Page 51

EETE SEPT 2013

A44EET_EURO_2_37x10_87_A44E.qxd 9/7/12 11:03 DC-DC CONVERTERS Measuring performance in the field 2V to 10,000 VDC Outputs The cell datasheet will not provide the answer to this question. It will also not tell the 1-300 Watt Modules pedelec manufacturer how the capacity of a battery pack is affected by a continually Regulated/Proportional/Programmable Isolated/Single/Dual Outputs High Reliability Greater than 1,000,000 hrs. Mil Hbk 217F • Military Upgrades Expanded operating temperature -55º to +85º C, no derating required • Environmental Screening Selected Screening, Mil Std 883 • ULTRA Miniature From 0.5" x 0.5" x 0.2" • Surface Mount/Thru-Hole • Custom Models • US Manufactured • AS 9100 Approved High Reliability AC/DC Power Supplies, Transformers and Inductors See PICO’s full line catalog at www.picoelectronics.com PICO Electronics,Inc. 143 Sparks Ave. Pelham, N.Y. 10803 E Mail: info@picoelectronics.com Pico Representatives Germany ELBV/Electronische Bauelemente Vertrieb E-mail: info@elbv.de Phone: 0049 89 4602852 Fax: 0049 89 46205442 England Ginsbury Electronics Ltd. E-mail: rbennett@ginsbury.co.uk Phone: 0044 1634 298900 Fax: 0044 1634 290904 varying discharge current, nor how cycle life is affected if the battery is normally charged in the user’s garage at 5°C rather than the 25°C specified in the datasheet. One way of measuring the performance of a battery pack in the field is to conduct field trials, which may be done with a pilot product or a pre-production prototype. This can provide useful data: for instance, total failure or reduced run-time between charges can be readily observed. Such field trials, however, suffer from two important drawbacks: control, and timing. In a field trial, the usage conditions cannot be precisely controlled. In a field trial involving multiple samples, it is unlikely that any two samples will undergo the same stresses. This makes it hard to derive general conclusions. Also, while performance of the battery as a whole might be impaired, a field trial might not isolate components of the system to show which is responsible for the impairment. In addition, field trials can necessarily only take place once the end product in which the battery pack is embedded has been designed. If the field trials then reveal that modifications to the battery pack are required, a wholesale re-design of the end product might be necessary: this will be costly, and will also delay the full release of the product to market. Lab testing: a better way? Laboratory testing avoids the drawbacks inherent in field trials. While the main advantage of a field trial is that it exposes the battery to real-world conditions, with careful modelling of the conditions that the battery will encounter in the field, laboratory tests can be equally realistic. In other respects, laboratory testing provides many advantages. Test conditions can be precisely controlled. In a pedelec field trial, riders might be asked to collect range and power output data on mountain rides, thus subjecting the batteries to widely varying test conditions. In a lab test, a sample of batteries can be stressed precisely at peak power output for a precise period of time, producing repeatable results that are valid for all production units. Lab testing of a battery pack can be carried out in parallel with development of the end product in which it is to be embedded. Testing and subsequent modification of the battery can thus be completed before the end product design is finalised, entailing no delay in its release to market. Laboratory testing can isolate specific parts of a battery system. For instance, drop testing of multiple samples in laboratory conditions enables the battery assembler to provide a universal failure rate - see figure 2. But the batteries under test can also be closely examined during the course of the drop testing to find at an early stage the weaknesses that will eventually cause failure. This can inform a design modification, such as a change to the technique for welding the housing, which can make the pack more robust and improve its failure rate. Laboratory testing of many kinds of use and abuse conditions is possible. For instance, electrical testing can measure performance for various power output profiles, charge conditions and operating temperatures. Abusive testing can measure the effect of shock, vibration, over- and under-temperature operation, humidity and fire. Testing the right things in the right way Independent industrial testing facilities are equipped to provide laboratory tests of these kinds. Varta Microbattery, a cell manufacturer and battery pack assembler, also offers lab testing services. Unlike general test service providers, Varta is able to bring its knowledge and understanding of the operation of batteries. This means that it can not only perform battery tests in the right way – it can help ensure that the OEM is specifying the right tests. For many end product types, the battery is a source of anxiety and concern in the mind of the end user. Success in the market for pedelecs, for instance, depends on the users’ confidence in the range and lifetime of the battery power source. As shown above, the cell datasheet provides performance information for only a limited range of usage conditions. For an OEM to feel confidence in the performance of their power pack under non-standard conditions, laboratory testing is an excellent and helpful complement to the design process. www.electronics-eetimes.com Electronic Engineering Times Europe September 2013 43


EETE SEPT 2013
To see the actual publication please follow the link above