Aluminium V Copper cable for automotive starter

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I am engaged in a friendly discussion at
http://www.fordforums.com.au/showthread.php?t11%300518&page=1&pp30%
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?
--
Regards
Blue

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Re: Aluminium V Copper cable for automotive starter


As I said in the ford forums thread it explains here
http://www.engineeringtoolbox.com/r...sfer-d_431.html

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

q = ε σ (Th4 - Tc4) Ac (3)

where

Th = hot body absolute temperature (K)

Tc = cold surroundings absolute temperature (K)

Ac = area of the object (m2)

ε = emissivity

σ = 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.

--
Regards
Blue

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Re: Aluminium V Copper cable for automotive starter


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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.


Re: Aluminium V Copper cable for automotive starter


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.

--
Regards
Blue

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Re: Aluminium V Copper cable for automotive starter


Quoted text here. Click to load it

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.

Re: Aluminium V Copper cable for automotive starter




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.

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