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Old 30-03-2010, 12:09   #1
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Wire Sizing for Installing Solar Panels / Wind Generator

I am adding an Air breeze to my boat with a one way wire run of 25 feet. To get <3 % voltage drop calls for 6awg. My solar panels are 210 watts each 12 v wired in parallel. This run will also be almost 25 feet one way. A 3% voltage drop would call for 4 awg. I am using a Blue sky 3024 controller. I would like to go down one size on each installation but not if it will create a problem. Any comments on wire sizing. Also the panels came with mc-4 connectors. I am thinking of cutting these off and hard wiring the panels. Or are the mc-4 connecters ok to use. The panels will be mounted on an arch. Thanks
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Old 30-03-2010, 13:34   #2
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you can use one of many wire calculators and make your best guess. here's one:
www.csgnetwork.com/wiresizecalc.html
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Old 30-03-2010, 14:11   #3
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RE: the wire sizes - Oh hell, why not just run some 14ga and be done with it? All that math and science is such a bother....

OK, sorry to be so sarcastic, but you have already answered your own question as to wire sizes, but now you've turned to the forum for permission to skimp. Don't skimp on wire size. If anything, go one bigger; never smaller.
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Old 30-03-2010, 14:31   #4
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it would only create a problem at max current capacity operation and then how you going to put that electrical fire out? LoL
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Old 30-03-2010, 14:32   #5
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Eddie,

You can size the wire from the solar panels to the controller at the MPP voltage which depends on your panels and is higher than 12v (more volts less amps).

You can size for a 10% voltage drop and everything will probably work fine but you'll be wasting an additional 7% of the output of the panels, panels are expensive so may as well get all the output you can.

I would calculate the actual voltage drop using formula VoltageDrop=Amps*Resistance for various wire sizes and decide if it's worth it to you to use to use heavier wire.

Doug
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Old 30-03-2010, 15:06   #6
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No, not looking for an excuse to skimp, I just thought I might not already know everything about wiring alternative energy. Thanks for the input.
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Old 30-03-2010, 15:26   #7
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Planning for a 3% drop is best, as Thea pointed out, to take advantage of your invested capacity. A 10% drop is usually accepted in "non-critical" uses like lighting.

Amps, volts and resistance inside the wires don't change based on the charging source, be it conventional or alternative. 20amps at 12volts solar power is exactly the same as 20amps at 12volts put out by your alternator.
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Old 30-03-2010, 15:27   #8
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You could install either an Outback flexmax or Xantrex XW charge controller, and wire the panels in series. Then a smaller wire size would be fine.
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Old 30-03-2010, 15:36   #9
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Considering the wires that come out of the AirX unit are 10ga why would you upsize them from there to the battery all things being equal? I guess while we are on the subject of wire I have to ask "If all the manufacturers of our fine marine products insist on you, the owner, using tinned wire for all your boating needs, why do they use regular old untinned wire coming out of their equipment?" Inquiring minds(like mine) want to know. ...........m
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Old 30-03-2010, 15:37   #10
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Considering the wires that come out of the AirX unit are 10ga why would you upsize them from there to the battery all things being equal? I guess while we are on the subject of wire I have to ask "If all the manufacturers of our fine marine products insist on you, the owner, using tinned wire for all your boating needs, why do they use regular old untinned wire coming out of their equipment?" Inquiring minds(like mine) want to know. ...........m
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Old 30-03-2010, 16:14   #11
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Originally Posted by cantxsailor View Post
Considering the wires that come out of the AirX unit are 10ga why would you upsize them from there to the battery all things being equal?
I'll give them the benefit of the doubt on this one and assume that they expect the unit to be mounted immediately adjacent to the battery bank.....
Quote:
I guess while we are on the subject of wire I have to ask "If all the manufacturers of our fine marine products insist on you, the owner, using tinned wire for all your boating needs, why do they use regular old untinned wire coming out of their equipment?"
Write a capital letter S. Now draw a vertical line through it. Really, it comes down to money- yes, there should be proper tinned marine-grade wire coming out of the thing, but that's more expensive- especially when summed over ten thousand units.

As for the wires from the panels- I used to work on solar racing cars, on which we would have six to nine square metres of solar array operating at 120 to 200 volts. The array umbilical would typically be a pair of very hefty aluminum conductors, on the order of 2-gauge or larger. We saved a kilogram or two by using aluminum, and cut the power losses by a few percent by going oversize- great for a solar car, but I swear I will never use aluminum wiring again, period. Oversizing the cables, though, makes sense in a lot of cases- especially on solar panels.
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Old 30-03-2010, 16:15   #12
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Originally Posted by cantxsailor View Post
Considering the wires that come out of the AirX unit are 10ga why would you upsize them from there to the battery all things being equal? I guess while we are on the subject of wire I have to ask "If all the manufacturers of our fine marine products insist on you, the owner, using tinned wire for all your boating needs, why do they use regular old untinned wire coming out of their equipment?" Inquiring minds(like mine) want to know. ...........m
Is there about 1 foot of total wire at the panel? 10 gage is about 1 milliohm per foot. So 1 foot would be 0.035 volts drop or 0.3% drop, so a negligible drop. Also if your installation were a 10 foot round trip you would be using 10 gage wire and saying how clever they were instead of how dumb they were. They don't know how far you're going.

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Old 30-03-2010, 16:20   #13
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In my experiance wicking is an eventual reality in even the best of splices. Untinned wire will work as well as solid wire in conducting voltage. It's just a matter of how soon one will fail over the other. There are plenty of boats out there with untinned wire that have lasted years without major failure. But the cost of tinned wire over untinned wire is minor. I'd go for the extra insurance.
You just can't get around proper wire sizing, voltage drop and resistance on electrical wire especially in 12 volt configurations. Air X specs wire size at 8AWG for 0'-30' runs. Smaller wire will lower the voltage at which the wind generator enters regulation and stops charging. From their instructions
Note: Wiring Resistance and Regulation
Depending on your exact system configuration including other charging
sources in your system, wiring resistance may affect the regulation set point
of the turbine. Higher wiring resistance (smaller wires) will tend to lower
the voltage at which the turbine enters regulation and stops charging. The
recommended wiring sizes should provide little effect on the regulation set
point, but all installations should be observed over time to ensure that the
batteries are charged to the proper voltage.

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Old 30-03-2010, 17:05   #14
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I would not recommend dropping down a size. You've got to figure that each of those 210 watt panels can reach a maximum output of 17.5 amps when new, which means the run should be capable of carrying 35 amps for 25 feet one way. On the chart I use, that calls for 4 awg.

35 amps is a lot of power, even in a 12v system. In my way of thinking, heat/fire danger is more a consideration than minimizing voltage drop.
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Old 30-03-2010, 18:00   #15
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I would not recommend dropping down a size. You've got to figure that each of those 210 watt panels can reach a maximum output of 17.5 amps when new, which means the run should be capable of carrying 35 amps for 25 feet one way. On the chart I use, that calls for 4 awg.

35 amps is a lot of power, even in a 12v system. In my way of thinking, heat/fire danger is more a consideration than minimizing voltage drop.
The ampacity of the wire is the spec for how much current the wire can carry without degrading the insulation due to heat. 14 gage wire with 105 degree C. insulation is rated at 35 amps. 8 gage is rated at 80 amps (non-engine space). I don't think heat is a problem here.

John
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