(15) present a thorough discussion of the 

 genesis from in-hull placement of batteries 

 to the use of external pods in the Perry 

 submersibles; their observations and experi- 

 ences constitute the backbone of the follow- 

 ing discussion. 



Installation of batteries in an external pod 

 offers the following advantages: Internal 

 pressure hull space is not required; any toxic 

 battery gasses which may evolve will not 

 affect the occupants; the pods can be made 

 droppable to serve as emergency deballast- 

 ing; maintenance and repair is made easier 

 by incorporating roller plates on which the 

 battery may be removed from the pod; the 

 battery tray can be made of a high dielectric 

 material and thereby reduce leakage resist- 

 ance problems; both ends of the pod can be 

 removed and forced air ventilation applied to 

 dissipate hydrogen gas generated during 

 charging; and for quick turn-around time 

 between dives the used batteries can be eas- 

 ily replaced with fresh ones. 



Conversely, this procedure has the follow- 

 ing disadvantages: Total vehicle weight is 

 increased; the drag force of the vehicle is 

 increased and thereby requires increased 

 power for propulsion; electrical penetrations 

 for power are increased; and total cost of the 

 vehicle rises. 



One problem of major concern in the Perry 

 vehicles is battery gassing during sub- 

 merged discharge (15) and the lack of suffi- 

 cient oxygen within the pod to recombine in 

 the Hydrocaps with the hydrogen generated. 

 To alleviate this problem the battery pod on 

 SHELF DIVER was pressurized prior to seal- 

 ing to provide adequate oxygen. To prevent 

 poisoning of the palladium catalyst the Hy- 

 drocaps in Perry vehicle pods are located in 

 the top of the pod such that overcharging 

 will not contaminate the catalyst with elec- 

 trolyte. 



This procedure, then, offers a number of 

 advantages and disadvantages, the greatest 

 penalty being weight. Compared to the pres- 

 sure-compensation system, external pres- 

 sure-resistant pods are far less trouble and 

 considerably more reliable. There is a point, 

 however, where the added weight would be- 

 come prohibitive in the deeper diving vehi- 

 cles. 



Pressure Compensation 



In this arrangement the batteries are lo- 

 cated outside the pressure hull and within a 

 non-pressure-resistant container. A dielec- 

 tric fluid (oil) completely surrounds the cells 

 and provides both electrical insulation and 

 pressure equalization. A typical compensa- 

 tion system is shown in Figure 7.10. The 

 system conserves vehicle weight and pres- 

 sure hull volume, while offering no direct 

 safety hazards to the occupants. In some 

 vehicles the batteries are jettisonable to pro- 

 vide emergency buoyancy. On the debit side, 

 the present systems are messy, generally 

 difficult to maintain, and, according to Work, 

 ". . . destined to get salt water in them tit 

 one time or another.'''' 



Packaging batteries in this manner must 

 satisfy two, relatively simple requirements: 

 Hold the dielectric fluid in and keep sea- 

 water out. While the requirements are sim- 



MANUAL 



VENT& FILL 



VALVE 



RELIEF 

 VALVES 



SALTWATER - 

 BAFFLES 



ELECTROLVTE 

 SCRUBBER 



P«- 



ur. 



Fig. 7.10 Typical battery compensation system. [From Ref. (16)] 



328 



