Pros and cons of coil diameter please.
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Smaller diameter coil = less resistance (less wire being used)
Larger diameter coil = more resistance (more wire being used)
I haven't seen a pro or con yet of using different diameter coils of the same resistance. I just use 2-2.4mm coils because it's easier to wick for me.
Larger diameter coil = more resistance (more wire being used)
I haven't seen a pro or con yet of using different diameter coils of the same resistance. I just use 2-2.4mm coils because it's easier to wick for me.
I make my coil with a large inside diameter because I pull a double piece of Silica or cotton yarn through it (need the room)
Usually make a 1.5 - 2.0 ohm coil using 28 AWG Kanthal wound on a 7/64" (2.8mm) drill rod ..... Then feed it 10.5 watts of power.
Obviously, this wick is too long and will be cut shorter
BTW .... After you get tired of changing cotton wicks all the time, you might want to try silica .... Lasts a long time and can be dry burned (unlike cotton)
Usually make a 1.5 - 2.0 ohm coil using 28 AWG Kanthal wound on a 7/64" (2.8mm) drill rod ..... Then feed it 10.5 watts of power.
Obviously, this wick is too long and will be cut shorter
BTW .... After you get tired of changing cotton wicks all the time, you might want to try silica .... Lasts a long time and can be dry burned (unlike cotton)
I'm still learning about coils but normally build anything between 1.0 and 2.0ohm usually 2mm diameter in kayfuns on mech mods. Can anyone give me some basic pros and cons of changing diameter of coils. All hints and tips welcome. Please tell me which is better and why, don't just " I use".
The length and thickness of resistance wire are the only things that determine resistance... diameter and wrap count have no effect.
For a given wire gauge, length and resistance, say... a 1.3Ω coil, made from a 72.6mm long piece of 28 gauge Kanthal, wrapped on a 2mm mandrel for a wrap count of 9/8 with 4mm legs - will have a the exact same surface area (69.2mm²) as a coil made from the same length/gauge of wire, on a 3mm mandrel with a wrap count of 6/5.
The difference, for our purposes, is the exposure of juice to heat... sufficient to be vaporized.
The differences are... how the wick (and juice) is exposed to heat, and as you've determined vs. the relative ease of fitting wick into the larger ID coil... which is why I frequently use a 3/32" (2.4mm) mandrel myself, Raguvian. ;-)
The longer, smaller diameter coil - with a closer radial separation (the "walls" of the coil) - exposes the wick in the axial centerline to more heat (within a typical vaping draw time constant) than the shorter, smaller diameter coil, with a greater separation of those walls.
This is the reason micro coils (1/16" (1.59mm) ID or less) became so popular in the first place - juice held in the wick axial center is exposed to a higher temperature... the result of which is the vaporization of a larger volume of juice.
If there's a downside, it's that the smaller diameter wick may not have adequate capillary action to "refill" the wick-in-coil, before it overheats.
There are other variables... optimal wire gauge / resistance (desired heat flux) for a fixed wattage, or maximum Continuous Current Discharge (CCD) of an unregulated mod... but heat to juice volume in X time or draw length are what I consider when those other variables are attended to.
Nice reply State. I understand the basics of the ohm/resistance of the coils and that I can change it with the awg of wire used and the amount of wraps. You have tried to explained the difference between large and small diameter coils which is the part I wanted. Too small could reduce the flow of juice and basically strangle the wick or make it to hot for my preference, where as an over large coil could take too long to get to the temperature needed to vaperise the juice.
So far I've only built coils 2mm and 1.6mm dia and found that the smaller wick burns out quicker but I do normally vape my rta till it's empty.
So far I've only built coils 2mm and 1.6mm dia and found that the smaller wick burns out quicker but I do normally vape my rta till it's empty.
The coil inner diameter determines how much wick will be inside the coil, and that determines how much juice is available to the coil. For wick sensitive devices (like kayfuns) it also determines how much wicking material is available to assist in feeding juice to the coil and preventing juice from leaking. Too small of a diameter here can lead to insufficient wick material to prevent leaking.
I have found that a good rule of thumb is that for a device that relies on wicking to deliver juice to the coil from a well or tank, the coil length should be no more than 1.25 to 1.5 times the coil diameter. (I wick with rayon, YMMV). For devices that rely on wicking as a reservoir (drippers) this is not a critical dimension and coil diameter should instead be determined by the design of the atty (physical size constraints) and the way you use it. Longer lung hits require more juice in the coil (and therefore a larger diameter) than shorter mouth to lung hits.
I have also found that for best results with kayfun like devices that the neither the coil inner diameter nor the coil length should grossly exceed the diameter of the air channel.
I have found that a good rule of thumb is that for a device that relies on wicking to deliver juice to the coil from a well or tank, the coil length should be no more than 1.25 to 1.5 times the coil diameter. (I wick with rayon, YMMV). For devices that rely on wicking as a reservoir (drippers) this is not a critical dimension and coil diameter should instead be determined by the design of the atty (physical size constraints) and the way you use it. Longer lung hits require more juice in the coil (and therefore a larger diameter) than shorter mouth to lung hits.
I have also found that for best results with kayfun like devices that the neither the coil inner diameter nor the coil length should grossly exceed the diameter of the air channel.
An over large diameter of the same resistance and gauge would not take longer to heat up.
The biggest diameter coil you can make is a 1 wrap ----- that's basically the problem right there.
a 1 wrap coil is impractical.
the other extreme is a very long wrap coil - I think nobody wraps 20 wraps for example ... the long long coil gets wicking problems.
'edyle' is absolutely correct. With coils made of the same wire gauge, length and resistance... ID and wrap count have no effect on "heat capacity" (also called "lag" or "dwell" time).
Two things control lag time... wattage and wire thickness. Of the same resistance, thicker wire requires a higher wattage than thinner wire, to produce the same heat flux value.
A random example - A 1.0Ω 25 gauge coil requires 56 watts to provide a heat flux value of 350 mW/mm²... while a 1.0Ω 29 gauge coil requires only 13.93 watts to produce the same heat flux value. (heat flux is a measurement of radiant heat in milliwatts per square millimeter)
Very interesting, and thanks for the info.
In general ... Are these folks that use a low sub-ohm coil made with heavy wire that require 50 watts of power really getting a better vape than some guy that makes a 1.7 ohm coil from 28 AWG wire and feeds it 11 watts of power?
Well, Fit... lets run some numbers through good 'ol Steam Engine.
28 gauge, 1.7Ω at 110 watts would be a "cool" heat flux (HF) of 115 mW/mm². To bump that to a mW/mm² value in the, say... 300 range, you'd need about 29 or more watts. Not too bad, and a good build for someone with a KFL and a 30 watt mod.
Deep sub-ohm... lets try a 22 gauge, dual parallel build at 0.3Ω. We need 164 watts to run 300 mW/mm²... not the most efficient way to obtain 300 mW/mm², because if we up the gauge to 24, we need only 82 watts for 300 mW/mm².
Does that mean 22 gauge sucks? Nope... but we need to go to a lower resistance to make it worthwhile. At 0.15Ω, that same 82 watts will provide 300mW/mm² with 22 gauge.
Let's go the other way. Say you have a MVP2 (11 watts max)... can we get decent heat out of that, with maybe 32 gauge?
A 2.6Ω single coil at 11 watts... 300 mW/mm², again.
None of the above take into account "heat capacity" (HC) - the coil/mods ability to gain and lose heat. In other words, the higher the HC value... the slower to heat, slow to cool down.
Adjustments to keep the HC, desired HF, available (or desired / limited to - with an APV) wattage, desired net resistance and surface area - just a semi-complicated balancing act to obtain the... "perfect vape". ;-)
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Not to go against the grain here, but a larger diameter coil of the same resistance/power/gauge will have more wick inside the coil, which means more juice to heat up, so shouldn't that effect ramp up time? The juice acts as somewhat of a heat-sink for the coil, and more juice would be able to absorb more heat.
It would seem having the same amount of power acting upon a larger mass of juice would in theory increase heat up time, as it would take more time to heat up that additional juice. Kind of like having a pot on the stove, it takes longer to heat up a full pot vs a half-full pot because the additional water takes more time to heat.
While I haven't done any extensive and specific testing related to this, I've toyed around with coil diameters on the same attys, with the same wire at the same resistance and the larger coils always seemed to give a cooler vape until a few hits in when everything heats up so I'm trying to figure out where this discrepancy comes from.
This is getting very technical now but I do seem to think the same way as you Uncle Chuck.
Hi Chuck,
You're not going against the grain... just adding in more variables, which I referenced in post #4, and omitted, for clarity, in post #11. Wick type and density, capillary action and juice blend (viscosity) are all additional variables the effect heat capacity and/or heat flux.
If one were to sit and write down every performance variable and it's effect... you'd have a long list of: "makes it (the coil(s) warmer - makes it cooler" - "makes it heat faster - or slower" etc etc.
I'd say the possible combinations, given all the choices, are infinite, but only because I've not taken the time to calculate them all. ;-)
In the end, we choose which variables are of value to us, what to control... and to what extent we control them at the exclusion of others.
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No problem Miata.
Like many, I started using Dampmaskin's Steam Engine modelling calculator in February of last year, when it was originally called "Vape Calc", and it didn't have all the great features that Dampmaskin has added to it over time.
I focused mostly on modelling coil builds, and didn't pay much attention to things like heat flux and capacity... my primary concern was surface area for a wire gauge at a desired resistance. Desired resistance being what ever a particular mech battery would tolerate... without setting my mustache on fire.
Over time, I started playing with heat flux wattage values ("hey, look at this shiz - I can change the f'ing watt value!")... and figuring out the various wattage outputs for mech batteries, with a particular resistance drain - and then how wire gauge dramatically effected those heat flux values.
Like anything, it was a learning curve, and the only reason I'm fairly well versed on these variables is from the hours of time spent "playing" with the programe.
Still, one has to keep in mind that, were it not for Dampmaskin's efforts... it's likely that only a small handful of people (read - electrical engineers/theorists) would ever have a decent understanding of all the variables associated with a "simple" resistive heating coil.
Well I think I'm roughly at the same point you were last February if not a bit before. I know how to change the resistance of my coils to suit the batteries for safety etc, I'm only using 28awg at the moment. So I'm really grateful that people you, State, are willing to put your time in here and try and steer us in the right direction and save us time going in the wrong direction. Cheers.
State O' Flux -
First, let me just say this: you're, like, smart 'n' stuff
Second, I'm curious to hear what your experience has been with the effect of surface area (specifically twisted wire) on vapor production and flavor. I've heard a number of people say that twisting wire provides better surface area and better flavor as a byproduct. Thoughts?
Thx,
Mike
First, let me just say this: you're, like, smart 'n' stuff
Second, I'm curious to hear what your experience has been with the effect of surface area (specifically twisted wire) on vapor production and flavor. I've heard a number of people say that twisting wire provides better surface area and better flavor as a byproduct. Thoughts?
Thx,
Mike
I think, if you're anything like me, Davan... that you'll end up with a selection of wire as thick as 20 gauge and as thin as 30.Well I think I'm roughly at the same point you were last February if not a bit before. I know how to change the resistance of my coils to suit the batteries for safety etc, I'm only using 28awg at the moment. So I'm really grateful that people you, State, are willing to put your time in here and try and steer us in the right direction and save us time going in the wrong direction. Cheers.
Although I'm fairly happy with my mechs, my neighbor - who buys every new thing that comes out - got one of those nutball 260 watt APVs, and as he has fine motor skill issues, I build his attys. 250 watts to a 0.15Ω dual parallel makes for a warm, bordering on too warm (458 mW/mm²)... juice eater. ;-)
Honest Mike, I'm about as dumb as a monkey on a rock.State O' Flux -
First, let me just say this: you're, like, smart 'n' stuff
Second, I'm curious to hear what your experience has been with the effect of surface area (specifically twisted wire) on vapor production and flavor. I've heard a number of people say that twisting wire provides better surface area and better flavor as a byproduct. Thoughts?
Thx,
Mike
I really can't help you out with twisted (or parallel wire) coils, Mike... I played with both for awhile and in all honesty, I didn't see that impressive of a reward to effort ratio. ;-)
There are lots of folks who swear by twisted... but I'm afraid I'm not one of them. Perhaps I prefer the "KISS" way of things.
If you click on the "Advanced" box in the upper left/center of SE, you'll open a coil and wire "dimensions" box that includes surface area... among other things. Play around with it and see what you come up with.
Oh... I wrote a Steam Engine users guide, for those having troubles with some features. I don't know if you'd get anything useful from it, but here it is.
Honest Mike, I'm about as dumb as a monkey on a rock.
I sincerely doubt that, but if you insist does that make the rest of us the rocks???
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