On Jan 19, 2011 4:32 PM, <rwolf99@aol.com> wrote:
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> Concerning home-packaged lithium batteries, Hamid wrote:
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> <<You can not just take a bunch of cells and put them in series/parallel to make a pack and put it in your airplane to replace the lead acid battery. You need to charge balance the pack and pay attention to the charging voltage and over-charge/over-discharge. Better to pay some reliable company to do the integration and testing than do it yourself and risk an in-flight fire. The $100 you saved by doing it yourself will feel the most expensive $100 in your wallet as you are dealing with an in-flight fire.>>
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> I have to agree with Hamid here. I spent a very long two years as a battery engineer in the mid 1990's and learned a bunch of stuff. Among these was the requirement to balance the individual cells during the recharging process (which happens at the beginning of every flight, right after you start the engine). Screwing it up results in overcharging some cells and undercharging others. Lead acid is rather robust in this regard, as it turns out, but lithium is another story. In fact, the R/C model guys charge each cell individually and discharge them in series. (They also do this in fireproof bags, but that's the more twitchy Li-Po chemistry). I think it's the overcharging of an individual cell that results in fires, but excessively rapid discharge could also do it, I suppose. (Maybe due to a short in the packaging???)
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> WARNING! I KNOW NOTHING ABOUT MODERN BATTERIES! But I do know that lithium batteries can catch fire and lead acid batteries don't. So I'd be reluctant to take a chance here -- let the professional research lab do it.
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> I also understand that this technological reticence is why I installed a 1940's Lycoming in my 360. Modern stuff is generally better but we each draw the safety / efficiency / experimental line in different places, I suppose.
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> - Rob Wolf
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