EG4 and Victron System Fuse and Cable Size Help

[PaleBlueDotFarm]

Hello!

I'm having 6x EG4-LL 24V 200A battery professionally placed in my existing system operating off old used AGMs. I have 2x MP2 3000s in split phase, and 250/100 MPPT, and will be using a Lynx distributor. I am trying to verify my components before install and would appreciate some help and verification.

Am I correct that the fuses and wires should be sized on the nominal draw?

Inverter to Lynx - 6000W/24/.85 = 294A, thus 2/0 cable and 300A fuse
MPPT 250/100 to Lynx - 100/.85 = 118A, thus 4 AWG cable and 125A fuse

On the Battery to Lynx, I'm lost. Manual says 200A max current per battery. If this combined in parallel, the wire and fuses would be insane. I must be missing something! SignatureSolar sent me 2x 2/0 cable and 2x 1/0 cable with 300A and 125A breakers, but I'd like to understand why I can't figure that out.

Many thanks to any who can opine!

 

[aliarifat794]

Maximum current rating (200A per battery) does not necessarily mean that each battery will constantly draw 200A. The actual current draw will depend on your system's load and charging conditions.

 

[PaleBlueDotFarm]

Ah, so the draw is limited to the max load of the inverters. I've also realized that 2x Inverters in split phase changes the requirements. I now think:

Inverter(s) to Lynx - 3000W/24/.85 = 147A, thus 150A fuse and 1/0 cable (cause I got it)
Battery to Lynx - 6000W max constant = 294A, thus 300A fuse and 2/0 cable

Signature sent me 125A fuses, which must be for the inverters, but appear too small now that I do the math. What's the best route here?

 

[sunshine_eggo]

Fuses should be 1.25X (rounded up to nearest size) wire rating. If you run a fuse/breaker at > 80% continuous rating, they will eventually trip.

Consult the Victron manuals. They recommend both wire and fuse sizes to the inverter.

Do you have a victron shunt?

Are your batteries in a rack, daisy chained together with a single (+) and (-) coming from the battery bank?

 

[PaleBlueDotFarm]

Fuses should be 1.25X (rounded up to nearest size) wire rating. If you run a fuse/breaker at > 80% continuous rating, they will eventually trip.

Appreciate that! Is there a reason vendors keep recommending 300A and 125A in this set-up? That seems low given this factor.

Consult the Victron manuals. They recommend both wire and fuse sizes to the inverter.

Got it. Will review the Victron Documentation.

Do you have a victron shunt?

No shunt in this set-up. I am hoping the comms with Cerbo will give me the functionality needed, but I have time to get a Lynx shunt out here if needed.

Are your batteries in a rack, daisy chained together with a single (+) and (-) coming from the battery bank?

Yep, as boring of a 24V box as I can make it.

 

[sunshine_eggo]

Appreciate that! Is there a reason vendors keep recommending 300A and 125A in this set-up? That seems low given this factor.

Bad decisions.

Your MPII calc is correct.

You MPPT calc is incorrect. There is no conversion penalty, so 100A wire and 125A fuse/breaker is appropriate.

Got it. Will review the Victron Documentation.

They tend to be over-spec on both cable and fuse/breaker because Victron hates DC ripple, and it has a strong influence on an inverter's ability to handle surge.

No shunt in this set-up. I am hoping the comms with Cerbo will give me the functionality needed, but I have time to get a Lynx shunt out here if needed.

That generally works. I use a batrium, but I also have a BMV-702. The BMV was present before the batrium, but I'm glad I have it.

The biggest challenge will be how the batteries handle SoC deviations among themselves. The system will receive ONE SoC value, but it's an aggregate of the six. New batteries often arrive imbalanced, and that can create a bit of a headache during commissioning.

Yep, as boring of a 24V box as I can make it.

 

[PaleBlueDotFarm]

They tend to be over-spec on both cable and fuse/breaker because Victron hates DC ripple, and it has a strong influence on an inverter's ability to handle surge.

Victron manual 50 mm with a 300A fuse per inverter. Assuming the recommended fuse is 1.25x wire size, wouldn't that wire need to handle 240A? Why do they recommend a 1/0 equivalent?

 

[sunshine_eggo]

Victron manual 50 mm with a 300A fuse per inverter. Assuming the recommended fuse is 1.25x wire size, wouldn't that wire need to handle 240A? Why do they recommend a 1/0 equivalent?

They tend to be over-spec on both cable and fuse/breaker because Victron hates DC ripple, and it has a strong influence on an inverter's ability to handle surge.

0 Gauge (1/0 AWG) Battery Cable with Ends OFC Copper Flexible Stranded UL MTW/THW/SGT

www.batterycablesusa.com

This 1/0 UL rated cable is good for 285A

EU standards may not follow the 1.25X rule of the NEC.

 

[PaleBlueDotFarm]

This 1/0 UL rated cable is good for 285A

EU standards may not follow the 1.25X rule of the NEC.

What’s your go-to ampacity chart? I come across lower ratings but a ton of variation, and I don’t know the best source.

 

[nimajneb]

What’s your go-to ampacity chart? I come across lower ratings but a ton of variation, and I don’t know the best source.

I would like to know as well.

 

[sunshine_eggo]

Wire ampacity depends on ratings (copper and insulation) and routing (open air, in conduit). I linked a specific source for specific UL "battery cable".

 

[PaleBlueDotFarm]

Wire ampacity depends on ratings (copper and insulation) and routing (open air, in conduit). I linked a specific source for specific UL "battery cable".

Much appreciated. I was ignoring some of the parameters. Can’t wait to do the final diagram and get these things hooked up.