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/bb9c2e30/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)
