So I was playing with the new gizmo I bought to measure battery internal impedance, and it appears it is also able to measure pretty low resistances. Accuracy is not the best, it's an entry level cheap tool, but it's precise down to 0.1mohm or so it claims (yes that's one tenth of a milli-ohm)
I first compared the value I got for my iHeat 510, as this value is also measured relatively precisely by my various e-cig mods (in order to do power or TC regulation you need a ohmmeter able to go down to the 0.01 ohm or even 0.001ohm range) and it was spot on at 0.36ohm.
Of course you can't just measure these low resistances with your average digital multimeter, you usually need pricier tools. But this new tool I got is quite alright and it's using the 4 wires measurement method to minimize the impact of the probes themselves.
I proceeded to measure my Milaana circuit resistance and I got 0.31ohm, not too shabby! This resistance translates to almost 57W of power at the theoretical 4.2V voltage. Of course we're not getting that much and not for long: cells don't rest at 4.2V anymore when they age, and their voltage sags due to their internal impedance (sum of internal resistance and internal reactance, cf
http://en-us.fluke.com/training/tra...nary-batteries/what-is-battery-impedance.html)
I'll do a separate post in the battery safety thread about my experimentation with the tool, as it's very useful to determine any cell health, and it's easier and faster to do than measuring the IR using the old-school way with a power resistor. Basically you can track over time how this value evolves and determine how close to end of life your cells are.
I did a quick SPICE simulation to determine how much one of my cells would sag with the Milaana, knowing the cell IR, then I did a quick empirical test to confirm by setting one of my mods in power mode at 57W and watching the real-time circuit voltage value drop.
I got more apparent sag on the mod than in the simulation, but let's say that for an average not too old cell with around 0.050ohm internal resistance, resting at precisely 4.2V when full, as soon as you hit the trigger the circuit voltage drops to 3.61V and I'm "only" getting 42.2W of output power.
I used quotes around only because it runs bloody hot already and can definitely combust very fast. It requires constant attention in order to not brown the load too quickly or worse, and I must admit that I tend to forget all the technique needed since I've been using regulated vapes nearly exclusively.