Sub ohm newbie question

[EmeraldLeo1982]

I've seen that most VV/VW devices won't go below 1.2ohms or so. Mech mods are made for sub-ohm but generally don't have VV unless somebody adds it with a DNA20

 

[WattWick]

I wonder how much research the VV mod crowd has done on how many amps they pull from their batteries when boosting voltage.

 

[dr g]

Explain, because this statement makes absolutely no sense. If the VV circuitry was subohm your battery would get hot from just turning the device on, not mind actually firing an atomizer

Only if VV circuitry did nothing at all. VV goes through cycles of on-off switching to produce the variable voltage (very simplified). The switch in the VV device cannot have a high resistance, or the device will not be able to get enough power out of the battery and will be inefficient.

Taking the example of the Provari with a ~15w limitation, at 3.3v battery volts, it needs to pull 4.55a from the battery, which requires a .73 ohm load maximum, without any switching, and disregarding efficiency. The switch is likely far more efficient than that.

I wonder how much research the VV mod crowd has done on how many amps they pull from their batteries when boosting voltage.

There's not much research to do, but it is often not understood that output amps is not the same as battery draw.

 

[LucentShadow]

I wonder how much research the VV mod crowd has done on how many amps they pull from their batteries when boosting voltage.

I'd bet that most of them have not done any. There are some of us that have been trying to spread some knowledge about that, though.

Here's a recent thread about that:

http://www.e-cigarette-forum.com/forum/battery-mods/425673-boost-circuit-math.html

And there are a couple of blog posts by Rader2146 on the subject, here:

E-Cigarette Forum - Rader2146 - Blogs

.

 

[dr g]

Only if VV circuitry did nothing at all. VV goes through cycles of on-off switching to produce the variable voltage (very simplified). The switch in the VV device cannot have a high resistance, or the device will not be able to get enough power out of the battery and will be inefficient.

Taking the example of the Provari with a ~15w limitation, at 3.3v battery volts, it needs to pull 4.55a from the battery, which requires a .73 ohm load maximum, without any switching, and disregarding efficiency. The switch is likely far more efficient than that.

Take fore example this 3A output buck/boost converter with specs that would make it appropriate for vaping:
http://www.ti.com/lit/ds/slvs916c/slvs916c.pdf

The switch on impedance is 50mOhm ... or .05 ohm.

 

[volume control]

Take fore example this 3A output buck/boost converter with specs that would make it appropriate for vaping:
http://www.ti.com/lit/ds/slvs916c/slvs916c.pdf

The switch on impedance is 50mOhm ... or .05 ohm.

Dude thats the resistance of the SWITCH mechanism of the circuit, you add whatever that resistance is with the resistance or your atty for total circuit resistance....Its not a subohm circuit unless you put a subohm atty on there, which most VV devices cant even come close to handling.

 

[GrandSam]

I've never been a fan of sub-ohm builds. The lowest I have ever gone is 1.0 ohms on a mini RDA. Great flavor, probably the best out of all my atomizers, amazing vapor, and overall nice build. I made mine with 30 gauge kanthal and cotton wick (boiled 3 times prior to using).
4 wraps of wire, cotton wick wrapped 3 times around my pointer and middle finger (very tight wraps). Trimmed down to fit in the RDA.
Be sure to clean whatever atomizer you are using.

 

[UncleChuck]

Dude thats the resistance of the SWITCH mechanism of the circuit, you add whatever that resistance is with the resistance or your atty for total circuit resistance....Its not a subohm circuit unless you put a subohm atty on there, which most VV devices cant even come close to handling.

While you are correct that the switch resistance isn't the load on the battery, the load on the battery in a VV device is higher than just the load of the atty. As you turn up the voltage the load increases even more.

Boost circuits draw higher current, then change that higher current into higher voltage. That's why IMRs are needed for VV devices.

If you have a vamo set to 15 watts, and the internal battery is at 3.5v, the vamo will have to draw current equal to a .8 ohm coil at least. If you add if inefficiency of the chip, it's even more current drawn to produce a given voltage.

The chip is the weak point there, as usually the chip is simply unable to draw more current before the current rating of the battery is reached, so there aren't issues with drawing too much current.

Just an anecdote, but when I use my VW devices with 18350s at a 10w setting the batteries get pretty warm. I use the same 18350s with my .8ohm gennys and the batteries stay cool. Granted I do have to take 2-3 puffs directly in a row and hold the button down until the cutoff is reached to get a decent vape out of a cartotank at 10w, where as a 3 second puff on the .8ohm will do me just as well, so vaping habits are probably a factor. Either way I'm stressing my batteries less with subohm builds than with VW devices.

 

[WattWick]

(Snip)
Either way I'm stressing my batteries less with subohm builds than with VW devices.

... and that's what aggravates me the most about the holier than thou anti sub-ohm campaigns.

Edit: Bile removal service.

 

[dr g]

Dude thats the resistance of the SWITCH mechanism of the circuit, you add whatever that resistance is with the resistance or your atty for total circuit resistance....Its not a subohm circuit unless you put a subohm atty on there, which most VV devices cant even come close to handling.

When the switch is closed, the load is bypassed and at that time the switch is the significant resistance in the circuit. The bottom line is the switch circuit is indeed well subohm, or the booster would not be able to output a "subohm" power level. The point being there's nothing inherently wrong with a subohm circuit.