Coil consistancy

[macpeace]

So I have a few questions about coils on my KayfunLite +
I have noticed for a few month stretch I was able to 4/5 wrap with 32g and get right at 2ohms every time. That is right where I like it.
I ran out of wire and switched to some cheap stuff I got from ebay. Ever since my coils are all over the map.
So my question is....

Can changing wire brands effect ohms?
Does the amount of Ekowool affect ohms?
Does the tightness of the wrap effect ohms?

What are the factors that can cause differences?

Thanks very much

 

[dud3r]

From what I have gathered all of the above can have an effect on your resistance. Wire with different consistencies can and will. More ekowool would make your internal diameter of your coils bigger. Tightness would be the opposite.

This is all my opinion. I've actually never had anything other than temco spools. If I were you I'd grab a spool of temco in 30g and experiment with that kfl.

Sent from my SGH-M919 using Tapatalk

 

[numbskull]

Agree with dud3r, however, I have used 2 different brands- temco and lightning vapes (not sure where lightning vapes sources the kanthal from though, could be from temco also) and found both to be the same as far as consistency. I usually use 26g 6/7 wraps around a 3/32 drill bit wicked with cotton. That puts me around .84 ish(my sweet spot) Lightningvapes.com usually has competitive prices 100ft of 30g for about $5 a few cents less than temco in this example.

Anyways, hope this info helps!

Cheers!

 

[ScottP]

There are only two things that affect resistance. The resistance per inch of the wire and the length. So length x ohms/inch = total resistance. That said, if you build a coil by wrapping directly around a soft wick, so that your diameter varies then yes the resistance will vary due to using more or less wire for different diameter coils. It is also possible that some manufacturers are mass producing shoddy wire that does not have consistent specs. This is why I only buy wire from Temco and wrap all of my coils on something like a nail or drill bit so I know my diameters are going to be consistent.

 

[Topacka]

There are only two things that affect resistance. The resistance per inch of the wire and the length. So length x ohms/inch = total resistance. That said, if you build a coil by wrapping directly around a soft wick, so that your diameter varies then yes the resistance will vary due to using more or less wire for different diameter coils. It is also possible that some manufacturers are mass producing shoddy wire that does not have consistent specs. This is why I only buy wire from Temco and wrap all of my coils on something like a nail or drill bit so I know my diameters are going to be consistent.

You know, I've heard this a few times. But I've noticed that when I compress a coil, the ohms increase, sometimes by .3 or even .4 ohms. Any thoughts?

 

[rurwin]

That shouldn't happen. But if you mean you compress the coil by torching it then it may be that you oxidise its surface turning some of the metal into non-conductive oxide. Or I suppose it is possible you might change the crystal structure of the metal.

It is a well-known fact that coils increase in resistance with use, and they don't generally get much above 100C in service, so I'd probably go with the oxide theory.

 

[ScottP]

That shouldn't happen. But if you mean you compress the coil by torching it then it may be that you oxidise its surface turning some of the metal into non-conductive oxide. Or I suppose it is possible you might change the crystal structure of the metal.

It is a well-known fact that coils increase in resistance with use, and they don't generally get much above 100C in service, so I'd probably go with the oxide theory.

Oxidation it's part of it. The other part is also very likely due to warping at the molecular level. When something is heated it's molecules move faster (this is basically how a microwave works) they can rearrange themselves in a way that alters their resistance...slightly.

 

[Topacka]

That shouldn't happen. But if you mean you compress the coil by torching it then it may be that you oxidise its surface turning some of the metal into non-conductive oxide. Or I suppose it is possible you might change the crystal structure of the metal.

It is a well-known fact that coils increase in resistance with use, and they don't generally get much above 100C in service, so I'd probably go with the oxide theory.

I compress my coils by dry firing them and squeezing with tweezers. They don't raise in ohms from the heat, it's definitely the compression.

 

[ScottP]

One more thing it could be, if compressing it while mounted you could be slightly moving it so that the legs of the coil are getting moved thus increasing or decreasing the the electrical path through the coil.

Edit : This is probably going to be more noticeable building a BCC head. If by moving it, you change the point closest to the coil that the legs are touching their respective post then the length of the circuit will change slightly.

 

[Topacka]

One more thing it could be, if compressing it while mounted you could be slightly moving it so that the legs of the coil are getting moved thus increasing or decreasing the the electrical path through the coil.

Edit : This is probably going to be more noticeable building a BCC head. If by moving it, you change the point closest to the coil that the legs are touching their respective post then the length of the circuit will change slightly.

Food for thought most definitely.

 

[rurwin]

How many turns and what diameter are you using? VV devices use switched DC voltages, but they switch in the Hz or kHz region and I would not expect change in the impedance below 100MHz. Even then, compressing a coil has a fairly marginal effect.

I suppose it is possible that the device you are using measures current within nano-seconds (literally) of turning the voltage on, while the coil impedance may have an effect, but I would be mildly surprised.

Can you measure the resistance with a multimeter with the coil mounted? Do you see the same effect then?

 

[Topacka]

How many turns and what diameter are you using? VV devices use switched DC voltages, but they switch in the Hz or kHz region and I would not expect change in the impedance below 100MHz. Even then, compressing a coil has a fairly marginal effect.

I suppose it is possible that the device you are using measures current within nano-seconds (literally) of turning the voltage on, while the coil impedance may have an effect, but I would be mildly surprised.

Can you measure the resistance with a multimeter with the coil mounted? Do you see the same effect then?

I measure all my ohms with an ohm meter and then a multimeter, partly because I'd like to make sure my gear is staying calibrated and partly because it's engrained in me to "measure twice, cut once". I've noticed it when building dual coils on my helios, but that's the only rda I've ever built compressed micro coils on. It's not always that extreme of an increase, but it always does increase.

Edit: 28g kanthal, 6/7 wrap dual coil, ~1/16in screwdriver - 0.67ohms

 

[retired1]

Moved to Rebuildable Atomizer Systems

 

[dice57]

yes
yes
yes

One of the reasons I do micro coils is that the are easily repeatable for a consistent build and vape. Also only have to change out the wick every few weeks or so, dry burn the gunk off the coil, re-wick and the build is good for months at a time, or whenever I want to try something different, whichever comes first, usually it cause I want to try something, lol

 

[dice57]

There are only two things that affect resistance. The resistance per inch of the wire and the length. So length x ohms/inch = total resistance. That said, if you build a coil by wrapping directly around a soft wick, so that your diameter varies then yes the resistance will vary due to using more or less wire for different diameter coils. It is also possible that some manufacturers are mass producing shoddy wire that does not have consistent specs. This is why I only buy wire from Temco and wrap all of my coils on something like a nail or drill bit so I know my diameters are going to be consistent.

In theory yes, in practice, no. wrap a micro coil and mount it, measure ohms, you will get one reading, heat it up red hot and pinch it together to set the coil, then measure it again, you will get a different reading, usually slightly lower, now wick it, wick it good, lol, measure again, resistance will increase. Kay now juice it up, fire it up and measure again, yep it will decrease when at operating temperature. It will approach the measured un wicked value, but through the coil the wick does add up to .04 ohms, sometimes more, some times less depending on the ohms of your build, the length of the coil and the watts fired at. Measure the ohms while hot, allow to cool and you will see the value increase as the temperature drops. All this I have physically seen.

 

[ScottP]

In theory yes, in practice, no. wrap a micro coil and mount it, measure ohms, you will get one reading, heat it up red hot and pinch it together to set the coil, then measure it again, you will get a different reading, usually slightly lower, now wick it, wick it good, lol, measure again, resistance will increase. Kay now juice it up, fire it up and measure again, yep it will decrease when at operating temperature. It will approach the measured un wicked value, but through the coil the wick does add up to .04 ohms, sometimes more, some times less depending on the ohms of your build, the length of the coil and the watts fired at. Measure the ohms while hot, allow to cool and you will see the value increase as the temperature drops. All this I have physically seen.

I measure them using my SVD with only has 1 decimal place, but I have never seen a change to a coil once mounted, until it has been used for a while. Definitely nothing immediate from juicing and wicking.

 

[Christopherja]

I think anyone with any long-standing coiling experience under their belt can attest to the fact that certain factors other than length will have minute effects upon resistance readings - prolonged heat, coil "scrunching", etc.

But, of course, they are only minor effects - and, as in the rest idealised scientific practice, and for all practical purposes, resistance is a function of length (taking into consideration the resistance per inch, of course).

 

[macpeace]

Thank you for the suggestions.

 

[rurwin]

You asked:

What are the factors that can cause differences?

The first answer has been useful to you, and all the rest have been exactly on topic answering the same question. If some of the answers were too abstract for you, there's little anyone else can do about that. Compared to some threads, this one is refreshingly consistent.

There's a lot to be said for moving the thread too. Your question had been answered and several knowledgeable people were engaged with it. Posting first in General and then moving the thread in those circumstances makes sense to me.