Over the few years I've been building coils, my "typical" or "go-to" build has changed many times. Sometimes it was basic single strand dual coils, other times it was twisted single or dual coils, or single or dual Clapton coils, or single or dual fused / twisted core Clapton coils. While I have (and still do) experiment with more exotic coils, they have never become an everyday thing, just something to try every now and then.
Lately I've been experimenting with twisted coils using more than two strands of wire, and the results have been rather remarkable.
Let's examine the numbers. I take long drags and thus prefer a fairly cool vape, so these numbers are for a low heat flux of 150 mW/mm². But since heat flux scales linearly, the comparison is still valid, even if you like a much hotter vape.
Building for equal resistance and similar wraps:
2-strand 24 gauge twisted dual coil, 3 mm @ 0.25 ohms (7/6 wrap)
Heat capacity per coil: 188.82 mJ/K
150 mW/mm² heat flux: 136 watts
4-strand 28 gauge twisted dual coil, 3 mm @ 0.25 ohms (8/7 wrap)
Heat capacity per coil: 118.15 mJ/K
150 mW/mm² heat flux: 135 watts
Both have the same resistance, same heat flux, and similar total wire length (just +1 wrap on the 4-strand 28 gauge twisted coils). Yet the 4-strand twisted coil's heat capacity is dramatically lower, almost 40%.
Building for equal heat capacity and equal wraps:
2-strand 24 gauge twisted dual coil, 3 mm @ 0.20 ohms (6/5 wrap)
Heat capacity per coil: 151.05 mJ/K
150 mW/mm² heat flux: 109 watts
4-strand 26 gauge twisted dual coil, 3 mm @ 0.13 ohms (6/5 wrap)
Heat capacity per coil: 155.34 mJ/K
150 mW/mm² heat flux: 141 watts
Both have the same heat capacity and the same total wire length. Yet the 4-strand twisted coil can handle a 30% higher wattage with the same heat flux.
So what does all this mean?
Building coils is a balancing act. In order to support higher wattage without getting too hot, you need to minimize heat flux. But this usually requires more wire mass with a higher heat capacity, causing a longer ramp-up time, often even with the higher wattage being taken into consideration.
A higher strand count twisted coil seems to somehow get around this particular issue. For the same heat capacity, they have a lower heat flux, allowing a higher wattage without being a hotter vape. And for the same heat flux, they have a lower heat capacity, allowing a quicker ramp-up at the same wattage, also without being a hotter vape.
And the coils have more nooks and crannies compared to a standard 2-strand twisted coil, which helps with wicking. In fact, if instead of twisting all four strands at once, and you build a chain coil by twisting 2 strands normally, then twisting that wire in the opposite direction, you end up with a complex twist which looks like interlocking links in a long chain (hence the name "chain coil"). It wicks juice so well that it can even be used as a wickless coil – it will hold several drops of juice by itself without needing any cotton, enough for a couple of pulls before drying out. While not at all convenient for normal use (since you would have to re-drip every two or three hits), this is incredibly useful for rapidly testing juices if you mix your own. A quick dry burn and you can try a new flavor without any of the old flavor lingering.
Of course nothing in this world is perfect, so there are drawbacks to these types of builds. The obvious one is the quantity of wire required. Depending on how tightly you twist it, you will need about 5–7 times the length of wire than for an untwisted build, and more than twice as much than for a standard 2-strand twisted build. But if you're an experienced builder, you are already buying wire in 100+ foot spools for cheap, so you'll be just fine. And if you're still buying wire in overpriced short lengths, then stop! 100-foot spools can be purchased for not much more than what a lot of places charge for 3–5 foot lengths.
But the other major drawback is springiness. A 4-strand twisted build is quite a bit more springy than a 2-strand build of similar final diameter. And while you can get even more of the benefits (lower heat flux or heat capacity) by twisting more than four strands of a thinner-gauge wire, a 6-strand coil, and especially an 8-strand coil, is excessively springy and difficult to work with. Torching the twisted wire before coiling it does help, but a 4-strand twisted build is about the practical limit. Maybe a 6-strand twisted build will work for you (for this, I would recommend the chain coil technique, with three strands twisted in one direction, then twisted itself in the opposite direction), but four strands is what I will be sticking with for my builds.
There is still a lot of things that can be done with "just" four strands though. You can make a staged-heating version, twisting together two lengths of twisted wire of different gauges. Or take a 3-strand twisted wire and twist that with a single strand of a thicker wire. Varying how tightly you twist each section of wire can change the final twist "pattern" quite a bit. And that's just round wire – throw in some ribbon wire and that opens up even more possibilities.
I actually prefer the performance of a 4-strand chain coil over Clapton coils, and they are quicker and easier to build, especially if you haven't quite been able to master the finesse required for making Clapton wire. They can handle surprisingly high wattages without getting too hot, and their self-wicking ability is at least as good as Claptons, if not even better.
For someone who wants to move beyond basic twisted or parallel builds, multi-strand twisted coils are an excellent option with lots of potential. The only drawbacks are the lengths of wire required, and the springiness, but torching the twisted wire before you coil it will definitely help. But it's not really that bad at all if you stick to four strands, even without pre-torching.
Lately I've been experimenting with twisted coils using more than two strands of wire, and the results have been rather remarkable.
Let's examine the numbers. I take long drags and thus prefer a fairly cool vape, so these numbers are for a low heat flux of 150 mW/mm². But since heat flux scales linearly, the comparison is still valid, even if you like a much hotter vape.
Building for equal resistance and similar wraps:
2-strand 24 gauge twisted dual coil, 3 mm @ 0.25 ohms (7/6 wrap)
Heat capacity per coil: 188.82 mJ/K
150 mW/mm² heat flux: 136 watts
4-strand 28 gauge twisted dual coil, 3 mm @ 0.25 ohms (8/7 wrap)
Heat capacity per coil: 118.15 mJ/K
150 mW/mm² heat flux: 135 watts
Both have the same resistance, same heat flux, and similar total wire length (just +1 wrap on the 4-strand 28 gauge twisted coils). Yet the 4-strand twisted coil's heat capacity is dramatically lower, almost 40%.
Building for equal heat capacity and equal wraps:
2-strand 24 gauge twisted dual coil, 3 mm @ 0.20 ohms (6/5 wrap)
Heat capacity per coil: 151.05 mJ/K
150 mW/mm² heat flux: 109 watts
4-strand 26 gauge twisted dual coil, 3 mm @ 0.13 ohms (6/5 wrap)
Heat capacity per coil: 155.34 mJ/K
150 mW/mm² heat flux: 141 watts
Both have the same heat capacity and the same total wire length. Yet the 4-strand twisted coil can handle a 30% higher wattage with the same heat flux.
So what does all this mean?
Building coils is a balancing act. In order to support higher wattage without getting too hot, you need to minimize heat flux. But this usually requires more wire mass with a higher heat capacity, causing a longer ramp-up time, often even with the higher wattage being taken into consideration.
A higher strand count twisted coil seems to somehow get around this particular issue. For the same heat capacity, they have a lower heat flux, allowing a higher wattage without being a hotter vape. And for the same heat flux, they have a lower heat capacity, allowing a quicker ramp-up at the same wattage, also without being a hotter vape.
And the coils have more nooks and crannies compared to a standard 2-strand twisted coil, which helps with wicking. In fact, if instead of twisting all four strands at once, and you build a chain coil by twisting 2 strands normally, then twisting that wire in the opposite direction, you end up with a complex twist which looks like interlocking links in a long chain (hence the name "chain coil"). It wicks juice so well that it can even be used as a wickless coil – it will hold several drops of juice by itself without needing any cotton, enough for a couple of pulls before drying out. While not at all convenient for normal use (since you would have to re-drip every two or three hits), this is incredibly useful for rapidly testing juices if you mix your own. A quick dry burn and you can try a new flavor without any of the old flavor lingering.
Of course nothing in this world is perfect, so there are drawbacks to these types of builds. The obvious one is the quantity of wire required. Depending on how tightly you twist it, you will need about 5–7 times the length of wire than for an untwisted build, and more than twice as much than for a standard 2-strand twisted build. But if you're an experienced builder, you are already buying wire in 100+ foot spools for cheap, so you'll be just fine. And if you're still buying wire in overpriced short lengths, then stop! 100-foot spools can be purchased for not much more than what a lot of places charge for 3–5 foot lengths.
But the other major drawback is springiness. A 4-strand twisted build is quite a bit more springy than a 2-strand build of similar final diameter. And while you can get even more of the benefits (lower heat flux or heat capacity) by twisting more than four strands of a thinner-gauge wire, a 6-strand coil, and especially an 8-strand coil, is excessively springy and difficult to work with. Torching the twisted wire before coiling it does help, but a 4-strand twisted build is about the practical limit. Maybe a 6-strand twisted build will work for you (for this, I would recommend the chain coil technique, with three strands twisted in one direction, then twisted itself in the opposite direction), but four strands is what I will be sticking with for my builds.
There is still a lot of things that can be done with "just" four strands though. You can make a staged-heating version, twisting together two lengths of twisted wire of different gauges. Or take a 3-strand twisted wire and twist that with a single strand of a thicker wire. Varying how tightly you twist each section of wire can change the final twist "pattern" quite a bit. And that's just round wire – throw in some ribbon wire and that opens up even more possibilities.
I actually prefer the performance of a 4-strand chain coil over Clapton coils, and they are quicker and easier to build, especially if you haven't quite been able to master the finesse required for making Clapton wire. They can handle surprisingly high wattages without getting too hot, and their self-wicking ability is at least as good as Claptons, if not even better.
For someone who wants to move beyond basic twisted or parallel builds, multi-strand twisted coils are an excellent option with lots of potential. The only drawbacks are the lengths of wire required, and the springiness, but torching the twisted wire before you coil it will definitely help. But it's not really that bad at all if you stick to four strands, even without pre-torching.
