You must consider how many WATTS your atty is using, of course, at a lower atty resistance, you will need a lower voltage.
I am using a 3-ohm (approx) 801 carto (MV says they are 2.5 ohms, but my meter says 3.2) at 4.7V gives you
(4.7*4.7) / 3.2 = 6.9 watts
Now, with a 2.5 ohm carto, it would be more like
(4.7*4.7) / 2.5 = 8.8 watts (too hot in my opinion,so less voltage is required)
Or let's do a 3 ohm at 5 volts:
(5*5) / 3 = 8.333 watts
See, it's a problem you can use your calculator to solve. You just need to pick your target power (watts) and calculate your ideal voltage based on the resistance of the atty / carto. You can search the forums to see how many watts people prefer, for my favorite it's about 7 watts, others like 8 watts or ??? It's a matter of personal preference.
Why do I need a variable voltage at all? I can use an LM350T volt regulator and fixed resistors to set it to any voltage I want!
Well, the answer is so you can match your voltage to the resistance of your current load (atty/carto) once you find your "sweet spot" wattage (which is the actual work done by the device).
Hope I haven't muddied the water even more
Edit ... Moved from Madvapes thread
