Copper vs Aluminum Electrical Resistance

[LewTwo]

Well the USPS managed to lose the copper bus bars I ordered for my Headway battery. Seeing as how copper is so god awful expensive and is not available in the proper 2-1/2 inch bar width anyway, I started considering Aluminum as an alternative. Now I know that copper wire has a lower resistance than aluminum wire but what effect do the various Aluminum alloys have? I found a comparative table on the internet but the values were not the same order of magnitude and made it bit like comparing apples to strawberries. So downloaded the table and imported it into a spreadsheet. Then I normalized all the values. I made a copy of this table in another tab and added in some additional materials of interest ... specifically common Aluminum alloys, solder, carbon steel as well as a few others. Then I sorted according the the resistance values.

A few things surprised me. I have always thought gold was an excellent electrical conductor. Turns out it is just a tad better than Aluminum. I was also surprised to learn that Electrical Solder (60/40) has more than six times the resistance of copper. Lastly extruded Aluminum bars are most likely 6063-T5 which has nearly twice the resistance of copper.

I offer this file up to anyone that may have a similar question.
View attachment ELECTRICAL RESISTIVITY.xlsx

 

[SafeDiscDancing]

Don't forget that it's nearly impossible to solder a wire onto anything aluminum.

Copper is very easy to solder.

So if you go down the aluminum route realize electrical connection to it will have to be based on rigid physical things like nuts and bolts which might add weight, cost and complexity.

As a rule:

* Aluminum is for anything involving heat transfer.

* Copper is for anything involving electrical connectivity.

* Steel is the easiest building material.

* Fiberglass is great for things that you expect to bend slightly.

* Carbon Fiber is stronger than Fiberglass but very directional. (and expensive)

...at least those are my rules.

 

[LewTwo]

Don't forget that it's nearly impossible to solder a wire onto anything aluminum.

Actually thought about that. With the headway cells, all the cell connections are mechanical anyway. The problem is the sense wires on the bus bars. Turns out there are some silver solders that can be used between copper and aluminum.

 

[SafeDiscDancing]

Actually thought about that. With the headway cells, all the cell connections are mechanical anyway. The problem is the sense wires on the bus bars. Turns out there are some silver solders that can be used between copper and aluminum.

You might think of the possibility of using washers that double as electrical connectors for your sense wires.

That way you entirely avoid any soldering onto aluminum.

Obviously you need to correctly choose the size that fits the Headway cell's bolts.

 

[Chalo]

Where resistance becomes a problem with aluminum is at joints. Between the passive layer that develops on aluminum from exposure to air, and galvanic corrosion from contact with other metals, you have to do a lot more surface prep and protection when using aluminum wiring.

When I worked in power electronics, we used a caustic paste called Alcoa EJC #2, along with tedious Scotchbriting of the conductive surfaces, to keep everything moving electrons as intended.

In the '70s, many houses were wired with aluminum, and some of them burned down because electricians used techniques developed for copper wires. Aluminum wiring still works great (most high kV transmission lines use it), but you have to do the joints with utmost care and corrosion protection or they become a resistance problem.

 

[neowizard]

Just like Chalo said, Aluminium doesn't make good connection without a lot of work and knowhow.

The conductivity of Al isn't a big deal, it's not going to amount to a big % V drop since the total length isn't long (my 24S Headway pack has less than 1m of internal conductors between the cells), and heat is usually not an issue with Al conductors.

Some people like to use those toothed look washers to bite into the Al (mechanically break the oxide layer). I don't know if that makes sense, as you're adding yet another metal into your connection (these washers are usually stainless), but ppl do it, so I don't know.

P.S. That's an awesome table. Thanks!

 

[Trevonsphere]

Lot of good information here.

I just want to add 2 points:

Whereas Cu and Al/alloys have comparable conductivities - apart from surface, as mentioned already, they have VASTLY DIFFERENT DUCTILITIES. In anything being shaken around by bikes, that would mean far more risk of connections snapping. I've even had ally plate breaking around a stud, forming a neat invisible washer, that then forms that non-conductive passivated area around the break. So careful material selection and detailing needed.

Second point, note how over-rated nickel strip is, compared to its cost. I think early battery builders used nickel plated steel because it was cheap and solderable, then someone with a box full of solid nickel scrap started selling that idea. I've gone back to solid copper wire soldered direct to cells using 220C solder, a solder tip with a lot of thermal inertia, followed by a quick quench. Not had a cell go on me yet as a result, whereas I was getting lots of grief from poor welds, difficult to perfect in a non-production environment with endless variables.

 

[LewTwo]

Where resistance becomes a problem with aluminum is at joints.

There are some silver bearing greases available. I was thinking of using some of that between the cell terminal and aluminum. I am waiting a few days to see if the USPS finds the packages with the copper bus bars (as they claimed they had).

In the '70s, many houses were wired with aluminum, and some of them burned down because electricians used techniques developed for copper wires. Aluminum wiring still works great (most high kV transmission lines use it), but you have to do the joints with utmost care and corrosion protection or they become a resistance problem.

Yep .. I have one of those. I also had one 120AC duplex outlet burn up because of it. I have stubbed a few of the outlets with special connectors and copper leads. I have enough of those connectors to do the entire place but in most cases the outlet box needs to be replaced to make room for the connectors. They also now manufacture CO-AL switches and outlets. What most people fail to mention is the aluminum wiring is also more susceptible to fatigue breaks.

P.S. That's an awesome table. Thanks!

You are welcome

 

[LewTwo]

You might think of the possibility of using washers that double as electrical connectors for your sense wires.

That way you entirely avoid any soldering onto aluminum.

Obviously you need to correctly choose the size that fits the Headway cell's bolts.

Problem is those sense/balance leads appear to be something like 22 AWG. I would need to solder the leads to the ring terminals. It does have the advantage of making them removable.

 

[DogDipstick]

Lol I got every size, shape, and type of copper bar in stock. Literally tons. XRF tested 99.995% pure.

10$ a pound plus shipping. I have also been trying to sell the Eriflex Flexibus to the Headway Car audio guys.
https://www.ebay.com/itm/115242039079


I also sell aluminum plates with 2000 holes in them ( 10mm holes).. Tryig to get the car audio guys to bite on them to bolt Headways, Planos, DingDongs together with. I am gonna send some friend ( car audio lithium head) a pair to try for free. He gonna try to build a headway bank out of them. Lol. They are not perforated metal, but a cast, quarter inch thick, machined on every face, fixture pallet. They have been selling like candy on Halloween.

Where resistance becomes a problem with aluminum is at

I love mea good bottle of Bundy Penetrox. Ah put that shiz on errytang.

I really try to be the busbar king. I got tons. Literally tonnage. More than you could fill any ( 53') truck with.

Don't forget that it's nearly impossible to solder a wire onto anything aluminum.

I disagree with this. It is very easy to accomplish with the correct process.

 

[spinningmagnets]

lots of good information here. Copper is an excellent heat transfer material, but rarely used for that due to price compared to aluminum.

8176-Aluminum alloy is what electrical wire is made from. It has an IACS conductivity number of 61 (pure copper 100 out of 100)

Common 6061 Aluminum is 43/100.

Common 7075 Aluminum is 33/100

Many of the Tesla cars use an aluminum bus-plate, and the connection to the cell is through an ultrasonically-vibrated fuse-wire which welds them together.

 

[speedmd]

My solution for good - cheap busbars is my copper pipe surplus- scrap bin. If you know any plumbers, they will most likely have a pile of stuff they will sell cheap or share with you. As long as its cleaned off, it's a solid way to go. I Never give aluminum a thought in bus apps as the alloys for ele apps is not handy to me.

 

[DogDipstick]

My solution for good - cheap busbars is

By Gods grace, that is not any problem.

However, any well paid engineer will have to tell you this is not the best way, and there are better options ( that you may buy from them).

You know what you are doing though.

Just remember, 100 million dollar power plants can be brought to its knees,.. because the .. poor quality bus bars were tarnished and an unused emergency backup system malfunctioned.


Story time:
Melted busbars cost Titus Generation Station about 25 million dollars in about one day ( 24 hrs.) . 30kW load tripped a system designed for 100kW DC. Could have supplied those hydrogen seal pumps for days on end, .. instead.. melted in seconds under a 30kW load. Lights went out. For the third time that day.

When the "light(s)" came back, it was, from the leaked hydrogen, ignited by the sinking turbine(s), on its bearing... as all three sunk to a halt , grinding.

***Engineer shrugs**

Damn emergency lights on the fritz again. Lol.

 

[dominik h]

Aluminium oxid is an insulating material!

In my 21S5P 100Ah battery i used at first 40x3mm lasered aluminium busbars, but after a few weeks my problems began, massive cell drift during charging with 10A (The battery is able to be charged with 500A). After weeks of slow charging and balancing it got even worse. Disassembled the battery( 252 screws) took out the bad and good cells and tested them, to find out that the bad ones are equal to the good ones.
Found the problem in the aluminium busbars as a few of them had oxidation around the screw holes.

Finally made new copper busbars and everything is ok now.

Don't waste your time with aluminium.

 

[spinningmagnets]

The Tesla aluminum bus-plates are surface-prepped and have the fuse-wires ultrasonically welded on immediately.

I also believe that this operation is likely accomplished by robots in a low-oxygen room.

Ever since I found the copper/nickel sandwich method, it is the only way I would use to group cylindrical cells.

 

[speedmd]

I could understand going Aluminum in flight hardware, but not where I would go to save a few grams in land base apps unless you were needing miles of it.

Nothing purrdier than nice bright Nickle plate over well finished copper. It's Cadillac for certain. Most tin or zinc coatings work well to keep copper cancer away also. Bare copper works well long term also in my experience if kept out of the weather and in a air tight connection. BTW Even home duty 1/2" copper pipe can safely (barely warm to touch) carry much more than 200 Amps Cont..

 

[LewTwo]

As PFC Gomer Pyle would say "SUPRISE, SUPRISE, SUPRISE".
The USPS actually found my packages.
The 2 hole nickle plated copper bus bars measure 20mm wide by 1.00 mm thick.
That is roughly the equivalent of single conductor number 4 AWG copper cable.
I was hoping for at least 1.5 to 2 mm thickness.

 

[Chalo]

The 2 hole nickle plated copper bus bars measure 20mm wide by 1.00 mm thick.
That is roughly the equivalent of single conductor number 4 AWG copper cable.
I was hoping for at least 1.5 to 2 mm thickness.

You could stack 'em if 4ga don't do the job.

 

[LewTwo]

The 2 hole nickle plated copper bus bars measure 20mm wide by 1.00 mm thick.
That is roughly the equivalent of single conductor number 4 AWG copper cable.
I was hoping for at least 1.5 to 2 mm thickness.

You could stack 'em if 4ga don't do the job.

I would have to order another full set and they ain't cheap ... not from US suppliers anyway. I think it would be more practical to make my own from copper bar. For now these will do to allow me to test and document the Daly Smart BMS.

 

[DogDipstick]

You could stack 'em if 4ga don't do the job.

order another full set and they ain't cheap ... not from US suppliers

I AM CHEAP AS HELL AND MINE IS 1.3MM X 32MM! MORE THAN A 2g! Lol. 10$ FOR SIX FEET!

Lol.
https://www.ebay.com/itm/115242039079

The plated bar I have is shown in red.

I do have alot of the wider stuff too but I let that sit cause i dont thing anyone's pushing 2000A. Teh 40, mm, 50mm,... 63mm, 80mm wide sections sitting in the warehouse.


10 layers, 1000A. (1230A, actually, given a Delta-Temp of 70* Kelvin, continuous)

 

[speedmd]

Medium wall cu pipe in 2" diameter is 0.070 and in 2-1/2 diameter 0.080 thick. In K series (heavy wall) 0.083 and 0.095 respectively. It band saws very easily and a cake walk to drill.

 

[Chalo]

Medium wall cu pipe in 2" diameter is 0.070 and in 2-1/2 diameter 0.080 thick. In K series (heavy wall) 0.083 and 0.095 respectively. It band saws very easily and a cake walk to drill.

Who the heck is using copper plumbing in those diameters anymore? That's asking for a meth addict to cut up your expensive work before it's even inspected.

 

[larsb]

[youtube]kD_p2kN13ac[/youtube]

I have to trust him, he’s russian

 

[speedmd]

Medium wall cu pipe in 2" diameter is 0.070 and in 2-1/2 diameter 0.080 thick. In K series (heavy wall) 0.083 and 0.095 respectively. It band saws very easily and a cake walk to drill.

Who the heck is using copper plumbing in those diameters anymore? That's asking for a meth addict to cut up your expensive work before it's even inspected.

I hear you my friend. New prices are crazy. I occasionally will find boxes of clean scrap bits of these at estate sales going for pennies on the dollar scrap rate. A few years back I picked out a chubby bin of solid carbide bits that made a fast $100 for just the broken- damaged pcs. The old Case of folks not knowing what they had. This thick walled cu, I never let go to scrap yard unless it's covered in lead-tin.

 

[LewTwo]

Medium wall cu pipe in 2" diameter is 0.070 and in 2-1/2 diameter 0.080 thick. In K series (heavy wall) 0.083 and 0.095 respectively. It band saws very easily and a cake walk to drill.

Who the heck is using copper plumbing in those diameters anymore? That's asking for a meth addict to cut up your expensive work before it's even inspected.

There is copper in 'dem 'dar hills ... and what it is being used for we can not say