Hi David and All, While a good BMS could be nice, their quality, price at this stage leaves a lot to be desired. What makes quality lithium, Volt modules in my case, possible to not need a cell BMS it seems is their tight specs. And BMS introduce failure points themselves.
One can avoid most of the problems simply by controlling charging, discharge to safe levels like 10% and 95% once they are all balanced. Since my cells are all within 1/100th of a volt 4 yrs old and sitting for a yr+, I'm betting they are balanced and will stay that way with a little care.. Done with a Lightobject wthr meter that turns off the charger and off the controller if too low built in, to monitoring charge state, voltage, amps, etc too. Add to that multiple Lee Hart Batt Bridges and maybe Lee's diode array he recently mentioned. Though I might go the meter route Batt bridge to detect much smaller cell offsets. I'd like even .25vdc change be noted so any problem that is just starting to develop can be caught early.. And regularly, say 1/month once taking the pack down to see which cell goes first, then check voltage of all and balance if needed. MPJA electronics has an interesting 8 cell voltage monitor, alarm meter designed for E Bikes, model planes, drones would work well for this? At the present this seems to me to be the best, safest, lowest cost lithium battery system for someone comfortable around EV's, electricity at $220/kwhr system cost. It would be $300-350kwhr with many of the present good BMS out there. I can't afford that if not needed. And it doesn't seem needed for me. Jerry Dycus From: EVDL Administrator via EV <[email protected]> To: Electric Vehicle Discussion List <[email protected]> Sent: Sunday, June 28, 2015 5:44 PM Subject: Re: [EVDL] Good data or bad? How do you know? Or is it the interpretation? I find these chatty video presentations annoying. I'd rather read. But I sat through this one, and got a few bits of useful info out of it. 1. You need a BMS that properly prevents over-discharge. Hardy murdered six 2000-cycle Headway LiFePO4 cells in 226 cycles (~11% of rated life) because his test gear didn't properly shut down the entire load (including its own) when the first cell dropped below 2 volts. 2. A simple standalone shunt regulator board might be no better, or even worse, than no BMS at all. This is especially likely to be the case if you're cycling your cells in open air in your house or garage, where they're all the same temperature; instead of in an EV's battery, where they aren't. 3. It's probably not a great idea to go on a trip and leave your battery test jig running unsupervised for days or weeks. 4. I see why they call this "EVTV." It's a lot like television, and not at all like peer-reviewed publications. 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) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150629/7145325c/attachment.htm> _______________________________________________ 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)
