Dual coil question - especially for sailorman

[Trollkin]

In recent posts, Sailorman mentioned that dual coil cartos really need 4+ volts to work correctly. That statement reminded me of my (bad) early experience with my lavatube; like a dummy, I bought some Smoktech 1.5ohm DC cartos, which (of course) my LT fired at under 3.7 volts max, regardless of my setting (the whole 2.4-ish amp cutoff thing). Performance was dismal, as I should have expected. I quickly realized what I had done, and scored some 3ohm cartos (which turned out to be dual coil as well) which perform beautifully - of course, only at 4.3+ volts. Anyway, Sailorman mentioned that he would be willing to better explain DC cartos' higher voltage requirements, and I bet others are curious about this as well. So here is my thread, to beg him to do just that.

Please shed some light on this for us - I'm actually kind of excited to learn about something I had only vaguely suspected before today, and thrilled that these boards are populated with crazy-knowledgeable people (like him), willing to share.

Anyway, spill!

 

[sailorman]

Puttin' me on the spot, eh? I should be good at this by now. I need to save one of these threads so I can just C&P, but here it is.. Why DC cartos suck at 3.7v.

It's a matter of watts to the coil. A 1.5ohm DC carto is 1.5ohm total resistance. It has two 3ohm coils, wired in parallel for a total resistance of 1.5ohms. For this reason, you can't expect a 1.5ohm DC to perform any better than if you took two e-cigs, fitted them with 3ohm cartos and vaped them at the same time.

Nobody wants to use a 3ohm coil on a 3.7V battery. Why would they want to do it twice?
Looking at the numbers, it is only a good vape if you like cold fog.
With a 3.4V eGo, it's even worse.

Most people prefer to vape somewhere between 6 and 10 watts.
The popularity of 1.7ohm Ressurectors bear that out.
Look what a 1.7ohm Resurrector does on a 3.4V eGo.

3.4 x 3.4 / 1.7 = 6.8 watts at 2 amps. Not bad.

Now, look at the number for a 1.5ohm DC carto.

3.4 x 3.4 / 1.5 = 7.7 watts at 2.27 amps.

But those 7.7 watts are split between two 3ohm coils.

7.7 / 2 = 3.85 watts, and at the same, relatively high, 2.27 amp battery draw.

3.85 watts is cold. Two ice cubes don't become warm because there are two of them.
You just end up with twice as much cold fog as you would with a single 3ohm carto.
For the same current draw, you would be getting 7.7 watts with a Single Coil 1.5ohm carto.
If that's how you like your vape, then go for it.
But I don't hear anyone talking about how good an eGo works with a 3ohm carto.

However, at 4.5V, a 1.5ohm DC works very well.
(4.5V x 4.5V / 1.5) / 2 = 6.75 watts per coil. That's a lot of warmer vapor.

If you use 5V, it's even better at 8.3 Watts, which is a common "sweet spot".

It's that simple. If you like 3ohms on low voltage, you'll love a DC twice as much.
I'm not contending anything so simple as more watts are always better. I'm not into hot vaping.
But there's difference between hot and downright cold.
Even the cheapest mini-cigs vape at more than 4 watts.
Some people are o.k. with 4-5 watt vaping. That's cool (pun intended), but I don't understand the kerfuffle raised about the Lavatube regulating a 1.5ohm DC carto down to 3.7V from the same people who swear by a DC carto in their egos.
Even the vendors who wouldn't dream of recommending a 3ohm carto in an ego, turn right around and sell you a 1.5ohm DC carto with it.

 

[Trollkin]

Ah-HAH! That is so simple that even I understood it. Many thanks - I knew my brain was missing part of that equation. Your analogy to vaping a pair of 3 ohm devices at once is spot-on.

Once again, I salute you!