<html><body><span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>More important than loss of capacity at low temps, (at least in my world), is the fact that battery freeze points rise considerably -- with a reduced State of charge... So you get a sort of double whammy... not only do you get less capacity, but they freeze easier.<br></div><div><br></div><div><br>Dan Brown<br>President<br>Foxfire Energy Corp.<br>Renewable Energy Systems<br>(802)-483-2564<br>www.Foxfire-Energy.com<br>NABCEP #092907-44<br><br></div>
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-------- Original Message --------<br>
Subject: Re: [RE-wrenches] discharging Rolls batteries<br>
From: Hugh <hugh@scoraigwind.co.uk><br>
Date: Wed, January 13, 2010 5:47 pm<br>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org><br>
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</style> <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 target="_blank" href="http://www.rollsbattery.com"><font color="#0000ff" face="Lucida Grande"><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 target="_blank" href="http://www.scoraigwind.co.uk"><font color="#0000ff" face="Lucida Grande"><u><i><a href="http://www.scoraigwind.co.uk">http://www.scoraigwind.co.uk</a></i></u></font></a><br> </blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">_______________________________________________</font><br> </blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">List sponsored by Home Power magazine</font><br> </blockquote> <blockquote type="cite" cite=""><br></blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">List Address: RE-wrenches@lists.re-wrenches.org</font><br> </blockquote> <blockquote type="cite" cite=""><br></blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">Options & settings:</font><br> </blockquote> <blockquote type="cite" cite=""><a target="_blank" href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org"><font color="#0000ff" face="Lucida Grande"><u><i><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a></i></u></font></a><br> </blockquote> <blockquote type="cite" cite=""><br></blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">List-Archive:</font> <a target="_blank" href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org"><font color="#0000ff" face="Lucida Grande"><u><i><a href="http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org</a></i></u></font></a><br> </blockquote> <blockquote type="cite" cite=""><br></blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">List rules & etiquette:</font><br> </blockquote> <blockquote type="cite" cite=""><a target="_blank" href="http://www.re-wrenches.org/etiquette.htm"><font color="#0000ff" face="Lucida Grande"><u><i>www.re-wrenches.org/etiquette.htm</i></u></font></a><br> </blockquote> <blockquote type="cite" cite=""><br></blockquote> <blockquote type="cite" cite=""><font face="Lucida Grande">Check out participant bios:</font><br> </blockquote> <blockquote type="cite" cite=""><a target="_blank" href="http://www.members.re-wrenches.org"><font color="#0000ff" face="Lucida Grande"><u><i>www.members.re-wrenches.org</i></u></font></a><br> </blockquote> <blockquote type="cite" cite=""><br> <br> <br> <br> <br> This email and its attachments have been scanned by iConnection E-Mail Firewall for viruses, spam, and malicious content.<br> <br> The information transmitted in this email is intended only for the entity or person to which it is addressed and may contain confidential/privileged material. 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</pre></x-sigsep> <div>Hugh Piggott<br> <br> Scoraig Wind Electric<br> Scotland<br> <a target="_blank" href="http://www.scoraigwind.co.uk">http://www.scoraigwind.co.uk</a></div> <hr>_______________________________________________<br>
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