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Is the 787 a failure ?
On Sat, 26 Jan 2013 06:46:22 -0700, Daryl
wrote: On 1/26/2013 6:00 AM, Jim Wilkins wrote: "Daryl" wrote in message ... It sounds like they are being overcharged. That is prevented by a simple card addition that prevents it on only of overcharging but undercharging. Easy fix. Daryl The Lithium medical and electric vehicle packs I worked on were controlled by ICs that monitored and recorded individual cell voltage and overall charge and discharge current. Those are point measurements that are easy to do. What's harder is detecting unexpected hot spots away from the temperature sensors. Minor differences (improvements) between the acceptance sample and production devices can change heat flow paths. http://www.mpoweruk.com/lithium_failures.htm I can see a problem that is being addressed in Electric Vehicles. Heat and cold. On an electric vehicle, getting the battery too cold will (not can) result in a degrading of the performance of the cells. The fix is adding an "Electric Blanket" to keep the battery warm (not hot). The residual power required by the blanket is negligible. You get back much more than you lose. Heat. I can see problems with the Lipo batteries. The battery they chose is one that is not on the list of Vehicle safe batteries. It is the best, the highest output but with it comes problems. Lithium cobalt oxide (LCO), for vehicles, is listed as unstable compared to the rest. It's very suspeptable to heat. And sitting on the ground running up on a hot day, the battery compartment will sky rocket in heat. The safest to use is the lead acid but it's very short lived in this application. To use any Lipo battery, it requires a cooling and a heating system to keep the battery at an optimal temperature. The LCO is just the worst of the lot for overrunning (catching fire, generating Oxygen when it burns) than any other Lipo battery. The Fix? Get rid of the LCO and temperature control the battery compartment. Even a Lead Acid doesn't like excessive cold or heat. But it won't turn into a major oxygen fire. Sometimes, newer isn't better. But the various other Lipo batteries are safer than the LCO which has a proven track record of burning. Lead acid is and has for quite some time been a "non-starter" for the application - for good reason.Nicads have been the standard for decades - and have their issues as well Lithium iron would be a better choice . BTW, the LCO isn't the cheapest by far. The LipoMG battery is the cheapest but it has a low service charge rate. The Lipo4 has a decent service rate and is what is primarily used in various vehicle applications. But, maybe, the old Lead Acids may be the way to go on this one. They are the most stable and the most safe if you keep them in a wide range of temperatures. Newer isn't always better. Daryl |
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