Fuse question

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Mikes240z
Mikes240z Registered Users Posts: 12 ✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
I'm installing my system and have a question on the fuses. I'm using a 60 amp AC disconnect between the panels (2 SolarWorld SW275), CC and battery's. 60 amps for CC to battery is perfect but should I use a smaller fuse on the panel side? The panels put out around 19 amps so would a 30 amp fuse be better? Also should a time delay fuse be used or a non current limiting fuse? Thanks you for your help.
Mike
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    a non current limiting fuse
    Tell me more about those things, please.
    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 ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Mikes240z
    Mikes240z Registered Users Posts: 12 ✭
    #3
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    I guess that is part of my question. Time delay fuses cost $12 and non current limiting cost $3. I thought that time delay would take longer to blow. But after doing some more reading on the net it appears that the time delay which is current limiting would blow faster and that would work best to protect against a short circuit. Maybe somebody can explain.
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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #4
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    I thought all fuses were current limiting by definition? Maybe the incorrect terminology is being used? ???

    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #5
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    Mikes240z wrote: »
    I'm using a 60 amp AC disconnect between the panels....

    I hope you mean a DC disconnect..... An AC disconnect will not last through too many cycles especially if cycled with current flowing.




    Re the fuses: I believe a type T fuse is ideal for catastrophic short circuit protection. Virtually an instant blow at the rated amps.

    Breakers are good as most can be used as a disconnect
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • scrubjaysnest
    scrubjaysnest Solar Expert Posts: 175 ✭✭✭
    #6
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    I use breakers as fuse fail over time to heat build up from volt drop, and your panels should be marked with a fuse recommendation.
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  • Mikes240z
    Mikes240z Registered Users Posts: 12 ✭
    #7
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    Mountain Don wrote: »


    I hope you mean a DC disconnect.....

    No a disconnect normally used for air conditioners or other 240V equipment. The pullout disconnect has space for two fuse cartridges. One side for the panels and the other for the battery's. I've seen several systems on the web that use them.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #8
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    Mikes240z wrote: »
    I've seen several systems on the web that use them.

    My brother runs red lights!
    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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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #9
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    Mikes240z wrote: »
    I've seen several systems on the web that use them.

    .... and everything seen on the internet is true, is best practice and is absolutely reliable and safe. Right?


    Because AC goes to zero 120 times per second it makes a much cleaner break than the same DC current which is a constant flow. Interrupting a DC current makes for a much bigger and longer lasting spark. A flame arc. Just like in arc welding. To combat that, DC contacts are made much heavier. They are also often made using spring loaded contacts that are very rapidly pulled apart or pressed together. Make and break a DC current enough times using AC equipment and sooner or later it will fail. It might fail in open circuit or it might fail welded together.

    A breaker like the MNEPV ones Midnite sells for combiner boxes, the Baby Box, etc. are not expensive and are up to the task of switching, disconnecting.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • Mikes240z
    Mikes240z Registered Users Posts: 12 ✭
    #10
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    Yes I agree that not everything on the web is true. That is one reason that I joined this forum to hopefully get some usefully information.
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  • Iceni John
    Iceni John Solar Expert Posts: 103 ✭✭
    #11
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    Carling Type C breakers, sold by NAWS under the MidNite name for about $15, are good for DC loads. Some info suggests that they can be used at their rated current, but to be safe it's prudent to derate them to 80% as per NEC to prevent false trips, i.e. 19A from the panels x 1.25 = 23.75A, so a 30A (the next largest size) will be OK. Remember, breakers and fuses protect the wiring, not the loads, so you would need cable with an ampacity of at least 30A. I'm using a pair of these 50A breakers for my 4AWG PV feeds and a pair of 80A breakers for the 2AWG CC-batt feeds, mounted in a small home-made panel made from an LMG/Heeger aluminum box.

    Otherwise, Square D QO breakers (but not the Homeline ones) are also DC-rated up to 48V, making them suitable for both AC and DC breaker panels, and they're available from Home Despot, Lowes, et al.

    John

    40' Crown bus with 2kW of tiltable panels on the roof:

    Eight Sharp 255W, two Morningstar TS-MPPT-60, Magnum MS2000, Champion C46540 generator converted to propane, eight golfcart batteries, and maybe a small Exeltech inverter for the fridger.

    Southern California

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  • Mountain Don
    Mountain Don Solar Expert Posts: 494 ✭✭✭
    #12
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    One thing I like about the Midnite is the DIN rail mount and relatively easy access, plus the wide range of amperages. NAWS also sells DIN rail by the foot so they can be mounted in your own enclosures / spaces if permitted by your inspector or if there is no inspector.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
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  • Mikes240z
    Mikes240z Registered Users Posts: 12 ✭
    #13
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    Thanks for the information. I'll look at the MidNite breakers.
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  • Iceni John
    Iceni John Solar Expert Posts: 103 ✭✭
    #14
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    Mikes240z wrote: »
    Thanks for the information. I'll look at the MidNite breakers.

    MidNite offers two lines of breakers - the DIN rail type that are up to 63A, and the Carling Type C that are available to much higher ratings. The latter will require a home-made enclosure (like I did - I used a SL141 box for four breakers). NAWS sells them both.

    John

    40' Crown bus with 2kW of tiltable panels on the roof:

    Eight Sharp 255W, two Morningstar TS-MPPT-60, Magnum MS2000, Champion C46540 generator converted to propane, eight golfcart batteries, and maybe a small Exeltech inverter for the fridger.

    Southern California

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  • Ethan Brush
    Ethan Brush Solar Expert Posts: 235 ✭✭
    #15
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    Mikes240z wrote: »
    I'm installing my system and have a question on the fuses. I'm using a 60 amp AC disconnect between the panels (2 SolarWorld SW275), CC and battery's. 60 amps for CC to battery is perfect but should I use a smaller fuse on the panel side? The panels put out around 19 amps so would a 30 amp fuse be better? Also should a time delay fuse be used or a non current limiting fuse? Thanks you for your help.
    Mike

    You generally dont even need a fuse between the PV and the CC. The panels are current limited and their short circuit current is only slightly higher than the MPPT current so there isnt a point for fuses. IF you have (typically) three or more modules or module strings paralleled, then you want fuses to prevent a short from two strings backfeeding another and damaging the modules in that string, but again the combined output is fine without a fuse. Having a disconnect though may be handy for maintenance troubleshooting, etc.....I think your AC disconnect will be fine with your small current and voltage, plus it will likely never get used anyway.
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