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--></style><title>Re: [RE-wrenches] discharging Rolls
batteries</title></head><body>
<div>Thanks, Bruce,</div>
<div><br></div>
<div>I have lived with batteries for thirty years so I do know some of
the basic things but for most of that time I used secondhand
batteries. The last couple of years using expensive new ones I
find that they often perform less well. I would like to tap into
the enormous experience of this forum to calibrate some of my
assumptions. </div>
<div><br></div>
<div>I got a nice speedy and informative reply to my first post but
when I asked too many questions in the second one it produced a lot
less information. Maybe I need to go straight to Rolls tech
support for discharge curves at lower temperatures and lower
currents.</div>
<div><br></div>
<div>I do have one more question for any wrench who programs
'genstart' voltages on Outbacks and the like. At what battery
volts do you start the generator for a system with a large battery and
small loads, in the winter? </div>
<div><br></div>
<div>I would habitually use about 23.5 or 47 volts as a discharge
limit voltage (time delayed). However I am finding that from
full charge at a temperature around 5 degrees C, I am getting under
25% of the battery capacity using this rule. I this what I have
to accept? Is the capacity that much reduced by temperature?
Will I reduce the life expectancy and invalidate the warranty if I
discharge it to 23/46 volts instead? </div>
<div><br></div>
<div>I wonder why there is no temperature compensation on low battery
voltage settings like there is on charging set points. Do I just
have to use the generator much more?</div>
<div><br></div>
<div>There I go asking too many questions again. I do have a few
more that I will save for now. Thanks for any more
comments.</div>
<div><br></div>
<div>best wishes</div>
<div><br></div>
<div>Hugh</div>
<blockquote type="cite" cite>
<blockquote><br></blockquote>
</blockquote>
<blockquote type="cite" cite><font face="Arial" size="-1">Hi Hugh,
When discussing battery characteristics with a chemist at my supplier
years ago I was told the capacity at 0 deg c is around 50% of that at
25 deg c because the ion transfer rate within the cell is slowed by
the low temperature. This "loss" of capacity is
recovered once the battery warms again. The same reason
why a fully charged cranking battery in a car can fail to
turn the motor in cold weather. Ion rate is so low it simply
can't deliver enough current to the starter motor.</font></blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite><font face="Arial" size="-1">So, the
answer to the second part of your question is yes.</font></blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite><font face="Arial" size="-1">A good
thread with lots of useful background into how batteries really
operate.</font></blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite><font face="Arial" size="-1">Bruce
Geddes</font></blockquote>
<blockquote type="cite" cite><font face="Arial" size="-1">PowerOn (at
the other end of the world)</font></blockquote>
<blockquote type="cite" cite> </blockquote>
<blockquote type="cite" cite><br>
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<div><br></div>
<div><br></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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