Solar PV system DC fuse keeps blowing

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solarrox
solarrox Registered Users Posts: 1 ✭
in PV Installers Forum - NEC, Wiring, Installation #1

Hi!


I have a 6.5Kw system installed with a SMA Sunnyboy inverter. Works great normally. One DC fuse blew 2 years ago and I replaced. However, it blew again repeatedly every 6 months. There are four DC fuses and this particular one keeps blowing. Any idea why this is happening?


I am not a Pro.

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  • Photowhit
    Photowhit Solar Expert Posts: 6,017 ✭✭✭✭✭
    #2
    So, I'm guessing these are fuses for the incoming solar panels, perhaps someone with a dc clamp meter could check to see if the current coming in from each string is even...

    Perhaps they wired your panels incorrectly. Do you have panels in a multiple of 4? maybe 28 panels which would be strings of 7 panels...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,017 ✭✭✭✭✭
    #3
    Alternately, you might shut everything down and read the voltage coming in on each fused string one at a time. Or at least do the one that keeps blowing and another to get a comparison. The fuses are rated for amps, which shouldn't change regardless of how many panels are in a string. but they could be past the max voltage with additional panels.

    What mightbe happening is a bad connection internally, if the string is plugged into the inverter near the fuse and the connection is a bit loose or other connections are loose, the added heat will run along the line and may trip burn the fuse.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,696 admin
    #4
    What size or amp rating of fuse?

    Around 1 amp is s ground fault detection fuse.

    Most arrays, if you have any fuses, are around 15 amps or so.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SkipperLipper
    SkipperLipper Registered Users, Users Awaiting Email Confirmation Posts: 1 ✭
    #5
    I am having a similar problem.   I have 24 375 watt solar panels, with three sets of 8 run in series.  All three series ran fine for the first 4 months, then the inline fuse blew in series 2.   Then a couple months later, series 3 blew.   I originally has a 10 amp fuse, so I tried a 15 amp fuse.  Now series 1 blew, and it actually melted the fuse holder!!! Yikes?   Admittedly, it was touching the back of the solar panel, so that may have caused the melting/warping of the fuse holder.  Under normal conditions, the open circuit voltage at the inverter is about 300 volts, but when powering the inverter, it drops down some.  Each panel is rated at 11 amps.  But the puzzling thing is, when the #2 series blew, you could see some deformation in the fuse holder (clearly it got very hot), and it was hanging in free space under the ground-mounted array (no touching the back of a solar panel).  Any ideas on why I keep blowing fuses?   When everything is working normally, I am getting over 2000 watts per series, and sometimes upwards of 2500-2600 watts.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,134 ✭✭✭✭✭
    #6
    Heat is coming from a high resistance connection. Check all hardware and if the fuse is being retained by pressure, clean all contact surfaces and ensure it has adequate pressure holding it.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Vic
    Vic Solar Expert Posts: 3,211 ✭✭✭✭
    edited November 2023 #7
    One additional thought:

    Are the fuses that you are using rated for DC voltages that the system will encounter?

    If  the fuses are not rated for about 500,  or 600 VDC,  then when a fuse blows,  there can be a destructive ARC,  that could start a fire,  melt fuse holders,  etc.

    FWIW,  Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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