It should be noted here that the French bathyscaph, FNRS-3, 

 has had some degree of success in operating with externally 

 carried batteries, but because there is a lack of information 

 concerning their methods of operation and because their 

 dives have been limited to depths of less than 14, 000 feet, 

 it was decided to complete a full series of tests to evaluate 

 this type of power supply. 



TEST CONSIDERATIONS 



It was necessary to insulate the batteries from the water to 

 prevent shorting and to keep the water from mixing with the 

 electrolyte. It was also necessary to transmit pressure 

 from the water through the insulation to the electrolyte and 

 thus throughout the battery to prevent the casing from collaps- 

 ing. This was accomplished by placing the battery in an oil 

 filled case as shown in figure 1. As the oil and the electrolyte 

 compress due to pressure, water flows into the bottom of the 

 case through the equalizing tube, thus retaining a balance of 

 internal and external pressures. Compressibility tests on 

 the transformer oil used as the insulating fluid show a volume 

 loss of only 4. 7 per cent at 16, 000 psi. Since electrolyte is 

 even less compressible, the water level in the bottom of the 

 case could not rise high enough to short the battery as long 

 as at least 5 per cent of the case volume in addition to that 

 occupied by the battery itself is located below the battery 

 top. In the final design of the operational battery cases, the 

 batteries are supported several inches above the bottom of 

 the case so that the water can never reach the bottom of the 

 battery even in the deepest dives. 



Because battery electrolyte in the fully charged state (specific 

 gravity 1.260) sustains a volume loss of 3 per cent at 16, 000 

 psi, it is necessary to provide a small reservoir of electro- 

 lyte above the top of the battery plates to prevent oil from 

 coming in contact with the plates when the electrolyte com- 

 presses. The batteries used in the laboratory tests already 

 contained a large enough void area above the plates to con- 

 tain the needed additional volume of electrolyte, as can be 

 seen in figure 2. The standard Navy 12 -volt automobile 

 batteries which were obtained for operational use, however, 

 required an additional reservoir. This was provided for by 

 attaching small polyethylene bottles to the top of each cell 

 in place of the filling cap, as shown in figure 3. 



