Hi Mark, I did my last balance on 7/12/11 and on my last check on 12/03/12 they were still in balance. The 7/12/11 difference between the extreme cells was 0.021V and the at the 12/03/12 check they were at 0.024V. The largest difference was on 6/5/12 with a difference of 0.047V. As of 12/3/12 the pack has delivered a little over 14,951Ah over the course of 6654 miles. I say a little over because I have regen which constitutes a 2-4% "savings." The pack has delivered about 33,480Ah in its life. This is a 200Ah pack made up of 40 TS-LFP100AAHA cells in a 2p20s arrangement. The whole pack is in one box so the cell temps are quite similar to each other. I haven't noticed any patterns that I can correlate to position in the pack. The "low" and "high" cells generally stay with a small group with a little swapping around.
HTH, On Wed, Dec 26, 2012 at 5:24 AM, Mark Hanson <[email protected]> wrote: > > Hi David etc,How many miles are you driving a week/month? I saw this out of > balance condition after 7k miles or 7 months (350 miles per week). My BMS > leakage is about 3ma & I'll check the low one's #12 & 13 that show up on the > battery scanner as lower than the rest at EOC and EOD. The BMS tested ok on > the bench at min (2.6V) and max (3.6V) operation. the cell that went down to > .9V now appears OK after charging back up with a Triton charger and measuring > the discharge Ah at 125ah on the 130ah cell.Have a renewable energy New > Year,Mark www.REEVA.info Subject: [EVDL] LiFePO4 batts drifting out of > balance *with* balancer > Message-ID: <[email protected]> > Content-Type: text/plain; charset="iso-8859-1" > > > Hi Cor etc, > > I increased the final taper to 2A. (They {36ea CALB 130ah} drifted out in 7k > miles in 5 months.) I checked the cell that sagged to .9V on the Triton > charger, by charging to 3.6V then discharging and got 125ah out of it so I > charged it up again, seams fine. > > With the final taper set to 2A all the cells appear to be coming up when two > hours match at dv/dt=0 (.o1V per cell per hour = stop), like previous EV's, > lead, ni-cad, now LiFePO4. The balancers (see www.evdl.org/lib/mh ) signal > the charger to drop from 10A charging current to 1 or 2 amps (selectable) > when any one cell hits 3.6V or bulk charge hits 127V on 36 cells. If any one > cell hits 4.0V or drops below 2.6V the charger is shut off and displayed what > the malfunction is. Fortunately the battery scanner caught the low cell going > up the hill. > > So having a stiffer final charge current during final taper seams to solve > the problem (in the 9 hours I'm at work or at home). Before I would unplug it > (120vac) before it was done tapering. I had a 4A taper when I had a ni-cad > car and previously lead cars back to the 70's. Due to all the balancers/with > low current shunting capacity I had to lower the final taper - but then it > takes *much* longer to taper. Anyway, 2A appears ok, I'll see in the next 7k > miles in a few months. (350 miles per week, 70 per day Mon-Fri). Usyually > only do 30 miles per day on week-ends. > > Have a renewable energy Christmas, > Mark in Roanoke, VA > www.reeva.info > > ..> Message: 2 >> Date: Thu, 20 Dec 2012 13:26:33 -0800 >> From: "Cor van de Water" <[email protected]> >> To: "Electric Vehicle Discussion List" <[email protected]> >> Subject: Re: [EVDL] FW: LiFePO4 Calb cells drifting out of balance >> *with* 1Abalancer >> Message-ID: >> <a73bc4b8b3218642a56a2c9eb01b44e001a36...@exchange.corp.proxim.com> >> Content-Type: text/plain; charset="us-ascii" >> >> Mark, >> >> It may not be the current, but the charge algorithm. >> What is the condition to stop charging? >> Only if *all* cells report that they are up to 3.6V? >> Or is the charger stopped at a certain voltage level? >> If one cell is self-discharging more than most other cells, >> the pack voltage when all other cells except this one is >> 3.6 might be enough to kick the charger off, even though this >> one lagging cell is still around 3.0V - it could be almost empty >> while the charging thinks everything is OK. >> This is not a problem of the BMS, unless the BMS is controlling the >> charger to do this, but I expect that the charger continues to >> charge at below 1A until the *last* cell starts shunting. >> Anything short of that (and it sounds that either the charger >> voltage was set too low or the charger switch off voltage threshold >> was too low) and you will find the highest self-discharging cell >> the hard way - when it suddenly hits zero because it is not fully >> topped up every cycle.... >> >> Regards, >> >> Cor van de Water >> Chief Scientist >> Proxim Wireless Corporation http://www.proxim.com >> Email: [email protected] Private: http://www.cvandewater.info >> Skype: cor_van_de_water Tel: +1 408 383 7626 >> > > Mark, > > I'm seeing nothing of the sort you are seeing with LiFePO4 cells going > out of balance. I'm also not the only one who isn't seeing any drift > with the prismatic LiFePO4 cells (TS or CALB). Either you have a bad > cell or something external to the cell is draining it more than the > rest. There is no internal self-discharge mechanism in a LiFePO4 cell > so if it is self discharging then it has a problem. > > Do you have any way to measure the drain your BMS is causing on each > individual cell to see if that one is getting drained more than the > rest? I'm afraid that changing the tapering current is just a band-aid > covering up an underlying problem. > > -- > David D. Nelson > http://evalbum.com/1328 > http://2003gizmo.blogspot.com > http://www.levforum.com > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20121226/8a636e3b/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) > -- David D. Nelson http://evalbum.com/1328 http://2003gizmo.blogspot.com http://www.levforum.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)
