openinverter forum

At some point I'm going to have to alter the aluminium cables on the BMW i3 battery modules to allow them to be connected together in the new pack orientation and to the inverter etc. Not only are the cables aluminium but the bus-bars coming off the battery terminals are aluminium and are laser welded to the battery terminal.

The main difficulty I see the dissimilar metal reaction between Copper and Aluminium when joined which with the slightest moisture will be an intermetallic nightmare. Also the practical process of joining two aluminium cables with good electrical integrity is a bit of a mystery to me.

I've no experience working with aluminium cables let alone large high power power ones like this so an after any experience or workarounds for this problem.

Some photos of the battery terminals and bus bars.

Probably not useful but, Cunningham's Law and all...

I think in home use, old aluminum wire is made safer by removing it from its terminals, crimping it to a copper wire stub, and then connecting the copper to the terminals instead. I dunno what the aluminum/copper crimp looks like but perhaps it's sealed well enough, or you could seal it well enough, to not worry about moisture inclusion and the ensuing galvanic corrosion.

Getting good contact to aluminium is a tricky business.
There are special AlCu terminals available, for example.
https://www.elpress.net/en/products/elp ... terminals/
Usually requires expensive press tools though.

This might be an alternative.
https://www.elpress.net/en/products/elp ... 20-010100/
Specified to work with both Al and Cu.

Then covered with glue coated heat shrink tube to reduce ingress of moisture.

Yes, shear bolt connectors are commonly used in the electricity industry to join copper & aluminium cables. They have to withstand many thousands of amps of fault current and several hundred amps continuous, so should be good enough for this application...

https://www.powerandcables.com/product/ ... 11kv-33kv/

bexander wrote: ↑Thu Oct 22, 2020 5:52 pm Getting good contact to aluminium is a tricky business.

Agreed, this is my main concern.

bexander wrote: ↑Thu Oct 22, 2020 5:52 pm Then covered with glue coated heat shrink tube to reduce ingress of moisture.

Water ingress is one of my major concerns for the whole project.
I've seen some sort of aluminium specific rust inhibitor goop especially for electrical connections on the internet. But I lost the link and will have to re-find it.

Aliexpress to the rescue.
It would appear they do a whole range of different Aluminium:Copper connectors available. The two sides are proportioned for the same current capacity in the different metals.
https://www.aliexpress.com/item/4000879274215.html

Maybe TIG welding the aluminum cable to the lug will give you the best result.

Mouse wrote: ↑Sun Oct 25, 2020 9:59 pm

bexander wrote: ↑Thu Oct 22, 2020 5:52 pm Getting good contact to aluminium is a tricky business.

Agreed, this is my main concern.

bexander wrote: ↑Thu Oct 22, 2020 5:52 pm Then covered with glue coated heat shrink tube to reduce ingress of moisture.

Water ingress is one of my major concerns for the whole project.
I've seen some sort of aluminium specific rust inhibitor goop especially for electrical connections on the internet. But I lost the link and will have to re-find it.

Aliexpress to the rescue.
It would appear they do a whole range of different Aluminium:Copper connectors available. The two sides are proportioned for the same current capacity in the different metals.
https://www.aliexpress.com/item/4000879274215.html
GTL-16-GTL-25-GTL-35-GTL-10-Compression-Copper-Aluminum-CU-AL-Tube-Bimetallic-Crimp.jpg_Q90.jpg

Hi. I am using i3 batteries for my conversion aswell. I am using the juyron al-cu connectors. Beware that their 50-50 mm2 connector is 50mm2 on the Al side but tighter on the Cu side. I had to drill the copper side out slightly to fit a 50mm2 copper cable. This is because the current carrying capacity is better on the Cu side and the expected application is to use a thinner Cu cable for the given Al size cable. I wanted to use 50mm2 copper anyway for my longer cable runs.

I tried to get hold of the elpress connectors but they and their distributors wouldn't sell to private customers, only to registered companies. So, as you say, AliExpress to the rescue

https://www.ensto.com/building-systems/ ... locks/ke61 These are widely available where I'm based. Specifically designed terminal blocks that take both Al and Cu. They can be bought for a few Euro. Obviously only useful if you have cables either end and don't need waterproof setup. There are insulation piercing connectors used on overhead lines that also provide environmental protection. Cost is about the same.

There is also stuff like this https://www.wago.com/us/syringe/p/249-130 specifically for making good electrical connection but avoiding all the Al/Cu problems.