Im currently using a coil that has 1.8 ohms printed on the side of it, whats the difference between the numbers?
Ohms are the units of electrical resistance. Basically they measure how "hard" it is to "push" electricity through the coils. The higher the resistance, the harder it is to push through, and so fewer amps (and, consequently, fewer watts) will be delivered at the same voltage. Resistance (ohms), current (amps) and voltage (volts) are all related to each other by Ohm's Law:
Amps = Volts / Ohms
In a mechanical (unregulated) mod, the only part you have direct control over is the resistance, by building your coils (or choosing pre-made ones) at higher or lower ohms. Voltage is determined by the battery's charge and usually falls in the range of about 3.2-4.2v (the battery tops out around 4.2v at full charge, and by the time it gets down around 3.1-3.3v it's time to charge the battery or swap out with a fresh one), and the current (amperage) is a factor of the other two. The lower the resistance of your atomizer, the more current will be applied to it at any given voltage.
With a regulated device like your iStick, though, it's a different story. Another related quantity is power, measured in watts and is equal to Volts * Amps (or V^2 / R). A regulated mod has a chipset inside that will adjust ("regulate") the power based on user-selected settings. In this case, power into the chip = power out. The chip varies the input power by internally adjusting its resistance, which in turn varies the amp draw from the battery which, when combined with the battery's current voltage (that's current as in "right now, at this moment," not current as in amperage) determines the power (wattage) level.
So if, for example, your battery is currently sitting at 3.7 volts and you set the mod to 15 watts, then the chipset adjusts its resistance (ohms) to provide that amount of power. So it sets it resistance to roughly 0.91 ohms, which leads to an amp draw of 3.7/0.91 = 4.05 amps. This 4.05 amps, multiplied by the battery voltage (3.7 volts, remember) comes out to 14.985 watts (or exactly 15 watts, if the mod didn't round the numbers like I did.)
So, there are 15 watts being delivered to the chip. On the other side, there are still 15 watts coming out of it, but now this time the resistance is determined by the atomizer coil. So say you've got a 1.8 ohm coil, and we know that power (15 watts) is equal to voltage squared divided by resistance (1.8 ohms); now we have an equation that we can solve for x (or in this case, v):
15 = v^2 / 1.8
15 * 1.8 = v^2
27 = v^2
sqrt(27) = v
So the voltage applied to the atomizer in this case is sqrt(27) or about 5.19 volts. So unlike a mechanical mod, where lower resistance results in increased power, in a regulated mod, lower resistance simply leads to less voltage being applied to deliver the specified power level.
Of course there are many factors that go into determining the resistance of a coil. Okay, maybe not "many" but at least two. Resistance is directly proportional to the length of the wire, and
inversely proportional to its cross-section (thickness), so you can have a long, thick wire with the exact same resistance as a shorter, thinner wire. So even though they have the same resistance, and therefore the same power applied at a certain voltage, the vape experience could be quite different between the two coils. But
in general, a lower resistance will allow you to use more power for a fuller, warmer vape, as long as the device you're using, and the battery that's powering it, are up to the task.
