The thing about VV/VW and their electronics control module is that they effectively seperate atomizers and batteries. It's like it appeared a voltage transformer between both parts (and in many senses it is). They call it DC-DC converter, and their maths are relatively simple. All the energy (or energy per time unit, i. e. power) drawn from the battery is converted in the same energy (power) applied to the atomizer, it just interchanges voltages and currents. but remembering that P = V * I it's a simple math.....
Well, there are some energy losses inside the converter, a yield (or efficiency) factor involved, which usually falls in the 0,90 through 0,96 (or 90% up to 96%), which means that the energy drawn from the battery is partially lost (the difference between 100 and the yield in %) as heat in the innards of the converter. It's an unavoidable toll to get constant power through the decay of the batteries.
Having said all that, your applied current through the atomizer, even in the case of very low resistance (nickel and temperature control active), doesn't matter much. It's about power applied, and then requested to the battery, plus the losses. The batteries always works at its natural voltage output (4,2 fully charged, and so on), so it doesn't matter (at first approach) how the electronics feed the atomizers, it does count how much power the electronics pull from the battery, and from that power, the current is fixed by the P = V * I formula, as V is a fixed parameter.
On second approach, yields do change over the current and power applied over the atomizer, but its changing is not so big if you work between boundaries of the electronics (and usually the electronics are controlled by some logics to cut output outside the boundaries, hence the low resistance, check atomizer, high load, etc., messages).
Some people have said that as the electronics cut off partially power once the temperature of the coil pass over the setting point, in this mode the power consumption (i.e. draw from the batteries) is even lower. But that supposes you're running your atomizer dangerously near the dry-hit without temperature control. My opinion is that temperature control is a big step forward, but it cannot improve our taste buds, and surely it wasnt their intention: they are far better detectors of the 'dry-hit' situation......
About your example:
39 W of power plus the losses are drawn from the batteries, now the resistance does not count, we have the power! The 'at X
Ω' does not add more relevant info . Let's say for the sake of this example they are about 50 %, that is, at 3,7 V of output voltage. In the side of the atomizer (with 0,5
Ω coil) you are effectively putting about 8,8 A, but in the side of the batteries, with a typical 93% of yield, you are pulling out 42 W, and at 3,7 V that means 11 A. The atomizer resistance (being that with nickel or with any other material) does not count for these calculations, it only appears in the atomizer side once you need to know the current applied, but with very different resistances (like kanthal and nickel ones), provided they are inside the electronic boundaries, the power and battery drain are essentially the same.
Now about the 'weak battery' message. DC-DC converters monitor the voltage output of batteries so they can warn us about their state (cut off near depletion). They do that in two ways: monitoring voltage output without load (it should be over 3,2 - 3,4 V) and monitoring the voltage drop when batteries are under load. If the voltage drop is bigger than some specified parameter the converter interprets this as a low battery or a weak battery, if the voltage without load appears normal.
But in your HCig mods, or at least some of them, the battery is not properly connected to the board. Under heavy loads (near the 40 W upper limit) the improper connection adds some voltage drop to the battery under load, and the converter takes that as a weak battery, but instead is a weak connection. Same happens with the improper battery, one that cannot pull out enough current due to its internal resistance or state. Improve the connection (taking out the anodized, putting additional wiring) and the problem will be fixed.
Just to end this hefty volume (someone should cut my fingers!....
), the equations involved, a derivative of the well known ones from Ohm's law:
where
η is the greek letter 'eta', usually used for this yield/efficiency matters in engineering and physics.... According to Evolv's statements, DNA40 is rated at 93%.
That said:
