Test & measurement


Cutting-edge test equipment gets the most out of batteries


By Cliff Ortmeyer, global head of Technical Marketing at Farnell Battery chemistry and test objectives play


heavily into instrument design. Kai Scharrmann, engineer and head of Sales at Hioki Europe, says it is relatively easy to determine the state of a lead-acid battery using simple voltage measurements coupled with internal-resistance estimates. “You can very quickly say whether a battery needs to be replaced or not, and that’s typically a measurement that you do at just one frequency. If you only measure one frequency, it’s very, very hard to judge from that one measurement level whether a lithium- ion battery is OK or not.” In the move to lithium-based chemistries,


the structure of the battery plays a major part in maintenance and production test as well as research and development, says Scharrmann. “One of the things that is really important is making precise measurements on cell level. Just measuring a pack doesn’t show you anything, because if it’s in series, then you don’t know which cell is affected. You might have cells which are absolutely fine, however one is broken. How do you plan to find that broken cell if you just measure the whole pack?” In many cases, the cells inside lithium-ion


batteries are organised in series, Scharrmann adds. “If you put it in series, you need a battery management system or protection board. When you measure, you are also measuring that battery management system. You can still do this, but you need to consider many more things than you would do with a standard old- style lead-acid battery.”


AppliCATiOns drive need FOr greATer eFFiCienCy How the individual cells perform is becoming important to a growing number of applications. One area where this level of detail is needed is in the automotive sector as the performance of the complete electrical system determines the range of an electric vehicle. “Sometimes the battery cells themselves are matched. For example, in motorsport,


Instrumentation Monthly February 2022


where extracting the maximum performance is crucial, when they choose the battery cells to make up the packs, that's all handmade. They will do a frequency sweep over every cell and from those measurements decide which ones they will put together in a pack,” says Scharrmann. Whereas production and maintenance test


needs good support for throughput and easy- to-understand results, instruments for research and development need to satisfy the demand for accuracy, says Scharrmann. “Actually, the instrument’s accuracy can make or break your approval.” He points to the US Environmental Protection Agency’s requirements for determining the efficiency and range of electric vehicles as an example. “Good test and measurement equipment can really help to achieve certifications,” he adds. Accuracy is vital for developing systems that


can take best advantage of the behaviour of lithium-ion batteries. As efficiencies increase, accuracy becomes more important. This is true of power supplies that need to waste as little as possible when driving downstream electronics as well as the inverters in larger systems that are used to drive electric motors. Today, efficiencies are approaching 90 per cent. Even a small efficiency improvement dramatically reduces the wasted energy. For example, one percent better efficiency means 10 per cent less wasted energy. Scharrmann says there is significant effort


going into high-frequency inverter design thanks to the arrival of silicon carbide and gallium nitride processes. “The switching clock rates are going up so much now, you need really precise measurement equipment to be able to measure the gains,” he explains. Sustainability also plays a key part in driving test requirements. “Lithium-ion batteries tend to have a lot of cobalt, which is not exactly the greenest product on the planet.” Designing systems that can accommodate batteries built using different materials can go a long way to improving sustainability metrics.


insTruMenTs TO undersTAnd pOwer COnsuMpTiOn In low-energy systems, the many types of sleep and turbo-processing states they can use complicates the analysis of how well batteries will perform. Careful design of capacitor reservoirs can help prolong battery life by reducing the size of peak currents that the cells need to supply. In addition to conventional power analysers, source-measurement units (SMUs) are now being used to characterise how these systems perform. “We are starting to see SMUs being used in


battery testing,” says Bradley Odhner, technical marketing manager at Tektronix and Keithley Instruments, adding that the many start-ups building Internet of Things (IoT) devices can benefit from them. “SMUs are great for companies that want to have one instrument that can do a lot of things, but also very complex things, particularly as we start to talk about the miniaturisation of devices. People are trying to get the most bang for their buck from any piece of equipment that they use so they can make the best products possible.” Weigell explains: “An SMU allows you to take


measurements at high precision, achieve accuracy at very low currents, and within a second at high currents. This allows you to really understand the power consumption. You can then correlate this to other features.” He adds that the flexibility of the measurements makes it easy to analyse at a fine-grained level how power consumption and the demands on the battery change over time, such as when a user switches from reading emails to watching videos. From the IoT to electric vehicle fleets,


batteries play a vital role. In order to maximise efficiency and equipment lifetimes, there is a clear need to understand how batteries behave in-system and in the field. Test and measurement equipment therefore plays an essential role across the entire lifecycle and leading global manufacturers are stepping up to the challenge.


Farnell www.farnell.com 57


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