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Re: [RoboMower] Switching to lithiums for RL500

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  • Lee Hart
    ... I agree with Danny. Your typical 18650 laptop cell is *highly* combustible. Extensive safety measures need to be taken to prevent them from ever catching
    Message 1 of 8 , Jan 5, 2013
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      On 1/4/2013 3:20 PM, Danny Miller wrote:
      > I would strongly caution you against building a large pack like that out
      > of cobalt-cathode 18650s. That's just dangerous.

      I agree with Danny. Your typical 18650 laptop cell is *highly*
      combustible. Extensive safety measures need to be taken to prevent them
      from ever catching fire, because if they do, it will be spectacular.
      Think of them like a box of matches.

      The LiFe cells still burn, but it's harder to get them started, and the
      resulting fire spreads much slower. Think of them more like a box of
      kindling.

      > you need to consider the overall layout and space-efficiency because
      > the volumetric density is only moderately better, but the ability to
      > utilize the volume is always much less.

      Again, I agree. The watthours per pound of lithium is about 3 times
      better than lead acid, but the watthours per cubic foot is only slightly
      more. When I do talks, I have three batteries that graphically
      illustrate this: One Hawker lead-acid 12v 60ah, one GM/Ovonic nimh 12v
      90ah, and one Thundersky 12v 90ah. All three are the same size. But the
      lead-acid weighs 60 lbs, the nimh 40 lbs, and the lithium 22.5 lbs.

      When you have a fixed size battery box, you'll wind up with about the
      same watthour capacity no matter which battery chemistry you pick.

      --
      Results! Why man, I have gotten a lot of results. I know several
      thousand things that won't work. -- Thomas A. Edison
      --
      Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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