LOL! Skin effect in our application with a DC current? Ever heard the phrase a little knowledge can be a dangerous thing.

Anyway, solder the ends to the terminals and use fine stranded wire for its designed purpose in this aplication which is preventing flex fatigue, not improving/avoiding skin effect.

You mention audio speaker wires and the skin effects can be noticed there due to AC and high frequency of the current. That is when you think of hollow copper tube and other unusual conductors.

But in this case forget skin effect, the solder is to prevent corrosion, supplement mechanical strength, improve conductive interface and while we are at it, add to conductive cross section.

 

Okay, I wanted to clairify something. It is my understanding that the electorons travel along the outside of the strands only in AC applications. Am I correct?

 

IceShark,

The only point I claimed to have definite knowledge about was that electrons run on the outside of the copper not in the middle.
and that multiple strands carry more current for the size wire.
Do you agree/ disagree?

The soldering I ASKED about, if soldering was creating resistance. Sounds like there are many benefits. And I checked some of the wire ends on the 968 and they are soldered, to silver plate.

I appreciate your effort to clarify. But, are you claiming that a 1.0mm copper wire single strand can carry the same current as 1.0mm wire fine strand? lets say its DC 12vt. and fatigue is not a factor. Which can handle more amps and develop less heat?

Secondly, You mention "skin factor" is a "factor" with higher frequency and AC. Are you claiming it is not happening in DC low voltage?

Lastly, your "little bit of knowledge can be dangerous comment" is unappreciated. We are all learning as we go, Perhaps your deep study of the electron has caused you to be "negatively charged" Doug

 

Doug, sorry about you not liking the knowledge comment. I am no electrical engineer, and this area is fairly complex if you get into theoritical exactness so I am reluctant to make broad statements because I'm sure there is some effect I'm not aware of. So I know my limited kowledge is dangerous if taken too far.

But to answer your question in a general and practical fashion, yes; a solid core wire will carry the same current as stranded in DC applications for the same cross section. Skin effect, which I thought you were referring to since you were talking increased surface area and current primarily flowing at the surface, flat out doesn't occur in Direct Current and really only becomes an issue in AC at very high frequencies way, way, way above what your household current is at (50/60 Hz).

So yes, I disagree that your general premise is true to any practical degree in our common applications (and totally in DC) and the real reason welding cable is finely stranded is handling considerations .... you imagine what it would be like dragging a solid core around the shop and work pieces?

As far as heat for the same two cross section sized wires (assuming we now agree they will generate the same resistive heat) that would boil down to an issue of thermal transfer to the enviroment. So ignoring the insulator jacket, stranded would probably start out better with greater surface area but fall behind due to the insulating air pockets in the wire and fall behind even more if there was any surface oxidation on the thin strands hindering heat transfer of the core strands, etc. See how complicated this gets?

You may see tables which rate the same gauge stranded wire as higher capacity than solid. This is due to the fact that there are standard wire sizes and stranding configurations which, due to "rounding error", result in the stranded wire having slightly more conductor material, i.e. it is oversized by say 5%.

There are many refinements which can be made to the general statement but from a practical standpoint, it holds for the applications we are talking about. And wire fatigue and ease of installation because of flexibily are the big reasons to go with stranded wire.

Soldering: Soldering in and of itself DOES create additional resistance if you are using something more resistive than copper (i.e. tin & lead) as the solder. Best would be a crimp (or copper welding) that would squish the copper and terminal together in one homogeneous solid mass. But that is tough to do and corrosion and oxidation are already in place or show up evetually and there goes resistance through the roof. So that is why people solder with tin especially since the path through the solder is so short that that slight resistance is basically inconsequential.

The primary reason you see crimped only connectors is they are cheaper to apply while achieving an adequate result.

 

IceShark, Thanks for the kind and detailed response. So your saying "skin effect" does not happen in DC 12vt situations. So the electrons DO run through the entire cross section of the solid wire. Interesting, I appreciate that. I remember my KC Daylighter kit came with 44 strand #10 wire and the instructions "claimed" the fine strands carried greater current. the lights were 150 watts so about 11 amps each. I also, in reading about basic electricity, thought I had read that electrons will cover the surface of a metal object if it is charged, and that it ran only on the outside of the wire. It made no stipulations. Interesting stuff indeed. With so much around us in the realm of electrical matter, it never hurts to learn more about this phenomanon we call electricity. Thanks, Doug

 

Doug, yes I am absolutely sure "skin effect" doesn't happen in DC and DC flows through the entire connector cross section. Skin effect is a frequency issue and DC has no frequency ... well it has zero/null frequency. Probably a reason it is called "direct" current. -g-

Now there are other issues in current flow but they don't matter to our discussion to any significant degree especially since we have already agreed to use stranded wire for other beneficial reasons. Current capacity just isn't on the true laundry list.

Lighting marketers are the last people to believe about ANYTHING! If they told me the earth was round I would have to rethink my basic beliefs and see if I could get on the space shuttle or something to check and make sure.

 

What I like to see...a real technical, gentlemanly discussion! Way to go guys...

There is an excellent article on skin effect on HTTP://clicket.goto.com by Willem Naegels. It starts out very broadly and gets as detailed as anyone would want. In essence, the skin effect is a function of frequency; the higher the frequency, the more the charge is carried on the surface, due to the lag between the charge and the resultant magnetic field.(the magnetic field can't react as fast as the shift in polarity.
In essence, lightning, for example, is technically high frequency AC (at least one pulse, sometimes more). A person in a car is safe because of the skin effect which turns the car into a Faraday cage. THe skin effect is why "magicians" have so much fun having people grab a high voltage Tesla coil. DC has a uniform charge throughout.

Cheers, guys....

Bob S (loves to watch lightning storms from a safe distance...God's fireworks)

 

This seems counter-intuitive and really surprised me when I learned it, and of course, feel free to continue the debate, but you're better off NOT soldering. Crimp is the best connection for the type of stuff we're talking about here.

Mil-spec is to crimp everything, as the solder actually causes a stress point. And we know cost isn't an issue for the military stuff!

My $.02 worth

 

That, stress riser, is a very old argument. Boils down to the monkeys in your labor force can't put on a solder joint correctly all the time to justify trying to improve on a swagged terminal. And cost *does* matter.

You actually believe the crimp is not a stress riser?

We are not talking about the best way to mass produce an item with a limited design life, but rather small, one off quality jobs which will last and be superior.

Besides, we are talking about big #4 terminals. Doubt many listers have a tool that can properly swag that. So they have to do a half assed crimp with pliers and solder to complete.

 

Well the electron/mechanical debate continues I LOVE IT! keep it up guys. Well I now have a even higher respect for electrical connections. I have to thank Tabor for starting this thread. I have been having a heck of a time with my "oil level light" in my 93 968. AND it turns out that there is a Porsche technical bulletin out on the 93 and 94 968s that says..." The oil level warning lamp circuit board located inside the instrument cluster may be damaged in the area of the integrated circuit due to a ground difference potential between the engine and the instrument cluster, If a customer complains of the above mentioned concern, proceed as follows: 1,Clean and check tightness of ground points 2,3,6,8,and 9. and if that does not fix the problem, replace the circut board with new version.

So the $115 moral of the story is those ground connections are very important.

Tabor and IceShark, thanks again for the great topic. Doug

 

Yes, ground is as important as the positive feed as I've been preaching for quite awhile.

Unlike many applications, cars use the steel frame and sheet metal for the ground. Cheaper. Lighter. Electricity makes a round trip from negative source to the positive so obviously there is a big problem potential in the ground section.

Steel is a poor conductor compared to copper (about 10/15%) but in a regular car it should have a huge conductor cross section and make up for that. In empirical practice it doesn't. And it gets much worse with age. I suspect that there are a couple key bottle necks in body/frame design that corrode with age and kill the electrical flow.

So rather than chase down the bottleneck ghosts just slap on a few more grounds where it is important, like the headlights which started this whole thread. This also improves the other suffering items.

Here we are, off arguing skin effect and the best conductor construction when the other half of the system is total crap!

 

On the subject of crimps, just how does the Mill Spec specify how to make the crimp ?? It seems to me that a tight crimp could be had with my 6 inch vise and die. It also seems to me that adding little extra cable length would compensate for stifining due to solder. --Roy--

 

Roy, who knows which mil spec he is referring to. Hope it isn't in a nuk we might need 50 years after manufacture down in them deep wet holes.

If you solder, which you are all free not to do, the important part is to have a flexible stiffener at the back when it goes to the regular strand. To prevent hard flex spots, which I think I noted way up front in the thread, make sure the solder doesn't wick down the wire.

Heat shrink tube and a sealing compound that extends beyond the solder joint.

Oh, on the crimp. If you really wanted to do this right you would use the type of swagging machine used on rigging. It is a "rolling" type swag. Not just a simple crush that you see in hand tools. But even these sophisticated swags in monel or stainless wire rope fail due to corrosion in the interface. Just ask rigging manufacturers. The key is keeping the corrosion away so you need a seal.