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 <ev@lists.evdl.org> 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 <ev@lists.evdl.org> 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)

Reply via email to