Help with panel count and wiring configuration

[Stepandwolf]

Hello, I bought a LV6048 knowing it has some voltage limitations, but I am ignorant of all the electrical talk I am not sure what options that leaves for panels.
The LV6048 manual says it has two MPPT controllers with these specs:

Max PV Array Open Circuit Voltage 145Vdc
PV Array MPPT Voltage Range 60~115Vdc
Min battery voltage for PV Charge 34Vdc

It isn't clear if that is the total for both, or each. Suspect someone here knows.

It is my understanding, to get the highest capacity, that a combiner would be needed. A local is selling used Trina 250W panels with this spec:

60 cell, 240-255W
Max power voltage 30.2
Max Power Current 8.13
Open Circuit Voltage 37.5

I intend to install them on top of a CONEX where I can install a single vertical row of 10 panels or two horizontal rows of 14 total panels. Can that inverter handle 10 or 14 panels?

Could someone help me calculate how many total panels I could use and how many strings to get the right combiner.

Thanks!

 

[sunshine_eggo]

It's each MPPT

You can go 3S with those panels on that LV6048.

To nearly max out each MPPT, you need a 3S5P array on each MPPT, so 30 panels total.

Combiner boxes can be spendy. Midnight MNPV6 is a good option.

Watts247.com has some as well.

 

[Stepandwolf]

It's each MPPT

You can go 3S with those panels on that LV6048.

To nearly max out each MPPT, you need a 3S5P array on each MPPT, so 30 panels total.

Combiner boxes can be spendy. Midnight MNPV6 is a good option.

Watts247.com has some as well.

So....if I only go with the two CONEX top options, and if 3S is best, then it seems like 12 panels would be the right mix vs the 10 or 14 panel limit. So, two rows of 6 giving me 4 strings if I am understanding?

Is something like this too wimpy?

Seems the strings might exceed the amperage?

 

[wheisenburg]

So....if I only go with the two CONEX top options, and if 3S is best, then it seems like 12 panels would be the right mix vs the 10 or 14 panel limit. So, two rows of 6 giving me 4 strings if I am understanding?

Is something like this too wimpy?

Seems the strings might exceed the amperage?

You figure this out like this:

Max volts: 145 / 37.5 = 3.87. Then round down to 3
Max power: 4000 / 155 = 15.69. Then round down to 15.

This is for each MPPT

If you can fit 14 panels, you could do 4 strings of 3 on one MPPT (5 is the limit),
and possibly 1 string of 2 on the other MPPT.

This issue with 2 panels on a string is that the minimum MPPT voltage is 60, while the max power voltage on the panels is 30.2. That might mean two panels isn't quite enough to drive the MPPT controller.

If you don't care about maxing your panels out, just go with 4 strings of 3 and split them between the two MPPTs.

You could also just combine all 4 into one string, since the MPPT would handle it and you would only need a single combiner. If you go this route the output of the combiner needs wire that can handle 40 amps.

 

[OffGridForGood]

Do you have any plans for future expansion?
if not, split the PV between the two MPP's use smaller wire.
If future expansion is planned, put everything into one, with appropriate wire size, leave one MPP for expansion.

 

[Stepandwolf]

You figure this out like this:

Max volts: 145 / 37.5 = 3.87. Then round down to 3
Max power: 4000 / 155 = 15.69. Then round down to 15.

This is for each MPPT

If you can fit 14 panels, you could do 4 strings of 3 on one MPPT (5 is the limit),
and possibly 1 string of 2 on the other MPPT.

This issue with 2 panels on a string is that the minimum MPPT voltage is 60, while the max power voltage on the panels is 30.2. That might mean two panels isn't quite enough to drive the MPPT controller.

If you don't care about maxing your panels out, just go with 4 strings of 3 and split them between the two MPPTs.

You could also just combine all 4 into one string, since the MPPT would handle it and you would only need a single combiner. If you go this route the output of the combiner needs wire that can handle 40 amps.

I found the max volts values, but don't see where you got the max power values from? Either way, you agree with Eggo on number of panels. I could possibly put another 3rd row across the face of the CONEX

The LV manual suggested 8 ga, 80 amp PV cables so your suggestion fits easily into that and the distance won't be great. I suspect even 10 ga would be adequate for 20'.

I should have asked how much power I could expect from a dozen panels? The worst case would be powering a 15k BTU AC..typically the AC would be needed when it is the sunniest....this setup would be installed in the AZ high desert.

Thanks again..

 

[OffGridForGood]

The LV manual suggested 8 ga, 80 amp PV cables so your suggestion fits easily into that and the distance won't be great. I suspect even 10 ga would be adequate for 20'.

DC cable calculator, 20 feet one-way length, 75C cable
30A = 10ga
40A = 8ga
50A = 8ga
60A = 6ga

Your max MPP input is 4000W Each, no way you can run 80 Amps 100 volt - it will clip half of the power - or melt something.

 

[Stepandwolf]

Do you have any plans for future expansion?
if not, split the PV between the two MPP's use smaller wire.
If future expansion is planned, put everything into one, with appropriate wire size, leave one MPP for expansion.

I just asked about what power I could expect from 12 panels, and if not enough, I could probably go with 21 panels by adding a row of panels on the face of the CONEX. My TT will have it's own solar system, but not powerful enough to power the AC for long...

 

[Stepandwolf]

DC cable calculator, 20 feet one-way length, 75C cable
30A = 10ga
40A = 8ga
50A = 8ga
60A = 6ga

Your max MPP input is 4000W Each, no way you can run 80 Amps 100 volt - it will clip half of the power - or melt something.

I am not sure what that is in reference to? Did one of us say 80A 100V? I quoted the manual which said "8 ga, 80 amp". I am the one that doesn't know any of this which is why I am asking, I can only quote manuals and hope the mfg. has a clue. thanks

 

[sunshine_eggo]

So....if I only go with the two CONEX top options, and if 3S is best, then it seems like 12 panels would be the right mix vs the 10 or 14 panel limit. So, two rows of 6 giving me 4 strings if I am understanding?

Sounds like you got it.

Is something like this too wimpy?

Seems the strings might exceed the amperage?

It's borderline for sure, and it combines 6 into 1. YOu need to combine 4 into 2. Honestly, since each MPPT will have a 3S2P array, you don't need any combiner or fuse/breaker protection of any kind. You could simply use the MC4 parallel connectors.

 

[sunshine_eggo]

You figure this out like this:

Max volts: 145 / 37.5 = 3.87. Then round down to 3
Max power: 4000 / 155 = 15.69. Then round down to 15.

This is for each MPPT

If you can fit 14 panels, you could do 4 strings of 3 on one MPPT (5 is the limit),
and possibly 1 string of 2 on the other MPPT.

This issue with 2 panels on a string is that the minimum MPPT voltage is 60, while the max power voltage on the panels is 30.2. That might mean two panels isn't quite enough to drive the MPPT controller.

If you don't care about maxing your panels out, just go with 4 strings of 3 and split them between the two MPPTs.

You could also just combine all 4 into one string, since the MPPT would handle it and you would only need a single combiner. If you go this route the output of the combiner needs wire that can handle 40 amps.

Since this lovely gentleman actually tried to each you how to do this, I'll include my logic. It's simply this basic rule:

on a 150V controller:

3S 60 cell panels max
2S 72 cell panels max

This allows for adequate temperature margin. It gets pretty cold up there (forecast for 8°F this Tuesday), so you definitely need some temperature margin.

 

[Stepandwolf]

Sounds like you got it.



It's borderline for sure, and it combines 6 into 1. YOu need to combine 4 into 2. Honestly, since each MPPT will have a 3S2P array, you don't need any combiner or fuse/breaker protection of any kind. You could simply use the MC4 parallel connectors.

Lets see if I understand. You are saying taking that the 12 panels would be two 3s2p. So, rather than combining 4 or 6 strings into 1 and using one mppt, you are proposing run 6 on each side....then what if I go with 18 or 21 panels? I still don't know the expected power from these various options to know if I need to go beyond a dozen panels? thanks

 

[Stepandwolf]

Lets see if I understand. You are saying taking that the 12 panels would be two 3s2p. So, rather than combining 4 or 6 strings into 1 and using one mppt, you are proposing run 6 on each side....then what if I go with 18 or 21 panels? I still don't know the expected power from these various options to know if I need to go beyond a dozen panels? thanks

Since this lovely gentleman actually tried to each you how to do this, I'll include my logic. It's simply this basic rule:

on a 150V controller:

3S 60 cell panels max
2S 72 cell panels max

This allows for adequate temperature margin. It gets pretty cold up there (forecast for 8°F this Tuesday), so you definitely need some temperature margin.

glad you will be helping me install the system

 

[sunshine_eggo]

Lets see if I understand. You are saying taking that the 12 panels would be two 3s2p. So, rather than combining 4 or 6 strings into 1 and using one mppt, you are proposing run 6 on each side....

Yes. I'm just thinking about speed, ease and cost.

then what if I go with 18 or 21 panels?

If you need to add more than two strings on either MPPT, you need fuse protection on each string. Given your panels, you could actually use the MC4 parallel connectors for 3 strings and put an MC4 fuse in each string... still cheaper than a combiner box.

https://www.amazon.com/BougeRV-Solar-Branch-Connectors-Parallel/dp/B0B6HZ6QQH

https://www.amazon.com/BougeRV-Controller-Waterproof-Connector-Protection/dp/B08L56RDNP

(five in pack, but you'd need 6 - one per string)

 

[Stepandwolf]

If you need to add more than two strings on either MPPT, you need fuse protection on each string. Given your panels, you could actually use the MC4 parallel connectors for 3 strings and put an MC4 fuse in each string... still cheaper than a combiner box.

Are the 15A fuses the appropriate value. I think I saw a 8A max on the panels?

Wouldn't I also need a 2 into one? 3 panel to one, then a two into one for a total of six on the string?

I would still need to buy a disconnect as well....

Thanks!

 

[sunshine_eggo]

Are the 15A fuses the appropriate value. I think I saw a 8A max on the panels?

Fuses need to be 1.25X greater than the wire/Isc rating. The panels themselves will have a max fuse rating on them. That's the max you want to use. I'm guessing it's going to be 15A, possibly 20A. 15A is fine.

Wouldn't I also need a 2 into one? 3 panel to one, then a two into one for a total of six on the string?

You have two MPPT. Up to 3S3P on one set to one MPPT and up to 3S3P on the other set to the other MPPT.

 

[Supervstech]

I am not sure what that is in reference to? Did one of us say 80A 100V? I quoted the manual which said "8 ga, 80 amp". I am the one that doesn't know any of this which is why I am asking, I can only quote manuals and hope the mfg. has a clue. thanks

8ga is capable of a max amperage of 40A...

The manual is wrong.
Do not use 8ga to handle 80A...

 

[Stepandwolf]

Fuses need to be 1.25X greater than the wire/Isc rating. The panels themselves will have a max fuse rating on them. That's the max you want to use. I'm guessing it's going to be 15A, possibly 20A. 15A is fine.




You have two MPPT. Up to 3S3P on one set to one MPPT and up to 3S3P on the other set to the other MPPT.

got that, but I guess I didn't ask the question properly. If I start with 12 panels, and I use the 3>1 adapter, I now have 4 sets of cables. Don't I then need a 2>1 adapter to get down to two total pairs?
Mr. Confused As Usual

 

[sunshine_eggo]

got that, but I guess I didn't ask the question properly. If I start with 12 panels, and I use the 3>1 adapter, I now have 4 sets of cables. Don't I then need a 2>1 adapter to get down to two total pairs?
Mr. Confused As Usual

There are two sets of connectors for two arrays of 3S3P (18 panels total).

Each set of connectors can convert three parallel 3S strings to a single pair, so the two sets take up to 3 parallel strings each and convert them to a single pair.

What I linked would allow for TWO of these:

 

[sunshine_eggo]

8ga is capable of a max amperage of 40A...

The manual is wrong.
Do not use 8ga to handle 80A...

The manual is confusing.

The 8awg reference is specifically for the PV connection. The table confusingly lists the output current of the MPPT, but that also implies a potential maximum PV input current limit.

Based on the 5P configuration, I reference above, 8awg would be acceptable if it's a premium wire. 8awg can be good for significantly more. 90°C 8awg wire is good for 55A. 8awg "battery cable" can handle up to 80A, BUT voltage drop may be ugly.

3S3P on each MPPT would be fine with 10awg.

The manual requires between 1/0 and 2/0 for the battery cable connection if you use the metric 60mm^2 requirement.