The Four Characteristics of Ohm's Law
Watt - The unit of measure for power created in a circuit representing Wattage (P).
Wattage can be related to the water that is coming out of the other end of the hose.
Most people in every day life use wattage when picking out a light bulb, typically the higher the wattage the brighter the bulb will be.
In regards to Vaping, the higher the wattage or power being delivered to your coil, the more vapor that will be created. Keep in mind, the higher the wattage you use the more airflow will be needed.
Amp - The standard unit of electric current representing Amperage (I).
An amp is quite a large measure of current flow and you will probably find that most circuits will have milliamps flowing through them - that is one thousandths of an amp.
Due to the high wattage (power) that is creating during vaping we will stick to Amps for the time being.
When water or an electric current flows then a resistance to that flow is encountered, the measurement of resistance is an ohm.
Definition of Ohm's Law - the principle that the electric current passing through a conductor is directly proportional to the potential difference across it, provided that the temperature remains constant. The constant of proportionality is the resistance of the conductor.
The definition above is quite a mouthful, it simply states that the current passing through a conductor increases if you increase the voltage.
Obvious really - increase the pressure (voltage) and you will find more current will flow.
Volt - The unit of electromotive force or electric pressure representing Voltage (V).
The water that flows through a hose can be considered similar to that which flows through an electric wire or atomizer coil.
The current flow in a wire cannot of course come out of a coil like water can leak out of pipes or come out of the tap.
However a force is required to drive it and resistance to this flow is encountered, the flow of current is measured in amps.
One the most important and fundamental laws of electronics is that of ohm's law.
This law defines the relationships between current, voltage and resistance.
A good way to understand ohms laws is an analogy with a water hose.
The same way that an electric current flows through a wire or coil, water flows through a hose that you may have around your house.
When you turn on the faucet the water comes out as a result of the pressure that is provided by a pumping station some miles away.
This water pressure is similar to that used to drive electricity around a circuit, the potential difference or pd for short is the term that is used - this is measured in volts.
This driving force is provided by a battery or series of batteries in a vaping device.
Ohm - The unit by which electrical resistance is measured representing Resistance (R).
The size of the hose can be a direct analogy to the thickness of wire we use when wrapping coils.
The thicker the wire or hose the more amps it will allow it to push and essentially faster throughout the circuit.
Higher ohms = Higher resistance
Lower ohms = Lower resistance
The Relationship of Voltage, Resistance and Wattage
In this section let's completely ignore Amperage. We will discuss this shortly. Below are some examples that we can tie directly to Vaping. We will be using a basic Ohm's Law calculator to input our variables and get our results. This can be found at www.ohmslawcalculator.com and we highly recommend you try it out for yourself and become familiar with these principals.
Let's look at a standard Lithium Ion 18650 battery. Fully charged these batteries are capable of outputting 4.2v. If you install a single 18650 into a mechanical, typically a tube device, you will not have the ability to adjust the voltage. This type of device pulls volts straight from the battery without any help from a power converter.
This is a coil or replacement head in your atomizer or tank. Once installed you cannot make any adjustments to it's resistance. Diving a little deeper, when wrapping your own coils:
- The thicker the wire you use the less resistance you will get (this is like having a larger hose allowing more water to flow through)
- The thinner the wire used the more resistance you will have (like having a smaller hose, water will have to fight to push it's way out)
- If we add more wraps to the coil, essentially making the hose longer, this will add more resistance to the coil
Many people like using dual coil atomizers. To touch on this briefly, if you have two coils of the same resistance (same number or wraps and overall length) you essentially opened up your "hose" and you are now able to allow twice the amount water of through it. This now cuts your resistance in half.
- Real life scenario: if you have two 0.4 ohm coils and install them into your device your resistance is technically cut in half and you now have 0.2 ohms of resistance in your circuit.
Wattage is the power that is created throughout the circuit. It is the easiest value to understand because it is the end result of vaping.
Vaping with a Mechanical Device
Let's say that with a fully charged 18650 our Voltage is 4.2v. The only way this can change is as we vape and the battery discharges voltage. Typically it is best to put your batteries back on the charger when they are no less than 3.3v.
Because our wattage is based on the voltage and resistance we must next introduce a coil or head into the circuit. Depending on the resistance it will adjust the wattage in different ways. If we put less resistance into the circuit this will increase the wattage or power that is created. On the opposite end, the higher the resistance the lower the power that will be created.
Below are two examples of this. You will see that in both examples our voltage is a constant 4.2v. In Example 1 we have a 1.0 ohm coil producing measly 17.64 watts. This would be considered a higher resistance in most cases for vaping. In Example 2 we lowered our resistance to 0.2 ohms and you can now see that our wattage increased to a much larger 88.2 watts. Now this is more like it!
When using a device, like a mechanical mod, you have no option to adjust the voltage. The only way to create more power is to decrease the resistance of your coil(s).
Vaping with a Variable Voltage or Variable Wattage device
Above we discussed having to change your resistance if your voltage is constant. In this section we will assume that our resistance is the constant. Now there is plenty of information regarding what types of coils you should use at certain wattage but a lot of it comes to personal preference so let's just talk about the overall premise of ohm's law in regards to a constant resistance.
Every Variable Power device is variable voltage. It must be able to adjust the voltage to increase the wattage. This is once again assuming we have a constant resistance. Once we put on an atomizer or tank it pretty much sets the resistance and we get to increase our power based on that. Keep in mind that most atomizers will hit a max wattage limit due to airflow capabilities. If you can't supply enough airflow to your coils you most likely need to turn your device down to prevent burning.
In the following examples we will work with a 0.2 ohm coil as our constant. The only way to change this is by either adding more wraps to your coil (raising the resistance) or removing wraps (lowering your resistance). Regardless though, once you are set on a coil resistance that is the constant in your set up. Example 3 shows our 0.2 ohm coil set to 60 watts. The voltage needed to get to this wattage is only 3.46v. Now if we increase our wattage to let's say 100 watts you can see that our voltage increases to accommodate the additional power demand. Example 4 shows that at 100w we need 4.47v.
What to know about Amperage and Batteries
Amperage can be described as the flow of current through a device. Because batteries are a direct part of the circuit and the main power house it is very important to know the amp ratings and limits of your batteries.
We will discuss batteries further in another course but for the time being understand that all batteries have an amperage rating. Knowing this and understanding how much current your circuit is producing is crucial to ensuring that you are vaping safely and not putting you or someone else in danger.
This is much more important for mechanical devices. Variable Power devices typically have protection circuits built it so it is not as important. As a matter of fact, most devices will not let you fire an atomizer below a certain ohm to prevent over discharging of the battery.
In the following examples we will look at a constant 4.2v coming off you device. We will alter the resistance on the circuit to see how this will affect the amperage across the circuit. Let's say that we have a battery rated at 20A (Amps). In Example 5 we will try intruding a 0.5 ohm coil into the circuit. When doing so you can see that it is only pulling 8.4A from the battery. This is considered a safe resistance for the battery. Let's try reducing the resistance a little. In Example 6 we have 0.15 ohms of resistance on the circuit and it is pulling 28A from the battery. This IS NOT safe and can potentially turn ugly. Your battery could vent producing hot gas and even flames if the device continues to fire for too long! In Example 7 we have found that a resistance of 0.21 ohms gets us right at the battery's limit of 20A.
It is safe to say that if you have a 20A rated battery you can safely install any combination of coils as long as the overall resistance is above 0.21 ohms.
Try out the ohm's law calculator for yourself!
The following will teach you how to properly use the Ohm's Law Calculator. Click the link below and follow the guide: http://www.ohmslawcalculator.com/
We will use the scenario of a customer coming into your store with a mechanical device and a 30 amp battery. This means that the circuit cannot exceed 30 amps. They ask you, "What is the lowest possible resistance I can build to that will be safe for my setup?"
We already discussed that when 18650 batteries are fully charged they can output up to 4.2 volts. And we know that the customer's battery is rated at 30 Amps, representing the current. Example 8 shows these two variables entered into the calculator with an arrow next to the Calculate button. This is all we need to determine the missing variables to the equation. After clicking "Calculate" Example 9 shows that a fully charged 18650 battery with a 0.14 ohm coil in the atomizer will pull 30 amps of current. If we go any lower than 0.14 ohms you will put strain on the battery and potentially damage you and your device. The more common method of achieving 0.14 ohms would be installing two coils or a "dual coil" setup. Each coil will need be exactly 0.28 ohms. Note: The overall resistance of your circuit is determined by many other variables than just your coils. The resistance of the device and even how tight the screws are tightened in the RDA can play a large factor.
Which of these are NOT one of the four characteristics of Ohm's Law?
- Wattage (Power)
Which of these is the end result of a completed circuit?
Pick the option that make this following statement true: If you increase the voltage in a circuit . . . .
- the resistance will also increase.
- the amperage will also increase.
- the amperage will decrease.
- the wattage will decrease.
True or False? If your Voltage is constant and you lower your resistance you will also lower your wattage.
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Choose the incorrect statement.
- If your resistance is constant and you increase your wattage you will also increase your voltage.
- If your resistance is constant and you increase your wattage you will also increase your amperage.
- If your resistance is constant and you decrease your wattage you will increase your voltage.
- If your resistance increases and your voltage is constant you will decrease your wattage.
True or False? If your Voltage is constant the only way to ensure you are building safely for a Mechanical device is to adjust the resistance of your circuit so you don't exceed the batteries Amperage Rating.
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Using the Ohm's law Calculator (www.ohmslawcalculator.com), determine what the lowest, safe resistance would be for a battery rated at 25 amps. Remember, when fully charged an 18650 can output up to 4.2 volts.
You have successfully completed the "Vaping Basics" Course on Ohm's Law. We highly recommend that you visit http://www.ohmslawcalculator.com/ and try out some of the examples for yourself!
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