<div dir="auto">One time I had similar, but different problem: 1 Amp ground fault fuse consistently blowing, sometimes after 1 day sometimes after weeks/months. I tried everything - replaced home runs, checked VOC, VMP, swapped DC input into a different inverter, etc. it kept coming back to this one string. I checked every module VOC, ISC, every connection, no pinched wires, no discernible problem, but fuse blowing.</div><div dir="auto"> Luckily it was a medium size commercial job (on a fire station) so I was able to scatter all the modules of this suspect string all over the roof, and carefully track where I had put them. That\u2019s when the problem went away and never came back..\U0001f602</div><div dir="auto"> Best I could figure was a slight manufacturing error that had a compounding/cumulative effect. So once I got those consecutive serial numbers away from each other no more problem. Either that or the fire chief was fucking with me and he was burning out the fuses, which I doubt </div><div dir="auto"><br></div><div dir="auto"><br></div><div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, Apr 11, 2025 at 8:05\u202fAM Mac Lewis via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div dir="ltr">Hello Amos,<br><div><br></div><div>Have you checked for voltage imbalance for each string? If you have a bad diode, that string may run low on voltage and be trying to send current toward the weak string (this is the reason you have these breakers). I'd run each string independently and see what Vmp is. If you are missing some voltage that may be a clue. You can also independently clamp each string during operation.</div><div><br></div><div>I like IR cameras for this type of thing. It may just be a bad connection, heat build up, fuse holder issue.</div><div><br></div><div>Let us know what you find out</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Apr 11, 2025 at 8:07\u202fAM Amos Post via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div>Hi Wrenches,<div><br></div><div>I have a bit of a puzzler that I\u2019m trying to get sorted out. I\u2019ve been servicing a Grid-Tied Battery Backup system that\u2019s about 17-18 years old. The system comprises of 2-GVFX3648s in series, with 2-MX60(at least I think they are 60s) CC\u2019s. Each CC has 3 strings of 3 tied to it, and each string has a 15A in-line 600V fuse. The modules are I believe are like 230/240Watt 60 cell modules (sorry I don\u2019t have pictures/specifics). We replaced the flooded batteries with AGMs about a year and a half ago. </div><div><br></div><div>The situation is one of the 15A string fuses keeps blowing. It\u2019s now happened 3 times and its the same fuse every time. First we just replaced the fuse and under the surge/lightning assumption. Fuse blew again. Then I thought I found the culprit. The #6 PV output from the combiner to the PV input breaker for the CC was a bit darkened and very warm to the touch when I replaced the fuse the first time. So I though maybe it was a loose connection on that lug and that caused everything to heat up and eventually blow the fuse. I cut and stripped the wire back and cleaned the lug and re-seated the wire in the lug. Fuse blew again within a few months time. I then checked the Junction box on the roof where the USE-2 wire connects to THHN, and did a visual inspection of all the wiring on the roof. All of the Jbox connections and everything on the roof \u201clooked\u201d ok. I have also check all of the connections inside the Outback DC load center, and they look ok. Fuse replaced 3rd time and then it blew again. </div><div><br></div><div>Before I take all of the panels off the rack, check panels, re-check string wiring on the roof, is there anything else I should be checking? Seems like that warm wire in the Combiner box is telling me something but I can\u2019t figure out what...I believe this is a new problem in the last 2-3 years but we are not 100% sure when the problem first came up\u2026</div><div><br></div><div>As always, thanks for your help/ suggestions!</div><div>Amos</div><div><br></div><div><br><div>
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</blockquote></div><div><br clear="all"></div><div><br></div><span class="gmail_signature_prefix">-- </span><br><div dir="ltr" class="gmail_signature"><div><br></div><div><font face="'times new roman', serif" style="font-family:"times new roman",serif;color:rgb(48,90,120)"><br></font></div><div><br></div>Mac Lewis<br><br><span style="font-family:"Times New Roman";font-size:medium;color:rgb(255,153,0)"><b style="font-family:"Times New Roman""><font face="Arial, Helvetica, sans-serif" size="3" style="font-family:Arial,Helvetica,sans-serif;color:rgb(255,153,0)"><p align="left" style="font-family:Arial,Helvetica,sans-serif"><font face="Verdana, Arial, Helvetica, sans-serif" style="font-family:Verdana,Arial,Helvetica,sans-serif;color:rgb(0,0,0)"><span style="font-size:small;font-family:Verdana,Arial,Helvetica,sans-serif"><span style="font-family:arial;font-weight:normal;color:rgb(48,90,120)"><font face="'times new roman', serif" style="font-family:"times new roman",serif;color:rgb(48,90,120)">"Yo solo sé que no sé nada." </font><span style="font-weight:700;font-family:arial;color:rgb(104,104,104)"><font face="'times new roman', serif" style="font-family:"times new roman",serif;color:rgb(104,104,104)">-Sócrates</font></span></span></span></font></p></font></b></span></div>
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