OK guys- I have decided to take the next step and dive into the world of sub-ohming. So I have been watching vids on youtube and I am confused. So I realized that the equation is wattage=v^2/r, but how do you know what wattage you are going to want based on your resistance? What I mean is that- if someone is going at like 0.5 ohms, they are going to crank their wattage up rather than if you are at like 1.2 ohms. Why is this? Also what do I need to know about battery safety before I get into sub-ohming? Thanks!
Ohm's Law Confusion and General Q's Before Sub-Ohming
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Explain it for the dumb noob: Ohm's Law calculations
The two most important things to know when rebuilding coils is to know the amp limit of the battery you have and to know the resistance of your coil. This is where Ohm's Law comes into play.
List of Batteries and Amp Limits
When you build your coil and fire it on your mod, it will draw a specific amount of current (amps) from the battery. That current must not be more than the total amps in continuous discharge rate of the battery, or very bad things could happen. *
Never fire a coil without first confirming the ohm resistance on an ohm reader or multimeter. You can't just rely on a coil wrapping calculator or somebody's recommendations, there's too much chance for human error. The smallest error can be catastrophic. Even seasoned veterans always check the resistance of their coils on a meter to make sure they are safe.
To find out what current the coil will pull from the battery, you use an Ohms Law Calculator.
You have the resistance of the coil (what you measured with your ohm meter) and the voltage (always use 4.2 volts of a fully charged battery), so type those figures into the calculator and then click calculate. The resulting current is the amps that coil will draw from the battery. Not so hard, right?
Below calculations demonstrate that the lower you go in ohms the higher the amp requirement becomes. We are also putting a lot of faith into a cheap ohm reader in being precisely accurate to the tenth/hundreth of an ohm. Always tend to err on the side of safety when you make your builds by allowing some safety head room.
1.0 ohm = 4.2 amp draw
0.9 ohm = 4.6 amp draw
0.8 ohm = 5.2 amp draw
0.7 ohms = 6 amp draw
0.6 ohms = 7 amp draw
0.5 ohms = 8.4 amp draw
0.4 ohms = 10.5 amp draw
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw
0.1 ohms = 42.0 amp draw
0.0 ohms = dead short = battery goes into thermal runaway
* When bad things happen
Vape Blast had a vape blast
The two most important things to know when rebuilding coils is to know the amp limit of the battery you have and to know the resistance of your coil. This is where Ohm's Law comes into play.
List of Batteries and Amp Limits
When you build your coil and fire it on your mod, it will draw a specific amount of current (amps) from the battery. That current must not be more than the total amps in continuous discharge rate of the battery, or very bad things could happen. *
Never fire a coil without first confirming the ohm resistance on an ohm reader or multimeter. You can't just rely on a coil wrapping calculator or somebody's recommendations, there's too much chance for human error. The smallest error can be catastrophic. Even seasoned veterans always check the resistance of their coils on a meter to make sure they are safe.
To find out what current the coil will pull from the battery, you use an Ohms Law Calculator.
You have the resistance of the coil (what you measured with your ohm meter) and the voltage (always use 4.2 volts of a fully charged battery), so type those figures into the calculator and then click calculate. The resulting current is the amps that coil will draw from the battery. Not so hard, right?
Below calculations demonstrate that the lower you go in ohms the higher the amp requirement becomes. We are also putting a lot of faith into a cheap ohm reader in being precisely accurate to the tenth/hundreth of an ohm. Always tend to err on the side of safety when you make your builds by allowing some safety head room.
1.0 ohm = 4.2 amp draw
0.9 ohm = 4.6 amp draw
0.8 ohm = 5.2 amp draw
0.7 ohms = 6 amp draw
0.6 ohms = 7 amp draw
0.5 ohms = 8.4 amp draw
0.4 ohms = 10.5 amp draw
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw
0.1 ohms = 42.0 amp draw
0.0 ohms = dead short = battery goes into thermal runaway
* When bad things happen
Vape Blast had a vape blast
Last edited:
Have an ohms meter?
As a rule I stay above 0.3
And I try to stay at 0.5
Make sure you have okay Batteries.
see these?
https://www.google.co.jp/search?q=e...mah-30a-flat-top-battery-p-217.html;2448;2088
now, Purple EFest... i only trust them at a 20Amp because its been proven that is their continuos draw. so that means at 0.2 I am already pushing the battery past its cont. draw limit. My battery could blow off my face! not a fun time.
that means if i take this purple Efest, Description
Efest IMR 18650 2500 mAh 3.7V LI-MN High Drain Rechargeable Battery , Flat Top , Purple , 35 AMPS. S. The Efest IMR 18650 2500mah 35amp Flat Top High-Amp batteries are the newest most powerful battery Efest has made to date!
its 3.7 volts
3.7 /(divided by) 0.5 =7.4 continuos draw (I think Baditude was using a different Amp battery for his law )
but anyways...
I stick it at 0.5.... you should be okay there.
As a rule I stay above 0.3
And I try to stay at 0.5
Make sure you have okay Batteries.
see these?
https://www.google.co.jp/search?q=e...mah-30a-flat-top-battery-p-217.html;2448;2088
now, Purple EFest... i only trust them at a 20Amp because its been proven that is their continuos draw. so that means at 0.2 I am already pushing the battery past its cont. draw limit. My battery could blow off my face! not a fun time.
that means if i take this purple Efest, Description
Efest IMR 18650 2500 mAh 3.7V LI-MN High Drain Rechargeable Battery , Flat Top , Purple , 35 AMPS. S. The Efest IMR 18650 2500mah 35amp Flat Top High-Amp batteries are the newest most powerful battery Efest has made to date!
its 3.7 volts
3.7 /(divided by) 0.5 =7.4 continuos draw (I think Baditude was using a different Amp battery for his law )
but anyways...
I stick it at 0.5.... you should be okay there.
We use 4.2 volts (the voltage of a fully charged battery), not 3.7 volts for the Ohm's Law calculators.
Oh. That's probably better. I thought efest batteries were 3.7 fully charged, as that's what it says on it...
OK...
OP. Change my 3.7 to 4.2..... my bad.
OK...
OP. Change my 3.7 to 4.2..... my bad.
The original poster was asking about wattage and resistance. All of the information above is correct and important for safety, but doesn't address the issue of why you would pick a particular wattage in the first place. Let me break that part down.
First, wattage (W) is equal to voltage (V) times current (A). For example, if you draw 4V at 3A, that's 12W, or if you draw 6V at 2A, that's still 12W. So is 1V at 12A. For the most part, the amount of W is directly related to the amount of heat the coil will produce. Any coil that's powered by 12W will produce the same amount of heat, whether it's 6V at 2A or 1V at 12A. If the coil is bigger, that heat will be spread over more surface area of juice, and if the coil is smaller, that heat will be concentrated over less area of juice (hotter juice in a smaller spot).
Things start to get tricky when you consider that V and A are not entirely independent. They are related by the amount of resistance you are running the voltage through. If resistance is R, then A = V/R. So, given a fixed V (4.2V for example), if you halve R, then A doubles. Since W = V*A, if you halve R and keep V the same, you double A. When you're building with a mech mod, you have no control over V. Your battery will produce somewhere between 3.7V (or a little less) and 4.2V, depending on how fresh it is. That means if you want to adjust W, the only way to do it is to raise A by lowering R. So, with a mech mod, it might make sense to use a lower resistance coil in order to raise the total wattage. The question is not what wattage to run for a coil with a particular resistance, the question is what resistance is necessary to produce a certain desired W (and, therefore, heat). For example, if your battery is fresh and produces 4.2V, and you want to output 12W, you'd pick a coil resistance of 1.47 Ohms (12W/4.2V is 2.857A. To produce 2.857A at 4.2V, you need a resistance of 1.47 Ohms). If you want to output 20W, you'd pick a coil resistance of 0.882 Ohms (same calculations as above, just plug in different numbers).
For a variable voltage or variable wattage device, you get to pick either V or W independent of R, within limits. The exact limits depend on what mod you're using.
Things also get a little trickier when you consider that there are different ways of constructing a coil to have a target resistance. For example, 27ga kanthal is about half the resistance of 30ga kanthal, so you could make 5 wraps of 30ga at a particular diameter or you could make 10 wraps of 27ga kanthal at the same diameter and end up with about the same resistance. Or, you could make 5 wraps of 27ga kanthal at twice the same diameter, and end up with the same resistance. If you powered all three coils at 12W, you probably wouldn't get the same vape, because the coils are producing the same amount of heat, but they're spread out over the wick differently. Or, you could also make two coils using 10 wraps of 30ga and then run them in parallel (ohms law says that when you have two equal resistance coils in parallel, the total resistance is 1/2 the resistance of one of the coils). Once again, the two coils in parallel will produce the same heat at 12W as the other coils, but that heat will be spread over more wick, and having two separate wicks will also have a profound effect on how juice reaches the coil. So, same wattage, same resistance, but a different vaping affect.
These are ALL things you need to understand and play around with at safe and sane resistances and amps (like 1.5 ohms total) until you understand what affect they have on vaping before you start trying to increase your wattage. Try lots of different builds out at 1.5 ohms and see what works and doesn't work, and then if you still can't find something that produces the flavor and vapor you want, then maybe start gently lowing the resistance or raising the wattage. But, don't fix it if it ain't broke.
First, wattage (W) is equal to voltage (V) times current (A). For example, if you draw 4V at 3A, that's 12W, or if you draw 6V at 2A, that's still 12W. So is 1V at 12A. For the most part, the amount of W is directly related to the amount of heat the coil will produce. Any coil that's powered by 12W will produce the same amount of heat, whether it's 6V at 2A or 1V at 12A. If the coil is bigger, that heat will be spread over more surface area of juice, and if the coil is smaller, that heat will be concentrated over less area of juice (hotter juice in a smaller spot).
Things start to get tricky when you consider that V and A are not entirely independent. They are related by the amount of resistance you are running the voltage through. If resistance is R, then A = V/R. So, given a fixed V (4.2V for example), if you halve R, then A doubles. Since W = V*A, if you halve R and keep V the same, you double A. When you're building with a mech mod, you have no control over V. Your battery will produce somewhere between 3.7V (or a little less) and 4.2V, depending on how fresh it is. That means if you want to adjust W, the only way to do it is to raise A by lowering R. So, with a mech mod, it might make sense to use a lower resistance coil in order to raise the total wattage. The question is not what wattage to run for a coil with a particular resistance, the question is what resistance is necessary to produce a certain desired W (and, therefore, heat). For example, if your battery is fresh and produces 4.2V, and you want to output 12W, you'd pick a coil resistance of 1.47 Ohms (12W/4.2V is 2.857A. To produce 2.857A at 4.2V, you need a resistance of 1.47 Ohms). If you want to output 20W, you'd pick a coil resistance of 0.882 Ohms (same calculations as above, just plug in different numbers).
For a variable voltage or variable wattage device, you get to pick either V or W independent of R, within limits. The exact limits depend on what mod you're using.
Things also get a little trickier when you consider that there are different ways of constructing a coil to have a target resistance. For example, 27ga kanthal is about half the resistance of 30ga kanthal, so you could make 5 wraps of 30ga at a particular diameter or you could make 10 wraps of 27ga kanthal at the same diameter and end up with about the same resistance. Or, you could make 5 wraps of 27ga kanthal at twice the same diameter, and end up with the same resistance. If you powered all three coils at 12W, you probably wouldn't get the same vape, because the coils are producing the same amount of heat, but they're spread out over the wick differently. Or, you could also make two coils using 10 wraps of 30ga and then run them in parallel (ohms law says that when you have two equal resistance coils in parallel, the total resistance is 1/2 the resistance of one of the coils). Once again, the two coils in parallel will produce the same heat at 12W as the other coils, but that heat will be spread over more wick, and having two separate wicks will also have a profound effect on how juice reaches the coil. So, same wattage, same resistance, but a different vaping affect.
These are ALL things you need to understand and play around with at safe and sane resistances and amps (like 1.5 ohms total) until you understand what affect they have on vaping before you start trying to increase your wattage. Try lots of different builds out at 1.5 ohms and see what works and doesn't work, and then if you still can't find something that produces the flavor and vapor you want, then maybe start gently lowing the resistance or raising the wattage. But, don't fix it if it ain't broke.
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