<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I think you're right: it's hot enough there that the Voc never hits the 57 v BLue Sky death point. Problem is, if you rewire those modules for parallel, their mpp won't match the SB50. According to Blue Sky's Tech bulletin #100214, it wants to track MPP between 33 v -37 v. YOu could add some special jumper (which doesn't help in Senegal) that would allow it to track between 24v -28 v. <div>This is why we quit using Blue Sky for the most part: the range of voltages they'll work with is extremely limited. Not like an Outback which seems to be able to MPPT almost anything up to 100 v or so, and step it to any battery voltage.</div><div>Might have to just leave it alone. Tell them not to wash the modules! the dust is probably keeping the Voc down a bit, and if they cooled them with water on a sunny day, it could all be over.....as the Voc could exceed 57v.</div><div>Whoever "designed" that system was a hack. Probably just throwing whatever module they were trying to get rid of, with an SB50, and had no experience with off grid systems.</div><div>Seems the Africa scams go both ways, and one of our fellow Americans ripped some very poor people off.</div><div>In the heat there, the actual MPP for the module series is probably down at 50 v, so the SB 50 is probably running the array at 37 v. Pretty inefficient, but better than nothing.</div><div><br><div><div><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>R. Walters</div><div>Solarray.com<span class="Apple-tab-span" style="white-space:pre"></span></div><div>NABCEP # 04170442<span class="Apple-tab-span" style="white-space:pre"><span class="Apple-style-span" style="white-space: pre; "> </span></span></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span> </div><br><div><div>On Jun 26, 2009, at 4:22 PM, Walt Ratterman wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> <div class="Section1"><p class="MsoNormal">Hello,<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">I am in a very remote part of Senegal, (near the Guinea and Mali borders…) and I have come across some prefabricated “plug and play” American made systems installed for educational institutions.<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">The systems use two Sharp panels that are 220Watts, 33.6 Voc, 29.2 Vmp, wired in series, using #10AWG home run wire from the panels back to the charge controller.<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Charge Controller is a Solar Boost 50. <o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Batteries are Dekka AGM – two strings of 250AH, 12V batteries. (four batteries total).<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">My specific question is about the controller. This is a 24V in / 24V out charge controller with MPPT. I have not used this before, so I am not familiar with the details of operation.<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">The data sheet that I downloaded says that the maximum open circuit voltage is 57 VDC. But, this system is hitting the charge controller with two panels of 33.6 VDC wired in series for 73.2VDC. So, why is the controller not fried, or what am I seeing wrong here. I suppose with the panel temperature being elevated maybe 35 degrees above 25 degrees and a resulting 17.5% loss, coupled with some voltage drop, the system may actually be seeing less than the 57 volts. <o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">But…..isnt this a dangerous way to design a system? (it will get cooler here ….)<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Or am I missing something? <o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">What would be the appropriate application here….<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Sorry, I cant do a lot of internet research from here – limited download capability on the satellite….<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Thanks!!<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal">Walt<o:p></o:p></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">Walt Ratterman<o:p></o:p></span></b></p><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">SunEnergy Power International</span></b><b><span style="font-size:10.0pt;font-family: "Times New Roman","serif""><o:p></o:p></span></b></p><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Times New Roman","serif""><o:p> </o:p></span></b></p><p class="MsoNormal"><span style="font-size:8.0pt;font-family:"Arial","sans-serif"">11 Laurel Lane South Washougal, WA 98671<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:8.0pt;font-family:"Arial","sans-serif"">(360)-837-3680 ▪ fax (360)-837-1315 ▪ Skype Walt-Mobile<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:8.0pt;font-family:"Arial","sans-serif""><a href="mailto:wratterman@SunEPI.org">wratterman@SunEPI.org</a> </span><span style="font-size:10.0pt;font-family:"Arial","sans-serif""> </span><span style="font-size:8.0pt;font-family:"Arial","sans-serif"">▪ <a href="http://www.sunepi.org/">www.SunEPI.org</a><o:p></o:p></span></p><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal"><o:p> </o:p></p> </div> <br><br>__________ Information from ESET NOD32 Antivirus, version of virus signature database 4193 (20090626) __________<br><br>The message was checked by ESET NOD32 Antivirus.<br><br><a href="http://www.eset.com">http://www.eset.com</a><br><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">List sponsored by Home Power magazine</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Options & settings:</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><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></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">List-Archive: <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></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">List rules & etiquette:</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">www.re-wrenches.org/etiquette.htm</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Check out participant bios:</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">www.members.re-wrenches.org</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div> </blockquote></div><br></div></div></body></html>