EG4LL to 6500EX-48 battery to inverter cable size - I'm confused

[BondJmsBond]

I bought 4 - (will be 6 shortly) - EG4LL (v2) 48v batteries w/rack and a 6500EX-48 inverter.

In future there will be 2 inverters for 240, but for now just a 1 inverter system is the plan.
It's off-grid house backup for outages for now and will add solar.

Signature solar just told me "For the EG4 6500W inverter, we recommend 1awg battery to inverter cables"

- I look at will's blueprint and he has 4/0 and 2/0 battery to inverter cables.

48V Offgrid Solar Power System

If you wish to build the ultimate offgrid solar power system, look no further: All-in-one units make setup a breeze. Each unit has it's own Inverter, MPPT, Transfer Switch and Battery Charger. Budget...

www.mobile-solarpower.com

Will's is a 240v 2-inverter system, with 2 sets of batteries apparently connected, so that may be the difference, and 1 or 2 awg is sufficient for me; but I don't know.
I'm reluctant to oversize now for a future 2nd inverter/more batteries as that seems the wrong thing to do, and of course don't want to undersize either.

Please advise. thank you for your help

 

[JCSchwarb]

I bought 4 - (will be 6 shortly) - EG4LL (v2) 48v batteries w/rack and a 6500EX-48 inverter.

In future there will be 2 inverters for 240, but for now just a 1 inverter system is the plan.
It's off-grid house backup for outages for now and will add solar.

Signature solar just told me "For the EG4 6500W inverter, we recommend 1awg battery to inverter cables"

- I look at will's blueprint and he has 4/0 and 2/0 battery to inverter cables.

48V Offgrid Solar Power System

If you wish to build the ultimate offgrid solar power system, look no further: All-in-one units make setup a breeze. Each unit has it's own Inverter, MPPT, Transfer Switch and Battery Charger. Budget...

www.mobile-solarpower.com

Will's is a 240v 2-inverter system, with 2 sets of batteries apparently connected, so that may be the difference, and 1 or 2 awg is sufficient for me; but I don't know.
I'm reluctant to oversize now for a future 2nd inverter/more batteries as that seems the wrong thing to do, and of course don't want to undersize either.

Please advise. thank you for your help

I would be careful with any advice from that company. They are known to give lots of misleading information. The installer is responsible for following NEC or other suitable wiring sizing best practices. Try this calculator: https://www.jcalc.net/cable-sizing-calculator-nec

This shows you the variables needed to properly size the wiring, including amperage, volts, wire material (use pure copper not CCA), conduit, and distance.

Between my two racks of 6 100 Ah batteries I use 4/0 to the Busbar. From the Busbar it goes to a 200A CB via 2/0, then 2/0 to each inverter. I included some images to give an idea of my custom battery interconnect box.

Hope this helps.

-Jay

 

[John Frum]

6500 ac watts / .85 conversion factor / 48 volts low cutoff = 159.31372549 inverter amps
159.31372549 inverter amps / .8 fuse headroom = 199.142156863 fuse amps
That means you you could go as thin as 2 awg(35mm2) on the inverter circuit with a 200 amp fuse.
That assumes pure copper wire with insulation rated for 90C or better in free air.

If you are putting the wire in conduit or raceway or anything other than free air then you need to go up to 2/0 awg(70mm2).
If you going more than a few feet then voltage drop also has to be considered.

Many of us deliberately oversize the wires to keep them cool and to minimize voltage.

 

[BondJmsBond]

Can't thank you folks enough for the input. I have decided to use 4/0 awg from battery to fuse, then 2/0 from fuse to inverter. This is what Will and JCSchwarb did from mostly the same setup as I.
I will omit the busbar until I get a 2nd inverter.

4/0 from batteries to 200 amp fuse; I read in a thread here the 125 amp breaker on each battery protects from most problems while the fuse protects from a dead short which may fuse the breaker.

I was worried about oversizing but John Frum saying "Many of us deliberately oversize the wires to keep them cool and to minimize voltage."
has helped me get over that - of course please tell me if I'm doing wrong.

I know nothing and am doing this anyway - with Will's examples and this forum and the people here I'm confident I can figure it out and get it done. I've already learned a lot in 1 day reading threads here.

Talk to you soon with many other questions as I go along - Cheers

 

[PreppenWolf]

I used 2/0 to each inverter, but I'm straight from battery busbar to Inverter unlike Will's where it goes from busbar to single cable to another busbar, then split.

Will only used 4/0 because of how he ran one cable to the wall from the battery tower.

 

[Browse]

I went with 1 AWG and a 200A fuse for my 4 rack mount batteries to a single inverter. The inverter feeds a 30A interlock, so I'll never draw more than 30A continuous @240VAC from the system, which is about 7.2 kW from the batteries or 150A total from the 4 units.

 

[BondJmsBond]

Thank you PreppenWolf and Browse. Making me think. It's hard

I will ultimately have a 2 inverter system with possibly 2 battery banks so I know I may be oversizing a bit with the 4/0 with just 1 inverter now; but it will be similar to Will's and JCSchwarb's in future, so I'm trying to look ahead to that time and use what they used to make it work.

Now if there is a drawback besides price in using the 4/0 for what I have now please let me know, otherwise I'll go ahead with the 4/0 for future use with what I have planned.

 

[John Frum]

Thank you PreppenWolf and Browse. Making me think. It's hard

I will ultimately have a 2 inverter system with possibly 2 battery banks so I know I may be oversizing a bit with the 4/0 with just 1 inverter now; but it will be similar to Will's and JCSchwarb's in future, so I'm trying to look ahead to that time and use what they used to make it work.

Now if there is a drawback besides price in using the 4/0 for what I have now please let me know, otherwise I'll go ahead with the 4/0 for future use with what I have planned.

6500 ac watts * 2 inverters / .85 conversion factor / 48 volts low cutoff = 318.62745098 inverter amps
318.62745098 inverter amps / .8 fuse headroom = 398.284313725 fuse amps

Pure copper 4/0 awg with insulation rated for 90C is good for 400 amps in free air and can be fuse as high as 400 amps.

This means that the 4/0 awg trunking between the batteries and inverters is the choke point of the system.
Put another way 4/0 awg is just barely adequate for 2 of those inverters.

 

[John Frum]

I will ultimately have a 2 inverter system with possibly 2 battery banks

If you are planning for more than one rack of batteries then you need to have a very high capacity main busbar system.
These are the 2 highest capacity off the shelf options that I know of.

DC Distribution systems & Fuses - Victron Energy

Victron Energy's DC distribution systems monitor the state of charge of your battery and the state of each fuse. View products now.

www.victronenergy.com

https://www.bluesea.com/products/category/18/111/BusBars/PowerBar_1000

 

[PreppenWolf]

Bigger is always better.

For combining batteries go to common oversized busbar and branch it to the inverters. The inverters are limited to 2/0 each anyway.

 

[PreppenWolf]

Here is a 600A option. Plan ahead and keep all your battery cables equal length between the banks.

Iztoss 600A Bus Bar 3/8" Heavy Duty Module Design High Current BusBar Box Power Distribution Block 48V 8X M10 Terminal Studs Battery Junction Block for Battery Marine RV Truck.(Black) https://a.co/d/11rE56q

 

[BondJmsBond]

Bigger is always better.

For combining batteries go to common oversized busbar and branch it to the inverters. The inverters are limited to 2/0 each anyway.

It looks like I will have to install a busbar on the negative side anyway to reduce to 2/0 cable for inverter connection, in that case.
Keep all battery cables the same length, check.

Thank you for the heads up!

This is fun

 

[JCSchwarb]

It looks like I will have to install a busbar on the negative side anyway to reduce to 2/0 cable for inverter connection, in that case.
Keep all battery cables the same length, check.

Thank you for the heads up!

This is fun

Busbars are cheap. For 10 terminals $39. Consider this one. And ensure to use pure copper bars and wire… I purchased TEMCO battery wire and used a hydraulic 4/0 crimper and copper lugs with heat shrink tubing. It is a lot of fun…

GOUNENGNAIL-.157" x 2.36" x 7.87" Copper Ground Bar Kit, with 5/16''x10 Terminal Positions,Copper Grounding Busbar Bar Kit https://a.co/d/iU2Usv7

 

[McRod]

Bigger is not always better.

Read your inverter manual. Look at the specs. It should have a very specific "DC" or "battery input data" section. It will tell you the max DC charge and discharging current. Don't be dazzled by some internet math guy that doesn't take into count the limits of the inverter. If the inverter can only charge and discharge at 100 amps, it doesn't matter if you have 50 batteries. The max amps on the wire is going to be 100 amps - period. The manual may also tell you the maximum battery input conduit or even specify the maximum wire size.

My inverter is an 8kw 240v split phase and it can't accept wire greater than 2/0. So no, 4/0 wire would just be a waste of money when you realize it's too big to attach to the terminals. I have seen that with PV wire too. People oversize then realize when they go to connect the wire to the PV inputs it wont fit into the wire connectors because it's too big!

 

[John Frum]

Don't be dazzled by some internet math guy that doesn't take into count the limits of the inverter.

Be dazzled, you know you want to.

 

[McRod]

Ok, I looked at your manual for you!!!

Page 8. Max charge current 120 amps = 1 AWG wire (probably why SS recommended)

Not so fast!

Page 12. Recommended battery cable and terminal size. Typical amps 153A = >/=1/0 cable. They give some sizing in metric and I am not bored enough to do the conversion, but I bet 2/0 is your max wire size.

 

[John Frum]

They give some sizing in metric and I am not bored enough to do the conversion, but I bet 2/0 is your max wire size.

And that is what OP plans to use for the inverter circuits.
2/0 awg ~= 70mm2.

Metric AWG to MM2 Conversion Chart – Mueller Group

muellergroup.net

Yours truly,

Internet math guy

 

[JCSchwarb]

And that is what OP plans to use for the inverter circuits.
2/0 awg ~= 70mm2.

Metric AWG to MM2 Conversion Chart – Mueller Group

muellergroup.net

Yours truly,

Internet math guy

Bigger is not always better.

Read your inverter manual. Look at the specs. It should have a very specific "DC" or "battery input data" section. It will tell you the max DC charge and discharging current. Don't be dazzled by some internet math guy that doesn't take into count the limits of the inverter. If the inverter can only charge and discharge at 100 amps, it doesn't matter if you have 50 batteries. The max amps on the wire is going to be 100 amps - period. The manual may also tell you the maximum battery input conduit or even specify the maximum wire size.

My inverter is an 8kw 240v split phase and it can't accept wire greater than 2/0. So no, 4/0 wire would just be a waste of money when you realize it's too big to attach to the terminals. I have seen that with PV wire too. People oversize then realize when they go to connect the wire to the PV inputs it wont fit into the wire connectors because it's too big!

4/0 connects battery racks to bus terminals. 1/0 or prefer 2/0 from CB to inverters. Some of the inverters like MPP, EG4s have battery lug terminals for the batteries.

 

[BondJmsBond]

Here's what the EG4 6500EX 48 User Manual says, I think it's 2/0AWG minimum. I don't know what "1*2/0AWG" means exactly though.
I'm still thinking about 4/0, but McRod makes a point about the wire being too big to fit - and I remember Will said "Wow that was a bear to install" in a video when he hooked a 4/0 cable to his battery rack, which is the same as mine; but he did get it done and it works.

 

[John Frum]

Here's what the EG4 6500EX 48 User Manual says, I think it's 2/0AWG minimum. I don't know what "1*2/0AWG" means exactly though.
View attachment 128397

Yes, that means 1x 2/0 awg wire.