52 “It is rated up to 1000 V, so that means we can use complete OEM battery packs, whereas before we had to take the battery packs apart and change the voltage on them. “Now we can take a complete Tesla, VW or JLR battery pack, for example, and put them in at 400 V or 800 V. They stay completely sealed just as they came from the OEM vehicle.” All the AC components are connected by a distribution board from Proteus Switchgear. “It all comes into and out of that one board.” Battery management Qube’s main control computer, which is based on a Raspberry Pi, oversees the battery packs, along with the rest of the subsystems. “We’ve had to write all custom software to work with those battery packs. We run all the OEM software on it, including all the safety systems you get in an OEM vehicle,” Hazell says. Also, all the original BMSs are retained unmodified. “If there are six packs in the Qube, there are six BMSs. Each pack runs completely stand-alone. It’s got its own set of contactors and its own safety systems, so if there is an issue a pack can take itself fully offline,” he says. As a further precaution, every pack is managed by the same version of the BMS software, which runs on the main computer. Another benefit of using unmodified packs is that they retain all the resistance to stressors such as fire, vibration and impact that the OEM built in for the original application in a car. This means they are robust enough to shrug off any stresses to which they are subjected when Qube is moved between locations, he points out. “We mount each pack in the same way,” he adds. “We keep in the same orientation using the same mounting point, so we know it’s going to be rugged.” All the battery packs are liquid-cooled, and Qube has its own cooling system that serves all the packs with multiple pumps sourced from Davies Craig. The coolant is piped to a heat exchanger that consists of a pair of OEM-supplied Tier 1 radiators and fans, which also cools the interior of the Qube and all its electronics, including the air-cooled inverter, which does not need much cooling. “As long as we maintain the same cooling systems, we know the batteries are cooled correctly internally because they’ve all been designed by the OEM to be super-efficient without us having to design a whole new system from scratch,” Hazell says. “It has covered a lot of the hard work for us once we get the software right.” The coolant pumps come on for a minute every 10 minutes just to circulate the water ethylene glycol (WEG) mixture through the battery packs to make sure they are all at the same temperature, he explains. “They are not running all the time because the batteries are making minimal effort, far less than they would in the original car, but we still run the pumps for set periods just to make sure there are no hotspots,” he says. “But, if the batteries go over a set temperature, the pumps kick on continually and then the fans can kick on in addition.” Separate temperature sensors inside the container are also monitored by the computer, which switches the fans on to cool it, even if the batteries don’t need cooling. There is also a tube heater system that comes on automatically to prevent the temperature inside Qube falling below 10 C. For hotter climates, Fellten plans to fit an air-conditioning system. “The batteries have an easier life in the Charge Qube than they do in the car because they’ve got so much extra capacity,” Hazell explains. “On the smallest one we do, which has a 150 kWh battery capacity with a 50 kW inverter, we’re doing a 0.3 C or 0.4 C discharge, whereas a Tesla or EVD | Fellten Charge Qube March/April 2025 | E-Mobility Engineering This Qube has two Tesla Model 3 packs, but the system is battery agnostic. Packs are attached to the steel support frames using the standard mounting points (Image courtesy of Peter Donaldson)
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