As you say David R. batteries such as Nicads and sla can take quite a bit of overcharging without significant harm, whereas LiFePO4 cannot. However, I think David N. is saying that if you simply don't charge LiFePO4 cells up close to fully charged, then you can use a simple charger. You just have to ensure it shuts off when the pack is less than say 90% charged. That is how many people set up chargers such as the Elcons. The CC to CV transition occurs below full charge and charging stops in CV mode when current decreases to 0.05C, which they set up to be at a pack voltage below full charge. This is fairly easy to do because the voltage on LiFePO4 cells starts to increase exponentially with Ah added as they get within a few Ah of full. This will ensure that the current decreases rapidly at that point, reaching 0.05C and terminating the charge.
Many choose to set it up to reach end of charge before that point by having the charger set up for lower CC/CV transition point. As some of us have said for several years now, life is simple with LiFePO4 if you just stay away from the ends of the charge/discharge curves. You need to set up your charger correctly, use an Ah counter (to avoid over-discharge), and use some type of monitor to keep an eye on individual cell voltages to do that repeatably and reliably. Most packs remain well enough balanced to avoid over-charging/discharging a cell as long as the charger is set up correctly and an Ah counter is used, but to be reliable they need to be monitored in case of an errant cell. This can be simple such as a monitor that compares half pack voltages (based on the Hart monitor), giving some indication of pack balance/imbalance, or more complex such as a digital bms with many functions. I think a bms is a good backup, in that the HVC and LVC functions will give further insurance that an individual cell is not over-charged/discharged. My experience over the last 3 1/2 years is that when set up properly the charger always terminates the charge, not the bms, and I terminate the discharge due to a warning from my Ah counter, not the bms. -- View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/100ah-pack-on-the-cheap-tp4663470p4663547.html Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com. _______________________________________________ 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)
