Different wire sizes - which first?

MOAC Man
MOAC Man Registered Users Posts: 3
in Solar Beginners Corner #1
I hope you all can help.
I have a bit of a problem with wiring. I have three 135 watt panels 75 feet away from the batteries. They are connected to the batteries via a charge controller.
I have been given 150 feet of 6 gauge wire and 150 feet of 3 gauge wire. Unfortuately at present I am unable to afford to purchase the remaining wire in 3 gauge.
Which gauge would be best to connect from the solar panels - 3 gauge or the 6 gauge?
I appreciate any help you can give.
Thanks,
Howard.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Different wire sizes - which first?

    Welcome to the forum.

    Yes, I think we can help you out here with just a bit more information.
    Would it be safe to assume those panels are Kyocera 135's?
    The other question is: what is your charge controller?

    What your looking for here is to size the wire right so that it can handle the current and not suffer too much Voltage drop over the 75 feet. But there are two possible ways of connecting those panels: in parallel or in series. The parallel connection will give the lowest Voltage and highest current, resulting in the greatest power loss. The series connection will give the highest Voltage and lowest current resulting in the least power loss. But the series connection requires an MPPT type charge controller capable of taking the higher Voltage.

    That's why we need to know the details. Otherwise it is simply a matter of apply the data to a V-drop calculator like the one hosted by forum member Solar Guppy: http://forum.solar-electric.com/showthread.php?t=29
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Different wire sizes - which first?

    Hmm. Just tried the numbers based on my assumptions and it doesn't look good for either wire gauge on a 12 Volt system for that 75 foot run. Whereas the 6 AWG would work for all panels in series on an MPPT controller.
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  • Fullpower
    Fullpower Solar Expert Posts: 69 ✭✭
    #4
    Different wire sizes - which first?

    Thats a long run for 12 volt nominal.
    Connect the modules in series, to run the voltage up, Low current means less line loss.
    I run my pole mounted modules in series strings, 105 volts Open Circuit.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: Different wire sizes - which first?
    Fullpower wrote: »
    Thats a long run for 12 volt nominal.
    Connect the modules in series, to run the voltage up, Low current means less line loss.
    I run my pole mounted modules in series strings, 105 volts Open Circuit.

    that will work if he has an mppt controller to downconvert the higher seriesed pv voltage.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Different wire sizes - which first?

    MOAC Man;

    I've deleted your duplicate post and moved the original thread to this section where it might get more 'traffic'.

    Please review this thread and ask for any clarification you need.
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  • MOAC Man
    MOAC Man Registered Users Posts: 3
    #7
    Re: Different wire sizes - which first?

    Thanks everyone.
    I will try and get some more information for you all. I would really like to solve this issue with the panels where they are as that is the best use of the sun. Still sounds as if moving them might have to be looked at. That will be difficult though as the cabin is really shady.
    The panels are 135 watt. Two are Sharp and one is Kyocera which I added this year. I understand the Sharp ones are not made anymore but I could be incorrect.
    What I do not know is what the charge controller is as regards to MPPT but I will get the model number for you. It is a Xantrex for sure but the model is no longer made I understand. I will check and get back to you all.
    Thanks.
    Howard.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Different wire sizes - which first?

    You're right about the Sharp panels being discontinued; they're not making anything under 200 Watts now.

    For long distances on panel wires sometimes changing the charge controller may be cheaper than buying a lot of thick wire.
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  • MOAC Man
    MOAC Man Registered Users Posts: 3
    #9
    Re: Different wire sizes - which first?

    Well that took some time! Sorry about that.
    The charge controller is a Xantrex C40, which looks as if it may not be suitable for this distance from what I read.
    Still if you have more suggestions I would be very grateful to read them.
    Thank you.
    Howard.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #10
    Re: Different wire sizes - which first?

    The C40 is still in production, but it is not an MPPT controller, which you may be forced to use for your setup. You could get wire large enough to avoid any serious voltage drop, but with the price of copper now, it is probably cheaper to get a new controller.
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  • Generic
    Generic Registered Users Posts: 27 ✭
    #11
    Re: Different wire sizes - which first?

    What if he put the charge controller out near the panels and ran a length of 6 gauge and 3 gauge for both the positive and negative to the battery?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Different wire sizes - which first?
    Generic wrote: »
    What if he put the charge controller out near the panels and ran a length of 6 gauge and 3 gauge for both the positive and negative to the battery?

    The output of a PWM controller like the C40 is pretty much the same Voltage and current as the input, so there's no advantage to having the "long run" on the output side instead of the input.

    Possibly the solution is to run the thickest wire you've got for the + & - input to the controller towards the panels 'til you run out of wire (or gain too much V-drop) and then place the combiner there and continue to the panels with separate cables for each one. Kind of a messy, jerry-rigged set-up but ...
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