Fuse type?

Shasta1
Shasta1 Registered Users Posts: 15 ✭
in Off Grid Solar & Battery Systems #1
I will be running 4 135w/12v panels to a J-box then to a 45a Morningstar controller.

Can I use this type of fuse holder and fuse between the J-box and the controller, and between the controller and the battery bank?

I'll be running 6ga and 4ga respectively, should I fuse with a 50 amp fuse?

Thanks

http://www.solar-electric.com/maxfusholinw.html
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Fuse type?

    Are we talking all panels in parallel? If so, each panel needs its own fuse and those fuses ought to be about 10 Amps, not 50 (based on Isc of the panels).

    Not too sure about those holders being weather tight either, even with the optional cap, so placement is important. You could use a small automotive type fuse block inside a weatherproof box to join the panels.
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  • Shasta1
    Shasta1 Registered Users Posts: 15 ✭
    #3
    Re: Fuse type?

    The panels are to be connected in parallel, however I'm asking about between the junction box (all panels combined) and controller.


    Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Fuse type?
    Shasta1 wrote: »
    The panels are to be connected in parallel, however I'm asking about between the junction box (all panels combined) and controller.


    Thanks

    With the panels properly fused it isn't necessary to put an additional fuse on the line from combiner to controller.
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  • Shasta1
    Shasta1 Registered Users Posts: 15 ✭
    #5
    Re: Fuse type?

    Be that as it may, I'm still looking for an answer to my question........:roll:


    A couple of points I considered before deciding where to fuse:

    1) The block diagrams I've referenced have all indicated a fuse before and after the controller.

    2) The one fuse that I'm inquiring about (after the junction box and before the controller) will do the same basic function as the four you're recommending.

    3) If the fuse on one panel faulted, I might not as easily detect it as opposed to a fuse that shuts off all panels.

    My concern is will the fuse holder, and fuse that is designed to fit this holder, which will be mounted in a protected environment, be adequate for my application? And, if so, should I be fusing to the 6ga wire run from the 4 panel junction box to the controller, and after the controller fuse to the 4 ga wire run to the battery bank.

    These fuses and the holders are relatively inexpensive and easy to place and service. If I can safely incorporate them in to my system, I would like to! :D

    I'm new to this, so please don't think I don't appreciate any suggestions or recommendations.

    Thanks
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Re: Fuse type?

    As Cariboocoot stated, if you have a fuse in line with each panel, which is required in your case, you don't need another fuse in series with the already existing fuses. The solar panel fuses are the fuse/s between the panels and the controller. Adding another fuse in series with existing fuses will give no advantage, but will provide opportunities for unnecessary problems. I am familiar with the type of fuse holder shown in your photo. I had one of them almost cause a fire. It handled a continuous 10 amps DC from my micro hydro, and had a 30 amp fuse installed. Luckily I had a volt meter on the micro hydro, and one day noticed about a 2 volt difference between it and the battery voltage. Got to checking and found smoke coming from the fuse holder and it was all scorched and too hot to touch. Once cooled, cut the whole thing open and discovered the crimp on the wire connected to one of the clips the fuse pushes into, had developed enough resistance to cook everything around it, and weld the fuse leg into the push-in clip. The fuse had not blown, and could not be removed. I've had the same high resistance crimp problems with motorcycle electrical systems. Now if I use an automotive fuse of the type that fits that holder, I solder the wires directly to the fuse legs, then I KNOW I have a good connection with no crimps to cause problems.
    Thus, I have good reason NOT to add extra fuses in series with fuses, it means extra, unnecessary connections. Yes, you need fuses, but extra, unnecessary ones only cause problems. Perhaps not today, perhaps not tomorrow, but why do it?
    By the way, one single fuse servicing the 4 panels WILL NOT do the same thing as one fuse for EACH panel! The reason for one fuse per panel, is that if one panel develops a short, the other still good panels will start dumping their power into the shorted panel, and it's fuse will blow instead of setting that panel on fire. Thus there is a VERY good reason to do it right, and supply each panel with it's own fuse. As to detecting a possible blown panel fuse, you only have 4 panels, so you should easily notice a 25% drop in power.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: Fuse type?

    i don't see any reason that you couldn't use them on individual pvs providing the fuse itself meets the requirements of the pv. for higher currents be sure the wiring in the fuse holder or connection points can take the current. 45a is allot of current and many of these type fuse holders may only have #14 or #12 pigtails at best and the nec specifies the max current that flows through those wires is at 15a and 20a respectively. 4 of those pvs at imp will be in the area of providing an imp of around 30a and short circuit current rating are even higher so my answer would be no to using it between the combiner and cc as i don't believe it will handle that much current. i side with the guys here that 1 main fuse isn't necessary, but the 4 individual fuses are for paralleling the pvs are and i would not recommend that fuse holder for between the cc and the battery for the same reason.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #8
    Re: Fuse type?

    Hi Shasta,

    As stated by others, each solar panel string needs to be fused to protect each of the panels from the others when there are three or more strings. Circuit breakers are also often used for this. A string is one or more panel(s). This protects against FIRE and damaging panels.

    IMHO, it is a good idea, and probably required that there be an overcurrent protective device (circuit breaker) at the input of a charge controller, in addition to fuse/breaker for each sting of PV panels. Using a circuit breaker at the CC input allows safe and convenient disconnection of the PV input.

    The fuse holder that you have shown, as neil and others stated, is prob not rated for continued direct outdoor exposure, and does not have sufficient current handling capability for close to 45 Amps continuous. Think that it is rated for water resistance, not direct exposure. These are often used for auto circuits, under the hood.

    YMMV, 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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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #9
    Re: Fuse type?

    Definitely a disconnect of some sort before the controller, and that disconnect could be a proper DC rated breaker.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Fuse type?

    DC rated disconnect between the array and the controller is definitely a good idea. The use of a DC breaker for that purpose is fine. A big DC rated switch will also work. Absolutely essential that any such device is rated for DC, for the Voltage, and for the potential current. Better to have no disconnect than one that doesn't meet the specifications.

    But if you do not fuse the individual panels separately you're asking for trouble. Should one of the panels short, the remaining ones will try to push all their collective current through the shorted panel. In this case that would be 3 times the short circuit rating of he panel. No fuses = possible roof fire.
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  • Shasta1
    Shasta1 Registered Users Posts: 15 ✭
    #11
    Re: Fuse type?

    Thanks!

    I'll contact NAW&S for the proper equipment.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
    Re: Fuse type?

    many times what they describe is usually in an electrical panel type box complete with disconnect, main breaker, and satellite breakers for the individual strings. or you could piece meal these things as in diy.
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