LifePO4 Cables to 12KW Inverter

[UncleSam]

I know this has been asked, but every thread I read always deals with a lower output inverter. I have the 12KW All In One Growatt Inverter. The sticker on the side of the unit says it is rated for 300A of battery input at 48VDC.

Here's my setup:

1. I have 4x48v LifePO4 100AH batteries.
2. Batteries are to be installed on the open battery server rack from Signature Solar, which has busbars.
3. The battery rack will be connected from the busbars to the inverter.

Each battery came with a 6 AWG wire, which as far as I can tell seems to be correct since I'm connecting these all to the busbar in parallel. However, I can't for the life of me find out what cable size I need for the batteries to the inverter. It sounds like I need to support 300A (and, from what I understand, a little more for safety). But this chart doesn't go beyond 200A: https://www.bluesea.com/resources/1437

In fact, most charts don't seem to. Am I missing something obvious here?

Also, my understanding is I should use a 320A inline T-Class Fuse on the positive cable between the inverter and battery rack. Is this correct?

Thanks for your help.

 

[Quattrohead]

The recommended wire size is in the manual. RTFM.

 

[UncleSam]

Yes, it is in the manual. But it makes no sense! What is "3*2AWG" supposed to mean? Surely this doesn't mean 3x of the 2 AWG wires combined together? That would never pass inspection. What size wire would be the equivalent of this because I'd much rather pay for that.

 

[Quattrohead]

That is indeed what it means. I dunno what type of inspection you are hoping to pass, those inverters are not UL listed.
Your batteries have breakers, they will protect the wires.

 

[UncleSam]

Thanks for the message. They are not UL listed but they are indeed certified by Intertek, to UL standards. Intertek is recognized by the NEC so it should be fine. That said, I'm still interested in knowing what wire would be the equivalent of 3*2AWG. 4/0?

 

[UncleSam]

Here's info about certification: https://ramuk.intertekconnect.com/W...e5daea9b30cb7d3c862587ec0012f22c?OpenDocument

I am permitting this project and trying to do everything to code. I am trying to set this up in a legit way and not cut any corners or do things in a non-standard way. To me, bundling 3 wires seems non-standard.

 

[Solar Guy Richard]

Thanks for the message. They are not UL listed but they are indeed certified by Intertek, to UL standards. Intertek is recognized by the NEC so it should be fine. That said, I'm still interested in knowing what wire would be the equivalent of 3*2AWG. 4/0?

I'm interested if you find an actual gauge that is supported. Most charts that I see (and wire that is available for purchase easily) only goes 4/0 which is not quite large enough.

 

[UncleSam]

I'm interested if you find an actual gauge that is supported. Most charts that I see (and wire that is available for purchase easily) only goes 4/0 which is not quite large enough.

I'll let you know if I do. What size do think I need? Does it need to support 320A? If so, what is the cable size for 320A DC current? I can't seem to find that answer.

 

[Solar Guy Richard]

Look at the inverter to see how many amps it pulls - typically on the data plate. I don't have one in front of me so I can't check but that's the size I would base it on...not the total possible output of the batteries.

 

[UncleSam]

Look at the inverter to see how many amps it pulls - typically on the data plate. I don't have one in front of me so I can't check but that's the size I would base it on...not the total possible output of the batteries.

Yes, that's what I mentioned above (the sticker says it's rated for 300A DC Battery Input). I know what the rating is, my question is just what size cable I need to cover that for DC current.

 

[Solar Guy Richard]

Ah sorry, I misread. Ya, I'm unsure if there is a specific size rated that high. You could look at the actual volume of the cables recommended and add them together to see if it works? But not 100% positive on that answer.

 

[UncleSam]

Ah sorry, I misread. Ya, I'm unsure if there is a specific size rated that high. You could look at the actual volume of the cables recommended and add them together to see if it works? But not 100% positive on that answer.

Thanks for the reply. It just blows my mind that there isn't a common answer for this. Hopefully people aren't just using the 4 AWG cables that come with the battery rack. There really should be easy-to-access info for things like that with common wire sizes (not bundling).

 

[UncleSam]

There are also varying opinions. I called someone at Signature Solar yesterday and was told to use one 2 AWG. Now I see that can't possibly be!

 

[Solar Guy Richard]

Thanks for the reply. It just blows my mind that there isn't a common answer for this. Hopefully people aren't just using the 4 AWG cables that come with the battery rack. There really should be easy-to-access info for things like that with common wire sizes (not bundling).

Ya, it's hard to determine because there are so many possible set ups. I know there are charts out there that show conductivity but like you said, they only go up so high.

 

[Solar Guy Richard]

There are also varying opinions. I called someone at Signature Solar yesterday and was told to use 2 AWG. Now I see that can't possibly be!

I'm sure they meant 2/0.

 

[UncleSam]

Ya, it's hard to determine because there are so many possible set ups. I know there are charts out there that show conductivity but like you said, they only go up so high.

Exactly.

 

[UncleSam]

I'm sure they meant 2/0.

That's possible. But you were saying you're not sure that even 4/0 is big enough. So that's why I'm feeling like there's no clear answer. ?

 

[HRTKD]

What is the distance between the battery and the inverter. Cable size calculations depend on voltage, amperage and distance.

According to the wire gauge calculator I use, 300 amps @ 48 volts with 10' round trip distance could use 2/0 for a .5% voltage drop.

My Victron 12/3000 inverter calls for a 400 amp fuse and twin 2/0 cables, but I'm not going to ever come close to pulling 200 amps continuous. I still ran twin 2/0 cables.

 

[UncleSam]

What is the distance between the battery and the inverter. Cable size calculations depend on voltage, amperage and distance.

According to the wire gauge calculator I use, 300 amps @ 48 volts with 10' round trip distance could use 2/0 for a .5% voltage drop.

My Victron 12/3000 inverter calls for a 400 amp fuse and twin 2/0 cables, but I'm not going to ever come close to pulling 200 amps continuous. I still ran twin 2/0 cables.

Thank you for the comment. I'm curious which calculator you use? I doubt I will be using more than 10' round trip. I'd like it to be as short as possible.

 

[John Frum]

@UncleSam does the growatt have mechanical lugs or studs?
If it has mechanical lugs what is the largest wire that will fit?

12000 ac watts / .85 conversion factor / 48 volts low cutoff = 294.12 service amps
294.12 service amps / .8 fuse headroom = 367.65 fault amps
That means 4/0 awg pure copper wire with 105C insulation and a 400 amp fuse.
If it has multiple terminals you could do 2 * 2/0 awg.

The batteries should not be daisy chained.
4 awg with a 150 amp class t fuse will be fine if the are sensibly paralleled.