Wire Size

With54
With54 Registered Users Posts: 21 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
I have a 1000 watt solar system at the cottage that is wired into a Midnite Solar Combiner Box. What size wire would I need to run from the combiner box to the XW charge controller at 30 feet apart?

Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Wire Size

    For an accurate answer a few more details are needed, such as the Voltage and current of the panels and how they are wired (series, parallel or combination). The XW controller http://www.solar-electric.com/xaxwmp60amps.html is an MPPT type so several different input options are possible.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #3
    Re: Wire Size
    With54 wrote: »
    I have a 1000 watt solar system at the cottage that is wired into a Midnite Solar Combiner Box. What size wire would I need to run from the combiner box to the XW charge controller at 30 feet apart?

    Thanks

    It's impossible to answer that question with the information supplied. The wire gauge needed is determined by the amount of current the conductor is to carry, not the amount of power. Power is voltage multiplied by current; 1000 Watts could be 1A at 1000V or 1000A at 1V (it's probably neither ;)), but the 1000V system (illegal, of course) would require much smaller wire.

    Also to consider are ampacity (amount of current a wire can carry) deratings for conditions of use, i.e., ambient temperature, number of wires in a conduit, and rooftop insolation.
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  • With54
    With54 Registered Users Posts: 21 ✭
    #4
    Re: Wire Size
    Cariboocoot wrote: »
    For an accurate answer a few more details are needed, such as the Voltage and current of the panels and how they are wired (series, parallel or combination). The XW controller http://www.solar-electric.com/xaxwmp60amps.html is an MPPT type so several different input options are possible.

    Oops! My apology. It is a 24 volt system. The panels are 1 Sharp 235 Watt (24 Volts)- ISC =8.60A, IMP = 7.84 and 4 Ramsond 120 Watt (12 volts) - ISC=7.71, IMP = 7.02. The Ramsonds are joined in pairs. Consequently, three strings going into the combiner box. Thanks for any assistance.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Wire Size

    Let's see.
    The four Ramsonds have a Vmp of 17.1 and an Imp of 7.02
    The one Sharp has a Vmp of 30 and an Imp of 7.84

    Right away we see problems.
    The Sharp panel's Vmp is not high enough to charge a 24 Volt system. The Vmp's of the two panel types are too far apart to be paralleled or to be connected as two Ramsonds to one Sharp.

    In short, this isn't going to work.
    Two Ramsonds in series would give a Vmp of 34.2, which is just enough to charge a 24 Volt system. The Vmp of the Sharp @ 30 will contribute almost nothing to charging as the charge Voltage for a 24 Volt system is 28.4 to 31 Volts.

    You wouldn't like to go buy three more Sharp 235 Watt panels, would you? :D
    As it is you're looking at maybe 22 Amps @ 24 Volts and a need for at least 6 AWG wire to handle it.
    Even so, it's not going to work very well; the panel specs are too far apart.
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  • With54
    With54 Registered Users Posts: 21 ✭
    #6
    Re: Wire Size
    Cariboocoot wrote: »
    Let's see.
    The four Ramsonds have a Vmp of 17.1 and an Imp of 7.02
    The one Sharp has a Vmp of 30 and an Imp of 7.84

    Right away we see problems.
    The Sharp panel's Vmp is not high enough to charge a 24 Volt system. The Vmp's of the two panel types are too far apart to be paralleled or to be connected as two Ramsonds to one Sharp.

    In short, this isn't going to work.
    Two Ramsonds in series would give a Vmp of 34.2, which is just enough to charge a 24 Volt system. The Vmp of the Sharp @ 30 will contribute almost nothing to charging as the charge Voltage for a 24 Volt system is 28.4 to 31 Volts.

    You wouldn't like to go buy three more Sharp 235 Watt panels, would you? :D
    As it is you're looking at maybe 22 Amps @ 24 Volts and a need for at least 6 AWG wire to handle it.


    Even so, it's not going to work very well; the panel specs are too far apart.

    Would the system work if I connected panels in 24 volts and changed the batteries to 12 volts?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Wire Size
    With54 wrote: »
    Would the system work if I connected panels in 24 volts and changed the batteries to 12 volts?

    The basic problem is that the two different panel types won't work well together. Changing to a 12 Volt system would allow the Sharp to "contribute" more, but the difference between the panels is still going to end up losing some of the power. You can't get around that.

    So let's go back to the beginning; what size battery (Volts and Amp hours) are you trying to recharge?

    The four Ramsonds add up to 480 Watts on their own. That would support about 154 Amp hours @ 24 Volts, enough for roughly 1.8 kW hours maximum (not including system conversion losses). If there were an "ideal" way to include the Sharp panel it would only add about 75 Amp hours to the potential battery bank size; around a 50% increase (as you would expect from comparing 235 Watts to 480 Watts).

    On a 12 Volt system you could get another charge controller and either run the Ramsonds in parallel through a less-expensive PWM type or buy another MPPT type for the Sharp; but the Sharp would have to have an MPPT controller.
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