32 July/August 2024 | E-Mobility Engineering Flexibility is a key requirement for heavy-duty electric vehicle (EV) applications. These vehicles are based on existing chassis designed for diesel engines, so battery packs with various chemistries have to be manufactured to fit a wide range of form factors. With all the different battery cell formats for different chemistries, from cylindrical to prismatic, and varying safety requirements, there are many design tradeoffs. These designs cover commercial trucks from light Class 3 to heavy Class 8, as well as buses, and they need a standard connector for the charging system. The Megawatt Charging System (MCS) is being rolled out to enable them to charge in a wider range of places, rather than being limited to the depot because they use a proprietary system connector. Heavy-duty applications also include mining and drilling machines, which have varying ways of providing power, from long cables and overhead power gantries to swappable battery packs. Battery chemistries Lithium-ion cells with nickel, manganese and cobalt (NMC) currently have the highest power commercially available, with capacity of 150-270 Wh/kg. Lithium iron phosphate (LFP) cylindrical cells have a lower energy density, of 90-160 Wh/kg at cell level, but their inherent safety, avoiding thermal runaway, means the pack can be made lighter than an NMC one. This increases overall energy density, especially as there are hundreds of cells in a heavy-duty application. Lithium titanate oxide (LTO) cells are also used for heavy-duty applications, particularly as they operate at low temperatures down to -30 C without the safety concerns of lithium-ion cells. They have a lower typical power density of 50-80 Wh/kg but the supply of the prismatic cells is more limited. Pack designs When it comes to powering alternative propulsion systems for heavy-duty applications, a modular plug-and-play design offers maximum flexibility as packs and controls can be easily adapted to a variety of use cases. Removable battery packs give heavy-duty mining equipment more flexibility (Image courtesy of Sandvik)
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