Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!wuarchive!waikato.ac.nz!canterbury!elec140 From: elec140@csc.canterbury.ac.nz Newsgroups: sci.electronics Subject: Re: NiCd Memory (True or False, opinions?) Message-ID: <1991Jun25.113001.1188@csc.canterbury.ac.nz> Date: 24 Jun 91 23:30:01 GMT References: Organization: University of Canterbury, Christchurch, New Zealand Lines: 51 In article , clemon@lemsys.UUCP (Craig Lemon) writes: > > I'd like to start a little discussion on NiCd memory (notice > little, I don't want to be solely responsible for starting a noticeable > bandwidth flare-up net-wide. Moderate's OK :-) Okay, here's my $0.02 What I'm posting here has been gathered from talking with many people who have used nicads, including some who have worked extensively with them, and reading a lot of literature about them (including this and other newsgroups). Obviously everybody has their own opinion about these things, and I'm no exception, however I do think that what follows represents a resonably informed opinion. As I understand it, the nicad memory effect does exist, BUT only in very special circumstances. If a nicad is constantly charged and then discharged to WITHIN A FEW % OF THE SAME AMOUNT EACH TIME, it will eventually develop a memory. Note that it needs to be very precisely the same amount of charge/discharge each time. This effect was found in satellite systems, where the charge/discharge cycle of the nicads was extremely regular. For your average domestic (or even industrial) nicad user, the memory effect effectively does not exist. What does degrade the performance of nicads is poor charging, in particular overcharging. Although they are designed to withstand an overcharge, constant overcharging seems to gradually destroy them - it appears that leaving nicads on a constant float charge is the worst thing to do to them. The reason for totally discharging nicads (down to 1.0-1.1 volts per cell) then is so that when they are subsequently charged for 15 hours (depending on the charge rate of course) they are fully charged but not excessively overcharged. Other factors also cause nicads to fail. As several posters have already mentioned, heat is a major factor. A good indication of when a cell is fully charged at a high charge rate is that the cell temperature rises 5 degrees C (9 degrees F). Any higher than this indicates that the cell is being overcharged and is not good for it. If the nicad is hot to the touch after charging, it is probably being damaged. ********************************************************* Chris Kaiser Postgrad - Elec Eng Dept Canterbury University Christchurch, NEW ZEALAND E.MAIL: kaiser@elec.canterbury.ac.nz ********************************************************* "When you're fresh out of lawyers You don't know how good it's gonna feel" - Al Stewart, 1988 *********************************************************