Since the cells might not be perfectly balanced, I would expect that when one cell dips to 2V, you can expect the others still to be around 3V, so I guess that it would be prudent to disconnect when the voltage dips to 11V (3x3+2)
BTW, I did not suggest to float-charge the cells at 3.45V indefinitely, since no car is running 24/7. Typically a car is used a short period, sometimes a few hours, and then shut down, from which moment the battery is slowly discharged until the car has been started again. I believe the highest current in a (ICE) car is starting cold. That can run close to 1000A peak. Because AFAIK most alternators are in the 100A region, but it is certainly good to check for max charging current and adjust for it. NOTE that the net charging current is the difference between the alternator's generated current and the consumption of the car. Regards, Cor van de Water Chief Scientist Proxim Wireless Corporation http://www.proxim.com Email: [email protected] Private: http://www.cvandewater.com Skype: cor_van_de_water XoIP: +31877841130 Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 -----Original Message----- From: [email protected] on behalf of Jerry Yue Sent: Fri 2/15/2013 11:56 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] 12V LiFePO4 batteries Generally, the low voltage is set as 2.0V/cell or 8.0V/pack for high power LFP and 2.5V/cell or 10.0V/pack for energy type LFP. Since we're using the lithium batteries for ourselves, so you can measure the voltages of the cells periodically. I have only one suggestion that, you'd better measure the charging current from your alternator and be sure that your lithium battery is capable for taking that current. Generally, the peak charging current ranges from 200A-500A. Ideally, choose a LFP battery with 1/3 or 1/4 of the original lead acid battery. Of course, if you like to consume too much electricity when engine is off, you'd better use bigger LFP battery. Jerry On Fri, Feb 15, 2013 at 2:12 PM, Bruce EVangel Parmenter < [email protected]> wrote: > Thanks Jerry for your response. > Now, there are Low Voltage Disconnect circuits that I could add that > would break the circuit at a set voltage. But the disconnect voltage on > most of them are likely set for use with PbSO4 batteries. > > -What voltage would be a good disconnect voltage set point for that 12V > Li-ion drop in battery? What voltage would prevent draining the Li-ion > battery too low causing damage? > > > {brucedp.150m.com} > > > - > On Thu, Feb 14, 2013, at 09:38 PM, Jerry Yue wrote: > > Sure, it will be ok to use the lithium battery on your car. I used a 12V > > lithium battery without bms on a SUV in 2008. It lasted half an year > > before > > it failed due to two times of over-discharge (I forgot to close > > headlamps). > > > > On Fri, Feb 15, 2013 at 1:32 PM, Bruce EVangel Parmenter < > > [email protected]> wrote: > > > > > Ah Ha! That is what I saw in the back of the J.B. Straubel's Porsche > > > conversion when I followed him using his pusher trailer to his home > > > (many years ago). The pack just behind the front seats and had little > > > light dimly lights between the cells. So, that was the BMS he used in > > > his EV conversion design ... neat! > > > > > > ... > > > OK, no one has posted about one of my queries as to if the prepackaged > > > 12V Li-ion battery that would drop as a replacement to my dying 12V > > > group-24 deep cycle. So, I will assume there is no problem trying one. > > > > > > > > > {brucedp.150m.com} > - > > -- > http://www.fastmail.fm - Or how I learned to stop worrying and > love email again > > _______________________________________________ > 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/20130215/140fab23/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)
