WET SUITS 



283 



W. and V, are determined from: 



b b 



W,, = K/a^^^ and V^ = K/a , 



where 



K is the stored energy, watt-hours 

 a^_ is the watt-hours stored per pound of battery 

 a is the watt-hours stored per cubic inch of battery 

 Finally, the apparent weight is: 



W = K 



75 a 



Table 38 shows the calculated weight and bulk of various battery candidates. The figures 

 for weight and bulk are conservative (on the low side) and are based on nominal characteristics. 

 The calculations are for the batteries alone and do not include the weight and volume of other 

 components of the power pack. 



Table 38 

 CALCULATED WEIGHT AND BULK OF ONE KILOWATT-HOUR BATTERIES* 



* a^^ and a^ from Reference [12]. 



tPrimary (not rechargeable) sea-water activated. 



tWa = weight in water (apparent). 



Lead acid, nickel cadmium, Leclanche, and sea-water batteries were ruled out because of 

 the bulk and weight required for storage of one kilowatt-hour of energy. Silver cadmium cells 

 were just a little too large and heavy for the purpose. 



Silver-zinc, the most efficient of the secondary cells for energy storage per unit weight 

 and per unit volume, were selected for the application. Thus, the portable power pack would 

 provide chemically stored energy which would be released as electrical power. This suggested 

 that the most efficient means of using the stored power would be direct conversion to heat 

 through use of resistance wires. 



In a sense, selecting immersible silver-zinc cells opened Pandora's box because of the 

 need for rather demanding maintenance and charging procedures. Off-the-shelf silver-zinc 

 cells cannot be immersed in seawater without design adaptations for pressure equalization and 

 waterproofing to prevent electrical shorting. 



Pressure-compensation of the individual cells can be provided by filling the cells almost 

 completely with electrolyte (potassium hydroxide, 40 percent aqueous solution) and installing a 

 deformable rubber bladder. Total filling is not possible for three reasons; gases are occluded 

 in the plates, hydrogen is generated in the cells, and it is difficult to purge the gas bubble en- 

 trapped at the top of the cell without spilling the caustic electrolyte. An alternative to pressure 

 compensation would be to insert the cells into a single pressure housing, but this would increase 

 the weight of the battery pack, and the weight of the cells alone is almost to the acceptable 



