High-Wattage Vaping - Resistance Differences?

[ThrownClear]

Hello there!

So I got my first high-wattage capable device in the mail about a week ago (an IPV2s) - I popped on my Magma on which I had built my first sub-ohm coil (26-gauge Kanthal, dual-coil, 0.35 ohms), made sure my Sony VTC4 was fully charged, set it to 30 watts and had my first high-watt vape.

I was instantly a convert. I'd never experienced a "warm" vape before.

So I started bumping up the wattage and didn't notice any difference... it was then that I remembered that SX330 chip isn't capable of "stepping down" - with my fresh 4.2 volt battery, I was vaping at about 50 watts, and there was nothing I could do about it except wait for the battery to die down a bit if I wanted lower wattage.

So, here's my question (sorry it took me so long to get to...) if I want to take advantage of the lower range of my device I need to build at higher resistances, but will I notice any differences in the vape quality if I do this? Do the coils take longer to heat up? What's the difference in battery life? Any difference in the vape experience itself?

Thanks in advance!

 

[readeuler]

Using the ever-handy Ohm's Law pie chart, the current is given by sqrt(P/R), where P is the power (watts), R is the resistance. So if you make R smaller, the current goes up. That means that to maximize battery life, you want as high of resistance as possible. I'm not a build-master (some day, some day...) so I can't comment on the experience, but your battery will last longer with the same wattage and higher resistance.

 

[ThrownClear]

Readeuler - thank you for the reply!

At first you had me a little confused, because when you say "current", I was still thinking "voltage" - but of course by current, you mean amperage. This does indeed fit in with what I notice when I start plugging in different numbers into an Ohm's calculator.

So then I finally broke down and googled "Ummmm... what's an amp, exactly?"

I think the concepts of Watt vs. Volt vs. Amp are starting to sink in.

Still on my original topic, I think I once saw somebody post something about the great battery life you'd get if you built an 8 ohm coil, but that it would take forever to heat up. I'm still not sure I get how it all fits together, and I'm still wondering what kind of results non-sub-ohm, high-watt-device users are getting and what they recommend.

Believe me, I know all the answers are here on e-cig forum somewhere, but I'm having trouble figuring out just what keywords to search to find them. No luck so far. So, thanks again!

 

[rusirius]

Using the ever-handy Ohm's Law pie chart, the current is given by sqrt(P/R), where P is the power (watts), R is the resistance. So if you make R smaller, the current goes up. That means that to maximize battery life, you want as high of resistance as possible. I'm not a build-master (some day, some day...) so I can't comment on the experience, but your battery will last longer with the same wattage and higher resistance.

Not exactly... Well yes, but no...

You're right about the current, but all too often I see those who look at it this way, from your perspective and think "Oh, well if I run a higher resistance I get a longer battery life..." But you're only considering the regulated side of the mod, not what's happening on the battery side...

A battery's life can be directly converted into watt hours. It doesn't matter HOW you generate those watts, it's still all the same in the end...

A lot of people think of it like this... Well, if I run a 2.5ohm coil at 8.67V then I get 30W... If I run a .25ohm coil at 2.7V then I get 30W... But the first build is only drawing 3.47A while the second is drawing 10.95A... So I'll get much better battery life out of the first build...

Unfortunately that's flawed thinking... Because your battery can't "adjust" the voltage. It has a fixed (though changes through discharge curve) voltage. The "regulator" in the mod is what changes the voltage output, and it does so by "exchanging" voltage for current.

If I run a mod at 4.2V and draw 5A then that's roughly what the battery sees (varies slightly due to effeciencies in the regulator, etc)... However if I ramp that power up to 8.4V and STILL draw 5A, then the battery will actually get 10A drawn since it's only supply 4.2V. The regulator doubles the voltage and in doing so doubles the current being drawn from the battery.

When looking at these kinds of things, you have to consider the input and output of the regulator as two separate sides.

So in the end, the battery will last exactly the same amount of time regardless of what voltage or resistance you run given the same wattage.

Wh = mAh x V / 1000

So if we have a 2000mAh battery that supplies 3.7V, 2000mAh x 3.7V / 1000 = 7.4Wh...

If we had a regulator efficiency of say 90% that would mean we could run at 6.6W for an hour off that battery... Doesn't matter what voltage and resistance we use to generate that 6.6W...

 

[daviedog]

Elegant analysis..

 

[readeuler]

Aw shucks, rusirius... Turns out I'm not an anything expert

Good to know, thank you for the correction and clarification!

 

[ThrownClear]

That's some really interesting math...

So...

that answers some battery questions...

Maybe I should ask my other questions a different way -

Is there any difference between a 40-watt vape using a 1.2-ohm coil at 6.9 volts, and a 40-watt vape using a 0.44-ohm coil at 4.2 volts?

If the answer is no, then I'm afraid I've wasted everybody's time, but it gets kind of overwhelming around here, with people vaping all different resistances at similar wattages... I thought maybe there were different vape qualities involved with sub-ohm vs. not-sub-ohm (ohm-plus?).

 

[BrushyHillGuide]

I'm pretty lost but I'm still following the thread, hoping I'll figure this stuff out.


Sent from my iPhone using Tapatalk

 

[Papa Lazarou]

There isn't a really simple answer to that. Being spot on with resistance is less important with a VW mod because you can adjust the power to suit. You do not have this option with mechanicals. For example, you could make a 1.2 ohm coil with 5 wraps of 0.25mm Kanthal (assuming a 2mm diameter coil) or 11 wraps of 0.4mm Kanthal. The links will take you to a coil calculator website (Steam Engine).

Both coils will have the same resistance, but completely different properties as far as heat at a given voltage is concerned. The one made with the thicker 0.4mm wire will handle a lot more power than the one made with 0.25mm. In fact it will need a lot more power to heat up and should work quite nicely at 40w, while the 0.25mm coil will burn and taste like **** if you attempted to run it at 40w The larger coil also has more surface area, so this should translate into a larger amount of juice vaporised in a given time, if the wicking is able to keep up, which is another important factor.

The site I've linked to is really useful because it works out the heat flux at a given wattage, so you can predict whether something is likely to be "too cold" or "too hot" before you start.

 

[rusirius]

That's some really interesting math...

So...

that answers some battery questions...

Maybe I should ask my other questions a different way -

Is there any difference between a 40-watt vape using a 1.2-ohm coil at 6.9 volts, and a 40-watt vape using a 0.44-ohm coil at 4.2 volts?

If the answer is no, then I'm afraid I've wasted everybody's time, but it gets kind of overwhelming around here, with people vaping all different resistances at similar wattages... I thought maybe there were different vape qualities involved with sub-ohm vs. not-sub-ohm (ohm-plus?).

If you have the exact same surface area and heat flux, then no... But chances are you won't, and that's where the difference is...

When you get right down to it, wattage = vapor production. Assuming everything else is right, i.e. airflow is good enough to remove heat created by wattage, wicks are good enough to deliver juice as fast as it's being vaporized, etc... As long as it's a "happy coil", then wattage just determines how much juice is vaporized...

However, there's a lot of other variables that you have to think about...

If I take 26awg wire and wrap a .4 ohm dual coil and vape it at 30W... I have a heat flux of 166mW/mm2 and a heat capacity of 29.87mJ K-1. That's a pretty decent heat flux, a fair amount of surface area, and not too bad of a heat capacity... In case you don't know, heat flux is how much heat is being generated in a given area. So is it an extremely high heat in a very small pinpoint, or is it a little bit of heat spread out over an entire room, etc... Heat capacity is how much heat the wire holds, meaning will it lag and take a bit to come up to temp? or will it instantly heat? likewise will it keep cooking juice long after I stop firing it or does it just stop immediately, etc...

Now imagine I decide to take that same 26awk wire and make a higher resistance coil... So now I make a 2 ohm dual coil build... Now if I run that same build at 30W I've got a heat flux of 33mW/mm2 and a heat capacity of 149.39mJ/K-1. So it's not even going to produce vapor... it'll never get hot enough... and even if it did it would take a REALLY long time to heat up and a REALLY long time to cool down... Because there's SO much more mass of wire there...

BUT... We don't have to use the same wire... Imagine if instead we made a 2 ohm coil out of 32awg... We'd have a heat flux (at 30W) of 268mW/mm2 and a heat capacity of 9.24mJ/K-1. So we've actually got a higher heat flux (quite possibly too much) and yet very little heat capacity... It's basically instant on and instant off...

If we took that same 32awg wire and made a 3.2ohm dual coil, we'd have a heat flux of 167mW/mm2, so about the same as our 26awg... 32awg wire is .202mm diameter... So at 18 wraps (to get 3.2ohm at 2mm i.d.) we'd have a a total length (both coils combined) of 7.27mm... For our 26awg coil it's .405mm diameter... and we'd need 7 wraps to make our .4 ohm coil... A total of 5.67mm...

So we're not only getting instant on and instant off, combined with the same heat flux, but with 32awg we now have 1.6mm of additional surface area. Which means we'll be more efficient at creating vapor... As long as we have enough airflow and the wick can supply all of our larger surface area with juice, we'll actually get more vapor out of the longer coils while still maintaining the same heat flux.

 

[JeremyR]

Good info you've got here.. If it hasn't been said, lighter gauge wire at higher ohms will heat faster. I vape a parallel 32g 1.4ohm at 6v on my apv and it's great. Heats faster & hotter than 28 at same ohms & power

 

[ThrownClear]

Great stuff, my friends.

All this time I'd been thinking of wire gauges as a simple way to adjust resistance... "I like the look of this coil, but with 28 gauge it's at 1.2 Ohms - let's use 26 gauge and knock it down to a 0.9!"

The whole temperature / heat flux thing, well, I guess I'd seen some posts on it here and there, but I didn't really understand it. It's beginning to click - and MY GOD thank you for introducing me to steam-engine.org!

I was a little freaked out that suddenly I was going to have to start taking "heat flux" into consideration - but it's all there on steam-engine, and its got so many more variables to play with than the simple Ohm's Law calculator I've been using on my phone.

Looks like I'm going to have some fun building experiments in my future - up till now, it's really only been about resistance.

 

[ThrownClear]

Good info you've got here.. If it hasn't been said, lighter gauge wire at higher ohms will heat faster. I vape a parallel 32g 1.4ohm at 6v on my apv and it's great. Heats faster & hotter than 28 at same ohms & power

Very interesting...

So, I ran some numbers through steam-engine (like I do ), and it looks like you're vaping at about 25 watts? I tend to live in the 35-45 range, but if I use 30 gauge, it looks like I'll be in a good temperature range.

I think I'll try it on my next build.

 

[ThrownClear]

If we took that same 32awg wire and made a 3.2ohm dual coil, we'd have a heat flux of 167mW/mm2, so about the same as our 26awg... 32awg wire is .202mm diameter... So at 18 wraps (to get 3.2ohm at 2mm i.d.) we'd have a a total length (both coils combined) of 7.27mm... For our 26awg coil it's .405mm diameter... and we'd need 7 wraps to make our .4 ohm coil... A total of 5.67mm...

So we're not only getting instant on and instant off, combined with the same heat flux, but with 32awg we now have 1.6mm of additional surface area. Which means we'll be more efficient at creating vapor... As long as we have enough airflow and the wick can supply all of our larger surface area with juice, we'll actually get more vapor out of the longer coils while still maintaining the same heat flux.

Okay... I've been plugging all sorts of numbers into steam-engine, and this is fascinating stuff...

How come I don't hear more about guys making 3.2 Ohm dual coils with 32awg? It makes sense, and with our newfangled high-watt regulated devices, it seems to make even more sense. Is there a downside I'm not seeing?

15 minutes later -

Okay... I found a downside. With my device, which maxes out at 8.5 volts, the most I could get out of a 3.2 ohm coil would be 22.58 watts. Still not too bad... but I'm getting used to the feel of a 35-45 watt vape. Still... this is all good food for thought.

 

[tj99959]

Don't know, but I can get a pretty nice vape at 2 ohms .. 4v (2 amps)

There really is such a thing as how you wrap a coil that fits into the equation. I can wrap your .35 ohm coil about a dozen different ways, and get a dozen different results.

 

[rusirius]

Okay... I've been plugging all sorts of numbers into steam-engine, and this is fascinating stuff...

How come I don't hear more about guys making 3.2 Ohm dual coils with 32awg? It makes sense, and with our newfangled high-watt regulated devices, it seems to make even more sense. Is there a downside I'm not seeing?

15 minutes later -

Okay... I found a downside. With my device, which maxes out at 8.5 volts, the most I could get out of a 3.2 ohm coil would be 22.58 watts. Still not too bad... but I'm getting used to the feel of a 35-45 watt vape. Still... this is all good food for thought.

Exactly. It's why previous to my dna40 the t5 was my favorite mod, cause it went up to 9.3 volts. The dna40 does as well. The t8 really interested me when the specs said 14v, but then they changed it at the last minute to 7v and I lost all interest. I love high voltage vaping!

 

[DaveP]

When you look for variable voltage/wattage devices the most efficient variable devices use buck/boost type regulators (in terms of delivering what you need). Any time you use a regulated device you will lose some battery power to buck or boost. All regulators involve some tradeoffs to get you where you want to be, so you might as well be able to buck (vape at lower than battery voltage) AND boost (vape at higher voltages than your battery can deliver). Those features allow you to find the right heat for your coil at any time. Buck regulation is more efficient and easier on the battery than boost regulation.

High watt vaping will always be hard on batteries. If you can find a coil that vapes well at 3.5v to 4.2v you will be in the most efficient range, since the battery will be doing most of the work and the electronics don't have to play extreme games as much to give you what you need. When you vape at close to the battery voltage the regulator circuit gets to sit back and relax a little more.

In the video below, Phil Busardo shows some o-scope screen shots at different settings on a Vamo V5. You can see what the actual voltage is to achieve and equivalent buck or boost level. It's pretty revealing as to how the regulator has to work to do what we ask it to do. The scope shots start around 22 seconds in.

 

[JeremyR]

Very interesting...

So, I ran some numbers through steam-engine (like I do ), and it looks like you're vaping at about 25 watts? I tend to live in the 35-45 range, but if I use 30 gauge, it looks like I'll be in a good temperature range.

I think I'll try it on my next build.

Yes about 25w on parallel 32 @ 1.4 ohm. And it gets hot fast.




This is the coil at less than 3 seconds on a dry burn.




The biggest thing one needs to consider is the wire gauge in relation to wattage and what it takes to heat that wire. Also the amount of that gauge wire you have to heat(wraps).

I think you will be surprised by how fast the 30g will heat and cool. And the amount of instant vapor you get with it.

 

[JeremyR]

Okay... I've been plugging all sorts of numbers into steam-engine, and this is fascinating stuff...
How come I don't hear more about guys making 3.2 Ohm dual coils with 32awg? It makes sense, and with our newfangled high-watt regulated devices, it seems to make even more sense. Is there a downside I'm not seeing?
15 minutes later -

Okay... I found a downside. With my device, which maxes out at 8.5 volts, the most I could get out of a 3.2 ohm coil would be 22.58 watts. Still not too bad... but I'm getting used to the feel of a 35-45 watt vape. Still... this is all good food for thought.

Well the first question is hard to answer... People actually think heavy gauge wire heats faster, for many reasons I won't get into.. But it doesn't... So we have a lot of educating to do on the option. Good thing is Now we have tools to figure all the calculations and now we can show it. Back in the day we figured all this out on our own.

The incredible difference in the example you give is the heat up time and temprature. As well as wick coverage.

A vape that takes 7 seconds to heat up at 40w and a build that takes 2 seconds to heat up at 22 watts equals out. Especially if you want to take 3 second pulls an blow clouds without going low sub ohm

 

[edyle]

Readeuler - thank you for the reply!

At first you had me a little confused, because when you say "current", I was still thinking "voltage" - but of course by current, you mean amperage. This does indeed fit in with what I notice when I start plugging in different numbers into an Ohm's calculator.

So then I finally broke down and googled "Ummmm... what's an amp, exactly?"

I think the concepts of Watt vs. Volt vs. Amp are starting to sink in.

Still on my original topic, I think I once saw somebody post something about the great battery life you'd get if you built an 8 ohm coil, but that it would take forever to heat up. I'm still not sure I get how it all fits together, and I'm still wondering what kind of results non-sub-ohm, high-watt-device users are getting and what they recommend.

Believe me, I know all the answers are here on e-cig forum somewhere, but I'm having trouble figuring out just what keywords to search to find them. No luck so far. So, thanks again!

In the OP you mentioned:
"(26-gauge Kanthal, dual-coil, 0.35 ohms)"
That consists of 1.4 ohms of 26 gauge kanthal.
If you made quad coils with the same 0.7 ohm coils, that would contain 2.8 ohms of 26 gauge kanthal.
If you made octo coils, with the same 0.7 ohm coils, that would contain 5.6 ohms of 26 gauge kanthal.

As for 8 ohms, that's equivalent to more than an octocoil.