Sea Technology

JUL 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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20 st / July 2017 www.sea-technology.com from its contemporaries. It is built in such a way that the cell has a distinct lack of void space underneath the false cap, thereby removing any need to breach. Armed with this knowledge, Energy Sales initiated testing at the University of Washington's Applied Physics Laboratory. Believing they had uncovered a possible solution to the repeatability and reliability issues uncovered in earlier developments, Energy Sales' objective was to prove the cells could withstand pres- sures up to 10,000 psi and temperatures down to 0° C while retaining the amp-hour capacity of cells at sea level. The design of the battery enclosure assembly and process was executed over a two-year period by Energy Sales and Sealand Innovations. Manufacturing, materials and design techniques were analyzed specifically to address all gas re- moval, while ensuring that the battery pack could withstand the rugged ocean environs. We found that adhesives, en- capsulants and welding techniques used in battery packs for terrestrial applications were not effective at high pres- sures in the dielectric protective fluid. The team explored several potential solutions, each showing positive results but not fully deployable. Finally, the team identified new materials and methods that met their criteria and withstood each test. In addition, special care went into ensuring a simple design and minimal number of parts. An important com- ponent in the final design is the end cap, where the exit leads connect with the bat- tery and the internal fluid is introduced through a vacu- um methodology. Pressure-Tolerant Battery Solution Ultimately, a pressure-toler- ant cell or battery doesn't require protection from an additional pressure housing. However, the battery still needs hous- ing to keep conductive and corrosive seawater from the battery cells. Furthermore, to achieve pressure tolerance, the design must eliminate any trapped air or compressible gases. By selecting the right cells and applying the appropriate manufacturing processes and procedures, the final product should feature a lack of any interior gas and assist the cells in resisting or preventing outright deformation of the cell can. During the concept phase, the batteries were arranged in a traditional positive-negative "puck" assembly. The inher- ent modularity of the pattern would facilitate ability to scale the following design stages to almost any oceanographic application. The proof of concept called for the finished as- sembly to be immersed in a fluid medium to protect the assembly against deformation. Numerous manufacturing strategies, materials choices and design techniques were applied to address the other challenges of ocean environs. work, done by Dr. Roger Cortesi and his col- leagues, focused on Duracell's MN1300. The team invested a significant amount of labor to safely breach the false cap of each cell with the goal of finding an inexpensive, nonrecharge- able power supply with twice the energy den- sity of lead-acid batteries that would be viable for use under pressure. After modifications, they found the batteries were able to match the manufacturer's operating specifications to a pres- sure of 10,000 psi. While their results were positive at the time, the concept was set aside due to manufactur- ing repeatability and performance reliability issues. Other work in this area has come from collaboration between the University of Washington and NOAA's Pacific Marine Environmental Laboratory. Much of that research, however, concluded in the same way: tested cells ultimately failing due to pressure-related cell geometry changes attrib- uted to air that is trapped in the cells. Batteries from most manufacturers, while great in ter- restrial applications, showed similar results to the studies that preceded our own exploratory testing when put in the pressurized environment. The common denominators, re- gardless of manufacturer, were a significant loss of power and a disconcerting deformation of cell casings. In con- trast, Energy Sales has helped design a cell that stands apart (Top and Right) The unique design of the alka- line cell features a distinct lack of void space underneath the false cap. Energy Sales' PTBS is designed to provide a cost-efficient battery so- lution that will operate safely and successfully down to 3,000-m depth.

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