welp, i know i'm going to take some heat from both sides for saying this...
while i disagree with dr g's approach, i agree completely with the substance of his statements (quick disclaimer - i am an engineer, so i apologize in advance if this gets too heavy on the technical side...):
first, sub-ohm vaping isn't inherently any more dangerous than anything else, lack of knowledge is what's dangerous. for example, i use 0.5 ohm coils on my dripper. on a fully-charged battery at 4.2 volts, i'm running 8.4 amps, so i only use batteries rated for 10 amps continuous discharge or higher. i'm well within the spec, but regardless, i test fire the battery before vaping, and check regularly to make sure it's not getting hot.
i like to use 18350's for my genny. the 18350's are rated at 6 amps continuous, so i wrap my coils at .8 ohms or higher, which gives me a max draw of 5.25 amps at full charge. again, battery is fine, no heating, etc.
of course, both scenarios are assuming that the only load is the atty and coil. the mod will add a little bit more resistance, as will the battery itself, both of which will lower the current draw, but i prefer to leave those out of the calculation as a factor of safety.
next, regarding vv mods, let's assume you're vaping a 3 ohm carto at 6 volts on your provari. this would yield an even 12 watts of power. your battery doesn't care at what voltage your provari is set, it only knows that it needs to provide 12 watts to your coil (plus a little extra to power the electronics). for a fully charged battery, you will need to pull about 2.9 amps, meaning the circuitry in your provari is acting as a 1.4 ohm load as far as your battery is concerned.
but, what about when your battery is almost dead (3.3v)? in order to put out this same 12 watts, the provari needs to pull 3.6 amps from the battery (this has nothing to do with the 3.5 amp output limit of the circuitry). in order to do this, the circuitry needs to act as a 0.9 ohm coil, so as far as your battery is concerned, you're sub-ohming.
this isn't even the limit - if you have a provari v2, it is guaranteed to be capable of an output of 14.5 watts. in order to achieve this on a battery with 3.3 volts left, you need to pull 4.4 amps, meaning the resistance of the circuitry adjusts to 0.75 ohms. now you're not only vaping at a lower resistance than my genesis, but you're doing it with a much weaker battery (i measure the charge left when i change batteries, and i'm very good about swapping them out when they get down to about 3.6 volts).
last point for the moment is regarding the temperature - does anyone happen to know how a rice cooker works? you basically just throw in rice and water, turn it on, and it somehow knows when to turn off, right? what's actually going on is there's a heater and a thermometer in the bottom, and the heater stays on as long as the thermometer reads around 212°F (the boiling point of water). liquid water can't physically exist at a higher temperature than this (it needs to become steam first), so as long as there's any liquid water in the rice cooker, it keeps the base at around 212°F as well. as soon as all the water has either been absorbed by the rice or boiled off, the temperature jumps, which tells the rice cooker to shut off.
similarly, eliquid can only exist at a certain temperature before it vaporizes, so as long as it's in contact with your coil, it will prevent the coil from heating up very much beyond this point (assuming you're not providing enough power to cause it to combust, which is almost impossible to do on a well-saturated wick without an external heat source, eg, a lighter). obviously, there are other factors that go into it - the outside of the coil, for example, also relies on air and vapor to help it stay cooler - but there just isn't enough room on a 28-32 gauge wire to have a huge temperature gradient.
whew, that was long, hopefully somebody reads it
