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Often people seems to be somewhat confused about how battery drain is calculated, so here is a short summary.
But first: There are two main types of mods: Regulated, and unregulated (mechanical). Putting a Kick in a mech mod automagically makes it a regulated mod.
We will start with the simplest type, and then use a little more time on the more complex type.
Unregulated (mech) mods are very simple. They have one circuit. This circuit can be easily modelled using Ohms law. In other words, if you have a basic understanding of Ohm's law, that is all it takes.
The battery drain is determined by two factors:
There is not much more to mech mods. The circuit is about as simple as a circuit can get. The voltage hitting the atomizer is the voltage from the battery (minus the tiny voltage lost in the switch and conductors). The current flowing through the battery is the current flowing through the atomizer. A multimeter and some straightforward use of Ohm's law you will give you all the numbers you need.
- The resistance of the atomizer, which is more or less constant after you have built your coil(s).
- The voltage of the battery, which gets lower as the battery drains. Using a single battery, it starts at 4.2V or 4.1V, and sinks a volt or less (measured under load) before the battery needs to be recharged.
Regulated mods are not as simple as mechs, and not so easy to model. But even though they are much more complex than mechs, with some selective simplification we can ignore most of the complexity.
So let us break these mods down into two circuits and a black box. This makes our regulated mod model little more than twice as complex as our mech mod model.
The two main circuits of a regulated mod, is the battery side, and the atomizer side, and never the twain shall meet. The regulator circuit takes care of that. The regulator can have lots of more or less advanced circuits in itself, and they all use a little bit of power, but for the most part we can envision it as a black box separating the battery circuit from the atty circuit.
On the atomizer side, the voltage is (ideally) whatever the user has selected, but take note that some APVs promise more than they keep: Unless you know that your APV is accurate, you should probably measure and confirm the output voltage.
Variable wattage devices simply measure the atomizer resistance, and uses this measurement and Ohm's law to calculate what voltage to set.
When you know the voltage and resistance, you can calculate the current and power.
On the battery side, the voltage is whatever the battery has in it at the moment (just like with mech mods). The power is whatever the regulator needs to pull in order to produce the desired voltage in the atomizer. And the current is the power divided by the ever-decreasing battery voltage.
Since we are looking at two separate circuits, you can never mix numbers from both sides of the regulator in your calculations. For instance: You cannot determine the current drained from the battery by measuring the resistance of the coil and the voltage of the battery. Using the current from one circuit, and the voltage from a different circuit, will result in a nonsensical answer. Nor can you determine the current going through the coil by determining the current from the battery. They are two different circuits. The regulator makes sure of that.
But not all hope is lost. There is one way to "transfer" information from one side of the regulator to the other. The trick is simple: Use the power (wattage).
The power hitting the atomizer equals the power flowing from the battery, minus the power lost in (or used by) the regulator circuit.
The efficiency of these regulator circuits are typically between 80-95%. In practice this means that the regulator "steals" about a tenth of the power between the battery and the atomizer.
Knowing this, we can use our multimeter and Ohm's law to calculate what is going on at either side of the regulator. Then we can convert it to watts, and voila! Subtracting (or adding) the loss in the regulator circuit, we now know the watts on the other side as well.
So we use Ohm's law again, break down the power to current and voltage, and that's that: Now we have all the numbers we need.
And that's it.
As you can see, there is no voodoo going on in regulated mods. And if there is, we just tuck it away in a black box and assign an efficiency percentage to it.
If you can use Ohms law once, you can use it twice. So now there is really nothing stopping you from figuring out what is going on in your mod, whether it's one of our future robotic overlords that you're vaping on, or a simple metal tube with a battery in it. Vape on, and vape safely!
Update: After I wrote this blog post, it occured to me that I could easily model this, so I made another calculator for you.
Here you go, the brand & spanking new battery drain calculator!