Calculating Current Drain | Understanding Your Vape Batteries

Calculating Current Drain | Regulated vs Unregulated

Richard WinterBatteries Leave a Comment

Calculating current drain as it relates to vaping can be confusing to say the least! Making matters worse is the fact that calculating current drain is completely different for regulated and unregulated mods (mechanical).

Where the confusion arises is that people often use Ohm’s Law to work out the Current (I), irrespective if their mod is regulated or unregulated.

While this is perfectly correct for  mechanical mods (unregulated), other factors need to be taken into consideration when calculating current drain if you’re using a regulated mod.

In brief, when discussing unregulated (mech) mods, the current drain on the battery(s) is calculated by assuming a fully charged battery (4.2V) and the resistance of the coil in Ohms. This determines the Power (wattage) that you’re vaping at.

A regulated mod however, incorporates a regulator board which means the current being drawn is NOT dependent on the resistance of the coil. The wattage you’re vaping is controlled by the on-board control circuits.

Confused…………lets break it down a bit further.

Calculating current drain; why do I need to worry?

The powerhouse of your mod (whether regulated or unregulated) is the battery. This battery will have a given capacity in terms of voltage and current.

A fully charged battery will output 4.2V. The maximum current it can draw continuously will be specified on the battery in Amps. This value is called the Continuous Discharge Rating (CDR). The length of time the battery will last, before requiring a re-charge, is specified in milliamp hours (mAh).

A typical battery will have a CDR value of 25A and a mAh rating of 2500mA.

The critical parameter we need to worry about is the CDR value of the battery.

Everything will be fine if the set-up you’re using in terms of the mod, resistance of your coil and the power you vape at fall within the CDR value of your battery.

The danger arises if your set-up is such that you try to draw more current from your battery than it’s capable of delivering. If you have a battery rated at a CDR value of 20A and you draw more than this, you could potentially cause the battery to overheat. This could cause the battery to go into thermal runaway, start to vent and in the worst case scenario……..explode!

By calculating current drain you can safeguard against this. Once you’ve identified the current your set-up is capable of drawing, you can use an appropriate value battery to run your mod.

Let’s take a look at how calculating current drain will depend on the type of mod you’re using.

Calculating current drain; Unregulated Mods

These are the simplest of devices having no electronics inside to confuse matters, yet should really only be used when you have a pretty good understanding of Ohm’s Law and battery drain. They consist of a battery, a fire button and a tank with a coil inside. It’s this coil’s resistance that will govern the current being drawn from the battery and the wattage being produced.

The important thing to understand is that the wattage achieved from this type of mod will slowly decrease as the battery starts to drain. Also battery drain is at its highest when the battery is fully charged (4.2V). This is explained by the use of Ohm’s Law.

Let’s have a look at a few examples…

If we have a fully charged battery (4.2V) and a coil resistance of 0.5 Ohms, the current drain on the battery will be 8.4 Amps. This is determined by:

I=V/R.  I=4.2/0.5, therefore I=8.4A.

As the voltage (V) reduces so will the Current (I).

The wattage produced will be 35.28W. This is determined by:

P=I2xR.  P=8.4×8.4×0.5, therefore P=35.28W.

Alternatively, you can also use P=V2/R. P=4.2×4.2/0.5, therefore P=35.28W.

Equally as the voltage (V) reduces so will the wattage.

Calculating current drain; What if you’re using two or more batteries?…

If you have a dual or triple battery unregulated mod, just remember that batteries in series will add their combined voltages. So two batteries, each measuring 4.2V will equate to 8.4V. Three batteries will equate to 12.6V and so on. Batteries in parallel will always be that of a single battery, this being 4.2V.

Alternatively, you can use our Series and Parallel Battery Calculator to determine the combined battery voltage and use this figure in the above calculations.

It’s as simple as that.

If you don’t want to work it out in this manner, then simply use our Ohm’s Law Calculator, which will give you the basic Voltage, Current, Resistance and Power results.

Our Power, Resistance and Current Calculator will also help you determine your Build Deck Resistance, Power and Battery Current Drain. It will also let you know if you’re working within the safe operating range of your battery. An alarm message will be displayed if the set-up you have exceeds the specified CDR value of your battery.

Calculating current drain; Regulated Mods

Just like mechanical mods, regulated devices have a battery, a fire button and a tank with a coil inside. The addition is a regulated chip board that controls the variable wattage and voltage of the device as well as providing a plethora of safety features.

Unlike an unregulated mod where the wattage decreases with battery drain, a regulated mod will maintain the wattage you specify from full battery charge down till the battery drains to cut off.

This is where the confusion takes place.

The coil resistance when used on a regulated mod has nothing to do with the wattage. The user specifies the required wattage via variable controls on the device.

In simplified terms, the battery is separated from the tank by a control regulator. The output of the regulator is what is connected to the tank and will follow the Ohm’s Law equation. The input side of the regulator is the important section in terms of battery safety, this being the real current drain on the battery.

When calculating battery drain, the following equation is used.

Current Drain = Wattage/Battery Low Voltage Cut Off/Number of Batteries/Mod Efficiency.

Before we get into a few examples, let’s explain the above formula…

Wattage should be the maximum the device is capable of going up to. It is calculated like this in case of inadvertently increasing the watts to maximum. In order to have a lower spec battery, you could use the wattage you would never exceed if it is lower than the max wattage.

Battery Low Voltage Cut Off is typically about 3.2 Volts. This is the point at which your specific mod will shut off saying the battery requires charging.

Number of batteries is the amount of batteries your device takes, i.e. 1 for single, 2 for Dual, 3 for Triple etc.

Mod Efficiency is how well the on board regulator works. Typically set at 85%, some are higher while others are lower. To determine the exact efficiency of the mod you are using, you would need to look up the value specified in its specifications.

The configuration of the batteries is not important, it doesn’t matter if the batteries are in series or parallel.

So…….let’s look at a couple of examples

If we take a regulated mod with a maximum wattage of 75W, a low voltage cut off of 3.2V, a single battery and a mod efficiency of 85%, we get the following:

Current Drain (I) = 75/3.2/1/0.85. Therefore I = 27.57A.

This tells us that our battery at the worst case scenario will draw just over 27A. Which means that using a 25A battery is not ideal as it will be operating above its specified CDR (Continuous Discharge Rating). In this instance, a 30A battery should be used.

Obviously, there are parameters that could be tweaked in order to use a 25A battery safely. You could reduce the wattage from the maximum the device can deliver to the maximum you would likely vape at. Or recharge your batteries before they reach the low voltage cut off.

If we say we would reduce the wattage to 60W, the following would happen:

Current Drain (I) = 60/3.2/1/0.85. Therefore I = 22.06A.

From this, you can see that the result is now within the 25A CDR value.

If we now look at another example of a dual mod with a maximum wattage of 75W, a low voltage cut off of 3.2V and an efficiency of 85%, we get the following:

Current Drain (I) = 75/3.2/2/0.85. Therefore I = 13.79A.

So what does that all mean?

From this result, you can see straight away that the current is being split between the two batteries for the same wattage. This means that you could use lower CDR batteries which in turn could mean you can get increased mAh batteries which would last longer between charges.

Equally, triple or quadruple battery mods can be worked out in this manner by just inputting the number of batteries.

In summary, a regulated mod will draw less current (Amps) from the battery at full charge (4.2V) and maximum current (Amps) at the Low Voltage Cut Off (3.2V). And don’t forget, Ohms (your coil resistance) have no relevance when calculating current drain in a regulated mod.

It’s as simple (ish) as that. If you don’t want to work it out in this manner, then simply use our Battery Amp Draw/Drain Calculator to achieve your results.

Most importantly, NEVER exceed the CDR value stated on your battery. It’s there for a very good reason. It’s always best to be safe rather than sorry.

Lastly, the only other thing to mention in terms of batteries……..

What if my mod has an internal battery?

It’s fair to say that the manufacturer of your mod will have taken the battery drain requirements into consideration. Internal battery mods are only applicable to regulated devices. From what we have already learnt, the coil resistance has no effect on calculating current drain.

Therefore, the battery of the particular device will be sufficient to operate at the maximum wattage the mod is capable of providing.

So in short, you don’t have to worry about calculating current drain if you’re using a mod with an internal battery.

That’s it folks…….. Hopefully by now you know enough about calculating current drain to stay safe when vaping! We hope you found this useful, please feel free to leave a comment below.

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