diy solar

diy solar

RV Cable entry / roof gland

RoadTurtle

Solar Enthusiast
Joined
Mar 30, 2022
Messages
365
I'd think this wouldn't be this difficult...

I "think" I need either 4 port unit, or a 2 (or 4) port gland to run the wires through. Two sets of wires, each coming off three 24V 200 watt panels. going to two SCC. Found a set of glands on Amazon, ship between Feb 3rd to Mar 3rd.

Trailer did come with Zamp and their ridiculous SAE connector, which is rated for 20A each. Obviously this would be the easy way out and not the best solution.

Is there a well equipped solar parts store that might have either 4 port inlet or a have 2 wire gland? Is there an issue with 4 wire 10g wire gland?
 
Is the refrigerator vent viable? I skipped the gland on my Rv and used vent. No holes in roof and fridge runs cables straight down under cabinets which made it easy to route cables to SCC in electrical compartment.
 
STW and zulu, already have a hole in the roof where it makes the most sense. zulu, that gland is for one pair of wires, I looking to run two pairs of wires through one "box".
 
I used the fridge vent as a pass through for 2 of my 3 installs, it's super easy, and no more holes. The 3rd I used a gland, and only a 2 wire. That went pretty well with lots of proper sealant (dicor). It was just a matter of positioning of the rest of the solar equipment that dictated this gland use.

PARALLEL setup: 3s2p: ----->>> So.. you have 3x 25v 200w panels together on one string.. like it's 75v then, so it's in series going down. And you did that twice. That's 8 amps per string through the roof, which is OK for MC4 connectors. You could then put both strings together that way, so it's 75v one string in parallel to the other 75v string, and just run one line set down, that will come through the roof at 75v and 16amps, which is fine for MC4 plugs. One controller needed.

SERIES setup: 3p x 2: ------->>>> If you did 3x 24v panels in series, for 24v down, but 25amps through each string, then you'd need to have dual lines down through the roof, and 2 controllers, and you're reaching the limit of power through those MC4 plugs. They are supposed to be rated for 30 amps, but I've seen a few melted ones at 30.
 
Generis,

I'm constrained on height, width, and junk running down the entire center of the roof.

I decided on 2 strings of 1S3P and going with two SCC. As much as I hate two SCC, given some of the physical constraints, this came out to be the best solution. I did go with 24v panels on 12v batteries, so I shouldn't have an amp issue, let the SCCs straighten it out :),

Thinking here, if one string is shadowed, the other string isn't impacted. More of a deep winter issue, but I don't see a negative down side to this configuration.
 
I’m going to recommend a project box which will be good for the two or four you want plus can add more in the future.

I did project boxes and cable entry glands. The boxes come in different sizes along with the cable glands. Just simply drill a hole for the cable gland and it attaches to the box easy.

To stick the box to the roof, I use Eternabond double sided tape. I liberally applied Dicor lap sealant. Prior to securing it to the roof, I cut a hole in the bottom of the box to get cables through, and made it big enough to count for expansion. The expansion could be an extra set or two of panels in the futire or even a Starlink antenna.


Some lessons learned, are
-know where the crossbeams are and avoid those.
-know where the AC ducts are and avoid those.
-Carefully make the drill through the roof with just enough pressure to puncture the roof, but not the wires that could be underneath.

I did not do any of those lessons learned, but lucky for me, I did not puncture.
 
combiner on the roof. I have a difficult installation and it made sense (to me anyway) to go with 24v panels and handle it as two strings due to shading issues
 
combiner on the roof. I have a difficult installation and it made sense (to me anyway) to go with 24v panels and handle it as two strings due to shading issues
I like that idea.

There will be plenty of days where that 6P setup will help you with shading, especially if you travel. Might lose a little production from voltage loss in sunny days, but at worst 10 or 15 minutes extra to charge your battery.
 
I like that idea.

There will be plenty of days where that 6P setup will help you with shading, especially if you travel. Might lose a little production from voltage loss in sunny days, but at worst 10 or 15 minutes extra to charge your battery.
We're in full hookup right now and will be here for a few more weeks, 12v was running off solar. I was getting less than 30% rated capacity As I started looking at it, my largest panel (closely matched voltages), with it's shadow from the air conditioner was losing almost 1/2 it's rated capacity. Some of it was due to panel angle, but also the shadow that was present every day. For the overall system, the PWM controller losses didn't happen. Sun angle in general across all the panels, and even possibly poor wire termination.
 
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