Wow lots of great info. So I guess the counteraction of temp rise & voltage compensates for any losses from Peukert's equation in Lithium under normal operating conditions. I suspect the equation is still applicable to Lithium but at much higher draws, far past the C rating i.e. the battery will eventually lose more energy to heating than it can compensate with voltage rise. Of course that heat will destroy the battery so staying inside the C rating will avoid damage and Peukert effect? As suggested I have decided to do as close to real world loads and will do as close to the amperage my boat typically draws, 100amps @ 48v. Where as I may be testing with a smaller set of battery (don't want to order the whole lot and get 100% ripped off if they are garbage) I may reduce the load to what it would see with a full pack and not exceed the stated C rating (if I go with 2 x 48v 100ah packs, each pack would only see a 50 amp draw)
The concern on Alibaba battery quality had me double think this yesterday and I dug through the web trying to find a reasonably priced alternative. There is an aftermarket GM parts company called GMpartsdepot Canada, they sell a refurbished 2013 volt pack online for 2400 dollars CAD. It didn't say anything about a core return so I inquired to confirm. Apparently it didn't matter, they won't sell it to me without going through a dealer, bummer. On Fri, Mar 15, 2019 at 9:56 AM paul dove via EV <[email protected]> wrote: > Peukert's law was developed for Lead-Acid batteries, and works well in > that application. > > It does not necessarily apply to other battery chemistries, especially > Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid > discharge, and the Nernst Equation predicts battery voltage will increase > with temperature. Thus, the effect of increased resistance is offset by the > self-heating effect. This advantage of Lithium-Ion batteries is a > well-known advertised feature. In a research paper, a 50Ah lithium-ion > battery tested was found to give about the same capacity at 5A and 50A; > this was attributed to possible Peukert loss in capacity being countered by > the increase in capacity due to the 30◦C temperature rise due to > self-heating, with the conclusion that the Peukert equation is not > applicable. > > > https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp > > Sent from my iPhone > > > On Mar 14, 2019, at 10:19 PM, Lee Hart via EV <[email protected]> wrote: > > > > Michael Ross via EV wrote: > >> I am not sure about previous discussions and you may know this: > Peukert's > >> Law is not applicable to Li ion cells in any way. It only relates to > lead > >> acid cells. > > > > I agree with the rest of what you said, but not with this. Peukert's law > says nothing about the chemistry involved; it applies to *all* types of > batteries and all chemistries. > > > > Peukert's equation applies to any battery or cell that has internal > resistance, and that has a minimum "cutoff" voltage below which it is > harmed. It simply states that the higher the load current, the lower the > apparent amphour capacity. High currents cause a larger voltage drop, so > you reach the "cutoff" voltage before the cell is truly dead. > > > > The amphours are not "missing"; you just can't get them without reducing > the load current, or pulling its voltage below the safe minimum. If you're > willing to shorten the life of the cell, you can still get it. > > > > Peukert matters more for lead-acids because they typically have a higher > internal resistance. In particular, lead-acid internal resistance goes up a > lot as the cell approaches dead. Most other chemistries do not have this > large change in internal resistance as a function of state of charge. > > > > -- > > Any intelligent fool can make things bigger, more complex, and more > > violent. It takes a touch of genius, and a lot of courage, to move > > in the opposite direction. -- Albert Einstein > > -- > > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com > > _______________________________________________ > > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > > Please discuss EV drag racing at 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/20190315/23251fe5/attachment.html > > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > Please discuss EV drag racing at 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/20190315/10d66668/attachment.html> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
