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Combiner Box Output Help

Schuldtp08

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Mar 27, 2022
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Last fall I built an off-grid hunting cabin and have decided to power with solar/battery bank and generator backup. I purchased the Hybrid MPP LV2424 All in one inverter/charger system and 8 x 230 Watt solar panels (37.0 VOC per panel) . I plan on running the solar panels in 2S4P configuration to stay under the 145V maximum input PV voltage and under the max input watts of 2000. I purchased a solar combiner box box from watts247 (4-2 Solar Panel Combiner Box – 4 circuits to 2 (2 to 1)- (2 x 63A max output) thinking I could use it in the same manner as the 4 to 1 box easily and it was $10 dollars cheaper! I have received the combiner box and realize I will need to branch the outputs for a single PV input into the inverter (goodbye 10 dollars saved). I now have several questions based on my mistake.

1.) Is there a specific bridge connection type that I should use for this purpose?

2.) Is 6 awg wiring sufficient to handle the bridged amperage?

3.) Do I need to fuse the bridged connection in some way?

Thanks for all the help! I cant wait to post my whole set up once I get it all figured out.

Cheers.

 
I purchased a solar combiner box box from watts247 (4-2 Solar Panel Combiner Box – 4 circuits to 2 (2 to 1)- (2 x 63A max output) thinking I could use it in the same manner as the 4 to 1 box easily and it was $10 dollars cheaper! I have received the combiner box and realize I will need to branch the outputs for a single PV input into the inverter (goodbye 10 dollars saved).

Is this the box you have?

1649806420934.png

It is interesting because the lower priced 4x1 has *less* in it:
1649806518462.png

The Green Diode board at the top is the same, but they soldered the output posts on differently (The 4x1 post is soldered on in a way that bridges the output of all 4 diodes. The 4x2 has Two posts that separate the outputs)

Another interesting thing is that they fuse both the positive and negative side of the PV strings. This is overkill.

For my following answers, I will assume I am looking at the correct box.

1.) Is there a specific bridge connection type that I should use for this purpose?
Not that I am aware of.

2.) Is 6 awg wiring sufficient to handle the bridged amperage?
Without more detail on the panel specs it is hard to say for sure, but my *guess* is 6AWG would be more than enough for the jumper.

We would have to know the distance back to the charge controller to specify a wire size, but I am guessing 6AWG will be fine unless it is a *really* long run.

Your biggest issue is likely to be that you can't get both the jumper and the wire back to the charge controller into the circuit breaker.

I can not tell from the pictures, but I am pretty sure you could re-build the box to match the circuit in the 4-1 box. The hardest part would be re-soldering the output lug on the diodes.


3.) Do I need to fuse the bridged connection in some way?
No....as long as you have the proper wire sizes for the set-up

You should study this resource about PV Fusing and Wire Size.
 
Is this the box you have?

View attachment 90972

It is interesting because the lower priced 4x1 has *less* in it:
View attachment 90973

The Green Diode board at the top is the same, but they soldered the output posts on differently (The 4x1 post is soldered on in a way that bridges the output of all 4 diodes. The 4x2 has Two posts that separate the outputs)

Another interesting thing is that they fuse both the positive and negative side of the PV strings. This is overkill.

For my following answers, I will assume I am looking at the correct box.


Not that I am aware of.


Without more detail on the panel specs it is hard to say for sure, but my *guess* is 6AWG would be more than enough for the jumper.

We would have to know the distance back to the charge controller to specify a wire size, but I am guessing 6AWG will be fine unless it is a *really* long run.

Your biggest issue is likely to be that you can't get both the jumper and the wire back to the charge controller into the circuit breaker.

I can not tell from the pictures, but I am pretty sure you could re-build the box to match the circuit in the 4-1 box. The hardest part would be re-soldering the output lug on the diodes.



No....as long as you have the proper wire sizes for the set-up

You should study this resource about PV Fusing and Wire Size.

You are correct in finding the correct box that I have. I have attached a picture of the wiring guide that is provided in the box. I was thinking I could use two Y branch connectors, one for each of the + outputs (A and B) and - outputs (A and B) in 6 awg to connect to the inverter. Thoughts?

What other panel specs would be helpful? I have attached a picture of the panel specs. My guess is I'll need about 20 ft from panels to box which will be 10 awg extension cables, and then another 3 feet with the planned 6 awg to the inverter, but I haven't confirmed exact measurements. I'll make sure to study the guide after verifying the lengths. Any other advice would be greatly appreciated.
 

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My guess is I'll need about 20 ft from panels to box which will be 10 awg extension cables, and then another 3 feet with the planned 6 awg to the inverter,
That is interesting. Most people put the box near the panels and make a single run back to the inverter.

Input Circuits (Individual strings)
Isc = 8.26. The calculated max current is 8.26*1.56=13A
10 AWG is certainly large enough to be safe for the individual strings and it would have minimal voltage drop for 40ft round trip. You could probably get away with 12AWG.

Output Circuits:
Isc = 4*8.26=33.04A The Calculated Max is 33.04*1.56=51.54A
The 6 AWG for the 6ft round trip to the inverter is more than enough. You could probably get away with 8AWG

I was thinking I could use two Y branch connectors, one for each of the + outputs (A and B) and - outputs (A and B) in 6 awg to connect to the inverter. Thoughts?
What kind of Y connectors? Are you thinking MC4 connectors? That would probably work. ( I would probably solder up a Y on the end of my 6AWG cable and then cover it in heat shrink)


Could you provide a picture of the wiring on the back of the negative side and the surge protectors?

1649812926488.png
 
What kind of Y connectors? Are you thinking MC4 connectors? That would probably work. ( I would probably solder up a Y on the end of my 6AWG cable and then cover it in heat shrink)
I *think* the output breakers will take a 25mm wire which is about a 4AWG. You *might* be able to get two 6AWG wires in. You certainly could get Two 8AWG wires in.

Assuming you can get the two wires into the breaker, you can just make some short jumpers from one of the outputs to the other

1649814195627.png
 
I like the idea with fitting the two 6 awg wires into the breaker (jumper plus output to inverter). Much better than myself trying to solder things! I will try that first. Would you still like a picture of the back of negative side and surge protectors?

What is the benefit of having the combiner box near the panels versus the inverter? I couldn't find a lot of resources on the planning of where to put the solar combiner box, but am open to suggestions. I thought it would be easier to avoid weather issues to put it next to the inverter to potentially troubleshoot.
 
Would you still like a picture of the back of negative side and surge protectors?
If it is convenient. I am curious about how it is wired. (No big deal if you can't)
What is the benefit of having the combiner box near the panels versus the inverter? I couldn't find a lot of resources on the planning of where to put the solar combiner box, but am open to suggestions. I thought it would be easier to avoid weather issues to put it next to the inverter to potentially troubleshoot.
The primary benefit is that it is easier and probably cheaper to run 2 wires than 8 wires. The box you have is supposed to be weatherproof.
 
Removing the back is more difficult than is convenient at this time of day, but I attached a better picture of the top of anode and a included schematic.

I agree that it is likely cheaper to include a single run from the box and have it closer to panels. However, if I would want to turn off the PV, it may be more convenient to have it inside. I could wire an on/off switch of some sort. This cabin will not be used most weeks, so it's probably best to have the system ( PV, inverter, battery bank) shut down when leaving.
 

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I *think* the output breakers will take a 25mm wire which is about a 4AWG. You *might* be able to get two 6AWG wires in. You certainly could get Two 8AWG wires in.

Two wires under a screw terminal, not to code I don't think.
I've used split bolts to join two together, put one into the terminal.


That is interesting. Most people put the box near the panels and make a single run back to the inverter.

I mostly have individual strings run in 12 awg, combiner at the inverter. As I swap to other size inverters I can rearrange them. Some inverters have their own combiner, and some don't.

But paralleling two different orientation strings at the array would be more efficient - lower IR losses.
 
Two wires under a screw terminal, not to code I don't think.
I've used split bolts to join two together, put one into the terminal.




I mostly have individual strings run in 12 awg, combiner at the inverter. As I swap to other size inverters I can rearrange them. Some inverters have their own combiner, and some don't.

But paralleling two different orientation strings at the array would be more efficient - lower IR losses.
I've used split bolts to join two together, put one into the terminal.

What does this look like? I'm not too worried about being up to code or this cabin to be inspected, but also want to ensure no fires are started outside if the fire pit. ;)
 
I think two wires in a guillotine terminal would generally work.
Those DIN rail parts often don't have much bite or depth of engagement, however.

Wrap split bolt in rubber tape, finish with vinyl tape.



1649820717246.png

1649820743202.png
 
Okay, thanks for the support! I'm very much learning as I go with this stuff, and I would prefer for things to be as safe as possible.
 
Removing the back is more difficult than is convenient at this time of day, but I attached a better picture of the top of anode and a included schematic.
That is perfect. It took me a while but I finally figured out how the box is wired.

1649865570546.png
The dashed lines show wires that run underneath the mounting board.
The black rectangular lines are metal tabs that connect posts together
The blue lines are the negative connections to the surge protectors.
In the diagram below, the orange and purple dashed lines show the current path from one of the strings.
1649866765951.png
The really interesting thing is that the output positive and negative both go through the breaker twice.... I wonder why they do that?
 
That is perfect. It took me a while but I finally figured out how the box is wired.

View attachment 91085
The dashed lines show wires that run underneath the mounting board.
The black rectangular lines are metal tabs that connect posts together
The blue lines are the negative connections to the surge protectors.
In the diagram below, the orange and purple dashed lines show the current path from one of the strings.
View attachment 91087
The really interesting thing is that the output positive and negative both go through the breaker twice.... I wonder why they do that?
Thanks for making it easier to see what's going on! I have an understanding of what I want to do moving forward. I plan on posting my system schematic for review, but clearing these initial hurdles has been very helpful.
 
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