[RE-wrenches] String fuse blown
Amos Post
integrityenergy101 at gmail.com
Tue Apr 15 05:40:41 PDT 2025
Hi all,
I decided to start with the simple stuff. While I don’t have a string curve tester (I should have one), yesterday I tested strings 1,2,3 individually under load. String 3 is the one that’s been blowing the fuse. I did not test strings 4-6 which are on a separate charge controller and combiner. Here are the results:
String 1- 7.1A at 76V
String 2- 7.77Aat 79V
String 3-7.13A at 78.3V
I did notice that the second charge controller with strings 4-6 was running about 100watts more (1800w vs 1700w). The conditions were clear blue skies. I replaced the fuse holder and fuse. If it blows again I’ll try switching strings to see if it follows…
Thanks for your feedback and I’ll keep ya’ll posted.
Amos
Amos Post
Integrity Energy
W 802.763.7023
C 802.291.2188
ienergyVT.com <http://www.ienergyvt.com/>
Facebook <https://www.facebook.com/integrityenergyllp?ref=hl>
> On Apr 11, 2025, at 4:07 PM, Jerry Shafer via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
>
> Wrenches, Amos, blowing of a 15 amp fuse is not a ghost in the machine, it is an actual issue no way around it, shorted modules, shorted diodes, in most cases it's a home run, way back when USE-2 white wure was failing and would crack and break off mostly this would result in a GFI trip. The fuse is blowing because of over current and a single string of your vintage will max out at far less than 10 amps but the other two strings will back feed this fuse with close to 20 then pop.
> Sharp had module failures resulting in cell shorts, look very close there. I have inspected arrays with extreme exposure differences, this will effect performance but should not pop a fuse. Do you have a module string curve tester, this very well may show an issue of the string but eyes on the array is required to located the cause.
> I have seen nails through wires, conduit, racking in contact with the back of the module but this will trip the GFI breaker not the string fuse.
> Fun times.
>
>
> On Fri, Apr 11, 2025, 12:49 PM david quattro via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>> wrote:
> 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.
> 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’s when the problem went away and never came back..😂
> 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
>
>
>
> On Fri, Apr 11, 2025 at 8:05 AM Mac Lewis via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>> wrote:
> Hello Amos,
>
> 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.
>
> I like IR cameras for this type of thing. It may just be a bad connection, heat build up, fuse holder issue.
>
> Let us know what you find out
>
> On Fri, Apr 11, 2025 at 8:07 AM Amos Post via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at 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
>
>
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> Amos Post
> Integrity Energy
> W 802.763.7023
> C 802.291.2188
> ienergyVT.com <http://www.ienergyvt.com/>
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