More Noob Combiner Box Confusion

[sethile]

After searching and reading here, I find I'm apparently not the only one that finds the options for combiner boxes surprisingly limited, pricey, and a little confusing.

I'm looking for a combiner box (or a pair of them) for an Off Grid system based on the MPP LV6548 I have on backorder.
The LV6548 controller specs are: 120A Mppt at max 250Voc – 2 x ( 4kW MPPT Charge Controllers).

I've got 26 used 250W panels. Their specs:
37.6 Voc
30.3 VPmax
Current @ Pmax 8.27A
Max System 600V
Fuse ratting 15Aw

Configuring the panels in series pairs would seem to optimize the yield due to shading and orientation challenges for my installation, but it makes for a lot of strings to parallel . Maybe it's not worth it?

Plan A:

Input 1: 2S8P (spilt up in two arrays of 2S4P each, one on a south facing garage wall, and the other on an East facing roof. If my math is correct, this yields 4KW, 75.2Voc, 66.16A.

Input 2: 2S5P on the East facing roof, which I think yields 2.5KW, 75.2 Voc, and 41.35A.

Combining solutions:
2 of the 8-1 Watts247 boxes that Will reviewed would likely be great for this, but they're back ordered until March 15th. I'd really like to have things ready to go when my back ordered MPP LV6548 shows up. It supposedly ships February 22.

I'm trying to overcome the sticker shock on a pair of Midnight Solar Mnpv12s and 13- 20A breakers (closest to 15A I could find on Amazon?) for a total of $706.30. Or I can get the 15A breakers along with a pair of the Mnpv12s for $765.64 at Wind and Sun (Northern AZ, anyone dealt with them?). Their breakers are cheaper, but the boxes are more. Guess I could split it up.

Main questions:
1. Am I missing some obviously less expensive or any easier solutions? I had thought about branch connectors with in-line fuses, but that sounds like a mess of wires and potential failures. Worth considering?

2. Should I consider a different configuration with more panels in series and less parallel strings in spite of the shading and orientation challenges?

3. If I go with the Midnight solar set up, Is it a safe to go with 20A breakers instead of 15A?

I've been fiddling with the solar array layout in case that's relevant. The first is what's on the east facing roof, and the second is what's on the south facing wall, which I intend to mount at an adjustable angle. (sorry for the ghetto graphics):

 

[p8ntman]

Hi, question. Why 2 in series? Your mppt can take 250v. You should be able to safely put 6 in series. Your volts will be up there but your wire size going back to your mppt will kill the pocket book. Not to mention you might be able to get away with a different combiner box.

FYI, graphics are nice

Edit x2: how bad is the shading? Is it even? For instance. I have a tree that shade moves from left to right across my array. My panels are wired (in series)so full sun hits the first access panels and then hits the next series set as the shade moves. You wouldn't want the shade to break up a string if possible.

 

[John Frum]

If these are the correct specs

SOLAR CHARGER


2 PV inputs
Algorithm: MPPT
Min PV input 90V DC
Max PV Input / Output: 4000W x 2
Max Charging Current: 18A
Max PV Input Voc: 250V
MPPT Range: 120A DC
Number of PV input: 2 per unit
Standby Power: 2W

MPP Solar Charge inverter 6500W 48V DC, MPPT 120A, 90A AC charger all in one Hybrid System, LV6548 – Azimuth Solar Products

azimuthsolar.ca

Then the device has 2 solar charge controllers

37.6 VOC * 6 series = 225.6 volts
If its cold where you live the low temperature over voltage may exceed the 250 volt limit for the solar charge controller.
you could do 3 strings of 5 to one controler and 2 strings of 5 to the other or...
3 strings of 4 to each controller.
In either case you would need 2 combiner boxes.

 

[sethile]

Thanks for helping!

Hi, question. Why 2 in series? Your mppt can take 250v.

Yes, the MPPT input can handle 250V. My initial thinking was to have 6S2P heading to each controller. But after reading up, and watching the array locations, I found the shading was uneven across the roof before it settles into full sun. It's from trees, which adds to how uneven it is, and it's somewhat unpredictable. It will be a little worse when the trees leaf out in the Spring.

I was also concerned the two different orientations (roof and wall) might be an issue. And with 6S2P going to each controller I'd have two extra panels, although I'm sure I could find a use for them eventually

If these are the correct specs

SOLAR CHARGER


2 PV inputs
Algorithm: MPPT
Min PV input 90V DC
Max PV Input / Output: 4000W x 2
Max Charging Current: 18A
Max PV Input Voc: 250V
MPPT Range: 120A DC
Number of PV input: 2 per unit
Standby Power: 2W

Yes, those are the correct specs and it does have 2 controllers. It gets cold, but very seldom bellow 0°F (-17.78°C). We see lows in the teens (F) several times during winter. Cold sunny mornings like the last couple might pose a problem for 6 panels in series.

I have room for 8 panels on the south facing wall, and that is my best sun. Assuming the strings should be even on each controller, I could put 4S2P there, then another 4S2P on the roof and parallel those (4S4P), yielding 4000W, 150Voc, 33.08A into Controller 1. That leaves me with ten panels, which I could configure 5S2P on the roof for a total of 2,500W, 188Voc, 16.54A into Controller 2. That would be safe and use all the panels.

Still two combiners, of course, but a lot less capacity, and the higher voltage saves on wire and loss. Question is how much power I'd loose due to shading...

Thoughts?

Maybe I could still buy a pair of the Mnpv12s in case I want to reconfigure or increase the number of panels at some point. But I would only need 6 breakers to start, bringing the cost down to $546.98.

Tempting to go with a pair of the cheaper combiners, although a lot of those seem to be limited to 10A arrays. And these would be 16.54A if my math is correct (big if!). Also, they would be useless if I end up wanting to reconfigure to 2 panels in series or add a bunch of strings down the line.

Now my head is spinning

 

[Bud Martin]

BTW, according to MPP Solar, the input can be as high as 25A.
Post #387:
Ok, definitive answer from Andy Y. with MPP Solar Support Team:

"Please don't worry. PV input current 22A is ok and it will not cause the unit damage. We suggest that please keep the max PV input current within 25A. Thank you."

Without that 18A max PV input, this is quite a capable box for the price ...

MPP-SOLAR LV6548

I'd have to go to four to NOT rewire ... with three I'd need to rewire: two used for single phase 120V, the third for 240V appliances (I think - I haven't done the load calcs), which means I'd have to basically pull apart my main panel and separate the two systems. Trying not to spend an extra...

diysolarforum.com

 

[John Frum]

Thoughts?

I defer to those more knowledgeable on the pv side of things. I bud @Bud Martin has this well in hand.

 

[sethile]

BTW, according to MPP Solar, the input can be as high as 25A.
Post #387:
Ok, definitive answer from Andy Y. with MPP Solar Support Team:

"Please don't worry. PV input current 22A is ok and it will not cause the unit damage. We suggest that please keep the max PV input current within 25A. Thank you."

Without that 18A max PV input, this is quite a capable box for the price ...

Wow, so I apparently grossly misunderstood the specs and I don't understand the charging amps spec versus the spec indicating
MPPT Range: 120A DC What dose that refer to?

So my original idea of 2S8P at 66.16A into controller 1 and the 2S5P at 33.08A going into controller 2 would have blown the controllers up?

 

[Bud Martin]

MPPT range: https://www.powerfromsunlight.com/e...er-inverter-specifications-part-1-input-data/

According to MPP Solar "We suggest that please keep the max PV input current within 25A." so do not exceed it, I do not want to try and find out. You can contact MPP Solar and ask them questions.

 

[sethile]

MPPT range: https://www.powerfromsunlight.com/e...er-inverter-specifications-part-1-input-data/

According to MPP Solar "We suggest that please keep the max PV input current within 25A." so do not exceed it, I do not want to try and find out. You can contact MPP Solar and ask them questions.

Thank you, Bud! Man, I don't want to either!!

This forum is so great!! I could have easily let the smoke out of my new toy.... No more than 2 string in parallel. Glad to hear it can do 25A. That's a lot better than 18...

I just reexamined the specs in the manual see where I went off the rails. The 120A I saw is apparently referring to "Charging Current (UPS) @ Nominal Input Voltage 120A".

This graphic through me, too. What does the "2 X 4KW MPPT (80A x 2) @250VDC" refer to in this? Easy for me to see how I could assume that meant what I could throw at the controllers. It also mentions the 120A MPPT Charger, which apparently refers to the UPS function off of grid AC.

Lots to learn, that's for sure!! Thanks again, Bud!

 

[WYtreasure]

renogyDOTcom $109.99

MidNite Solar Combiner Box 510-0006 SKU: MDN-OS-MNPV6-US ​

 

[Bud Martin]

Thank you, Bud! Man, I don't want to either!!

This forum is so great!! I could have easily let the smoke out of my new toy.... No more than 2 string in parallel. Glad to hear it can do 25A. That's a lot better than 18...

I just reexamined the specs in the manual see where I went off the rails. The 120A I saw is apparently referring to "Charging Current (UPS) @ Nominal Input Voltage 120A".

This graphic through me, too. What does the "2 X 4KW MPPT (80A x 2) @250VDC" refer to in this? Easy for me to see how I could assume that meant what I could throw at the controllers. It also mentions the 120A MPPT Charger, which apparently refers to the UPS function off of grid AC.

Lots to learn, that's for sure!! Thanks again, Bud!

View attachment 80995

They need to make correction to show as 120A Untility charger.

 

[sethile]

Hmm... puzzling out new configurations with no more than 5 panels in series (to have sufficient cold weather safety on the 250Voc max), and 25A max means barley being able to do 3 series strings in parallel. Having two locations for panels with one very limited (but with the best sun) is another complicating factor.

From what I can figure, the maximized configuration for a single input on the LV6548 with these panels seems to be 5S3P, which is 3,750W, 188Voc, 24.81A (pushing it on the amps, but these are used panels, so I doubt I need to worry too much about that). I'll do that for the larger array on the roof.

That leaves 11 panels out of the 26 for the second input, so unless I buy more, I'll do 5S2P for the second input yielding 2,500W, 188Voc, 16.54A, and squeeze that onto the South facing wall somehow. That should be a total of 6,250 Watts total.

It seems overkill to go with 2 combiner boxes, one for 2 strings, and the other for 3. I'm starting to lean in the direction of branch connectors and in line fuses, and then a couple of 25A breakers for the two controller inputs. That will protect the LV6548, be affordable and easy, and it should also be relatively safe, right?

To some extent this first set up is proof of concept. Trying to keep it expandable but also affordable. If I can find the real estate for enough panels to make it worthwhile I'd love to add a second LV6548 and parallel them for split phase 220-240.

 

[WYtreasure]

It seems overkill to go with 2 combiner boxes, one for 2 strings, and the other for 3.

The box I mentioned can be divided so you can run two separate strings by splitting the busbar.

"The MNPV6 enclosure can be split into two sections making it equivalent to 2 MNPV3 combiners in one".

Product Documents - MidNite Solar

MidNite Solar's list of Product Documents.

www.midnitesolar.com

Under "Manuals"
Select "MNPV2-3-4-6 Manual"
Read page 4

 

[sethile]

The box I mentioned can be divided so you can run two separate strings by splitting the busbar.

"The MNPV6 enclosure can be split into two sections making it equivalent to 2 MNPV3 combiners in one".

Perfect! Thank you for pointing that out. It looks like exactly what I need--much better solution!

 

[WYtreasure]

Perfect! Thank you for pointing that out. It looks like exactly what I need--much better solution!

Happy to help.

1) Have you considered a Class T Fuse at your battery positive wire?

Class T vs ANL fuse

I'm about to start my upgrade to our RV electrical system. It will be a Victron MultiPlus 3000 with 4 Battleborn Batteries and 700 watts of solar. I went and go everything from BattleBorn but noticed that they supplied me with a 400 Amp ANL fuse to place between the battery and the inverter (it...

diysolarforum.com

Use a fuse - and wear safety glasses... This could have been very bad.

If she did not have that fuse, this would have been a lot worse... Definitely worth the cost of the Class T fuse.

diysolarforum.com

2) Many folks use disconnect switches which are not meant to be used under load. Just when you need it the most is when it may fail.

 

[newbostonconst]

The box I mentioned can be divided so you can run two separate strings by splitting the busbar.

"The MNPV6 enclosure can be split into two sections making it equivalent to 2 MNPV3 combiners in one".

Product Documents - MidNite Solar

MidNite Solar's list of Product Documents.

www.midnitesolar.com

Under "Manuals"
Select "MNPV2-3-4-6 Manual"
Read page 4

Depending on how you are using it you can flip the breakers if needed to get the current to flow through the breaker in the right direction.

I am using it and have 4 strings going into it with 15 amp breakers then through the breakers to the bus bar and the bus bar feeds to a 25 amp breaker (that is flipped) and then the power goes out a single cable to me Solar Charge Controller.

So panels go into breakers up to bus bar, across bus bar to main breaker upside down and power flows down through that one and out to large cable to SCC....

Love that box...cheap and effective.

 

[WYtreasure]

Depending on how you are using it you can flip the breakers if needed to get the current to flow through the breaker in the right direction.

I am using it and have 4 strings going into it with 15 amp breakers then through the breakers to the bus bar and the bus bar feeds to a 25 amp breaker (that is flipped) and then the power goes out a single cable to me Solar Charge Controller.

So panels go into breakers up to bus bar, across bus bar to main breaker upside down and power flows down through that one and out to large cable to SCC....

Love that box...cheap and effective.

Nice shootin Tex. Thanks for sharing.

 

[sethile]

I am using it and have 4 strings going into it with 15 amp breakers then through the breakers to the bus bar and the bus bar feeds to a 25 amp breaker (that is flipped) and then the power goes out a single cable to me Solar Charge Controller.

So panels go into breakers up to bus bar, across bus bar to main breaker upside down and power flows down through that one and out to large cable to SCC....

Sounds like a great set up! I've ordered the box and 5 15 Amp breakers. I'll have a total of 5 strings coming in, and two feeds heading out to the SCC. 2 of the strings coming in will be combined and run out to controller 1. The other three will be combined and run out to controller 2.

My guess is there is not room to add two additional breakers for the two outputs, but that would be cool. I'll likely end up putting breakers or fuses and switches inside before the SCC.

Happy to help.

1) Have you considered a Class T Fuse at your battery positive wire?
2) Many folks use disconnect switches which are not meant to be used under load. Just when you need it the most is when it may fail.

Thanks for the tips! I have a 48V 100AH LCD Battery by EG4 coming from Signature Solar. It has a built in 100Amp breaker. Should I still fuse it, or is that in combination with the BMS protection adequate?

 

[WYtreasure]

Sounds like a great set up! I've ordered the box and 5 15 Amp breakers. I'll have a total of 5 strings coming in, and two feeds heading out to the SCC. 2 of the strings coming in will be combined and run out to controller 1. The other three will be combined and run out to controller 2.

My guess is there is not room to add two additional breakers for the two outputs, but that would be cool. I'll likely end up putting breakers or fuses and switches inside before the SCC.



Thanks for the tips! I have a 48V 100AH LCD Battery by EG4 coming from Signature Solar. It has a built in 100Amp breaker. Should I still fuse it, or is that in combination with the BMS protection adequate?

I'm confused. One battery but two charge controllers??

Here is a fusible disconnect which may work for you. Siemens GF222NA, 2 pole

 

[sethile]

I'm confused. One battery but two charge controllers??

Here is a fusible disconnect which may work for you. Siemens GF222NA, 2 pole

Yes, the MPP LV6548 has two controllers built in. It combines them to feed the one battery array. Ideally I'd like to add another battery or two in parallel, but I'll see how this all works first.

The Siemens GF222NA, 2 pole disconnect looks like a great solution, thanks!