Fellten Morgan XP-1 | Dossier 29 together to create a self-maintaining, continuous force. They’re about £1 per washer, so not cheap, but they basically never come loose and the pressure isn’t on the thread. That means if you ever have to replace a module in the XP-1, there isn’t a risk of ripping the thread or damaging it inside the module itself. “Contrast that with instances we’ve seen in some packs where the customer, or their technicians, couldn’t apply heat to remove their Loctite washers, because it would have risked damaging the modules, and that made maintenance and repair really difficult. There are other alternatives, like liquid PTFE thread seals, but, for us, the Nord-Lock is easier to work with because there is no chance of variation or inconsistency with how much liquid sealant gets applied, or how much gets in between the busbar layers as you’re putting it in. It’s a solid washer that gets torqued to a set figure.” Manufacturing plans As of writing, Fellten is constructing a new, 15,000 ft2 facility, adjacent to its main building, to expand its pack manufacturing. Another unit adjacent to the new facility is being refitted as a stock holding and control warehouse. Next to that will be its aforementioned module-manufacturing centre, the design for which is now complete and intended not just for resto-modding applications, but also for batch production of high-end packs for low-volume EV manufacturers. “The module facility will be a temperature-controlled, insulated unit, stocked with production machinery revolving around prismatic cells,” says Hazell. “That will enable us to make equivalent solutions to VDA 355 and 590 modules using the same machines, outputting a mix of the two at will, instead of minimum runs of one or the other.” First in this production line will be the sorting machinery, which puts incoming cells into eight different channels (plus a ‘no good’ channel), depending on what each cell exhibits during resistance testing prior to sorting. This ensures cells of similar resistance are grouped together in modules for consistent charge and discharge pressure. “That’s especially important if you’re stringing cells together in parallel. You don’t want one cell with a slightly different resistance to the others around it, because it will charge and discharge at a different speed, leading to degradation in the cell group and then huge knock-on effects in its later life,” Hazell says. After being sorted, the cells will run through a machine that lasercleans each of their terminals of contaminants and scans their barcodes for traceability. Then, the cells will be stacked into a compression rig, where the module casing is put on and pressed to a set torque value (like pouch cells, prismatic cells must be compressed to a minimum amount of pressure) with either a non-conductive glue or sheet lining between and around the cells to prevent metal-to-metal contact. Some laser welding of the edges may occur to maintain compression of the modules, after which they will move into a station for installing the busbars in series or parallel, as needed, with a laser-welding system to bond them simultaneously as another rig applies pressure to hold them in place. “We will also be running imaging analysis all the way through to make sure each weld shows the right penetration, no contaminants, just consistency all around. Each module will then be delivered with a photograph of every single weld – all that and additional data being accessible via its barcode,” Hazell says. “Then the BMS gets installed. A lot of OEMs will use ribbon cables or small wires to link all the cells, temp sensors and so on. But, as mentioned, we’ll use a slave BMS board instead, with just a four-pin connector to do all the cell balancing within the module, and that will be standardised across all our modules, whether 6S, 4S or something else.” Fellten produces all of its own wiring harnesses in-house via automated crimping machines, TUV-approved training programmes (as wire harnesses still largely need human hands to be E-Mobility Engineering | July/August 2024 The nickel-plated, copper busbars are treated with a special powder coating for HV insulation, resulting in the orange coat visible here
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