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Regulated 18650 Mods and Battery Life/Power Consumption

Introduction to Regulated Mods

In researching how regulated mods work and what kind of performance you get with different batteries, I found a dearth of well described information about these specific details. I decided to gather here all the information that I have discovered and try to explain it in as simple of a way possible to help other people understand how these devices work exactly, in as minimal of techno jargon as possible.

We'll start at the top. Compared to a mechanical device that is just a single circuit from the battery to the coil, a regulated device has two circuits. The first circuit is between the battery and the chipset that regulates the power. This chipset controls exactly how much juice is pulled from the battery. Then there is the second circuit between the chipset and the coil. This provides a layer of safety, as the chipset can monitor the battery and detect when its voltage output is outside the safe operating parameters of this style battery and cut off the battery before it overheats and vents. This also allows for "wattage regulation". Instead of how a mechanical mod has slowly decreasing wattage as the battery is drained, a regulated device can force the battery to output at a consistent wattage even as the battery is drained.

So, knowing this, we can determine the load on the battery with a far simpler calculation than you need to use for mech mods. The values in these calculations are just for showing how this works; so on a mech mod, the load (further to referred as amperage or amps) on the battery is determined by:

Voltage/Resistance=Amperage

So at max capacity, a .5ohm coil will pull 4.2v/.5ohm=8.4amps (which is 35.28watts) and at the minimum safe discharge it would be 3.2v/.5ohm=6.4amps (which is 20.48watts).

But on a regulated device, let's say you set the wattage to the same starting wattage of 35.28watts. Since the chipset is regulating the output to maintain that 35.28watts, the drain will start out at 4.2v just like the mech mod. The calculation is

Watts/Volts=Amps

So you have the same 35.28w/4.2v=8.4amps. But at minimum battery discharge of 3.2volts with wattage regulation you have 35.28w/3.2v=11.025amps. Then you have to factor in the efficiency of the regulator, so say it is 96% efficient. That means the regulator eats 4% of the current in doing what it does, so that could increase your amp draw by another 4% to maintain the 35.28watts. So that puts maximum amp draw on your battery at 11.46amps.

What does this mean?

So when looking at a regulated mod, you have two considerations in terms of performance. What is the max wattage of the chipset, and what battery should I use? I will use a popular example:

The Evic VTC Mini. This is a 75 watt device that holds a single 18650 battery. So in using our battery load calculation we can determine that at max wattage, the VTC will pull:

75w/3.2v=23.4375amps, plus a probably 90% efficiency =25.78125amps.

Now, if we do a little reading on Mooch's battery tests you'll see that to get a battery that can safely discharge at almost 26 amps, you have to drop down to at least a 1500mah battery like the HB2/4/6. But realistically, who's going to run at 75watts? The Samsung 30Q is 3000mah and can easily handle 20amp discharges (but reduces its capacity to about 2600-2700mah), and does not have much significant voltage sag all the way up to 25amp (although it does have significant loss in total capacity when discharged at 25amps). This means with the Samsung 30Q you can safely run

20w*3.2v=64Watts (then the 90% efficiency loss puts it at 57.6watts)

If you keep the Evic Mini under 57watts, you can maximize your power output with the 30Q without overstressing your battery and minimizing capacity loss. And you can even safely push up to 75watts without venting your battery, but you will lose a noticeable amount of total capacity in doing so. But, let's say you use the 2500mah Samsung 25R. This battery, according to Mooch, can handle 20amps safely without any voltage sag or overheating causing noticeable capacity loss. But when you push it towards 25amps you get significant voltage sag. This means it is unusable past 20amps. So you will not even be able to fire the Evic VTC Mini at 75 watts with a Samsung 25R, or if you do you'll only get a few puffs before it gives a battery warning due to the voltage sag. So even though it is a higher CDR battery, it has less performance at higher wattages.

How do we determine overall battery life?

Now we get into the real tricky part of regulated mods. On a mech mod, we can estimate battery life based on what coil you are using and what mah your battery is. But a regulated mod is different because of the isolated circuit the battery is in. Mah doesn't solely determine battery life, the wattage the device is set to does. It's better to use a "watt-hour" calculation. This means how many hours it can push that many watts. That tells you roughly what your battery life will be.

WattHours=Mah*Voltage/1000

So let's use the Evic VTC Mini with the Samsung 30Q 3000mah battery. This means your watthours are (assuming minimum safe battery discharge voltage of 3.2v):

3000w*3.2v/1000=9.6watthours.

That means, if set to 1 watt you'll get 9.6 hours of firing before the battery is drained. If you set it to 50watts, you'll get 9.6wh/50w=.192hours of use, or 11.52minutes of holding the button down.

This is an estimate, because your voltage is going to start out at 4.2 and slowly drop to 3.2 as you discharge, plus adding in the efficiency loss of 90%(or whatever), but it gives you a baseline to compare to other mods and batteries. And your battery's voltage sag is going to come heavily into play here, but that's too complicated to make formulas for.

Note how coil resistance didn't factor into this at all. The resistance of your coil does not affect battery life at all on a regulated device. The only difference coil resistance might make is affecting the efficiency of the regulating chip, but it would be minor from what I understand. The wattage you set the mod to, the mah capacity of the battery, and the voltage stability of the battery under the amp load it is experiencing are the only determining factors of your battery life. So that emphasizes the importance of making sure you get a battery that outputs stable voltage at the amp load you're expecting to be putting it under.

Multi-Battery Mods

Now, for the final piece of the puzzle we've all been waiting for: dual+ battery mods. Almost every regulated mod I know of runs multiple batteries in series. Many mech mods run batteries in parallel because it is safer for the batteries. But with a regulated device you have the chipset managing the battery, so safety is less of a concern. To explain the difference:

- In parallel, current draw is split evenly between batteries. That means the outputting voltage stays the same, as it is limited to the voltage of each individual battery. It does, however, mean that you get almost twice the mah and it splits the amperage between the batteries.

- In series, current is fed through one battery into the other, grossly oversimplifying it. This means that you get double the voltage output, but the amp load isn't split and the mah of the individual batteries doesn't stack together.

So to put this into math, with wattage set to 100:
Parallel: 100w/3.2v=31.25amps/2=15.625amp per battery (this doesn't factor in the 40% or so actual efficiency of stacking batteries in parallel, but that makes the math too much for me)
Series: 100/6.4=15.625amp per battery

Everything seems equal, right? But what about the doubled mah of parallel you ask? Well, let's not forget everything we've learned already! Let's calculate the actual expected battery life of these two contrasting setups!

Let's take 2 of those same Samsung 30Q's at 3000mah and see how many watt hours we get in series vs parallel.

Parallel: 6000mah*3.2volts/1000=19.2watt-hours
Series: 3000mah*6.4volts/1000=19.2watt-hours

Yup, that's right. In a regulated mod there is absolutely no gain whatsoever in actual battery life for a parallel configuration despite it actually doubling the mah capacity of your setup.

But wait! There's more! We're forgetting to calculate in the efficiency of the chipset! From what I've read, most chipsets are more efficient in regulating a series configuration than a parallel. You may get 96% efficiency from a series configuration, but it might drop to 92% when running in parallel. I'd assume this has to do with the higher voltage being easier to step up or down to deliver consistent current to the coil, but I'm not certain. So you actually likely get a slight improvement in battery life in series over parallel, even though you don't get to double the mah with 2 batteries.

 

Hopefully this helps you wrap your head around these devices and gives you all the technical background data you need to make informed decisions. The biggest takeaway I can give you on this is: don't believe that just because a mod says it can do 200watts you can actually draw that much from your batteries. Do some research on Mooch's battery tests and make an informed purchase on what battery you should get based on exactly what wattage you actually plan on running your mod at. Proper wattage combined with the right battery will give you good performance and battery life. But pulling too many watts from a battery that can't handle it will ruin your battery and not give you any kind of decent performance at all. A dual battery mod with 2 3000mah 30q's will give you great performance and battery life if you keep it under 115 watts (give or take), just as a single battery mod will work great under 57 watts (give or take). Any more than that and you'll start permanently losing capacity in your battery, or in the case of a battery like the 25R that experiences significant voltage sag at these loads it may not even fire at all, even though it's fully charged.

Now, this doesn't factor in Pulse Width Modulation (PWM) or the fact that most vapers only hold the button down for a few seconds per puff, meaning that continuous discharge isn't really happening. Most dual battery mods will use PWM after 150 watts to reduce strain on the battery, which is how they can advertise 200w on 2 batteries. But it's still safer to use continuous discharge calculations in determining battery safety to give yourself some headroom on your batteries. Plus, if you use pulse ratings to do your calculations, you're running the risk of your longer chain-vaping sessions over stressing your battery. Continuous discharge ratings give you the safety of knowing exactly what your limits are and giving you the freedom to vape your device as hard as you want within those limitations without fear of hurting your battery.

But I want to try out 200w to see if I can vaporize my lungs!

So, say you want to run one of these new 200w devices at 200watts. Let's assume it starts PWM at 150watts. That means your battery has to handle continuous discharge up to 150watts, and pulsing discharge up to 200w. The first calculation is:

150w/6.2v= 24.19amps (at 90% efficiency means around 27amps rounded up)

Let's find a 27amp battery. We have the Aspire ICR Cell7, LG HD2, VTC4, and LG HB6 (listed in order of performance). The Aspire had the longest runtime, but it also had the fastest voltage drop, meaning it was pulling higher amperage the whole time (increasing heat and likelihood of venting). The HB6 didn't last as long, but also ran the coolest meaning it will lose the least total capacity being fired at this load and be the least likely to vent. Other than the VTC4, though, these are all 1500-1800mah batteries. None of the 2500 or 3000mah batteries can handle amp draws over 25amps continuously. So the 30Q, HG2, 25R, or any of the other popular batteries are not recommended if you want to set a dual battery device to 150watts or higher (remember the 115w limit mentioned earlier). Keep in mind, this is with continuous discharge as our limiting factor. Most people will never hold the fire button down for more than 5-10 seconds, which is technically classified as a "pulse". But when chain-vaping you can build up internal heat on the battery over time, causing damage similar to continuous discharge, which is why it's recommended to use continuous discharge as your baseline to determine battery safety. Can you run a Samsung 30Q at 150w in a dual box mod? Actually, yes, almost. It has enough voltage stability to handle 25amps, and possibly a few more.  Will you vent the battery? Probably not. But you will wear it out a lot faster. It has at least 2.5% capacity loss at a 25amp discharge. And if you feel the case starting to heat up, you definitely want to give it a rest to cool off, and maybe turn your wattage down a little. The 2500mah LG HE2/4 can handle pulsed discharges up to 30amps without enough voltage sag to get cut off in a regulated mod. But in doing so it can exceed the recommended heat limitations of these batteries, meaning you increase your risk of venting and you are causing permanent capacity loss in your battery, even when just pulsing.

I'd like to do an explanation of PWM and how it enables you to fire higher watts on a battery without overheating them, but I cannot find any test data on it. Mooch does pulse tests on batteries doing a 5-10second on, 30 second off pulse, but that isn't anywhere the same as PWM. That's more akin to how a vaper will actually vape, so may give you better data to base your battery decisions on than his continuous discharge tests. My recommendations above are generous safety limits for people who aren't interested in taking risks, or don't really fully understand the risks of pushing batteries to their limits. If you think you know what you're doing, feel free to ignore continuous discharge ratings and go with the pulse ratings and run higher mah batteries at ludicrous speed.

It may sound like I'm basically trying to say that no 2 battery setup can handle 200w with current batteries, and I'm not. The LG HB6 actually can just fine. And the LG HE2/4 can with only minimal risk. Many batteries probably will fire 200w just fine. You just need to know that it probably wears out your battery much faster, and if it starts to get hot you may permanently kill it, or even vent it. The regulated mod will most likely cut it off after only a handful of hits though, and prevent you from blowing anything up. But if you're getting "battery weak" errors on your mod at max wattages, now you know why!

 

And of course, the most important thing to note is that this is all theoretical calculations based on estimated data. Your actual performance will vary greatly depending on battery integrity and actual usage. One guy might get hours of actual use out of a battery, where someone else may only get minutes depending on age of the battery and wattage setting, and all the other little factors we can't calculate into simple formulas like corrosion on the contacts, etc.