30 September/October 2023 | E-Mobility Engineering Specifications Nyobolt EV All-electric Central motor drive Dimensions: 3880 x 1800 mm Gross weight: 1246 kg Maximum power output: 350 kW (470 bhp) Battery energy: 35 kWh Charging time: less than 6 minutes Charging rate: 10-12C Range: 250 km Some key suppliers Battery: in-house BMS: in-house Cooling plates: in-house EV design: Julian Thomson EV design: CALLUM Powertrain integration: CALLUM Motors: Helix Battery testing equipment: Rohde & Schwarz Battery testing equipment: Teledyne LeCroy Inverter: Cascadia Motion “From a manufacturing perspective, I’ve worked with both cylindrical and pouch cells, and found that cylindrical ones suffer from tolerance stack-up, which makes welding challenging,” Ward reports. “When you’re welding materials together, the materials need to be in contact to make the joint, but variations in cylindrical cell length often means that in an automated production line you might not be able to make the weld. But I can form the tabs on pouch cells exactly where I need them to be in order to make the weld successful.” Module structure and manufacturing The demonstrator pack in the Nyobolt EV integrates units of its current prototype battery module. Each module consists of six strings of cells connected in series, with each string consisting of eight cells connected in parallel (hence a 6S8P solution). “We use our small pouch cell format in this module, with the cells mounted within an aluminium construct that clamps them together and contains the channels for liquid coolant to extract the heat generated by the cells, before transmitting it to a cooling plate,” Ward explains. “While we’ll continue using these modules in tests for gathering longterm performance data on our battery chemistries, our next steps towards commercialisation will be to develop a replacement module that’ll be built with the larger pouch cells, to look for efficiency improvements in the module as well as the pack.” Regarding future module designs, he says, “At the moment, we have a simple system of electrical conductors running between each cell group, and each cell has a tab that needs to be welded to those conductors. We’ve worked with a partner to develop the exact process for our cell welding, and to understand the parameters necessary for our process to work given our cell and module materials. “Future cells might use different combinations of anode and cathode materials, so it’s critical for us to know how our choice of conductors and hence our welding approach would change accordingly. “And even if we stick with the mixture we have at the moment, we want to manufacture our modules in reasonable volumes in the future, so learning about all the different considerations that go into welding optimisation has been vital.” The cooling plate typically sits at the bottom of the module. It is a bespoke plate designed in-house, and features a liquid-coolant channel with a zig-zag flow pattern across its breadth, as is common among COTS liquid-cooling plates. However, Nyobolt found existing COTS plates prohibitively heavy to integrate and expensive to manufacture, so it sought to make one that was lighter and easier to build in-house while still retaining good performance in extracting and dissipating heat from cells. “Our coolant is still standard water-glycol, but our engineers have carried out CFD analyses to model the directions and pace at which coolant moves around the modules in combination with different plates,” Ward says. “Essentially, they’ve sought to put metal only where it’s needed, then cut back on liquid too, using the minimum amount of water-glycol needed. “Initially we looked at a radiator-based cooling system, then at a chiller-based system, before settling on cooling plates as the simplest and least costly approach to thermal management. We also incorporate layers of thermal transfer Dossier | Nyobolt EV Nyobolt aims to build 1 GWh of its batteries over the next 3 years, equating to about 30,000 EV packs (Author’s image)
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