Combiner box confusion

12VoltInstalls

Photon Sorcerer
Joined
Jan 18, 2021
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Vermont
So maybe it’s that amazon doesn’t search well but I can’t find what I’m looking for. My own unfamiliarity may be a part but I’m not an idiot.

Backstory: had sudden sun today with batteries at 12.0-12.1ish. Blew 20A fuse for my 2S2P @400W setup. (I am aware fuse should have been 30A; neglected at upgrade, cables are 8ga)

So I got to thinking I should actually just get a combiner box to accommodate the max I’ll likely ever do for this RV trailer which is 3S3P (I have the panels for 3S2P right now, just only running 2S2P)

My issue is if I blew a 20A fuse, that suggests that the boxes like the ecoworthy come with 10A breakers. I’m assuming they can be replaced but why not just buy it loaded with 15A but I can’t find that option.

Second, the combiner boxes I’m seeing appear to only be made with MC4 plugs on the box, and for exterior use - not a provision for interior clamp fittings to connect the cable inside the box mounted inside. I intend to pass two or three pairs inside and simply connect them in the box like a breaker panel. That’s all I need, it feels simple and neat and clean but I’m not seeing these. There’s some midnite boxes that seem ok too but, again, this is a lot of why I’ve been hanging here, to get to know what I know I don’t know.

Am I reinventing the wheel here? Or should I just buy a small empty box and populate it how I want?
 

Bud Martin

Photon Sorcerer
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Aug 27, 2020
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2,359
Which fuse that blow? The fuse for the individual string or the fuse for the total output string?
What is the spec of the panel
Details info about the combiner?
Pictures of how you wire up the system?
Dose the system ever work before?
 

12VoltInstalls

Photon Sorcerer
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The fuse that blew was a 20A on the 8ga cables to the battery bank. When I went to the mppt and installed two more 100W panels for 2S2P this spring I neglected to change the fuse from when I was 200W; I usually overcable stuff but use a fuse for a lesser value around the max expected load (as if it were 12ga in this case). “User Error”

The panels 100W, 19.xVOC with?? 5.x max listed amps.

No combiner- yet. Just Y cables at the PV cables going to the SCC. I want to buy a combiner sufficient to handle if I play with 2kW of panels and a minisplit but still handle my ‘little’ system without going to pentagon purchase levels.

Picture not necessary- currently 2S2P with Bouge Y cables. Simple. Wanting to 3S2P right now with eventual 3S3P but have the combiner inside for breakers and parallel joining.

The system has always worked great but I had water/corrosion in the diode box of one pair of the current setup. I discovered that a few weeks back and fixed it and apparently that was attenuating the pair.
Now that it’s fixed I guess it hit 20A for the first time and blew the fuse.

I would like a suggestion of a part number for a combiner box that:
- doesn’t have MC4 inputs
- has at least four solar inputs
- has populated breakers

The blown fuse wasn’t an issue, it was just what got me motivated to finish my intended upgrade and I want it to be very clean and by natural progression it will be safe.
 

Rednecktek

Solar Addict
Joined
Sep 8, 2021
Messages
782
Fortunately those MC4 connectors in the bottom of the boxes are just regular 1" wire penetrations and should unscrew from the box.

Find a box that has the other stuff you need and a crescent wrench will solve the last problem. :)

Just as a note, I went with This eco-worthy 4-port box for my camp revamp. It's standard size fuses if I ever futz around with my panels and has a 40a DC breaker. Yes, it's Eco-Worthy, but options were limited.
 

12VoltInstalls

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options were limited.
I’m going to go to midnite’s website and research a little. The company has a good rep and the prices don’t seem crazy more than ecoworthy- EXCEPT that you have to buy the breakers separately, they’re not shipped populated.

Of course I realize I can take apart the MC4 fittings on the low-priced ecoworthy and polyenergy boxes. Some question the quality of the breakers and that makes me hesitant. Though- not having experience with the larger system components- I was just surprised that ‘hands on’ install components aren’t broader in selection! Midnite offers those but price bothers my head if I think about populated 240AC panel prices.

Basically I had the preconceived notion I could just buy something prepopulated in whatever config I wanted which obviously isn’t the case. At $130 that’s the cost of a small metal box with knockouts and the fuses and bussbars to roll my own, but that’s messier and not very scalable imho.
I’d prefer a metal box but ecoworthy might be what happens. Was hoping for suggestions beyond amazon but I guess they aren’t out there.
 

wiseacre

Solar Addict
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Aug 8, 2021
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211
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North of the Adirondacks
I'll be looking for one soon too, and this has caught my eye-

I have an Eco Worthy combiner box in use for a little over a year. It has served me well.

The Watts247 boxes appears to be a better quality build.
wished I saw the Watts247 boxes before I purchased the eco worthy
I'd pay the premium for a better box but don't get me wrong, the eco worthy so far has been "faultless"
 

12VoltInstalls

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I watched or rather listened to that video on the way home yesterday.

I’m evaluating my needs. I’m going to decide if I’m going to go with a future-think big system (combiner box makes sense) and incorporate a minisplit, OR if I should go with my original progression to 900W max.

You see the driver for this is two things: some likely expansion to accommodate a new RV furnace (ads claim 3.5A/12V) which is an easy choice if I go there, but mostly due to my annoyance with breaking MC4s for no reason. (See pic). On the left is a Bouge RV MC4 I installed last week when the MC4 shattered that I’d installed two weeks prior from a 40mph gusting wind day along with this now-shattered example that I spotted yesterday. It’s not been below freezing but it was ~43*F the other day and the cheapo MC4s apparently don’t muster in the wind.
On the left is a Bouge RV unit. It will be interesting to see if it lasts but the seem to.
I’ve had several crack and I’m sick of it- a combiner solves the issue.
 

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