Another Battery Wire Gauge Thread

fwunder

I know this subject is beat to death, but I'm still a little confused and trying not to spend more on cabling than necessary.

2023 Tab 400 single BB 100ah battery configuration pictured below. I did add the shunt.

I am getting ready to add second BB 100ah battery ( parallel of course ). I will be using 18 inch 2/0 battery interconnects which seems a bit overkill, but recommended.

All of the factory wiring is 4 AWG which seems just a bit undersized ( 1200 watt inverter ) for two battery configuration. I have noticed when battery is low, the WFCO really cranks amps into battery.

Am I overthinking this? Would you leave 4 AWG wiring in place with the two batteries? I'm thinking it's OK, just not ideal.

Thanks folks!

Yoshi_TAB

Hi,

I looked into this extensively when I installed new lithium batteries and an inverter in my 320.  I found some variations out in this world, but found this to be a good guide.  Calculating Inverter DC Wire & Fuse Size | DIY Solar Power Forum (diysolarforum.com)  Click on the orange tab in the upper right corner to download the file

Fuse Sizing Calculator - EXPLORIST.life
Wire Sizing Calculator - EXPLORIST.life

The first step is too correctly size the fuse for the load of your inverter, once that is know, than you pick the size wire for the size fuse.  The size wire is also dependant on the distance beteween the inverter and fuse/battery.  The lengh of wire used to calculate the size is round trip.

What size fuse do you have for the inverter?  You want the wire size to match the fuse protection.

For a 1200W inverter @90% efficency the fuse size should be 111 amps  plus 25% safety factor about 138 amps rounded up to 150 amps.  From the chart 1 AWG size wire would be ok (for up to 15').   Going bigger (2/0) on wire never hurts .  I bought premade lengths from Windy Nation Inc  They have an Amazon site and you can easily return them if you bought the wrong size or connection.  I would use the same size  wire between the batteries as you do from inverter to batteries.

(Wire size doesn't matter for batteries in parallel; without an inverter 10 AWG is stock...it's the inverter and system draw amps that matter)

As an aside; Are those items in your picture on the top right pos. and neg, busbars?  They look very close and uncovered?  If something accidentically fell or placed on them, seems like they could arc very easily.  But maybe it's just the angle of the photo?

Jilong

You size wires based on the number of amps that the wires will carry. That 1200W inverter can pull up to 100A continuous from the batteries, so I think you want 2AWG to the inverter, and at least 2AWG for the batteries to the busbars but for everything else the factory wiring sounds just fine.

fwunder

Yoshi_TAB said:

Hi,

I looked into this extensively when I installed new lithium batteries and an inverter in my 320.  I found some variations out in this world, but found this to be a good guide.  Calculating Inverter DC Wire & Fuse Size | DIY Solar Power Forum (diysolarforum.com)  Click on the orange tab in the upper right corner to download the file

Fuse Sizing Calculator - EXPLORIST.life
Wire Sizing Calculator - EXPLORIST.life

The first step is too correctly size the fuse for the load of your inverter, once that is know, than you pick the size wire for the size fuse.  The size wire is also dependant on the distance beteween the inverter and fuse/battery.  The lengh of wire used to calculate the size is round trip.

What size fuse do you have for the inverter?  You want the wire size to match the fuse protection.

For a 1200W inverter @90% efficency the fuse size should be 111 amps  plus 25% safety factor about 138 amps rounded up to 150 amps.  From the chart 1 AWG size wire would be ok (for up to 15').   Going big on wire never hurts .  I bought premade lengths from Windy Nation Inc  They have an Amazon site and you can easily return them if you bought the wrong size or connection.

(Wire size doesn't matter for batteries in parallel; without an inverter 10 AWG is stock...it's the inverter and system draw amps that matter)

As an aside; Are those items in your picture on the top right pos. and neg, busbars?  They look very close and uncovered?  If something accidentically fell or placed on them, seems like they could arc very easily.  But maybe it's just the angle of the photo?

Thanks for looking. As I said, everything in pic except shunt is factory.

Inverter fuse is 150 amp.

I do think battery interconnect wire size is important. We'll see what Battleborn says. I queried them too.

I do agree the distribution block is sloppy and crowded. I will replace that with two four post blocks. It is normally covered. Removed for pic.

Yes, the folks @ Windy nation are great! I have purchased cable and inverter from them for previous camper. Very responsive.

Thanks again.

Yoshi_TAB

Hi, 

I just updated my response and agree with you that your battery interconnect wires are on the small size.  I would use the same size as between the inverter and battery.  Those wires also have to be sized to handle the 150 amp fuse.  Glad you have covers for the busbars.  I also would recommend battery post covers for the battery(s).  I bought these and can fit the larger cables along with some smaller AWG wires I have running to my batteries.  Amazon.com: Recoil STC40-4 4 Pack Silicone Terminal Covers for Alternator Battery Stud and Power Junction Blocks, Fits 3/0AWG to 4/0AWG Wire, 2 Red and 2 Black Pairs : Automotive

fwunder

Just to followup...

The Battle Born recommendation is to go with 1/0 battery interconnects and leave everything else as is. This will be fine for up to three batteries.

Cables ordered from Windy Nation.

Yoshi_TAB

Hi @fwunder

Just curious if I understand your last post... Battle Born said 4 AWG wire is ok with a 150 amp fuse on your inverter circuit?  If so, that seems to be under sized and contrary to most wire size selection guides.  Although I do know there is variations in wire sizing charts.  Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems

fwunder

From Battle Born:

Hi Fred,

Thanks for the email.

I would go with 1/0 between the batteries unless you eventually want to have more then 3 batteries then I would start at 2/0.

No other wiring should need to be changed in any way since we are not upgrading any of the chargers.

Yoshi_TAB

Hi,

There may be some terminnolgy differences here and not comparing apples to apples.

The note says chargers, not inverter (different devices).  I would agree the charging circuit wiring is ok, but still seems IMO that the inverter wiring circuit is undersized for 150 amps.  Although out of curosity, I looked up your inverter manual and it does say to use 4 AWG.  I'd keep an eye on it and occasionally feel the wires after using the inverter while using a heating device such as a hot kettle or coffee pot that pull higher wattages.  Just want to be safe...best wishes.

Robermcm

fwunder said:

Just to followup...

The Battle Born recommendation is to go with 1/0 battery interconnects and leave everything else as is. This will be fine for up to three batteries.

Cables ordered from Windy Nation.

Old post - hope you see this…

‘’when you say ‘battery interconnects’, is that just the two wires between old and new battery, or all battery wires from the bussbar to shunt or to any battery terminal?

fwunder

It refers to battery parallel connects. I went with 1/0 between batteries and to shunt and bus bars. Everything else I left stock.  

Robermcm

fwunder said:

It refers to battery parallel connects. I went with 1/0 between batteries and to shunt and bus bars. Everything else I left stock.  

That’s what I plan to do too. Still confused about the 150a inverter fuse and the 4awg wire it uses. But can fix that separately. 

Yoshi_TAB

Robermcm said:

That’s what I plan to do too. Still confused about the 150a inverter fuse and the 4awg wire it uses. But can fix that separately. 

Hi, There are many out there..but here is a source to a document you can download   to calculate  fuse and wire size. I conversed with the author one on one and he seemed very knowledgable on the subject.  This site has a lot of good resources under beginner resources.

Calculating Inverter DC Wire & Fuse Size | DIY Solar Power Forum (diysolarforum.com)