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Low/High resistance, at equal wattage: what's the difference?

Discussion in 'Variable Voltage APV Discussion' started by godzilla93, Oct 2, 2012.

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  1. godzilla93

    godzilla93 Senior Member Verified Member

    Joined:
    Sep 11, 2012
    Location:
    Brooklyn
    I was wondering: what is the difference between a low and high resistance atty (or carto, or whatever), at the same wattage? In other words, if the only difference is that the same wattage can be achieved with lower voltage for LR attys, then LR attys would seem to be the way to go in terms of battery life... What's the point in using medium or high resistance with a VV device? Does it have to do with vapor heat? Help please... :confused:
     
  2. A17kawboy

    A17kawboy Senior Member Verified Member ECF Veteran

    Joined:
    Jul 20, 2012
    Location:
    Northern BC, Canada
    Weirdly and counter-intuitively, the way electricity works (I read something about it on here and just now had to prove it to myself on paper) the higher resistance atomizer running at a higher voltage actually draws less amperage from the battery and therefore the battery lasts longer. Seems strange but the formulae don't lie.
    Low resistance atties were developed mainly for people with constant voltage devices that wanted more wattage (heat) from their vape. That's the only way to do it if you can't crank up your volts.
     
  3. godzilla93

    godzilla93 Senior Member Verified Member

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    Location:
    Brooklyn
    Interesting (and, yes, totally counter intuitive!). Thanks!
     
  4. dragginfly

    dragginfly Senior Member ECF Veteran

    Joined:
    Nov 3, 2010
    Location:
    Missouri, USA
    This is part of the difference... almost.

    More accurately, it has to do with the vapor temperature.

    Heat is energy. The energy stored in a PV is expelled as heat.

    A given battery will provide a fixed total amount of heat regardless of
    the voltage, resistance, or output wattage. At higher wattage the heat
    is generated more quickly.

    The power output of a PV is measured in watts, which is how fast
    energy (heat) is dissipated. The heat can be dissipated slowly or more
    quickly depending on the wattage (rate of energy output).

    Vapor quality is not dependent on heat, but on temperature.

    At a fixed vapor temperature, the vapor quantity depends on
    the overall amount of heat.

    Transfer more heat to a given quantity of e-liquid and the vapor
    production is warmer (or hot). Or with more liquid in contact with
    the heat source, the vapor temperature is cooler.

    A fixed amount of heat transferred to one drop of e-liquid will
    have a higher temperature than the same amount of heat
    transferred to two drops of e-liquid.

    Now this is where the difference between a "small" coil with
    low resistance and a "big" coil with high resistance at the
    same power output becomes evident.

    The "big" coil comes into contact with more e-liquid and creates
    more vapor at a lower temp than from a "small" coil even with
    the same power output rate (watts).

    Now carry this one step further...

    Compare a 2.5 ohm coil to a 2.5 ohm dual coil setup.

    In the dual coil setup you have two 5 ohm coils operating
    at the same time in parallel.

    At 5 volts and 2.5 ohms, the current is 2 amps and the total
    power output is 10 watts in both the single and dual coil
    configuration. But in the single coil all 10 watts are laid on
    a small 2.5 ohm coil, and in the dual coil the power is split
    between two larger 5 ohm coils with 5 watts each.

    Same power. Same heat. Totally different vapor temperature,
    quantity, and quality.

    Finally, comparing a single low resistance coil to a single
    high resistance coil at the same power output, the heat
    is dissipated over a greater area (and volume of e-liquid)
    in the high resistance coil resulting in a lower vapor temp.

    The HV setup can push more power (watts) and generate
    more vapor with a given (desired) vapor temperature.

    Or at the same power output, the HV setup will generate
    more vapor at a lower temperature.
     
  5. Rader2146

    Rader2146 Ultra Member Verified Member ECF Veteran

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    Mar 11, 2012
    Location:
    Waco, TX
    Unfortunately, that is only half the formula. Below is a post from another thread, but it boils down to voltage doesn't matter; as long as wattage is the same, the battery drain current will be the same....regardless of the resistance.


    This holds true for buck (multiple battery, high voltage "bucked" down to a lower voltage) devices as well, but the math is slightly different.
     
  6. A17kawboy

    A17kawboy Senior Member Verified Member ECF Veteran

    Joined:
    Jul 20, 2012
    Location:
    Northern BC, Canada
    @Rader2146: Thank you once again sir! Very much appreciate your time and patience explaining these fundamentals. So why the heck are manufacturers not working on variable resistance atomizers that will work on fixed voltage devices?
    If I understand the concept correctly that would enable users to vary power and still have maximum battery usage efficiency.
    "Early days..." I guess. :)
     
  7. Nurzrachit

    Nurzrachit Ultra Member Verified Member ECF Veteran

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    Location:
    Gray,GA.
    Just look how far we have come in the past few years! At this pace the e-cigs of the future will not resemble what we have today at all.
     
  8. cozzicon

    cozzicon Ultra Member Verified Member ECF Veteran

    Joined:
    Jun 19, 2010
    Location:
    Chicago IL
    Coil size... coil size... coil size..... Many times an LR atty has a small coil. Not always... but often.

    Not many people talk about this... but the size of the coil matters in addition to the wattage supplied or ohms of the atty.

    If you have one coil, three ohms, four wraps- and another three ohm coil with eight wraps... they vape differently.

    It's not *just* wattage. It's also the coil, wicking material, and variations in the atomizers- none of them are the same.

    So while the electrical math is useful. It doesn't paint the whole picture... which is why people have preferences in atomizers. Some coils are tight around the wicking material. Some coils are loose around the wicking material. Some coils have no wicking material. Some coils are large.... small.... ect.

    So really... wattage is very much a general measure for the purposes of vaping. Which is to say something like "I generally prefer 6.5 watts". But the particular hardware you might be using can change that drastically- a good example being Vision Clearomizers which perform nicely at lower wattages but are about 2.4 ohm.
     
  9. Slurp812

    Slurp812 Super Member ECF Veteran

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    Jun 18, 2011
    Location:
    Northwest Ohio
    I was just going to mention coil size. A longer coil would spread out the heat a bit more.
     
  10. dragginfly

    dragginfly Senior Member ECF Veteran

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    Nov 3, 2010
    Location:
    Missouri, USA
    Excellent way to state it!

    It took me nearly a full page of explanation to conclude with this above...


    I have GOT to learn to be more concise.
     
  11. hrtserpent6

    hrtserpent6 Full Member

    Joined:
    Sep 25, 2012
    Location:
    Reston, Virginia
    Holy smokes, I was *JUST* wondering the answer to this very question. I've got a Provari on the way, and looking at the Safe Vaping Chart, I came to the same thoughts as the OP.

    Thanks so much for the great explanations!
     
  12. Shub

    Shub Full Member Verified Member

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    Oct 6, 2012
    Location:
    South Daytona, Florida, United States
    great, but slightly confusing post! Thanks
     
  13. Moueix

    Moueix Moved On Verified Member

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    Aug 20, 2012
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    Michigan and Iowa
    I learned something here, I'm just not sure what...
     
  14. johnlacie

    johnlacie Senior Member Verified Member ECF Veteran

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    Folks, this is mostly correct. But what most people forget is the internal resistance of the battery and power circuitry. For the same wattage setting, a low ohm atomizer will cause the battery+circuitry to waste more power on the internal resistance than a high ohm atomizer. This applies to PWM circuitry as well. Hope, that helps.
     
  15. godzilla93

    godzilla93 Senior Member Verified Member

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    Sep 11, 2012
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    Brooklyn
: provari
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