Hello Rick and everyone,
Rick – this is VERY helpful information. Let me digest this for a few minutes and get back to you with some more input, and maybe some questions relative to what is going on. We are going to see some more units in the morning. (There are 9 total, but only a couple of them are in operation so far….) Thanks, Walt From: Rick Cullen - Blue Sky Energy, Inc. [mailto:r...@blueskyenergyinc.com] Sent: Monday, June 29, 2009 10:14 AM To: wratter...@sunenergypower.com; 'RE-wrenches' Subject: RE: [RE-wrenches] Solar Boost Controller in Senegal Hello Everyone, 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. 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. 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... 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. Regards, Richard A. Cullen Blue Sky Energy, Inc. 760-597-1642 x102 fax 760-597-1731 <mailto:r...@blueskyenergyinc.com> r...@blueskyenergyinc.com <http://www.blueskyenergyinc.com/> www.blueskyenergyinc.com _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Walt Ratterman Sent: Friday, June 26, 2009 3:22 PM To: 'RE-wrenches' Subject: [RE-wrenches] Solar Boost Controller in Senegal Hello, 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. 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. Charge Controller is a Solar Boost 50. Batteries are Dekka AGM – two strings of 250AH, 12V batteries. (four batteries total). 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. 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. But…..isnt this a dangerous way to design a system? (it will get cooler here ….) Or am I missing something? What would be the appropriate application here…. Sorry, I cant do a lot of internet research from here – limited download capability on the satellite…. Thanks!! Walt Walt Ratterman SunEnergy Power International 11 Laurel Lane South Washougal, WA 98671 (360)-837-3680 ▪ fax (360)-837-1315 ▪ Skype Walt-Mobile wratter...@sunepi.org ▪ www.SunEPI.org <http://www.sunepi.org/> __________ Information from ESET NOD32 Antivirus, version of virus signature database 4193 (20090626) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 4193 (20090626) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com
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