David, I think you missed some of what I said and maybe I've misunderstood what was needed to properly charge various lead acid batteries.
With LiFePO4 cells all you need is a charger which can terminate on two values: target voltage followed by target minimum current. Nothing else is needed. For example, charge to 3.6vpc and end when the current drops to 0.05C. If the ending current is going to be lower than 0.05C then the target voltage must be lowered to keep from overcharging the battery. For example, my Zivan is in capable of terminating based on a minimum current so I have to lower the target voltage to around 3.45vpc. If I could eliminate the pesky lead acid equalization phase I could avoid this problem. Playing around with some LiFePO4 cells BY HAND and carefully recording the results can give a person a much better understanding of how these cells behave than any reading/listening to others can. I'm not saying one shouldn't read/listen to others, just that that isn't enough. Charging lead acid properly sometimes means minimum charge currents, LiFePO4 doesn't care about minimum charge current (see qualification on ending charge parameters above). From everything I have read here and on battery manufacturer's websites, lead acid has a bulk charge phase, an absorption charge phase, and an equalization phase whose time and current depend on pack size and how, possibly, how long it took to get to that final phase of charging. All overcharging of lead acid batteries shortens the life of the battery but it is unavoidable because of the need to balance the pack since lead acid has a built in self discharge, something that LiFePO4 does not have to worry about (provided of course that the cells are not defective). That is what I meant that LiFePO4 was much easier to properly charge than lead acid. Note again that I said, properly charge, not abuse. Another thing, even though I clearly state that I'm talking about LiFePO4 cells many seem to generalize that to all lithium cells. I do not have enough hands on experience with other lithium chemistries to generalize my statements to them. I do know that their voltage vs. SOC curves are different so I will not generalize my LiFePO4 statements to them with out sufficient information to justify such generalization. As such, the BMS in your laptop, etc. does not apply to my statements since I'm not talking about those lithium variations. BTW, I was talking with Gary Graunke yesterday about the battery pack he built out of DeWalt batteries for his Honda Insight. He noted that he didn't have to constantly balance them once they were in balance. I didn't get any info on time or cycles between balancing needs but it was very minimal. Remember, the DeWalt packs were made with A123 LiFePO4 cells. On Tue, Jun 11, 2013 at 5:22 AM, EVDL Administrator <[email protected]> wrote: > On 10 Jun 2013 at 23:27, David Nelson wrote: > > > It is much more complicated to properly charge a lead acid battery than > > a LiFePO4 or most any other rechargeable lithium based cell. > > I'm not very experienced with lithium, but that's not been my experience. > A > lead battery can be safely charged with a simple power supply regulated at > the battery's float voltage, as long as you don't mind it taking a rather > long time to reach 100% SOC. > > Flooded lead especially is quite sturdy, and can take a lot of overcharging > abuse without drastic reductions in service life. I've charged a lot of > flooded lead with constant current chargers controlled by nothing more than > a simple mechanical timer. > > I don't get the impression you can do any of that with lithium, though. I > was under the impression that it was much easier to overcharge lithium, and > that the consequences for battery life (if not for survival of the gear > itself) were more dire. Perhaps I've missed something here? > > Consumer electronics makers are notorious for cutting corners as much as > they can when it comes to charging batteries. They'll knock 75% off > battery > life to save 50 cents per unit. However, I haven't yet seen a lithium > battery product (save for the very cheapest junk, a crummy crank-charging > flashlight) which is as crudely and carelessly charged as, say, a lead > battery rechargeable lawn mower. My laptop battery has a BMS; so does the > lithium battery in my cordless drill. > > 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) > > -- David D. Nelson http://evalbum.com/1328 http://www.levforum.com Nokia Lumia 920 Windows Phone 8 -------------- next part -------------- An HTML attachment was scrubbed... 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