“LR” stands for low-resistance (for use on 3.7V or less batteries). “HV” stands for high-voltage and, although that is the term such attys go by, it really is a misnomer. They are used on high voltage mods, but the atomizers are high resistance. When appropriately matched with the voltage of the fat batt or mod, LR and HV atomizers are quite safe [do make sure to keep your atty constantly moist] … and can dramatically enhance the intensity of the vape (vapor, flavor, and throat hit).
To understand this HV and LR stuff, it helps to be familiar with Ohms Law … which really isn’t a big deal to grasp. If this non-techie (i.e., yours truly) can do it, anyone can:
Power (measured in watts) is the intensity of the vape. 6-8 watts is the “sweet spot” for most vapers.
Current (measured in amps) is what can burn out atomizers. Roughly speaking: around 1.5 amps is fine; 2.0+ amps is risky.
But watts and amps are not properties of atomizers or batteries. They are derived from atomizer resistance (measured in ohms) and battery voltage (measured, of course, in volts). The formulae are:
Watts = Volts X Volts / Ohms
Amps = Volts / Ohms
So we need to balance battery voltage with atomizer resistance to get an ideal vape intensity (6-8 watts or so) without burning out the atomizer (i.e., not let those amps get too high). If the voltage is too low and/or the atty resistance is too high (relative to each other), the watts are low and you get a wimpy vape (little TH, vapor, and flavor). On the other hand, if the voltage is too high and/or the atty resistance is too low, the amps are high and you can burn out the atomizer.
Caveat Regarding Resistance and Voltage Numbers
In what follows – and throughout the vaping community – we refer to atomizer resistance and battery voltage as a set number, e.g., 2.3 ohms and 3.7V. In fact, atomizer resistance should be viewed as +/- 0.1 ohms, e.g., a “2.3” ohm atty is more like 2.2-2.4 ohms
And actual battery voltage drops considerably from fresh off the charger to stopping. The “nominal” voltage is more of an average or midpoint. For example, a “3.7V” battery starts out at 4.2V fully charged and drops down to 3.2V before demanding to be recharged. [Part of the appeal of high mAh batteries is that they stay at the higher end of the range longer than a low mAh battery.]
Standard (510) Atomizers
A standard 2.3 ohm 510 atty on a 3.4V eGO (i.e., a typical eGO/Tornado, Riva, or Hello 016 kit) generates a safe 1.5 amps … but only 5 watts of power: not bad, but not intense enough for many vapers.
That same atty on a 3.7V mod (or Kr808 battery) yields 6 watts and 1.7 amps: nice vaping with little risk of atty burnout.
Most “HV” atomizers are 4.5 ohms resistance and are intended for use on 6V mods (using two 3.0V batteries). This results in 8 watts of vaping (very nice) and 1.3 amps current (a conservative level).
Some HV attys are 3.5 ohms, intended for use on 5V mods: 7 watts and 1.4 amps. [BTW, 3.5 ohms is the resistance of a standard 801 atomizer. Unsurprisingly, prior to the advent of LR and HV atomizers, the 801 was very popular with users of 5V mods like the Prodigy V1 and V2.]
Others are 5.2 ohms, intended for 7.4V mods (using two 3.7V batteries): 10.5 watts (too high for me, but good for some I guess) and 1.4 amps.
So a correct matching of these “HV” atomizers with these 5.0, 6.0, and 7.4 voltage levels delivers a powerful yet safe vape.
LR atomizers are intended to yield vape intensity (watts) on 3.4V or 3.7V similar to what the higher voltage mods deliver. But some of them generate atomizer-blowing current.
The further you push the amps above 1.5, the greater the risk of burning out an atomizer (although I wouldn’t worry too much about anything up to 2.0 amps).
The typical resistance of LR atomizers is 1.5 ohms. Vapers routinely use such 1.5 ohm LR attys on 3.4V egos (7.7 watts and 2.3 amps) all the time: excellent vape intensity … but notice that suppliers warn about limited life spans of such LR atomizers. [Used on a 3.7V mod, the amps are 2.5 … and start out at 2.8 amps when the battery is a fully charged 4.2V.] There is no physical danger in such high amps – nothing blows up. It’s just that these 1.5 ohm attys die faster than standard (or high) resistance atomizers.
Another consequence of the high amps created by 1.5 ohm LR atomizers is that they should only be used on batteries of at least 450 mAh. Otherwise, you risk damaging the battery as well.
I like to use 2.0 ohm LR atomizers on my 3.7V mod: 6.8 watts (which is great for me) and 1.85 amps (pretty safe). On an eGO, that would be a fairly satisfying 5.8 watts and non-risky 1.7 amps.
Most suppliers carry LR atomizers and cartomizers. HV attys are more difficult to find.
Those various resistances on 5V, 6V, and 7.4V will generate the following watts (i.e., intensity of the vape) and amps (i.e., the current that fries attys):
3.5Ω: 7.1 watts and 1.4 amps on 5V … 10.3 watts and 1.7 amps on 6V
4.2Ω: 5.9 watts and 1.2 amps on 5V … 8.6 watts and 1.4 amps on 6V
4.5Ω: 8 watts and 1.3 amps on 6V … 12.2 watts and 1.6 amps on 7.4V
4.7Ω: 7.7 watts and 1.3 amps on 6V … 11.6 watts and 1.6 amps on 7.4V
4.8Ω: 7.5 watts and 1.25 amps on 6V … 11.4 watts and 1.5 amps on 7.4V
5.0Ω: 7.2 watts and 1.2 amps on 6V … 11 watts and 1.5 amps on 7.4V
5.5Ω: 6.5 watts and 1.1 amps on 6V … 10 watts and 1.3 amps on 7.4V
All are fairly atomizer-friendly with the current. Your desired intensity is likely to be somewhere in there. [Mine is at the low end, i.e., ~6.5 watts.]
FYI: I didn’t do all those watts and amps calculations in my head. Rather I used this simple online calculator: enter any two values (e.g., ohms and volts) and it calculates the other two (e.g., watts and amps).