On 8/14/11 11:31 AM, Burns Fisher wrote: > What about another strategy? Suppose we did exactly what the battery was > spec'ed for: Deep cycles.
Almost every type of battery does better with shallow cycles than deep cycles. So this is almost certainly true for Ag/Zn as well. These batteries just aren't designed for many cycles. There is a company (Z-power) working on a Ag/Zn battery with a decent cycle life, intended for use in laptops. They claim the price of silver isn't an impediment because laptop li-ion batteries are also expensive and the silver in their batteries can be reclaimed and reused indefinitely. One advantage they keep citing is the increased safety of a battery with a water-based electrolyte. But newer li-ion batteries have also been developed with different positive plate materials that greatly reduce the inherent fire hazard of these batteries. I don't know what the recent run-up in precious metal prices has done to their business plans. I would like to investigate super/ultracaps for spacecraft use. Their energy densities are low (a Maxwell ultracap the size of a D-cell battery holds about 0.35 watt-hour) but their cycle lives are extremely high: about 500,000 for a 20% degradation in capacity. These could still run a satellite computer through a LEO eclipse, eliminating one of the major problems with a modern satellite whose battery has failed. If a few of these caps could be flown, it might also be possible to run a low power, efficiently coded telemetry beacon through eclipse. But of course the caps would have to be safety rated. They do contain small amounts of potentially hazardous materials, but then again so do Ag/Zn batteries: their electrolytes consist of a strong lye (KOH) solution. It's hard to understand why these batteries would be approved but not NiCd and NiMH as they also use KOH in H2O as their electrolytes. If stored energy is considered a hazard, they could always be launched discharged and charged after deployment. -Phil _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
