Solar combiner box questions

[johnm1]

I'm looking for a solar panel combiner box for the RV's roof.

I'm going to start with 2 panels with the option to add 2 more if needed. I've seen some that are stupid expensive and some that aren't even remotely weather resistant (and still really pricey). Some people say to use waterproof junction boxes (like from the home stores) and some say they don't last very long.

Also, do I need to add fuses/circuit breakers in the combiner box of do I add them down nearer the charge controller? Seems in the combiner box is "better"?

What are my options here?

[Searching_Ut]

I've got my system set up with 10 X 100 watt panels on the roof, all wired in parallel in two 500 watt banks. Used a gray plastic combiner box on the roof, group of waterproof strain reliefs. Inside two fuse blocks combining off the panels into two 500 watt banks, two buss bars for neg wires. 6awg wiring from each fuse block to the two Bogart SC2030 controllers in the front compartment of the 5er. SC2030's are regulated by a trimetric. I spray painted the combiner box with white liquid rubber to protect from UV. System works great at handling the assorted partial shading I almost always encounter in the areas we like to camp. Of course the twin full height AC units, vents, TV antenna etc all tend to contribute to shading of some of the panels at certain times of the day as well, especially in the winter months.

With the panels you're looking at, you're going to have to use an Mppt controller, which don't do well in my experience with parallel panel strings when encountering shading. The way the bypass diodes work on the panels, they are basically panel strings even if you only have two panels in parallel, and with the mppt controller you'll loose pretty much the entire output of a parallel string that is partially shaded. None of the mppt controllers I played with seemed to be able to figure out a good setpoint under conditions where the parallel strings didn't balance out fairly well. I'd recommend a series configuration if you're going mppt, or a separate controller for each string.

[Unyalli]

time2roll wrote:
Great source for #4 custom cable: (or larger)

http://www.genuinedealz.com/custom-cables/custom-battery-cable-assembly?size=57

Verify the battery stud size and the controller lug size for perfect fit.

Great people. They built my 4/0 cables exactly to my measurements center of lug to center of lug with heavy duty lugs and hydraulic crimp.

- Jeff

[SkiSmuggs]

time2roll wrote:

So so easy to just snap these together in series. MC4 #10 extension cut in half. MC4s to the panels, cut end to the controller. No box, no fuses, no extra connections to give trouble, minimal power loss.

Thank you! After a year of anguish over how to do it, this ^^^^ is what I did to a PWM controller and it works. I finally added a breaker just before the controller so I could easily disconnect the panels for battery work.

[rocmoc]

RoyB wrote:
Using the PVC boxes and tubing on the roof will be getting alot of the SUN UV rays... The PVC Electrical lines and products sure don't do well over time having to be sitting in the high sun like that... I still however like the LOWES/HOME DEPOT PVC Electrical Boxes idea with weather tight lids and PVC tubing. On the edge of the trailer roof line you can drill out a large hole in the center of the PVC Electrical box and route your solar lines into the trailer coming inside on the ceiling mounted cabinets we all have... Then you go from there using the PVC lines to where the cables need to go to... This allows all of your solar cabling be inside PVC boxes and tubing...

I am referring to these type of PVC ELECTRICAL Boxes with tubing connections on their sides. These come in all sizes and multiple number of tubing connections to suit your needs...






This is the way I am going to install my solar install on my off-road POPUP trailer roof. No drilling on the roof line at all... I can only drill into the wood side portion of the roof and will want to do that on the side of the trailer - not on the top...

I think I would want my electric components inside my trailer near the tie-in point for the batteries with meters and controls etc... Mainly so I can easily see what is going on. The combiner boxes will up near the roof and all feeding a solar panel inside the trailer near the battery install area.... Just my thoughts...

Roy Ken

This is what I used for 6 panels and I also place aluminum duct tape on the top and sides to reflect sunlight and heat.

rocmoc n AZ

[mchero]

They are called MC4 branch connectors, not Y connectors. No combined boxes on my rig.

[time2roll]

Great source for #4 custom cable: (or larger)

http://www.genuinedealz.com/custom-cables/custom-battery-cable-assembly?size=57

Verify the battery stud size and the controller lug size for perfect fit.

[red31]

now look at voltage drop from the CC to batt. 5'? 40A? this is the place to use 4 awg and/or batt voltage sensor.

[johnm1]

I already verified that the H4 (or whatever they are) connectors are compatible with MC4. Either way, I'd absolutely make sure I get the proper cabling ... this us expensive enough without making mistakes.

[time2roll]

Spec sheet does show a different connector as: H4/UTX connectors

Wait until you get the panels to verify... just do not buy any MC4 until confirmed. Basically same functionality but you need to make sure you get what fits this panel.

[red31]

johnm1 wrote:


red31 - your data shows a 20' run. That's the distance from the pv panels to the CC right? As in, they are 20' apart, not 10 feet.

Using MC4 10 guage extension wire gives a ~ 0.38V drop at 20' ... and this is OK? So using 8 gauge extension wire would be even better at ~ 0.23V drop at 20' ... right?

yes the distance in question is between the solar panel connectors and the CC.

.38v voltage drop for series is at max performance, will be less anytime the amps are less than 9.25, absorption and float, not pointed at sun, clouds ...!

.38/64.6 (Vmp 32.3v X 2) see the correct spec sheet for the 290-300.
is .00588

295 X 2 X .00588 is less than 4 watts, ya loose more from panel heating, gonna trow dough at some sort of panel chiller?

[johnm1]

Thanks for that time2roll. Once I saw it on the data sheet you posted, I found it on the one I had.

[2oldman]

.

[time2roll]

ALL of these home panels have bypass diodes. The panels in home and commercial installation would burn up when shaded if the diodes were not there.

Here is another spec sheet that says 3 diodes:
https://www.wholesalesolar.com/cms/specs-2801912752.pdf

(near the bottom right of page 2)

[johnm1]

We're completely off topic from my original question about combiner boxes, however, that's not always a bad thing.

Time2roll - Not questioning you, just asking ... how do you know the panels have bypass diodes? I don't see it in the spec sheet. If they do, then wiring in series would be acceptable for my set up? As in, series would be virtually the same as parallel using smaller 12v panels?

red31 - your data shows a 20' run. That's the distance from the pv panels to the CC right? As in, they are 20' apart, not 10 feet.

Using MC4 10 guage extension wire gives a ~ 0.38V drop at 20' ... and this is OK? So using 8 gauge extension wire would be even better at ~ 0.23V drop at 20' ... right?