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Aluminium V Copper cable for automotive starter

I am engaged in a friendly discussion at

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about the relative merits of using copper or aluminium cable in for an automotive starter circuit. I hijacked a thread about the merits of copper V brass V aluminium radiators. It is claimed that aluminium cable dissipates heat more efficiently and that with repeated use copper becomes more brittle. To quote in part: "...copper cable deteriorates when being heat cycled over and over again, aluminium cable is more brittle than copper when used within the limits of it's current carrying capacity but once you start drawing big current for short amounts of time through smaller conductors the heat cycling affects the copper more over time and from years of experience I have found that the ally cabling when used in this situation very rarely fails, I have found that the copper cable becomes very stiff and brittle and fails a lot at terminals with vibration and slight movement but the ally cable stays flexible. I don't have any formulas or anything to explain why this is the case, I can only speak from personal experiences. Also copper cable oxidises and builds up a green grease like film when exposed to air over time probably worse than any ally cable ..."

It seems counter intuitive to me as I always thought copper was more thermally efficient than aluminium and that aluminium was more likely to form a non conductive and brittling oxide coating. However, I guess that the need with aluminium to use a bigger cross sectional cable to have the amperage rating might change the thermal performance difference between aluminium and copper cables. What are your views and your real world experiences with copper V aluminium cable in high current DC applications?

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Regards
Blue

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Reply to
aussiblu
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As I said in the ford forums thread it explains here

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If an hot object is radiating energy to its cooler surroundings the net radiation heat loss rate can be expressed as

q = ? ? (Th4 - Tc4) Ac (3)

where

Th = hot body absolute temperature (K)

Tc = cold surroundings absolute temperature (K)

Ac = area of the object (m2)

? = emissivity

? = the radiation constant

so if you are comparing copper and aluminium cable of the same amps rating the simple fact that the aluminium cable needs a greater cross sectional area means that it will have greater thermal radiation as the greater the cross sectional area the greater the thermal radiation and copper has only marginally better emissivity than aluminium. If we were comparing cables if identical cross sections I would come down in favour of copper.

I'm still interested if this holds up in real world experiences and if the brittling claims are true.

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Regards
Blue

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Reply to
aussiblu

As far as use in starter motors is concerned, I've had to replace, or have replaced, several starter motors in my life, but never had to replace a starter motor cable.

Since aluminium cable costs more for a given current, one would immediately have to ask whether the extra expenditure might be better used to improve the longevity of starter motors instead.

Indeed, one could overspecify the copper cable for the same cost as the aluminium cable, thus reducing the heat cycling of the copper.

Sylvia.

Reply to
Sylvia Else

Aluminium cabling was famous for starting fires in houses in the USA as it had problems with cold flowing and fretting in terminal blocks and was only really solved once special techniques were used to make joins such as special crimps and copper tails.

Reply to
Mark Harriss

I thought aluminium cable was much cheaper than copper cable and one of the reasons for CCA (copper clad aluminium) cable coming onto the market - advantages of coppers conductive and thermal properties together with aluminium's cheapness and lightness. Also the high theft rate of copper cable being sold as scrap.

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Regards
Blue

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Reply to
aussiblu

As far as the cost of the metal is concerned that's true, but there are costs associated with technical risks. The fact that we have so far seen little penetration of aluminium wire outside of specialised areas suggests that that cost has not been seen to be worthwhile. OK, I'm arguing somewhat circularly.

Sylvia.

Reply to
Sylvia Else

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