate the BMS before interacting with actual battery systems, you may need to simulate battery pack voltages. This means controlling precise 1,000 V (or higher) voltage sources, or even simulating hundreds of individual battery voltages. An ambient pressure chamber is another key sub-element for temperature and test environment control. From an SMU perspective, the Keithley-supported 2470 model offers testing capabilities exceeding 1 kV.
In addition to specific data loggers and acquisition switching cards (such as the DAQ6510), we will now focus on the requirements for voltage and current pulsers selected for specific test setups designed for the BMS's response to low-energy collisions during DC fast charging.
Let's consider this scenario: a car plugged into a parking lot DC charger experiences a low-speed collision. How will the BMS react? How will it handle critical faults such as isolation? Depending on the situation, the BMS's collision signal might be a voltage pulse or a current pulse. Regardless of the type, the signal must be clear and stable enough to resist interference. We also offer solutions with AFG (Automatic Feedback Group) to simulate error frames in CAN bus message communication, to reproduce potential fault conditions and test the system's robustness.
in conclusion
Electrical measurement of lithium-ion batteries is a very broad topic, requiring different sets of measurements with varying requirements depending on the manufacturing stage or the testing phase in application integration, using intelligent automated test equipment. Tektronix has historically been a leading supplier of oscilloscopes and probing solutions for testing battery behavior under motor-driven inverter loads, but the Tektronix and Keithley product portfolio supports the battery manufacturing field, particularly when high-precision resistance, isolation, or voltage and current measurements must be performed, while simultaneously collecting data at multiple sensing entry points. In particular, specialized source measurement units like the 2470 SMU can provide voltages exceeding 1 kV while accurately measuring current.
