Aluminum busbar instead of copper?

[Ceefiveceefive]

Greetings!
I'm thinking about making my own busbars for my three EG4 48V 100Ah server rack batteries. I am wanting to buy local from a Lowes or Home Depot as it will take weeks for copper bars to arrive where I live if I order online.

1. It was suggested that I can crush copper pipes flat to form busbars. Someone else said that would make an inferior version.

2. Can aluminum bars be an adequate substitute for up to 300Ah?

 

[42OhmsPA]

You want a high conductive aluminum, 6061 if I remember correctly. There are calculators online to determine how much current they will handle.

 

[MisterSandals]

It was suggested that I can crush copper pipes flat to form busbars.

I had 3/4” copper laying around so gave this a try. Pinched it to rough form in a vise and then hammered flat with a large faced hammer (no ball peen dimples).
Good scouring and coat of nolox for good measure.
Works great for my 2P4S battery, over 2 years uninterrupted service.

 

[Warpspeed]

If you are the government, you would probably specify solid silver busbars.
Copper for the snobs.
For practical people on a budget, fat aluminium busbars work every bit as well if sized adequately.

Many different grades of aluminium for many different purposes, some resist corrosion better, some are better for machining, others better for welding, and some form more easily into reaally complex shapes without cracking.
Electrically there is pretty much zero difference.
Use whatever you can get your hands on, it will work fine for you.

 

[mmame]

But take care: Aluminium could be very annoying due to the strong surface oxidation.

 

[yabert]

Electrically there is pretty much zero difference.

Well, aluminum has 61% of the conductivity of copper. This is a difference to me.
Still, aluminum can do perfect busbars, but the most important thing is to clear/brush the natural oxidation coating of the aluminum contact surface and add NO-OX grease to stop oxidation at the contact surface.

 

[ghostwriter66]

Well, aluminum has 61% of the conductivity of copper.

Thats why there are conversion charts to determine what SIZE / AWG of ALUM u need to use instead of Copper

 

[42OhmsPA]

Well, aluminum has 61% of the conductivity of copper. This is a difference to me.
Still, aluminum can do perfect busbars, but the most important thing is to clear/brush the natural oxidation coating of the aluminum contact surface and add NO-OX grease to stop oxidation at the contact surface.

There are also different grades of aluminum that have differing electrical conductivity. I chose 6101-T61 for my bus bars.

aluminum 6101 Product Guide from Online Metals

Learn important details about aluminum 6101 and other metals using the OnlineMetals.com® Product Guide.

www.onlinemetals.com

 

[Delphinus]

Greetings!
I'm thinking about making my own busbars for my three EG4 48V 100Ah server rack batteries. I am wanting to buy local from a Lowes or Home Depot as it will take weeks for copper bars to arrive where I live if I order online.

1. It was suggested that I can crush copper pipes flat to form busbars. Someone else said that would make an inferior version.

2. Can aluminum bars be an adequate substitute for up to 300Ah?

If you can't source copper now use what you can but order it and replace the bars when arrive, resistance transform in heat, is lost energy, your batteries are not cheap don't save on copper, your are better connecting them together with their cables than using a bad bus bar.

 

[Warpspeed]

Well, aluminum has 61% of the conductivity of copper. This is a difference to me.
Still, aluminum can do perfect busbars, but the most important thing is to clear/brush the natural oxidation coating of the aluminum contact surface and add NO-OX grease to stop oxidation at the contact surface.

I meant very little difference between the various aluminium alloys and heat treatments, of which there are a very large number.

Sure there is 61% difference in conductivity.
But a 61% bigger aluminium bar still costs a lot less than copper.
Unless you have a real need for really compact busbars, copper is just not cost effective.

There are various special greases, aluminox, no-ox, and others specially formulated for using aluminium in electrical applications.
Aluminium is being used increasingly in the electrical trades, because its both very cost effective, and an easier metal to cut and drill.

 

[OzSolar]

But take care: Aluminium could be very annoying due to the strong surface oxidation.

But is that a problem under the clamping surfaces?

 

[MisterSandals]

Unless you have a real need for really compact busbars, copper is just not cost effective.

Asking because I am not sure...
Is the small surface area on some of the LiFePO4 cells a meaningful limiting factor with a bus bar with lower conductance?

You could have a huuuuuge bus bar but the small interface with the cell has to play a part, no?

 

[yabert]

...are better connecting them together with their cables than using a bad bus bar.

Why?
To have more resistive contact?
Busbar: Contact battery 1 to busbar + contact battery 2 to busbar
Cables: Contact battery 1 to lug + lug to wire + wire to lug + contact contact battery 2

If it's about flexibility, it's possible to use multi-layer busbar or simply a busbar with a bend who allow some flexibility.

About aluminum, here are commonly available grade:

6061: easily machinable, bend can crack
6063: fairly machinable, can be bend
5052: fairly machinable, easy to bend, excellent corrosion resistance

 

[Delphinus]

But a 61% bigger aluminium bar still costs a lot less than copper.
Unless you have a real need for really compact busbars, copper is just not cost effective

Resistence in contact point is more important than size, use copper.

 

[John Frum]

Is the small surface area on some of the LiFePO4 cells a meaningful limiting factor with a bus bar with lower conductance?

The small surface area of the terminal face limits the current in and out of the battery.
As long as the busbar has the same contact surface area and enough thickness for the planned fault current then I don't see a problem with properly prepared aluminum busbars.

 

[yabert]

I meant very little difference between the various aluminium alloys and heat treatments, of which there are a very large number.

Oh! Right, I agree.

 

[OzSolar]

Greetings!
I'm thinking about making my own busbars for my three EG4 48V 100Ah server rack batteries. I am wanting to buy local from a Lowes or Home Depot as it will take weeks for copper bars to arrive where I live if I order online.

1. It was suggested that I can crush copper pipes flat to form busbars. Someone else said that would make an inferior version.

2. Can aluminum bars be an adequate substitute for up to 300Ah?

I'll likely get dogpiled for suggesting McMaster Carr but dang they can get anything to me two days after I order it. Often for less than $10 of shipping.

Here's the link to thier bus bars.

 

[Warpspeed]

Some really interesting points of discussion.

Contact point resistance will be greater of course, but the current density very quickly reduces over even a small distance.
For instance, I am amazed at the current ratings of some of the larger high power mosfets, and I look at the skinny legs on the device, and wonder how those could carry such a high current. But they still seem to work, and there is not much of a choice in the matter either.

If you have ever dismantled old equipment, crusty pitted old grey aluminium busbars, or poo brown copper busbars are always bright and shiny under where the original clamping bolts did there job. A bit of grease will keep the air and moisture out, and what happens outside that is of no real importance functionally.

Total resistance is where the losses are. An electrical joint that has a very short length may not contribute much extra ohmic resistance in the whole great scheme of things.
Some kinds of crimp lugs look fairly suspicious to me, where a big fat wire is crimped to a fairly thin looking thing with a hole in it.
But that is what is used in industry, and it all seems to work.

 

[Delphinus]

Asking because I am not sure...
Is the small surface area on some of the LiFePO4 cells a meaningful limiting factor with a bus bar with lower conductance?

You could have a huuuuuge bus bar but the small interface with the cell has to play a part, no?

I'm sure it is, recently I bought a KEL-103 resistance load, that came with nice 10 AWG silicone cables and I discharge a cell and got a lower value than it should and measuring the voltage drop it was big, quickly found that the brass nickel fork terminals had 4 m Ohms, replace it with good copper ones and the value drop to 1 m Ohm, second test even without sense cables got full cell capacity.

We are talking about 51,2V and 50A for battery, any resistance make a big difference.

In my country Aluminium is not allowed in power installations.

 

[MisterSandals]

The small surface area of the terminal face limits the current in and out of the battery.

Then the surface area should be the maximum "effective" cross section of the bus bar?

So if you are counting on using (100-61=) 39% more aluminum, you may hit the surface area limitations first.