How to choose the right device to monitor battery temperature

Author: Bernard Ang, Product Marketing Manager, Keysight Technologies

In today's information age, almost all portable electronic products are powered by batteries. Batteries can also serve as backup emergency power supplies for large venues. In addition, pure electric vehicles are also using large series and parallel battery packs to provide sufficient power to meet performance requirements.

The battery pack needs to have sufficient power density (W/kg) to distribute sufficient current to achieve the acceleration index of electric vehicles. At the same time, high power density (Wh/kg) can achieve longer driving time or driving range.

Why is it important to monitor battery temperature?

Most of today's rechargeable batteries are lithium-ion batteries, which have an operating temperature range of 15 °C to 35 °C, providing the highest performance and capacity within this temperature range.

If the battery is used at an ambient temperature below 15 °C, the electrochemical reaction rate in the battery will decrease, and the battery performance and power will decrease accordingly.

If you use a battery or battery pack at an ambient temperature above 35 °C, the battery will age faster. You may experience reduced battery life, uneven aging due to uneven temperature distribution, increased safety risks, and higher lifecycle costs. If the temperature is too high, the battery may even swell and cause leakage, smoke, fire, or even explosion.

Figure 1. A power graph shows the power limits of a cell or battery pack over temperature (Source: Kandler Smith, NREL Milestone Report, 2008).

When to use a data acquisition (DAQ) system to monitor battery temperature

Data acquisition (DAQ) systems are the most common instrumentation for measuring the temperature of a single object or multiple objects. DAQ systems can monitor the temperature of multiple points in a product battery system. Typically, you will first perform functional testing on the design module, and then further integrate several functional modules for development phase testing. Experimental testing of battery packs and systems is usually completed in the early product design phase using several common R&D laboratory instruments.

The DAQ system can be used to: monitor the temperature of multiple points in a product's battery system; charge the battery system using a DC power supply, and discharge the battery system using a DC electronic load.

Figure 2 below shows a common lab test setup using a DAQ system. If you happen to have a bidirectional DC power supply that can both source and sink current, you can use it to replace both the separate DC power supply and the DC electronic load.

Figure 2. A lab test setup uses a DAQ, a DC power supply, and a DC electronic load to test a product battery system.

Figure 3 below shows an example of data acquisition software running on a PC that can work closely with DAQ hardware to improve work efficiency. Using such data acquisition application software, you can quickly set up and execute tests and get test results faster. Some PC data application software allows you to build automated tests through a graphical interface, which can significantly reduce test development time. Such software basically supports intuitive instrument setup and measurement sequence generation through a graphical interface, and can work with multiple instruments to help you create your own complete automated test.

Figure 3. The graphical interface of Keysight’s PathWave BenchVue PC data acquisition software.

Figure 3 shows an example of data acquisition software running on a PC that can:

• Test the battery management system in your product by charging it with different currents and powers and discharging it with an electronic load while monitoring the temperature and characteristics of the battery system.

• Perform multi-point temperature measurements to evaluate temperature fluctuations and distribution between cells.

• Set up alert triggers to monitor if temperature, voltage, or current exceed acceptable thresholds.

When to use a dedicated battery test system to monitor battery temperature

A fast and flexible approach to testing on a benchtop test instrument is a great way to quickly diagnose faults and validate battery system designs. However, if you need to run comprehensive and reliable battery tests for standards compliance and conformance testing, use a dedicated battery test system with dedicated integrated battery control and test software.

To accurately and reliably test your battery system, whether it is a cell, module or pack, you need a fully-equipped dedicated battery test system. A good battery test system can run customized performance tests, functional tests, aging tests and environmental tests.

Figure 4 below shows an example of a dedicated battery test system that can scale from a standalone solution to a fully integrated test system and ready-to-use test lab.

Figure 4. Keysight Scienlab SL100XA Series battery test system.

For example, the battery pack test system shown in Figure 4 can be expanded up to 1000 V, ± 2400 A, and ± 360 kW. Excellent scalability can greatly protect your test hardware investment. The battery test system must also be flexible and cost-effective enough to meet the needs of a variety of energy storage applications, including automotive transportation, industrial and other large-scale use scenarios.

A good battery test system should be equipped with a comprehensive test environment suitable for the device under test (DUT), such as temperature test chambers and climate test chambers, conditioning facilities for the DUT, and standardized connection systems for easy integration to the DUT. In addition, the system must also have built-in safety and security mechanisms, which can help you avoid potential hazards.

To control single or multiple cells, modules and packs to complete comprehensive battery testing, you also need to use a central battery test system software. A good, Internet-based central battery test system software can also:

• Monitor all components in the test environment

• Use pre-defined test criteria to customize dedicated test steps

• Perform test measurements and record data, with time stamping to support simultaneous analysis

• Provide powerful measurement data display function

Finally, the central battery test system software should also be able to perform validation tests to meet the compliance requirements of various standards organizations such as the International Organization for Standardization (ISO), the German Institute for Standardization European Standards (DIN EN) and the Society of Automotive Engineers (SAE).

Summarize

Battery temperature needs to be strictly monitored throughout the product life cycle of the battery system. In the early stages of the product life cycle, engineers can use benchtop instruments (such as DAQ) with current input and output DC power supplies to quickly diagnose battery system failures and perform battery system design verification. In the characterization and verification phase of the product life cycle, a dedicated battery testing solution must be used, which can help engineers obtain a comprehensive, reliable and scalable testing solution.