With its solid-state batteries, Daimler Buses has begun a new chapter in e-bus power. The innovative batteries make certain demands of the electrical infrastructure and require particular care during charging. For this reason, Daimler Buses carries out extensive interoperability tests with various different charging device manufacturers. The goal: ensuring the safety and efficiency of every charging device.

April 2022: for an interoperability test, an eCitaro Solobus is sent to Delft in the Netherlands for a whole week. The destination is the ultra-modern ABB innovation lab and test centre, just opened in 2020. Here, at a long-established company dating back 130 years, which has built chargers for electric vehicles since 2010, three charging devices are to be tested for compatibility with the solid-state batteries of the eCitaro. Oliver Kaerkes, test engineer responsible for charging devices at Daimler Buses in Mannheim: “We want to be prepared for every charging scenario. And the test centre in Delft offers ideal conditions for this.”

Kaerkes works very closely on site with colleagues from ABB, the global product specialist Andrei Ghiran and his team leader Rolf Bilderbeek. The bus is first laboriously wired up for the series of tests. Inside it, a true work station with computers has been set up, as is standard in test vehicles for their annual winter and summer tests. In addition, the innovation lab’s test devices and the charging devices are connected to a so-called “break-out box”, which can then be connected to the fully electric Mercedes-Benz eCitaro. “Using this box, we then input unexpected scenarios and errors to the system to test the behaviour of the battery management of the bus,” Rolf Bilderbeek says.

During tests the currents can often reach up to 500 Amps, which is why all the arm-thick charging cables in the test lab are water-cooled – a technology that will also be deployed in practice for future charging facilities. Over 100 individual charging processes are then simulated. Some last only a few seconds to check the start of charging; others simulate full charging lasting several hours. “With the oscilloscope, a high-frequency measurement device, very rapid electrical signals can then be viewed during the individual charging processes in high resolution and real time,” explains Kaerkes, while manhandling various cables. This shows up errors that could lead to undesirable charging shutdowns.

Already before the onsite test, many charging scenarios were prepared by remote maintenance and using data from the ABB cloud. “There are already many standards and norms which manufacturers and suppliers have to comply with. But for us, the most important thing is their technical interpretation for the vehicle on the one side and the charging device on the other,” explains Rolf Bilderbeek. To this end, a list of test cases was drawn up with Daimler Buses relating to the interfaces, which were then meticulously worked through. “In the global CharIN Association, working groups are currently turning their attention to the hardware and software of test devices to ensure the certification of charging devices and vehicles,” adds Bilderbeek. “The results from these groups have already been incorporated in our interoperability tests.”

At the end of the testing, all those involved are pleased with the results. The basic compatibility of solid-state batteries from Mercedes-Benz with the three tested charging devices from ABB has been confirmed by the results. “Naturally, there is plenty of ‘big data’ to deal with afterwards. There’s no such thing as a quick fix with charging systems; these are long-term processes,” explains Oliver Kaerkes, clearly happy after the successful work of the team. “And of course, human interoperability is at least as important as that of the electrical parts.”