The Peukert effect is there and while the final discharge (0%) capacity
is very similar, Yes the effect under these conditions is about 1.05 as
you say. However the discharge curves for different discharge rate are
quite different in shape and this in combination with BMS can cause the
Peukert effect to apparently increase.
The cutoff point on most BMS to prevent a 0% discharge happens earlier
with higher drain currents. The resulting capacity reduction can be as
much as 20-30% depending on the individual cell. Battery University and
Richtek.com have the curves which show this. If there was no BMS to
protect the battery then this would not happen but the downside is the
potential damage to the cell.
On 15/03/2019 03:27, Bill Dube via EV wrote:
Diffusion rates are vastly less in Li-Ion. Thus, Puekert exponents are
very near unity (1.0).
Yes, there is some tiny effect, but no, the Puekert equation is not
really applicable.
The one hour capacity is essentially the same as the 20 hour capacity
in Li-Ion.
Bill D.
On 3/15/2019 3:19 PM, Lee Hart via EV 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.
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