Hello Bill If the state of charge is the same. Where did the energy come from that heats up some cells more then others. You added an equal amount of current to each cell in series. The cells with higher resistance are warmer and heat takes energy. If anyone knows how to get heat without using energy. Please let me know as I would like to heat my work shop. I have noticed that the higher the state of charge the greater the resistance reading increases. If you take a resistance reading at 50% SOC the differences between cells can be fairly close. Then when reaching a full charge resistance differences between cells increases. All my current EVs are older OEMs and regen is as high as 80 Amps. I believe what is happening is the regen with a pack in a higher state of charge is adding to the pack becoming unbalanced. By the way a while back I stated the A123 2.3AH cells did vary some. Your reply was to question where they came from. These cells were bought directly from A123. 10,000 cells to be exact through Steven Colello There was about a 1% drop out in these cells over a period of several years. Not that they were bad cells but their voltage was just slightly less then the other 99%. Over 3000 of these cells were stored under much warmer conditions and they varied a lot. Cells stored at 55 degrees at yearly average held their voltages for four years with very little change once the 1% was taken out. Don Blazer In a message dated 6/18/2013 12:23:53 P.M. Pacific Daylight Time, [email protected] writes:
Message: 7 Date: Mon, 17 Jun 2013 21:54:16 -0600 From: Bill Dube <[email protected]> To: Electric Vehicle Discussion List <[email protected]> Subject: Re: [EVDL] Resistance Message-ID: <[email protected]> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Intuition would make you think so, but your intuition turns out to be wrong in this case. Reread Lee Hart's post on this subject. He has it correct. All cells get/produce the same current because they are in series. The cells all are charged and discharged at the identical rate. Thus, have the identical state of charge. Any imbalance is caused by unequal self-discharge, which is a strongly influenced by temperature. The variations in temperature are indeed caused by variations in internal resistance. You can visualize that resistance as a separate resistor in series with the (ideal) cell. It does not influence the state of charge because the current is the same in all cells. It is the fact that the current is identical that is the key. All electrons that enter one end of the string emerge on the other end. None are lost. Each electron flips an ion in each cell. Whatever voltage is needed is what there _will_ be, or electron flow will stop. True fact. Bill Dube' -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130618/b3b0f8d3/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)
