WIXLIB

Monitoring Battery CellTemperature with a Keithley 3706ASystem Switch and Multimeter––APPLICATION NOTE

Monitoring Battery Cell Temperature with a Keithley 3706ASystem Switch and MultimeterAPPLICATION NOTEIntroductionBattery Cell Environmental TestingIn the next decade, many governments and companiesAnother reason to measure the temperature of batteryhave pledged to transition to fully electric fleets of vehicles.cells during testing is to help characterize the temperatureThe electric vehicle depends on battery packs, and batterydependent behavior of the battery. Battery cell charging andmanufacturers must increase volume to meet the demanddischarging is not linear with temperature, and manufacturersfor new vehicles. All batteries manufactured must meetmay wish to test the cells in varying environmental conditionsstrict standards for safety, reliability, and efficiency. Todepending on the application. To provide the most accurateensure these standards are met, a variety of electrical andunderstanding of the pack behavior with respect tomechanical tests are performed during manufacturing.temperature, the temperature should be measured at theOne such test is monitoring the temperature on the batterycell level.cells. This test has multiple functions, and test solutionsthat are fast, dense, and automated are highly desirable formanufacturers to keep test time from becoming a bottleneck.Test systems should also remain highly accurate, so thatmanufacturers can be confident in their test results. TheKeithley 3706A System Switch and Multimeter combines thebest of both, which makes it a great solution for monitoringbattery cell temperature during testing.Cell Temperature and Thermal RunawayMonitoring Cell TemperatureBattery pack testing can be time consuming due to the time ittakes to charge and discharge the batteries. Therefore, a keygoal for manufacturers is to reduce the test time necessary tocollect the required data. A multi-channel digital multimeter(DMM) is a great solution for this. Battery packs may containhundreds of cells, and to get an accurate measure of the celltemperature, the transducer should be placed as close tothe cell surface as possible. A multi-channel DMM meansDuring normal operation of a battery cell, heat is generatedthat you can measure the temperature at more points on theas part of the chemical reaction within the battery and frompack with a single box. DMMs are also highly accurate, andsmall amounts of internal resistance. When this excess heatmost models provide built-in conversions for a wide varietyenergy is allowed to dissipate from the battery, it does notof temperature transducers, eliminating the need to convertaffect the performance. However, when multiple batteriesmeasurements after the test.are connected into a pack, the heat from one battery cancontribute to heating up adjacent batteries. Overheatingbatteries triggers a chain reaction called thermal runaway.Thermal runaway occurs when the internal temperature of thebattery is hot enough to cause the chemical reaction inside tooccur faster, acting as a short. The increased rate of reactionin turn generates more heat, creating a cycle that often endsin battery failure.The accuracy of the measurement directly contributes tothe accuracy of the battery behavior model. Temperaturemeasurement accuracy depends on the accuracy of thetransducer used. Thermocouples are cheap and simple;however, they have larger tolerances than other transducers,so the measurements will be within 1–2 C of the correctvalue depending on the type used. They also have highertemperature drift over time, meaning measurement accuracyThermal runaway can result in dangerous failures, such aswill decrease over their lifespan. RTDs are highly accurate,fires and explosions, in the battery pack. Therefore, manywith tolerances within as little as 0.01 C but are expensivebattery testing standards such as IEC 62660-2 and UL 2580and slow, making them unideal for manufacturing solutions.include stressing tests to test battery behavior under potentialThermistors provide a good middle ground between accuracythermal runaway conditions. Monitoring the temperature ofand speed. Typical thermistor tolerances are betweenthe battery cells during testing can provide early insights0.05 C and 1 C. They are stable over long periods of time;into cell and pack behavior and weaknesses in the qualityhowever, they have a more limited temperature range thanof the pack.thermocouples.2 WWW.TEK.COM

Monitoring Battery Cell Temperature with a Keithley 3706ASystem Switch and MultimeterAPPLICATION NOTEThe Keithley SolutionThe Keithley 3706A System Switch and Multimeter provides an excellent solution for testing temperature on battery cells.Figure 1 shows the options for measuring temperature using the 3706A.Switch and MeasureHigh DensityBest for Thermocouples3706A System Switch/Multimeter3722 Dual 1 48 Multiplexer3720 Dual 1 30 Multiplexer 7.5 digit digital multimeter6 slots for switch cards0.01 C resolutionSupports 2.2k, 5k and 10kthermistors 0.08 C accuracy at 1 year 96 2-pole channels With 6 cards, total 576 channels in1 mainframe Scan and measure over 110channels per second 60 2-pole channels Optional 3720-ST Screw Terminalaccessory for easy connectionsand on board automatic CJC forthermocouplesFigure 1: Keithley solution for multi-point temperature monitoring.The 3706A has several options for switch cards. The 3722Multiplexer Bank 1is the highest density solution with 96 two-wire channelsOutput 1(Not Used)per card, and a total of 576 channels in one mainframe. ForHI3706A DMM(Analog Backplane)LOapplications requiring less channels, the Keithley DAQ6510Data Acquisition and Logging, Multimeter System and7708 card provide up to 80 channels. For applicationsusing thermocouples, the 3720 card paired with the3720-ST screw terminal module provide on-board coldChannel 1Thermistor 1Channel 2Thermistor 2Channels 3–47junction compensation (CJC) to increase the accuracy ofChannel 48the thermocouple measurements. For more informationThermistor 48on temperature transducers, refer to Keithley’s Low LevelMultiplexer Bank 2Measurements Handbook.Output 2(Not Used)The 3706A can be controlled remotely using Keithley’s TestScript Processor (TSP ) programming language, via USB,Ethernet, or GPIB. This provides a fully-automated solution toHILO3706A DMM(Analog Backplane)Channel 49Thermistor 49save time and effort collecting data.Channel 50Thermistor 50Figure 2 shows an example of measuring multiple channelsChannels 51–95using the 3706A.Channel 96Thermistor 96Figure 2: Measuring multi-point temperature with the 3706A and3722 High Density Multiplexer Card.WWW.TEK.COM 3

Monitoring Battery Cell Temperature with a Keithley 3706ASystem Switch and MultimeterConclusionTemperature measurements during battery pack testingprovide crucial information about battery performance andquality. Keithley’s 3706A System Switch and Multimeterprovides up to 576 channels using the 3722 card, and theDAQ6510 Data Acquisition and Logging, Multimeter Systemprovides up to 80 channels with the 7708. These high-densitysolutions are perfect to collect all the data you need — faster.4 WWW.TEK.COMAPPLICATION NOTE

Contact Information:Australia 1 800 709 465Austria* 00800 2255 4835Balkans, Israel, South Africa and other ISE Countries 41 52 675 3777Belgium* 00800 2255 4835Brazil 55 (11) 3759 7627Canada 1 800 833 9200Central East Europe / Baltics 41 52 675 3777Central Europe / Greece 41 52 675 3777Denmark 45 80 88 1401Finland 41 52 675 3777France* 00800 2255 4835Germany* 00800 2255 4835Hong Kong 400 820 5835India 000 800 650 1835Indonesia 007 803 601 5249Italy 00800 2255 4835Japan 81 (3) 6714 3086Luxembourg 41 52 675 3777Malaysia 1 800 22 55835Mexico, Central/South America and Caribbean 52 (55) 56 04 50 90Middle East, Asia, and North Africa 41 52 675 3777The Netherlands* 00800 2255 4835New Zealand 0800 800 238Norway 800 16098People’s Republic of China 400 820 5835Philippines 1 800 1601 0077Poland 41 52 675 3777Portugal 80 08 12370Republic of Korea 82 2 565 1455Russia / CIS 7 (495) 6647564Singapore 800 6011 473South Africa 41 52 675 3777Spain* 00800 2255 4835Sweden* 00800 2255 4835Switzerland* 00800 2255 4835Taiwan 886 (2) 2656 6688Thailand 1 800 011 931United Kingdom / Ireland* 00800 2255 4835USA 1 800 833 9200Vietnam 12060128* European toll-free number. If notaccessible, call: 41 52 675 3777Rev. 02.2018Find more valuable resources at TEK.COMCopyright Tektronix. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supersedes thatin all previously published material. Specification and price change privileges reserved. TEKTRONIX and TEK are registered trademarks of Tektronix, Inc. All other trade namesreferenced are the service marks, trademarks or registered trademarks of their respective companies.121621 SBG 1KW-73865-0

in turn generates more heat, creating a cycle that often ends in battery failure. Thermal runaway can result in dangerous failures, such as fires and explosions, in the battery pack. Therefore, many battery testing standards such as IEC 62660-2 and UL 2580 include stressing tests to test battery behavior under potential thermal runaway conditions.