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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:
<blockquote
cite="mid:8EA9619B465C95438B31C92F854FB7966C12EC@exchange.fafcosolar.local"
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<p class="MsoNormal"><span
style="font-size: 11pt; font-family: "Calibri","sans-serif"; color: rgb(31, 73, 125);">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 11pt; font-family: "Calibri","sans-serif"; color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Cambria","serif"; color: rgb(31, 73, 125);">Jason
Szumlanski<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family: "Cambria","serif"; color: rgb(31, 73, 125);">Fafco
Solar<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size: 11pt; font-family: "Calibri","sans-serif"; color: rgb(31, 73, 125);"><o:p> </o:p></span></p>
<div
style="border-style: solid none none; border-color: rgb(181, 196, 223) -moz-use-text-color -moz-use-text-color; border-width: 1pt medium medium; padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif";">From:</span></b><span
style="font-size: 10pt; font-family: "Tahoma","sans-serif";">
<a class="moz-txt-link-abbreviated" href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a class="moz-txt-link-freetext" 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<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom: 12pt;">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 moz-do-not-send="true" href="http://www.abrahamsolar.com">www.abrahamsolar.com</a><br>
<br>
Voice: 970-731-4675<br>
<br>
<o:p></o:p></p>
<div>
<p class="MsoNormal">On Mon, Jan 31, 2011 at 6:52 AM, Jason
Szumlanski <<a moz-do-not-send="true"
href="mailto:Jason@fafcosolar.com">Jason@fafcosolar.com</a>> wrote:<o:p></o:p></p>
<div>
<div>
<p class="MsoNormal" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);">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" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);"> </span><o:p></o:p></p>
<p class="MsoNormal" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);">Can anyone recommend
a photosensor source, and maybe a model number?</span><o:p></o:p></p>
<p class="MsoNormal" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);"> </span><o:p></o:p></p>
<p class="MsoNormal" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);">Other ideas welcomed…</span><o:p></o:p></p>
<p class="MsoNormal" style=""><span
style="font-size: 11pt; color: rgb(31, 73, 125);"> </span><o:p></o:p></p>
<div>
<p class="MsoNormal" style=""><span
style="font-family: "Cambria","serif"; color: rgb(31, 73, 125);">Jason
Szumlanski</span><o:p></o:p></p>
<p class="MsoNormal" style=""><span
style="font-family: "Cambria","serif"; color: rgb(31, 73, 125);">Fafco
Solar</span><o:p></o:p></p>
</div>
</div>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
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