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Old 04-28-2021, 08:49 PM   #1
Sharko
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M.O.C. #26528
SOLAR Questions "Newbie"

I Have a Montana 3830 with a pre-installed 265W and 30A controller with 2- 6V 225Ah AGM batteries.
If I understand correctly a 10 gauge wire has a max capacity of 30amps (used by factory) allows MAX of 365W @ 12V. OR 26A @ 14v if batteries are full.

I want to add 2 more 350W panels. Since the existing wire won't handle this much current how hard is it to pull another wire through roof and fish it through? What size should I run?

With a total of 225Ah in batteries how many watts is over kill, bad for batteries? My combination would make 965W.

I would need a 2nd controller, looking at Victron 50A/100V to run the 2 - 350W in parallel to combat shading. This enough?
Original and NEW panels would be on their own and the 50A controller would be in parallel with my original 30A.
Would this work???
Thanks in advance for any advise.
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Old 04-28-2021, 10:29 PM   #2
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If your conttroller can handle the voltage of the resultant array you can wire your panels in series to keep the current at or below Isc of the panels. Number 10 wire ampacity ratings are sufficient for this deisgn. If your panels have bypass diodes any panel shading effects will be confined to the shaded panel only. If you solar panels do not have bypass diodes shading can be a much more significant issue to a PV array wired in series.



I would not count on being able to pull new wire to the roof using the original path. Your labor will be minimized and chances of success will be greatly increased by using one of hollow wall voids or tank vents to pull new wire. You should be able to find lots of examples via Google search.


Just a final tip...you may surprised to find that those same 350w panels wired in series and using an MPPT charge controller will out perform the same configuration in parallel all things equal. If you can mount the panels to remove any shading caused by roof mounted equipment the resultant higher voltage of your array will increase your harvesting time significantly. The Victon MPPT will start bulk mode sooner in the AM and charge further into the PM.


I forgot to add don't worry about too many watts for your battery size. Since you are using AGM/FLA your bulk mode charging will be fine it's the absorb mode that will take forever and thats because of the battery type. You will want all the wattage you can get. I am willing to bet that you might go days without getting to float unless you are in a southern lattitude with Aug sun directly overhead and hazing from light clouds.
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Old 04-29-2021, 08:17 AM   #3
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Thank you for info. In last statement, are you saying AGM batteries are not good for this application? "Rarely getting to float mode" I believe float means fully charged?
Do you recommend me adding another controller for the 2 panel add or putting all 3 in series? Shading was the main reason I was staying away from series. I can put the adds in series.
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Old 04-29-2021, 08:54 AM   #4
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I did not mean to give you the idean that AGM or FLA are bod options. That's not it. The chemistry and limitations are what they are and with a array wattage of less than 1000 watts I think you may have difficulty getting through the absorption phase during harvesting unless under absolutely optimum conditions. While you may begin bulk charging between 0830-0900 and you may go from 50 to 80% by 12-1300... it will be that last 20% that will take at least twice as long as the bulk phase to complete and the sun has peaked and is getting lower and lower in the horizon as the day goes on. It just is what it is but don't let that stop you. Just like series vs parallel it's a trade off and choices that meet your needs.
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Old 04-29-2021, 10:09 AM   #5
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Thanks for clarifying. Can you answer as I plan to proceed with adding the 2 panels with another wire.
Can I have both controllers in parallel, original and new? With one loop producing 265 and other 700w. Will there be a downfall to this configuration?
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Old 04-29-2021, 10:53 AM   #6
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PNW is spot on. Pulling wires through a coach can be very difficult. If you swap to a higher voltage charger you can retain the 10awg from panel to charger and would only need to upgrade from charger to battery. That's a much more practical solution.
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Old 04-29-2021, 11:33 AM   #7
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Thanks. Do you recommend. All in series or can I pull the 2 new 350 in series with each other than in parallel to existing both connected to the 10gauge. Math would say the both legs would run 10amps max rating of panel then add other leg giving total of 20amps. 10 gage can handle 30 amps. Thoughts, please?
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Old 04-29-2021, 01:37 PM   #8
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Quote:
Originally Posted by Sharko View Post
Thanks. Do you recommend. All in series or can I pull the 2 new 350 in series with each other than in parallel to existing both connected to the 10gauge. Math would say the both legs would run 10amps max rating of panel then add other leg giving total of 20amps. 10 gage can handle 30 amps. Thoughts, please?
You need to get the voltages as close as possible when you parallel them in. Mathematically, (2) 150w panels that operate at 25v are the same as a 300w panel at 50v when you put them in series. What's the VOC and VMP of the panels you want to install?
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Old 04-29-2021, 03:25 PM   #9
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Stats of new panel. Watts (STC)350 WMax Power Voltage (VMPP)34.07 VMax Power Current (IMPP)10.27 AOpen Circuit Voltage (VOC)40.73 VShort Circuit Current (ISC)10.79 AMax System Voltage (UL)DC 1000 V

It really seems like I should pull another line through. I camp in some areas with trees
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Old 04-29-2021, 07:45 PM   #10
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If your original panel is not the same don’t connect it to the new string in series. I would be tempted to just replace the original panel with a third new one and wire them all in series. No extra wire to pull, no trying to find the path. Sell the old panel on CL or use it as a ground deployed unit if you need. With regards to paralleling the charge controllers you can but I would only parallel like controllers or those that can communicate to one another.
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Old 05-12-2021, 01:20 PM   #11
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[QUOTE=Sharko;1219752]I Have a Montana 3830 with a pre-installed 265W and 30A controller with 2- 6V 225Ah AGM batteries.
If I understand correctly a 10 gauge wire has a max capacity of 30amps (used by factory) allows MAX of 365W @ 12V. OR 26A @ 14v if batteries are full.

I want to add 2 more 350W panels. Since the existing wire won't handle this much current how hard is it to pull another wire through roof and fish it through? What size should I run?

With a total of 225Ah in batteries how many watts is over kill, bad for batteries? My combination would make 965W.

I would need a 2nd controller, looking at Victron 50A/100V to run the 2 - 350W in parallel to combat shading. This enough?
Original and NEW panels would be on their own and the 50A controller would be in parallel with my original 30A.
Would this work???
Thanks in advance for any advise.[/QUOTE

Your panels should be pushing a lot more than 12 volts. Check behind your panels and u will notice that they push less than 8 amps. I have 560 watts of panels with gage 10 wire and a 40amp mppt charger with an inline fuse from solar of 30 amps. Fuse of 30 amps was never blown and never got close to 30 amps to the charger. Most I had was close to 20 amps. So your gauge 10 wire is sufficient. Check specs of each panel and I think u should be below 30 smps
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Old 05-12-2021, 02:29 PM   #12
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Iím no solar pro but when I added panels I was told all 3 need to be the same output & not mix. I have about the same setup you are shooting for. 3 panels and 2 li-ion batteries. I am thinking to add a couple more batteries since storage is important as panel output IMHO. Cloudy/shaded day can be offset by amount of energy is stored.
Again not a solar expert at all but this is working for me.
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Old 05-12-2021, 03:37 PM   #13
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You are correct. By default the system will go to the lowest wattage panel and adjust the bigger ones to the wattage of the smallest
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Old 05-12-2021, 05:54 PM   #14
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Don't forget that solar panels produce their best in cold temperatures. A safe plan includes upsizing cabling. Solar is complicated enough. Adding these systems to an rv adds to complexity esspecially when wanting to increase the capacity of an existing system. Spending a few bucks on a solar designer would be advised.
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Old 05-17-2021, 11:54 AM   #15
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From Jaboni



Supports up to two panels 600W max.
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