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Old 07-14-2019, 08:23 AM   #1
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DIY Combiner Box

I used this generic junction box, a couple of these buss bars, and this bushing for the hole thru the roof...

The box will combine a 2S4P set of solar panels. So there will be 4 positive and 4 negative leads in, and one set coming into the bus. The buss bars are a bit too long, but once trimmed down they fit securely into the slots in the box. A hole had to be drilled into the bottom of the box to install the bushing for mounting thru the roof.




The split loom is for mock up only. I will be using a heavier duty and weather proof solution for the permanent install. Also once I clean up the roof I will be applying Dicor around box for an additional level of protection.



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Old 07-14-2019, 09:01 AM   #2
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Looks good! Nice work.

One question: What prevents water from entering through the inlet?

FYI, We've used similar wire loom before for roof-mounted lighting on our truck, and before long (well... a couple years) it became brittle and cracked from UV & heat exposure. I'm pretty sure it was supposedly UV resistant - as I'd think that's something I'd have looked for. Just a heads-up. Don't know if there aren't other products out there that might give you both better life and a waterproof seal.
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Old 07-14-2019, 09:39 AM   #3
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Looks good! Nice work.

One question: What prevents water from entering through the inlet?

FYI, We've used similar wire loom before for roof-mounted lighting on our truck, and before long (well... a couple years) it became brittle and cracked from UV & heat exposure. I'm pretty sure it was supposedly UV resistant - as I'd think that's something I'd have looked for. Just a heads-up. Don't know if there aren't other products out there that might give you both better life and a waterproof seal.
Thank you for your feedback. As for your question regarding water intrusion, I haven't decided what route to take yet.

And again, the split loom is for mock up only. I will be using a heavier duty and weather proof solution for the permanent install.
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Old 07-14-2019, 11:15 AM   #4
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Oh, gotcha.

Well, whatever you use in the place of the split-loom will hopefully kill both those birds with the same stone.

Don't know if you've seen this, but below the combiner-box on the following website (the $80 version of what you're building) there are water-tight strain-relief fittings. Probably rebranded versions of commonly-sourced items, but not sure. Appear to fit a standard e-box cutout (you'd obviously need a different weatherproof box w/o the female outlets).

Also, the video on that page shows their 10/2 weatherproof cable - which you can find elsewhere on the site - which they say is custom made for them (may or may not be). Either way, it appears to offer a really clean solution, and might be good additions to your project, either directly from them or the equivalent found elsewhere.

https://amsolar.com/rv-combiner-box/20-roof
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Old 07-14-2019, 11:41 AM   #5
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Originally Posted by ComfortEagle View Post
Thank you for your feedback. As for your question regarding water intrusion, I haven't decided what route to take yet.

And again, the split loom is for mock up only. I will be using a heavier duty and weather proof solution for the permanent install.
Sealtite 1/2" You will get sticker shock at the price of the connectors but ... Hopefully, your j-box has 1/2 fem threads.
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Old 07-14-2019, 12:08 PM   #6
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4 pos and 4 neg coming in on two terminal strips? .... I assume you are connecting the panels in parallel..
Are your individual solar panel wires capable of taking the short circuit of three parallel solar panels incase one gets shorted out?


How about your CC frying and a short circuit in one solar panel... shorting one panel thru the main breaker ??



Normally a combiner box has a fuse or breaker for each string.


Murphy never sleeps.
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Old 07-14-2019, 05:52 PM   #7
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Normally a combiner box has a fuse or breaker for each string.
Was going to fuse at the panels with these.

Here is the current plan; if it's gooned up, please let me know...
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Old 07-14-2019, 09:12 PM   #8
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Looks slick.

With more than two parallel strings I would recommend overcurrent protection on each string at the combiner.

I have never attempted to build my own. I am a bit partial to the way it's done in the Midnite Solar combiner boxes.
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Old 07-14-2019, 09:29 PM   #9
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That is good but still does not take care of murphy in full force.
The wire from your solar panel is probably 12 gauge. That limits the current to 20 Amps. Now if any of the wire is exposed before the inline fuse ( abrasion of insulation) to a short then how many amps can come out of your remaining solar panels or how many amps can come out of your fried CC.


In your diagram the CC shows 60 amp fuses in pos and neg. Only one is required, normally on the pos conducter assuming that you have your neg dc tied to ground.


So your inline fuses are acceptable if you would directly after your combiner box and / or the wire between the combiner box and the inline fuse can handle the largest short circuit current of all the other panels combined.


This is mostly done by integrating the breakers directly in the combiner box. Most likely also less expensive then the inline fuses.


I do like your clever use of lower cost materials to make your own combiner box but I do not think it is handy to have the inline fuses outside with your panels. And that is besides the potential of non current protected wire under worst case situation.


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Old 07-15-2019, 06:21 AM   #10
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BLUF:For the setup to be safe, the panel fuses need to be on/in/intergated into the combiner box, yes?

Quote:
Originally Posted by joeblack5 View Post
The wire from your solar panel is probably 12 gauge. That limits the current to 20 Amps. Now if any of the wire is exposed before the inline fuse ( abrasion of insulation) to a short then how many amps can come out of your remaining solar panels or how many amps can come out of your fried CC... So your inline fuses are acceptable if you would directly after your combiner box and / or the wire between the combiner box and the inline fuse can handle the largest short circuit current of all the other panels combined. This is mostly done by integrating the breakers directly in the combiner box. Most likely also less expensive then the inline fuses.
So I think I finally understand... Just to restate: the concern with fusing anywhere other than at the combiner box is that even if a fuse pops at the panel, the possibility still exists for an unprotected short between the combiner box and the blown fuse (or a non-blown fuse for that matter).

Quote:
Originally Posted by joeblack5 View Post
In your diagram the CC shows 60 amp fuses in pos and neg. Only one is required, normally on the pos conducter assuming that you have your neg dc tied to ground.
I had read that a breaker on both sides, while not required, is a nice to have in terms of ability to easily and fully disconnect the panels from the rest of the system.

Quote:
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...Most likely also less expensive then the inline fuses... I do like your clever use of lower cost materials to make your own combiner box but I do not think it is handy to have the inline fuses outside with your panels...
I disagree that it would be less expensive, however, it is not only about cost...
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Old 07-15-2019, 07:33 AM   #11
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Yes, in the combiner / breaker box, is the most common set up.

By the way you can use square D.. QO breakers. They are UL approved for AC and DC upto 48VDC. So depending on your voltage you can use that. The square D / schneider boxes are a lot cheaper then the "official" hyped prices on solar stuff. But as said only to 48 VDC.



https://www.schneider-electric.us/en...cuit-breakers/



I am with Steve that the midnight solar breaker combiner boxes stuff is pretty nice and I use that in our house solar systems because the voltage is higher then 48 Volt DC..



Having a breaker instead of a fuse is handy because at an convenient location you can shutdown and disconnect a string and see how much each string is contributing to the total.



Yes the essence is that all wiring and components are protected against the highest current possible under worst case situation / damage.


Of course this line of thought is often abandoned for cheap reasons.


So your main battery wire in your vehicle running to your starter motor is completely unprotected.



Keep on going , get that solar on, you will love it.


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Old 07-15-2019, 09:23 AM   #12
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box

I used a QO square d box inside the bus as a combiner box, the breakers are useful as on/off switches,
I have 6 panels hooked up in pairs so they put out ~24v, each pair go to their own breaker, I can turn all or some of them on/off for testing or repairs purposes.
I also have a separate breaker located between the charge controller and the bus bars for similar reasons.
I have 60amp fuses on the positive post of each battery before the bus bar to prevent an accidental "welding" incident, If I ever replace these fuses them I will probably use a 30 amp breaker for better protection.
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Old 11-05-2019, 04:38 AM   #13
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Here is the revised "combiner box" assembly.


I added a second box near the escape hatch (for easy access) to hold the fuses for each string. I realize the ~18in of wiring in the conduit between the two boxes are still unfused...


Two of the four strings are wired (fuses removed).


I understand the fuses themselves are waterproof but I put them in an IP67 box anyway to keep them together.


More info about the solar panel install is here.
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