Combiner and Cirtcuit Breakers for RV?

[chrisski]

I'm wondering what you use for a rooftop mounted combiner with circuit breakers/fuses on an RV?

I wanted to purchase a combiner, but I can't seem to find what I'm looking for, so I'm intent to build my own. I have a 3R rated combiner that is for normal vertical mount only, it would leak if I mounted it horizontally.

What I will probably build this out of is two plastic electronic waterproof boxes, 8.5 X 9 X 3. The first box will hold a set of six circuit breakers, 150V 10 amps each. Each circuit breaker would hook to a 120W solar 12v panel rated at Short Circuit (21.6 Volts, and 7.72 Amps) and Operational of (18V 6.67 Amps). Each of these panels will be fed into the circuit breaker with a DC loss of no more than 2% with 10 Gauge copper Wire. The longest run comes close to a 2% loss, the shorter ones a bit less. The Second Box will hold the Combiner. For the combiner, I'm using a 10 connection Gang Box Connector to DIN rail Combiner, that can be fed in up to 20 inputs at 20 gauge to 6 Gauge Wires. If I can keep my Cable length to 10' or less, I will hit the 2% VDC loss rule.

I would love to have the combiner and circuit breakers fit in a single Box, but I can't find one. I'm sure its out there, I just don't know where to look.

My Block Diagram of this is attached. Pictures is better than words.

Really looking for a better option than two Boxes. So the specifics of where to purchase a box would be good or where to get combiner that meets my needs would help.

[NCmountainsOffgrid]

as an RV owner with solar, I'm just wondering about what you are planning here - why do you need some type of 'combiner' box? Aren't you just wiring your panels to your Charge Controller and then to your battery bank, like any typical RV?

[SunEagle]

as an RV owner with solar, I'm just wondering about what you are planning here - why do you need some type of 'combiner' box? Aren't you just wiring your panels to your Charge Controller and then to your battery bank, like any typical RV?

I would guess that the panels are wired in parallel which would require a combiner box with overcurrent protection for each string. My other guess is the CC is a PWM type which will be better with parallel wired panels.

[chrisski]

Long time solar forum lurker and total newbie here. Goal here is to get 720 Watts of panels and effectlively use them to charge a solar battery bank and have a 2000 Watt inverter plugged to the system.

How would you wire six panels to your Combiner? Just Y Cables?

I looked at a couple of systems for sale that have six panels, and also a 600watt Youtube video, and all three of those used a combiner box to feed into the Charge Controller. Also thought you needed to have fuses or circuit breakers for each seperate panel. I could be off base here.

I'd like this to be a DIY project and have my plans finalized and equipment purchased for October, so when the weather cools, I can start the install.

[chrisski]

I would guess that the panels are wired in parallel which would require a combiner box with overcurrent protection for each string. My other guess is the CC is a PWM type which will be better with parallel wired panels.

All isx would be wired in parralel.

[SunEagle]

Long time solar forum lurker and total newbie here. Goal here is to get 720 Watts of panels and effectlively use them to charge a solar battery bank and have a 2000 Watt inverter plugged to the system.

How would you wire six panels to your converter? Just Y Cables?

I looked at a couple of systems for sale that have six panels, and also a 600watt Youtube video, and all three of those used a compbiner box to feed into the converter. Also thought you needed to have fuses or circuit breakers for each seperate panel. I could be off base here.

I'd like this to be a DIY project and have my plans finalized and equipment purchased for October, so when the weather cools, I can start the install.

As I mentioned above if you have a high quality MPPT charge controller you might be able to get away with all of the panels wired in series or 2 sets of 3. Once you go above 2 panels or strings wired in parallel you need some type of circuit breaker or fuse to protect each string and doing that in a combiner box is the best way.

[NCmountainsOffgrid]

if you are thinking that these panel outputs would be 'wired to your Converter', that's not a typical install for an RV... a converter takes 120v power and 'adapts' it down to 12v power, though I 'assume' you are just using the term Converter since it's a normal RV term some use to mean a 'battery charger', which is really just a built-in function of the Converter, not what the Converter does itself, when on shore power.
Your panel outputs will go to a charge controller, and then to your battery bank. An inverter will be attached then from the battery bank, to a sub-panel, for your 120v needs, typically only to your outlets, which can include the microwave and residential fridge, but not for air conditioning, or water heating....and your fuse panel will receive it's power directly from the battery bank, also, for all your 12v lights and fans and appliances, etc., as it already does. This is how RVs are designed.
The Inverter typically has an internal Auto Transfer Relay so that when you are on shore power it will allow the 'pass thru' of that 120v power and not need to use the batteries. Many also have built-in Battery Chargers which are also beefier and better for battery bank charging. If you have this, you probably won't even need a Converter.

[SunEagle]

NCmountainsOffgrid is correct. You would wire the 6 panels to a Charge Controller and not a Converter. Unless you have used the incorrect language.

[NCmountainsOffgrid]

Many motorhomes, like my own, have 4 or more 6v batteries, wired in series and parallel, similar to solar panels, for a 12v output. This output is the common denominator to systems within an RV. 12volts represents the output of the Alternator, which can charge the house batteries while driving, along with the chassis batteries, of course, represents the 12volt system for interior lights, fans, appliance controllers, slide wall hydraulics or electric systems, leveling hydraulic systems, etc., thru the 12v Fuse Panel, represents the 12volt 'input' to the INVERTER, to then provide 120v output to those circuits wired from the Inverter, typically a sub-panel of individual breakers, and also the 120v output of the Shore Power or Generator power to the Battery Charging system, either built in to a Converter, or built in thru an Inverter.

The output of the solar panels don't typically power anything DIRECTLY within the RV, but serve to charge the house batteries, which provide those mentioned electrical needs, ESPECIALLY when parked and no other charge source is available.

I've seen a little info about the 'Hybrid' Inverters... I can imagine that it might can offset the need to use battery bank power with any incoming solar power, which is a nice option, especially if the RV is parked, and, even if the RV has shore power, it might can minimize any 'electrical fee charge' used by the RV, if the rv site is metered.

While I only have 2 12v 100w panels, wired in parallel with 'Y' connectors supplied with the panel package, thru a 20amp charge controller, to my 4 6v battery bank, it seems simple enough.

[chrisski]

Alright I did use some wrong terminology in Post #4 and that derailed what I wanted to ask, which is the question I started the post for, and changed it to read:

"How would you wire six panels to your Combiner? Just Y Cables?

I looked at a couple of systems for sale that have six panels, and also a 600watt Youtube video, and all three of those used a combiner box to feed into the Charge Controller. "

Pictures or links would be nice.

Right now the plan is to have four six volt AGM batteries in series / Parallel to 12 Volts. Supposed to get something like 400+ amp hours from the set up.

What I'm trying to do with this system I am taking the next five months designing and acquiring parts for is to get this as close to UL or National Electric Code, or to find the code and follow it that involves solar installation.

I would not describe myself as totally clueless, but archaically skilled. Many, Many moons ago I worked as an Avionics Technician for about six years.

[chrisski]

I also went back and updated the pictures in the block diagram to reflect I'm talking about a Charge controller and not the other thing. Amazing how one wrong word creates such confusion. This is also not the first time I've done something like this, but hopefully (doubtfully) the last.

[Mike90250]

Six panels in parallel, will REQUIRE a combiner box to be safe. Y cables will not accomplish this safely. (Bruce recently posted a pic of a melted Y connector)

The decision now comes down to
Rooftop or External combiner box (harder to troubleshoot) ( you could be close to 50A , so the 2 cables need to be 6ga for safety, and maybe 4ga for lower resistance)
Inside combiner box. Easier to troubleshoot ( many more roof penetrations, 2 for each PV panel) and then run the 6ga the short distance to the controller.

[chrisski]

This is how I picture building this on my roof. I can only find a box big enough to fit circuit breakers, or the combiner, and I can't find a waterproof box big enough for both or a pre-made combiner box capable of being mounted horizontally. I'm sure there is a box big enough for both, but I just can't see where to purchase it.
Combiner Circuit Breaker Combo.jpg

[SunEagle]

Using two boxes for your "combiner" should be ok. Just remember that while you have circuit breakers for each panel you still need some type of overcurrent protection to protect the final set of wires that go to the charge controller.

[chrisski]

Using two boxes for your "combiner" should be ok. Just remember that while you have circuit breakers for each panel you still need some type of overcurrent protection to protect the final set of wires that go to the charge controller.

My plan for the circuit protection for the finial set of wires would be a 30 amp fuse for each of the two strings. I plan on using a KUMEED 12V DC 20A 30A 40A 50A 60A Car Audio Inline Circuit Breaker Fuse for System Protection 30 amp fuse just prior to the junction box where the combiner and battery wiring merge. I’m not sure if that specific fuse is good for solar power, and I may just create a third box for those two fuses that are rated for solar instead of using fuses intended for stereo inside this compartment where the batteries, charge controller, and RV DC appliance 12 V circuit is.