I've been driving mine for years and several hours after charge the voltage is exactly the same. Like you said self discharge till you reach OCV.
Sent from my iPhone > On May 28, 2015, at 1:01 PM, Cor van de Water via EV <ev@lists.evdl.org> > wrote: > > Nope, > I have a little experience with charging older style Li-Ion batteries > by hand and the resting voltage is typically a rather fixed amount (delta) > below the charging voltage, > no matter how high you charged them. > If you charge to 3.8V then they rest at say 3.65 > If you charge to 4.0 then they rest at 3.85 > If you charge to the max recommended 4.25 edge then they rest at 4.1 > If you overcharge to 4.5 then they rest at 4.35 (they will self-discharge > faster but not immediately) > > So, from measuring the rest voltage it is not clear that they are balanced - > you really need to measure each cell to make sure, > that is why a BMS is important. > > BTW, the only thing that I found different between charging and resting > voltage was > the indication of a bad cell with high resistance, but even those were pretty > consistent in just a slight larger delta between charge and rest. > Hope this clarifies, > > Cor van de Water > Chief Scientist > Proxim Wireless > > office +1 408 383 7626 Skype: cor_van_de_water > XoIP +31 87 784 1130 private: cvandewater.info > www.proxim.com > > > This email message (including any attachments) contains confidential and > proprietary information of Proxim Wireless Corporation. If you received this > message in error, please delete it and notify the sender. Any unauthorized > use, disclosure, distribution, or copying of any part of this message is > prohibited. > > > -----Original Message----- > From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV > Sent: Thursday, May 28, 2015 10:54 AM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] FW: On the road again. > > I disagree. > > Assuming by your example the OCV of the cell is 3.8v and one charges to 4v. > > After cycle 1 the OCV will be 22.8v > After cycle 2 the OCV will be 19v > After cycle 3 the OCV will be 19v > Etc. > > One can tell if there is a bad cell immediately after every charge because > the OCV will be lower. > > Sent from my iPhone > >> On May 28, 2015, at 12:44 PM, Lawrence Harris via EV <ev@lists.evdl.org> >> wrote: >> >> Just remember to check each cell periodically to ensure they are staying >> together. If one cell is weak it will drift down each cycle and eventually >> you will overcharge the good ones and destroy the weak one (this is where >> fires come from). >> >> A little exaggerated perhaps but this is what happens, maybe not exactly >> cycle by cycle but over time. Your charger is set to chart to 24v and then >> cut back. >> >> cycle 1: 6 x 4v = 24v >> cycle 2: 5 x 4.1 + 3.5v = 24v >> cycle 3: 5 x 4.2 + 3.0v = 24v >> cycle 4: 5 x 4.3 + 2.5 = 24v >> : >> >> eventually the good ones are being charged over their max values and the >> weak one is being pushed towards zero or negative at the end of each >> discharge cycle. Now we get heat and overpressure and poof! >> >> Lawrence >> >>> On May 28, 2015, at 10:18 AM, damon henry via EV <ev@lists.evdl.org> wrote: >>> >>> Thanks David... >>> for pointing out the forgetfulness factor. Been there, done that. There >>> are a couple of fairly simple solutions to that particular problem. First, >>> a charger that is set at a low enough voltage to limit that danger. So far >>> it has been my experience with this pack that there is not enough of a >>> voltage rise to set a dumb charger up for this function, but I am >>> considering getting a smart charger that will do constant current to a >>> specific voltage then shut off. Another easy solution is a mechanical >>> timer. I have an e-meter on the motorcycle so I know how much energy I >>> have taken out. That makes it pretty easy to set a timer as a fail-safe. >>> I think my e-meter may even have an alarm function that I could use to shut >>> the charger off. >>> I thought the joke about the tarp was clever :) Finally, as Cor >>> pointed out, it is my motorcycle which has the 3.4kwh pack on it now. >>> Since I have not done lithium before I brought out the old test mule from >>> under the tarp so that if I do learn from the school of hard knocks, as is >>> often the case, I will be well educated before investing in a much more >>> expensive lithium for my truck. I don't believe I will do the lithium >>> without a BMS, but that is a decision for some future time. >>> I have two normal scenarios. MWF - round trip to the gym and back 10 >>> miles - opportunity charge for an hour while I get ready for work then 8 >>> miles to the office where I have the full day to charge if I like. Then >>> back home 8 miles. The other two days of the week I do not do the gym >>> first, so overall this pack is getting very light duty. In fact, I think >>> the hardest thing for me to get used to is not fully charging it. I'm so >>> used to charging as much as I can whenever I can that it is a hard habit to >>> break. In this case though, why get close to the danger points? Bad >>> things usually happen to batteries when they are nearing full or empty. >>> Keeping them away from those danger zones makes a lot of sense. The most >>> stress I am likely to put on them will be if I go to visit my good friend >>> John Wayland who lives 17 miles of mostly freeway from me. It's no problem >>> picking up a charge at his house before I head back home, though, so even >>> that should not be too bad. >>> damon >>> >>>> To: ev@lists.evdl.org >>>> Date: Wed, 27 May 2015 15:52:20 -0400 >>>> Subject: Re: [EVDL] On the road again. >>>> From: ev@lists.evdl.org >>>> >>>>> On 27 May 2015 at 9:23, damon henry via EV wrote: >>>>> >>>>> After 5 years under the tarp, I put my EV motorcycle back on the >>>>> road this week. >>>> >>>> You must have been awfully bored, living under that tarp for all >>>> those years! ;-) >>>> >>>>> I purchased 16 Calb CA60ah cells which fit well in my existing >>>>> battery boxes. >>>> >>>> So if my math is right, ~3.4 kWh. That's the equivalent of about >>>> four T-125 golf car batteries (useful capacity 900Wh each). I'm >>>> thinking this is going to be a short-range truck, and probably >>>> short-lived batteries from working so hard. >>>> >>>>> I do not have any BMS installed, but on such a small pack with good >>>>> access it is easy to be my own BMS >>>> >>>> As long as you don't get busy with something else and forget. I >>>> know of a guy around here who destroyed an entire set of rare and >>>> expensive Saft STM5- >>>> 180 NiCd batteries when he forgot he was charging them. >>>> >>>> I wouldn't even do an E-bike lithium battery without a BMS. But >>>> that's me, and I know how forgetful I can be! >>>> >>>> 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/20150528/b >>> b9c2e30/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) >> >> _______________________________________________ >> 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) >> > _______________________________________________ > 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) > > _______________________________________________ > 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) > _______________________________________________ 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)
