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Old 01-17-2011, 03:20 AM
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Join Date: Apr 2008
Location: Wisconsin, USA
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Originally Posted by grhm View Post
One other thing. Batteries. What kind of C rating should I be looking for? 30C, 40C ect.
Usually, (again, usually!) the higher the C rating, the better quality the battery. Unless the mfg is lying about their batteries performance. Many wattflyer readers have found that actually running their battery at its maximum "C" rating results in shorter battery life. Sometimes much shorter. A local electric flyer found that his three batteries lasted five flights each at their maximum rating!

Something else on that "C" rating. Take 60 minutes, divide 60 by the "C" rating you are using, that is the flight time. Example, 60 minutes divided by 40C equals 1.5 minutes at full power. That is true, regardless of the ampere hour capacity of that battery. Worst of it is, at 1.5 minutes discharge time, the batteries internal heat has a problem getting to the outside of the battery quickly, so the batteries internal temperature can be higher than what the batteries exterior shows. And, various threads have indicated that the maximum safe internal temperature of these lithium based batteries is about 140 degrees F.

I don't run my A123 cells much over 10-15 degrees above ambient temperature, and never past about 60 or 70% of battery ampere hours on a typical flight. And after three years and 200 flights on each of my 6S2P A123 packs, they have the same performance as when they were brand new.
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