Hello David The statement by Jack as I recall was this. That LiFePo4 cells resistance, because it is so low, resistance is no longer relevant. I very strongly disagree. I believe the lower the battery resistance, it can even cause a greater the impact. While resistance readings on LiFePo4 cells, is much lower then many other chemistries, battery resistance is always relevant. I have been measuring resistance readings for years and consider it critical information. Under a load, cells with less resistance hold a higher voltage. During charging, the cells with lower resistance will have a lower voltage. This is nothing new and known by almost everyone on this list. Energy moves in and out of LiFePo4 with far less resistance. Since LiFePo4 can have up to 1/20 resistance or even less compared to new lead or NiMH battery. At first take it would seem reasonable to assume with resistance being so low, its just that much less of a factor over prior battery chemistries. Seems logical at first, lower resistance should mean less loss of energy to heat in the battery, so this should have all around less impact.
However there is an error, in assuming with these very low loses, resistance is no longer anymore a concern. As good as the CALB cells are, the resistance readings do vary. When you compare cell to cell, in a pack of 50 or 100 cells of LiFePo4, between the lowest and highest resistance can be almost 100% off from one another. Since cells are being charged in series, these losses as small as they are, impact the amount of the energy remaining in each cell. Over time these small differences change the SOC of the cells, and throw the pack out of balance. If you have 100% differences in resistance readings in a lead or NiMH pack it would quickly become a noticeable problem. Just because it may not be immediately noticeable, does not mean that slight differences no longer have an impact. The CALB cells come with test sheets showing both capacity and resistance readings. Overseeing these group buys I have looked at many thousands of the CALB CA gray cells. Compared to lead or NiMH yes they are extremely low. I believe the CALB cells are the best value for the money. If resistance readings were all exactly the same when new, and during service then none of the above would apply. However in the real world where nothing is perfect, any differences between cells used in series regardless of how minor will always lead to a pack becoming out of balance. Your losses in moving energy both in and out is far less with LiFePo4, but compared cell to cell the percentage of difference is even greater then lead or NiMH. Resistance readings can change a lot with temperature, SOC and cycle life. Resistance readings are very useful information. However they can be frustrating at times because its a moving target. If your assembling a pack they all have to be very close to the same SOC and temperature. I don't claim to be an expert or know it all. However to say that resistance is no longer a concern in batteries, shows a clear lack of completely understanding batteries and losses used in series. David hope I gave enough context here to address your reply "makes my statement not correct 100% of the time." I have tried to watch three of Jack's Video's and three times he made a comment that I could hardly believe he said. This resistance statement just happen to be the last one I tried to watch. I appreciate Jack's or anyone else's testing batteries. However it would be better to keep random thoughts not based on real data out of them. There is so much misinformation around in general about electric vehicles and its not just EVTV. Its sad to have someone misinform others looking to learn about EVs. I have tried to watched three of Jack's video's and each time he made a comment that was ridiculous. I don't think I have made it more then half way through before I could no longer listen to nonsense ramblings. Don Blazer In a message dated 6/13/2013 7:38:22 A.M. Pacific Daylight Time, [email protected] writes: Message: 7 Date: Wed, 12 Jun 2013 22:38:50 -0700 From: David Nelson <[email protected]> To: Electric Vehicle Discussion List <[email protected]> Subject: Re: [EVDL] Jack Rickard of EVTV.me was 100ah pack on the cheap Message-ID: <calxn3-i_oex_ejua8wwvh95zlqlqhyh-yzq_vf9hubsvj-q...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Don, You gave no context to the statement you said that Jack said so that makes your statement also not correct 100% of the time. Depending on the context, resistance in an electrical circuit/system may or may not be a factor. I know what you mean about lack of sufficient support for some of Jack's statements. Like I said, however, many of them which apparently had not enough basis have over several weeks/months/years been finally supported but I would expect that a significant number of people miss it and then just write off practically everything he says. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20130614/4ef6ae6a/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)
