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<font size="3" face="Lucida Grande">Hugh,</font> </p>
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<font size="3" face="Lucida Grande">Sorry if you found my response limited but have been traveling since early this am and don't have all information at hand, at the moment.</font> </p>
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<font size="3" 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> </p>
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<font size="3" face="Lucida Grande">Approximate Temp effects;</font> </p>
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<font size="3" face="Lucida Grande">40C = 104%</font> </p>
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<font size="3" face="Lucida Grande">25C = 100%</font> </p>
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<font size="3" face="Lucida Grande">5 to 10C = 90%</font> </p>
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<font size="3" face="Lucida Grande">-5C = 80%</font> </p>
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<font size="3" face="Lucida Grande">-22C = 60%</font><br><font size="3" face="Lucida Grande"></font> </p>
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<font size="3" face="Lucida Grande">If you need more immediate responses, always feel free forward your questions to support@surrette.com, support@rollsbattery.com (both go to Serge) or phil@Barden-Uk.com (Technical Manager for Rolls Europe).</font> </p>
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<font size="3" face="Lucida Grande">Hope this helps,</font> </p>
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<font size="3" face="Lucida Grande">Jamie</font> </p>
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>>> Hugh <hugh@scoraigwind.co.uk> 1/14/2010 12:49 PM >>><br> </p>
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Thanks, Bruce, </p>
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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. </p>
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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. </p>
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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? </p>
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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? </p>
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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? </p>
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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. </p>
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best wishes </p>
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Hugh </p>
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<SPAN STYLE='FONT-SIZE:"-1" ;FONT-FAMILY:"Arial"'>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.</SPAN> </p>
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<SPAN STYLE='FONT-SIZE:"-1" ;FONT-FAMILY:"Arial"'>So, the answer to the second part of your question is yes.</SPAN> </p>
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<SPAN STYLE='FONT-SIZE:"-1" ;FONT-FAMILY:"Arial"'>A good thread with lots of useful background into how batteries really operate.</SPAN> </p>
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<SPAN STYLE='FONT-SIZE:"-1" ;FONT-FAMILY:"Arial"'>Bruce Geddes</SPAN> </p>
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<SPAN STYLE='FONT-SIZE:"-1" ;FONT-FAMILY:"Arial"'>PowerOn (at the other end of the world)</SPAN> </p>
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<br>
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Hugh Piggott<br><br>Scoraig Wind Electric<br>Scotland<br>http://www.scoraigwind.co.uk
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