LV6548 build - combiner box - please critique my plan

[RGUY777]

Hello,

I need some veterans to please look at the attached documents. Please view, critique and make any suggestions.

My main question is, what power comes out of the combiner box? I bought the combiner box at the suggestion of Ian at Watts 24/7.

Thank you,

Robert

 

[Kornbread]

Four panels at 50voc would be 200volts + cold temp rise, maybe ~225v (figured that in my head so it 'should' be kinda sorta close but I'm sure it's not exact) at what ever amp one panel is rated for (cannot see what it is in your drawing). 4s2p.

It looks like the lv6548 has two mppt inputs with 4000watt, 18amp max, so not sure why you would need a combiner box, or why one would be suggested, unless, maybe you are planning on expanding later? The combiner box does as it's name suggests; it combines the pv inputs.

 

[RGUY777]

Four panels at 50voc would be 200volts + cold temp rise, maybe ~225v (figured that in my head so it 'should' be kinda sorta close but I'm sure it's not exact) at what ever amp one panel is rated for (cannot see what it is in your drawing). 4s2p.

It looks like the lv6548 has two mppt inputs with 4000watt, 18amp max, so not sure why you would need a combiner box, or why one would be suggested, unless, maybe you are planning on expanding later? The combiner box does as it's name suggests; it combines the pv inputs.

Thanks for the reply Kornbread. I apologize, the drawing is not correct. There are I will actually have 4 strings going into the combiner box. So double the amount of panels in the drawing. Then, into the LV 6548.

16 total panels
455 watts, 50 voc, 10.74 amps - per panel.

Each 4s2p measures 1820 watts (455w X4), 10.74 amps going in to the combiner box. 4 strings "combine" to 2 at the box.

Since we are combining the solar panel strings, does the combiner increase amps or volts or neither? I'm confused on the output of the combiner box. Am I thinking about this all wrong?

 

[Kornbread]

Thanks for the reply Kornbread. I apologize, the drawing is not correct. There are I will actually have 4 strings going into the combiner box. Then into the LV 6548.

So, does the combiner add amps or volts? I'm confused on the output of the combiner box.

Four strings of four in a series?

What goes into the combiner box comes out of the combiner box. In your case, four inputs into two outputs. For ease of my math abilities ... excuse the math ... we'll say four panels in series with a vmp of 45 volts and imp of 10amps = 450 watts per panel x 16 panels = 7200 watts. When the mppt controller and panels are in the happy spot that would be 4panels x45v=180v and 10amps for each string since these panels are connected in series, and series connection adds voltages while amperage remains the same. Now you have four of these strings feeding the combiner box; the combiner box connects these strings in parallel, so the voltage remains 180v (parallel adds amps but voltage remains the same) but the amperage is 10x4=40amps, 40amps x 180v = 7200watts, but in your case, the combiner box is 4into2, so 10amps x 2outputs =20amps for each output from the combiner box, which should also equal 7200watts.
What puzzles me is your controller has two mppt inputs, why use a combiner box?

 

[RGUY777]

Four strings of four in a series?

What goes into the combiner box comes out of the combiner box. In your case, four inputs into two outputs. For ease of my math abilities ... excuse the math ... we'll say four panels in series with a vmp of 45 volts and imp of 10amps = 450 watts per panel x 16 panels = 7200 watts. When the mppt controller and panels are in the happy spot that would be 4panels x45v=180v and 10amps for each string since these panels are connected in series, and series connection adds voltages while amperage remains the same. Now you have four of these strings feeding the combiner box; the combiner box connects these strings in parallel, so the voltage remains 180v (parallel adds amps but voltage remains the same) but the amperage is 10x4=40amps, 40amps x 180v = 7200watts, but in your case, the combiner box is 4into2, so 10amps x 2outputs =20amps for each output from the combiner box, which should also equal 7200watts.
What puzzles me is your controller has two mppt inputs, why use a combiner box?

Four strings of four in a series - Correct.

Kornbread quote - "The combiner box connects these strings in parallel" - That's the information I needed. THANK YOU! I didn't know if the combiner box connected the strings in series or parallel. I searched multiple threads and couldn't find this answer.

I'm using the combiner box as a disconnect and shortening my wire runs. I'm installing the combiner box near the panels, then making about a 100ft run to the LV6548. Would you not recommend using a combiner box? I'm a novice, so trying to put all my thoughts together.

455W each panel * 4 = 1820W per string. 1820W X 2 = 3640W, 200VOC, 20amps per MPPT. If my math is correct, that should work perfect for the LV6548.

LV6548 SPECS: Solar input max is - 4000W per MPPT, 250VOC, 18amp. I read in multiple threads the unit will actually take up to 25amps.

Another question: Did I put the T class fuse in the right spot?

Thanks again Kornbread. I really appreciate any further recommendations.

 

[Samsonite801]

Four strings of four in a series - Correct.

Kornbread quote - "The combiner box connects these strings in parallel" - That's the information I needed. THANK YOU! I didn't know if the combiner box connected the strings in series or parallel. I searched multiple threads and couldn't find this answer.

I'm using the combiner box as a disconnect and shortening my wire runs. I'm installing the combiner box near the panels, then making about a 100ft run to the LV6548. Would you not recommend using a combiner box? I'm a novice, so trying to put all my thoughts together.

455W each panel * 4 = 1820W per string. 1820W X 2 = 3640W, 200VOC, 20amps per MPPT. If my math is correct, that should work perfect for the LV6548.

LV6548 SPECS: Solar input max is - 4000W per MPPT, 250VOC, 18amp. I read in multiple threads the unit will actually take up to 25amps.

Another question: Did I put the T class fuse in the right spot?

Thanks again Kornbread. I really appreciate any further recommendations.

Yeah, a Support Rep for MPP Solar said 25a is absolute max, and to try and stay around 22a as your working maximum, was my understanding...

 

[Samsonite801]

On a side note, I personally decided to also add in surge protection onto the solar circuit for my LV6548 build (32x panels, 4s2p per PV run), since we get a lot of lightning out in the open desert...

I purchased some of the Midnite Solar surge protectors (I went with MNSPD-300-DC, I just bought a 6-pack off an eBay seller):

Manufacturer Ref:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

eBay Ref:

MidNite Solar MNSPD-300-DC Surge Arrestor, Surge Protection Device | eBay

Midnite Solar MNSPD-300-DC The color of the item may be blue, green or red depending on stock available. All three work the same. The MidNite Solar Surge Protector Device (MNSPD) is a Type 1 device per UL1449 rev3. It is designed for both AC and DC systems and provides protection to service...

www.ebay.com

The combiner that Ian at Watts247.com had you buy may already have surge protectors in it, you can check, my Midnite Solar DC combiner boxes didn't have surge protectors by default...

 

[RGUY777]

On a side note, I personally decided to also add in surge protection onto the solar circuit for my LV6548 build (32x panels, 4s2p per PV run), since we get a lot of lightning out in the open desert...

I purchased some of the Midnite Solar surge protectors (I went with MNSPD-300-DC, I just bought a 6-pack off an eBay seller):

Manufacturer Ref:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

eBay Ref:

MidNite Solar MNSPD-300-DC Surge Arrestor, Surge Protection Device | eBay

Midnite Solar MNSPD-300-DC The color of the item may be blue, green or red depending on stock available. All three work the same. The MidNite Solar Surge Protector Device (MNSPD) is a Type 1 device per UL1449 rev3. It is designed for both AC and DC systems and provides protection to service...

www.ebay.com

The combiner that Ian at Watts247.com had you buy may already have surge protectors in it, you can check, my Midnite Solar DC combiner boxes didn't have surge protectors by default...

Thanks for the suggestion Samsonite, I'll check on surge protectors. Sounds like we are doing similar projects.

 

[Kornbread]

Four strings of four in a series - Correct.

Kornbread quote - "The combiner box connects these strings in parallel" - That's the information I needed. THANK YOU! I didn't know if the combiner box connected the strings in series or parallel. I searched multiple threads and couldn't find this answer.

I'm using the combiner box as a disconnect and shortening my wire runs. I'm installing the combiner box near the panels, then making about a 100ft run to the LV6548. Would you not recommend using a combiner box? I'm a novice, so trying to put all my thoughts together.

455W each panel * 4 = 1820W per string. 1820W X 2 = 3640W, 200VOC, 20amps per MPPT. If my math is correct, that should work perfect for the LV6548.

LV6548 SPECS: Solar input max is - 4000W per MPPT, 250VOC, 18amp. I read in multiple threads the unit will actually take up to 25amps.

Another question: Did I put the T class fuse in the right spot?

Thanks again Kornbread. I really appreciate any further recommendations.

Yes, use the combiner box near the panels and make a single, or in your case, a double home run. Much less wire to buy. Initially, I did not know you had more than eight panels. Be sure and use the correct size wire for the home run voltage drop calc notice it asks for distance one-way, not round trip.
There is some temperature coefficient information, forgot what it's called, on the solar panels that state how much the voc can increase in cold temperatures. Find that and figure it into the voc equation to insure voc remains under the mpp's max voc input.
When most SCC are overpaneled, they simply throttle back the panels, but some do have hard limits.

 

[RGUY777]

Yes, use the combiner box near the panels and make a single, or in your case, a double home run. Much less wire to buy. Initially, I did not know you had more than eight panels. Be sure and use the correct size wire for the home run voltage drop calc notice it asks for distance one-way, not round trip.
There is some temperature coefficient information, forgot what it's called, on the solar panels that state how much the voc can increase in cold temperatures. Find that and figure it into the voc equation to insure voc remains under the mpp's max voc input.
When most SCC are overpaneled, they simply throttle back the panels, but some do have hard limits.

Copy that. Thanks for the feedback Kornbread.

I'll investigate the max voc input (as related to the temperature), and thanks for the wire size calculator. I believe LV6548 can be over paneled, but I need to double check.

Sorry for the confusion on number of panels. My fault, the drawing was not correct to begin with.

Another question: I plan to install a 200A or 250A T class fuse between my buss bar (Victron Power In) and the LV6548 inverter. Is this the correct location for the T class fuse?

 

[Zil]

You need a Class-T fuse on each of your four 48V batteries. At the battery terminals before the BusBar.

 

[Kornbread]

Is that a Victron shunt? I only have one class-t fuse between the batteries and the Growatt. Some say to put a fuse on every battery pre-bus bar and others are fine with one before the inverter. Most of the server rack batteries have built-in breakers so why add a fuse pre-bus bar ... in case of a major malfunction, the breaker may not be able to stop the full current dump of the battery. IIRC, SigSolar states the breakers on their server rack batteries will interrupt the flow of current if a major malfunction occurs. YMMV.

... ordered my fuse/holder for a good price, more in stock, and they shipped quick, from shunts dot com, would post link but not sure what can and cannot be posted on this forum without getting busted.

 

[Zil]

? A built-in Breaker? Or a BMS? We want to design our systems so the BMS never trips. It should only be the last step emergency disconnect.

 

[RGUY777]

Is that a Victron shunt? I only have one class-t fuse between the batteries and the Growatt. Some say to put a fuse on every battery pre-bus bar and others are fine with one before the inverter. Most of the server rack batteries have built-in breakers so why add a fuse pre-bus bar ... in case of a major malfunction, the breaker may not be able to stop the full current dump of the battery. IIRC, SigSolar states the breakers on their server rack batteries will interrupt the flow of current if a major malfunction occurs. YMMV.

... ordered my fuse/holder for a good price, more in stock, and they shipped quick, from shunts dot com, would post link but not sure what can and cannot be posted on this forum without getting busted.

OK, thanks Kornbread.

Question: Is that a Victron shunt? No, it is basically, a very nice 1000amp busbar, with the ability to add mega fuses to each positive battery connection. I could add mega fuses to each positive terminal from the battery. I think I may switch out the "Power In" for "Distributor". Here is a link to the Victron system.

Upon further consideration, I think I will upgrade to the Victron Distributor, which includes mega fuses to each battery connection. Glad I'm talking this through.

My batteries are the pre-welded EG4 from signature solar. I would not recommend anyone buy these. It is so much simpler to buy the finished package. After buying a BMS, the additional hardware and labor time, these packs aren't worth the $500 you save (per 2 pack). After additional expenses, you only save approx $350 per 48V 2 pack.

EG4 8-Cell Pack Lithium Cells | 25.6V 100AH

EG4 (25.6V/100AH) 8-Cell PackEG4 Lithium battery 25.6V (24V) 2.56kWh with 100AH. Made of UL Listed Battery Cells. Off Grid Solar Batteries - Off Grid System - Solar Batteries for Home - Lithium Solar Batteries - Deep Cycle Solar Batteries - Power Reserve - Solar Panels Plus Battery - LifePo4 -...

signaturesolar.com

I've got a JBD 16S BMS from Overkill Solar for each of my 48V packs. They are very nice BMS's.

16s BMS 100a for LifePo4 without Wires

Without wires soldered to the board. You will need to solder your own wires. Do not bolt connections directly to the circuit board. BMS For 16 cell, 48v volt Lithium-iron-phosphate DIY batteries 10…

overkillsolar.com

Thanks for the heads up on the Shunts.com website. I'll save it for future reference.

 

[RGUY777]

You need a Class-T fuse on each of your four 48V batteries. At the battery terminals before the BusBar.

Thanks for the input Zil. I have decided to go with Victron Distributor (glorified 1000A busbar) with a mega fuse at each battery, then a 200A T class between the LV6548.

 

[Zil]

Mega fuses are not recommended for catastrophic fuse at LiFePo battery. Mega fuse has only 2000A interrupt capacity. A LiFePo short circuit will be spectacular.

 

[Kornbread]

Mega fuses are not recommended for catastrophic fuse at LiFePo battery. Mega fuse has only 2000A interrupt capacity. A LiFePo short circuit will be spectacular.

Class t fuses are rated for a much higher interrupt capacity. Grainger says 200ka interrupt rating for class t. MEga fuses 2000a. ANL 5000a. LiFepo4 can dump a krapton of current almost instantly. Just me, but if I were doing fuses/breakers at each battery, or anywhere on that side of things, they would be class t fuses. YMMV

 

[RGUY777]

Class t fuses are rated for a much higher interrupt capacity. Grainger says 200ka interrupt rating for class t. MEga fuses 2000a. ANL 5000a. LiFepo4 can dump a krapton of current almost instantly. Just me, but if I were doing fuses/breakers at each battery, or anywhere on that side of things, they would be class t fuses. YMMV

Got it. Then I'm going with your setup. One T class between the busbar and the inverter.

Thanks again.

 

[wayne530]

Got it. Then I'm going with your setup. One T class between the busbar and the inverter.

Thanks again.

I know this thread is almost a year old, but was curious if you got your system up and running successfully? I am planning to build a similar system (4s2p) and would love to hear your thoughts/learnings/etc in building and connecting this up to the LV6548. Thanks in advance!