Regarding a discharge load ... a 10 ft length of #8 steel fence wire rolled into a coil and submerged in water in a 20 gal. metal trash can makes a good one, and it is more compact than 20 feet of re-bar...
*Dennis Lee Miles * *E.V.T.I. Inc.* *Director/Chief Technology Officer:* *E-Mail:* *[email protected]* <[email protected]> *Phone #* *(863) 944-9913* * Office:* 33408 Trilby Road, Dade City, Florida 33523-6435 USA On Sat, Mar 8, 2014 at 11:11 AM, Michael Ross <[email protected]>wrote: > Marcus, > > A reasonable question. For LFP I think you want to go lower like 1.5V > maybe. I think a lot of the historically acceptable target voltages are > arbitrary (adopting a RIckard opinion). 1.5V might even be higher than > necessary. 1.5V is perhaps a reasonable cut off voltage for a bottom > balanced LFP pack. I don't think there is anything definitive about this. > > Voltage being such a crappy surrogate for State Of Charge you definitely > want to be far away from the flat part of the V/SOC curve where small > changes in V are large changes in SOC. Around 1.5V there a la much greater > change in V for a small change in SOC. > > When BB'ing you want a low open circuit voltage....the way I have seen it > done, the cell is loaded down, and at a target voltage the load is lifted, > the voltage recovers, the load is added, the load is lifted, again and > again until the voltage settles where you want it and the recovery is very > small. Best to automate this if you can. You can throw a 20 foot rebar > out on the sand and run 1000A through it if that works for the cell in > question and the C rate you desire. > > I think if you put two cells in parallel, and you run them to a low target, > you have the same old issue that BB'ing is trying to cure maybe? If one > cell goes empty before the other , the other cell has significant charge > left in it, then a loop gets going between them lots of current flows > backwards through the empty cell and one or both of them are cooked. > > I think. FWTW > > > > > On Sat, Mar 8, 2014 at 7:04 AM, Marcus Reddish <[email protected] > >wrote: > > > Am I crazy or could bottom balancing be done at 3V with all the cells in > > parallel? They will all be perfectly balanced together at 2.75V or > > whatever you chose. Use a JLD and contactor with a resistive load to get > > down to the target voltage. Reconnect them in series and charge. > > > > Please note that hooking them in parallel for balancing would only work > at > > the extremes (low for BB, high for TB). If you hook them in parallel at > > half full (3.2v) they won't be balanced at either extreme. Obviously, > this > > only would work for groups of individual cells, not pre-made modules. > Are > > there any issues with this approach? > > > > > > On Fri, Mar 7, 2014 at 1:36 PM, Michael Ross <[email protected] > > >wrote: > > > > > There is a real possibility that BB'ing saves you more than you put > into > > > it, but this is pretty speculative. > > > > > > There are hidden costs too - I have to come up with a resistive load > than > > > can dump significant amps (rebar and an 200Ohm wire wound). Some > people > > > just jack up the vehicle and spin it, but that is unappealing to me > when > > I > > > can always use an excuse to weld something. You need contactors, and > > > JLD404s and shunts, stuff like that. Once you have it you can do more > > > packs. The tools are general purpose. > > > > > > I investigated DIY BMS and this all seemed easier. > > > > > > > > > > > > > > > > > > On Fri, Mar 7, 2014 at 3:06 PM, EVDL Administrator <[email protected]> > > > wrote: > > > > > > > On 7 Mar 2014 at 3:08, Michael Ross wrote: > > > > > > > > > So there is an appeal to bottom balancing in terms of life, cost > > > > > (ignoring labor, but we are DIY'ing so that is ignored always), and > > > > > ease of use. > > > > > > > > I see your point, but I don't agree that DIY labor cost is "ignored > > > > always." > > > > OK, it's not like I'm paying a mechanic, but every hour I spend under > > the > > > > hood or under the car is an hour I don't have for other things I like > > > doing > > > > just as much or more. > > > > > > > > But hey - if you have the time and you enjoy it, why not try? > > > > > > > > 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) > > > > > > > > > > > > > > > > > -- > > > Put this question to yourself: should I use everyone else to attain > > > happiness, or should I help others gain happiness? > > > *Dalai Lama * > > > > > > Tell me what it is you plan to do > > > With your one wild and precious life? > > > Mary Oliver, "The summer day." > > > > > > To invent, you need a good imagination and a pile of junk. > > > Thomas A. Edison< > > > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> > > > > > > A public-opinion poll is no substitute for thought. > > > *Warren Buffet* > > > > > > Michael E. Ross > > > (919) 550-2430 Land > > > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google > > > Phone > > > (919) 631-1451 Cell > > > (919) 513-0418 Desk > > > > > > [email protected] > > > <[email protected]> > > > -------------- next part -------------- > > > An HTML attachment was scrubbed... > > > URL: < > > > > > > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140307/5fa24547/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) > > > > > > > > > > > > -- > > Marcus Reddish > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: < > > > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140308/fba10f4c/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) > > > > > > > -- > Put this question to yourself: should I use everyone else to attain > happiness, or should I help others gain happiness? > *Dalai Lama * > > Tell me what it is you plan to do > With your one wild and precious life? > Mary Oliver, "The summer day." > > To invent, you need a good imagination and a pile of junk. > Thomas A. Edison< > http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> > > A public-opinion poll is no substitute for thought. > *Warren Buffet* > > Michael E. Ross > (919) 550-2430 Land > (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google > Phone > (919) 631-1451 Cell > (919) 513-0418 Desk > > [email protected] > <[email protected]> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140308/13a27b04/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) > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140308/8cf66fae/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)
