Need Help With Wire Gauging

mbsimonds
mbsimonds Registered Users Posts: 11 ✭
in Solar Beginners Corner #1
I have 4x 115w 12v solar panels. The voltage is dropping dramatically by the time it gets to my controller. I need some help in figuring out what gauge wire I need to have and even what brand I should get. The distance from my panels to my controller is about 65 feet.

Also, if someone can suggest a decent charge controller at a reasonable price, that would be great.


Thanks!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Need Help With Wire Gauging

    You're running them all in parallel on a PWM type controller, right?
    The actual Imp rating of the panels would help, but I'm guessing it's about 6.5. That means you're trying to send roughly 26 Amps @ 12 Volts down 65 feet of wire. You'd need to run ridiculously large wire to achieve less than 3% V-drop there. We're talking 0 AWG.

    So the alternative is to wire them as two parallel strings of two in series for 13 Amps @ 24 Volts, which would make the wire size about 6 AWG. In order to do that on a 12 Volt system you'd need an MPPT type charge controller.

    Darn it but this is another case where the now discontinued Rogue 3024 would be perfect. There really isn't anything comparable right now and the new model hasn't been released. So you'd either have to go up to a "big" controller ($500 range) or perhaps adapt the system to be 24 Volt?

    Give us some more info on the system and I'm sure there's some other options available.
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  • rocmor
    rocmor Registered Users Posts: 11 ✭
    #3
    Re: Need Help With Wire Gauging

    Another option to span that 65 feet might be copper tubing. Just randomly googling some tubing specs comes up with rolls of 3/8" tubing, with a total cross-sectional area a bit larger than 2/0 cable, for $1.33 per foot. Being 12VDC, who really cares about insulation. Who knows, if you live in a sunny spot and are clever, you could run water through the lines and have on-demand hot water... for a cup of coffee or the like.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Need Help With Wire Gauging
    rocmor wrote: »
    Another option to span that 65 feet might be copper tubing. Just randomly googling some tubing specs comes up with rolls of 3/8" tubing, with a total cross-sectional area a bit larger than 2/0 cable, for $1.33 per foot. Being 12VDC, who really cares about insulation. Who knows, if you live in a sunny spot and are clever, you could run water through the lines and have on-demand hot water... for a cup of coffee or the like.

    Really not a good idea to run power from a current source over 65 feet via uninsulated conductors of any kind. Adding water through the middle could potentially be even worse.

    I'm not even going to bother to explain why. If you don't know, don't mess with this kind of stuff. :roll:
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    Re: Need Help With Wire Gauging

    Midnite just anounce they intend to come out with a 30 amp Charge controller in 2013!

    If you live in Missery (Missouri) I have the original design Rogue, I'd sell cheap, only set up once just to check some panels, but it won't help a bunch, you could only run in pairs (I think) so you'd still have a sizable voltage drop.

    I am heading to Cincy Ohio for Christmas, if your interested in the CC and along the way...
    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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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Need Help With Wire Gauging
    Photowhit wrote: »
    Midnite just anounce they intend to come out with a 30 amp Charge controller in 2013!

    Oh boy! That would fit so well with my own expansion plans. :D
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  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    #7
    Re: Need Help With Wire Gauging
    mbsimonds wrote: »
    I have 4x 115w 12v solar panels.

    Sounds like you have the same thing as I do. . . check out this thread. . . http://forum.solar-electric.com/showthread.php?17543-Solar-to-run-a-fridge . . 12 V run about 35 feet. . . #4 wire . . there is a wire size calculator on here somewhere. ....

    Just thinking :
    There is no way you would be able to make the solar water heater idea work, how would you separate the "+" and the "-" ? . . . the water flows in a loop. . . :p If you did go with plain old (empty) copper pipe, you would HAVE to insulate it, add that to the cost, and you might as well buy the proper wire for the job....
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #8
    Re: Need Help With Wire Gauging

    You might try craigs list or recycling centers for copper wire. End rolls and such of #4 might not be something worth saving for some. The recycle centers sell wire longer than 10' lengths around here for a premium above scrap. worth checking out! I'd try to check out any deal from craigslist as I'd hate to buy stolen wire, but once it's at the recycle center it will likely be used by someone. It goes quick!

    Also habitat centers will have wire from time to time!
    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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  • rocmor
    rocmor Registered Users Posts: 11 ✭
    #9
    Re: Need Help With Wire Gauging

    Good point, Cariboocoot. Though the part about heating water wasn't serious, it would, in fact, be a bad idea to try without building in impractical and expensive safeguards. Ironic.. I fell into the same trap I was warning about in a different thread: using AC thinking in the DC world.

    It does bring to mind something you would probably know about: a frequent question seems to be what to do with "excess" PV power, say, in an off-grid system, once any batteries are fully charged. I'm sure someone must have come up with a way to accumulate H2 and O2 gases from electrolysis and then turn around and use them to fire up a genset and/or supply heat for living spaces, but I haven't seen it discussd, nor have I heard of anything commercially available. Any thoughts?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #10
    Re: Need Help With Wire Gauging

    The gases out of the battery are mixed together--So very explosive. And, to get enough hydrogen to be "useful", would damage the battery by over charging.

    It would be better to direct the excess energy to a dedicated hydrogen generator (or water pump, start the washing machine, etc.).

    -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 ✭✭✭
    #11
    Re: Need Help With Wire Gauging
    rocmor wrote: »
    Good point, Cariboocoot. Though the part about heating water wasn't serious, it would, in fact, be a bad idea to try without building in impractical and expensive safeguards. Ironic.. I fell into the same trap I was warning about in a different thread: using AC thinking in the DC world.

    It does bring to mind something you would probably know about: a frequent question seems to be what to do with "excess" PV power, say, in an off-grid system, once any batteries are fully charged. I'm sure someone must have come up with a way to accumulate H2 and O2 gases from electrolysis and then turn around and use them to fire up a genset and/or supply heat for living spaces, but I haven't seen it discussd, nor have I heard of anything commercially available. Any thoughts?

    Contrary to what some would have you believe, batteries do not off gas enough to supply any usable amounts of hydrogen. That whole "run your car on water" scam is a scam; you simply cannot operate the process fast enough to produce usable amounts of fuel for the rate an engine would consume it. (And you sure better not be producing it that fast on your solar power system or the batteries will be "boiled dry" in no time.) We are talking about losing a 1/3 of a cup of water per cell per month, not a gallon an hour. Switching the PV output over to a dedicated electrolysis process would be essentially the same as the rate from the batteries. Would you really want another tub of acid water sitting about with tanks filling up with explosive gas? I wouldn't. It's bad enough to have to make sure the batteries aren't building up any in their case - yes, they can produce just enough to start a fire with a spark from some loose wire or switch arc, but not enough to run an engine.

    Technically it would be possible to do this. But it sure isn't very practical. It could take a long, long time before you had enough stored hydrogen to do anything with.

    But making use of the energy the PV's can produce once the batteries are full is a common off-grid practice. That's why we like the top-end charge controllers with their programmable AUX functions: reach Absorb or Float and use it to trigger an opportunity load such as pumping or heating water. Exactly what you can do with it depends on the individual system and how much "extra" power you can count on. You could control a freezer cycle (they don't really need to run 24/7) or the air conditioning in Summer or whatever else you need.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
    Re: Need Help With Wire Gauging
    rocmor wrote: »
    I'm sure someone must have come up with a way to accumulate H2 and O2gases from electrolysis

    It won't work, as others have noted, so this is just an additional quibble: Except in space or underwater there is no point in trying to collect the oxygen from electrolysis. It is common enough in our atmosphere that storing it under pressure just does not make any sense. And to store a useful amount of hydrogen you either need a very large bag (which will leak) or you need to pressurize it.
    SMA SB 3000, old BP panels.
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