1996 - 2016
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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Charles Murray over at Design News posted a video of a lithium-ion (Li-Ion) battery going up in flames, as a reminder of the potential (pun intended) danger posed by the chemistry used by the vast majority of our portable devices as well as the current fleet of electric cars. In it, a guy whacks an iPad battery pack with a hammer causing it to immediately burst into flames - an act that could easily go way wrong and automatically self-nominate the performer for a Darwin Award. Just as the Ford Pinto and early model Mustangs were discovered to include an unadvertised explode-on-impact feature with trunk-mounted gas tanks, so too have early model Teslas with inadequately protected Li-Ion battery packs.
As Mr. Murray suggests, good engineering will eventually eliminate or at least significantly reduce the likelihood of such events. He points out that the energy density of gasoline is about 12,000 Wh/kg versus about 200 Wh/kg for lithium-ion. "Somehow, automotive engineers have figured out how to control the high energy of gasoline. There's absolutely no reason why they can't do the same with electric cars."
The news media crave such stories so badly that you might recall when NBC News rigged a GM pickup truck with incendiary devices to fake a crash-related explosion. However, there are plenty of unstaged fires involving Li-Ion batteries. There have been numerous stories of cellphones burning people while being carried around in a pocket or left charging under a pillow. The biggest danger seems to be during the charging cycle since that is when the most rapid creation of gasses occurs and the temperature increases. Fast recharging is particularly risky. Model airplane and car hobby magazines print safety articles quite often since fast charge modes are frequently used while at the flying field or car track in order to minimize time between flights and runs, respectively. The most damaging fires usually happen, however, while charging at home or even in a personal vehicle on the way to the field since there is more likely to be other flammable objects nearby to catch fire.
The thumbnail to the left is a photo I took of one of the Li-Po (lithium-polymer) battery packs I was using for an R/C airplane (see "Lithium-Polymer Battery Characteristics"). It arrived that way from the mail order house. I safely disposed of the pack by soaking it in a brine solution for a week and then throwing it away. A couple months ago another pack needed to be disposed of for the same reason. I never charge my Li-Pos at a rate greater than 2C and probably never draw from them at greater than 15C so they have a pretty easy life. In fact, my batteries' biggest threat is lack of use since, alas, I rarely take time to go flying (more time spent publishing my Airplanes and Rockets website).
It is a wonder there are not more fires than we see reported.
Note: "C" is the charging or drainage current multiple of the pack's rated capacity. For instance, a 1,500 mAh pack is being charged at or delivering a current of 1,500 mA (1.5 A) at 1C. 5C would be 7.5 A, etc.
Thanks to Design News for posting this video
Posted October 28, 2014