Does low voltage dc travel on surface

[aboard_epsilon]

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

[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.

[aboard_epsilon]

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

[Lew Hartswick]

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...

[Rosco-P]

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.

[high country]

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.

[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.

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

[danlb]

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

[high country]

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.

[MaxHeadRoom]

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.

[Forrest Addy]

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

[danlb]

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.

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

[macona]

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".

[rohart]

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 ?

[J Tiers]

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.