The Lunar Roving Vehicle's Electrical Power Subsystem included two 36 VDC silver-zinc batteries, and wiring harnesses with connectors, circuit breakers, switches and meters. The batteries were engineered by Eagle Picher of Joplin, Missouri, and both minimum weight and power generation capability were the overriding parameters. The batteries used a lightweight magnesium case with a Plexiglas core, having twenty-three cells containing silver-zinc plates in a potassium hydroxide electrolyte. Each 27 kg battery was rated at 121 amp-hours. The electrical power subsystem was designed to have both batteries operating simultaneously. However, through the use of selective switching from the Control and Display Console, either battery could be called on to power the entire vehicle and its various systems if one of them should fail or need to be turned off.
The batteries were located in the forward chassis of the LRV, and benefited from a comprehensive thermal control subsystem which included thermal blankets and dust covers, explained below. Each battery had a relief valve to prevent excessive pressure building up due to high operational demands or prolonged elevated temperatures. Battery electrical capacity and temperature were monitored on the Control and Display Console.
Much of the data of the electrical power subsystem would be transmitted back to the Lunar Module, which would relay the data back to Earth and Mission Control. The electrical wiring harness was carefully routed along or within the LRV's chassis with particular attention paid to securing and protecting the wiring harness from damage due to fraying. One engineering aspect that had to be sacrificed due to weight limitations was a real-time battery monitor that could be read by the crew inside the Command Module, as was provided for other systems. After the batteries were installed in the LRV on the launch pad about three days before launch, they would only be monitored up to eighteen hours before launch. The astronauts venturing down to the lunar surface would not know if their rover would power up until it was fully deployed.
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