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Wires and resistance heating questions

  1. Oct 5, 2015 #1
    Hey everyone,

    I had a few questions about resistance of wires and heating. I'm a materials engineer looking to replace traditional copper with something more lightweight, however, the alternatives have high resistance. For comparison say copper wire has .01 ohm/ft the other material could be 1 ohm/ft.

    What would the heat given off by the new material? Would it give off too much? Assuming 14V potential. Also, will higher resistance affect signals sent along the wire? Any other issues using a higher resistance material?

    Thanks
     
  2. jcsd
  3. Oct 5, 2015 #2

    anorlunda

    Staff: Mentor

    If the resistance is R per meter, and the current is I amps, then the power per meter is I*I*R joules per second.

    The only voltage that matters is the voltage difference between the two ends of the wire, not the voltage relative to ground.
     
  4. Oct 5, 2015 #3

    russ_watters

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    Staff: Mentor

    Needless to say, wire sizes are picked based on resistance so a hundredfold increase in resistance is a big issue.
     
  5. Oct 5, 2015 #4
    Signals can be sent through high resistance materials. Sending power is more of a problem.

    Most electrical engineering tricks are built around the large difference in conductivity between conductors and insulators. Thus we tend to think in these terms. But with a little work, I suspect we could find ways around the higher resistance of your material.

    Is your material clear at any frequencies the way fiber optics are clear at light frequencies? If so it might work as a waveguide at those frequencies.
     
  6. Oct 5, 2015 #5

    phyzguy

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    Science Advisor

    Aluminum is only about 60% worse than copper in terms of resistivity, and is much more lightweight. There are issues with dealing with the oxide layer that forms on aluminum, but these can be overcome, so aluminum is often used as a conductor in applications where weight and cost are important.
     
  7. Oct 5, 2015 #6
    Zach - your post is very vague... do you want more resistance or less? What Signals - etc....
     
  8. Oct 5, 2015 #7

    meBigGuy

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    Gold Member

    You need to describe specific scenarios in order for any answers to have meaning.

    The main issue is increased voltage drop along the wire because of the increased resistance. Whether that is too much depends on what you are trying to do.

    It will affect power transfer, signal levels, voltage levels, etc. It is just the same as adding a resistor in series with a copper wire.

    So, 5ft of copper is .05 ohms, 5ft of X is 5 ohms. What does 4.95 additional ohms do to your application, simple as that.
     
  9. Oct 6, 2015 #8

    Baluncore

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    Science Advisor

    There are many alloys with different resistivities and temp coefficients. NiCr alloys are widely used for heating.

    For power distribution conductors you should be using Cu or Al. At first sight Cu appears more efficient than Al, but thicker Al still works out cheaper per mile for the same resistance and support structure investment.
     
  10. Oct 6, 2015 #9

    sophiecentaur

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    Gold Member

    I'm not sure you would get good value by using something different from copper unless you are using overhead cables. In the UK, at a time when copper prices were high, there was a fashion for aluminium house wiring. I have only heard bad comments about it from today's installers. I believe that corrosion in terminals and long term mechanical weakness have caused problems. But, for long distance HV overhead distribution, the usual practice is to use steel reinforced aluminium I believe.
    Resistive losses will be I Squared R but the actual rise in temperature will depends on how easily the heat can escape. There are recommended standards for the choice of cable specs and you should read the regs for your part of the world. Actually, it may be that you need to pay a professional EE for this task. (Think Insurance Cover)
     
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