Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

8 August/September 2019 | Unmanned Systems Technology Intelligent Energy has developed a hydrogen fuel cell power module for unmanned vehicles up to 25 kg (writes Rory Jackson). “It’s a 2.4 kW fuel cell power module,” said the company’s Andy Kelly. “Much of the same technology has been used in it as in our 800 W product, but this one is aimed at much bigger UAVs, such as those with MTOWs of roughly 55 lb or 25 kg. “It will give a UAV of that weight roughly 2 hours of flight when paired with an 11 litre 350 bar hydrogen gas cylinder.” The new system weighs 3250 g, measures 430 x 230 x 130 mm, and is rated to a peak power level of 4.8 kW (with 2.4 kW being the maximum continuous power output). It is being tested to operate at temperatures from -5 C to 40 C, up to a ceiling of 3 km. It uses the same AC64 fuel cell stack technology as the company’s other UAV power modules but with 144 cells integrated into the energy stack, compared with the 34 cells in the 800 W unit. As this also means more heat being generated, and concentrated within the thicker cell volume, the 2.4 kW module comes with two cooling fans of 15 cm diameter each, compared with the two smaller fans of about 7.5 cm diameter each and a smaller overall vent area on the 800 W module. “That also means the 2.4 kW unit’s cooling is more efficient overall, and is lighter and has a lower material cost just because there’s more open space on the housing,” Kelly added. “We did a bit of CFD to check the cooling fans would be sufficient to dissipate the heat generated by the stack, but that was a relatively short test. We quickly moved on to real-world flow measuring equipment, which allowed us to judge exactly how to control the fan given the amount of heat we are dealing with.” The fans are driven by a T-Motor F40 Pro II electric motor and propeller, which has a 2400 kV rating, measures 23 mm across and uses a resin on the stator wires to insulate against temperatures of up to 240 C. Also, and unlike Intelligent Energy’s other systems, the 2.4 kW module is designed with a higher peak power range, allowing approved compatibility with VTOL aircraft. The system’s two hybrid batteries have a peak power rating of 4.8 kW each by default, but technically the module can produce up to 8 kW and end-users can pair it with a larger battery if they so choose. Each default battery has a capacity of 2700 mAh and weighs 340 g. Fuel cells Weight gain for hydrogen As this means more heat being generated, it comes with two cooling fans of 15 cm each Platform one Intelligent Energy’s 2.4 kW fuel cell

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