(14) Ohm's Law for Dummies (Vapers) - Blogs - E-Cigarette Forum
View RSS Feed


(14) Ohm's Law for Dummies (Vapers)

Rate this Entry
by , 05-22-2014 at 06:45 PM (9216 Views)
So here is my take on an ohm’s law explanation using a power wheel as an anology. Strap your butts on and let’s go!


Section 1: The parts of Ohm's law
If we take a look at the graphic below you will see what’s known as the Ohm’s law triangle, aka your cheat sheet for this section. To understand what this all means we first need to understand the three components of Ohm’s Law: Voltage, Resistance, and Amperage. To achieve this we are going to use the analogy of a water basin with a flood gate pooring onto a water wheel. Bear in mind on a technical level this isn’t a perfect analogy but for our purposes it will do the trick. So here we go again!


  • Work - The wheel in this analogy refers to the work being done. The faster the wheel spins the more work that is done.
  • V - Voltage - Voltage is the water basin itself. It is the potential for energy, or the potential amount of water you have to work with.
  • R – Resistance (ohms) - Resistance is the flood gates. It is what controls how much water can flow out of our basin. The lower the flood gates the more water that can flow through.
  • I – Amperage - Amperage is the stream of water coming out of the flood gates. This is what actually does the work. Imagine the water wheel is right under the flood gate. The more water that comes out (amperage) the faster the wheel spins, let water flow through too fast and the water wheel breaks!

Section 2: Let the water flow - How Voltage, Resistance and Amperage Relate
Now that we know what V (voltage), R (resistance) and I (amps) are, let’s talk about how they function and what it means to us vapers. The easiest one of these three to grasp is work. Work is simply energy being used to accomplish something. For vapers that energy is electricity and the work is our coil heating up. The more work the warmer our coil.

Resistance is our flood gate. If we raise our flood gate (raise our resistance) less water is allowed to flow through. If we lower the flood gates (lower the resistance) more water is allowed to flow through. In our ecigs our resistance is in our coils. If you increase the resistance of the coil then less electricity is allowed to flow through the coil. The lower the electrical flow through the coil the cooler your vape will be. On the inverse if we increase the electrical flow by lowering the flood gates (lower the resistance in our coil) we will see a higher electrical flow that will result in warmer temperatures.

Remember back to our water wheel for a bit, if you let too much water flow into the wheel it’s going to break, right? So if you run too low of a resistance there will be too much electrical flow and the “wheel” will break. What is the “wheel” with ecigs? Your battery! And when it breaks bad things happen, sometimes very bad things. This is really only a concern with mechanical mods as most regulated VV mods have a low ohm cut off to prevent these types of issues.

Next, Voltage, our water basin. This is where the analogy falls a little short but bear with me. So what happens when you have a bunch of water above an opening? The pressure increases. So the larger your basin (voltage) the more pressure you have trying to push through the opening. This means that if you have a small basin and suddenly make it a large basin (increase the voltage) you now need to raise the flood gates a little bit to maintain the same flow rate (amperage). This can be seen by using a low resistance coil at low voltage and then switching to a higher resistance coil at higher voltage. They should vape very similarly.

Bring back the water wheel again, if we don’t raise our flood gates when we increase the size of the basin (raising resistance when we raise the voltage) you will have a higher amount of water flowing through the gate (electrical flow). When we do this the wheel spins faster and our vape is warmer, but once again, spin the wheel too fast and it will break. In this instance though the “wheel” can be several things. You may still damage your battery in a mechanical mod but you might also pop a coil or even burn your juice. So the “wheel” in this instance expands to not only be the battery but also the coil and the juice. Regardless of what it is, things breaking is bad.

Finally our water flow, Amperage. Our water flow is what does the actual work. Amperage is the actual flow of electrons through our coil and what causes our coils to warm up. I’m sure the relationship is starting to shine through at this time. If you lower the flood gate our water flow increases and if we increase the size of our basin the water flow increases too. In vaping the water flow (amperage) is the one thing you have no direct control over. We adjust the amperage by raising and lowering our flood gates (resistance) and by increasing or decreasing the size of our basin (voltage). Amperage is what’s dangerous in electricity, it’s what makes things work and causes things to break.

Section 3: Bringing it Back to Earth - Application of Ohm's Law

So let’s bring this analogy into the real world and show you how to use your new found knowledge. Grab your text book or review the second image I listed above. Even though you now know what V, R and I are this thing still might not make sense. Well we’re about to change that! This is what’s referred to as the Ohm wheel, or... er… I guess triangle in this case. This handy little guy has packed in it every basic formula you need when applying Ohms law.

“But Baditude, this thing is just a triangle!” you might be thinking, and that’s where you’re wrong. Using this you can calculate any one value assuming you have the other two. Simply cover up the value you don’t have and BAM! There’s you’re formula.


Trying to calculate voltage (V) and have resistance (R) and amperage (I)? Cover the V and we get I x R = V and that’s your formula.

Have voltage (V) and amperage (I) and need resistance (R)? Cover up R. V / I = R.

Finally the most important to us vapers, when you have voltage (V) and resistance (R) and need to know the amperage (I) that a coil will pull from the battery? Cover the I and we get V / R = I. This is the formula we will use the most when rebuilding coils. We can control our voltage with VV devices and we can control our resistance with different coils, so we almost always have V and R and need to find amperage (I) to verify we’re safe.

Ohm's Law Calculator
-- Hate formulas or math? For those of us who are math challenged like myself.

YouTube Video: Watts, Amps, Ohms, & Volts explained

Section 4: Closing Remarks & Some Tips
So there it is! That’s a basic run down on Ohms Law as it relates to vaping (and water wheels).

If using a regulated variable voltage battery device, a simple little formula to use to find the voltage needed to fire a coil is the Ohms Plus Two Formula. If you know the resistance of the coil, add the number two and the sum will be the voltage to use. For example, 2.0 ohms + 2 = 4 volts. This is a good starting point, and you can adjust + or - to find your "sweet spot".

For RBA users: When using the Ohm's Law Calculator to calculate the battery amp draw of a coil in a RBA, always use 4.2 volts as the voltage (a fully charged battery's voltage).
You should never pull more amps than the continuous discharge rate in amps for that battery, and you should allow for some safe headroom on top of that. Amp ratings for batteries

Never fire a coil in a RBA without first checking the resistance with a reliable ohm reader or digital multimeter. Routinely re-check the resistance after use to insure the resistance remains what you built. Something as simple as a post screw becoming loose can change your resistance.
Susan~S, TamiP, dopamine1 and 24 others like this.

Updated 08-31-2014 at 06:32 PM by Baditude



  1. Fisheeboy's Avatar
    Thank you Bad, This will be coming in very handy very soon. This Dummy is getting ready for his first try at Mechs and I'm gonna need every bit of good info I can wrap my Fishee brain around. This works well for my brain.
    I don't need any more scary battery issues in my life.
  2. Nikkita6's Avatar
    Nice work Bad I've bookmarked it so I can refer newbie's to it as I encounter them.
  3. Susan~S's Avatar
    Thanks Bad! Well written and easy to understand. I've added it to my ever growing blog list of articles from you (and a few others) to help others understand their e-cigarette gear and the math/chemistry/physics behind it.
  4. Bunnykiller's Avatar
    how about an add on with watts ( Vsqrd/R)
  5. AngryCagen's Avatar
    always love coming back and reading your work. Such an amazing writer. You should write a book, or just tally up everything you have written already, edit and BAM!....no pun intended...lol
  6. DetraMental's Avatar
    ah ha! Thank you for this!!
  7. QueenBeast's Avatar
    Thanks this was very helpful.