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Ohm’s Law: A Brief Guide for Vapers

Vapers who use mods have a lot of new terminology to learn. With people throwing out words like watts, ohms, amps and volts as if they’re common knowledge and talking about things like Ohm’s law that you’re lucky if you remember from high school physics, feeling overwhelmed by it all is pretty common. But the good news is that it doesn’t take long to get up to speed with the basics you’ll need to safely and effectively work your mod. So here’s a brief guide to everything you need to know to get started with your VW or mechanical mod.

 

Watts, Volts, Amps and Ohms: What Do They Mean?

 

The first thing you need to know is what all of the key terms used in Ohm’s law actually mean. You might have an idea about volts and watts already, but these simple definitions should tell you what you need to know.

 

  • Volts: Volts are a measure of the electrical potential between two points. In a battery, for example, there is one end with positive charge and one end with negative charge. The difference between charge at these two ends means that if you connect them using a wire, current will flow down the wire. The voltage tells you how big the charge difference is and therefore how big the current will be. More volts give your vaping device a bigger “push” to get the current going.
  • Amps: Amps are a measure of electrical current. In the same way that you call running water a current, an electrical current is a flow of electrons through a wire or conductive material. The current flowing through your coil is what makes it get hot and turns your liquid into vapor. You’ll need to know the number of amps your setup is drawing from your battery to ensure you stay safe when you’re vaping.
  • Ohms: Ohms are a measure of the resistance to the flow of current. If you imagine water flowing through a pipe as being the electrical current, resistance is like the friction between the water and the insides of the pipe. Volts kick-start the current and ohms slow it down. Your coil has resistance, and this is really why it gets hot when current flows through it. For the same voltage, a higher resistance means less current.
  • Watts: This is a measure of electrical power. This is basically the amount of energy passing a point in the circuit per second. Most regulated mods these days are variable wattage, so you set the number of watts you want to send to your coil. The wattage calculation takes the resistance and voltage in account for you, so it’s really easy to get the right setting with VW mods. Generally speaking, a higher wattage means more vapor.

 

Why Ohm’s Law Matters

 

Vapers often give the advice that “you should learn Ohm’s law before you start vaping with a mod,” but in some cases they don’t really explain why. Ohm’s law tells you the relationships between voltage, current, resistance and power, and so it is central to how vaping works.

 

The main reason that Ohm’s law is important is working out how much current your coil will draw from the battery. This is important because batteries can only safely provide so much current. This amount of current is called the “maximum continuous current” for the battery, and you need to make sure you stay under this number when you’re vaping. It’s best to avoid drawing the maximum current you’re allowed to, but realistically as long as you stay within the limit you’ll keep vaping safely.

 

The only extra piece of information you need (which won’t be shown on your mod) is the maximum continuous current of your battery, which you can find through a Google search, on the site you bought it from or other places like Steam Engine (check the drop-down menu beside “battery presets”).

 

You can also use Ohm’s law to work out the wattage you’re vaping at if you don’t have a regulated mod or a VV/VW device, too.

 

Using Ohm’s Law for Mechanical Mods

 

Mechanical mods don’t have the same in-built protections you’ll find on regulated devices, so using Ohm’s law before vaping using them is particularly important. Mech mods don’t read the resistance of your coil, though, so you have to test your coil on a regulated mod or dedicated ohm reader before you attach it and try to vape.

 

Once you know the resistance of your coil, you can use the following form of Ohm’s law:

 

I = V / R

 

Or, in words

 

Current = voltage / resistance

 

If you have a single-battery mechanical mod, the fully-charged voltage is 4.2 V, and it decreases as the charge drains. You should always use the full voltage when you do calculations, though. Here’s an example calculation using a 0.5 ohm coil:

 

I = V / R = 4.2 V / 0.5 ohms = 8.4 amps

 

This is well within the capabilities of most 18650 vaping batteries, and many offer up to 30 amps of continuous current. The same calculation with a 0.2 ohm coil works out at 21 A, so as long as you have a very capable battery this can be done safely too.

 

If you want to work out wattage (i.e. power = P), use this version of Ohm’s law:

 

P  = V2 / R

 

So in the example above:

 

P = 4.2 V × 4.2 V / 0.5 ohms = 35 W

 

Using Ohm’s Law for VV/VW Mods

 

Although the previous section is what most vapers know, calculating Ohm’s law for VV/VW mods is a bit different. Instead of the version above, you need to use:

 

I = P / V

 

So current = power / voltage.

 

When you’re using this version of the equation, the minimum voltage is the most important thing to use, rather than the maximum. A regulated mod sometimes needs to “boost” the voltage to put out a certain amount of watts, but batteries top out at 4.2 V per cell. To account for this maximum, they increase the current drawn. The less voltage remaining in the battery, the more they have to do this to make up for the difference.

 

You can calculate the current for anything but really low voltages by using 3.7 V, but if you want to be extra-careful you can go down to 3 V or even 2.5 V. Using one battery vaping at 75 W, this shows:

 

I = P / V = 75 W / 3.7 V = 20.3 A

 

Or with a bigger safety margin for a “worst case scenario” calculation:

 

I = P / V = 75 W / 2.5 V = 30 A

 

This gives you an idea of why many single-battery mods top out at 70 or 75 W, or 150 W for dual-battery mods. It’s the safest way to go based on some worst-case assumptions.

 

Ohm’s Law Calculators

 

This post should have shown you that it really isn’t hard to work out what you need to know to vape safely. However, there are plenty of Ohm’s law calculators you can use to take the work out of the process.

 

Steam Engine’s battery drain calculator is a really good tool, with presets for the most widely-used vaping batteries and modes for both mech mods and VV/VW devices. There’s another simple option at Li-Ion Wholesale too for regulated mods. As well as this, there are many vaping apps that can perform these same functions and more.

 

Ohm’s Law Matters, But It’s Easy to Use

 

The good news is that while Ohm’s law is important, it’s easy to work out what you need to know, and most regulated mods have plenty of safety features built in to protect you anyway. If you don’t want to do the math yourself, there are plenty of tools to take some of the work away, and as long as you get a capable battery (with a high maximum continuous current), you’ll find you rarely (if ever) have anything to worry about anyway. But it’s better to understand why you don’t have anything to worry about most of the time to walk blindly into a potential problem.

Lee Johnson is a writer and vaper from the UK. He started vaping in 2012, and since then has contributed to E-Cigarette Reviewed, E-Cigarette Direct’s Ashtray Blog and Vaping360. He strongly believes smokers need accurate information about vaping and other reduced-harm alternatives to smoking. He has a degree in physics from the Open University and a passion for all forms of science.

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