Support Systems

Air Compressor and Compressor Motor

The most critical subsystem of the fuel cell support system is undeniably that of the air compressor. It was clear from the beginning of the program that an efficient, small and lightweight package would need to be identified. Several types and manufacturers of compressors were considered, and in the end, a modified screw compressor provided by VAIREX was selected. The compressor is directly coupled to a Uniq Mobility DC brushless permanent magnet motor/controller assembly, chosen for its high efficiency. Together, this combination delivers a maximum of over 20 cfm at 20 psig to the fuel cell stack.

Hydrogen Storage and Delivery

Early in the design of the vehicle, it was decided that range and run-time would meet or exceed the ability of the existing ICE powered vehicle. In support of this goal, two EDO LiteRiderâ„¢ composite cylinders were chosen to carry the hydrogen fuel. Factors such as simplicity, weight, volume and cost were carefully considered prior to making this decision. The use of compressed gas allows for a simple delivery method, controlled by the operation of solenoid valves on both of the cylinders. By using two of the model 60L cylinders, a maximum internal volume of 25,000 standard liters of hydrogen can be carried at 3000 psig, allowing for a minimum run-time of over 4 hours.

Water and Heat Management

The required humidification of the membrane is accomplished through the use of an Energy Partners designed and manufactured humidifier. This device is located on the air-side of the system, simply and reliably delivering de-ionized water from the cooling water reservoir into a chamber, where the entering air stream carries the humidifying mist into the fuel cell stack. The bulk of the excess water diffuses across the membrane and exits from the hydrogen side of the stack.

Cooling of the stack is accomplished by the circulation of de-ionized water through the stack. After exiting the stack, the water travels through a series of stainless steel heat exchangers which dissipate the heat. The degree of cooling is further controlled through the use of fans mounted on the radiators, which are individually operated by the microprocessor controller.

Power Conditioning

Several methods of power conditioning are employed in the Gatorâ„¢ fuel cell power system. The air compressor motor controller allows a 30-100 V input voltage range, and a 42 V battery bank provides the initial power to start the system. Once fuel cell voltage rises above 50 V, the fuel cell contactor is engaged, powering the system and recharging the batteries. Two Curtis DC-DC converters are utilized to provide the 12 V required for operating the bed lift, pressure switches, solenoid valves, fans and water pump, as well as the microprocessor controller.

Additional power conversion is provided by the inverter, located in the bed of the vehicle. A Trace inverter delivers 120 VAC (modified sine wave) power for operation of hand tools at remote sites.

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