solar wiring December 17, 2010, 09:24:16 pm Yahoo Message Number: 119133ld uses #10ga. wiring for their solar system. does anyone know how many watt system that ga.wire can handle. i'm guessing 300watts?
solar wiring Reply #1 – December 17, 2010, 09:57:20 pm Yahoo Message Number: 119135Quoteld uses #10ga. wiring for their solar system. does anyone know how many watt system that ga.wire can handle. i'm guessing 300watts? I think 10ga wire would be marginal with 300 watts of panel. There could be some voltage drop during max solar hours. I would use 8ga. In fact I did.Tom Johnston
Re: solar wiring Reply #2 – December 17, 2010, 10:27:17 pm Yahoo Message Number: 119136Peter, It's not quite that simple. The gauge of the wire is one of a number of variables. Another important variable is the length of the wire. These are the things that will limit what is a safe current (i.e. the max safe Amps) and also a practical current (i. e. there is only a small voltage drop due to the wire). When the wire length is too long, much of the energy would be wasted as heat in the wire and not delivered to the device you want to power. An peripheral variable is the insulation on the wire. It needs to be OK for the voltages involved. So, for example, 15 feet of a 10 gauge wire pair would be good for 20 Amps or so. At 12 Volts, that is 240 Watts. (W = V x A). But the circuit voltage would be another variable. The same wiring for 120 volts is good for 2400 Watts. If it was 1000 Volts, it would be good for 20,000 Watts! But, in the LD, for solar panels putting out 18 Volts that would be 360 Watts. If it's the newer panels with 20.8 Volts, that would be 416 Watts.Alex Rutchka, SE #4 '05 MB
Re: solar wiring Reply #3 – December 17, 2010, 10:36:30 pm Yahoo Message Number: 119137Quoteld uses #10ga. wiring for their solar system. does anyone know how many watt system that ga.wire can handle. i'm guessing 300watts? A 300W system would have less than 17A maximum current to the charge controller, which is well below the capacity of 10ga wire. The resistance of the wire is about 1 Ohm per 1000ft. If you have a 20' run, double that for both conductors, then at maximum current you would have a voltage drop of about 0.68V. If you used 8ga wire, the voltage drop would be about 0.45V. I doubt if rewiring would be worth the minuscule improvement.Steve
Re: solar wiring Reply #4 – December 17, 2010, 10:48:24 pm Yahoo Message Number: 119138Quote A 300W system would have less than 17A maximum current to the charge controller, which is well below the capacity of 10ga wire. The resistance of the wire is about 1 Ohm per 1000ft. If you have a 20' run, double that for both conductors, then at maximum current you would have a voltage drop of about 0.68V. If you used 8ga wire, the voltage drop would be about 0.45V. I doubt if rewiring would be worth the minuscule improvement.Steve Oh, I agree completely. Its just in starting an install from the beginning 8ga was my choice. I do tend to overbuild a bit. Besides, maybe even more panel may be added later. Tom
Re: solar wiring Reply #5 – December 18, 2010, 12:03:30 am Yahoo Message Number: 119139Peter, One way to look at it is to determine the maximum current the panels can provide (listed as isc on the panel's spec sheet) and make sure the total (the sum of all the panel's isc values) doesn't exceed the maximum current handling capacity of the 10ga. wire. Most respected charts list the maximum current capacity of 10 ga wire in conduit at 33 Amps (much higher in open air, by the way). As far as solar panels go, AMSolar's new 150 W panels (model RV150) list their isc at 8.2 Amps. 4 of these panels (or 600 Watts of solar) could at max produce 32.8 Amps, still under the 33 A capacity of 10 ga wire. Of course the panels will never reach that output in the real world so a natural safety factor is built in. The other side of the coin, of course, is voltage drop, which is dependent on length of the wire and the current thru it. My gut feeling on that is that for the short runs we are talking about, it's not a big deal, especially when you realize that it increases as current increases which is when the sun is bright and you probably are having little trouble keeping up with demands at that time anyway. Just another way to look at it, and YMMV, but you did ask for maximums.Rich Gort - 2000 MB - Birch Bay, WA
Re: solar wiring Reply #6 – December 18, 2010, 12:10:46 pm Yahoo Message Number: 119146QuoteOh, I agree completely. Its just in starting an install from the beginning 8ga was my choice. I do tend to overbuild a bit. Besides, maybe even more panel may be added later. Tom Another consideration is energy 'wastage' - 17A X 0.68V = 11.6W, 17A X 0.45V = 7.65W. So, with the smaller gauge you would be wasting about 4W more than with the larger gauge wire - out of 300W. This too would occur only with a very heavy demand - using lots of appliances during sunny hours and/or a very discharged battery bank. So, choice would depend heavily on individual circumstances, but for up to 300W of panels, I don't think switching the wiring from that LD supplies would be worth the effort or cost. For OUR uses, I'm saving the pennies toward funding the sort of interior lighting LED conversions Mike has done, which will conserve a whole lot more charge capacity than any difference in PV upgrading could possibly compensate for.Steve
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