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Old 04-12-2017, 07:23 AM   #1
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Merging Portable with Roof Mounted Panels

I have two 100w panels on the roof of my fiver going to a 30 amp charge controller. I also have a 100w suitcase portable with its own 10 amp controller. Rather than run two controllers when parked in the shade, I want to bypass the suitcase controller and easily connect to the 30 amp in the battery compartment. I plan to use SB50 connectors to join into the system, but am wondering about a clean merge of wiring in the battery compartment. Should I use bus bars or buy some solar Y connectors or is there a way I haven't thought about that is better?
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Old 04-12-2017, 07:44 AM   #2
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I would mount a solar combiner box next to your charge controller...

MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels

That way you can put proper PV circuit protection on the supply legs, add Ground Fault Protection if you like...easily isolate strings of panels for diagnostics.

The panel has a DIN mounting rail and will accept the DC breakers that have the din mounting.

This way you can flip the breaker for your portable line, when not being used...so your solar panels aren't keeping the SB50 connector charged all the time.


Here's a very nice installation with a similar box by irv2 contributor baphenatem...

http://www.irv2.com/photopost/showph...&ppuser=151758
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Old 04-12-2017, 08:29 AM   #3
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Very elegant and WAY beyond complexity and cost of what I was thinking. I already have an in-line circuit breaker just before the 30A controller on the positive wire from the roof. I just want to merge the wiring and put SB connectors there to plug in from the suitcase. The SB connectors are like MC4 connectors, but made for repeated connect/disconnect and absorb no power. I thought of using SAE connectors as well as I could do a panel mount to an outside wall. It is the merging of cables that I am really concerned with, possibly with something like this https://www.amazon.com/Signstek-Bran...5GJS1BWA6H4E2N
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Old 04-12-2017, 10:17 AM   #4
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Well...I'm assuming the three panels would be connected in parallel to the 30A controller with 10ga wire then??


If you multiply the Isc of your panels x 3...and multiply that times 1.25 ===will it still be below 30A rating for 10ga wire???


There is some simplicity to keeping it like it is with two different charge controllers. Rewiring is like spending money to reduce your redundancy...which you may prefer...but having some solar is better than no solar should one or the other decide to opt out.
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Old 04-12-2017, 12:01 PM   #5
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Quote:
Originally Posted by C.Martin View Post
Well...I'm assuming the three panels would be connected in parallel to the 30A controller with 10ga wire then??


If you multiply the Isc of your panels x 3...and multiply that times 1.25 ===will it still be below 30A rating for 10ga wire???


There is some simplicity to keeping it like it is with two different charge controllers. Rewiring is like spending money to reduce your redundancy...which you may prefer...but having some solar is better than no solar should one or the other decide to opt out.
The controller will handle four panels with a small reserve. The two on the roof are already merged in parallel prior to leaving the roof. But you have a good point about reducing redundancy. I was hoping to do the wiring at the suitcase so that I could revert back readily, but maybe two controllers is not such a bad thing. I had already replaced the alligator clips with ring terminal and had them mounted on the previous set of batteries. The driving force to merge to one controller is for longer wire from the suitcase panels, say 30' vs 15' to give me more flexibility for placement if parked in the shade. There is greater loss in long wire from the controller than in long wire from the panels.
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Old 04-12-2017, 10:59 PM   #6
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There are a couple of ways to do this, some completely code compliant, some not.

From a safety aspect consideration, DC is a lot harder to disconnect than AC power. In AC, an arc will self quench pretty quickly, (example, unplug a vacuum sweeper while it is on, there is a spark, but it goes out)

In DC, even at much lower voltages, the arc will tend to keep going surprisingly far. For that reason, it is ideal to have a DC switch or even better, a DC breaker in the line that you are going to disconnect for the portable panel. Ideally you would put a breaker in the other PV line as well for maintenance reasons or it will be live unless you cover the panels to prevent power generation.

A DC breaker that can handle the load is under $20 and will prevent sparks from flying around and making black marks all over the connectors. Typical suppliers are blue sea, midnight solar and carling.

If you have a switch or breaker in the line, you can use pretty much any connector that you like, anderson power poles, even a good quality cigarette lighter type plug can handle 5 - 10 amps.

From a safety standpoint, don't worry too much about putting an extra panel or so in parallel into the 30 amp controller, it mostly just makes them able to produce useful power over a longer part of the day.

Technically, the MN baby box is the most code compliant approach.
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Old 04-13-2017, 06:49 AM   #7
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Just wire the suitcase panels in parallel, at the existing controller (before the PV side disconnect). I did this with my previous system (six 100w on the roof, two 100w portable). I had a ~25' #10 wire, with Anderson connectors at the portable panels.

My current 1500w system needed a combiner box (used the Midnite Solar as pictured above), so I just added another breaker and wire / connector for the portable panels.
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Old 04-16-2017, 11:11 AM   #8
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Portable panel merge

I wired my 100W panel into my 540W system with a connector similar to your plan. We've been using it like this for most of a year and it works great. Since I was only adding a single panel ( max 5 amps ) I used different, less expensive connectors, but the idea is the same.

I have a 10A fuse inline, since the power from the other panels could feed back if there is a short.

I left the small PWM controller on the panel and added connectors so I could easily reconfigure it back to the original wiring with the battery clamps so I could take the panel with me when we're overlanding in our Jeep or have some other need to separately charge a battery from the panel.

My only warning is that your rooftop panels need to be in parallel, not series. If you did them yourself and know, fantastic. If you've got a PWM controller in the RV, they're in parallel. If you've got an MPPT controller, you may want to verify the input voltage to the controller while both roof panels are in the sun to confirm. If it's over 23V, they're in series.

The long cable run to the portable ( sometimes 30' ) can slightly reduce the power output, but if the RV is in the shade and there is sunlight 30' away, it's better than nothing.
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Old 04-17-2017, 05:57 AM   #9
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Airmon - thanks! You are doing just what I had in mind. I installed myself and my roof panels are in parallel with a PWM controller. I could use SAE connectors to plug the portable in as that would be cheaper than SB connectors. And I do plan to leave the 10A controller on the suitcase to switch back if needed. I thought my idea was sound and it is good to have confirmation.
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