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Old 03-20-2012
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Solar panel wiring question

I currently have two panels wired together going to my controller.

I want to add two more panels. My current panels are wired together and then use size 10 wire to the controller. I want to wire all my panels together so I was thinking of putting in two bus bars to connect them to and run 8 gauge wire from the bus bars to the controller. I was then going to keep the existing 10 gauge on the current panels and use more 10 gauge to go to the new panels from the bus bars.

Will this work if I calculated all my panels wired together and need to use 8 gauge wire for a 3% drop or will I need 8 gauge wire to all 4 panels?
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Old 03-20-2012
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Re: Solar panel wiring question

Volts? Amps? Watts? series? parallel? Controller type?

The 3% voltage drop in general boat circuits is useful, but consider the charging system to be a special case. At a nominal 13.8 volts, a 3% drop is 0.414 volts.

So if you would put 13.8 volts out of the panels into the battery at 'zero' loss, with a 3% voltage drop your 13.8 volts would now be only 13.386 volts. If the sun isn't high and bright, 3/10's of a volt means 30% less capacity in your battery before the charging stops.

I'd go for "Oh come on, this is ridiculous" sized cable in the front end of the charging systems.
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Old 03-20-2012
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Re: Solar panel wiring question

dem be some big ol panels...

i agree with hellosailor, thats a lot of current capability for the front end on panels. at 12v your looking at about 50A at 10g...

and yes there are a few other factors that will cause that to change... but not by THAT much lol


imho of coarse
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Re: Solar panel wiring question

ok i retract my last statment, though i have never had any problems with that guestamasion...
here is a link that gives size/length/watt
DC Wire Table
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Old 03-21-2012
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Re: Solar panel wiring question

Rozz, there's nothing wrong with 3% and all, it is just a matter of "you can pay me now or you can pay me later". Heavy tinned cable costs a bloody fortune. One gallon of fuel now costs what one minute of "not too far" overseas phone time cost forty years ago. And phone time globally costs, haha, a fraction of what fuel used to cost them. Hmmmm.

Some of us are "watt misers" who would just prefer not to waste power in the cables. Other folks figure, cable is damned expensive, they'll tolerate more losses in it.

So you roll the dice, you choose whatever compromise makes you happy. There's no right or wrong about it, unless the watt police come on board and audit you.(G)
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Old 03-22-2012
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Re: Solar panel wiring question

i was agreeing with u, and was just saying i wouldnt go up in size (or down in ga, how ever u wanna say
i have on the smaller side panels, and i think my wire is like 18gax20ft... and according to that chart im WAY in the red lol
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Old 03-22-2012
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Re: Solar panel wiring question

Ah, gotcha.

Don't worry, it can get worse. On a boat you want to be using "AWG" American Wire Gauge sizes. In the auto parts store, they sell SAE (Society of Automotive Engineers) sizes. An SAE-18G is about the same as an AWG-20G, there's a full two-step difference between "same" numbers from the two groups.
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Old 03-22-2012
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Re: Solar panel wiring question

For what its worth, I think always better going heavier on the wire cables, my be oever sized for the load when 100% new but a few months at sea, and everything starts to get attacked by the elements no matter how well made or sealed and after a year or 2? Best I think go heavier, just my 2 cents worth.
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Old 03-22-2012
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Re: Solar panel wiring question

With wiring the only disadvantage to going heavier is cost.

The panels feed to the controller may, some say be lighter because you are starting with a higher voltage - around 17.7 for a nominal 12 volt panel. But that is max output - earlier in the morning and later in the day it will be less, and voltage drop makes it worse. I would go heavier if possible.

For the run from the controller to the batteries heavy wire is important as is placement - the closer to the batteries without being in the same compartment the better, maybe the other side of the bulkhead. The voltage at the controller's output side should not drop before it reaches the batteries. as it does in many installations.
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Old 03-22-2012
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Re: Solar panel wiring question

Gus-
'and everything starts to get attacked by the elements no matter how well made or"

Fully tinned wire. Honest, the stuff lasts forever, especially if you do a decent job at sealing the ends. I'm a cheap SOB on some things, but I've come to appreciate tinned wire so much that I really hate to use plain copper for ANYTHING besides household power cords.
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