Wire Sizing?

[dsaint1884]

I've tried to answer this myself but there are so many tables out there it's hard to know, so I was looking for some direction.

I have 2x 12v 100ah batteries in parallel. Individually they can deliver 100amps, so in parallel I'm looking to size wire for 200 amps.

Everything running from the batteries is protected by an OCD, breaker or fuse, and the max size there is 150a. I still think I'd be sizing for the batteries though. Some charts say I'm fine with 1/0. Others say go up to 3/0. There is no run of the wire that would be great than 4-5ft full distance (pos+neg both).

1/0 - >https://theinverterstore.com/faq-items/what-size-of-cable-should-i-use-with-my-inverter-and-battery/
1/0 -> https://baymarinesupply.com/calculator
3/0 - >https://www.omnicalculator.com/physics/wire-size
3/0 ->https://www.cityelectricsupply.com/downloads/Ampacity Chart.pdf

 

[time2roll]

Is it really 200 amps near continuous? If so 1/0 is fine. I assume typical current will be generally less and #1 or even #2 is fine.

 

[Cyanlite]

Just get 4/0 and be done with it.

 

[dsaint1884]

Is it really 200 amps near continuous? If so 1/0 is fine. I assume typical current will be generally less and #1 or even #2 is fine.

It would not be, that would be the very max the battery BMS would even allow or that the batteries are rated for. Really I'd be pulling at max 150a because that's the largest breaker I have, anything beyond that and any line coming off the battery would be tripped. So for continuous current, it's 150 or less. My inverter is the largest thing in the system and it's 1000w, so 83amps would be the largest draw I would intentionally pull if I was maxing that out.

 

[rmaddy]

Why are you planning to wire based on the battery bank's max possible discharge current? If you size based on the total max load you might draw from the batteries then you can probably use smaller wires.

What size inverter do you have? Hopefully it's 2000W or less since that is all your battery bank can support at 12V.
Do you have a DC fuse box for DC loads? What is the max total amp draw of your DC loads?

 

[dsaint1884]

Why are you planning to wire based on the battery bank's max possible discharge current? If you size based on the total max load you might draw from the batteries then you can probably use smaller wires.

I suppose that was part of my question and was curious if I could just size based on max draw or if I needed to size based on max discharge current.

What size inverter do you have? Hopefully it's 2000W or less since that is all your battery bank can support at 12V.
Do you have a DC fuse box for DC loads? What is the max total amp draw of your DC loads?

1000w inverter is what I'm using and would be the largest load I have on the system. I also have a DC fuse box which can technically handle 100a but the loads connected to it are much less than that, the DC fuse box has <50amps of devices running from it.

 

[rmaddy]

OK, a 1000W inverter on a 12V system can draw up to 100A from the battery. Let's assume 50A of DC loads. That's a max of 150A draw from the batteries with your setup. So you could wire to handle those loads. That would be 1AWG from the batteries to the bus bars with a 200A main battery fuse. 2AWG would be good from the inverter to the bus bars.

Or if you want to plan for a little growth you can wire for the full 200A the batteries can support. Given your DC loads of 50A that leaves up to 150A for an inverter which means a max inverter size of 1500W. If you think you will ever upgrade from a 1000W to a 1500W inverter with your existing two batteries then using 1/0AWG and a 250A main battery fuse would be a good choice.

 

[dsaint1884]

OK, a 1000W inverter on a 12V system can draw up to 100A from the battery. Let's assume 50A of DC loads. That's a max of 150A draw from the batteries with your setup. So you could wire to handle those loads. That would be 1AWG from the batteries to the bus bars with a 200A main battery fuse. 2AWG would be good from the inverter to the bus bars.

The 1000w inverter came with 4awg wire out of the box. Do you have a chart or resource I could learn to reference to know if I need to switch out that 4awg for the 2awg that you suggest?

Or if you want to plan for a little growth you can wire for the full 200A the batteries can support. Given your DC loads of 50A that leaves up to 150A for an inverter which means a max inverter size of 1500W. If you think you will ever upgrade from a 1000W to a 1500W inverter with your existing two batteries then using 1/0AWG and a 250A main battery fuse would be a good choice.

Wonderfully helpful thank you. Sounds like I'd be safe to go with 1/0 wire for this system. It confuses me that so many suggest oversizing and going to 3/0 or even larger.

Thank you for the clarifications, the breakdown and the help. Much appreciated.

 

[niktak11]

The 1000w inverter came with 4awg wire out of the box. Do you have a chart or resource I could learn to reference to know if I need to switch out that 4awg for the 2awg that you suggest?


Wonderfully helpful thank you. Sounds like I'd be safe to go with 1/0 wire for this system. It confuses me that so many suggest oversizing and going to 3/0 or even larger.

Thank you for the clarifications, the breakdown and the help. Much appreciated.

No harm in oversizing (except cost)

 

[timselectric]

I always go larger if possible.
Less resistance, means less heat generated.
Less heat, means more efficiency and longevity.

 

[dsaint1884]

I always go larger if possible.
Less resistance, means less heat generated.
Less heat, means more efficiency and longevity.

That's all very reasonable. I just want to make sure I'm going large enough to be safe as well. For this it seems like I should be able to sleep at night with 1/0 wire on batteries and to the bus bars.

 

[timselectric]

That's all very reasonable. I just want to make sure I'm going large enough to be safe as well. For this it seems like I should be able to sleep at night with 1/0 wire on batteries and to the bus bars.

Definitely

 

[dsaint1884]

Definitely

Thank you