Basics for building your own Box Mod
In this section I teach you some basic knowledge you should have, if you want to learn how to build a Box Mod.
An electric cigarette is made of two main parts. You have the atomizer which is needed to create the vapor and you have the mod which contains the battery as well as the electronics (depending on the type of mod).
The Atomizer usually consists of a coil stuffed with cotton. The cotton is soaked with liquid. Once voltage is applied to the coil, it heats up and vaporizes the liquid in order to create the vape. You can either buy prebuild coils or buy just the wire and make your own coils. On this page though we are going to focus on the other half of the electric cigarette, the mod.
The mod houses the battery and according to the type of the mod sometimes even some electronics. The first step before you can start building your own mod would be to ask yourself what kind of mod you want to build. You can split it up into the following categories.
Types of Mods
They contain a chip with some safety features and furthermore they let you adjust the power by pressing a button or turning a knob. Often they also have a screen to display the power, battery life and more. There are different kinds of chips, but in most cases you do not have to worry too much about that, since they do all the control on the chip. Some Chips work with just one battery, while others (especially ones that can output a high power) need a higher voltage and therefor you need to use multiple batteries in series to increase the voltage (more about this topic down below)
The circuit in such a mod is closed all mechanically, for example with copper plates that touch each other. They usually are shaped like a tube (tube mod) or like a box (box mod). The power output of your electric cigarette is determined by the voltage of the battery (usually 4.2V when fully charged) and the resistance of your coil (the lower the resistance, the higher the current and therefore more power). See below for more information how to calculate the power of your e-cigarette.
They are similar to mechanical mods in terms of the fact that the power is determined by the resistance of the coil. But in contrast they do not use copper contacts or similar, you can use pretty much any switch you want. Unfortunately most switches can’t handle the high current the batteries can provide, therefor you need a MOSFET which basically is a Transistor, which again is similar to a relay. If you are not familiar with the functionality of either of this components, all of them use a weak signal to control higher current or voltage. Simplified: you use a weak, harmless signal to switch a higher voltage or current. Additionally you can also add a switch in series to the button to completely turn off the mod. The schematics for a semi-mechanical mod can be found at the end of this page.
What kind of mod do you want to build? If you want to adjust the power with a chip, you have to build a regulated mod. Otherwise it is up to you whether you build a mechanical or semi-mechanical mod. If you use a Semi-Mechanical or purely mechanical mod, you need to make sure that the battery voltage does not drop below 3V (better 3.5V). Since there is no battery protection in such a mod, you could discharge the battery all the way down, which can destroy the battery. Once the battery voltage drops, you will notice a decrease in power. After some time you should be able to tell when the battery is empty and you need to recharge it.
Types and amount of batteries:
The most common sized batteries are 18650s (18mm wide and 65mm high). There are also smaller (18350) and bigger (20700, 21700, 26650 etc.) sizes available, but they are not as common.
How much power do you need? If 75W or a bit more is enough for you, you are fine by using just one high drain 18650 battery (e.g. Sony VTC5—- link amazon). If you need even more power, you should either use a bigger form factor (20700, 21700 or 26650) or use multiple batteries. More about using multiple batteries in the next section.
In addition to these cylindrical shaped, removable batteries, there are also LiPo-Batteries available which can handle even more power, but are a bit more difficult and dangerous to handle and therefor I would not recommend them to a beginner.
Series vs. Parallel
If you decide to use more than one battery, you have multiple options to wire them:
- In Parallel: In this case the battery voltage stays the same, but the load splits to both batteries, which allows you to use a coil with lower resistance and therefor have
- In Series: In this case the voltage of both batteries together doubles. By doubling the voltage, the output power will quadruple if you use the same resistance of the coil.
To calculate the power we need some basic knowledge about physics, but don’t be afraid, these formulas are not that complex. If you do now want to do the math yourself, there is also a calculator at the end of this page, but I would recommend to at least read the section about how all these units go together.
U = R * I -> I = U/R -> R = U/I
These formula are important to find out how high the current will be. You have to make sure this is within the limits of your battery (e.g. 30A for the Sony VTC5)
A fully charged battery has a voltage of 4.2V. If your battery allows a maximum current of 30A we come to following conclusion: R = 4.2V/30A = 0.14Ω
The lowest resistance your coil should be, to be safe in this case is 0.14Ω
Now the next formula we will need: P = U * I -> P = U/R²
A resistance of 0.14Ω with a fully charged battery at 4.2V results in a (theoretical) power of 4.2V / (0.14Ω)²= 126W. (In reality it will be lower, since the voltage sags under loader)
If you use two batteries in parallel you will still have the same power, but you could use an even lower resistance to achieve a higher output power.
If you would use the same coil with 0.14Ω but double the voltage to 8.4V by connecting two batteries in series, the output power would quadruple!
P = 8.4V / (0.14Ω)²
This would be 504W! The battery would not be able to output such a high power and this would not be safe at all. So make sure to use a much higher resistance when you use batteries in series.
To make the calculation a bit easier you can also use this calculator to do the math for you:
You made it all the way down here on this page? Seems like you are really interested in making your own mod. Check out my free build plans to get some inspiration, how your first mod could look like: