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)
