LEEAMITe's Systems

A Lead-Acid Batteries will power the LEEAMITe submersible. These batteries will supply electrical power for all functions of the submersible except ascending and descending, which will be accomplished by the ballast systems. The applications of the electrical power include:

• Propulsion: an electrically-powered motor for lateral and vertical maneuvering
• Life Support: carbon-dioxide scrubbers
• Communications: two-way sub-to-surface communication
• Illumination: internal lighting
• Work and Operating Instruments: scientific and engineering instruments, including vehicle controls
• Ballast Drop: electrical impulse or signal to activate weight drops or jettison instruments
• Maneuvering: orient propulsion devices or dive planes and rudders
• Sensors: status sensors
• Emergency Indicators: seawater leak indicators
• Tracking: navigation systems

The Lead-Acid type battery will be used, as opposed to other types of electrical power suppliers, for many reasons. First of all, it has a simple construction where all components are self-contained within the battery. Secondly, these batteries can operate at ambient deep-sea pressure, meaning that they can be located outside of the hull, thereby taking less hull space and weight. These batteries have no moving parts and can also operate at temperatures well below those found in the deep-sea. Batteries are also highly reliable, failure occurs only one cell at a time, and particularly, the lead acid battery has been the most used battery in past submersibles. Lastly, these batteries are available commercially in a large variety of types, and are less expensive than other electrical power suppliers.

Connectors and cables will be used to carry the power from the batteries. An Electrical Hull penetrator will permit the passage of current through the pressure hull. Although the batteries will produce DC current, many instruments will need AC current. Inverters will be used to change DC to AC, and may be located within or external to hull. Other components may operate on lower DC voltages, so converters will be used. To keep track of the state of the batteries, equipment such as an Ampere Hour Meter, Voltmeter, and Megohm Meter (ground resistance readings) will be checked and read inside the pressure hull.

Pressure: In order to protect the batteries from seawater and pressure, an approach called pressure-compensation will be used. The battery will be placed within a sealed and vented case filled with a dielectric fluid, namely oil, and connected to a compensating fluid reservoir that acts to maintain zero or slightly positive pressure differential across the enclosed oil/seawater face.

Discharge Rate and Temperature: Most battery manufacturers define standard conditions as room temperature and low discharge. A high discharge rate reduces the total amount of energy that can be taken from a battery. As temperature decreases, the withdrawal of current becomes more difficult because the increasing viscosity of the electrolyte hinders the passage of reactants and products to and from electrodes. Because the LEEAMITe submersible must operate at very low temperatures, a heater will be used to warm the cells in extreme cold to maintain a more normal voltage and discharge.

Charging: Between trips the batteries will be recharged for 8 hours between each dive.

Gassing: During both charging and discharging, lead-acid batteries will give off hydrogen and oxygen gasses. Because the batteries on LEEAMITe will be pressure-compensated outside of the hull, there will be no safety hazards of poisonous gasses, however, this introduces other problems in short circuits and ballasting control. The gasses generated must be vented off.

Fuel Cells:In the research process, fuel cells were attractive candidates for LEEAMITe's power source. Fuel cells basically convert energy from the reaction of two chemicals into DC electrical energy. Unlike a battery that stores energy, a fuel cell produces current on demand as long as the chemicals are supplied. With a much shorter charging time, smaller and lighter dimensions, longer life, and lower operating temperature, fuel cells clearly have many advantages when compared against traditional batteries. In addition, fuel cells can be tapped at any voltage without affecting the cells' life. Nevertheless fuel cells are still experimental, despite the availability of a few commercial models, and they are more expensive. Finally, considering the fact that LEEAMITe's dives only last around five or six hours, there isn't a pressing for a power source more powerful than a lead-acid battery.

References

1. Busby, Frank. Manned Submersibles. Office of the Oceanographer: Annapolis, 1976.