With all due respect to Lee and his expertise in so many areas, I believe this is incorrect.
Lithium Ion has a nearly unity coulometric charge/discharge efficiency. Although high discharge rates depress the voltage more, and therefore cause your battery to reach "empty" sooner, you haven't actually depleted a greater number of amp-hours. 1.0 is the correct number if you want accurate SoC representation, particularly if you charge/discharge several partial cycles before you get to refill to full (and therefore 'synchronize' the link 10). A higher peukert number may help if you want to know roughly when you'll stop being able to deliver full current based on ESR, but it won't give you as accurate a picture of SoC if you aren't charging to full all the time. IMO, a better approach would be to simply get to know what your battery's ESR is at various temperatures and SoC. My 914 exhibits a nearly perfect 1:1 ratio of discharge/charge Ah. The only appreciable error seems to come from a 0.1A offset in the meter when the car sits for a couple days. I've also designed lithium ion battery systems for a number of commercial products. Finally, I point you to this paper to support my claims: http://qnova.ca/uploads/3/1/7/2/3172593/a_high_precision_study_of_the_coulombic_efficiency_of_li-ion_batteries.pdf It's the first result that comes up when you google search "lithium ion coulometric efficiency" -Ben On May 7, 2014, at 12:45 PM, Lee Hart <[email protected]> wrote: > Pestka, Dennis J wrote: >> I just completed a Lithium installation on my 65 Datsun. >> I'm resetting the parameters on my Link-10 E-Meter, and was curious what >> Puekert Exponent people were using. >> Based on what I've read, I was tempted to use 1.00, but wasn't sure if this >> was right. >> Have (50) 180 ah CALB CA series cells, nominal 160V, 28.8 Kw pack. > > It's definitely not 1.0. Any battery with an internal resistance greater than > zero will have a Peukert exponent greater than 1. > > Your best bet is to use the Link-10 to measure the actual capacity of the > pack at two different rates of discharge. There's an equation in the manual > to calculate the Peukert exponent from that data. > > -- > Ring the bells that still can ring > Forget your perfect offering > There is a crack in everything > That's how the light gets in. > -- Leonard Cohen, from "Anthem" > -- > Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.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)
