Copper or Brass?

[SlyCayer]

I am currently working on finding my self the correct bus bars needed for my packs.

My draw amps will be 450-500 amps,

Should I use Copper(expensive) or Brass(cheaper), or can I use Brass with not to much resistance?

What size should my bus bar be? 3/4" X 1/8"? 3/16"? 1/4"?

Please let me know your expertise.

 

[Ypedal]

I found brass does not tarnish as easily, makes for a cleaner looking setup .. :wink:

 

[Jeremy Harris]

The resistance of brass is a lot higher than copper. For a given size of buss bar it will need to be about 2.6 times greater in cross section to carry the same current with the same loss if made from brass rather than copper.

If a 1/8" x 3/4" buss bar was just OK with copper, then you'd need one that was about 1/4" x 1" if it were made from brass.

Jeremy

 

[liveforphysics]

Brass sucks as an electrical conductor in many ways. The only reason you see it used sometimes in switches and things is because it's cheap, mechanically strong, and easy to machine. Everything else about it sucks.

 

[Ypedal]

Damit..... :?

 

[liveforphysics]

Damit..... :?

If they aren't getting hot, then it should be fine.

 

[SlyCayer]

Ok, I will go with Copper, what size do you recommend for the amperage I will be using? 1/8"? 3/16"? 1/4"?

 

[liveforphysics]

If you're going to be pulling 450-500amps continuous, I would go at least 1/8" x 3/4" flat bar.

 

[SlyCayer]

Remember my bus bar will be 31" long from end to end, 20 cells will be connected in parallel using these bus bars with spacing of about 1-1/2" between each cell.

Let me know if 1/8" is still good.

 

[texaspyro]

Aluminium conducts better than most brasses. If you are really picky, use pure silver... but copper is almost as good. It takes VERY little alloying to screw up copper's conductivity.

 

[liveforphysics]

Remember my bus bar will be 31" long from end to end, 20 cells will be connected in parallel using these bus bars with spacing of about 1-1/2" between each cell.

Let me know if 1/8" is still good.

1/8"x3/4" works out to be sitting right between 0awg and 00awg.

It works out to be ~289uOhm (depending on the alloy) across the 31" bus.

So, if you're drawing say 1000amps from 1 side of the other (which is the worst case scenario, and not what you're doing), voltage drop would be 0.289v. If I'm reading your application correctly (paralleling strings side-by-side), it should be under 0.1v drop.


So, going to 1/4"x3/4" would make a worst case voltage drop of 0.145v, or going to 3/16"x3/4" would make it ~0.217v drop worst case.


If you're pulling 500amps rather than 1000amps, then you can just divide those voltage drop numbers in half.

 

[SlyCayer]

I will be using 1/4" X 3/4" for as little sag as possible.

I was also trying to spot weld my nickel tabs on to copper a few minutes ago and I am not getting any luck, is there any reasons why Copper and Nickel doesn't fuse/weld together? Again, I need your expertise on this.

 

[Ypedal]

how about a tiny tab of solder paste between the layers . ?? ( no clue if this is a good idea or not. just throwing it out there.. )

 

[Gordo]

I will be using 1/4" X 3/4" for as little sag as possible.

I was also trying to spot weld my nickel tabs on to copper a few minutes ago and I am not getting any luck, is there any reasons why Copper and Nickel doesn't fuse/weld together? Again, I need your expertise on this.

To weld nickel tabs to copper, both parts must be perfectly clean. This means look clean and then wiped clean with a solvent. You need the proper Flux (if you are going to use flux) not just any paste intended for lead/tin/copper. I have a can in my shop and will go get the name off it if you need. You need sharp tips on your welding points and lots of controlled pressure. You want the same pressure every weld. Then you turn the welder up until you blow holes in the nickel, then turn it down a tiny bit. If you burn the points off your tips, sharpen them again. Exact same angle.

I once spent a day in a battery plant. We had to figure out why the women were much more successful than the men tabbing cells. This drove several of us nuts until we figured it out. The women would change their tips when they started, every coffee break, lunch break and afternoon coffee break. The women paused and carefully inspected their welds every few minutes. The men were too lazy and just kept on turning out cells that the tabs fell off. Non-union shop so the solution was sooo simple.

 

[SlyCayer]

Hi,

I have a home made spot welder with 2 pneumatic cylinders to control each individual electrode(tips). I can control their pressure very accurately with a small scale under each tip.

I will give it a try with polishing the flat bar and then cleaning it with a heavy duty degreaser and flux. If that doesn't work, I might have to self tap/screw the nickel tabs on the copper flat bar and spot welded on the cells.

Thank you for all your help, it's greatly appreciated.

 

[999zip999]

SAND, CLEAN, FLUX. First if problem. Start after that.

 

[999zip999]

Oh brass is stronger copper con ducts better, copper rusts faster. ect.

 

[texaspyro]

I was also trying to spot weld my nickel tabs on to copper a few minutes ago and I am not getting any luck, is there any reasons why Copper and Nickel doesn't fuse/weld together? Again, I need your expertise on this.

Forget trying to spot weld with both electrodes on the copper... won't work. Also series welds with both electrodes on the nickel are crappy. You want the positive electrode on the copper and the negative on the nickel. For best results, positive electrode should be molybdenum. You also want to dimple the metal where you are making the weld and place the electrode. This will focus the weld energy at that spot.

 

[dnmun]

you don't need that size conductor for your parallel connections, a 24G wire is sufficient for balancing. for the series connection, use something sized to the C rate of each cell since that is all the current each series connector has to carry. everything else is just excess weight.

 

[SlyCayer]

you don't need that size conductor for your parallel connections, a 24G wire is sufficient for balancing. for the series connection, use something sized to the C rate of each cell since that is all the current each series connector has to carry. everything else is just excess weight.

Hmmm, My strings are paralled which means the first part of the bus bar will incur 450-500 amps, After the first cell and etc, the amperage should go down.

Do you mean going 1 wire from each cell to 1 big wire all together? My Balancing wires will be 12-14GA.

Also, texaspyro, do you think tungsten 99.95% pure would work? I read that Molybdenum is a cheaper replacement of Tungsten, please let me know.

 

[texaspyro]

Also, texaspyro, do you think tungsten 99.95% pure would work? I read that Molybdenum is a cheaper replacement of Tungsten, please let me know.

I have had very poor success with tungsten. It tends to blow off the end of the electrode (with a satisfying BANG!) and blow a hole in the material.

 

[dnmun]

your balancing current is only a few hundred mA so 24G is ok, and the series connections between cells would need to be minimum 12G if it is a 10Ah headway, to carry 50 A in series but your bus bar would collect all the series connections and then you would use opposing corners for the connections of the buss bar to your power out leads, and you can then use a large conductor as the buss bar where all the current is concentrated so that voltages of all the series connections remain close during higher current discharges. make sense yet?

 

[jonescg]

I have brass terminals on all of my CellMan packs. Brass is strong and while difficult to tap a thread, it's almost impossible to cause cross-thread damage. It's tough, that's why we used it because ally doesn't take tension so well and copper is a bit too malleable to take a thread.

 

[Jeremy Harris]

your balancing current is only a few hundred mA so 24G is ok, and the series connections between cells would need to be minimum 12G if it is a 10Ah headway, to carry 50 A in series but your bus bar would collect all the series connections and then you would use opposing corners for the connections of the buss bar to your power out leads, and you can then use a large conductor as the buss bar where all the current is concentrated so that voltages of all the series connections remain close during higher current discharges. make sense yet?

If you look back on this project you'll see it's using multiply paralleled cells in a high current pack (400 to 500A) with appropriately high balancing currents during charging. The pack is a 20P, 24S A123 pack, so is around 46Ah at about 77V, with a peak discharge current capability of around 1380A. To compare it with a meagre 10Ah Headway pack delivering maybe 40 to 50A tops isn't appropriate, stuff on this pack needs to be sized for the high current demand in this application.

I have brass terminals on all of my CellMan packs. Brass is strong and while difficult to tap a thread, it's almost impossible to cause cross-thread damage. It's tough, that's why we used it because ally doesn't take tension so well and copper is a bit too malleable to take a thread.

If you're happy to accept the very much higher I²R losses from using brass interconnects and have made provision to get rid of the heat from them, then that's fine. As you rightly say, brass is harder and easier to thread, so maybe the much poorer conductivity is a price worth paying in your case. The bottom line is that you need a brass buss bar that is between 2.3 and 4.4 times the cross sectional area of a copper one (depending on the exact brass alloy chosen) for equal I²R losses at a given current.

Jeremy

 

[jonescg]

It's only the terminals that are brass - the inter connectors are copper. I don't know how hot they will get when I really test them, but we'll see.