Wire Size & fuses for solar install

pigman1 wrote:
You can do a lot better than $80 for a combiner box. Buy a 5 or 6" square PVC box at Lowes or Home Depot and add an extra top

Yes. This was exactly what I was going to do before decided just to run series #10, following the steps of Smkettner and others. Easy, no box.

And, there are grey PVC waterproof boxes in the same Home Depot with top and gasket included. 4x4x2" or 4x4x4", cost $6 or so. I even bought one and immersion-tested in in a sink, it is waterproof indeed. Click on the link by Renoman69's in the middle of the list, there is this box on the roof and another one inside.

Luckily, I didn't need rooftop box with series wiring, and the OP also can "cheat" here with his parallel, here is how:

You have those MC4 Y-splitters included with 140W pairs. Buy MC4 cable #8, say, 40ft (see my link few posts above). Cut it in half and run from Y-splitters to inside, using strain reliefs on fridge vent or any cable grips - NOT important, on the vent it isn't a watertight seal anyway. Then install one PVC junction box inside, and run #6 from there. As estimated above, 35ft #8 is enough or very close. So, 17ft of #8 plus 17ft of #6 will be acceptable. No roof J-box. I don't like roof J-boxes. If left for summer in Mexico, this gray PVC would become white and brittle, don't know how waterproof the lid will be then.

I posted the link to the entire List of installs, because the very 1st link by Sleepy shows the above mentioned AM Solar $60 J-box for fridge vent, if you still want a roof J-box. Note how vent cover is bulging with this J-box.

pigman1 wrote:
You can do a lot better than $80 for a combiner box. Buy a 5 or 6" square PVC box at Lowes or Home Depot and add an extra top. Cut the PVC top to separate the box into 2 compartments and add 2 small ground bars, one for pos and one for neg. When your feeds come in from individual panels, splice a small flat fuse into each line and individual panels will be protected. I dropped the main feed to the controlled directly out the bottom ans sealed the box to the roof.

A bit of work can save a lot of $$$. Just take your time and keep your options open.

I used this LB because I piped the 4 AWG from this box down to the controller. A 4" plastic box would have been easier to use.

Niner and Almot just got added to the favored nation's list. You guys are on point on all these threads.

You can do a lot better than $80 for a combiner box. Buy a 5 or 6" square PVC box at Lowes or Home Depot and add an extra top. Cut the PVC top to separate the box into 2 compartments and add 2 small ground bars, one for pos and one for neg. When your feeds come in from individual panels, splice a small flat fuse into each line and individual panels will be protected. I dropped the main feed to the controlled directly out the bottom ans sealed the box to the roof.

A bit of work can save a lot of $$$. Just take your time and keep your options open.

McKenziek wrote:
I found this combiner that will accept inputs from the MC4's. Looks like I would mount this on the roof and run two 6 AWG wires, one positive, one negative, from it to the controller. Sound right?

http://www.solar-electric.com/misomnsoarco4.html

No. This is to mount vertically on the wall inside or outside, ex. on your shore cabin.

For roof junction box (IF you have to use one) you need the one from AM Solar. The smaller/cheaper one for $60 that mounts vertically on the fridge vent, is good enough for you. They say "...if you batteries are near your fridge", - nonsense, disregard it. The very 1st link on the List of installs by forum members - Sleepy - is using this fridge vent box, check his photos.

Or you can use MC4 Y-connectors and run MC4 #8 inside, and then use either that big ugly box in your link or $10 plastic junction box from Home Depot. Like I said, #8 is "almost enough" to run all the way to controller without without transition to a thicker cable, i.e. without any junction box.

Ok, so much for doing this on the cheap.

Solar Blvd is cheap to buy panels and sometimes controllers. They are not cheap to buy MC4, and MC4 #8 they don't even carry.

Ok, so much for doing this on the cheap. I found this combiner that will accept inputs from the MC4's. Looks like I would mount this on the roof and run two 6 AWG wires, one positive, one negative, from it to the controller. Sound right?

http://www.solar-electric.com/misomnsoarco4.html

Which fuse between battery and controller?

Thanks for the inputs.

Why did you parallel them? Higher voltage equals less voltage drop.
If they were in series than #10 would be more than enough and your charge controller should handle the voltage. no problem.

Now I understand why nobody ever heard of Solar Bvld installation consultants :)...

You have 17 vmp, 8.4isc*4= 33.6 isc.

There are many voltage drop calculators, results are usually the same.
Calculator says that AWG 10 will result in 13% V-drop. This is too much for PWM.

AWG 8 will get you 15.4V at the controller, so #8 is the bare minimum that you should use. Buy 80ft roll of MC4 AWG 8, and cut it in half (you need MC4 plugs at the panels and bare ends at the controller). Or 100ft roll, if you are not sure that it's precisely 35ft distance. Then with #6 cable to battery you will still get over 15V if each Pos and Neg cable to battery is shorter than 6ft. Run the calculator yourself.

You should've bought MPPT 45. Then with AWG 10 you would lose 13% of daily AH haul (more likely just a few % because conditions are not perfect all the day). But high voltage drop wouldn't affect the charging voltage at the battery.

PS: I hope that whoever you talked to at Solar Blvd, did not suggest to use AWG 10 from controller to battery. Because if they did, tell the management to fire this m.oron.

For that distance, to the controller, I'd run 6 gauge. I'd also run the charge controller no more than 3 or 4 feet, maximum, from the battery. Again, 6 gauge. I'd adjust the charge controller to get voltage to 15.0V measured, at the battery. You want to get the battery as close to a 100% charge daily, as possible. 14.4V might get you to 90%, if that.

The 10 AWG won't carry 40 amps. You need much larger wire and I would suggest to move the controller closer. Wire size from controller to battery also depends on distance and the battery wire fusing is based on wire size and load.