(14) Ohm's Law Explained for Vapers

So here is my take on an ohm’s law explanation using a power wheel as an anology.


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Section 1: The parts of Ohm's law
Look at the graphic below and 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 dam pouring onto a water wheel (see above animation). 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. The resistance (ohms) of a coil determines how much energy it can accept from the battery.
  • I – Amperage - Amperage (amps, or electrical current, or power) 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!

  • Watts is a derived unit of power. Voltage is a simple measurement. Wattage is a calculation.
    In a nutshell, wattage (power) is equal to the voltage squared divided by the resistance of the atomizer. In a variable wattage device, it reads the resistance of the atomizer and calculates the voltage needed based on your wattage setting. I know that sounds complicated, but you don't really have to understand that part. Let's move on...
  • Volts = the level of power (force) coming out of the battery.
    Watts = the amount of power (work) coming through your atomizer.
  • Ohms = measured unit of resistance of a wire coil. Determines the amount of electrical current that will pass through the coil and thereby determines the amount of heat generated by the coil.

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 from the battery 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.

Lower Ohm Coils Will:

Produce A Warmer Tasting Vape
Heat The Coil Faster
Produce More Vapor
Drain The Battery Faster
Use E-Juice Faster
Higher Ohm Coils Will:

Provide A “Cooler” Tasting Vape
Heat The Coil Slower
Produce “Less” Vapor
Use Less E-Juice
Prolong Battery Life​

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.

What's left after a mech mod explosion after a battery vented hot gas from a hard short. There was inadequate vent holes in the mod to allow gas to escape from the metal tube, so in effect it became a pipe bomb.

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. Thicker wire has lower resistance than thinner wire. Thinner wire has higher resistance than thicker wire.

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 the water flow, which represents theAmperage or electric current. 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.

The relationships should be 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.

:unsure: “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 - 4.2 volts of a fully charged battery)) and resistance (R - the measured ohm rating of the coil) 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 for mechanical mods -- Hate formulas or math? For those of us who are math challenged like myself you can use this Ohm's Law calculator link. Easy peasy.

online Ohm's Law calculator

By inserting two known numerical factors into the calculator one can find the other two unknown factors. We know that our fully charged battery has a voltage of 4.2 volts, so add that to the calculator in the Voltage box. Insert the measured resistance of your coil into the Resistance box. Now click Calculate.

The amount of current drawn from the battery to fire that coil will be revealed in the Current box. This is known as the "amp draw". This should not exceed the amp rating (continuous discharge rate) of the battery. Incidentaly, the wattage required to fire the coil is also displayed in the Power box, but this is irrelevant info for a mech.

List of Battery Tests Battery Mooch has bench tested hundreds of batteries and compared their advertised amp rating against real world amp rating.

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).:laugh:

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 begin with. For example, 2.0 ohms + the number "2 " = 4 volts. This is a good starting point, and you can adjust + or - to find your "sweet spot".

How does ohms law work with 2 batteries?

For RBA users: When using the Ohm's Law Calculator to calculate the battery amp draw of a coil in a RBA on a mechanical mod, 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

For Regulated Mod Users:

Regulated mods don't use Ohm's Law, but use Watts Law.

The voltage output from a regulated mod is not the battery voltage (as it is in a mechanical mod). It is converted using a combination of buck/boost and/or PWM (pulse width modulation) circuitry or pulsed DC circuitry in the processor to achieve the desired wattage to fire the atomizer.

On a regulated mod the coil resistance is essentially irrelevant. What dictates the amp draw on the battery is the wattage you set on the mod, and the remaining voltage in the battery. The amp draw will increase as the battery discharges.

In the interests of keeping things simple:

If you use a good quality 15 amp CDR battery like the Samsung 30Q or the Sony VTC6 then you are good for 45 watts per battery. If you have a two-battery regulated mod, don't exceed 90 watts.

If you use a good 20 amp CDR battery like the Lg HG2 or Samsung 25R, you are good for 60 watts per battery. 120 watts in a dual battery mod.

If you use a 30 amp CDR battery like the LG HB6 in a single battery mod, you could safely do 90 watts. 180 watts in a dual battery mod. Realize that a true 30A battery only has 1500mAh capacity, so battery time will be less than for a 20A 3000mAh battery.

Calculating the current being drawn from the batteries in a regulated device can be very confusing. You can't do it the same way as you would for a mechanical/unregulated device and there are so many different battery configurations; single, dual parallel, dual series, triple series, etc.

The way I keep it all sorted out is to remember that, in a regulated mod, the coil isn't connected to the battery. The regulator is. To calculate the current being drawn from each battery when using variable-wattage (VW) mode you need to calculate the maximum wattage each battery supplies.

(Total wattage doubles using 2 batteries; Triples using 3 batteries.)

Up to 45W:
Samsung 18650 30Q, 3000 mah 15 amp CDR

Sony 18650VTC6 3000mAh 15 amp CDR

Up to 60W:
LG 18650HG2 3000mah 20 amp CDR

LG 18650HE4 2500 mah 20 amp CDR

Samsung 18650-25R, 2500 mah 20 amp CDR

Sanyo UR18650NSX, 2500 mah 20 amp CDR

Sony 18650VTC5, 2600 mah 20 amp CDR

Sony 18650VTC4, 2100 mah 23 amp CDR

AW 18650 3000 mah 20 amp CDR

Up to 75W:
LG 18650 HD4 2100 mah 25 amp CDR

LG 18650 HD2 2000 mah 25 amp CDR

Samsung 18650-24S, 2500 mah 25 amp CDR

Sony 18650VTC5A, 2500 mah 25 amp CDR

Up to 90W:
LG18650HB6 1500mah 30 amp CDR

LG18650HB2 1500mAh 30 amp CDR

LG18650HB4 1500mAh 30 amp CDR

Samsung 18650-20S 2000mah 30 amp CDR

Calculating battery current draw for a regulated mod

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. This recently occured in my own RDA when a loose positive post screw lowered the coil resistance by 0.5 ohms. Thankfully I routinely check and recheck my coil resistance with an ohm reader, or I might have experienced a catastrophic battery event. I never build lower than 0.6 ohms. Had I been using a 0.3 ohm build when the screw came loose, I would have hard shorted my battery.

Understanding the relationship between power and coil resistance | E-Cigarette Forum

Now for some fun with electricity:


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.
Nice work Bad :) I've bookmarked it so I can refer newbie's to it as I encounter them.
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.
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

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