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Does low voltage dc travel on surface

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  • Does low voltage dc travel on surface

    over the last couple of years Ive fixed a few things that were sort of low voltage dc.

    examples

    two makita 9.6 volt drills

    they would not work until i completely cleaned the contacts that go against the battery in their entirity..

    i tried just cleaning the point of contact ..no go....had to clean the whole strip...a clear path from one end to the other

    torch 3 volt with spring at the back end

    only worked when i cleaned off corrosion off the whole spring ..not just the bits in contact...either end...again, i had to have a clear path from one end to the other

    Ive read posts on the web that say only high voltage or high tension goes on the surface ...

    but my recent exploits tell me the opposite....and that low volt dc travels on the surface .

    BTW ..when i say corrosion ..i mean plating oxidation

    all the best.markj
    Last edited by aboard_epsilon; 05-12-2012, 08:39 AM.

  • #2
    No, DC travels through the entire depth of the conductor, its high *freqency* AC that travels on the skin.

    What could of been happening is the connection to the terminal was failing and needed to be cleaned, as well as the connection from terminal to terminal.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      Originally posted by Black_Moons
      No, DC travels through the entire depth of the conductor, its high *freqency* AC that travels on the skin.

      What could of been happening is the connection to the terminal was failing and needed to be cleaned, as well as the connection from terminal to terminal.
      YES, THAT'S EXACTLY WHAT I READ ON THE WEB ..

      but my "short" experience of this tells me something else.

      i made very good jobs of either end ..but not until there was a clear path on the surface from one end to the other would they conduct .

      perhaps I need to find more dysfunctional makita drills ..to prove my point ..as two isn't conclusive proof.

      all the best.markj

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      • #4
        Originally posted by aboard_epsilon
        YES, THAT'S EXACTLY WHAT I READ ON THE WEB ..

        but my "short" experience of this tells me something else.
        Well your "short experience" is wrong. It's possible that the material
        under the surface has a higher resistance than the surface, ie. a steel
        spring with some plating on the surface, and this is what is causing
        your phenom.
        ...Lew...

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        • #5
          If the OP's assertion were true, the following statement would also be true.
          If I clean the post of my truck's battery and only the inside of the battery cable clamp, the truck should not start.

          I found the above statement to be false.
          Last edited by Rosco-P; 05-12-2012, 11:23 AM.

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          • #6
            If dc doesn't creep, why do they clean dc transmission lines? I have measured small amounts of resistance on top of a dirty battery. Dirt is conductive....just not highly conductive.

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            • #7
              I've never seen DC transmission lines (as in cross country). The ones I'm familiar with are always AC so that it's easier to step the voltage up and down.

              To the original post...

              If DC traveled only on the surface, then the cables used to transport it would be hollow pipes. Twice the surface area with a tenth of the materials.

              I've seen some instances where I cleaned the "contact area" without realizing that as I install the battery the metal tab bends and the area of contact moves one way or another. I was actually cleaning the wrong area.

              Is it possible that in cleaning the whole area you are also cleaning other contacts or joints?

              Dan
              At the end of the project, there is a profound difference between spare parts and extra parts.

              Comment


              • #8
                Originally posted by high country
                If dc doesn't creep, why do they clean dc transmission lines?

                DC leaks when there is dirt and moisture to provide a path to ground. I usually only see power lines cleaned near the insulators at the poles.

                The same applies to a battery pack. The right combination of dirt will cause a high resistance short that eventually will run the battery down.

                Dan
                At the end of the project, there is a profound difference between spare parts and extra parts.

                Comment


                • #9
                  Electricity does not care what or where the conductor is, it will always find the path of least resistance.....that may not always be one single path.

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                  • #10
                    Originally posted by danlb
                    I've never seen DC transmission lines (as in cross country). The ones I'm familiar with are always AC so that it's easier to step the voltage up and down.

                    Dan
                    It is commonly done now AC converted to DC for long distance transmission and back to AC at the end use point.
                    Done to lower losses.
                    http://www.energy.siemens.com/hq/en/...smission/hvdc/
                    Max.
                    Last edited by MaxHeadRoom; 05-12-2012, 02:57 PM.

                    Comment


                    • #11
                      Originally posted by danlb
                      DC leaks when there is dirt and moisture to provide a path to ground. I usually only see power lines cleaned near the insulators at the poles.

                      The same applies to a battery pack. The right combination of dirt will cause a high resistance short that eventually will run the battery down.

                      Dan
                      Nit pick point. Electriicity in a circuit proportions its current according to the resistance of multiple circuits. There's even a formula R = 1 / (1/R1 + 1 /R2 + 1/R3 ...) If you happen to be numbered among the R's then you can expect to be zapped according to the voltage present and your contact resistance to the electrical circuit. It doessn't take very many milliamps for the shock the be severe.

                      Here's someting interesting that prompted this nearly off topic response:

                      http://en.wikipedia.org/wiki/Electric_shock
                      Last edited by Forrest Addy; 05-12-2012, 05:20 PM.

                      Comment


                      • #12
                        Originally posted by Forrest Addy
                        Nit pick point. Electriicity in a circuit proportions its current according to the resistance of multiple circuits. There's even a formula R = 1 / (1/R1 + 1 /R2 + 1/R3 ...) If you happen to be numbered among the R's then you can expect to be zapped according to the voltage present and your contact resistance to the electrical circuit. It doessn't take very many milliamps for the shock the be severe.

                        Here's someting interesting that prompted this nearly off topic response:

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

                        that seems to be about the post by high country, not mine.
                        Originally posted by highcountry
                        Electricity does not care what or where the conductor is, it will always find the path of least resistance.....that may not always be one single path.
                        Dan
                        At the end of the project, there is a profound difference between spare parts and extra parts.

                        Comment


                        • #13
                          Originally posted by Black_Moons
                          No, DC travels through the entire depth of the conductor, its high *freqency* AC that travels on the skin.

                          What could of been happening is the connection to the terminal was failing and needed to be cleaned, as well as the connection from terminal to terminal.
                          Actually, all AC travels on the surface, the skin depth is relative to the frequency. Thats why conductors at sub stations and power plants are either aluminum pipe or flat bar. Even at 60H the skin depth is 1/3".

                          Comment


                          • #14
                            Mac, if all AC travels on the surface, why do old household cables consist of multiple stands, but these are replaced when modernised by single thicker strands to make up the same cross section for the capacity ? Surely you'd need the same circumference for the capacity to get the same surface ? I'll go with Black M.

                            And Lew, taking something off the surface, which might or might not conduct much, cannot possibly reduce the resistance with DC. If the muck - corroded salts possibly - on the surface has a high resistance and can conduct only a small proportion of the current, it is contributing to the conductivity of the whole.

                            Mark, you've deluded yourself somehow. But as the great and late electronics guru Bob Pease (not the member here) would have said : What's all this conductivity stuff, anyhow ?
                            Richard - SW London, UK, EU.

                            Comment


                            • #15
                              AC travels in a depth related to the frequency of the AC AND the resistance of the material.

                              The lower the frequency and/or the higher the resistance, the more it can penetrate. For 60 Hz or 50 Hz, the depth of conduction is quite substantial, for microwave frequencies, it may be very shallow indeed.

                              Even DC travels only on the surface for the first short time after connection.... then the conduction penetrates deeper and deeper. But that would never be noticeable to you.

                              I suspect a coincidence...... cleaning the surface also improved connections, etc.
                              1601

                              Keep eye on ball.
                              Hashim Khan

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