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System wiring help.

Kmartin

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Aug 12, 2020
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Anyone interested in helping figure out how to wire my 10 250 watt panels. Going by midnite sizing calculator I will have 2 sets of 5 parallel strings If I'm wording that right. I'm guessing I will need a combined box. The panels will be 50 feet from my battery house. I can't find a diagram anywhere. Need wire sizes too. Thanks
 
That would be abbreviated as 2S5P - 2 panels in series (string), 5 strings in parallel.

https://www.calculator.net/voltage-drop-calculator.html for voltage drop depending on voltage, current, gauge and distance.

Gauge needs to be able to handle your panel's 5X Isc.

A common combiner box setup would be:
Each string of two series panels into the combiner box with a 15A breaker.
A single pair of conductors coming out of combiner box to solar charge controller at whatever gauge is needed to handle the current and minimize the voltage drop (5% or less).

Link #2 in my signature has various wiring references.
 
thanks. So would I be able to use branch connectors instead? I would assume not as the current at the end would be too high for those but I'm not sure. Also if I use a combiner box would the normal 10 guage wiring from panels be ok to the combiner
box. I found a diagram on another thread that shows 2s5p using branch connectors but I cant find one with a combiner box. my panels already have 4 foot cables with mc4
connectors.
 
There are lots of missing details; like what's the system voltage, what's the controller's specs, how big is the battery, ect. Since you've already been to midnightsolar's site, go back. The wiring diagrams are there. Look in the documents section There are wiring diagrams for the Classic controllers.

One problem you have is that you have 10 panels. That means you only have four choices, 1S10P, 2S5P, 5S2P, and 10S1P. For most economical MPPT controllers, the only practical choice is 2S5P. If you could add 2 additional panels, configuration choices would improve. You could realisticly add 3S4P or 4S3P to your choices, depending on the max voltage of your controller.

For my own systems, I use a 4S configuration, running my arrays at 120VDC. Since I use Midnight 200 controllers, the open circuit voltage of 135V+ is a non-issue. Other controllers, like an Epever for example, could get fried.

Your panels most likely will produce a maximal amperage of about 8amps per string, at ~60V. Yes, you will need a combiner box, using 12A breakers. I believe that is what is standard for the Midnight combiner box. Five strings at 8A would be a total of 40A. Looking at a 2X safety factor of 80A, 4 gauge copper wire would carry that amperage from the combiner to the controller. Forty amps is right at the upper margin of lesser controllers like an Epever, but most likely would work. Me personally, I like to apply the 2X rule to everything I do.
 
Thanks for the reply. I will go back and look for the wiring diagrams. I have a midnite 150 sl and a shnieder electric context sw 4000 watt inverter. I have 16 280ah lithium cells on the way. My system voltage will be 24v. I have 60 feet from panels (which arent up yet) to the battery house which is my partially underground cellar. Im still trying to figure the best way to mount panels as they will be going on the side of a steep embankment. Then i will be running about 100 foot of cable from inverter to the house breaker panel.
 
Go here to see wire size necessary https://baymarinesupply.com/bosns_corner_wire_sizes Figure 120 feet of wire and however many amps your 2s5p system will produce as well as volts it will tell you what size wires work best. Im guessing a little differently than MichaleK, but we are both guessing, Im betting you have 60 or 70 volt 3 or 4 amp panels for a total of 30 amps at 80 volts once they are all configrured. Just a guess But the important thing is how many volts from the 2 s and how many amps for the 5p from there it is just math. If there is a posibility of going 3p3s that could actually be a better configuration and save you lots of money in wires
 
Thanks for the reply. I will go back and look for the wiring diagrams. I have a midnite 150 sl and a shnieder electric context sw 4000 watt inverter. I have 16 280ah lithium cells on the way. My system voltage will be 24v. I have 60 feet from panels (which arent up yet) to the battery house which is my partially underground cellar. Im still trying to figure the best way to mount panels as they will be going on the side of a steep embankment. Then i will be running about 100 foot of cable from inverter to the house breaker panel.
The steep embankment might be a plus for you? Is it facing south? If the answer is yes, you could make a very simple frame out of angle-iron or unistruts following the contour of the embankment.

Since your panels are 250W, I'm almost certain they are ~8A at 30-31V. The Voc at the freezing point might be 40.0V. With the Midnight150, you could wire 3 panels in series, using 9 for a 3S3P configuration. At freezing, the Voc would only be ~120VDC. With a Vmp of 90VDC, you won't have too much voltage drop using the same 10 gauge wire the panels themselves have. But, you have to set aside one panel. To use all 10 panels you'd have to go with 2S5P. You can't go to 12 panels because the Amp limit of your controller at 24V is 94amps (page 65 of your manual).

If you really wanted 12 panels though, you could use virtual tracking, and point 1 array SE, and another SW. Another alternative to deal with overpaneling is to have the panels on rotating mounts. Here's a pic of the kind I'm making now. Two of these would hold 12 of your panels. Then you just bump them a little east of south, and west of south to make sure you don't exceed 94amps.

BTW, I have exactly the same Schneider inverter for my 24V workshop. I highly recommend it, and I think you made a very good choice.
 

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Not to derail the thread but I’m about to fire up a Conext SW 48v system over the next few days and glad to hear there are other SW users on the forum.
 
Unfortunately its facing east and its pretty steep. Im in mountains of north carolina. I Still have to clear a small tree and lots of briars off of it. Its the only place i have as the house roof points east and west and is surrounded by trees. I thought of just buying a pole mount for all 10 panels but when i measured out how big and tall that thing would be i could just see me trying to get on a ladder on an embankment trying to get panels into place plus digging a large enough footer on an embankment for the single pole. It recommended 5 foot deep and 36 inches wide and thats on level ground!
What would be easier and make the most sense, a 3s3p or 2s5p configuration? I just remembered i actually have 11 panels as santan solar sent me and extra one. Im glad i made a good choice on the inverter. Got it on sale too. Didn't realize i needed the seperate controller for settings so i just got that in too. I guess i should get a roll of the 10 guage solar wire for the panels to combiner. I will run 4 guage from combiner to controller and i was going to also use it for the run to the house too. Thanks for help. I cant tell you how many things ive learned on forums on such a broad range of interests.
 
It recommended 5 foot deep and 36 inches wide and thats on level ground!

What would be easier and make the most sense, a 3s3p or 2s5p configuration?
That hole sounds a bit excessive to me? Is your soil type very loose sand? In my case, my soil type is fine silty loam, and the holes I drilled were 36" deep and 15" in diameter. I drilled those with a 2-man auger. My center posts are 8 foot long 3.5" schedule 40 pipe, sunk into that 36" hole with concrete. Next, the central pole of the rotating mount is a 4 foot long piece of 4.0" schedule 40 pipe, onto which the hinged frame is mounted.

I've used variations of this design for years now, and I've had zero problems. I'm on a ridgetop, and the wind storms can be scary. If you look at the Oak trees in the background, some of the storms have toppled Oaks 18" in diameter. The solar mounts sailed through all those storms for years now.

In terms of the wiring, I'd use a voltage drop calculator like this one to decide which wire to chose over what distance.
Remember that the Voc of your panels varies with the temperature, and a panel that puts out 30V in the summer might have a Voc of over 40+V in the winter. Midnight has a "string calculator" you can use to get exact values.

Go to http://www.midnightsolar.com/, select "Products", then select " Charge Controllers - Classics ", then select " Classic Sizing Tool". You then input the parameters for your panels, and other data like your system voltage, and winter lows. The calculator will then spit out a number for the voltages and amperages you can expect to see. You can plug your values in to determine what will work best for you.

Here's another pic of my V1.5 arrays, that are holding three 300W panels, for 900W per array. This is my oldest rotating design, being in position now for 4 years.
 

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Sorry i meant to reply earlier. Those are nice looking arrays. Im jealous of how flat the land is. Unfortunately my steep embankment is facing east so i will have post of probably 10 feet or so high at the tall end down to ground level at other end if i just do a ground mount style with all the panels stacked 2 high running sideways. Do you have a recommendation on a bms for my size system if i do a 2s8p bank. 320 amp should be overkill enough i would think
 
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