Wire resistance and coil legs, technical explanation please

[proteckt3d]

Was just searching and couldn't find the answer and I'm sure it must have been brought up before, but how come the coil legs of the coil don't glow red when applying a high current through the coil, aka dry burn? I understood how electrical resistance works in metals but I can't explain why there is more conductance - easy of current flow- in the legs. I have a hunch it might be due to the legs being firmly attached to the posts and these being far less electrical resistant might extend the effect on the coil legs. But is that the only cause? and more important is it a correct one?

 

[edyle]

Was just searching and couldn't find the answer and I'm sure it must have been brought up before, but how come the coil legs of the coil don't glow red when applying a high current through the coil, aka dry burn? I understood how electrical resistance works in metals but I can't explain why there is more conductance - easy of current flow- in the legs. I have a hunch it might be due to the legs being firmly attached to the posts and these being far less electrical resistant might extend the effect on the coil legs. But is that the only cause? and more important is it a correct one?

1: if you put enough power through they will also glow red.
2: there is not more conductance in the legs (unless you are using nr-r-nr prewelded coils)
3: Yes it is due to the legs connected to the metal of the posts; the posts act as a heat sink

 

[proteckt3d]

Thanks for the input Edy, but I'm not convinced it's that simple as you put it in in your 3rd point. By definition heat is only collision of electrons with the atoms in the lattice of a metal caused by a voltage applied. I have limited electrical knowledge but If I would have an atomizer with posts that would allow to make a coil with almost non-existent legs, would the first wraps on each end of the coil stay colder and not glow ( or partially glow ), in a dry burn situation? I am quite possitive they would not, although I might be terribly wrong. If true, it's obvious the terminals have this effect and it might need further explanation that heat transfer IMO. If partially true it will imply that it is caused by other effects too i.e by the round shape of the wrap or perhaps the proximity of the wraps has something to do with how the electric field travels through the metal. In both cases the effects would need more explanation. In my mind the answer would also explain the question why dry burning a microcoil or other contact coil accumulate most of their heat in the center. What do you think?

 

[rhm3769]

Thanks for the input Edy, but I'm not convinced it's that simple as you put it in in your 3rd point. By definition heat is only collision of electrons with the atoms in the lattice of a metal caused by a voltage applied. I have limited electrical knowledge but If I would have an atomizer with posts that would allow to make a coil with almost non-existent legs, would the first wraps on each end of the coil stay colder and not glow ( or partially glow ), in a dry burn situation? I am quite possitive they would not, although I might be terribly wrong. If true, it's obvious the terminals have this effect and it might need further explanation that heat transfer IMO. If partially true it will imply that it is caused by other effects too i.e by the round shape of the wrap or perhaps the proximity of the wraps has something to do with how the electric field travels through the metal. In both cases the effects would need more explanation. In my mind the answer would also explain the question why dry burning a microcoil or other contact coil accumulate most of their heat in the center. What do you think?

You could always do a coil with longer leg lengths to somewhat test that theory.... Or take the same length of wire normally used for a coil and connect it without coiling....

 

[proteckt3d]

Good point. Actually Pbusardo does it often lately with a dripper when stressing box mods at 0.2-0.3 ohms. Without checking I remember the entire wire glows red with the very ends not glowing the same as the rest of the wire length

 

[proteckt3d]

I know this subject might have limited practical use to vaping but it doesn't make it not worth asking, I'm just hoping the principle is easy for someone in here to elaborate on

 

[jpargana]

Also, I believe there might some "auto-heating" effect on the coil. By that I mean, coils are so close to each other that any heating in one of them will also heat it's neighbours, who will get more heated, heating even more the first coil... you get the idea.

A coil leg is surrounded by air and away from the coil itself.

Just my 2 cents.

 

[proteckt3d]

Agreed, there is exponential heat accumulation. My question is what causes that one coil to heat more in the first place. If this is answered the rest can be easily explained as the the same cause will apply to the rest of the coils as they would just follow the effect of the coil preceding them right?

 

[puffon]

.........and why does squeezing and/or strumming the coil, eliminate the hot legs?
why does a proper coil glow from the center out?.............

 

[Mooch]

The points brought up earlier in the thread touch on that.
The center glows first because it's the point furthest from the heat-sinking effect of the posts and it's where the wraps are the most insulated by the other adjacent wraps.

Each point along the entire wire length is trying to heat up just as much as the other. But, the legs are connected to a comparatively huge chunk of metal that sinks the heat away, preventing the temperature from rising as far as it could. The center wraps don't try to heat up any more than the outside wraps do but since the center wraps are essentially insulated (by the nearby other wraps) they can warm up easier than the outside wrap. Since the outside wraps are the closet to the cooler legs, they still have some of their heat pulled away. This means that they heat up slower than the center wraps.