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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Maybe try putting a few power zener diodes in series with a protection resistor across the DC positive and negative terminals. NTE makes 5W zeners with 150.0
and 200.0 volt reverse breakdown voltages that only cost $2 and are rated down to - 65C. You should pick the power rating of the zeners and size of the protection resistor to handle what maximum current you might expect from the array, but the theory is that
by the time you have enough sun on the modules to create a substantial current they should have warmed up above – 40 F or C dropping the voltage below 600. By selecting different diodes you could build something to go into reverse at 600 VDC, 590, 580, whatever
you want. I’ve never tried it and might be missing something but for $10 it’s something to consider. Just an idea!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Jeff Irish, PE</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Hudson Solar</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Rhinebeck, NY 12572</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">T.845.876.3767x110</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">F.845.876.3912</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><a href="mailto:jeff@hudsonsolar.com">jeff@hudsonsolar.com</a></span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Solar Electric Systems</span></i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">NYSERDA Eligible PV Installer</span></i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">NABCEP Certified Solar PV Installer</span></i><i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:purple">
</span></i><i><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:purple"><o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">NABCEP Certified PV Technical Sales</span></i><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org]
<b>On Behalf Of </b>Benn At DayStarSolar<br>
<b>Sent:</b> Thursday, November 29, 2012 11:23 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> Re: [RE-wrenches] PV String Over-voltage<o:p></o:p></span></p>
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<p class="MsoNormal">Larry, <o:p></o:p></p>
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<p class="MsoNormal">Would it not be a more straightforward approach to just size the strings, temperature compensating for the coldest anticipated temp?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Nonetheless, such a device could be useful in some circumstances. I'd be interested to know if your search comes up with something. <o:p></o:p></p>
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<p class="MsoNormal"><span class="apple-style-span">benn</span><o:p></o:p></p>
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<p class="MsoNormal"><span class="apple-style-span">Sent from a 'smart' phone, with touch screen keys. Please excuse shortcuts and typos. </span><o:p></o:p></p>
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On 2012-11-29, at 6:53 PM, "Larry Crutcher, Starlight Solar Power Systems" <<a href="mailto:larry@starlightsolar.com">larry@starlightsolar.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Wrenches,<o:p></o:p></p>
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<p class="MsoNormal">I seem to recall seeing something about a device for PV string over-voltage protection by bypassing a module. I can't find any info by Goggling.<o:p></o:p></p>
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<p class="MsoNormal">Some customers in the FAR north, ay, can see > 40° below zero with bright sun and snow reflection. I want to be able to switch off one or more modules in a string for protecting the controllers.<o:p></o:p></p>
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Thank you,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black"><br>
Larry Crutcher<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black">Starlight Solar Power Systems<o:p></o:p></span></p>
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