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discharge</title></head><body>
<div>At 09:34 -0800 19/1/10, Kent Osterberg wrote:</div>
<blockquote type="cite" cite><br>
The Peukert capacity equation gives a "pretty good" estimate
of the total amphours available at the present discharge current,
regardless of what the discharge current was in the past.</blockquote>
<div><br></div>
<div>In other words it tells you the 'capacity' at a particular load
current based on a fixed terminal voltage (end of discharge cut-off).
It does not tell you about all of the extra amphours you can still get
using a lower current and the same terminal voltage.</div>
<div><br></div>
<blockquote type="cite" cite> I certainly wouldn't want to treat
a set of batteries the way that Doerffel and Sharkh did.</blockquote>
<div><br></div>
<div>Nor me and it is a pity that the trials did not focus more on
partial discharge situations. But what's interesting is that
Peukert only works at constant discharge rates.</div>
<div><br></div>
<div>At 03:39 -0700 19/1/10, Warren Lauzon wrote:</div>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Calibri" size="-1">Some of
the loss is in heat due to internal resistance, and that cannot be
recovered.</font></blockquote>
<div><br></div>
<div>Of course. But in this debate we are discussing amphours
and the effect of rapid discharge on the amphours that a battery can
deliver. I was concerned to find out about missing amphours and
to estimate how many are lost and where they went. According to
Peukert (as it is normally interpreted) you lose big chunks of the
amphours capacity by rapidly discharging the battery. According
to the Doerffel and Sharkh data, only 5-10% of the amphours are lost
in a high discharge use of the battery. This is way less than
Peukert's law would predict.</div>
<div><br></div>
<div>At 10:45 -0500 19/1/10, Drake Chamberlin wrote:</div>
<blockquote type="cite" cite>What I think I understand is that if a
battery is discharged completely at a high discharge rate, a
significant number of amp hours will be lost due to heat and
inefficiency, and Peukert's equation will approximate the loss.
</blockquote>
<div><br></div>
<div>Most of the heat is due to the voltage loss. Some of it may
be due to the amphours loss. But in the end Peukert only tells
us how many amphours you can get at a fixed discharge rate and based
on a chosen terminal voltage. It does not actually tell you how
much of the battery capacity is used nor how much is still available
under conditions of slower discharge.</div>
<div><br></div>
<div>Naive use of Peukert over-estimates the DOD caused by high
discharge currents. Peukert can be correctly used to predict how
many amphours you can get from a battery at a constant charge rate
before it reaches a certain terminal voltage. It does not tell
you the SOC of a battery. This last is a very hard thing to
ascertain.</div>
<div><br></div>
<div>:-)</div>
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</pre></x-sigsep>
<div>Hugh Piggott<br>
<br>
Scoraig Wind Electric<br>
Scotland<br>
http://www.scoraigwind.co.uk</div>
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