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
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