help figuring wire size from combiner plz!

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lotek
lotek Solar Expert Posts: 65 ✭✭✭✭
in Solar Beginners Corner #1
Plz figure this for me. 12 210 panels 11.48 Imp, 18.3 Vmp, running 3 strings of 4 panels to the combiner
My math must be fuzzy, I thought running panels in sieries added voltage and watts remained the same. Here's the part I must be missing. I thought from the combiner box on all those strings, (being combined) were now running parallel.

My math went like this :4X18.3=73.2Vmp . 4 sets of panels at 210W = 840W 840 divided by 73.2 = 11.47 amps. If I add another 4 panels using the same math,its 14 amps
where did I go wrong?when you combine the strings are they still in seiries?

I was just sent by an "expert"

"When wiring solar panels in series the voltage adds and the current stays the same. 4 panels in series x 18.3 Imp = 73.2V at 11.8A

When wiring solar panels in series the current adds and the voltage stays the same. 3 series stings of 4 panels would be 3 strings x 11.8A per string = 35.4A. If you were to add another string the total solar current would be 47.2 A"
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #2
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    Re: help figuring wire size from combiner plz!
    Plz figure this for me. 12 210 panels 11.48 Imp, 18.3 Vmp, running 3 strings of 4 panels to the combiner

    You have 3 strings of 11.48 amp panels = 34.4 amps approximately at 4 x 18.3=53 volts. Now what is the distance from the combiner to the charge controller? You will need #8 or larger wire depending on distance and wire loss that you can accept.
    I would err on the larger wire size for less loss.
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  • lotek
    lotek Solar Expert Posts: 65 ✭✭✭✭
    #3
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    Re: help figuring wire size from combiner plz!

    15' from combiner to controller 48v sys
    looks like I need 6 gauge wire
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  • audredger
    audredger Solar Expert Posts: 272 ✭✭
    #4
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    Re: help figuring wire size from combiner plz!

    Another question is what is the open circuit voltage Voc? 4xVOC cannot exceed max voltage for your charge controler!

    Yes; oversize the wire! My MMP controler tends to regulate the panels at a slightly lower voltage than the panels published Vmp which equals more amps. More amps @ lower voltage = bigger wire.
    Mike
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #5
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    Re: help figuring wire size from combiner plz!

    you will have 4 panels in series so the voltage will be 4*18.3 which equals 73.2vdc then 3 sets of these panels in parallel so 3*11.48A which equals 34.4 Amps

    At that short a distance I would feel comfy with #8 but if you may expand later bump up to #6 or even #4 30ft of wire will be cheap compared to the rest of the system
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