Electric mobility is undoubtedly one of the most interesting innovations of the last years. The fundamental motivation that is driving the sector consists of a substantial reduction of the environmental emissions with the same driving performance of fossil fuels cars: the traditional OEM manufacturers, initially against such development, are now competing to be front-runners.
Despite being the core element of E-mobilty technologies, batteries are not the only new electric components of electric cars. Especially new components, which can make the difference for EVs, require at the current stage new testing capabilities, different from those of the traditional testing laboratories, because of specific technical requirements and performances.
CESI Group, thanks to its Berlin laboratories, has been at the side of the main manufacturers of these components since the first requests for R&D tests. Also in this new scenario, KEMA Labs, the CESI TIC Division, has found out an innovative and effective solution to meet the needs of its customers: a new system that consists of 14 control cabinets with bidirectional DC power supply for charging and discharging the device under test up to a maximum of 1,500 VDC, a capacitor bank up to 2 F to provide the necessary energy for a “shot”, an impulse generator, resistances and safety systems to set the current up to 35 kA.
The unicity of this system is exactly the capability to provide high current (35 kA) at constant voltage (1500 VDC) for several milliseconds with an inductance < 10 µH. Furthermore, to ensure tests under severe environmental conditions, the test object can be placed within an explosion-proof climatic chamber. This new test system allows to switch the full current “on” and “off” several times without completely discharging the capacitor bank; in case the test object fails the circuit absorbs the entire energy of the capacitor bank without risks.
This innovative solution was not found easily but after extensive studies and tests. During those initial tests, technical limitations of the test circuits emerged, to the extent that they were not able to support further development of the components under evaluation.
In this respect, the usual direct current (DC) test benches in KEMA Labs have a circuit inductivity of more than 10 μH, which leads to overloading the interrupting capacity of the tested devices. For that reason, OEM manufacturers started using their own test benches, but they are generally equipped with lower ratings than necessary in terms of voltage and current (below 800 VDC and 20 kA), due to the complexity to deal with high power ratings. Therefore, once the high-level characteristics for the new test circuit had been identified, technical work teams were organized, aimed at the engineering study of the solution.
These teams were formed by KEMA Labs test engineers supported also by potential component suppliers and manufacturers. The most critical issue that emerged from these studies consisted of the dangerousness of the test circuit, which requires energy storage solutions, either through batteries or capacitor banks, in order to deliver the high required capacity (2.0 F).
Using lithium batteries appeared the most economical choice, but safety implications (high risk of fire), maintenance and end-of-life (disposal of the same), led the technical team to evaluate this solution as very risky. The solution with capacitor banks looked immediately safer but showed decidedly critical aspects both from an economic point of view and, above all, in terms of availability of components and ease of installation, considering the high number of capacitors to be used to reach the required capacity.
Only by continuing on this path of research and thanks to our expertise we have been able to find our original innovative solution that today we can offer with confidence to our customers.