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?

[westend]

Why combine on the roof? Because MC4 wire is not cheap, nor is a Midnite "Big Baby" box --$35 without three breakers, wire entrance ferrules, and the terminal strip. If he DIY's a combiner box, he'll probably have $20 into the whole thing and has access to connect more panels without pulling wire into the RV.

For circuit protection (or the more practical interruption of current to the controller), install one of these Manual reset breakers between combiner wiring and solar controller.

[TechWriter]

johnm1 wrote:
I'm wiring in parallel to reduce the shading effects and it's been highly suggested that I run at least 4 gauge from the combiner to the charge controller.

Yes, each panel is 295W.

Why combine on the roof? For parallel, run all wires down to a fused combiner that's close to your controller. For your 4 panels that's about 82A battery charging current which a MidNIte Classic 150 can handle.

I did this with three, 245W panels.

[westend]

All right, I'll try this again. Between the RVnet server, Photobucket's code, and then using the special built photo posting app, it is getting ridiculous to post pictures on this Forum.

DIY combiner box made from 2" PVC LB and recycled terminal strips from discarded load centers:


Click For Full-Size Image.
MC4 wires from panel enter this water resistant box entry and a dab of sealant was added after termination.


Click For Full-Size Image.

I used 4 AWG from combiner to controller. It is piped down 2" conduit to a sidewall entrance close to the controller. I know most won't do it this way but I'm an amp squeezer and it was the most efficient way for me. A user could pull the wire through the roof, making sure the roof entrance is totally sealed. I later painted the conduit and none of it has ever leaked one drop.


Click For Full-Size Image.


Click For Full-Size Image.

[MEXICOWANDERER]

BLACK plastic contains carbon black and is inherently UV PROOF. Down here in 19+ UV land, gray plastic turns chalky in a year.

Sometimes I wonder if my sarcastic "19+ UV" rating isn't really close to the mark

[johnm1]

I didn't say anything about doubling the solar output. I said I want to start with 2 x 295W panels and might want to add more ... as in more solar, not necessarily more of the 295W units.

Also, I live in the NY and camp in the Adirondack Mountains ... I don't have a lot of choice when it comes to shade or no shade.

I will look at larger cable sizing.

[time2roll]

These panels should be closer to 9 Imp each. 18 amps through 30' of #8 loses less than 3 percent or 18 watts out of 600. Marginal loss is 12 watts compared to #4. Is the hassle worth 12 watts?

Four panels I suggest going series so amps would not increase. Just voltage increases and percentage voltage drop actually drops in half.

Yes from controller to battery go #4 wire.

[2oldman]

johnm1 wrote:
I'm wiring in parallel to reduce the shading effects

As a solar user myself, I do my best to avoid shade.

[johnm1]

I'm wiring in parallel to reduce the shading effects and it's been highly suggested that I run at least 4 gauge from the combiner to the charge controller.

Yes, each panel is 295W.

[time2roll]

Each panel 295W? These home panels will have MC4 connectors... just use MC4 parallel connectors and no box. Amazon has #8 MC4 extension cable to run down to the controller. Max 2 in parallel, any more should be in series and skip the fuses. You are already in the MPPT zone. Don't get all crazy with fat wire comparing to 12v solar installs.

[hedge]

I'm using 4 AWG, 8 is too small IMO but of course depends on how far it is to the controller. who knows what's inside the y plug but I doubt it's anything more than 12 AWG, I have some that came with my panels maybe I'll disassemble one some day.

I have my panels wired parallel, would be different if wired in series.

[corvettekent]

hedge wrote:

corvettekent wrote:
Why not use this?
or this?

because you can't get large wire into them.

I'm using 8 AWG.

[hedge]

corvettekent wrote:
Why not use this?
or this?

because you can't get large wire into them.

[2oldman]

Go series and forget about a box and the big wire.

[johnm1]

I'm looking at 295W panels and they'll be wired parallel.

The painted PVC boxes sound simple (and inexpensive) and I could always get a bigger box and install inline fuses for each panel.

[corvettekent]

Why not use this?
or this?