On Sat, 01 Aug 2009 12:52:39 +0100, Nigel Feltham
wrote:
Jeff Liebermann wrote:
On Fri, 31 Jul 2009 00:37:21 -0700, spamme0
wrote:
buy cells with tabs.
do not solder to lithium cells!!!!! unless you have very good fire
insurance, medical insurance and a death wish.
Well, you're right. Heat will cause a Li-Ion battery pack to
deteriorate rather rapidly. There's also the fire danger. Several
web sites recommend against soldering directly to the can on Li-Ion
cells. For example:
http://www.electronics-lab.com/articles/Li_Ion_reconstruct/
http://www.panasonic.com/industrial/battery/oem/images/pdf/panasonic_liion_precautions.pdf
"Do not short circuit, overcharge, crush, mutilate, nail penetrate,
incinerate, reverse polarity, heat above 100 degrees Celsius, solder
directly on the metal can."
I guess I've been lucky as my method of dunking the battery into water
after soldering seems to have prevented any problems. However, in the
future, I probably won't take the chance. It's too risky.
Especially once you know what happens when you mix lithium and water - the
lithium catches fire.
Yep. That happens with metallic lithium. Li-Ion and LiPo batteries
use Lithium salts. These will oxidize violently if heated
sufficiently, such as when the battery is overcharged or rapidly self
discharged by pounding a nail into it. Lots of nice fires and
explosions on YouTube. For example:
http://www.youtube.com/watch?v=YCWdnjLqVWw
However, water incursion is a problem in that it causes the battery to
swell:
http://www.electronicsweekly.com/blogs/engineering-design-problems/2009/04/li-ion-battery-bloat-moisture.html
The plastic encased cell phone batteries seem to be fairly well
sealed. The tape wrapped variety found inside PDA's and iPod's are
not so well sealed. I tried dunking a dead battery I pulled from an
Palm something PDA in a class of water. It took about a week to
swell. The LG cell phone battery did not swell after about 2 weeks.
My guess(tm) is that the inside variety rely on the PDA, iPod, or
phone to provide the water proofing.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558