Volts, Amps, Ohms & Watts: The Electricity Behind Your Vape
, by Liberty Vape, 5 min reading time
Voltage, current, resistance and power decide how much vapour your device makes. Here's how amps, volts, ohms and watts work together — with Ohm's law tables for one and two batteries.
Introduction
Vape products use electricity from batteries, usually lithium, to vaporize the e-liquid. The amount of liquid that can be evaporated during a period of time is related to the amount of power that comes out of the batteries. The amount of power is determined by the voltage of the batteries, the number of batteries present, and the resistance of the coil.
What’s an Amp?
The amp (short for “ampere”), symbol “A”, is the standard unit for electrical current, also known as amperage. It’s a measure of how many electrons are passing through a circuit per second.
An amp-hour is a measure of battery capacity. It is usually cited as milliamp-hours (with a milliamp being 1/1000th of an amp), and a milliamp-hour being the capacity to output 1 milliamp for one hour.
For example, the lithium Efest 18650 battery has a capacity of 3500 mAh. It might seem like this should mean it can provide 3.5 amps (3500 milliamps) for an hour, but batteries often drain significantly faster with high currents, so actual capacity for vaping is less.
What’s a Volt?
The volt, symbol “V”, is the standard unit for electrical potential. It can be thought of as the driving force of an electrical circuit. The more voltage applied, the higher the resulting current.
Batteries in vaping products are the source of the voltage. Lithium batteries have a starting voltage of about 3.7 V, and unlike most other batteries, lose voltage very slowly until they are almost empty.
What’s an Ohm?
The ohm, symbol “Ω”, is the standard unit for electrical resistance. It determines how much current (also called amperage) goes through a circuit for a given voltage.
In vaping, this amount of resistance is a characteristic of the coil used. A coil’s resistance is determined by its thickness (thicker is less resistive), its length (longer is more resistive), and its material. Coils are typically made of Kanthal wire, a metal alloy comprised of iron, chromium and aluminum that generally has a high resistance. Most coil resistances sit in the 0.2 through 1.2-ohm levels.
What Is a Sub-Ohm Device?
A sub-ohm device is a coil, tank or device with a resistance of less than 1.0 ohms. These are specifically meant for freebase e-liquid because they are high-powered and produce a lot of vapour.
What’s a Watt?
A watt, symbol “W”, is a unit of power, which refers to a change in energy over time. A more familiar unit for some readers would be the horsepower, equal to 746 W. Most often you’ll hear watts used for electricity or heat, as we’re discussing it here.
How Are These Units Related?
Volts, ohms and amps are all related by Ohm’s law, which states that amperage is equal to the voltage divided by the resistance. A lower resistance means that more current is flowing through the loop.
What’s most important here is that power is also related to these units. Multiplying the amperage (which is the voltage divided by the resistance) by the voltage again gives power. Voltage in a vaping system is essentially always the same (the lithium batteries used deliver a near-constant voltage), so the coil’s resistance dictates how much heat is given off, and thus how much vape juice can be evaporated in a given amount of time.
Now for a Little Math
Ohm’s law is stated as V = I × R, where V is the voltage, I is the current, and R is the resistance.
Power is given as P = V² / R, where P is the power, V is the voltage, and R is the resistance.
The following are tables of voltages, currents and power for varying coils (with 0.2-, 0.4-, 0.6-, 0.8-, 1.0-, 1.2- and 1.4-ohm resistances), for one or two batteries.
One Battery (3.7 V)
| Voltage (V) | Resistance (Ω) | Current (A) | Power (W) |
|---|---|---|---|
| 3.7 | 0.2 | 18.5 | 68.5 |
| 3.7 | 0.4 | 9.3 | 34.2 |
| 3.7 | 0.6 | 6.2 | 22.8 |
| 3.7 | 0.8 | 4.6 | 17.1 |
| 3.7 | 1.0 | 3.7 | 13.7 |
| 3.7 | 1.2 | 3.1 | 11.4 |
| 3.7 | 1.4 | 2.6 | 9.8 |
Two Batteries (7.4 V)
| Voltage (V) | Resistance (Ω) | Current (A) | Power (W) |
|---|---|---|---|
| 7.4 | 0.2 | 37.0 | 273.8 |
| 7.4 | 0.4 | 18.5 | 136.9 |
| 7.4 | 0.6 | 12.3 | 91.3 |
| 7.4 | 0.8 | 9.3 | 68.5 |
| 7.4 | 1.0 | 7.4 | 54.8 |
| 7.4 | 1.2 | 6.2 | 45.6 |
| 7.4 | 1.4 | 5.3 | 39.1 |
As an example, for one battery with a resistance of 0.6 ohms—such as a 0.6-ohm UWELL Caliburn GPP / G3 / G4 Replacement Pod—current can be calculated using a re-arranged Ohm’s law:
I = V / R
Current = 3.7 volts / 0.6 ohms
Current = 6.2 amps
Power for the same circumstance can be calculated as:
P = V² / R
Power = (3.7 volts)² / 0.6 ohms
Power = 22.8 watts
As an aside, there are several equivalent formulations for power. The most common is P = V × I, and there is also P = I² × R.
You can see from these tables that just by changing the resistance and number of batteries, the power can change dramatically—from 9.8 watts for one battery with a high resistance to 273.8 watts for two batteries with a low resistance.
A low-powered device such as the VOOPOO Argus SE Pod Kit provides an output of about 18 watts with an internal battery, while the most powerful devices, such as the GeekVape Aegis Legend 5 200W Starter Kit, can output 200 watts using two lithium batteries.
Conclusion
The coil resistance and the number of batteries determine how much power goes into the coil and how much heat comes out—and in turn, how much juice can be vaporized. Coils with less resistance will output more power and vaporize more liquid. The biggest mods are up to 200 watts, which comes out to over one quarter of a horsepower.