E-Mobility Engineering 014 l InoBat Auto dossier l In Conversation: Brandon Fisher l Battery monitoring focus l Supercapacitor applications insight l Green-G ecarry digest l Lithium-sulphur batteries insight l Cell-to-pack batteries focus

The structure about which they are mounted has been optimised for balancing weight and toughness. As Aretino notes, there is a limit to how much toughness a light refuse and logistics truck design can sacrifice in order to make a lighter and more energy- efficient EV. As per market research, the ecarry is designed to be strong enough to carry up to 295 kg of batteries and 1700 kg of waste or cargo on its frame. “That led to choices such as leaf spring suspension on the front and rear,” he says. “We couldn’t apply a normal suspension system, because these kinds of vehicles spend most of their time closer to full load than empty. “As for the axle, we went with one that is fixed on the front and rear, to guarantee that full loading wouldn’t risk damaging any of the powertrain components. That also reduces the number of components and hence the maintenance burden for the ecarry, compared with some of the other axle choices we could have made. Maintenance requirements for light refuse trucks are normally huge, so using fewer but tougher components was really important.” Future versions of the ecarry might be built with composite materials to save weight, but at present the structure is largely industry-standard steel parts for the sake of optimising strength versus cost, and to guarantee the availability of structural components. Battery After considerable research into what battery systems were available that could be homologated to the R100 certification standard, Green-G went with packs made by Webasto, as well as its BMS – R100 certification requires that compliant battery packs come with their own internal BMSs. Either one or two battery packs can be installed, each containing 35 kWh and weighing 147.5 kg, with up to 250 km of range between charges being possible (tested to WLTP standards) if two packs are installed. “Part of that research included looking into both nickel manganese cobalt (NMC) and lithium iron phosphate (LFP) cells, including making our own prototype packs with LFP cells to learn more about battery and BMS design,” Aretino says. “In 2018 though, LFP cells were around 30% bigger and heavier than NMC cells of equivalent energy capacity, so we went with NMC in the end. “We know NMC and LFP are coming to a par in terms of specific energy and energy density though, so we’re open to swapping cell technologies in the future if LFP enables our EVs to carry more payload weight during their working day.” While the standard-issue BMS hardware and signal buses from Webasto are used in the ecarry, Green-G wrote its own BMS algorithms in-house to enable the two battery packs (when two are installed) to be managed in parallel from a single BMS controller, so that if one battery and/or one BMS should be compromised, the remaining pack(s) can still be monitored and operated from the remaining BMS. “To be honest, we’ve not had to use that yet – we’ve found our battery packs to be of very high quality, so we’ve had no failures yet,” Aretino notes. Some key suppliers Battery modules: Webasto BMS: Webasto VCU: NXP ECUs: NXP Charging cables: Mennekes To date, Green-G has had no problems or failures with its batteries, even throughout its most intensive tests 52 Summer 2022 | E-Mobility Engineering Digest | Green-G ecarry