24 through the vast buffer cooling the pack provides. And, conversely, you can change the valves over and divert the motor-inverter heat through the pack to warm the batteries in cold conditions, saving you the need for a separate PTC [positive temperature coefficient] heater, which some OEMs use, despite the massive amount of electricity they consume.” BMS To date, Fellten has made extensive use of the Orion BMS (comprising a turnkey solution of combined hardware and embedded software), and while the company considers it an effective and capable system, it is moving towards making its own BMS hardware featuring customised software from Brill Power. “The only limitation we run up against when using a large, singular BMS supplied externally is that if we’re running a pack with a 96S configuration, we have to run all 96 wires through and around it to plug into every module, every cell group, and that’s a lot of work,” Hazell says. “We are getting ready to start battery module manufacturing in our facility at the end of this year. That will allow us to embed a slave BMS board inside each module, reducing the architecture to a four-pin connector per module, instead of 14 to 20 pins per module. That means less wiring and complexity in production and integration.” By constructing its own modules with integrated slave BMS boards, Fellten anticipates that it will connect the slaves to a master BMS board via a 12 V, CAN bus connection – making wiring an easier and faster process, while keeping Fellten’s voltage and interface architectures in line with those of widely used modules such as the VDA 355 (as of writing, Fellten points towards the high degree of variation in module connections and architectures as a major problem for the aftermarket and retrofitting part of the industry). The master BMS will monitor each cell and balance it accordingly with a top-end strategy. Hazell explains: “When a cell is over a certain threshold, say 3.8 V, during charging, it will start balancing the rest of the cells upwards to balance them towards the upper threshold. The Orion BMS does our charge and discharge limiting, including dynamic adjusting, and the data from that is leveraged by the XP-1’s inverter from iNetic to limit the motor accordingly, so as not to damage the battery packs.” As the BMS gathers battery pack temperatures, state-of-charge (SoC) and state-of-health (SoH) data, and other information across the cells and modules, it can decide on a current limit appropriate for the cell specification. Then, it will output a CAN bus message called a discharge (or charge) current limit to the inverter, which is programmed to monitor and track that message, even as it dynamically changes with the SoC, temperature and other parameters to adjust the motor’s performance. “Some of the cells will discharge at a certain rate for three seconds, then a certain rate for 10 seconds, then a certain amount continuously, and you can map that into the BMS such that if someone driving an XP-1 suddenly decides to floor it, they can get maybe three seconds at peak amperage, and after that the pack can step the current down bit by bit as the rate of acceleration and current draw drops,” Hazell says. July/August 2024 | E-Mobility Engineering The bottom of each liquid-cooling plate is designed with a bleed hole, two coolant inlets and two coolant outlets
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