Ohm's law
I feel the most common question is about Ohm's law and about understanding resistances for devices. Ohm's law is the most important piece of information pertaining to vaping since it's what we use all the time. There are four variables to know in the equations, but an easy way to help understand it is with the Steam Engine tool. In the online calculator you see resistance, voltage, current, power. The units are ohms, volts, amps, and watts respectively. An even easier way to understand it is thinking about it in an example.
The water pipe analogy
Think of the resistance like a pipe with water flowing out of the pipe and the water is amperage. There is also a valve on the pipe that you can turn to make the water(amperage) come out faster and that valve acts like a voltage control. The end result of the water flow out the pipe is expressed by power, also known as wattage. You can increase the wattage by either decreasing the resistance or increasing the voltage.
For example there is a pipe set up with a certain width(R) and water(I) is flowing at a constant rate. Lets also say the pipe has a resistance of 1ohm and our valve to control the speed(V) is set to 4volts. You can use Ohm's law and see that amount of water(I) coming out is 4amps and the pipe's power is measured to 16watts. Now if you widen the same pipe(R) more water(I) can flow and you change the voltage. Adjust the pipe's resistance(R) to 0.5ohms and as a result we see we just doubled the amount of water(I) to 8amps and doubled the power to 32watts with a constant voltage.
Take the same pipe, 1ohm, and instead of making it wider you just turn the valve/voltage and double the pressure or speed from 4volts to 8volts. You see 8amps of water flowing through the pipe and the power by the pipe went up to 64watts by adjusting the voltage only.
This can be applied to our coils and devices. Mechanical mods work like the first example in which we just made the pipe wider because that's the only thing you can adjust on a mechanical. You have a fixed battery voltage, and can only change the resistance. The second example is more like a variable voltage/wattage mod where you can keep the same resistance and just change the voltage.
Understanding how these variables work will give you a better understanding of ohms law and how to build for specific devices.
Ohm's law and a regulated PV
Each device has: a resistance range, a voltage range, a wattage range, and a amperage limit. You want to know all of these things because it will determine what resistances will work the best for a device. Some devices work well with a wide range, some work very well within a small area within that range. Lets look at an example.
Here is the DNA40(kanthal) and it's specs given by Steam Engine. I don't own one so I don't know the actual performance, but I want to use the numbers as an example. You can see the max voltage, max wattage, resistance range, and amp limit on the left. On the right there are three boxes where it all comes together.
Current limit 16 A vs 40 W
The box labeled “Current limit 16 A vs 40 W” measures the lowest possible resistance to get all 40watts. When you decrease resistance you can push more amps through your coil without using all the voltage. This is done by using ohm's law calculator and plugging in the max amp limit along with the max wattage. You can see that the lowest possible resistance to get all 40watts while using all the amps is close to the minimum resistance for the device. Not the best place to be, but it works as advertised.
Voltage limit 9 V vs 40 W
The next box “Voltage limit 9 V vs 40 W” measures the highest possible resistance to get all 40watts. When you increase resistance you are can use more voltage to get to higher wattage without using as many amps. This is done by plugging in the max voltage for the device and its max wattage. You can see that highest possible resistance to get all 40watts while using all the voltage is close to the maximum resistance for the device. Works as advertised.
Optimal resistance
The last box “Optimal resistance” sums it all up by giving you the resistance range along with the median resistance. Then it gives you a “sweet spot”. This is the median from the first median and the maximum. If you want all 40 watts and want to keep your battery life in good shape use a resistance around the “sweet spot”. You don't have to use the sweet spot, but keep in mind the less amps you pull, the more battery life you get while taking advantage of the device's voltage.
These numbers are unique for each device that uses a different chip. If you start looking at the higher powered devices like the Sigelei 150W you'll see that you can only get all 150 if you build within a certain range that it can fire. Too high of a resistance and you'll use all the voltage before 150w, but you can take advantage of it's available amperage by lowering the resistance. In order to to fire all 150w within it's 0.1-3.0ohm range the PV would have to give 20+ volts, which we don't have now.
Ohm's law and a mechanical PV
Check out how mechanical devices work, you only use the specs from the battery along with your resistance.
Take the Sony VTC4 for example. I used a resistance of 0.5ohms and a voltage of 4.1volts charged on this page. The page tells you how many amps you are pushing along with the wattage output. The amp limit is advertised to be 30amps and the box under shows the “headroom” or I like to call it the buffer. In this example you only use 8.2amps, this is safe for the battery. You really shouldn't use all the battery's amperage on an unregulated mechanical, it's not very safe. A lot of people agree on only using about 75% of the batteries amp limit, leaving a 25% headroom to be considered safe. This works out to be about 22amps used and around 0.18-0.19ohms. You should only do this if you are aware of the risks.
Finding your resistance
Now that you looked at the devices, look at choosing a coil for your device. Take your resistance you feel you would be comfortable with and go to the coil calculator.
I used a 0.5ohm resistance, selected the kanthal of choice, selected dual coils, and selected the coil's internal diameter. I also calculated the wattage with 0.5ohms and 4.1volts to get around 33 watts to plug into the heat flux(under results) to get an estimate of the vape temperature.
You want to pay attention to number of wraps, the coil width, and surface area. This will give you an idea of how big your potential coil is. What you can do from here is change the diameter, you’ll notice the surface area stays the same, but the width will change because the number of wraps change. You can also change the resistance and use a fixed diameter to change width and surface area. Try selecting different gauges too.
A few links I visit:
Steam Engine | free vaping calculators
*Baditude*
*State O' Flux*
*Mooch*
Basic Coil Building And Safety For Beginners | E-Cigarette Forum
The ECF Library
I feel the most common question is about Ohm's law and about understanding resistances for devices. Ohm's law is the most important piece of information pertaining to vaping since it's what we use all the time. There are four variables to know in the equations, but an easy way to help understand it is with the Steam Engine tool. In the online calculator you see resistance, voltage, current, power. The units are ohms, volts, amps, and watts respectively. An even easier way to understand it is thinking about it in an example.
The water pipe analogy
Think of the resistance like a pipe with water flowing out of the pipe and the water is amperage. There is also a valve on the pipe that you can turn to make the water(amperage) come out faster and that valve acts like a voltage control. The end result of the water flow out the pipe is expressed by power, also known as wattage. You can increase the wattage by either decreasing the resistance or increasing the voltage.
For example there is a pipe set up with a certain width(R) and water(I) is flowing at a constant rate. Lets also say the pipe has a resistance of 1ohm and our valve to control the speed(V) is set to 4volts. You can use Ohm's law and see that amount of water(I) coming out is 4amps and the pipe's power is measured to 16watts. Now if you widen the same pipe(R) more water(I) can flow and you change the voltage. Adjust the pipe's resistance(R) to 0.5ohms and as a result we see we just doubled the amount of water(I) to 8amps and doubled the power to 32watts with a constant voltage.
Take the same pipe, 1ohm, and instead of making it wider you just turn the valve/voltage and double the pressure or speed from 4volts to 8volts. You see 8amps of water flowing through the pipe and the power by the pipe went up to 64watts by adjusting the voltage only.
This can be applied to our coils and devices. Mechanical mods work like the first example in which we just made the pipe wider because that's the only thing you can adjust on a mechanical. You have a fixed battery voltage, and can only change the resistance. The second example is more like a variable voltage/wattage mod where you can keep the same resistance and just change the voltage.
Understanding how these variables work will give you a better understanding of ohms law and how to build for specific devices.
Ohm's law and a regulated PV
Each device has: a resistance range, a voltage range, a wattage range, and a amperage limit. You want to know all of these things because it will determine what resistances will work the best for a device. Some devices work well with a wide range, some work very well within a small area within that range. Lets look at an example.
Here is the DNA40(kanthal) and it's specs given by Steam Engine. I don't own one so I don't know the actual performance, but I want to use the numbers as an example. You can see the max voltage, max wattage, resistance range, and amp limit on the left. On the right there are three boxes where it all comes together.
Current limit 16 A vs 40 W
The box labeled “Current limit 16 A vs 40 W” measures the lowest possible resistance to get all 40watts. When you decrease resistance you can push more amps through your coil without using all the voltage. This is done by using ohm's law calculator and plugging in the max amp limit along with the max wattage. You can see that the lowest possible resistance to get all 40watts while using all the amps is close to the minimum resistance for the device. Not the best place to be, but it works as advertised.
Voltage limit 9 V vs 40 W
The next box “Voltage limit 9 V vs 40 W” measures the highest possible resistance to get all 40watts. When you increase resistance you are can use more voltage to get to higher wattage without using as many amps. This is done by plugging in the max voltage for the device and its max wattage. You can see that highest possible resistance to get all 40watts while using all the voltage is close to the maximum resistance for the device. Works as advertised.
Optimal resistance
The last box “Optimal resistance” sums it all up by giving you the resistance range along with the median resistance. Then it gives you a “sweet spot”. This is the median from the first median and the maximum. If you want all 40 watts and want to keep your battery life in good shape use a resistance around the “sweet spot”. You don't have to use the sweet spot, but keep in mind the less amps you pull, the more battery life you get while taking advantage of the device's voltage.
These numbers are unique for each device that uses a different chip. If you start looking at the higher powered devices like the Sigelei 150W you'll see that you can only get all 150 if you build within a certain range that it can fire. Too high of a resistance and you'll use all the voltage before 150w, but you can take advantage of it's available amperage by lowering the resistance. In order to to fire all 150w within it's 0.1-3.0ohm range the PV would have to give 20+ volts, which we don't have now.
Ohm's law and a mechanical PV
Check out how mechanical devices work, you only use the specs from the battery along with your resistance.
Take the Sony VTC4 for example. I used a resistance of 0.5ohms and a voltage of 4.1volts charged on this page. The page tells you how many amps you are pushing along with the wattage output. The amp limit is advertised to be 30amps and the box under shows the “headroom” or I like to call it the buffer. In this example you only use 8.2amps, this is safe for the battery. You really shouldn't use all the battery's amperage on an unregulated mechanical, it's not very safe. A lot of people agree on only using about 75% of the batteries amp limit, leaving a 25% headroom to be considered safe. This works out to be about 22amps used and around 0.18-0.19ohms. You should only do this if you are aware of the risks.
Finding your resistance
Now that you looked at the devices, look at choosing a coil for your device. Take your resistance you feel you would be comfortable with and go to the coil calculator.
I used a 0.5ohm resistance, selected the kanthal of choice, selected dual coils, and selected the coil's internal diameter. I also calculated the wattage with 0.5ohms and 4.1volts to get around 33 watts to plug into the heat flux(under results) to get an estimate of the vape temperature.
You want to pay attention to number of wraps, the coil width, and surface area. This will give you an idea of how big your potential coil is. What you can do from here is change the diameter, you’ll notice the surface area stays the same, but the width will change because the number of wraps change. You can also change the resistance and use a fixed diameter to change width and surface area. Try selecting different gauges too.
A few links I visit:
Steam Engine | free vaping calculators
*Baditude*
*State O' Flux*
*Mooch*
Basic Coil Building And Safety For Beginners | E-Cigarette Forum
The ECF Library
