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groingo
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# Posted: 9 May 2014 16:24 - Edited by: groingo
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Ok, the dust has settled and I found a legit source for the solar project but I need confirmation of wire guage to use, I want to have the batteries and charge controller at the house but that will be a 100 foot run (not 150) from panels to house.
The wire guage I am coming up with is 8 awg for 500 watts at 12 volts... ..or is theresomething I have missed?
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Don_P
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# Posted: 9 May 2014 18:37
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I'm coming up with about a 6 volt drop 
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MtnDon
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# Posted: 9 May 2014 19:40 - Edited by: MtnDon
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I believe the 12 volt figure is meaningless in this situation. I am making an assumption or two. This is based on using two 250 watt panels similar to the Hyundai panels mentioned in another thread and a charge controller like the once mentioned Outback FM60.
If you are running a distance of 100 feet (one way) the panels should be placed in series. This will drop the required wire gauge by several gauge numbers; like from gauge 4 to gauge 8, more or less. .
Two of the Hyundai in series the Vmp = 2 x 30.9 volts = 61.8 volts DC. The Voc on that series pair would be 2 x 38.2 = 76.4 ; then 76.4 x 1.25 x 1.25 = 119.375 volts DC. (that is for cold weather peak and NEC rules compliance) That is considerably less than the rated maximum voltage on an FM60.
The Imp (max current) on the Hyundai panel is 8.1 amperes. In series that remains the same. In parallel that would double while the voltage remains at the per panel spec.
So the calculation would then be based on a maximum current of 8.1 amps with a voltage of about 62 volts DC. For a distance of 100 feet and keeping the voltage drop to a maximum of 3% the wire gauge for copper is 8 AWG. That is a drop of 2.01% according to my EDR calculator (Electrical Designers Reference; there used to be a free limited time version available for download. Haven't looked for a couple years.) For aluminum wire it is 6 AWG.
A 3% drop is often considered as the ideal maximum for off grid situations. As the voltage rises it becomes a little less critical and 5% is sometimes used at 90+ volts. Using 5% as a maximum drop for the above data we get copper at 10 AWG and aluminum at 8 AWG.
Given the Imp, Voc and Vmp for the panels you have chosen, along with the CC model I could refine that.
The FM60 will take that incoming voltage and amperage and convert it to something to suit the battery bank voltage and state of charge. Maybe put out around 14.4 volts and maybe 35 or so amps when in bulk charge.
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groingo
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# Posted: 9 May 2014 22:58
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8 awg was the number I came up with too but I had forgotten about aluminum wire, I think copper would be best, have had my share of problems with aluminum wire overheating but maybe in this application may warrant a closer look.
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MtnDon
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# Posted: 9 May 2014 23:07
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Aluminum is fine when used with the correct connectors. In the past that has been where the issues arise. It is also helpful to use a torque wrench/screwdriver to tighten to the recommended values in heading off issues. Ones sold through electrical suppliers are expensive. I have found ones sold in the gunsmithing trade are priced more reasonably. I have one by Wheeler with a set of assorted bits.
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groingo
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# Posted: 10 May 2014 19:16
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Strange you mentioned that because for years in my 1500 sqare foot home I kept noticing dimming lights and a soft humming sound but could never get a handle on it till one day the lineman from the power company was out trying to see why (three others before him had been out over the 6 years), this guy went straight to the main box in the house, turned it off and pulled out his torx wrench to find the nut was finger tight, he checked the cable (minor melting) lubed it put it back and this time torqued it to 70 ft pounds, no problems after that, then several years later the house got totaled out by three large douglas firs.
Going to oder the solar Monday from the Solar Store in Oregon... .gonna stick with 500 watts which will be more than enough juice to do the job.
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