600U hydrogen fuel-cell power system

The Honeywell 600U is a 600 W hydrogen fuel-cell power system for unmanned aircraft: a liquid-cooled PEM fuel cell with a closed-cathode design that converts hydrogen and oxygen from air into electrical power. It supplies propulsion and payload loads on long-endurance UAVs and is used as a lightweight generator in place of, or alongside, a battery pack, with water as the exhaust product and very little acoustic noise.

The rated output is 600 W maximum continuous. The output voltage range is 12 to 33.6 V DC, so the unit connects to typical multirotor and fixed-wing bus voltages, with current of 30 A continuous and 50 A peak. The unit weighs 1.8 kg and measures 24.1 x 17 x 14 cm. For an integrator, the figures allow a mass and volume budget for a given hydrogen tank and a comparison with the energy a battery of equal mass would provide.

Efficiency is stated as specific fuel consumption: 53 g/kWh at 200 W and 63 g/kWh at 650 W. Hydrogen utilisation is 99.6 percent, achieved with a pump-free recapture method. Warm-up takes about 30 seconds. Time between overhauls, covering replacement of balance-of-plant parts, is 1000 hours, and the service life is 3000 hours.

Thermal and fuel integration needs planning. The stack runs at about 60 degrees C and rejects heat to a liquid loop and heat exchanger that the airframe builder sizes; the exchanger has to grow as ambient temperature nears 60 degrees C. Water is the standard coolant, with water-glycol or water-methanol mixes for sub-zero tests. The recommended ambient range is 5 to 45 degrees C, with testing down to -20 degrees C. Hydrogen comes from a carbon-overwrapped pressure vessel at 350 bar (5000 psi) in Europe or 414 bar (6000 psi) in the US; the regulator is rated to 414 bar and reduces the gas to 1 bar. A fill coupling and fuel-level sensor are available.

The 600U communicates with the host platform's autopilot over RS-232. The higher-voltage 600U-HV variant uses RS-422 or CAN bus instead.

Applications are military and commercial missions where silent operation and long flight duration matter, such as surveillance, inspection, mapping and logistics on Group 1 to 3 unmanned aircraft and similar platforms. Hydrogen storage, regulator, cooling loop and power management belong to the integrator and have to be designed with the cell.