I had one cell go bad early on and I knew it the first day because my voltage was lower the next morning after charging.
Sent from my iPhone > On May 28, 2015, at 1:09 PM, Paul Dove via EV <ev@lists.evdl.org> wrote: > > 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) > _______________________________________________ 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)
