I would do 2 things. 1. If it’s string 3 fuse blowing, swap string 3 to another fuse. 2. Replace the fuse holder, which is what I suspect is the issue. It’s a weak connection causing heat which is causing the fuse failure.
Jay On Apr 11, 2025, at 8:07 AM, Amos Post via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote:
Hi Wrenches,
I have a bit of a puzzler that I’m trying to get sorted out. I’ve been servicing a Grid-Tied Battery Backup system that’s about 17-18 years old. The system comprises of 2-GVFX3648s in series, with 2-MX60(at least I think they are 60s) CC’s. 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’t have pictures/specifics). We replaced the flooded batteries with AGMs about a year and a half ago.
The situation is one of the 15A string fuses keeps blowing. It’s 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 “looked” 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.
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’t 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…
As always, thanks for your help/ suggestions! Amos
<IE LOGO 150x78.jpg> Amos Post Integrity Energy W 802.763.7023 C 802.291.2188 ienergyVT.com
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