Question on factory solar wire limits and MP2 installation

[SWCamper]

Hi all, this is my first post but I have been a member for several years and read hundreds of threads, so thank you all for providing lots of helpful info and knowledge. As the title of the thread indicates, I have 2 very specific topics, but they are part of the same install and I didn't want to start 2 separate threads.

What we have: 2020 Reflection 337, purchased new in 2020, full timing in it since 2021. Preferred style of camping is boondocking, we rarely visit RV parks, so solar system was high priority. I knew nothing about it when we started, but I spent days/weeks educating myself, reading books, watching YT videos, browsing this forum. I built the system over time in stages, am very happy with its performance, this is the last minor tweak.

Current system: 6x200W Rich Solar panels on the roof, connected in 3S/2P, so 1200W total theoretical output. Panel wires connected to GD installed Jaboni box on the roof, utilizing 10 AWG wire that GD installed between Jaboni and the front battery compartment. There, it goes through the breaker box into Victron 150/100 MPPT (max output 1450W). Installed Victron Lynx Distributor as the new busbar last goaround, and have Renogy 3000W inverter, Victron MPPT, Cerbo GX, and SmartShunt connected to it, as well as 840AH Lion Energy battery bank.

All works really well, no complaints at all. Wanted to provide this info up front so you know exactly what the situation is.

When I upgraded from 2 panels to 6 panels, I wired them in 3S/2P (each string is on the same side of RV). I also measured remaining space and I have room for 4 additional exact same panels. I decided to add them now. I don't want to install one in the back middle between AC and rear wall, which leaves me with the choice of 2 or 3 additional panels. If I went with 2, I would just add one on each side in the front, and extend each string from 3S to 4S, so the total output would rise from 1200W to 1600W at roughly 100 volts and 20 amps (4x25V in series, 2x10A in parallel). That's my default choice. The downside is shading - one string is partially shaded by rear AC most of the daylight hours.

However, if I added another panel right in the middle of the roof, I could then wire the 3 new panels as a new string, which would be much less shaded due to its positioning, giving me much higher total output. Problem with that design is that you end up with 3S/3P configuration, so 75V and 30A. Hence my question: would 30A running through 10 gauge wire be acceptable? For reference, this panel's lmpp is 9.8 amps, and lsc is 10.2 amps. It feels bordeline OK, but this is where I would appreciate input from experts here. I understand workaround would be to rip out Jaboni box and install combiner box with thicker cable running from it to Victron MPPT, but the holes don't line up at all, and I have no idea how GD ran the wire from right side side of the roof to left side in battery compartment. I would much rather just install 2 new panels than start this project.

The second upgrade is going to be replacing Renogy inverter with Victron MP 2. I bought it months ago and now finally have the time to install it. The question relates to proper grounding. Between MP, MPPT, and Lynx, what's the best way to ground them? I have seen different ways online with huge differences in wire sizing so I am really puzzled, I am no expert at this. If people that have this or similar install could provide input and/or pictures, that would be wonderful!

I apologize for lengthy post, but I wanted to provide as much info as possible to avoid back and forth clarifying questions. Thank you so much for your help! If you have any questions, feel free to ask.

 

[Soundsailor]

It looks to me like you're already pretty close to the max a 10-gauge cable can handle without voltage drop. It would be nice if GD had either created a straight chaser where a new cable could easily be installed or provided a supplemental cable for future expansion. Unfortunately, they did neither. If it were me, I'd bite the bullet and install new cabling that could adequately handle your system.

 

[SWCamper]

Thanks Soundsailor for your response! I spent good part of yesterday on the roof and in the basement, still trying to decide where to mount Multiplus 2 and optimum solar panels placement/configuration. I dismantled the wall in pass through basement in the process so I could trace the solar wire and see if I can repurpose some of that space for solar equipment.

Tracing the wire in the basement, it comes from the left side of the battery compartment, through the storage area, into the jumble of wires behind the wall, and up the shaft between the kitchen (main cabin) and the bathroom. There is zero access to that area, I cannot see where the wire goes up. The reason I am puzzled is because if it went straight up to the roof, that would be perfect placement for the junction box, and fairly easy way to enlarge the hole in the future for additional wires. Really not sure why GD chose to put Jaboni box 7 feet forward next to front AC unit, as that meant running longer wire under the roof away from what it seems to be a perfect entry point.

https://www.renogy.com/learning-cen...=Taking 10-gauge wire as,drops to only 18-24A.

Looking at this chart, 18 feet seems to be the limit for 10 gauge wire in my scenario. I will play with it some more in the coming days. If you or anyone have any other suggestions, I am all ears. I also would like to know about grounding MP2 (where and wire size). I know several people on this forum installed one, but I never saw how they grounded it.

Thanks again!

 

[Harvestmoon]

https://www.renogy.com/learning-cen...=Taking 10-gauge wire as,drops to only 18-24A.

Looking at this chart, 18 feet seems to be the limit for 10 gauge wire in my scenario.

Reading the chart shows 10 ga at 30 amps is good to 28 feet. I have another chart I use from another mfg that shows something similar. So to answer a question with a question (or 2): Is your wire run really that long or longer? How sensitive is your application to voltage drop? Running a 3S panel config on a MPPT controller IMO is not one where voltage drop is a high concern, and 10 ga works ok as long as your run is not too long. It's just ok, but sometimes just ok is ok if the alternative is cumbersome.

BTW: Hats off to you, that is an awesome off grid system you have built.

 

[Soundsailor]

[MENTION=22052]SWCamper[/MENTION], after re-reading your first post and perusing the Renogy chart you shared, I think you might be OK with the 3S 3P system you describe. As [MENTION=50517]Harvestmoon[/MENTION] said, a small amount of voltage drop won't be a huge concern.

 

[SWCamper]

Thanks for your reply, Harvestmoon, I really appreciate it. It was a very steep learning curve, as I knew nothing about solar or electricity in general when we hit the road.

As far as the wire length goes, I followed Renogy's example just below their chart to calculate it. In my case, it was 3x10.2x1.25x1.25=47.81. Looking at the chart, 18 feet is the limit.

I will try to estimate current length of 10 gauge wire between Jaboni box and MPPT later today or tomorrow. I will play with different wiring setups. I am very much on the same page as you where just OK is better than cumbersome, I just wanted to be safe hence the reason for posting here.