Path: utzoo!telecom-request Date: Fri, 26 Apr 91 8:58:59 PDT From: "Jon T. Adams" Newsgroups: comp.dcom.telecom Subject: Shaving Ni-Cads (Removing 'Whiskers') Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 310, Message 1 of 11 Lines: 34 In article schwartz@nynexst.com (S. H. Schwartz) writes: > In article hayward@gargoyle.uchicago. > edu (Peter Hayward) writes: >> A good six months ago, there was a discussion in this group about a >> device that would "burn the whiskers" off nicad battery packs, thus >> defeating the dreaded nicad memory problem. I archived that message, > What does this device do that cannot be accomplished by running down > the battery in an ordinary flashlight, tape player, etc.? Ni-Cad "whiskers" are actually crystalline growths that form within the interior of the battery from the electrolyte and gasses released during charge ans discharge. These crystals are conductive enough that they begin to seriously reduce the capacity of the battery by putting low impedance bridges between the battery terminals. Sometimes, enough can act together to internally short the battery and make it useless. The only practical way to get rid of these crystalline growths is to apply a massive current that will essentially evaporate the crystals. The current pulse must be short enough to prevent undue damage to the battery yet enough current must be applied to destroy the whiskers. I know people who have resurrected their batteries using 50Vdc for several milliseconds. But this technique really only allows a temporary increase in the battery lifespan. Once the crystals have formed en masse, the battery longevity will continue to drop off. jon