Usefull information I don't wanna forget

bwh79 said:

Thing is, you don't get 50W from a mech at 4.2V on a .5-ohm load. You only get about 35 watts from that. Watts = Volts^2 / Ohms, so you're looking at 4.2^2 / .5 = 35.28 watts, and never anything else (until the volts and/or ohms are changed, and then the watts will change as well.) That's the thing about mech mods. You can always turn the power up on a regulated device; on a mech, you're stuck with what you get.

The key thing to realize here is that power, or wattage, is the conserved quantity. "Power in equals power out," as they say. So if the device is delivering 50 watts to the atomizer, for example, then it is also, by definition, pulling 50 watts from the battery (plus a few % to power the device itself, but we can ignore that for the moment.) One formula to determine amp draw is:

Amps = Watts / Volts

No matter what the output power of your device is set to, the battery only outputs a single voltage (roughly 4.2 at full charge, less as the battery depletes.) So if your battery is sitting at, for example 4.0 volts, and the device is set for 50 watts, then the amp draw on the battery is 50/4 = 12.5 amps.

Note that I didn't mention the ohms value at all. Note also that I came up with a perfectly valid amp reading, without even knowing what the ohms were! That's because for a wattage-regulated device, amp draw is determined only by the watts setting, and the battery's charge state (and the device's own efficiency, we'll get to that later), and not at all by the resistance value of the attached load. Or to put it another way, ohms don't matter on a wattage-regulated device! All you need to know to determine your amp draw, are what watts the device is set to, how many volts are the battery charged to, and how efficient is the device itself.

Ohms are in there, somewhere, but they're hidden. Watts are equal to Volts*Amps, but, because those "Amps" are themselves equal to "Volts/Ohms," then Watts are also equal to Volts*Volts/Ohms. So when you set the device for 50 watts, it has to read the ohms, multiply it with the watts you set, and then take the square root of that value, to find the appropriate number of volts to provide, so that the actual amount of watts delivered, will be the same as what you've chosen. So when we say that ohms don't matter, we mean they don't matter to you, the user, in determining how hard it will stress your battery. But they do matter very much indeed, to the device itself. You just don't need to concern yourself with them, again, for the purposes of determining amp draw. It will of course make a difference in the overall experience.

About that "device efficiency." When your device pulls 50 watts from the battery, it can't deliver them all to the atomizer. It needs to keep a little bit of that power for itself. So in order to deliver 50 watts, it has to draw a little more than that. To determine the actual amp draw, you take the one calculated earlier, and divide by the device's efficiency (or just use 90% if you aren't sure.) So then we would have a final amp draw of 12.5 / .9 = 13.888... amps, at 50 watts (on any resistance.)

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Now let's look at mech mods for a minute. If watts and volts are all that matter on a regulated, why aren't they all that matter on a mech? And they are, sort of. Again, let's say you're using a mech mod, you're getting 50 watts from it, and your battery is at 4.0 volts. Again, then, you're pulling 50/4 = 12.5 amps from the battery. HOWEVER, all of this is only possible if you have a very specific resistance. Specifically, 0.32 ohms. If it were anything else, then it wouldn't equal 50 watts, and for this example we have already defined it as being 50 watts. And, after you take a hit or two, and the battery drains down from 4.0v to 3.99v, then it won't be 50 anymore, either. But for a very brief moment, it all comes together. See, in a mechanical mod there is no regulation; battery voltage is delivered to the atomizer directly. So if Watts are equal to Volts*Volts/Ohms, and you change the ohms, then you change the watts. If you change the volts, then you change the watts. If you change any one thing, then one or both of the other values have to change as well, to keep everything balanced. But unlike with a regulated device, where you just "set" the watts and let it do the dirty work, with a mechanical mod, the only way to even know the watts in the first place, is to calculate them using the resistance value and battery voltage. Then, since what we're really after is the amps value, you don't even need to check the watts since the volts and ohms are all you need. Of course, you can still figure out the watts if you want to, it just isn't necessary.

To get the amp draw on a mechanical mod, divide battery voltage by resistance. You need to know the resistance, or you can't make this calculation. You could also calculate the watts if you like, but it won't tell you anything about battery safety.
To get the amp draw on a wattage-regulated mod, divide watts setting by battery voltage, and then by device efficiency. You do not need to know the resistance, because the device knows it already, and knowing the reistance wouldn't help anyway, since all you're looking at is watts over volts. Also keep in mind this is battery output voltage, not the same as voltage applied to the atomizer. If those were the same, it wouldn't be a regulated mod. That's the point of regulation, that's what it does. That's what it means.

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And how, pray tell, does the device know whether you have a 5A or a 25A battery installed? Maybe it has an amp limit of 17.5 amps, perfectly safe to put a 20A battery in there and push it as hard as the mod will allow. Try that with a 5A battery in there and you're going to have a problem. Whether or not it's a mech is not the issue here, you can still "draw too many amps" and damage the battery, the device, or yourself, if you expect it to do all of the thinking for you...

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