Copper Clad Aluminum vs Oxygen Free Copper use, trade off, voltage drop in DC circuits.

[alesserfate]

Hello all,

I am sure many have seen the debates on the internet by the car audio guys of the cheaper CCA wires vs pure copper wires when used to deliver high amp DC current.

I am here to ask your opinion based on my situation.

I have a 300w solar array, 400ah of 12v batteries, and a 50ft round trip circuit to my 2000w AC inverter using 1/0 AWG copper clad aluminum wires which I put together 2 years ago and is functioning off-grid correctly.

I went with cheaper CCA vs welding wire or marine wire at the time because of the cost.

After reading and watching many CCA (copper clad aluminum) vs OSF (oxygen free copper) videos, I was concerned my cables and crimp connections were a fire hazard. I went ahead and inspected all my connections and found zero marks of heat or corrosion. I also tried to run my circuit at maximum load (12V-150A) for a prolonged period and there was no heating up at any of the connectors or in the cables.

The cons about CCA wire that people were mainly bringing up are: 1. the corrosion of the aluminum at the crimp terminals, which in turn creates resistance and heat. 2. higher resistance of aluminum causes higher voltage drop over distance, and heating of the lines. All my connections are heat shrunk, I found no signs of corrosion or heat damage after inspection after 2 years of use.

The next thing is voltage drop. Many on the 'internet' claim that CCA cables have high voltage drop when it comes to delivering DC over distance. I did a volt meter test and this is what I found:

All chargers and loads off:

At the battery terminals: 13.01V
At the inverter terminals 25ft away: 12.98V
(50ft total distance including positive and ground lines of 1.0 AWG copper clad aluminum wire)

My question is: should I go through the trouble of rewiring my entire setup ? Is it unsafe ? Am I losing performance ? It's about 600$ worth of cable, connectors and supplies where I am. All my wiring is nicely secured using adel clamps and terminated with quality connectors and I really don't want to rip it all apart.

 

[(*steve*)]

For DC the whole story is resistance. You will lose more energy for a given current when the resistance is higher.

For a given metal, resistance is inversely proportional to cross sectional area. If you're comparing different metals then you also need to take into account their differing resistances.

If you can increase your DC voltage, resistive losses will be lower as for a given power the current will be lower. In your case where you presumably have the inverter, it is probably not viable to rearrange your site array to increase the voltage.

 

[Bluejets]

You will find many arguments for and against but the fact that copper will carry a given current at a given size more efficently cannot be denied.

As far as your tests go, any done under no-load conditions are useless, don't mean a cracker.

It is usual to use bi-metal lugs if joining any aluminium to copper but at least the use of an anti-corrosive paste would have been an essential item in my books, regardless if it is copper coated aluminium or straight aluminium cable.

Personally i find any oxygen-free copper to be a foo-fee, just a way to make more money on a supposedly better conductor. You will never see the difference basically. (now I bet that'll start a discussion)

If you do not have corrosion problems, no joints heating under load, then why bother with any re-working.
As they say in the old days, let sleeping dogs lie. or/ if it ain't broke , don't fix it.

One could argue that aluminium is far better ( if you live in Thailand) because there, anything remotely like copper gets the battery grinder chop and cash-in job almost as soon as your back is turned.

 

[(*steve*)]

I think the argument for aluminum cored wires is that the conductivity is higher for a given weight of material.

Copper cladding possibly reduces corrosion, and gives benefit for AC via the skin effect.

My answer above doesn't really consider corrosion in connectors.

 

[alesserfate]

Thanks @Bluejets and @(*steve*) . I was thinking a similar thing, gives me some piece of mind. I overkilled the wire gauge and it seems to have gone to a good cause.

What about the tests that I did, how can I do it properly under load, where should I measure and what should I look for ? I would like to know, so that if I ever do decide to rewire, I can do a before and after comparison.

Thanks again, I appreciate it.

 

[(*steve*)]

Measure the voltage at the generation end of the cable and the end simultaneously.

This can be difficult if the generation of usage changed rapidly.

What you want to do is measure the voltage drop across the cable, but unless you have VERY long multimeter leads this is very difficult.

 

[alesserfate]

Thanks Steve. I have a readout on the inverter, if I verify that my handheld multimeter reads the same as the readout on the inverter (hence same calibration). I can enable a constant load, then have someone read out the inverter display and at the same time measure the generation side of the line. If the calibration is different, I can take the difference factor into account.

 

[duke37]

What you want to do is measure the voltage drop across the cable, but unless you have VERY long multimeter leads this is very difficult.

A thin piece of flexible cable will be adequate to get the voltage across the fat cable.

 

[(*steve*)]

A thin piece of flexible cable will be adequate to get the voltage across the fat cable.

True, and he speaks of a 50ft round trip, so 25 ft of cable should be sufficient. I had in my head that the distance was 50 metres.

 

[alesserfate]

True, and he speaks of a 50ft round trip, so 25 ft of cable should be sufficient. I had in my head that the distance was 50 metres.

Thanks guys, I just want to clarify: when you use the long piece of wire.. do you mean I should measure using (+) of the multimeter lead from the inverter terminal end, and (-) lead of the multimeter end at the battery bank ground ? Or what did you have in mind with a 'long piece of wire' ? Hence measuring 'across' the distance and comparing it to what it is at the battery bank ? Correct me if I'm wrong..

 

[(*steve*)]

You use your multimeter to measure the voltage across one of the pieces of wire leading from the batteries to the inverter.

The piece of wire you need is to extend one of the meter leads so it reaches the 25 feet to the other end of the current carrying cable. Ensure your meter is in a voltage range.

 

[alesserfate]

You use your multimeter to measure the voltage across one of the pieces of wire leading from the batteries to the inverter.

The piece of wire you need is to extend one of the meter leads so it reaches the 25 feet to the other end of the current carrying cable. Ensure your meter is in a voltage range.

Thanks Steve, still a little bit confused when you say across, where exactly should I touch the leads in my circuit though ? The voltage range I was going to use is 20V DC setting on the meter..

 

[(*steve*)]

Imagine you have one red wire and one black wire running from the battery to the inverter.

What you want to do is measure the voltage across the red wire. So one probe on one end of the wire (at the battery) and the other probe on the other end of the red wire (at the inverter).

You can start on the 20V range, but you'll probably want to reduce that to a lower range as you're expecting a pretty life voltage.

Your total loss will be double the voltage measured because of the black wire is the same gauge, the voltage drop across it will be the same.

 

[alesserfate]

Imagine you have one red wire and one black wire running from the battery to the inverter.

What you want to do is measure the voltage across the red wire. So one probe on one end of the wire (at the battery) and the other probe on the other end of the red wire (at the inverter).

You can start on the 20V range, but you'll probably want to reduce that to a lower range as you're expecting a pretty life voltage.

Your total loss will be double the voltage measured because of the black wire is the same gauge, the voltage drop across it will be the same.

Thanks Steve. Wow didn't know I would get a reading like that, speaks about my lack of knowledge. Also good point on doubling for the total loss. I really appreciate it. As others said earlier, should I have as much amperage as possible running through the circuit at that moment and try to max out the current when measuring to get an accurate reading ?

 

[(*steve*)]

should I have as much amperage as possible running through the circuit at that moment and try to max out the current when measuring to get an accurate reading ?

That would be best.

 

[Tha fios agaibh]

It's best to do this mathematically.
The most important factor is determining what the maximum load is. Once you know the amperage, voltage drop or even the size wire can be easily calculated. Don't guess or try and measure it, Look at the inverter documentation to see what it's rated for and the fusing ahead of it (PV line side) at maximum load.

One piece needed for the equation: Resistance of 50ft of 1/0 aluminum is .01005 at it max temp rating.

 

[(*steve*)]

That calculation didn't take into account losses in connectors.

If measuring, you should take your readings from the battery posts as one end and the posts or whatever is on the inverter at the other.

Also, if you're measuring, you need to measure both conductors as you can't be sure that all connectors are equal.

If it's just the cable resistance and the pretty comfortable about the connectors and your knowledge of the gauge and quality of the wiring, then a calculation may be sufficient (but won't tell you if something is wrong)

 

[Tha fios agaibh]

That calculation didn't take into account losses in connectors.

True, but the main question was regarding wire type/ size. The first step in determining wire size is knowing your load.
If running maximum 150amps, 1/0 Al wire has a VD of 20% so the wire is way undersized.
Even at 25 amps you have a Vd of more than 3%. (The recommend maximum)
There may be termination problems (was anti-oxidation paste used at terminals?)
But let's begin with making sure the wiring is capable of delivering the amperage needed.

 

[alesserfate]

Thanks guys. So I'm going to remeasure and re-calculate my decision on replacing the wiring. I'm hoping to perhaps extend the operation time of my inverter by finding out the voltage drop - and if its significant, replacing the wiring which will give me longer run time before the inverter cuts out due to undervoltage protection limit when the batteries do happen to run very low.

 

[alesserfate]

Quick update, replaced all my wiring with 1/0 TEW tinned copper, shortened the length too. Works a lot better: able to run more loads simulatenously, longer time before bank voltage drops, can start larger motors.. A worthy investment for sure. Thanks again.