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Old 23-09-2010, 12:51   #1
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Solar Panels, What Size Wire ?

Good evening,

Help please. I am fitting two 45 watt solar panels onto my boat. They will be charging two 105 amp batteries.

What size (dia) must the wireing between the panels and the batteries be?

Also, what size must the wireing between the two panels be.
I plan the rig it up in paralel. Is that best, or should each panel be wired seperately to the batteries?

I really want to keep things as simple as possible as the boat has a very uncomplicated electrical system and I want to keep it that way. So I can understand it and fix it myself.

My boat is a minimalist Farrier trimaran. The solar panels wil be the only energy sorce.

Thanks in advance,

Banjo.
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Old 23-09-2010, 12:57   #2
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You'll need to know the distance of the wires, but try this:

Wire sizing calculator for Solar Panel Arrays
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Old 23-09-2010, 13:21   #3
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usually you would run from the panels to a controller and then controller to bank. A few in line fuses the bank. Get a controller thats bigger then the actual load so if you want to put an extra panel in it will handle the add. Same thing with your wire step it up a size so long as it will fit the terminals on the controller.
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Old 23-09-2010, 13:24   #4
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Parallel vs. Straight Runs

I would definitely rig them up parallel. I am a firm believer that battery terminals should have one thing connected to them. The rest of the nodes should be at junctions, terminals, bus bars, or whatever you use. Rigging in parallel is essentially the same as leading the panels to the batteries individually. It will take less wire, of a lower gauge, and leave you with a more organized circuit.
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Old 23-09-2010, 13:59   #5
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Originally Posted by rebel heart View Post
You'll need to know the distance of the wires, but try this:

Wire sizing calculator for Solar Panel Arrays

Thanks a lot!

It works out that I should use 10 gauge AWG (American wire gauge). Any idea what that would be in metric?

Regards,

Banjo.
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Old 23-09-2010, 14:39   #6
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Quote:
Originally Posted by Banjo View Post
Thanks a lot!

It works out that I should use 10 gauge AWG (American wire gauge). Any idea what that would be in metric?

Regards,

Banjo.
2.59mm

http://www.technick.net/public/code/...=util_awg_calc
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Old 23-09-2010, 14:53   #7
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2.59mm
That is the conductors diameter, but it will be sold as 6mmsq
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Old 23-09-2010, 16:56   #8
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Quote:
Originally Posted by Banjo View Post

What size (dia) must the wireing between the panels and the batteries be?

Banjo.
Hey Banjo, The panels have some wires already attached. Go the same size as them. Any bigger is uselss as it can't grow electricity in the wire.

no smaller as you don't want to lose any electricity.





Mark
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Old 25-09-2010, 12:48   #9
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Good evening,

Thanks a stack everyone. It is appreciated.

Banjo
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Old 27-09-2010, 12:52   #10
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Hey Banjo, The panels have some wires already attached. Go the same size as them. Any bigger is uselss as it can't grow electricity in the wire.

no smaller as you don't want to lose any electricity.





Mark
Definitely not true, Mark. In the DC world, a short length of smaller diameter (larger gauge) wire can carry the same amperage as a longer length of larger diameter wire - as long as the resistance of each is the same. If what you said is true, then the fuse-able link in the 25A ATC blade fuse I have protecting my head macerator motor would be the same diameter as the cable feeding it. One look at the fuse element inside the fuse tells you that's not the case...

A length of wire certainly can't "grow electricity", but it can certainly cut down on the available power delivered to your battery bank. Skimping along with undersized wiring will just make the solar panels look bad.

Banjo - make sure that the calculations you're using, whether it's a program or if you're consulting wiring tables, tell you whether the distance from the batteries to the panels is total round-trip distance (usually that's the case), or one way. You can come up way undersized if you're not paying attention...

Also, these solar panels are just to keep your two T-105's topped up while you're away from the boat, right? They certainly won't be able to keep up with any decent load...
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Old 27-09-2010, 13:26   #11
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Do you distance calcs for amps and use the largest size possible. I am using #10.
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Old 27-09-2010, 13:40   #12
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"The panels have some wires already attached. Go the same size as them. "
Not necessarily, Mark. That wire size is "correct" if and only if that wire is connected directly to the battery--and not extended. In fact, one might want to cut off the original wires and replace them with a heavier gauge in order to lower the voltage drop, when a longer wiring run is needed. Especially if it isn't tinned wire in the first place.
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Old 27-09-2010, 13:44   #13
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Banjo,

Based on the round trip distance, and the fact that I ran my wiring through my engine compartment enroute to my solar charger / controller, I needed some pretty heavy wiring (can't remember, but I think #6). This would have been too large to fit the terminal screws on either end, and difficult to run inside my bimini tubes, through a deck compression fitting, etc. So here's what I did:
1) #12 gauge wiring from the solar panels, down the bimini tubes, and through a waterproof gasket fitting in the deck.
2) A pair of power posts just below deck, where the wiring switches to #2 gauge cables and then runs forward.
3) Another set of power posts in the electrical panel, where the wiring switches back to #12 and makes a 6" run into the charge controller.

I calculated the resistance and voltage drop of these three segments independently in order to determine the right combination of wire gauge and length. It was easy to install, and I see a negligible voltage drop in my system. Hope that helps.
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Old 27-09-2010, 19:55   #14
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Another way to keep the wire size down is to connect the panels in series instead of parallel. My panels require 4AWG in parallel but only 10AWG if connected in series.

Mike
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Old 27-09-2010, 20:13   #15
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Over size the wire before you under size it. Make sure it's tinned marine wire. Buy a solar controller unless you're going to disconnect the panels when you're gone. I under sized wire when adding a 3rd, 125 watt panel and it created a problem with my "Blue Sky" solar controller. Fortunately Blue Sky diagnosed the problem.
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