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Explained: Under Load Voltage Drop

Welcome to the first of the “Explained” series in which we’ll take a simplified and hopefully not very technical view at some of the core concepts that are being used and abused in the vaping community. Technically this is the second such post since Drip Shields and how they Work was my first attempt at this.. but hey, this is the first one with “Explained” in the title!

Today we’ll take a look at Voltage Drop Under Load, a concept that is abused by modders and reviewers with increased frequency since the re-emergence of mechanical mods with the growing genesis rebuildable hype.

Voltage drop under load is, unfortunately, unavoidable and not quantifiable without some more much-needed variables. It does not only occur in mechanical mods but any non-regulated device.. and unfortunately to some regulated ones but that’s a completely different matter. The effect is caused by nothing else but a loss in efficiency which becomes more and more apparent in lower resistances.. let’s look at an example.

As a mechanical I love my old-school Omega, it was one of my first mods and thanks to some TLC it’s still working like it did on the day I got it. Heis Fictional has asked to borrow it to use with his genesis atomizers and has been completely unhappy with the voltage drop when he’s vaping on his sub ohm coils, his inline meter shows he’s only vaping at 3.5Volts.. so he gives the Omega to his sister She is also Fictional who has been happy as a pig in shit with it, she’s getting a much better vape out of it with her inline meter showing she’s vaping at a noticeably higher 3.9V.

As a result, they go on a random forum.. let’s call it ABF and make contradicting reviews on the same device.. which is as helpful as a third nipple, let’s look at why:

We’ll be using 0.1ohms as the mod resistance.. this isn’t the most accurate metering but since it’s the same device it cancels out anyway. Both batteries meter at 4.2V and for the calculations, I’m using data from Torchy the Battery Boy (epic name btw)

[learn_more caption=”Equations to be used (yes math!)”]
Current = \frac{Battery \: Voltage}{Mod Resistance + Battery Resistance + Atomizer Resistance}

Atomizer \: Voltage = Current \times Atomizer \: Resistance

Voltage \: Drop = Battery \: Voltage – Atomizer \: Voltage [/learn_more]

Heis Fictional

Vapes: 0.8ohm coils with an AW IMR

I =\frac{4.2}{0.1 + 0.05 + 0.8} = 4.42amps

V_{coil}= 4.42 \times 0.8 = 3.53Volts

V_{drop} = 4.2 – 3.53 = 0.67Volts

She is also Fictional

Vapes 2.2ohm clears with an Efest IMR

I =\frac{4.2}{0.1 + 0.085 + 2.2} = 1.76amps

V_{coil}= 1.76 \times 2.2 = 3.87Volts

V_{drop} = 4.2 – 3.87 = 0.33Volts

Comparatively, She is also Fictional is getting half the drop that Heis Fictional is getting at a much more reasonable 0.33V. The point here, however, is that no matter how well made the mod might be there is always a small drop due to internal battery resistance and the difference in atomizer/coil resistances. The lower the resistance of the coil, in fact, the bigger the loss.

Hence (I haven’t used the word hence since uni) any reviewer giving out a “voltage drop” value without mentioning his battery and coil is not being helpful in any way; there are too many variables for a comparison. Similarly, any vendor claiming a near zero drop under load is just using a term people are familiar with for marketing reasons, they’d be better off mentioning the resistance of the mod itself.

Questions? Do note I’m not an electrical engineer or otherwise expert on this stuff.. just a geek


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