Question about voltage drop with mech mod

[chiliphil1]

Ok, so this question may not make a lot of sense but it is something through my research that I cannot seem to find an answer to. If it has been covered on this forum ( I am sure it has) I cannot seem to find it through multiple searches.

My question is this. With an 18650 battery in a mech mod how do you account for the voltage drop of the battery?

If the battery says 3.6 volts with a 1.8 ohm coil then it would look like this. 2A 7.2W

however when the battery comes right off the charger and it is putting out 4V then it goes to this. 2.22A 8.89W

So, when you figure your coil resistance do you have to make sure it is within range for the full discharge of the battery? I assume you would.

My math also seems off to me, is 2A correct? It seems like it would be pulling more than that

If the battery has for example a 20A maximum, then 2A would only be 2% and therefore well into the safe range, right?

Help me out here please, I am confused on this.

Also, for those of you who run mechanical mods, do you remove the battery and check the voltage throughout the day? How do you make sure you don't drop below the 2.6V mark?

 

[supertrunker]

2A is 10%.

In practice you don't account for the v-drop at all. You assume a worst case scenario: you assume your battery is charged to 4.2v and if it's a 20A battery - R=V/I = 4.2/20 = 0.21Ω, so that is the absolute lowest coil you can make, ever, with no margin of safety.

When the battery depletes to about 3.6v, you'll notice it - the vape gets weak and that's when you change it. I have never managed to get down to under 3v, because it's such a feeble vape by then.

T

 

[tj99959]

In theory a regulated device can produce a good vape until the battery can no longer support it (most have a "low voltage" shout off tho')
So it would be easier to go to low with a regulated PV than with an unregulated. The unregulated PV just become way to anemic before you ever get close to the low voltage limit. The more modern batteries give the impression of "falling off a cliff" at about 3.5v.

My rule of thumb is I try to not exceed 50% of a batteries continuous amp limit figured at it's fully charged voltage of 4.2v.
ex: 0.4 ohms @ 4.2v = 44 watts @ 10.5 amps, so a 20 amp battery would be as low as I would want to use, and I would want to error on the high side of the 0.4 ohms.