E-Mobility Engineering 015 l EMotive Scarab off-road truck dossier l In Conversation: Giulio Ornella l Hall effect and magnetic sensors focus l Challenge of batteries for heavy-duty EVs l Alpha Motor Corporation digest l Automated charging insight l HVAC systems focus

duty cycles, perhaps from a depot to a site and back. “We have so many applications that we have a very diverse set of drive cycles, so the challenge has been to find equipment that will allow the vehicle to do all those things. We have selected our componentry and we are integrating now, hoping to fit them physically within 10 to 12 weeks.” At the moment, the vehicle is fitted with an electrically driven hydraulic pump for the steering, and a compressor for the truck-type air brakes, which are held off against spring loading by air pressure. Both of them are currently low-voltage devices but will be replaced by 800 V items in the next iteration of the system design, Williams says. The wiring in the Scarab development vehicle as it stands includes red 48 V cabling connecting the battery pack to the inverters, and orange cabling that links the inverters to the motors. While the orange cables don’t yet carry high voltages, they do carry AC and are screened so that they don’t cause EMI with other systems. They are also ready to handle HV power, so they won’t have to be changed, Williams notes. that every HV component is securely connected to the battery before the main contactors can close to energise the HV system. The HVIL wires also run alongside the HV cables so that any damage to them is likely to cut the power and open the contactors. The HVIL is used with an isolation monitoring system that will open the main contactors if the isolation between either side of the HV system and the chassis falls below a preset value, which would be a symptom of a short- circuit. Williams emphasises that the HV system the company is developing for the Scarab will comply with all these galvanic isolation and other safety regulations. In addition to the main contactors in the battery, the secondary contactors in EMotive’s power distribution unit will also open in response to such faults, and there is further redundancy in key control circuits. “There are a lot of people out there using this kind of vehicle, certainly maintainers, who may not have seen such high-voltage systems before. We will have to comply with legislation, but in terms of practicality we are designing it with both safety and maintainability in mind, which is important for end-users who have to train their technicians.” While the Webasto battery pack has its own compliant safety features built in, they have to work seamlessly with the related devices that EMotive is integrating into the vehicle, including the crash inertia switches, emergency stop buttons, service disconnects and so on. As is always the case when integrating subsystems and components from different suppliers and others developed in-house, it is vital to define exactly where these parts meet in an interface control document. As Williams explains, “That is a bit of a tiring exercise that I have been going through for a number of months now, finding out where those interfaces are and what they require in terms Electrical safely As a development prototype EV, the Scarab has multiple emergency stop buttons, including one in the cab, one inboard of each wheel on the centre axle module and one behind the rear axle module. The 800 V system is designed to comply with the tougher legislation that applies to such HV circuits. “We will be integrating all the service disconnects and crash inertia switches that open the main contactors internal to the battery pack, and there are pre-charge circuits in the battery pack as well,” Williams says. Any HV system containing capacitors or components with capacitance can be damaged by inrush current when first switched on, and contactors can even be welded shut by the heat generated, so pre-charge circuits containing resistors are used to limit the inrush current while the downstream capacitance charges up. The system also features HV interlock loop (HVIL) wiring that carries the low- voltage power supply to operate the HV contactors in the battery pack. Normally incorporated into all the HV connectors, the HVIL ensures The development vehicle has multiple emergency stop switches; this one is fitted to the upper mount for the air spring. The mount is welded to the fabricated steel ladder frame chassis (Author’s photo) Autumn 2022 | E-Mobility Engineering 29 Dossier | EMotive Scarab off-road truck