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)
