Electrical resistance ?

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ohmhead

ohmhead

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Well question for today ? When is aluminum wire at a lower resistance to copper no thermal or condition just old standard wire same length same cir mils? Take care
 
Volta said:
Hmmm. Good question.
High frequency AC source on widely separated copper wires
vs.
DC aluminum?:confused:
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Well your close kinda hit it!!! But yes not just high freq but at power freq also . SKIN EFFECT AC RESISTANCE

I was reading about skin effect and went back in a old book on this subject found this , ac resistance as the conductor size increases also as freq increases for a given diameter and length its ac resistance can be greater if the material is copper than aluminum .

How it does it would be a post nite mare but i think its all about magnetic flux in the center of the alu and the higher resistance in alu wire tends to make the current flow around the surface with less effort then copper as copper at that freq or size would push the current closer to the surface of conductor something like that .
Just thought id post to see if anyone cared to know that or could give me a better understanding of why ? Take care
 
K8MHZ said:
This is a rather in depth explanation of skin effect:

http://en.wikipedia.org/wiki/Skin_effect

Since Al and Cu are nearly identical in skin effect depths, I don't see where Al has an advantage over Cu for equal cross sections.

Where Al is a better conductor than Cu is by weight which has nothing to do with skin effect. Al is the best conductor by weight than any other metal.
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Well yes it has everything to do with skin effect.

Its a function of the relative resistance of the conductor material being less for materials of higher resistance for example the skin effect for a given diameter of cable is greater if the material is copper rather than aluminum .

The induced emf magnetic flux internal in the core of conductor can push the current flow to the outer surface of conductor higher dc resistance of alu to copper alu has higher dc resistance less induced current to push. Meaning flux induced is minimal less push current flows in more of a area in the aluminum conductor . more area less resistance to flow

Copper has less resistance it can push current to its outer surface with more of a induced current and with a higher magnetic flux produced by the nature of less dc resistance of conductor . meaning more current to push but less surface area to flow thur . Its all magnetic flux induced current ac freq and its effects and alu is less in ac resistance then copper . Best to ya
 
ohmhead said:
Well yes it has everything to do with skin effect.

Its a function of the relative resistance of the conductor material being less for materials of higher resistance for example the skin effect for a given diameter of cable is greater if the material is copper rather than aluminum .

The induced emf magnetic flux internal in the core of conductor can push the current flow to the outer surface of conductor higher dc resistance of alu to copper alu has higher dc resistance less induced current to push. Meaning flux induced is minimal less push current flows in more of a area in the aluminum conductor . more area less resistance to flow

Copper has less resistance it can push current to its outer surface with more of a induced current and with a higher magnetic flux produced by the nature of less dc resistance of conductor . meaning more current to push but less surface area to flow thur . Its all magnetic flux induced current ac freq and its effects and alu is less in ac resistance then copper . Best to ya
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Can you post some links?

For one thing, skin effect does not apply to DC. A kilogram of Al will be a better conductor than a kilogram of any other type of metal even at DC.

As this chart illustrates, skin effect is nearly identical for Al and Cu.

250px-Vdorna_globina.png


Please realize that in any AC circuit, the opposition to current flow is impedance with resistance only being one component of impedance. You speak of induced current which creates impedance, not resistance.

For illustration, the skin effect of 60 Hz in Cu is less than 9 mm. That noted, why is there a need for conductors any larger than 9 mm? There is some conjecture about skin effect on stranded conductors. Stranded vs. solid is virtually the same, with the exception of special 'Litz' conductors that have insulated strands.

I am not calling you wrong, I just don't understand your explanation. In my mind there is a graph somewhere that shows the crossing line of the phenomena you purport and that interests me.

the higher resistance in alu wire tends to make the current flow around the surface with less effort
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I find statements like this confusing, however.

Al is more immune, slightly, to skin effect than Cu and may provide for more usable conductor at high frequencies, but be aware that in real life thermal conductivity, ambient temperature, type or lack of insulation, power factor and duty cycle also come into play.

Skin depth has nothing to do with power. All you need to know is the relative permittivity and the frequency to calculate skin depth.

In lieu of a graph, I ask at what frequency does Al become a better conductor than Cu for the same given cross sectional area?

Thanks for putting up with my curiosity.
 
K8MHZ said:
Can you post some links?

For one thing, skin effect does not apply to DC. A kilogram of Al will be a better conductor than a kilogram of any other type of metal even at DC.

[We never said it did we said it control the induce ac part by dc resistance of conductor .]


As this chart illustrates, skin effect is nearly identical for Al and Cu.

250px-Vdorna_globina.png


Please realize that in any AC circuit, the opposition to current flow is impedance with resistance only being one component of impedance. You


[We see the dc resistance as a limit to the induced current of the ac reactance .
In the core of the wire or conductor .]


speak of induced current which creates impedance, not resistance.

For illustration, the skin effect of 60 Hz in Cu is less than 9 mm. That noted, why is there a need for conductors any larger than 9 mm? There is some conjecture about skin effect on stranded conductors. Stranded vs. solid is virtually the same, with the exception of special 'Litz' conductors that have insulated strands.

[Were not using litz wire high freq were talking 500mcm and larger conductors .]

I am not calling you wrong, I just don't understand your explanation. In my mind there is a graph somewhere that shows the crossing line of the phenomena you purport and that interests me.

[Well its ok we like talking electric and getting input on what others think .]



I find statements like this confusing, however.

Al is more immune, slightly, to skin effect than Cu and may provide for more usable conductor at high frequencies, but be aware that in real life thermal conductivity, ambient temperature, type or lack of insulation, power factor and duty cycle also come into play.


[alu is lower in resistance to skin effect but copper is higher in resistance to skin effect on the surface of the conductors .]

Skin depth has nothing to do with power. All you need to know is the relative permittivity and the frequency to calculate skin depth.


[ skin depth to me has lots to do with its effects over long distances .]

In lieu of a graph, I ask at what frequency does Al become a better conductor than Cu for the same given cross sectional area?

Thanks for putting up with my curiosity.
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[I enjoy debates but also learn from others ideas and views iam just a electrician with a different way of thinking about things electrical . iam just reading from a book .] TAKE CARE
 
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K8MHZ said:
What book? Really, I am curious.

Thanks.
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Well its the Standard Handbook For Electrical engineers Fink & Beaty Eleventh edition page 18 -86 Par 228 .
Electrical Characteristics of Cable Skin Effect copy 1977 it maybe a little old and maybe out of date but theres lots of good stuff . I collect electrical books have a few old and new its fun to see the different things that change thur the years meaning electrical theorems today and yesterday . Is that your call letters K8MHZ ? I was a ham operator my first call letters were WN2MQX in 1968 best to ya
 
ohmhead said:
Well its the Standard Handbook For Electrical engineers Fink & Beaty Eleventh edition page 18 -86 Par 228 .
Electrical Characteristics of Cable Skin Effect copy 1977 it maybe a little old and maybe out of date but theres lots of good stuff . I collect electrical books have a few old and new its fun to see the different things that change thur the years meaning electrical theorems today and yesterday . Is that your call letters K8MHZ ? I was a ham operator my first call letters were WN2MQX in 1968 best to ya
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Thanks! I like the old books too. I like looking at code books from two century turns ago.

Yes, I am guilty of being a ham. Guilty of knowing Morse Code and owning and operating a tube type radio, building my own antennas and filling shelves with various forms of electronic gear from throughout the ages. Did you know it was Samuel Morse's birthday just a few days ago and Google's logo was in Morse for a day?

Thanks for the reference, BTW 1977 isn't that old, OM. :grin:

_ _ --- --- _ _ _-- - _-_ _ _ _ -- _ _ ---- _ _--
 
K8MHZ said:
I couldn't tell. Every time I opened up a roll of lithium wire it caught on fire so I couldn't ever check it's resistance. :grin:

But as far as usable metal goes, I am sure Al is the least resistive per pound.
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No doubt. Even though silver is the most conductive, its weight knocks it down in the ratings. I looked up a few here is the rank (at room temperature):
Lithium (Li)
Aluminum (Al)
Magnesium (Mg)
Copper (Cu)
Silver (Ag)
Zinc (Zn)
Gold (Au)
Molybdenum (Mo)
Nickel (Ni)
Iron (Fe)
Tin (Sn)
Tungsten (W)
Tantalum (Ta)
Platinum (Pt)
Lead (Pb)
Manganese (Mn)
Mercury (Hg)

It might be interesting to see the conductivity ranking without the weight:
Silver (Ag)
Copper (Cu)
Gold (Au)
Aluminum (Al)
Magnesium (Mg)
Tungsten (W)
Molybdenum (Mo)
Zinc (Zn)
Nickel (Ni)
Lithium (Li)
Iron (Fe)
Platinum (Pt)
Tin (Sn)
Tantalum (Ta)
Lead (Pb)
Mercury (Hg)
Manganese (Mn)

What's the one that explodes in water? I remember our science teacher in high school dropping a small piece in a beaker of water for a demo (yes I can remember some things that far back...just nothing important).
 
K8MHZ said:
Thanks! I like the old books too. I like looking at code books from two century turns ago.

Yes, I am guilty of being a ham. Guilty of knowing Morse Code and owning and operating a tube type radio, building my own antennas and filling shelves with various forms of electronic gear from throughout the ages. Did you know it was Samuel Morse's birthday just a few days ago and Google's logo was in Morse for a day?

Thanks for the reference, BTW 1977 isn't that old, OM. :grin:

_ _ --- --- _ _ _-- - _-_ _ _ _ -- _ _ ---- _ _--
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7 3 d e k 8 m h z

Is that ok its only been 38 plus years but how did i do ? yes we also built our own transmitters and matching halfwave folded dipoles !! Take care nice
 
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