Bingo You got it. The energy stored in cell has been reduced by losing some of the energy as heat. Mostly upon discharge because the loads are higher but also when charging. Since resistance changes by the state of charge so does the amount of energy lost. Its why I recommend if possible to keep the SOC of the pack 40% to 80%. If your charging above 90% there is higher resistance and more heat. The cells that have the highest resistance lose more energy as heat which in turn causes them to have a shorter service life. If you deeply discharge a pack to where it is in a lower state of charge. Resistance again increases as the state of charge drops. The energy lost as heat is greater in cells with the highest resistance. So both by charging or discharging. Your loses are greater when you push cells to their limits as the resistance increases. Since resistance varies cell to cell under best case conditions. When pushed to their limits these differences between cells also increase and have a greater impact. Don Blazer In a message dated 6/14/2013 9:59:43 P.M. Pacific Daylight Time, [email protected] writes:
Date: Fri, 14 Jun 2013 22:57:43 -0400 From: "Al" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Subject: Re: [EVDL] Resistance Jack Rickard of EVTV.me Message-ID: <00a701ce6974$1bcff760$4101a8c0@alkb2ayu> Content-Type: text/plain; format=flowed; charset=iso-8859-1; reply-type=original That doesn't sound right. Wouldn't the cell with the higer resistance lose some of the Ah as heat? Al ----- Original Message ----- From: "Peter Gabrielsson" <[email protected]> To: "Electric Vehicle Discussion List" <[email protected]> Sent: Friday, June 14, 2013 10:22 PM Subject: Re: [EVDL] Resistance Jack Rickard of EVTV.me > While I agree that resistance is important you are unfortunately not > really > correct that it causes imbalance due to energy loss in series strings. > > Batteries are primarily electron storage devices, that's why their > capacity > is measured in Ah (1Ah= 5767*10^19 electrons). In a series string the > amount of electrons you shove through each battery is always the same > regardless of resistance. If you put 5Ah into a string of two empty 10Ah > cells they will both end up at exactly 50% SOC even if one has 1000 times > the resistance of the other. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130617/42e29a64/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)
