# Aluminum Cable



## Technologic (Jul 20, 2008)

iss407 said:


> Aluminum is very conductive, light and inexpensive, expecially compared to copper prices today. Aluminum is lighter than equivilant copper wire with the same current capacity. Aluminum is used for high-voltage, high-current power distribution in large quantities. What about using it in electric vehicles? I know about cu-al galvanic issues, but I am planning to use it, along with heavy-duty lead battery terminals between batteries and to connect the battery pack in the trunk with the one under the hood, and then to the controller. No copper interconnects except possibly at the contactor. Any corrosion isn't going to occur quickly, it takes time and I will be able to see it before any problems get dicey.
> 
> I was looking at making solid aluminum bar connectors between batteries, but the lead terminals and a short piece of 3/0 or 4/0 cable would work better and allow for thermal expansion and vibration. I plan to run rugged, sealed plastic conduit from the trunk to the front battery pack.
> 
> If I'm overlooking something, let me know. I want to stop by the local recycler tomorrow and see if they get scrap overhead aluminum cables in good condition. The stuff comes in 1000-ft rolls and I know the installers can't use smaller, left-over pieces from the end of the cable. They must do something with it.


When you run electricity through aluminum it will start to build up aluminum oxide on the surface quicker than normal. Aluminum oxide is extremely electricly insulative. I'm not sure how you plan to bond the terminals, but make sure the bond is near air tight and you should be fine... crimping the bar into the "contactor" is a must.


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## engineer_Bill (Jun 24, 2008)

Aluminum is lower on the galvanic scale than copper, and lead. When attaching aluminum wires to lead terminals the aluminum will experience galvanic corrosion. When connecting copper wires to lead the lead experiences galvanic corrosion especially on the POS terminal. The NEG counteracts some of the corrosion effects. I would not use aluminum for an EV application. In high voltage, high power circuits. The aluminum can be connected to airtight terminals that are made of a neutral alloy and coated with a compound that inhibits corrosion and keeps moisture out. In a car you will be subjected to vibration, low voltages and high currents, and humidity. IN a low voltage even a small amount of resistance will kill the connection. Copper is not THAT expensive for the 10-20 ft you need. Use the aluminum for something else, or you will regret the day. A high resistance junction can get hot enough to melt causing a vehicle fire or extensive (expensive) damage. I have relatives who work in the Aluminum industry so by all means use all the aluminum you can, just not for pack jumpers. Make your car out of aluminum, just use copper wire.


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## TX_Dj (Jul 25, 2008)

Additionally, large gauge Al wire, in my experience, is of the sort with large wires inside making up the greater conductor. The thicker the wire that makes the cable, the less flexible and vibration resistant it is as a whole. You need lots of flex and vibration resistance for a vehicle application.

Additionally, something like "welding wire" provides far more "skin" for the current to travel. Electrons conduct down the outer skin of the wire. More tiny filaments working together can conduct more volt-amps more effectively than fewer larger strands.


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## Technologic (Jul 20, 2008)

TX_Dj said:


> Additionally, something like "welding wire" provides far more "skin" for the current to travel. Electrons conduct down the outer skin of the wire. More tiny filaments working together can conduct more volt-amps more effectively than fewer larger strands.



incorrect this is a myth.

a solid core both heatsinks better and slightly (1% or less) conducts better.

the issue of course is how to bend it at 4/0 gauge


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## TX_Dj (Jul 25, 2008)

Technologic said:


> incorrect this is a myth.


Hmm. Not a myth with RF... perhaps I just assumed it behaved the same in DC. Apologize if I pushed any misinformation.

Edit: not just RF, all AC... so not a factor if your wire is from the traction pack, but perhaps could be if your frequency is high enough and you're talking about cables from the inverter forward.


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## Technologic (Jul 20, 2008)

TX_Dj said:


> Hmm. Not a myth with RF... perhaps I just assumed it behaved the same in DC. Apologize if I pushed any misinformation.


Electron "flow" (though I guess you can't really call near light speed movement "flow) through AC is another matter entirely. The electrons are cycled so quickly that they neither build up much heat or "use" much of the wire gauge.

Now back EM fields is another story in AC which can help to have stranded wires. But the only time I've heard of that is in a coil setting, and there's other reasons to use solid core wires then (ie. thermal conductivity). But to date I've never really heard any reason outside of flexability why to use stranded wire for DC current. There are numerous ways to "short" back EM fields anyway.


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## TX_Dj (Jul 25, 2008)

The good news, though, is that it would seem that if we were talking about AC, Al would be a better choice than Cu, as Al permits a little more skin depth.

Interesting.


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## Mjolinor (Sep 15, 2008)

TX_Dj said:


> The good news, though, is that it would seem that if we were talking about AC, Al would be a better choice than Cu, as Al permits a little more skin depth.
> 
> Interesting.


The skin depth is fixed by the frequency not the material. The corrosion present on all AL in air is such that at higher frequencies it is really crap as the magnetic fields created by the self inductance cause the power flow to try to be within the outer corrosion layer which offers high resistance.

Multiple conductors are not used to reduce skin effect, they are generally used for producing controlled, known, impedances within the wire (google litz wire) but I don't see that it can ever be relevant in an EV. For power uses they use stranded to give flexibility

Aluminium conductors are used by power utilities because it is cheap and does not get stolen as much for scrap, they have the devils own job during development of joints and fixings to make sure there are no osmotic reactions between components on the connections. If the cable is subject to any movement like overhead transmission / distribution then it will have a steel conductor down the core to give the needed strength otherwise it just fractures, this (I think) is what will kill it for EV use even if you could make the joints low Z.

High power coax cable is often made with a tube as the centre conductor instead of a solid core, mainly the reasons for this are cost and weight plus you can pump coolant down the core to increase the power rating of the cable

AC (power) travels down the cable at about 2/3 C but depends on the type of cable.


In the UK the telco discovered the joys of installing AL cable instead of copper for the phone lines, nice and cheap, it lasted about 3 years and caused loads of problems, they are still paying for those problems as bits of AL are all over the network in the UK and it will not transmit DSL at all.

Long post with not a lot of relevance, just some interesting info


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## almoore (Sep 2, 2008)

Do not use aluminum conductors.I am an Electrician in the construction industry.You must use de-ox compound on all of your connections.The connectors must be dual rated ,for both termination materials,lead and aluminum in your case.Aluminum must be sized two sizes larger than the copper.Aluminum is much softer material than copper ,so extra care must be taken when terminating.In my 30 years I have seen many more aluminun connections fail,due to improper installation and maintenence.The connections on an EV will be subject to moisture ,vibration,chemicals,and other factors that would create a maintenence nightmare.Aluminum wire is a great product and in the right applications is hard to beat.


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## TX_Dj (Jul 25, 2008)

Mjolinor said:


> The skin depth is fixed by the frequency not the material.


No offense, I think you're wrong about that.

Skin depth is fixed by the frequency and the material. The skin depth at a given frequency will be different for different materials.










Left side is skin depth, bottom is frequency.

Unless someone posted misinformation on wikipedia, which is quite possible...

But thanks for the additional explanations in your post. Very informative.


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## Mjolinor (Sep 15, 2008)

Yes it does depend on the transmission line parameters of the material but in a real world situation I have never met anything that would discriminate copper from aluminium when discussing the skin depth, they are pretty much the same for both metals.

Wikipedia is correct in the analysis given (I think) but it's not the whole picture, it is simplified. I spent 3 years of my life number crunching the transmission line parameters of power cables and just looking at some of the equations makes me feel like sleeping.


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## TexasCotton (Sep 18, 2008)

almoore said:


> Do not use aluminum conductors.I am an Electrician in the construction industry.You must use de-ox compound on all of your connections.The connectors must be dual rated ,for both termination materials,lead and aluminum in your case.Aluminum must be sized two sizes larger than the copper.Aluminum is much softer material than copper ,so extra care must be taken when terminating.In my 30 years I have seen many more aluminun connections fail,due to improper installation and maintenence.The connections on an EV will be subject to moisture ,vibration,chemicals,and other factors that would create a maintenence nightmare.Aluminum wire is a great product and in the right applications is hard to beat.


I agree(Amen) with above post
Copper will be coming back down in price since "oil" is dropping in price. Anyway if you search for scrap or salvage copper you save on price !


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## iss407 (Dec 6, 2007)

It sounds like the safe bet is to use copper. The recycling place was closed today but I'll check next week to see if they ever get an welding cable brought in. I'm not going to be getting to installing the cabling for a while (haven't even got the motor yet!) so I have time to look for a good deal.

How about terminals. If the batteries have posts is it not better to use a terminal that binds around the post? Are crimped ends the best?


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## Technologic (Jul 20, 2008)

iss407 said:


> It sounds like the safe bet is to use copper. The recycling place was closed today but I'll check next week to see if they ever get an welding cable brought in. I'm not going to be getting to installing the cabling for a while (haven't even got the motor yet!) so I have time to look for a good deal.
> 
> How about terminals. If the batteries have posts is it not better to use a terminal that binds around the post? Are crimped ends the best?



Well soldered/crimped together is the best post binding method usually.


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