a quick question on this topic, and i'm hoping someone can help me here...
why would a dual coil cartomozer be beneficial? i tried them, at low and standard res., and the vapor prod/flavor doesn't come close to a standard or 3 ohm single coil carto. plus, as a previous poster stated, it uses more juice and battery life. maybe i'm missing something, but i don't see why they would be a better choice over single coil cartos if you're using variable voltage/wattage. can someone please 'splain?
I'm not sure of the real reason manufactures started making them, perhaps they just were trying to cheat and get a lot more power by throwing 2 coils in there, but didn't realize that a lot of people wouldn't have devices with enough power to truly take advantage of them.
The only logical reason I can think of for using a DC is to increase vapor output with high power vaping. You can only increase the heat of a single coil so much before you stop increasing vapor production. Think of it like a pot of boiling water on the stove. Water boils at a certain temperature, increasing the heat pumped into the pot will increase the speed at which the water boils, which will vaporize slightly more water.
But if instead of just increasing the heat to the pot, you add another burner and pot all together, this will literally double the amount of water being boiled/vaporized. Same thing goes with vaping juice, increasing the power of the coil only works to a certain extent to increase vapor production, after that point all you are doing is getting a hotter vape, and eventually burning juice.
But having two coils being powered, you double the surface area that is vaporizing juice. If your goal is to increase the amount of vapor, then it's all about surface area, more than it is just temperature. Instead of having two coils, you could also just use a much longer coil, or thicker wire, which will have the same effect of increasing surface area, and increased vapor production, assuming you keep the coil at the same temperature. The amount of voltage that a carto needs/can handle is NOT solely dependent on the resistance of the carto. Coil design has a big part to play in how much voltage to put into it, as a coil with the same resistance, but more surface area will require more voltage, and handle more voltage, even though the resistance is the same. A 2ohm coil might burn at 5 volts, but you could have a differently design coil that is also 2ohms, but doesn't burn until 8 volts. Yet another reason that having "suggested voltages" for certain resistances is meaningless.
You could build a 15 wrap coil, for example, which would increase resistance, but then you could use thicker wire for this coil in order to bring the resistance back down. So this 15wrap coil could be the same resistance as a coil made with 3 wraps of thin wire, but have five or six times the surface area, which is what will cause a huge increase in vapor production. Using two coils is just a different method to achieve the same goal, more surface area.
I don't know why this issue isn't addressed more by manufacturers, instead of selling dual coil cartos they should offer cartos with different surface area coils. Use a longer coil with more wraps, but with much thicker wire, will give you the same resistance but way more surface area. But, just like with dual coils, you still need to increase the power, because you'd have the same amount of power being spread over a larger surface area, which would mean loosing temperature. More power will get the temp back up. The best coil design for vapor production really depends on what you plan to power your coil with. If you are using an eGo battery, with a fixed voltage, using less surface area will be better, because the battery won't have enough power to take advantage of the increased surface area, and would perform worse with a higher surface area coil.
But with a VV/VW device, or any device that can provide a lot of power, higher surface area will work a lot better than simply adding more power to a coil with a lower surface area. If you are trying to build a water gun that shoots a powerful stream that goes a long distance, you need to take into account how much pressure you can supply to your water gun. If you can't supply much pressure (power to the coil) then you need to make the nozzle much smaller diameter to still maintain a fast flowing stream. But if you can supply a lot of pressure to the water gun, then you can make a bigger nozzle which will still shoot water out far and fast. But if you tried to use that larger nozzle on the water gun with less pressure, then your water stream would be terrible because it doesn't have enough pressure to take advantage of the additional water flow of the larger nozzle.
Using a dual coil carto on low powered devices is like having a large nozzle on your watergun, but without enough pressure to force enough water through at once. So performance suffers. You need to match the nozzle size to how much pressure you can supply, just like you need to match a carto design to what you plan to power it with, and it's not JUST ohms law that you need to take into account, because if ohms law is all you think about then you'll get confused when it comes to dual coil cartos, thinking that you are overpowering them when your not even powering them enough.
Trust me. 
