Li cable size needed?

[cvretis]

I have three 100 Ah Battle Borns. In my new set up, EACH will have + and - cables to a buss bar. What size cable should I use. I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00. The runs to the buss bar will only be about THREE feet. Thanks in advance for any help.

[Country Campers]

I am the "bigger is better" person. I used 4/0, no voltage drop, no worries if the wire is the right size, only a few more dollars.

Brian

[TucsonJim]

According to the Blue Sea Circuit Wizard calculator:

System Requirements:

Current: 200 amps
Votage: 12 V
Length: 6 feet (3 feet out and back)
Allowable Voltage Drop: 3%
Load: Fixed
Temperature: 105C

Result - 2 AWG

So 2 AWG will supply the circuit safely with no more than a 3% voltage drop. But like Brian, I prefer to go larger when possible. 2/0 would provide quite a bit of buffer for your circuit.

Here's a link to the Blue Sea Circuit Wizard Calculator:
http://circuitwizard.bluesea.com/

Jim

[howson]

I have three 100 Ah Battle Borns. In my new set up, EACH will have + and - cables to a buss bar. What size cable should I use. I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00. The runs to the buss bar will only be about THREE feet. Thanks in advance for any help.

I've got four BBs in parallel to a bus bar. 2/0 from each battery to the bar, then 4/0 from the bar to the shunt and then out to the Multiplus. (More info than you asked for....)

Partial snip from my "schematic"...

[acoleman43]

I have three 100 Ah Battle Borns. In my new set up, EACH will have + and - cables to a buss bar. What size cable should I use. I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00. The runs to the buss bar will only be about THREE feet. Thanks in advance for any help.

1/0
With just 1% voltage drop you can use 1/0. Anything over that is overkill. I have a lot of overkill in my system

I used 12.8V, 5' length, 200 amps.

[Scott'n'Wendy]

I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00.

What start up? The A/C?

When going bigger than 'normal' recommendations, beware of the cable being able to fit the various terminals in your system. Bigger wires and lugs require bigger terminals with larger spacing. I think a lot of solar kit is designed with this in mind, but some isn't. So when 'going big' be sure when you purchase switches etc that there is enough room for anaconda sized wire.

[howson]

I have three 100 Ah Battle Borns. In my new set up, EACH will have + and - cables to a buss bar. What size cable should I use. I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00. The runs to the buss bar will only be about THREE feet. Thanks in advance for any help.

I agree with Scott'n'Wendy that thinking you'll pull 200 amps from each of the three batteries simultaneously is unlikely. That's 600 amps @12v = 7200W. That's a lot of power. Even a Multiplus will have a very difficult time handling that much load even for a short duration (if it will do it at all). More than likely the fuse you'll have in the system will blow first. (My 400A fuse would definitely not handle 600A!)

The "C" rating for the Battle Born 100aH battery is 100A. So the normal max from three batteries in parallel is 300A. Yes, the BB will surge (briefly) over that, but > 300A? 300A @ 12v is already 3,600W, typically already sending a 3000W inverter into overload. Bottom line: that shouldn't be normal or expected from a relatively small setup. If that much power is needed, doubling the battery capacity and paralleling two inverters is a more likely setup.

Howard

[cvretis]

Thanks for all the answers, I appreciate it very much.

[Kathy&Jim_Imagine]

I agree with Brian. Can't go wrong with bigger cables. I have 420AH and use 4/0 cable...

[howson]

I agree with Brian. Can't go wrong with bigger cables. I have 420AH and use 4/0 cable...

Jim,
My .02 (and it's OK if you and others disagree)--no single answer suffices.

For example, the battery being used can make a huge difference. If an individual is using a battery that has a C rating of greater than 100A, then the calculus for what wire is "right" changes. For example, BB's "Game Changer" has a C rating of 300A. (!) Put two in parallel and voila', 600A could be sustained. That's an entirely different wiring scenario than three BB's with a C rate of 100A each.

The length of the wire needed in an installation is also a factor.

One short (extreme) example. GD uses 6ga wire in a lot of their 12v system wiring. That's presumably based on an engineering assessment of load, distance, etc. Surely there's no argument that using a 4/0 wire would be overkill? Perhaps there could be a debate whether 4ga would be better than 6ga in some of the wiring situations, but surely there's a limit to the cost/benefit return on investment by going "big"?

Again, it's OK if there is a disagreement. For me, going to the maximum size wire available without factoring in all the variables will obviously work, but not sure why someone would do that if it's not needed and especially if it won't provide a reasonable performance gain.

Howard

[AlexPeterson]

I agree with Howard howson that bigger isn't necessarily better. They are crabbier to work with, but might be needed. The wires should not be sized for max battery output capability amperage unless one plans to see those currents sustained. I believe the inverter is far and away going to be the biggest amp situation. Then the question becomes for how long, which goes into heat generation in the wires, which in turn depends on their "openness" to air cooling. Stuff a bunch of highly loaded wires (for their size) into a tight conduit and the suggested current will be lower since heat transfer is limited. As to efficiency, (energy delivered)/(energy outputted from the battery), I suspect during high output inverter loading the efficiency is still in the high 90%'s in most cases of reasonably smaller, short wires (ignoring inverter efficiency for a moment).

I'm happy to do this calculation for anyone who might be interested in their own setup.

[Scott'n'Wendy]

bigger isn't necessarily better. They are crabbier to work with,

lol
At work we used to say that big stuff is just 'ignorant' to work with.

Agree with Alex, When it comes to wire sizing, you don't need to size for inrush current. Just sustained current.

[Yoda]

I have three 100 Ah Battle Borns. In my new set up, EACH will have + and - cables to a buss bar. What size cable should I use. I know I should consider that up to 200 Amps can be at start up, so I figure on probably 2/00. The runs to the buss bar will only be about THREE feet. Thanks in advance for any help.

I use this chart from Blue Sea https://www.bluesea.com/support/arti...r_a_DC_Circuit
Its showing 2/0 is needed from the battery to the buss bar. TucsonJim Jim I am puzzled at the major difference between the two. I used you link to double check. Any thoughts on the 2AWG verses the 2/0 the chart showes?

FWIW I set up my 4 6V batterys (540AH total) (Series/ Parallel) using 2/0 between the batterys and 2/0 to the Lynx power in bar from each pair on my install. Then from the power in bar to the Multiplus I used 4/0. Yep it is overkill, but I was also planning on future Lithium upgrade. Waiting for LI Time to have thier Black Friday sale this year.

Keith

[TucsonJim]

I use this chart from Blue Sea https://www.bluesea.com/support/arti...r_a_DC_Circuit
Its showing 2/0 is needed from the battery to the buss bar. TucsonJim Jim I am puzzled at the major difference between the two. I used you link to double check. Any thoughts on the 2AWG verses the 2/0 the chart showes?

FWIW I set up my 4 6V batterys (540AH total) (Series/ Parallel) using 2/0 between the batterys and 2/0 to the Lynx power in bar from each pair on my install. Then from the power in bar to the Multiplus I used 4/0. Yep it is overkill, but I was also planning on future Lithium upgrade. Waiting for LI Time to have thier Black Friday sale this year.

Keith

Keith - I have no idea and never noticed the disparity in the chart vs. the calculator. And to think they are from the same company who has a great reputation for quality in the marine industry.

Jim

[TedS]

Is the difference ampacity vs voltage drop?