Parallel 4 100watt 12v panels

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Mike at Energy Commission
Mike at Energy Commission Solar Expert Posts: 50 ✭✭✭✭
in Solar Beginners Corner #1
My portable charging station will consist of 4- 100 watt, 12v panels (w/ M4 connectors) and the Xantrex C40 charge controller. Now I need to figure out how to wire (8AWG) 4 in parallel safely without going broke. I assume that since these are in parallel, all the same model and voltage I don't need to fuse between panels, just one fuse prior to the charge controller. Prefer to run directly to the charge controller without combiner boxes as this is a portable system, I can't figure out how to build the wiring harness, any suggestions.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #2
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    Re: Parallel 4 100watt 12v panels

    You can use these. However, IMHO, a small combiner box would be better.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Parallel 4 100watt 12v panels
    Mike at Energy Commission wrote: »
    I assume that since these are in parallel, all the same model and voltage I don't need to fuse between panels, just one fuse prior to the charge controller.

    Wrong. You have four parallel connections. The combined current of two or three can "overwhelm" one if it becomes shorted.

    Sorry, but you are definitely in the realm of combiner boxes and fuses/breakers. :blush:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Parallel 4 100watt 12v panels
    NorthGuy wrote: »
    You can use these. However, IMHO, a small combiner box would be better.

    also wrong, as combiners like those are only good 1 time which means either 2 pvs being combined or 2 strings being combined. anymore involved in this can lead to the same problem coot just talked of.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #5
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    Re: Parallel 4 100watt 12v panels
    niel wrote: »
    also wrong, as combiners like those are only good 1 time which means either 2 pvs being combined or 2 strings being combined. anymore involved in this can lead to the same problem coot just talked of.

    You got me thinking.

    I remember, I read docs about MidNite DC breakers, which are probably the most used breakers in the solar installations. They have polarity. Midnite Solar warns that, If installed backwards, it is highly probable that DC arc will melt contacts together and breaker will not interrupt. So, they offer good protection in one direction and very weak protection in the other.

    In combiner boxes, these breakers are routinely installed to protect against power flowing out of panels. If we have 4 parallel strings and one of them get shorted, so that the other three will be "overwhelming" it, the power will flow into the panel. The breaker offer very weak protection for current flow in this direction. If breaker contacts melt together, the currect from other strings will be flowing into the shorted panel. Does that mean that such installations are prone to the same problem too?
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  • pods8
    pods8 Registered Users Posts: 16 ✭
    #6
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    Re: Parallel 4 100watt 12v panels

    I'm not the solar guru or anything but seems like it'd be pretty easy to make a small box with 4 fuses in it that also had a couple buss bars to combine the 4 +/- leads from each panel. If you used quick connections on the 10 box connections (8 inputs from the panels and 2 outputs to the controller) it would play into setting up for portability as well.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
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    Re: Parallel 4 100watt 12v panels
    NorthGuy wrote: »
    You got me thinking.

    I remember, I read docs about MidNite DC breakers, which are probably the most used breakers in the solar installations. They have polarity. Midnite Solar warns that, If installed backwards, it is highly probable that DC arc will melt contacts together and breaker will not interrupt. So, they offer good protection in one direction and very weak protection in the other.

    In combiner boxes, these breakers are routinely installed to protect against power flowing out of panels. If we have 4 parallel strings and one of them get shorted, so that the other three will be "overwhelming" it, the power will flow into the panel. The breaker offer very weak protection for current flow in this direction. If breaker contacts melt together, the currect from other strings will be flowing into the shorted panel. Does that mean that such installations are prone to the same problem too?

    It is very unlikely (probability zero) that the breaker will trip from excess current flowing out of the panel. Fault current from battery (via shorted CC) or from other strings of panels will indeed be flowing into the panel. So for protection, that is the way the breaker should be installed.
    But, the catch is that this is the wrong way around to use them as disconnects which can be opened while the panels (more likely strings of panels) are producing current. For single panels this is not likely to cause excessive wear on the contacts, but for high voltage strings the resulting arcing, even though low current, can still damage the contacts.

    With polarity sensitive breakers, there is no way you can serve both functions properly. :-(
    Which is why Midnight is looking for different breakers.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Parallel 4 100watt 12v panels

    And why some old fool around here keeps using the word "fuses" all the time. :roll:

    Believe it or not, they can be better than breakers for some parts of the installation.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
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    Re: Parallel 4 100watt 12v panels
    Cariboocoot wrote: »
    And why some old fool around here keeps using the word "fuses" all the time. :roll:

    Believe it or not, they can be better than breakers for some parts of the installation.
    Absolutely! One good combination for a combiner box would be fuses for protection and simple DC-rated switches for the disconnects. The switches would never have to open under fault current. Much easier to design each for its specific purpose than to try to combine incompatible characteristics in one device.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Parallel 4 100watt 12v panels

    Another point:
    There should be no problem with batteries back-feeding to panels. The charge controller effectively blocks power flow in that direction. If it should fail it will either 'open' (no current flow) or 'short' (in which case the circuit protection between it and the battery should trip).

    For panel protection the likely problems are shorted controller, which will not cause greater than Isc from the panels so no problem, or shorted panel which is where the CP comes into play. In that instance the 'good' panels are still a source and the 'bad' panel(s) become a load. That's how the polarized breakers should be installed. It is intuitively backward.

    And do remember that no matter what sort of problem you plan for there are always other possibilities unforeseen which can still cause the magic smoke to come out. Weird things happen.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #11
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    Re: Parallel 4 100watt 12v panels
    Cariboocoot wrote: »
    Another point:
    There should be no problem with batteries back-feeding to panels. The charge controller effectively blocks power flow in that direction. If it should fail it will either 'open' (no current flow) or 'short' (in which case the circuit protection between it and the battery should trip).

    With a PWM controller, there is no isolation between the input and the output. If the series switching element which interrupts the current from the panels to the batteries fails by short circuiting it would not be a short to ground or battery negative, so it will not by itself trip any breakers. The battery will end up getting overcharged, but no harm will come to the panels. What the breaker is protecting against there (in addition to protecting against the combined efforts of the other panels/strings as you describe) is the combination of a shorted pass element in the CC and a short in one of the panels. Not the most likely, but both could be caused by a single event such as lightning. The panels could then easily present a high enough resistance that the fuse or breaker between the CC and the battery would not trip, but the failed panel or string could get dangerously high reverse current.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
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    Re: Parallel 4 100watt 12v panels

    Toss lightning into the scenario and all bets are off. There is absolutely no guaranteed way of dealing with a sudden influx of enough Voltage to jump miles of air gap that creates temperatures capable of melting steel and exploding rocks.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #13
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    Re: Parallel 4 100watt 12v panels
    Cariboocoot wrote: »
    Toss lightning into the scenario and all bets are off. There is absolutely no guaranteed way of dealing with a sudden influx of enough Voltage to jump miles of air gap that creates temperatures capable of melting steel and exploding rocks.

    I was referring to the much smaller effects of a nearby lighting strike, not the effects of a direct strike, and only to illustrate that a simultaneous double failure is possible. Yes, in the case of a direct strike, you can count yourself lucky even if the whole solar PV system fries to protect your house and you.

    BTW, in the 787 case several unlikely faults appear to have conspired to happen at the same (or overlapping) times.
    SMA SB 3000, old BP panels.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #14
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    Re: Parallel 4 100watt 12v panels
    inetdog wrote: »
    It is very unlikely (probability zero) that the breaker will trip from excess current flowing out of the panel.

    Static electricity, lightning. That sort of things.
    inetdog wrote: »
    With polarity sensitive breakers, there is no way you can serve both functions properly. :-(
    Cariboocoot wrote: »
    And why some old fool around here keeps using the word "fuses" all the time. :roll:

    That's right. So, if the panel shorts (for example because water got inside), there may be no protection with DC breakers, and all the might of other parallel panels will go into heating the poor panel and may cause a fire.

    That should be better if there are several panels in the string because the other panels will protect the shorted panel. It'll be the same as if one of the strings had two panels instead of three (or 3 instead of 4). That's not harmful. So, the more panels in the string, the less sensitive it is to shorting of a single panel. It's a good argument for longer strings.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: Parallel 4 100watt 12v panels
    inetdog wrote: »
    I was referring to the much smaller effects of a nearby lighting strike, not the effects of a direct strike, and only to illustrate that a simultaneous double failure is possible. Yes, in the case of a direct strike, you can count yourself lucky even if the whole solar PV system fries to protect your house and you.

    That's the whole problem with lightning though, isn't it? Strikes in the area mean your system could be subject to anywhere from zero Volts of high-frequency on up. You can reduce risks, but never eliminate them.
    BTW, in the 787 case several unlikely faults appear to have conspired to happen at the same (or overlapping) times.

    I wonder how "unlikely" all the faults really were. We'll never know for sure. Or at least not be told. :roll:

    But it does happen. I've seen it first hand; all components within tolerances but the circuit as a whole doesn't work because on that particular unit all the tolerances conspired to prevent proper function.

    It happens.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #16
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    Re: Parallel 4 100watt 12v panels
    NorthGuy wrote: »
    It's a good argument for longer strings.
    And there is the arcing problem for switch that interrupts a normal current. And the hazard to the ubiquitous fireman on the roof. And.... that argue the other way.
    Certainly a factor to consider. Anyway, I still feel that a DC breaker which is intended to be a breaker rather than a switch needs to be oriented to limit current into the string it protects.
    SMA SB 3000, old BP panels.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #17
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    Re: Parallel 4 100watt 12v panels
    inetdog wrote: »
    Anyway, I still feel that a DC breaker which is intended to be a breaker rather than a switch needs to be oriented to limit current into the string it protects.

    They are easy to turn around. The million dollar question is - have you installed them backwards on your system?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #18
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    Re: Parallel 4 100watt 12v panels
    inetdog wrote: »
    With polarity sensitive breakers, there is no way you can serve both functions properly. :-(
    Which is why Midnight is looking for different breakers.

    I read on the their forums that Midnite is looking for non-polarized breakers because polarized breakers will not be permitted under the next NEC. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Mike at Energy Commission
    Mike at Energy Commission Solar Expert Posts: 50 ✭✭✭✭
    #19
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    Re: Parallel 4 100watt 12v panels

    Thanks guys, it's making more sense now. So the tentative design is run individual leads into a fused combiner box (CB) obviously the 4 positive go on the positive bus bar and likewise for the negative, this results in 1 positive and 1 negative into the charge controller (CC). Since this will be a portable charging station and to facilitate that provide 8 quick disconnects between combiner box and panel feeds coming into the CB and two quick disconnects between the CC and the various batteries that will be coming and going. I can use MC4 cable extensions to get to the CB, Which quick disconnects would be recommended? Suggestion on a fused CB? Should I use clamps or something else to connect from CC to batteries? Thanks for the help.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #20
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    Re: Parallel 4 100watt 12v panels

    Skip all the breakers questions, if your on a budget, find an auto fused power distribution block, You likely will spend less than $20 and have to find a box to put it in... 10-15 years ago, it was very common to just combine the panels with a distribution block and not worry about it, I had mine set up this way for 6-7 years and nothing fired, small 4 panel 200 watt system. If you overwelm a commercially made glass, aluminum and tedar panel, there isn't much to burn. I guess if you had a perfect day and back fed 300 watts, you might be able to melt a ribbon cable. You might also look into some inline water proof fuses often used on boats about $5 each.
    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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  • Mike at Energy Commission
    Mike at Energy Commission Solar Expert Posts: 50 ✭✭✭✭
    #21
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    Re: Parallel 4 100watt 12v panels
    Photowhit wrote: »
    Skip all the breakers questions, if your on a budget, find an auto fused power distribution block, You likely will spend less than $20 and have to find a box to put it in... 10-15 years ago, it was very common to just combine the panels with a distribution block and not worry about it, I had mine set up this way for 6-7 years and nothing fired, small 4 panel 200 watt system. If you overwelm a commercially made glass, aluminum and tedar panel, there isn't much to burn. I guess if you had a perfect day and back fed 300 watts, you might be able to melt a ribbon cable. You might also look into some inline water proof fuses often used on boats about $5 each.

    I can't find an inline fuse for 8AWG wire, I did find one for marine applications that said 8G, not sure if that is the same as 8AWG? How much efficiency difference do you think there is between using fuses and a combiner box w/ breakers?
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #22
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    Re: Parallel 4 100watt 12v panels
    Mike at Energy Commission wrote: »
    how much efficiency difference do you think there is between using fuses and a combiner box w/ breakers?

    I would think there would be nominal difference between the 2. I don't recall that ever having been asked, I use fused combiner boxes my self, that uses ATM fuses, but I have a 24volt system that requires fuses that can handle more than the 30-32 volts of Auto fuses (atc?) note that these fuses designed for cars will not meet NEC code for residential use, but likely you won't make code in many other areas... like wiring to and from inverters must be in conduit, DC-GFP, etc...
    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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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #23
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    Re: Parallel 4 100watt 12v panels

    Since this is a portable system, something like this should work
    http://www.onlinecarstereo.com/CarAudio/p_14646_Boss_Audio_DFB4.aspx

    Will take up to 4 gauge in with 4x 8 gauge wires out.
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  • Mike at Energy Commission
    Mike at Energy Commission Solar Expert Posts: 50 ✭✭✭✭
    #24
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    Re: Parallel 4 100watt 12v panels

    When confused read the directions! The manufacturer has instructions for exactly what I am trying to do. Interestingly they have no circuit protection shown in their instructions between panels or between panels and the CC. They suggest using a total of 6 - branched MC4 connectors to reduce the cabling down to 1 positive and one negative then go directly into the CC, no fuses, no combiner box. I will call their engineers and ask if the warranty is valid using their suggested design. Thanks for all info.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #25
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    Re: Parallel 4 100watt 12v panels

    There is no affect on the Charge Controller--So they would not care about a "combiner box + fuses/breakers".

    The requirement is, usually, the solar panels themselves. The "modern/larger" panels tend to list the Series Protection Fuse (or similar phrasing) that prevents a "shorted" panel from being "back fed" from the rest of the array with more than the rated fuse/series protection device--This is probably a UL/NRTL requirement (limit the risk of overheating/fire).

    Older/smaller panels tend not to list this requirement (and many smaller panels may not be UL/NRTL listed).

    I have seen a few panels that support more than two strings in parallel without needing the series fuse (2-4 or 5 panels in parallel)... But that was, as I recall, one Dupont thin film/higher voltage panel--Not one that we see used a lot here (and may no longer be in production).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #26
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    Re: Parallel 4 100watt 12v panels
    Mike at Energy Commission wrote: »
    I can't find an inline fuse for 8AWG wire, I did find one for marine applications that said 8G, not sure if that is the same as 8AWG? How much efficiency difference do you think there is between using fuses and a combiner box w/ breakers?

    Doubt your panels use 8 gauge wire, so you'll also have to increase the wire gauge from the panels native 10 or 12 gauge to a larger gauge. Mike's link to a "Distribution Fuse Block" would be a good place to make the change and combine the panels.
    Attachment not found.
    You could search for other "Distribution Fuse Blocks". you could put this into a 6x6" junction box ($10-14)
    Attachment not found.
    and add some Waterproof Strain reliefs
    Attachment not found.

    and have a pretty good combiner box, still need fuses...
    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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  • Mike at Energy Commission
    Mike at Energy Commission Solar Expert Posts: 50 ✭✭✭✭
    #27
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    Re: Parallel 4 100watt 12v panels

    Here is the link to the manufacturers schematics, I will be using the 400 watt parallel diagram. http://www.grapesolar.com/files/4313/4910/4245/GS-S-100-Fab36_Guide.pdf
    I spoke with tech support today and they said no circuit protection is needed between panels as they have a blocking diode installed in each panel. I like the idea of using a harness to pull them all together rather than running 8 individual wires into one box. Makes things more portable (hopefully!) You guys are great fantastic resource here.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #28
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    Re: Parallel 4 100watt 12v panels
    Mike at Energy Commission wrote: »
    I spoke with tech support today and they said no circuit protection is needed between panels as they have a blocking diode installed in each panel.

    Bzzzt! FAIL!

    A diode is NOT a fuse and shouldn't be used as one. Furthermore there shouldn't be blocking diodes built in to the panels: they are unnecessary as the charge controller will prevent power leakage from battery through panel at night. The only thing they will do is cut some Voltage from the panel output.

    Although these being "little" 100 Watt 12 Volt panels that may well be the way they build them. Doesn't impress me much.

    Proceed at your own risk.
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