Suitable materials for battery bus bars?

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m.art.y
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Suitable materials for battery bus bars?

Post by m.art.y »

Hi,

I have to rearrange my battery cells into 2P configuration and thinking of a best way to do it in terms of busbars. My cells come with screw holes so I can use 10mm2 cable with crimped lugs to make about 10 cm long busbars but would 10mm2 be suffiecient? Another option considering cutting out solid busbars from sheet metal this could be stainless steel of which I could get little offcuts. Is stainless steel at all suitable in this purpose? Not sure if I can get copper offcuts like that and would bare coper last? Another option using thick aluminium wire and flatten ends of it and drill holes? Any advice from more experienced would be appreciated. 😊
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Re: Suitable materials for battery bus bars?

Post by arber333 »

m.art.y wrote: Tue May 03, 2022 2:06 pm Hi,

I have to rearrange my battery cells into 2P configuration and thinking of a best way to do it in terms of busbars..... ....Any advice from more experienced would be appreciated. 😊
I advise against steel of any kind. Its IR will heat it up a lot and that will bring IR up even more.

I used copper where i could but where not i used brass. It is better material for cutting than copper. More than aluminum too since you need to have a clean sheet of Al, not the oxidized version and i have seen price for Al about 18€ per kg!

Brass is good also because you can solder it. For example i soldered M6 nut (yes it is covered in zinc) to the underside of my buss bar so i just fit the cable terminal and put a bolt through. Use of plummer solder paste advised. Lesser chance of the wrench explosion on bare contacts that way...
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Re: Suitable materials for battery bus bars?

Post by muehlpower »

electrical conductivitys:
36,9 10.E6 Siemens/m Aluminium
58,7 10.E6 Siemens/m Copper
1,37 10.E6 Siemens/m Stainless steel 304 EN1.4301

Stainless Steel is a bad idea.
for 200A you will need 70mm² Copper, 110mm² Aluminium
for 40A you will need 10mm² Copper, 16mm² Aluminium
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Re: Suitable materials for battery bus bars?

Post by m.art.y »

arber333 wrote: Tue May 03, 2022 2:44 pm I used copper where i could but where not i used brass. It is better material for cutting than copper.
Ok thanks, I didn't think of brass. In which form were you able to buy it? Sheets, bars or tube? Any advantage over copper if I'm not planning to solder? I though of simply buying some copper tube and flattening it.
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Re: Suitable materials for battery bus bars?

Post by arber333 »

m.art.y wrote: Tue May 03, 2022 3:48 pm
arber333 wrote: Tue May 03, 2022 2:44 pm I used copper where i could but where not i used brass. It is better material for cutting than copper.
Ok thanks, I didn't think of brass. In which form were you able to buy it? Sheets, bars or tube? Any advantage over copper if I'm not planning to solder? I though of simply buying some copper tube and flattening it.
Maybe one example would be good cutting properties. You could cut your threads into thick brass stock and it would hold firm against multiple tightening.

I can get brass in bars or sheets.
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Re: Suitable materials for battery bus bars?

Post by modellfan »

muehlpower wrote: Tue May 03, 2022 2:48 pm Stainless Steel is a bad idea.
for 200A you will need 70mm² Copper, 110mm² Aluminium
for 40A you will need 10mm² Copper, 16mm² Aluminium
How do you calculate the crossectional area? When I have a 350A Fuse, I should calculate the crossection for 350A or only for normal peakpower ~100kw?
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Re: Suitable materials for battery bus bars?

Post by muehlpower »

The cables must be designed for continuous power. Tesla uses 70mm² for 400kW maximum power and 69kW continuous power, fused with 650A at 360V battery voltage.
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Re: Suitable materials for battery bus bars?

Post by arber333 »

modellfan wrote: Thu Mar 23, 2023 12:30 pm How do you calculate the crossectional area? When I have a 350A Fuse, I should calculate the crossection for 350A or only for normal peakpower ~100kw?
Well untill now i go with the general rule to use 1mm2 cross section for every 10A that go through it. And i select cableby the fuse i use.
So for 400A rated fuse i select 50mm2 cables. Though i have seen 35mm2 battery cables on Opel Ampera and Chevy Volt which has main fuse rated for 350A. That is DC lines. Curiously Ampera uses less than 16mm2 cables for motor power with 600A IGBTs there. I guess motor cables can withstand more.
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Re: Suitable materials for battery bus bars?

Post by modellfan »

Thank you guys. So when I have a Nissan Leaf 350 A Fuse with 50mm² cables, with a rule of thumb for an aluminium bus bar I go 60% above. So min 60mm².
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Re: Suitable materials for battery bus bars?

Post by asavage »

Metals Conductivity Chart
Metals Conductivity Chart
Brass machines well (well, depending on the lead content) and is widely available but is a not a great choice for a conductor. Aluminum is a better conductor choice, if the environment is suitable. Copper conducts well but corrodes easily, which is why it's often tin-plated in corrosive environments (and why most terminal lugs are plated).

Iron, steel, and stainless steel are very poor choices for a conductor of any significant current.
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Re: Suitable materials for battery bus bars?

Post by arber333 »

asavage wrote: Fri Aug 25, 2023 12:46 am
Brass machines well (well, depending on the lead content) and is widely available but is a not a great choice for a conductor. Aluminum is a better conductor choice, if the environment is suitable. Copper conducts well but corrodes easily, which is why it's often tin-plated in corrosive environments (and why most terminal lugs are plated).

Iron, steel, and stainless steel are very poor choices for a conductor of any significant current.
I use brass for end terminals simply because you can solder a hex nut to the brass lug side. This than allows for singlehandedly attaching the bolt - a must be for safe assembly in HV enviroment.

I agree aluminum is a better conductor. But it requires TIG welding and or thicker terminals to offset its softness in case of threads.
The most commonly used aluminum alloy for electrical conductors is 1350.
If higher mechanical strength is required with good electrical conductivity, the 6101 alloy is chosen.
Myself i used 6082 alloy which is not as good conductor as it is a better construction material.
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