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<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2>Hello Everyone,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2>The SB50's maximum input voltage spec it 57VDC. This should be considered
an absolute maximum above which the controller will be damaged in a manner not
covered by warranty. Our recommendation is to not apply a total Voc at STC
of more than 57V/1.25= 45.6V. There are transient voltage protection diodes on
both battery and PV inputs on ALL Solar Boost charge controllers.
These are not "tell tail" indicators but real protection devices
designed/selected to protect down stream electronics from transient voltage
damage resulting from ESD, lightning, etc. On the PV side of the SB50 the
protection diodes will begin to clip at about 58-60V. They can eat a 1
millisecond 3000W transient without damage, but will burn up if they receive
more than about 10W continuously. These two diodes are located right behind the
PV terminals. </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2>In the application described below I would expect the SB50 to be damaged.
What typically happens with excess over voltage is the diodes fail
short, and then clamp PV voltage low and protect the down stream
electronics. If PV current is sufficiently high the diodes will burn
open and the SB50 may continue to operate since down stream devices have
somewhat higher voltage withstand capability, or it may suffer catastrophic
damage.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2>Why these systems continue to operate must be due to actual Voc not
getting high enough long enough to cause catastrophic damage. If the
controllers were to not switch to Float (unloading the PV's), the brief Voc
sample as part of MPPT may not have burned up the diodes and they are
successfully eating the excess voltage transients which would seem to occur
during the Voc sample. It may also be that the modules are so hot
that their actual Voc & Vmp are low enough that when PV voltage is
clamped to 60V by the SB50's protection diodes insufficient power is delivered
at 60V to burn up the diodes...</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><FONT face=Arial
size=2>Needless to say, this is a situation that need to be corrected.
Technical Bulletin #100214 available on our web site describes proper voltage,
current and power sizing for all Solar Boost charge
controllers.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><SPAN lang=en-us><FONT
face=Arial size=2></FONT></SPAN></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=035202416-29062009><SPAN lang=en-us><FONT
face=Arial size=2>Regards,</FONT></SPAN> <BR><SPAN lang=en-us><FONT face=Arial
size=2>Richard A. Cullen</FONT></SPAN> <BR><SPAN lang=en-us><FONT face=Arial
size=2>Blue Sky Energy, Inc.</FONT></SPAN> <BR><SPAN lang=en-us><FONT face=Arial
size=2>760-597-1642 x102</FONT></SPAN> <BR><SPAN lang=en-us><FONT face=Arial
size=2>fax 760-597-1731</FONT></SPAN> <BR><SPAN lang=en-us></SPAN><A
href="mailto:rick@blueskyenergyinc.com"><SPAN lang=en-us><U><FONT face=Arial
color=#0000ff size=2>rick@blueskyenergyinc.com</FONT></U></SPAN></A><SPAN
lang=en-us></SPAN> <BR><SPAN lang=en-us></SPAN><A
href="http://www.blueskyenergyinc.com/"><SPAN lang=en-us><U><FONT face=Arial
color=#0000ff size=2>www.blueskyenergyinc.com</FONT></U></SPAN></A><SPAN
lang=en-us></SPAN> <BR><SPAN lang=en-us><FONT face=Arial> </FONT></SPAN>
</DIV></SPAN><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <B>On Behalf Of </B>Walt
Ratterman<BR><B>Sent:</B> Friday, June 26, 2009 3:22 PM<BR><B>To:</B>
'RE-wrenches'<BR><B>Subject:</B> [RE-wrenches] Solar Boost Controller in
Senegal<BR></FONT><BR></DIV>
<DIV></DIV>
<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: 10pt; FONT-FAMILY: 'Arial','sans-serif'">Walt
Ratterman<o:p></o:p></SPAN></B></P>
<P class=MsoNormal><B><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Arial','sans-serif'">SunEnergy Power
International</SPAN></B><B><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Times New Roman','serif'"><o:p></o:p></SPAN></B></P>
<P class=MsoNormal><B><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Times New Roman','serif'"><o:p> </o:p></SPAN></B></P>
<P class=MsoNormal><SPAN
style="FONT-SIZE: 8pt; 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: 8pt; 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: 8pt; FONT-FAMILY: 'Arial','sans-serif'"><A
href="mailto:wratterman@SunEPI.org">wratterman@SunEPI.org</A> </SPAN><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: 'Arial','sans-serif'"> </SPAN><SPAN
style="FONT-SIZE: 8pt; 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
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