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batteries</title></head><body>
<div>Hi Jamie,</div>
<div><br></div>
<div>Thanks for the very quick response!</div>
<div><br></div>
<div>I note that the temp compensation slope for charging is more like
a curve. It would be great to have a few more data points on
this curve to match it against the linear compensation programmed into
a Tristar controller. </div>
<div><br></div>
<div>But I guess there is some leeway anyway? My personal 48-V
household battery is rather large (2 x S530 in parallel) and the max
charge rate is low (around 20-30 amps). Would that be a reason
to set a higher charging voltage maybe, or does it not make a
difference?</div>
<div><br></div>
<div>As far as the disconnect point, I now have one data point for 50%
discharge: 1.93V at C/20 and 25 degrees C. Again it would be
great to have a whole family of curves to work from in this area.
Most of the systems I work on have batteries that are sized for
several days usage rather than 20 hours. I don't really like to
see the LBCO setpoint as low as 46.3 volts.</div>
<div><br></div>
<div>Capacity is reduced at low temperatures. Now does this mean
that there really is less energy in the battery, so that if I take out
50% of this reduced capacity I will only end up with a 50% state of
charge once it has warmed, or is this just a performance hit that
reduces the voltage and makes the battery capacity appear to be less?
Will the battery actually have less amphours to deliver, or will it
just be delivering at a lower voltage? My point is to ask
whether it is legitimate to push the battery to a lower voltage in
cold weather on the assumption that it is not really running that low,
but just sluggish with cold?</div>
<div><br></div>
<div>I hope you don't mind all the questions. I hope the others
find the answers interesting too!</div>
<div><br></div>
<div>In an ideal world we could control our end-of-discharge based on
amphours measured, but I have no faith in the calibration of such
devices after a few partial charge swings up and down over period of
days. So the reality is that we rely on inverter LBCO settings
or rules of thumb such as "never let the voltage drop below 47"
to ensure that the batteries do not get abused.</div>
<div><br></div>
<div>Best wishes</div>
<div><br></div>
<div>Hugh</div>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Hi Hugh &
Wrenches,</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Regarding the
charge voltages you sited, you've got the gist.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">As battery
temperature drops, you need to increase the charge voltage to properly
charge and, conversely, as temperatures rise, voltage needs to be
decreased to reduce the risk of overcharging.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">I believe the
range we site to accommodate for temperature is (in C);</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">0-16C:
2.5VPC</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">17-27C:
2.4VPC</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">28-40C:
2.36VPC</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">These are your
max bulk / absorb voltage settings.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Regarding a
low voltage disconnect, there is a significant difference between on
load and at rest voltages at 50% SOC.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Below is a
table of a cell being discharged at a known constant load (C/20) over
time at 25C;</font><br>
</blockquote>
<blockquote type="cite" cite><br>
<br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">SOC
VPC</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">100%
2.1</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">75%
2.01</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">50%
1.93</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">25%
1.84</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">0%
1.75</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Please note,
this is for a cell(s) under constant load and at 25C. If the
load increased, you would see lower voltages more quickly,
Moreover, once the load is removed, resting voltages will
increase dramatically, i.e. 1.75VPC on load will equal ~1.95VPC at
rest. If you were using 2.0VPC (on load) as your cut off, you
would only have been able to discharge ~25% - which does not include
capacity reduction due to temps <25C.......and I know they are
lower than that here!</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Hope this is
of some assistance.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font
face="Lucida Grande">Regards,</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font
face="Lucida Grande">Jamie</font><br>
</blockquote>
<blockquote type="cite" cite><br>
<br>
<br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande"><br>
James Surrette<br>
<br>
Surrette Battery Co. Ltd<br>
1 Station Rd.<br>
Springhill, NS, CAN<br>
B0M 1X0<br>
<br>
Direct: 902.597.4027<br>
Fax: 902.597.8447<br>
<br>
<br>
<br>
<br>
>>> Hugh <hugh@scoraigwind.co.uk> 1/13/2010 2:26 PM
>>></font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Hi
wrenches,</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">I have been
selling and using a few sets of Rolls 4000 series S530</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">batteries
lately.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">I have
downloaded the Solar Battery manual from</font> <a
href="http://www.rollsbattery.com"><font face="Lucida Grande"
color="#0000FF"><u><i>www.rollsbattery.com</i></u></font></a><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">It's very
interesting. At 17 degrees C you need to charge at
14.4</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">volts.
At 16 degrees it's 15 volts. Hmm, Ok I get the idea. I
am</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">certainly
learning to compensate my temperatures this
winter.</font></blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">I did a search
in the document for the word 'discharge'. I am</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">cutting off at
just below nominal voltage and starting my generator.</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">I do not get
much capacity. A customer has suggested that a lot of</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">the discharge
capacity is to be had at 11.5 volts (he has a 12v</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">system
obviously). Hmm. Sounds a bit harsh. But what
voltage</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">should I be
considering to be 50% discharged, and time to start the</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">genny?
And in a hard frost, the same voltage?</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">No mention of
discharge in the solar battery manual. Any ideas
anyone?</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Please don't
tell me to buy an amphour meter (or worse still to sell</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">them).
Those things are way too confusing to calibrate. I can
tell</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">you that I am
not getting many amphours out of my batteries in these</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">low
temperatures before the voltage per cell drops below 2.</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">What do I tell
my customers about the end-of-discharge voltage for</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">sustainable
cycling of their Rolls batteries? And is it temp</font><br>
</blockquote>
<blockquote type="cite" cite><font
face="Lucida Grande">compensated?</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font
face="Lucida Grande">thanks</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">--</font><br>
</blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Hugh
Piggott</font><br>
</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><font face="Lucida Grande">Scoraig Wind
Electric</font><br>
</blockquote>
<blockquote type="cite" cite><font
face="Lucida Grande">Scotland</font><br>
</blockquote>
<blockquote type="cite" cite><a
href="http://www.scoraigwind.co.uk"><font face="Lucida Grande"
color="#0000FF"><u><i>http://www.scoraigwind.co.uk</i></u></font></a><br
>
</blockquote>
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<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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