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

[Rbertalotto]

Ok, ready to install my solar system and I need to buy wire to go from panels to the solar controller

Two, 140W panels, wired in parallel

Here are the specs on the panel:



The wire length of run from panels to controller will be 30-35'

I'm a bit confused on wire size......

Also, do these panels need to be fused at the panels? If so, what size fuse.

I really appreciate all the help this forum has afforded me over the years. Hope to repay it someday.

[RoyB]

My basic wire use here in the AMCOR very flexible 4AWG cable. For my panels I will run the 4AWG cable to a junction box close to the panels and then run smaller size cable from the the individual panels to the junction box.

I will want to use the quick disconnect cables at the panels so that they can be removed if needed... There are several install kits in the solar world that use the quick disconnect idea...

My goal for my upcoming solar panels will be be to produce at least 20AMPS of usable DC Current during high sun in hopes to re-charge my multiple battery bank to at least there 90% charge state before I lose the high sun. Then I can use the batteries for the next day/night run off the batteries...

I would love to have enough solar panels to re-charge my batteries to their 90% charge state in a three hour charge run but this is unrealistic cost wise to attain. My current battery banks want to use 52-53 AMPS DC current when first hit 14.4VDC charging voltage from the controller. This would require several solar panels in he setup since most 120WATT Solar Panels will only produce around 15-19VDC at 5-6 AMPS of usable DC Current. Just having a couple of these sized panels on the roof will take alot of hours of high sun to achieve this before your high sun goes away at the end of the day.

Just some of my thoughts here in my planning for solar panels to supplement my 2KW Generator run each day when camping off the power grid...

Roy Ken

[pianotuna]

If pwm #10, if mppt #8. Since you have the wire already consider doubling up on #10.

[red31]

smkettner wrote:
#12 is fine by my calculator(16+ volts at controller), kill it with #10.

Do ya just ignore Vmp dropping due to cell temp and let the panel operate of the right side of Vmp at way less current?

I figured on a sunny day Vmp ~15.3 and 2 sets of 10g/8A/pair and max controller input would be ~14.8 staying on the left of the curve.

[ewarnerusa]

Muddydogs wrote:
...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.

I agree with others about not needing to use as large of gauge wire as possible between panels and controller. However, when you are installing your own system it is nice to design it with expansion in mind. I used 4 gauge wire in and out of the controller which is the max size the controller terminals could accommodate. If I expand, no rewiring will be required. Plus piece of mind knowing I have minimal voltage loss due to wiring.

I definitely agree with Muddydogs' advice quoted above regarding fuse/circuit breaker between panels and controller. I use circuit breaker which is even more convenient than pulling a fuse.

[time2roll]

#12 is fine by my calculator(16+ volts at controller), kill it with #10.

http://www.genuinedealz.com/voltage-drop-calculator

You don't need more than 15 volts at the controller as the controller or battery will drop the voltage to 14.8 or less. #4 wire will have 17.7 volts at the controller and still just get clipped by the controller or battery.

What you really get is Isc 17 amps until the battery voltage rises to the controller set point. Then amps taper off like normal and eventually controller drops voltage to float.

No fuse needed with two panels. (series fuse rating is 17 amps or two panels)

[NinerBikes]

RJsfishin wrote:
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.

Not even 20 amps, run is a bit long, but yeah, 10 gauge or 8 gauge to controller is fine. I don't know why folks with adjustable Voltage Charge controllers don't compensate for loss in voltage from controller to battery, due to wire size, at the charge controller?

[Rbertalotto]

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.

[RJsfishin]

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.

[Housted]

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

[hypoxia]

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.

[Rbertalotto]

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.... 🙂

[Muddydogs]

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.

[Rbertalotto]

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.

[RJsfishin]

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.

[Muddydogs]

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.