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batteries</title></head><body>
<div>Hi Jamie,</div>
<div><br></div>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Remember, as
batteries cool actual capacity is reduced, so if 200AH is 50% @ 25C it
is significantly more than 50% @ 5C. Thus, you are
discharging more deeply.</font></blockquote>
<div><br></div>
<div>But earlier you put it this way:</div>
<div><br></div>
<blockquote type="cite" cite>
<blockquote type="cite" cite><font face="Lucida Grande">Regarding
temperature effects on capacity, earlier responses are spot on as the
lower capacity is totally as a result of slower reaction times as a
result of lower temperatures. </font></blockquote>
</blockquote>
<div><br></div>
<div>There is an issue here that I need to understand better.
You state that a battery has lower capacity in low temperatures.
Suppose you take a fully charged, 400 Ah battery and cool it down to
-5 degrees C where according to our numbers it will only have 80% of
its nominal capacity. You then remove 160 Ah (say 10 amps for 16
hours). It will then be 50% discharged. Now warm it up
again to 20 degrees or whatever. My question is: will you only
have 200 amphours left in it now? And if so, what happened to
the other 40 amphours? Does low temperature operation actually
lose amphours, or is it just more sluggish? What is the chemical
explanation for the lost amphours?</div>
<div><br></div>
<div>I understand batteries as a chemical process of converting
amphours into chemical changes. I assume that a given amount of
electrical charge converts a given amount of lead into lead sulphate
(and likewise) back again. I understand that cooling will make
this process less efficient and thereby result in a rise in charging
voltage and a drop in discharging voltage. But does a low
temperature actually mean that a given amount of lead being converted
to sulphate actually give you less amphours electrically?</div>
<div><br></div>
<div>(I have similar questions in relation to Peukert's equation where
high discharge rates impact on the amphour capacity. The
capacity apparently 'recovers' when the discharge rate is reduced.
To what extent is the capacity actually lost by using high discharge
rates and to what extent is it just a voltage effect that impacts on
the terminal voltage, rather than the actual chemical state of the
battery?)</div>
<div><br></div>
<div>I hope you can follow my descriptions.</div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div>Hugh Piggott<br>
<br>
Scoraig Wind Electric<br>
Scotland<br>
http://www.scoraigwind.co.uk</div>
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