# Bus Bar Material- Stainless Steel?



## itchyback (May 28, 2014)

Hi Folks,
I'm making some bus bars to join together 400v tesla pack in a diffirent physical layout to original so i need new bus bars. 
I happened across a sheet of 4mm stainless steel and i was pretty excited to use it to make bus bars. mostly because it wont corrode easily. 

A quick look on the internet reveals stainless steel has a higher electrical resistance.
Cooper for example has a resistivity of 1.68×10−8
Aluminium 2.65×10−8
carbon steel 1.43×10−7 (note the minus 7 not minus 8)
stainless steel 6.90×10−7 (note the minus 7 not minus 8)

So i can easily imagine copper is the most desirable choice. That said is Stainless steel still a problem? should i just make them slightly larger to compensate? 
Original was 25mmx3mm (75mm2) how much larger would be desirable? 25mmx4mm (100mm2)?

Aluminium is easy enough for me to get but i thought since i have the stainless, why not?


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## Coulomb (Apr 22, 2009)

itchyback said:


> A quick look on the internet reveals stainless steel has a higher electrical resistance.
> Cooper for example has a resistivity of 1.68×10−8
> Aluminium 2.65×10−8
> carbon steel 1.43×10−7 (note the minus 7 not minus 8)
> ...


Sure. Just make them 69/1.68 = 41 times as high cross section!



> Original was 25mmx3mm (75mm2) how much larger would be desirable? 25mmx4mm (100mm2)?


41 x 75 = 3080 mm², say 100 mm x 31 mm. Or to retain the original width, a thickness of 3080 / 25 = 123 mm. You'd need really, really long bolts, and drilling 123 mm stainless steel would be a bitch.

Now you can see why people don't make battery straps out of stainless steel.

I've never even heard of aluminium straps; always copper. Aluminium is brittle.


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## itchyback (May 28, 2014)

well that settles it. great info thanks!
Just confirming, would it be 6.9/1.68 = 4.1 instead of 69/1.68=41?
in either case, thats a huge stainless steel strap. 

I priced some copper yesterday. I need 4mm x 70mm x 300mm to cut the shape i need for each strap. the closest i could get was 5mm x 90mm in 4 metre length for $282!
I'll see if i can change the design to make them smaller.


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## brian_ (Feb 7, 2017)

itchyback said:


> A quick look on the internet reveals stainless steel has a higher electrical resistance.
> Cooper for example has a resistivity of 1.68×10−8
> Aluminium 2.65×10−8
> carbon steel 1.43×10−7 (note the minus 7 not minus 8)
> stainless steel 6.90×10−7 (note the minus 7 not minus 8)





Coulomb said:


> Sure. Just make them 69/1.68 = 41 times as high cross section!





itchyback said:


> Just confirming, would it be 6.9/1.68 = 4.1 instead of 69/1.68=41?


No, as you pointed out when you first shared these value, the value for stainless steel is more than an order of magnitude greater.

thickness ratio (compared to copper):
r = (6.90×10^−7) / (1.68×10^−8)
r = (69.0×10^−8) / (1.68×10^−8)
r = 69.0/1.68
r = 41
(as Coulomb already said)


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## PStechPaul (May 1, 2012)

If you make a stainless steel bus bar 4mm x 25mm and 100mm long, it will have a resistance of about 690 uOhms. If you are pulling 1000 amps that would be a voltage drop of 690 mV and power dissipation of 690 watts. The equivalent copper would be 16.8 uOhms and 16.8 watts.

You might be able to use copper water pipe for bus bars. Just use a press to flatten it for the terminations. 1/2" type L has a cross sectional area of about 0.08 in^2 which would make a 100mm bus bar with 33 uOhms resistance and a voltage drop of 33 mV and power of 33 watts at 1000 amps. 33 mV represents approximately 1% of the voltage of an LiFePO4 cell. 1/2" x 10ft type L pipe is about $14 at Home Depot, so you can make 30 bus bars for about 50 cents each.

It is a good idea to use silver plating (Kool-Amp powder) on bus bars for best conductivity of the joint. And some grease may also help avoid corrosion.


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## itchyback (May 28, 2014)

Thanks Brian_, now i understand why the decimal point moved. 

Thanks PSTechPaul, i was thinking of similarly dodgey ideas. Like collecting scrap copper and using my forget to make some forged copper bus bars. Cheaper, but way dodgy. I think given the amount im spending on the car, i dont think i should complain about $282 

THanks for your advice.


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## oudevolvo (Mar 10, 2015)

itchyback said:


> I priced some copper yesterday. I need 4mm x 70mm x 300mm to cut the shape i need for each strap. the closest i could get was 5mm x 90mm in 4 metre length for $282!
> I'll see if i can change the design to make them smaller.


And how about having them lasercut?
In The Netherlands there is a company that has up to 3 mm Copper (CU-DHP-R240) which they can cut. The challenge however is that single piece production is still quite expensive. Two of the same product is only a little more expensive than a single one. So it only helps if you can design in such way that you have multiple of the exact same busbars.


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## goingbush (Jun 20, 2017)

Yes copper is more ductile but I can't see any good reason not to use Aluminium , Aluminium is used extensively as power transmission cables and bus bars. 

I would definetly use it before stainless steel.


http://electrical-engineering-portal.com/copper-or-aluminium


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## Kevin Sharpe (Jul 4, 2011)

In the UK I had 50 busbars laser cut in 2mm copper for 1.18 GBP each including all setup and shipping costs;

http://www.cut-tec.co.uk


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## oudevolvo (Mar 10, 2015)

goingbush said:


> Yes copper is more ductile but I can't see any good reason not to use Aluminium , Aluminium is used extensively as power transmission cables and bus bars.
> 
> I would definetly use it before stainless steel.
> 
> http://electrical-engineering-portal.com/copper-or-aluminium


One thing perhaps to keep in mind is galvanic corrosion
Further read on http://www.anzor.com.au/blog/galvanic-corrosion-keep-those-metals-apart/
My contactors have stainless studs en bolts and therefore I prefer to use copper over aluminium.


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## GoElectric (Nov 15, 2015)

itchyback said:


> well that settles it. great info thanks!
> Just confirming, would it be 6.9/1.68 = 4.1 instead of 69/1.68=41?
> in either case, thats a huge stainless steel strap.
> 
> ...


3mm x 25mm should be just fine!!!!! What the heck are you thinking??

I found a 6mm bend allowance works.


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## itchyback (May 28, 2014)

I knew stainless steel having a higher resistence would need to be thicker, which is why i initially suggested 4 x 25, but i didnt know to what scale. now i know its 41 times thicker! so not practical to use stainless steel. 

The shape is a roughly a 'Z' on its side to create an angled bus bar to join stacked modules in series. I cant make that out of one piece without having a really wide piece of copper to start with. I dont want to solder or join the pieces, just to avoid complexity. Its a lot of wastage but i'll do it right the first time.


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## GoElectric (Nov 15, 2015)

Hi. I assume you need more than one of these? Rather than try to cut one out of a sheet, do you have the option of paying someone with a brake to bend one for you out of 3mmx25mm?

Jim


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## Hollie Maea (Dec 9, 2009)

goingbush said:


> Yes copper is more ductile but I can't see any good reason not to use Aluminium , Aluminium is used extensively as power transmission cables and bus bars.
> 
> I would definetly use it before stainless steel.
> 
> ...


If you are using Aluminum, you really should have it nickel coated, at least in the parts that are contacts, as Aluminum develops a resistive oxide coating.


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## GoElectric (Nov 15, 2015)

this tin-plating - I had a quick look on utube and it looks like one has to electroplate the tin onto the copper? How difficult is this anyway? I'm not feeling too bad about using my anti-corrosive paste, but would like to know what is involved before I go ahead and do 'final' assembly. 

I've done electroplating before, and to get a good result, one needs to heat the solution, have a bubbler, and it takes some time. 

Hmmmm, maybe silver-plating onto copper is easier - should spontaneously react with copper. 

Thanks.


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## AdamV (Jun 2, 2017)

Late to the party but what did you settle on? Im about to do the same...I wasn't able to find what Teslas original bus bars are; they're heavy and appear to be nickel coated but can't use them anyway...Thinking with just going with copper wire and crimping the ends with those heavy duty kits. Dropping a 2016 Tesla in a sand rail 🤞


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## cricketo (Oct 4, 2018)

One of my recent battery builds required some unusual terminals, which I figured I'd make, but I didn't have any copper stock of suitable size... I already had some experience melting things, so it turned out to be a piece of cake... some pictures below. Besides the obvious caveat with machining equipment being expensive, the actual copper element is pretty affordable - electric furnace can be purchased on Ebay for less than $200. I went the lazy route of making a very rough piece of stock with the intention to machine it, but it's possible to cast much nicer bus bars that are ready to use after minimum clean up. Source material for melting was scrap wiring, so definitely decent grade of copper in terms of conductivity.


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## remy_martian (Feb 4, 2019)

What did you use for molds?


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## cricketo (Oct 4, 2018)

remy_martian said:


> What did you use for molds?


Just two pieces of angle iron with two spacers in between. Spacers can be any flat stuff like square tubing or flat bar. Between thickness of spacers and the distance between them you can adjust the size of the resulting ingot. But like I said, this method is good enough when the intention is to machine some part out of the resulting metal. For something like bus bars, especially if need many at once, I'd use a more sophisticated mold. For my bus bars I opted just to buy flat stock, cut and drill it - got to pick the battles properly


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## cricketo (Oct 4, 2018)

Making bus bars out of flat stock on a milling machine is probably the easiest thing. Rough cut the pieces, then trim them to length with an end mill. Then drill multiple at once, without even having to measure anything ahead of time.


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## brian_ (Feb 7, 2017)

Since this thread has been revived, a couple of follow-up comments:


oudevolvo said:


> And how about having them lasercut?
> In The Netherlands there is a company that has up to 3 mm Copper (CU-DHP-R240) which they can cut. The challenge however is that single piece production is still quite expensive. Two of the same product is only a little more expensive than a single one. So it only helps if you can design in such way that you have multiple of the exact same busbars.


There are now more services to do this sort of work. SendCutSend (available only to customers in the U.S.) now laser-cuts copper up to 0.250" (6.3 mm), and mentions busbars as one of the applications; they will also do limited bending and tapping... but they won't plate it, so that would be a separate process after the busbars are cut, tapped, and bent.




goingbush said:


> Yes copper is more ductile but I can't see any good reason not to use Aluminium , Aluminium is used extensively as power transmission cables and bus bars.
> ...
> Copper or aluminium? Which one to use and when?





Hollie Maea said:


> If you are using Aluminum, you really should have it nickel coated, at least in the parts that are contacts, as Aluminum develops a resistive oxide coating.


As the article in Electrical Engineering Portal noted, both copper and aluminum are normally plated with silver or tin, rather than nickel.


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## remy_martian (Feb 4, 2019)

Copper bus bars for high voltage switchgear are normally nickel plated. Tin is horrible in high electric fields - it forms dendrites. 

Tesla's busbars appear to be naked copper - not sure if there's a passivation spray on them.


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## cricketo (Oct 4, 2018)

Those guys have reasonable prices, considering you don't spend any time making that stuff.










I got my flat bar from Amazon, but it was sold by OnlineMetals. I think it was this one : Amazon.com: 110 Copper Rectangular Bar, Unpolished (Mill) Finish, H04 Temper, ASTM B187, 1/8" Thickness, 3/4" Width, 72" Length : Industrial & Scientific
Ended up costing $80 delivered for two 72" pieces. So to compare to above quote, that would be $0.44 plus labor per bar vs $5.8 per bar.


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## brian_ (Feb 7, 2017)

remy_martian said:


> Copper bus bars for high voltage switchgear are normally nickel plated. Tin is horrible in high electric fields - it forms dendrites.


Of course there are no high voltages in an EV, by utility standards (where high voltages are many kilovolts, not just a few hundred volts).

The inside of a lithium-ion battery box or EV high-voltage distribution box may be a nice enough environment (compared to open installations in industrial settings, for instance) that corrosion isn't a big issue. I don't know.


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## remy_martian (Feb 4, 2019)

^^ Looks like you paid for, but didn't get, ~3 more pieces with the minimum order adjustment.


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## cricketo (Oct 4, 2018)

remy_martian said:


> ^^ Looks like you paid for, but didn't get, ~3 more pieces with the minimum order adjustment.


Well, I just wanted to see what the service would look like in practice. I think it's decent. There is a weird time/money optimization happening in these projects: on one hand your and my time aren't worth making bus bars by hand, it's better to pay 30-40-50 bucks and have them delivered with laser-cut precision. On the other hand sometimes I can't wait 3-4 business days, and sometimes I am just bored. So I guess in the end it depends...


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## remy_martian (Feb 4, 2019)

That and machining copper can be biotch.

I keep putting off getting copper for bus bars and it keeps going up in cost 🤬 $4.60/oz last I looked

Another reason to use these kinds of services is you only get what you need vs a sheet or 6ft length (or two) of it


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## cricketo (Oct 4, 2018)

remy_martian said:


> That and machining copper can be biotch.


That's the common wisdom! But I absolutely had no issues machining my ingots. I used a slitting saw to get the top off, then shell mill to square up the stock, then just a two flute end mill like if going against aluminum. I think a thing to mind is annealed copper, which can feel a lot more soft.


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## BlueHorizon (Nov 27, 2018)

@cricketo I purchased a similar bar (albeit 1/4 thick) from Amazon from the same vendor and machined my own busbars. I was able to cut the bars by hand using my Dremel Ultrasaw with a metal cutting wheel with a vice securing the bar. I then used my drill press to create the holes, leveraging cutting fluid (Tapmagic) to try to stop the bit from clogging up as the copper would get hot quickly. Definitely had to be progressive and move the drill up and down several times to remove some of the twisted debris. For the larger holes I used two drill bits, one acting as a pilot. I then did a quick polish, although nothing too great but I’ll be applying copper paste on the terminals. 

After all that I realized that I could fit the heat shrink from some of the 2/0 lug kits I had from Amazon around the bars. 

We’ll see how these work out..


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