Newb Question

Zakarume
Zakarume Solar Expert Posts: 143 ✭✭
in Solar Beginners Corner #1
I have a 12v 400 watt system. It goes approx 45 ft from panels to charge controller. WHAT SIZE WIRE DO I NEED? What do you recommend? What i am reading on different internet sites is to use either 2 or 4 gauge wire

There will probably be more questions to ask later, but this question is a start
1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: Newb Question

    What is the array? Vmp/Imp of panels, are they 1serial x 4parallel, 2serial x 2parallel, or what.

    What brand/model of charge controller do you have (i.e., MPPT, PWM, etc.)?

    What voltage/AH of battery bank do you have?

    You can put your system basics in your Signature so we don't have to keep asking you the same questions....

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Newb Question

    "That depends". :p

    If the array is 400 Watts at the standard 12 Volt level of 17.5 Vmp then the current would be about 23 Amps. Across 45 feet you'll get a lot of V-drop, so 2 AWG would keep it below 3% loss.

    This is a case where you should really look at the economics of using an MPPT controller so you can run a higher Voltage array and reduce that wire size: 35 Vmp, 11.5 Amps = 8 AWG for the same percentage loss (<3%).
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  • Zakarume
    Zakarume Solar Expert Posts: 143 ✭✭
    #4
    Re: Newb Question

    I cant afford the MPPT charge controller until next year. Just looking at ways to Twink my system to get it better
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    #5
    Re: Newb Question

    If you're using a combiner box, where is it in relation to the charge controller? (I'm assuming that four 40-foot wire runs from the panels to a combiner box would reduce the voltage loss by reducing the amperage carried by each wire run).
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  • Zakarume
    Zakarume Solar Expert Posts: 143 ✭✭
    #6
    Re: Newb Question

    My panels are tied together with a 4 way splitter similiar to this http://www.amazon.com/Vktech-1Pair-Connector-Female-2-5-6mm2/dp/B00JTMLBSA/ref=sr_1_3?ie=UTF8&qid=1413846528&sr=8-3&keywords=mc4+4+way+solar and then it goes to a 30 amp pullable fuse before it goes to charge controller. I rather it blows the fuse instead charge controller
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #7
    Re: Newb Question

    The 30 amp fuse doesn't do any thing for you...

    With 4 combined into one output you should have a fuse or breaker on each, they make MC4 fuse holders, but breakers add some convenience.

    I personally have had 4 in parallel with out fuses or breakers, the idea is that if there is a short in one panel the others could back feed it and create a fire, panels are made of stuff that isn't very flammable, glass, aluminum, even some of the backing sheets aren't very flammable. I did put in a fuse box on my larger systems, but with a small system, particularly one that would be switched out the following year for an MPPT charge controller (and 2 or less strings) I wouldn't bother... of course I'm not going to replace your home if you do burn down the house.
    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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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #8
    Re: Newb Question
    Zakarume wrote: »
    My panels are tied together with a 4 way splitter similiar to this http://www.amazon.com/Vktech-1Pair-Connector-Female-2-5-6mm2/dp/B00JTMLBSA/ref=sr_1_3?ie=UTF8&qid=1413846528&sr=8-3&keywords=mc4+4+way+solar and then it goes to a 30 amp pullable fuse before it goes to charge controller. I rather it blows the fuse instead charge controller
    Technically (and with practical consequences in the event of problems) you must have a fuse in each of the four panel lines. Unless the panel specs say that the maximum series fuse is equal to or greater than 30A you are violating that manufacturer/listing requirment. In practice, as long as you have only single panels and not strings, the fuse may not be as critical from a safety point of view.
    Also, the 30A fuse is not there to protect the CC, since the panel current is limited to Isc at a maximum (125% of Isc in winter, above 5000 feet and in perfect fringe clouded skies.) It is there to protect the panels in the event of a failure in the CC which puts battery voltage directly on the input.
    A breaker would at least be useful as a disconnect.
    You said a pullable fuse. Chances are very very good that it is not rated or safe to be pulled under a DC load. So only use it is a disconnect when the panels are dark or covered or the CC is turned off.
    SMA SB 3000, old BP panels.
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  • Zakarume
    Zakarume Solar Expert Posts: 143 ✭✭
    #9
    Re: Newb Question

    Main reason for quick disconnect is when i am gone for extended periods of time. (Parenting Time with children).

    As far as this http://www.amazon.com/Odyssey-Solar-In-Line-Holder-Waterproof/dp/B00J948E4W/ref=sr_1_1?ie=UTF8&qid=1413848446&sr=8-1&keywords=mc4+fuse. I didnt know they made those and i will get those. Thanks Photowhit for pointing this out. Also would i need 4 or 8 fuses ( + & - )

    Thanks Aurictech for pointing out the combiner box.

    Can a Electrical Panel Box work also instead of a Combiner Box
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #10
    Re: Newb Question
    Zakarume wrote: »
    ...and then it goes to a 30 amp pullable fuse before it goes to charge controller. I rather it blows the fuse instead charge controller

    It works the other way around, the PV cant really ever hurt the controller.

    Anyway to answer your question, in your setup you have to be a bit precious about voltage drop. Not super short PV home run plus low voltages, minus mppt.

    How well this works depends on the vmp of your panels. If they are "standard" 36 cell panels, then your vmp will be something like 17 or 18 volts. Check this figure. At the other end youve got your absorb/eq voltage which might be 15V, so theres not a lot of wiggle room... right?

    PV current peaks around 400w / 12V */0.77 or about 26A.

    Take it to the vdrop calc:

    http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.5127&voltage=17&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=26&x=61&y=14

    Likely to be an expensive roll of wire, and why mppt can save you money.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #11
    Re: Newb Question

    I believe the panels are 18.6 (or 18.9) when I checked earlier.

    You don't need both the fuses and a combiner box, just one or the other.
    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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  • Zakarume
    Zakarume Solar Expert Posts: 143 ✭✭
    #12
    Re: Newb Question

    Aurictech pointed out the Combiner box so i will be going with that. http://www.solar-electric.com/mnpv6.html?gclid=CKvV98iCwsECFQusaQodokgA_A MPPT Charge controller wil hold off until next year
    1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #13
    Re: Newb Question
    Zakarume wrote: »
    Aurictech pointed out the Combiner box so i will be going with that. http://www.solar-electric.com/mnpv6.html?gclid=CKvV98iCwsECFQusaQodokgA_A MPPT Charge controller wil hold off until next year

    The situation is that with the MPPT controller you won't need the combiner box. Saving the $90 + $12-15 a breaker (+ a couple mc4 wires though you'll want to buy a set of mc4 combiners for 2 strings so that's a wash) That gets you half way to a MPPT controller. Though if you intend to expand you will likely need a combiner in the future, though you could easily add a couple panels of the same size maxing out the controller at 12 volts.
    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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