Solar Wire Size..??? Fuses on panels...??

see page 5 of 16, 4 gauge (36') for 20A (Isc *2, 8.48A * 2 = 17A)
http://www.bogartengineering.com/sites/default/files/docs/SC2030-7-6-15-UsersInstruc.pdf

A circuit breaker with the ability to turn off is a good idea so the panels can be turned off at the controller when needed.

10 gauge wire seams to be about the best compromise between cost and loss, 8 gauge would be better for the length of run you have but 10 gauge will work fine. 4 gauge is probably the best and if you have the cash to run 35' of 4 gauge which will require 70 total feet of wire then go big. Basically it comes down to how much line loss is acceptable for the cost of the wire.
As for the fuse I would put a 40 amp inline fuse at the controller if for the only reason to have a way to disconnect the solar panels from the controller and batteries. Its nice to be able to disconnect the solar input if you need to take the batteries off the trailer for any reason like I had to do when I took my trailer into the shop for front wall work and I knew they would have to remove the batteries to do there work. With my controller the battery's need to be hooked up before the solar panels or the controller may be damage, well you know the guys at the shop don't know this and if they did they probably wouldn't do it right anyway. Its sure easy to pull a fuse right at the controller then getting on the roof to disconnect panels or pulling the wires from the controller plus a fuse is always a good idea.

You don't need anything between the panels and controller except wire, and a separate 10ga or at least 12ga for each panel will be fine. Your voltage loss on the panel side will not be noticeable.

This is why I'm confused......

Some folks are saying 4ga wire and other are saying 10ga wire. The place I bought the panels (AltE) said 10ga would be fine for up to 50'. But then I read that you need 4ga for 50' at 20-25amps...........

But, will these panels really put out 20-25 amps? That's the part I don't understand.

The hard core tech guys are going for as little line loss as possible between solar and controller. Your panels might in the perfect world, sun at perfect angle and perfect temp hit there max of 25 amps at least for a minute or two.

I understand your confusion as I just went through this as well. I have 200 watts on my trailer roof and 35 to 40 feet of 12ga wire to controller. Controller is about 6 feet from batteries with 4ga wire. I have a 20 amp inline fuse at controller and 40 amp fuse between controller and batteries. The kit I purchase came with the 12ga wire, if I knew what I know now I would have purchase a roll of 10ga twin lead from e-bay and used that. I now have a roll of the 10ga and will rework my wiring when I decide to put 2 more panels on the roof. The 40 amp fuse between controller and battery was in anticipation on have 400 watts of panels but due to other trailer repairs I haven't purchased them yet and I am wondering if I really need another 2 panels. My 2 week trip the end of the month will be the deciding factor on the other 2 panels.

Thanks Muddydogs,

I have a large roll of 10/2 UV protected outdoor wire that I'd like to use if I could. But after spending nearly $800 on the panels and controller, I don't want to cut corners where it could matter most.

I just returned from Lowes and I can buy 4ga for 71 cents a foot. Would only cost me $71 for 100 feet. My practical side says I should simply do it and not look back....All for a few minutes a day of perfect solar output.... :-)

The lower the DC Voltage the larger the wire has to be. In parallel you have to size it for 18VDC and add the amps from both panels. If you wire them in series you can use smaller wires as it will then be 36VDC and add the amps for one panel. There are reasons for either installation method.

I have 4 24VDC panels wired 2 in series & 2 parallel making it 48VDC. That allowed me to use 10 GA wire.

Go online & search for DC wire sizing calculator.

I just installed 2 150 watt panels on my 5er. I used 10 ga from each panel to a water proof junction box on the roof (about 8 feet). From the junction box to the controller is 8 ga with a 30 A fuse in the line to enable shutoff as well (about 8 feet). Same 8 ga from controller to batteries (about 8 feet). Works well.

Housted

Yeah, whats a lousy 71 bucks? Go ahead, overkill it w/ 4 gage, but don't come cryin back when you realize you made a costly mistake, when you have to fight that heavy stuff at every connection you will be making.
And if you think you need 4ga on the roof, that means you will need 1 ga from the controller.

Ran... I hear you! We used to use welding cable when I was installing high end car audio systems because you could bend it around corners easily.