Questions about DIY Busbars from 6063 Aluminum

[coreyzev]

Pre-posting edit note: Hindsight I figured out while posting this, I had not matched the units' magnitude while comparing resistances, and they're much closer than I thought, by about 10^2. I am now fixating MUCH less, but still curious what people think of the differences between the two, so the post will continue as follows.

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TLDR: I dont wanna undersize my sub-par grade 6303 aluminum busbars.
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Hi all, due to availability and cost I bought 32ft (9.7m) of aluminum flat bar stock from the big box hardware store. It's 3/4" wide by 1/8" thick, and I was gonna double it up to be 1/4" thick. (19mm w x 3.175mm th). I could return it, but I would like to use what I have in front of me, closest big store is an hour away, and idk if there's anywhere near me to get copper. These were also 1/4 the price of copper or 6101 aluminum, which has led to the following concerns.

I've found myself hyper-fixating on figuring out the actual conductive properties of this 6063-T5 grade aluminum, specs suggest it's got a 55% IACS conductivity rating. But they also say it's got a much higher resistance than pure copper or aluminum (*note above*). It's still more resistive than pure alu, but not as much as i thought. (not sure how that stuff works). Pure aluminum by IACS standards is about 61%. And I assume this is how most calculations for aluminum stock ampacity are done. 6061 alu is 59% IACS. Copper is 100% IACS. I tried measuring its conductivity w/ my DMM but it was not good enough.

Does that 4% IACS by volume make that big of a difference to be worth 4x as much?

For significantly more context and data, click here:

Spoiler

Specs of 6063-T5 found here: http://www.matweb.com/search/DataSheet.aspx?MatGUID=79875d1b30c94af39029470988004fb6

It seems like most providers of aluminum busbars use 6101 aluminum. McMaster-Carr sells 6101-T61 for their conductive aluminum. But it's $60/6ft vs $15/6ft for 6063.

So I've been looking at the numbers comparing the two trying to figure out exactly how thick I need to make these or if I just need to use something else (before I cut into them). They're going to be hidden away and very snug, so if they get too hot I likely wont be able to get to them in time to save from disaster.

I found this site, makeitfrom.com which compares the 2 grades of aluminum for me, this is their section on electrical but it doesn't mean much to me aside from one number is bigger than another. And they've got nearly identical thermal conductivity, 210 vs 220 W/m-K

6063-T5 Aluminum vs. 6101-T61 Aluminum :: MakeItFrom.com

www.makeitfrom.com

FilterGuy made this diagram of my battery setup. It'll be a 48v 300ah 16s3p LiFePo4 pack.

So each set of 3P will be directly connected in series to the next pack of 3P via a single busbar, 3 bolts, 1 thru each set of red & black.

And for one last bit of overkill:

Material	Resistivity	Conductivity	Price Per 6ft (1/4" x 3/4")
Pure Aluminum	2.65e−8 ohm-m	61% IACS	N/A
6063-T5 Alu	3.16e-8 ohm-m	55% IACS	$15.32
6101-T61 Alu	2.99e-8 ohm-m	59% IACS	$58.39
Pure Copper	1.68e−8 ohm-m	100% IACS	N/A
110 Copper	1.71e-8 ohm-m	101% IACS	$71.55

All that data and I still don't know exactly how big I need my 6063 Busbars to be. And the higher resistivity still concerns me for heat.

 

[chrisski]

Not much to help you out, but based off some stat I remember in my head about needing over two times the thickness of aluminum to match the copper, and I’m not good at off the top of my head which is not a good thing, I might expect the two 1/8” X 3/4” copper to have a conductivity of around 150 amps.

It seems like most providers of aluminum busbars use 6101 aluminum. McMaster-Carr sells 6101-T61 for their conductive aluminum. But it's $60/6ft vs $15/6ft for 6063.

I paid $60 for 6 feet for 110 hard copper delivered to my mailbox 5 days after ordered. I actually ordered 2’ and it came in two strips, 1 foot each. this was 1/8” X 3/4” and the conductivity charts put it at slightly above 200 amps.

 

[coreyzev]

I paid $60 for 6 feet for 110 hard copper delivered to my mailbox 5 days after ordered. I actually ordered 2’ and it came in two strips, 1 foot each. this was 1/8” X 3/4” and the conductivity charts put it at slightly above 200 amps.

That tracks, and the price matches what McMaster-Carr has for copper.

 

[chrisski]

How many amps do you expect from your batteries?

My two 8S battery packs are 280 amps each, but have designed it not to exceed 100 amps from each battery pack or 200 amps total. The BMS limits surge output and charging to 120 amps. So, my bus bars just need to be rated to perhaps 150 amps.

Frustrating thing is I have everything I need for this build except the RV. It’s in the repair shop until Mid-November with a rolling completion date. Until I get that back, not much for me to do for this build.

 

[coreyzev]

How many amps do you expect from your batteries?

My two 8S battery packs are 280 amps each, but have designed it not to exceed 100 amps from each battery pack or 200 amps total. The BMS limits surge output and charging to 120 amps. So, my bus bars just need to be rated to perhaps 150 amps.

Frustrating thing is I have everything I need for this build except the RV. It’s in the repair shop until Mid-November with a rolling completion date. Until I get that back, not much for me to do for this build.

that sucks. we're doing our own repairs, for better or worse ?

48v 300ah battery on a 3000VA inverter. So i'll be hitting 65A nominal, 120A peak. I should be in a relatively safe zone. But like i said in OP. sub-par Aluminum in an enclosed space. I dont want it heating up. I should probably overdo it, and i'm not sure I'm overdoing it at all w/ only 3/4 x 1/4. So hard to do the math for this without being a materials engineer.

 

[chrisski]

that sucks. we're doing our own repairs, for better or worse

Sheet metal is beyond me. Unfortunately, like everything else, its a supply chain issue.

Good luck and I hope you get an intelligent response to your question. I’ve run into things I’d like to be a “materials engineer” To get good answers to.

 

[noenegdod]

This might help:

https://www.aluminum.org/sites/default/files/aecd2.pdf

Aluminum 5052

Rolled Metal Products is one of the steel industry’s most respected service centers with facilities across North America. We stock Stainless Steel, Nickel Alloys, Aluminum and other Specialty Metals in coil form and also offer toll processing of various metals including: Stainless Steel, Nickel...

rolledmetalproducts.com

One thing to consider with busbar thickness is as it gets thicker, the amount of stress applied to the terminal if everything is not dead flat and in the same plane, the more stress is applied to the terminals.

The copper busbars supplied with the 280ah cells are about 0.080" x just over 3/4" (0.062" square) and are supposedly good for the full 280amps. To reduce any possible stress on the terminals I went with 1/16' (0.0625") x 1.5" 5052 aluminum for a total cross section of 0.09375" square. I am only going to be drawing a max of 150 amps so between the increase in cross section and drawing maximum just over half I should be good.

 

[coreyzev]

This might help:

https://www.aluminum.org/sites/default/files/aecd2.pdf

Aluminum 5052

Rolled Metal Products is one of the steel industry’s most respected service centers with facilities across North America. We stock Stainless Steel, Nickel Alloys, Aluminum and other Specialty Metals in coil form and also offer toll processing of various metals including: Stainless Steel, Nickel...

rolledmetalproducts.com

One thing to consider with busbar thickness is as it gets thicker, the amount of stress applied to the terminal if everything is not dead flat and in the same plane, the more stress is applied to the terminals.

The copper busbars supplied with the 280ah cells are about 0.080" x just over 3/4" (0.062" square) and are supposedly good for the full 280amps. To reduce any possible stress on the terminals I went with 1/16' (0.0625") x 1.5" 5052 aluminum for a total cross section of 0.09375" square. I am only going to be drawing a max of 150 amps so between the increase in cross section and drawing maximum just over half I should be good.

I'm not using batteries with terminals like that. Mine have lugs. But still relevant info. Thank you.

I think I'm just gonna buy 1/8" x 1" copper. I'm probably over doing it on mine then. Which is great.

 

[noenegdod]

Generally speaking, over doing it looses a little money, under doing it can cost you a whole lot more.

 

[coreyzev]

Also. I was gonna heat shrink my bus bars between batteries to prevent potential shorts, but now I'm worried about heat dissipation after all this research, fuck.