Combiner fuses melted

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System
System Posts: 2,511 admin
in General Solar Power Topics #1
I'm using TCB10 combiners and the fuses have blown and basically "fused" themselves into the fuse holders and can't be removed. The system is 5 years old and this has been happening over time but as long as I was generating more than using, the problem took a back seat to more pressing matters. Well... now's the time to fix it. My "solar contractor" is long gone so am planning on doing it myself. It looks like I can replace the TCB10 fused combiner boxes with PSPV boxes with DC breakers. I'd prefer breakers since they're simpler to tell if blown etc. Any problems you experts see with this idea? Would a better (read cheaper, easier here) way be to just replace the TCB10 circuit board or does someone do repairs on them?
Thanks,
Leann
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
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    Re: Combiner fuses melted

    Seems to me that a bunch of melted fuses/fuse holders suggests a fundamental flaw in design and/or application. I'm kinda partial to the Midnite solar PSPV products (3- and 6-circuit models) and their 150 VDC rated breakers.

    HTH,
    Jim / crewzer
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Combiner fuses melted

    1) There is some electrical "no corrode" paste for connections, that may be usefull

    2) fuses / breakers should hardly ever go, you should find out why, maybe post a sketch here for us to look at, or maybe on your webpage

    3) If you are pulling lots of amps, go to the next grade larger fuse holder. ie: use a fuise block rated 20- 200 amps, and put your 20A fuse in that, not a fuse block rated 3-20 A. (use the correct fuse, not my example)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • System2
    System2 Posts: 6,290 admin
    #4
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    Re: Combiner fuses melted

    Yes, I think the designer put too many panels on each fuse and then used too small fuses to boot. The first ones to go were 10A but now a lot of the 15A's have gone too. I'm not sure of the purpose of the fuses in the combiner box. It seems it would be to protect the inverter from overload but there's also DC breakers on the side of the inverter itself that would do that. When the panels were new, and we got high clouds in the spring, the power would spike as the cloud edges hit the panels and trip the breakers at the inverter. I'm sure that had something to do with the 15A fuses blowing too. Like I said, the designer/contractor is long gone so I'm in do-it-herself mode.

    Thanks for the suggestions. I'll take a look at the Midnight solar PSPV and try to get a good picture of the TCB10.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: Combiner fuses melted

    If the combiner box is wired as I would expect... The fuses are actually there to protect the other paralleled solar panels from shorts/fires...

    If you have more than two or three solar panels in parallel, I would expect there to be combiner fuses so that if any one solar panel failed (shorted), it would not see any more current that that allowed by the protecting fuse.

    For example my BP 4175 panels (175 watt, Isc 5.4 amps) says the "maximum series fuse rating" is 15 amps... So, if I have more than three strings of panels in parallel, I have to use a 15 amp fuse per string to protect that string from all of the current available on the other strings (three other strings can supply 3x5.4-16.2amps into one shorted string). With three strings or less, there is not enough current available to require a series protection fuse.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #6
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    Re: Combiner fuses melted

    Also,

    Fuses are prone to fatigue, especially at elevated temperatures. Thermal cycling seems to make the problem worse. Since combiners are almost always mounted in the direct sun this can be a real problem. Loose connections can make the fuse hotter via thermal conduction, further worsening the problem.

    Further, many fuse contacts are not plated with tin or similar, and corrosion worsens over time due to humidity cycles -- this can cause the fuses to "fuse" in place.

    Think that you will be much more satisfied with PSPV type circuit breaker combiners. And combiner breakers are only about $10. ea. Breakers can aid in troubleshooting the system, and a puller is not required to avoid the PV potentials.

    Good Luck 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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  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭✭✭
    #7
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    Re: Combiner fuses melted

    Leann, How many circuits in your combiner? What PV panels are you using and how many in series?
    I quit using fuses for combiners ten years ago. Your probllem is very common.
    The breakers we use just do not fail!! After hundreds of thousands sold, I can recall only two problems.
    Robin
    MidNite Solar
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