Aluminum busbar instead of copper?

[John Frum]

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

The surface area of the busbar should be equal to or greater than that of the battery terminal.

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

The battery terminal is aluminum and so is the busbar.
The minimum surface area is determined by the battery terminal.
The busbar has three dimensions.
Width which is somewhat determined by the battery terminal.
Length which is determined by the distance between the terminals.
Thickness which is determined by the required fault current.
Since the big blue prismatic cells surge to ~1c and should not be charged at > .5c continuous, that kind of sets an upper limit for the required thickness of the busbars.
Cells should have terminal surface areas commensurate to their charge/discharge c ratings.

 

[Warpspeed]

In my country Aluminium is not allowed in power installations.

That really surprises me.
Every microwave oven transformer I have seen uses aluminium windings.

All the very high voltage transmission lines here use a very strong stranded central steel inner cable, with aluminium wires bundled around the central steel core. Its the only way to get sufficient tensile strength, and low electrical resistance at reasonable cost.
https://www.vwcable.com/high-voltage-overhead-conductor-transmission-lines/

Copper is just too weak in tension, and its also heavy. Steel/aluminium combination allows much longer spans between pylons than pure copper.

No problem fitting copper crimp lugs to aluminium cable either, all the problems have been solved.

 

[Delphinus]

That really surprises me.
Every microwave oven transformer I have seen uses aluminium windings.

All the very high voltage transmission lines here use a very strong stranded central steel inner cable, with aluminium wires bundled around the central steel core. Its the only way to get sufficient tensile strength, and low electrical resistance at reasonable cost.
https://www.vwcable.com/high-voltage-overhead-conductor-transmission-lines/

Copper is just too weak in tension, and its also heavy. Steel/aluminium combination allows much longer spans between pylons than pure copper.

No problem fitting copper crimp lugs to aluminium cable either, all the problems have been solved.

Regarding high power lines I don't know but in residential you can only use copper cables.

 

[Warpspeed]

I am sure you are correct for domestic wiring, its the same here.
But I bet the suspended wires running down your street from pole to pole are aluminium/steel.

Go out and have a look.
If they are silver they are definitely aluminium, if brown (or green) probably bare copper.
Copper is just too expensive for overhead power, and too many supporting poles required.

 

[yabert]

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

The battery terminal is aluminum and so is the busbar.

In the case of who started this thread, the battery terminals seem to be copper with a hole for M6 screw.
Terminal seem to be at least 15mm x 15mm, so let say the contact under the screw is a round of 15mm with a 6.5mm hole for the screw. That is 143mm2.
It's a huge area equivalent to more than AWG 4/0 wire (107mm2). So the surface area is not the limitation in almost any case.

To discharge this battery at 1C (100A), a copper busbar only need to be the equivalent of AWG 2 wire (34mm2), so let say 1/8'' x 1/2'' flat bar is enough.
So for aluminum 1/8'' x 3/4'' will be fine.

 

[yabert]

Resistence in contact point is more important than size....

I fully agree, so it's why remove oxidation on aluminum is so important ?
And protect future oxidation with special greases, aluminox, no-ox.

 

[John Frum]

In the case of who started this thread, the battery terminals seem to be copper with a hole for M6 screw.
Terminal seem to be at least 15mm x 15mm, so let say the contact under the screw is a round of 15mm with a 6.5mm hole for the screw. That is 143mm2.
It's a huge area equivalent to more than AWG 4/0 wire (107mm2). So the surface area is not the limitation in almost any case.

To discharge this battery at 1C (100A), a copper busbar only need to be the equivalent of AWG 2 wire (34mm2), so let say 1/8'' x 1/2'' flat bar is enough.
So for aluminum 1/8'' x 3/4'' will be fine.

My bad, thought we were talking about aluminum cell terminals.

 

[Delphinus]

I fully agree, so it's why remove oxidation on aluminum is so important ?
And protect future oxidation with special greases, aluminox, no-ox.

Oxidation ends to be a protection for further corrosion, for mine what I will do is make sure they are clean, terminals are flat and clean and after tight with recommended torque, I will assume that contact is good in that point and wont oxidize further.

This a terminal of an EV, max current is 200A cable is 50mm, they make it bigger to increase contact area.

 

[BiduleOhm]

Every microwave oven transformer I have seen uses aluminium windings.

I have 5 of them and they're all copper, both primary and secondary. So I guess it's region related (I'm in France).

I am sure you are correct for domestic wiring, its the same here.
But I bet the suspended wires running down your street from pole to pole are aluminium/steel.

Same here but the wires in the streets are copper, only the higher voltage transmission lines have aluminium. It's also because we typically have one big transformer for a few dozen houses instead of a pole pig one per house like in the US.

 

[yabert]

This a terminal of an EV, max current is 200A cable is 50mm, they make it bigger to increase contact area.

View attachment 123800

To have opened dozen of EV battery, I can confirm those increase contact area are not typical.
To add, a large lug terminal don't imply large contact area because it's more related to the screw/washer who put pressure between surfaces.
Large lug with a small screw don't give a large contact surface.
For the purpose of this thread it's important to not mix OEM coated busbars/lug with DIY bare aluminum and bare copper stuff.
A coating can resolve many oxidation problem, but it's often not available in the case of DIY.

To add about EV terminal/busbar, do you know that Tesla use a lot of aluminum in their EV's. Aluminum between battery modules, aluminum from charge port to battery and aluminum from relays to battery terminals.
By example, many Model 3/Y battery have aluminum busbars passing more than 600A for few minutes (during recharge). Still, the contact between those busbars are done by a small M6 screws
But all those aluminum have coating and/or grease against oxidation

 

[rogerdw]

I have 5 of them and they're all copper, both primary and secondary. So I guess it's region related (I'm in France).

I fixed microwaves for 30 years here in Australia and I always assumed the windings were copper too. They are certainly a copper colour. But I recently cut one apart to build a small spot welder and was actually quite shocked to see the windings (secondary) were definitely aluminium.

All those years and I believed a lie.

I retained the primary winding, so don't know what material that is. Sure looks like copper, but so did the secondary.

 

[BiduleOhm]

I know the coating can make aluminium pass off as copper but I confirm it's not the case here, it's copper.

 

[SparkyJJO]

Same here but the wires in the streets are copper, only the higher voltage transmission lines have aluminium. It's also because we typically have one big transformer for a few dozen houses instead of a pole pig one per house like in the US.

Well it varies, my parents' old house and their neighbor's house (both circa 1960s built) shared a pole transformer. The houses had 200 amp service too (all electric houses so they needed it).

The power lines in our residential area that we live are buried, with green block transformers dotted every so often. While I cannot see the connections, just counting them looks like each one of those transformer blocks serves between 2-4 houses.

 

[BiduleOhm]

Actually it makes more sense that it's two houses instead of one as it allows better current sharing between the two phases.

But one or two (or even 4) is not a lot, for example in my area there's about 50 houses on the transformer.

 

[curiouscarbon]

Please also be advised that aluminum physically expands and contracts more for a given change in temperature than copper. Its thermal coefficient of expansion is higher by about 30%

 

[Delphinus]

Today I went to buy a copper bar and found those they are more expensive than the bar but very practical to wire in the internal of a battery, didn't bought because didn't had detailed specs but probably Monday will buy some, in Europe we have a bigger range of dimensions.

FLEXIBLE INSULATED COPPER BARS | Gindre Distribution

Flexible insulated copper bars (Maxiflex).The best solution when connections with plain bars aren't possible

www.gindredistribution.com

 

[Delphinus]

To have opened dozen of EV battery, I can confirm those increase contact area are not typical.
To add, a large lug terminal don't imply large contact area because it's more related to the screw/washer who put pressure between surfaces.
Large lug with a small screw don't give a large contact surface.
For the purpose of this thread it's important to not mix OEM coated busbars/lug with DIY bare aluminum and bare copper stuff.
A coating can resolve many oxidation problem, but it's often not available in the case of DIY.

To add about EV terminal/busbar, do you know that Tesla use a lot of aluminum in their EV's. Aluminum between battery modules, aluminum from charge port to battery and aluminum from relays to battery terminals.
By example, many Model 3/Y battery have aluminum busbars passing more than 600A for few minutes (during recharge). Still, the contact between those busbars are done by a small M6 screws
But all those aluminum have coating and/or grease against oxidation

This is from a Renault EV with 10 years it's build like a tank compared to actual EV, probably none arrived to your country, if you look at indent on the top, the bolt cover it all.

Compared to OEM our systems cost more because we buy small but we don't have a budget dictated by a corporation so why not do it better.

 

[Warpspeed]

I fixed microwaves for 30 years here in Australia and I always assumed the windings were copper too. They are certainly a copper colour. But I recently cut one apart to build a small spot welder and was actually quite shocked to see the windings (secondary) were definitely aluminium.

All those years and I believed a lie.

I retained the primary winding, so don't know what material that is. Sure looks like copper, but so did the secondary.

Yes !
In Australia at least, both primary and secondary are both aluminium, but the insulated varnish gives it a brownish copper look.
A bit of a scrape, and its definitely bright shiny aluminium under the varnish.
I was fooled for a long time too. It was quite a revelation.

 

[yabert]

so why not do it better.

To me it's not copper is better than aluminum. I used both in my designs and in my solar system.
Both can do the job and survive way longer than battery, solar panels, BMS or inverter, by example.
Copper cost more, is heavier and is often harder to find. So why don't use aluminum when you know how to properly use it?

 

[John Frum]

To me it's not copper is better than aluminum. I used both in my designs and in my solar system.
Both can do the job and survive way longer than battery, solar panels, BMS or inverter, by example.
Copper cost more, is heavier and is often harder to find. So why don't use aluminum when you know how to properly use it?

Silver is a better conductor than copper but just about nobody uses it because of the expense.