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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Kent,<o:p></o:p></span></p><p class=MsoNormal><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:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks for the great feedback. Your final question is key. I do want it to close at a fairly low voltage (low irradiance). I need the load to run pretty reliably from just after dawn to just before dusk. I think I’ll dig deeper and find a relay that a) fits, b) tolerates higher voltage, and c) is low cost. The higher pull in voltage with a resistor in series would probably make the load kick off too often.<o:p></o:p></span></p><p class=MsoNormal><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:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks again,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Jason Szumlanski<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Fafco Solar<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Operations Manager<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>239.574.1500 office<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>239.410.4985 cell<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><img width=170 height=67 id="Picture_x0020_1" src="cid:image001.jpg@01CBC214.5E62AA50" alt="Fafco%20Solar%20Logo%20Email"><o:p></o:p></span></p><p class=MsoNormal><b><span style='font-family:"Cambria","serif";color:#1F497D'> <a href="http://fafcosolar.com/">http://fafcosolar.com</a><o:p></o:p></span></b></p><p class=MsoNormal><span style='font-size:2.0pt;font-family:"Cambria","serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:2.0pt;font-family:"Cambria","serif";color:#1F497D'> </span><span style='font-size:8.0pt;font-family:"Cambria","serif";color:#1F497D'> <a href="http://www.facebook.com/pages/Fafco-Solar/93677317294">Visit us on Facebook!</a><o:p></o:p></span></p></div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Kent Osterberg<br><b>Sent:</b> Tuesday, February 01, 2011 1:05 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Photosensor for 12VDC System with load controller<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Jason,<br><br>I think that you would be pushing your luck a little with a 12-volt relay directly connected to a 12-volt PV module. I don't have the specs for the relay you have in mind so I looked up the coil spec for Omron's G2R relays:<br>12-volt coil: 275 ohms<br>24-volt coil: 1100 ohms<br>Both: must close at 70% of rated voltage, or below<br> must open at 15% of rated voltage, or above<br> max voltage 170% of rated voltage (assuming 23°C ambient temperature)<br>These are probably pretty typical specs for small relays. <br><br>The 24-volt coil is not guaranteed to close until 17 volts, so that is out of consideration. <br><br>The 170% of rating means the maximum for a 12-volt coil is 20.4 volts. Considering that the C40 is charging a battery, the module voltage normally won't be much higher than the battery voltage - unless the battery is fully charged. But in the event that the load were disconnected allowing the battery to reach full charge the relay could see a voltage close to the module Voc, around 22 volts maybe 25 volts if is cold.<br><br>You are left with putting a resistor in series with the 12-volt coil. If a 120-ohm, 1/2-watt resistor were in series with the 12-volt coil for the Omron G2R, the contacts would close at, or before, 12 volts; it would open at 2.5 volts; and it would tolerate 29 volts without overheating the coil. You should get similar results with your relay if you select a series resistor that has a resistance of 40% to 45% of the coil resistance.<br><br>The question is: should the load operate on days when the battery is charged but there isn't enough irradiance to activate the relay?<br><br>Kent Osterberg<br>Blue Mountain Solar, Inc.<br><br><br><br>Jason Szumlanski wrote: <o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Does anyone know if an automotive style 12V relay coil can handle the solar panel voltages common in a 12V nominal panel? This would be a low cost and small size solution that might work best in my case. A $6 relay can switch 40A – well over what I need to do. </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Jason Szumlanski</span><o:p></o:p></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Fafco Solar</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'> </span><o:p></o:p></p><div style='border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0in 0in 0in;border-color:-moz-use-text-color -moz-use-text-color'><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"'> <a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a> [<a href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>] <b>On Behalf Of </b>Mick Abraham<br><b>Sent:</b> Monday, January 31, 2011 9:43 AM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Photosensor for 12VDC System with load controller</span><o:p></o:p></p></div><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Maverick's suggestion would give the opposite action to what the original poster needs. The C12 "night light" function turns the load on after dark but Jason needs the opposite.<br><br>The solar array can serve as your "photocell", Jason. The PV +/- terminals in the C12 controller have no power on them at nighttime (check me on that with your voltmeter), but they are energized when there is sunshine. A relay coil connected parallel to the the PV +/- terminals on the C12 should fire when the sun is up and that coil would then release at sundown. Use a "single pole single throw normally open" relay with a DC coil, and connect the positive leg of your DC load across the normally open connection screws.<br><br>Make sure the relay coil can accept a wide range of DC input, since it may encounter 20 volts across a 36 cell PV module when the sun first comes up.<br><br>Jolliness,<br><br clear=all>Mick Abraham, Proprietor<br><a href="http://www.abrahamsolar.com">www.abrahamsolar.com</a><br><br>Voice: 970-731-4675<br><br><br><o:p></o:p></p><div><p class=MsoNormal>On Mon, Jan 31, 2011 at 6:52 AM, Jason Szumlanski <<a href="mailto:Jason@fafcosolar.com">Jason@fafcosolar.com</a>> wrote:<o:p></o:p></p><div><div><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>I have a customer with a Xantrex C12 charge controller with LVD controlling a 5A load. Their battery and PV are not large enough to run the load 24/7, and they don’t need it to run at night. I am thinking about recommending a photocell to disconnect the load at dusk and turn it back on at dawn. They are not interested in upgrading the PV and battery (too costly). </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>Can anyone recommend a photosensor source, and maybe a model number?</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>Other ideas welcomed…</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'> </span><o:p></o:p></p><div><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Jason Szumlanski</span><o:p></o:p></p><p class=MsoNormal><span style='font-family:"Cambria","serif";color:#1F497D'>Fafco Solar</span><o:p></o:p></p></div></div></div></div><p class=MsoNormal> <o:p></o:p></p><pre><o:p> </o:p></pre><pre style='text-align:center'><hr size=4 width="90%" align=center></pre><pre><o:p> </o:p></pre><pre>_______________________________________________<o:p></o:p></pre><pre>List sponsored by Home Power magazine<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Options & settings:<o:p></o:p></pre><pre><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><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>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><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>List rules & etiquette:<o:p></o:p></pre><pre><a href="http://www.re-wrenches.org/etiquette.htm">www.re-wrenches.org/etiquette.htm</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Check out participant bios:<o:p></o:p></pre><pre><a href="http://www.members.re-wrenches.org">www.members.re-wrenches.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre></div></body></html>