The airport professional's source for airport industry news, articles, events, and careers.
Issue link: http://airportbusiness.epubxp.com/i/397645
October 2014 airportbusiness 39 SUSTAINABILITY Airport. The lab used four of the airline's baggage tractors with the help of John Salter, reliability analyst for GSE with Southwest and Tony DiLuccia, lead GSE technician for operations at ONT. "No alterations to the fleet operations were made for the baggage tractors under test in order to allow for comparison with other GSE fleets," the report says. Corvus Energy Limited was chosen to supply the lithium-based battery packs used for the test. Corvus created a prototype battery pack configured with three battery modules in parallel with a junction box and vehicle control unit. Each module contained 24 series-connect- ed cells in order to allow for a similar voltage range as currently used within the baggage tractors. The three modules and junction box were placed in a structure that was specifically designed to fit the battery cavity of an airport baggage tractor. Two of the tractors had the Corvus batter- ies while the other relied on flooded lead-acid batteries. Minute-by-minute logs of battery usage information were collected for each battery over the duration of the demonstration to gain a better understanding of how the different battery chemistries handle the duty cycle of a ground support baggage tractor. To accom- plish this, the BIM needed to have a means for monitoring, recording and communicating to the data server. It was determined that the desired information to be communicated was cell voltages, pack voltage, pack current and pack temperature. For the FLA battery packs, this meant that the BIM hardware would contain the proper circuitry and software to monitor and record: • 20 high-voltage leads placed on the positive terminal of every other cell of a 40-cell, 80-volt nominal pack in order to record intermediate cell voltages and full battery pack voltage. • Pack charge and discharge current via a bus bar, connecting two battery cells and acting as a shunt. • Battery temperature with a thermistor placed on the pack. For the Corvus battery packs, each module was sealed without a means to connect the BIM analog circuitry to the modules. However, the Corvus BMS internal to each module commu- nicated analog data for maximum and mini- mum cell voltages, module voltage, module current, module temperature, and module state-of-charge via the BMS CAN bus. Because the BIM also had to be connected to the Corvus CAN bus for charging, all analog data were taken from each module's BMS using a secondary CAN bus on the BIM. Since the Corvus lithium battery pack weighed in at 500 pounds, about 2,700 pounds less than the flooded acid bat- tery, the weight difference was addressed with the addition of ballast and steel plate. Over the course of six months, battery usage and charging data were collected from four eGSE baggage tractors. The results proved positive for lithium. "The lithium battery packs can accept a full charge current for the majority of a full charge, while the FLA battery packs can only accept full charge current for approximately the first hour of a full charge," the report says. "After the first hour, or in the case of an opportunity charge, the charge current for the FLA battery drops in order to maintain a charge voltage limitation." The report also pointed out that the lithi- um batteries required less time for charging, resulting in less charge events. The lithium batteries were able to be charged more rap- idly, with essentially an equal capacity added during the charge. As for on-the-ramp performance, the evaluation showed the lithium batteries had a more consistent discharge to charge capac- ity efficiency at 85 percent and 86.7 percent, compared to the FLA batteries at 60.6 percent and 87.2 percent. "When comparing the amount of time spent driving the baggage tractors versus charging," the report says, "there is a clear advantage to the lithium battery vehicles, with more time available for driving than required for charging. The FLA battery vehi- cles remained inefficient, with the vehicles undergoing more hours of charging than they could be driven due to the longer charges and battery equalization cycles required for the FLA batteries." LEAD-ACID BATTERIES We recently heard from Todd Allen, president of Allen Energy, about the new battery that a couple of airlines are currently testing on their equipment. "We have a new battery out there called thin plate pure lead," he told us."They have the benefits of lithium at a lead acid price." While they may be new to the GSE mar- ket, the NexSys battery and charger system manufactured by EnerSys has been used in other industries. According to product information, the batteries are constructed from 99 percent pure lead. The plates are extremely thin so more of them can fit into the battery. "More plates means more power," Allen adds. Also, the batteries feature compressed Absorbed Glass Mat separator with high electrolyte absorption and stability to enhance cyclic capability. To resist vibration and elim- inate internal sparking, cell connectors are casted to the plates and bonded. Taken together, Allen says NexSys batter- ies offer optimized cycling performance and rapid recharging that conventional lead acid batteries—gel or flooded—cannot match. When A cross-section of the NexSys battery from EnerSys.