On 9 Mar 2014 at 1:18, Michael Ross wrote: > I think there is a recipe for very long life of LFP cells. ... Build > the cells right ... Balance them ... Never overcharge them ... > Operate them from SOC of 20% to 80% ... limit the current when the > temperatures drop in the cell ... Never charge them too fast so they > get hot ... Operate them within a well built system ... If you do > these things there is no mechanism for them to fail.
These rules are pretty much the same ones you'd use to extend the cycle life of ANY battery. Buy a high quality, well balanced battery; limit extremes of charge and discharge; charge it moderately; watch out for temperature extremes; maintain it properly. You'll get better life than if you ignore some or all of these things. These rules can and should be programmed into a good BMS. If they are, unlike when the user is the sole BMS, there's no way that he or she can circumvent or forget or neglect them (except possibly in an emergency). The user doesn't have to worry about them; the BMS takes care of it. In fact, a really good BMS will perform some of the maintenance (the way the Prius BMS balances periodically, for example). It will monitor the battery's condition continuously, not just when it has time, and notify the user if a problem is developing. All that said, the "there is no mechanism for them to fail" part I'm not buying. Every battery depreciates as it's used. Some are more durable, some less so, but every battery has the potential to fail, either gradually or catastropically. It seems to me that at some level this is a little like a manual vs automatic transmission discussion in the ICE world. Today, a sufficiently advanced automatic transmission can be just as efficient as a manual, and sometimes more so. Despite this, some folks just would rather shift for themselves. They just like it that way. But if you buy a manual trans ICEV, you'd better know not to overrev or lug the engine, or slip the clutch too much, or hold on hills using the clutch, and so on. If you don't, or are apt to forget, you're probably better off with a slushbox. (I've known such folks.) Similarly, some people would rather be their own BMSes. Others are better off buying them. David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
