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.

[Rbertalotto]

I stopped by the Welding Supply house yesterday morning. On the "Clearance" table was a roll of 4g welding wire with 80' remaining. EXACTLY the length I needed. Decision was made. Going with 4Ga on my install.


Got the panels installed and all wiring done on the roof



Interesting to note that the panels were outputting 5.6v even being covered with heavy cardboard!

Ran wires down the refrigerator vent and under the trailer to front area. I also realized that the screen Forset River uses in this area has very large holes that ants, bees, etc could access. I cover it with a piece of window screen while I was up there.



Built a panel for the solar controller, shunt and 12V main tap. Mounted a stainless steel bolt through a piece of Delrin plastic to bring all 12V leads to one place within the trailer. On this trailer the batteries sit on tongue.



This panel will ultimately be within a new front storage compartment with outside access as soon as the cargo door shows up.

Today I'll finish the install and get everything wired to the two group 31 AGM batteries.

Lots more detail on my web site
www.rvbprecision.com

[bukzin]

If you haven't seen this article it is well written with tons of great battery and solar info.


https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

[red31]

Morningstar string calc shows min Vmp @ temp (includes cell heating)

For a similar kyocera 140, min 15.58 Vmp @ 80F, 15.14 @ 90F, 16.9 @ 50F, full sun.

So if one takes 14.8v @ controller and adds 1.94v drop for 12g, 35', 17A, the result is 16.74v, this would be to the right of 15.58Vmp 80F, IV curve.

assuming a straight line from Vmp to Voc, 15.58 to 19.98 (mornstar sting calc @80F), ~2A loss or 26% of 7.78 Imp, more when hotter. @50F one should get full power, just to the left of Vmp on the IV curve.

Throw all this out claiming 14.3v charging AGM, full sun rarely, lpwer panel temp, 17A Isc vs 15.56A Imp, panel aging, never see 80F or higher, good enough, ...

[time2roll]

Video from alt-E on choosing wire.

https://youtu.be/89u8R_aUFO4

No idea why it starts in the middle. I recommend watching the whole thing.

[CJW8]

I'd go with no less than #4. You said the wire run was easy. Make it even easier with #4 welding cable. You'll be under 3% loss and out around $100. Guys that are recommending #10 and 12 wire are not getting maximum potential out of their systems. Yes, they work but could work better with bigger wire. my last system had 3- 135 watt 12 V parallel panels with #4 welding cable. My new system is getting 2-250 watt 24 V panels in parallel with # 6 Welding cable at 30 feet. If my controller would take the voltage, I'd wire them in series to be able to use smaller wire. A fuse is not necessary, in my opinion, but they are handy as a convenient disconnect. I do not know if they are required by any code.

[red31]

30C hotter, NOTC for a 140w is 45C @ 20C and that is 800 w/m^2 20C, back open to slight breeze.
Note Vmp NOTC is 16v.

So the coefficient for Vmp is -.5%/C, 30C * -.5%/C = -15%

18Vmp * (1-.15) = 15.3v
so another .5v loss is 14.8v to stay on the left of Vmp.

Do ya just ignore Vmp dropping due to cell temp, the current drops fast on the right side of Vmp.

[time2roll]

red31 wrote:

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.

Please show a detailed calculation.

[pianotuna]

Muddy,

Some of us are power hogs! I use up ever watt my solar panels produce and then some.

[westend]

It sounds like you already have a supply of good 10 AWG at hand. I would double that from the panels and install a circuit breaker like this Manual reset breaker before the controller. Since this breaker accepts large lugs, you can join the two panel 10 ga runs at the breaker and lead out a 4 awg wire to the controller. This will afford circuit protection but also an easy disconnect.

Good luck with your solar installation.

[pianotuna]

A circuit breaker before the controller is a good idea but may not be essential. A fuse at the panels is not a good idea, unless you have mountain goat genes.

[grizzzman]

Rbertalotto wrote:
The cable run on this trailer is incredible simple. Down the refrigerator vent and under the trailer to the front compartment. The controller will be 24" from the batteries.

Thanks for all the great comment!

For your information the Bogart system is equipped with voltage compensation as long as you keep voltage drop below 3% to 5% overall.
That being said i would stay below 3%.( personally i stay below 1%)

[Muddydogs]

RoyB wrote:

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.
Roy Ken

But why? From the time the sun comes up until its dark the panels will be pulling in power and unless you are using a lot of power during the night you battery's will probably be charged before the magical 3 hours of high sun. With 200 watts of panels on my rig by 11am my 2 12 volts are charged and floating. Its not like all the charging has to be done during the 3 hours of high sun, during this time its time to use any high draw stuff that might be needed since your throwing away power like running the 12 volt air compressor to check air pressure in the trailer tires.

[Rbertalotto]

The cable run on this trailer is incredible simple. Down the refrigerator vent and under the trailer to the front compartment. The controller will be 24" from the batteries.

Thanks for all the great comment!

[Rbertalotto]

My last truck camper had a single 120w panel with a Morningstar PWM controller and a single group 31 wet cell battery.

Every weekend I'm away on a three day event and all spring and summer I never ran my generator to recharge the battery.

All lights are LED. No TV. Recharge phone and laptop every dayt and in the early spring the furnace ran every 20 minutes for a couple minutes for two nights.

I was extremely pleased with that setup.

But the roof on the Palomino Bronco could only fit one panel.

This new Toy Hauler can only fit three panels without shadowing. I figured for the extra few $$ I'd add another panel and a second battery.

This TH will see a TV getting used from time to time and the grandkids play video games for an hour or two each day.

Hopefully, off the grid it will serve me well.....We'll see.

[More_To_See]

Your panels will provide about 15 amps maximum current and you have a 35 foot run. To hold your maximize voltage loss to 5 percent you should use 6 gauge cable.

Up at the panels you should fuse for 20 amps.

You must also fuse at the battery for 20 amps on the cable over to your charge controller.

Since the charge controller should be as close to the battery bank as possible perhaps within a few feet and no more than 5 say you could probably get away with 6 gauge cable there too or if you wanted to go to 4 and it wasn't too difficult do it.

if you were a solar installer company or a RV manufacturer you would very carefully trim every penny possible off the cost by using cable that was as small as possible and probably not quite adequate for a good installation.

But you are doing this one time on a run that will probably be difficult to snake a cable through so the last thing in the world you want to do is nickel dime yourself with too small of a cable.

If you have a difficult cable run you might look into super flexible cable but that stuff is real expensive.