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Old 04-18-2024, 01:53 PM   #1
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Bought 2 new panels, how to connect them

BogueRV had a sale on their 200W mono panels for $172. Couldn't resist so I got two. Mounting hardware on the way. I have 2xVictron 100/50 MPPT's with two sets of wires coming down from the roof. Panels are 20V so max is 3S on these controllers. Imp is 10A.

Thinking of going 2S/2P x 2 as shown below. I thought about 2P/2S but my brain hurt trying to figure out which would be better. Both are electrically identical. MPPT would see 40V and a max of 800W so a bit over paneled (720W is max output of each MPPT). 12V system.

I can't think of a better way to wire them. Do NOT want to add another MPPT.

Appreciate your thoughts.
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Old 04-20-2024, 04:44 PM   #2
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They are electrically identical, so your choice is really not a choice, is it?
I would try to keep one string on one side/end and opposite the other to minimize effects of shade hitting one vs. the other.
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Old 04-21-2024, 06:06 AM   #3
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I hesitated replying to this because it confuses me.

You have two 100/50 MPPT SCCs. You have 8 panels and are all 200 watt, 20v, 10A rated.
100 divided by 20 is 5. So that’s FIVE you can have in series. OR you could have five in parallel for 50 amps total. So four per controller works either way with room to spare. The only consideration is shading (parallel works best) or longer electrical production time (series reaches operating voltage earlier and stays later, but sucks if shaded).

I did see that Victron states that the 100/50 max solar wattage is 700 watts and that the SCC would limit input power if that was exceeded. So 800 watts is over paneling slightly but within tolerances for Victron IIRC. So at the peak of the day you might lose a little production but otherwise operate at better efficiency.

If my electrical math is wrong, please enlighten me.
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Old 04-21-2024, 06:40 AM   #4
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Quote:
Originally Posted by Boomerweps View Post
I hesitated replying to this because it confuses me.

You have two 100/50 MPPT SCCs. You have 8 panels and are all 200 watt, 20v, 10A rated.
100 divided by 20 is 5. So that’s FIVE you can have in series. OR you could have five in parallel for 50 amps total. So four per controller works either way with room to spare. The only consideration is shading (parallel works best) or longer electrical production time (series reaches operating voltage earlier and stays later, but sucks if shaded).

I did see that Victron states that the 100/50 max solar wattage is 700 watts and that the SCC would limit input power if that was exceeded. So 800 watts is over paneling slightly but within tolerances for Victron IIRC. So at the peak of the day you might lose a little production but otherwise operate at better efficiency.

If my electrical math is wrong, please enlighten me.
You should use Voc not Vmp. The issue is Voc when cold. The Voc spec is for 77 deg F. At 0 deg F, the Voc could be 15% or more higher. Four panels in series puts me awful close to the 100V limit on that SCC. One thing you should never do is exceed the V input limit on an SCC. It may release blue smoke.


You are spot on with over paneling.
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Old 04-21-2024, 08:02 AM   #5
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22.5 +/- 5% = 23.6 MAX Voc ? (from their website)

4 panels in series will work 94.5v
I doubt you'll never see 100v from the panels

and the controller will have a tolerance buffer built in too
doubt they will self destruct at 101v

------------------------------------------
if in doubt
go 2x strings of 2p2s one string to each controller not hard to wire up

then you can lessen any affect from shading
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Old 04-21-2024, 09:44 AM   #6
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Originally Posted by Aussieguy View Post
22.5 +/- 5% = 23.6 MAX Voc ? (from their website)

4 panels in series will work 94.5v
I doubt you'll never see 100v from the panels

and the controller will have a tolerance buffer built in too
doubt they will self destruct at 101v

------------------------------------------
if in doubt
go 2x strings of 2p2s one string to each controller not hard to wire up

then you can lessen any affect from shading

But the spec is for 77 deg F. When it gets colder, Voc goes up. And exceeding input V on the MPPT has the potential to fry it.


That's why I went with 2S/2P in two strings. Good V @ 48V. Plenty of headroom for the MPPT. And 22A is fine for my 10ga wire and the MC4 connectors.
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Old 04-21-2024, 03:38 PM   #7
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Just added 2 more 200W mono panels to my setup. I love using unistrut. I use the Renogy tilt mounts because they are cheap and make it easy to pre-assemble the unistrut on the ground.

This is aluminum untistrut and mounts so it doesn't weigh much. I just carry it up the RV ladder. Place it where I want it to check things out. I use a stud finder to find the cross braces. Then attach it with two 1/4 x 1 1/2" stainless lag bolts per side (4 total) with a large stainless fender washer. Four total penetrations. Lap seal under and over the bolts and that sucker ain't leaking and won't go anywhere.

Four penetrations for 2 panels does not scare me. If you can find your roof cross members, I think this is the way to go.
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Old 04-21-2024, 04:36 PM   #8
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AFIK, minilites use a foam sandwich that has zero cross races except for the ac unit. Just thin luan plywood.
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Old 04-21-2024, 05:15 PM   #9
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AFIK, minilites use a foam sandwich that has zero cross races except for the ac unit. Just thin luan plywood.
Without cross members, unistrut is probably not a good option. Rubber/membrane roofs suck for solar panel mounting and if there aren't any cross members to screw into, I'm not sure how I would install a panel.
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Old 04-21-2024, 05:37 PM   #10
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Without cross members, unistrut is probably not a good option. Rubber/membrane roofs suck for solar panel mounting and if there aren't any cross members to screw into, I'm not sure how I would install a panel.

Eight screws per panel using four Z brackets, with both butyl tape under the brackets and self-leveling sealant smothering it all when done. The two panels I added to my r-pod haven't blown off yet. I'm jealous of all your roof real estate.

https://www.renogy.com/solar-panel-m...cket-set-of-4/
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Old 04-21-2024, 05:44 PM   #11
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Eight screws per panel using four Z brackets, with both butyl tape under the brackets and self-leveling sealant smothering it all when done. The two panels I added to my r-pod haven't blown off yet. I'm jealous of all your roof real estate.

https://www.renogy.com/solar-panel-m...cket-set-of-4/

I wouldn't trust VHB tape on a membrane roof. The VHB tape will hold and the membrane will still be attached to the solar panel as it flies off my trailer.
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Old 04-21-2024, 05:53 PM   #12
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I wouldn't trust VHB tape on a membrane roof. The VHB tape will hold and the membrane will still be attached to the solar panel as it flies off my trailer.

The purpose of the butyl tape in this case is for it to be pulled down into the threads when the screw is inserted to better seal the screw holes. I wouldn't trust it as an adhesive.

I was following a how-to instruction video on the eTrailer site. They insisted on both the butyl and the self-leveler. Perhaps just to sell those products, but it seems like a good idea...
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Old 04-21-2024, 06:16 PM   #13
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The purpose of the butyl tape in this case is for it to be pulled down into the threads when the screw is inserted to better seal the screw holes. I wouldn't trust it as an adhesive.

I was following a how-to instruction video on the eTrailer site. They insisted on both the butyl and the self-leveler. Perhaps just to sell those products, but it seems like a good idea...
Agree
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Old 04-21-2024, 07:01 PM   #14
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Without cross members, unistrut is probably not a good option. Rubber/membrane roofs suck for solar panel mounting and if there aren't any cross members to screw into, I'm not sure how I would install a panel.
Well, you know my solution….
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Old 04-22-2024, 01:11 PM   #15
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Well, you know my solution….
Same as mine!
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Old 04-22-2024, 02:44 PM   #16
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larger panels 370w .. 80 inches long
I used 8 Z brackets on each.... 4 brackets along each side of a panel
and 2 screws into the roof on each bracket

32 holes...
if you gonna do one hole 32 is not any worse
wanted the extra hold down to the ply
each screw HAND tightened so there was zero change of stripping it with power tools

2400 miles and inspected when got home.. no sign of any movement
just add the extra time to your regular roof inspection routine

wires.... laid them down nicely in a natural position .... covered them with dicor in a couple of locations

-------------------------------------------------------------------
has anyone done a study of the G forces a trailer/RV experiences for normal running
maybe could use less holddowns ?

BUT I would rather err on the side of caution and have more than less
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Old 05-02-2024, 06:06 PM   #17
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Good read and educational

My brain is hurting… When I expand my solar, I’ll leave it to the professionals…
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