batteryless VV passthrough, volts and amps

[Nikkel]

Some questions about the batteryless VV passthrough like the one listed here:
$5.58 Variable Voltage USB Passthrough for E-Cigarette at FastTech - Worldwide Free Shipping
I think the actual VV settings are: 3.0, 3.6, 4.2, and 4.8.

The usual recommendation I've seen is to use a 5 volt 2 amp AC-USB adapter. That is what I'm currently using.
Using a 1.8 ohm atty at 4.2 V and 4.8 V requires more than 2 amps.
A = 3.0/1.8 = 1.7, W = 3.0 x 1.7 = 5.1
A = 3.6/1.8 = 2.0, W = 3.6 x 2 = 7.2
A = 4.2/1.8 = 2.3, W = 4.2 x 2.3 = 9.7
A = 4.8/1.8 = 2.7, W = 4.8 x 2.7 = 13.0

When I try the 4.2 V and 4.8 V settings with a 1.8 ohm atty, I don't notice much if any difference between them in terms of vapor production and heat.
What is going on here?
With a 1.8 ohm atty and a 2A adapter, does the device only output 3.6 V, even on the 4.2 V and 4.8 V settings?
If I had an inline volt meter, I could answer these questions myself, experimentally. But I don't, so I can't.
Maybe if I understood electronics, I could answer them theoretically. But I don't.
I read the Wikipedia article on buck converters but can't understand most of it.
https://en.wikipedia.org/wiki/Buck_converter
Articles says buck converters are very efficient, so I'm hoping when I use this passthrough with an external NiMH battery pack I will get battery life almost as long as if I weren't using the passthrough's converter.

I assume that the device assumes there will be 5 volts input. What if the input is 3.6 V, if connected to 3 NiMH cells in series? Or, 6 V, with 5 cells?

 

[100%VG]

Hello, Nikkel,

It is not stated whether this Passthrough uses a Buck Converter or not. I'm doubtful that it's a Buck Converter, because the Output Voltage at this Input Voltage level generally cannot be greater than the Input minus about 1.0V, so with 5.0V In, the max Out would be 4.0V. The internals are unknown.

No matter how this device actually works, I think you have already identified the major problem. Your 1.8Ω Coil requires more Amps than your 5V 2A USB Adapter can deliver when using a 1.8Ω Coil. It may well be putting out 3.0, 3.6, 4.2, and 4.8 Volts on each setting, but the Input Amps are limited to 2A, so it works fine at 3.0V and 3.6V, but you are not getting much difference between 3.6V and 4.2V, and hardly any difference at all between 4.2V and 4.8V.

To be clear about this, your 1.8Ω Coil would draw 2.3A at 4.2V, and 2.7A at 4.8V if it could, but the Input Amps are limited to 2A, so it cannot.

Purely looking at numbers with the 1.8Ω Coil . . .

3.0V x 1.67A = 5.00W . . . using 3.0V / 1.8Ω = 1.67A
3.6V x 2.00A = 7.20W . . . using 3.6V / 1.8Ω = 2.00A
4.2V x 2.00A = 8.40W . . . using 2A and ignoring Coil Ohms
4.8V x 2.00A = 9.60W . . . using 2A and ignoring Coil Ohms

So, since you don't experience much change at the higher Voltages, it is also possible that there are other limitations internal to the Passthrough that limit its operation at the higher Voltage settings when using a 1.8Ω Coil, along with the 2A Input limit. I would think you should taste and feel a 1.2 Watt increase at both higher Voltages.

With a 2.4Ω Coil, the numbers would be . . .

3.0V / 2.4Ω = 1.25A, 3.0V x 1.25A = 3.75W
3.6V / 2.4Ω = 1.50A, 3.6V x 1.50A = 5.40W
4.2V / 2.4Ω = 1.75A, 4.2V x 1.75A = 7.35W
4.8V / 2.4Ω = 2.00A, 4.8V x 2.00A = 9.60W

Your Max Wattage would be less than what you may desire in your reasoning for using 1.8Ω Coils, but you'd be able to experience the changes of each Voltage setting.

To answer your last question... the required Input Voltage is 5V, so I definitely would not connect it to anything other than 5V. With a Li-Ion or IMR at 4.2V, you'd never get a 4.2V or 4.8V Output, especially as the Battery drains. With 3 NiMH cells in Series, you'd never get a 3.6V, 4.2V, or 4.8V Output. This Device cannot Amplify the Output Voltage... it drops it below the Input Voltage. If you connect it to a 6V Source, you are likely to blow it up.

If anything will help your 1.8Ω Coils, you'll need a 5V Source that can deliver about 3 Amps... assuming the Device can handle that.

ATTENTION:
Before you attempt a 5V Source with greater than 2 Amps, you need to research this Passthrough to see if it can Safely handle a 5V Input with up to 3 Amps, and see if it is stated that the Passthrough is only supposed to use 2.4Ω Coils, or what. I mean, see what the Ratings and Specs are, and see if 1.8Ω Coils are even on the list. It is my feeling that this Passthrough is designed for 2.4Ω Coils.

 

[Rickajho]

What Mr VG said. These things are really a bad idea. Most places selling them have warnings - in bold - about not using devices below 2.5 ohms even for a reason.

You appear to have answered your own question, but still seem puzzled by the end result. The limit here is the current output of your power supply. The only thing happening trying to run 1.8 ohms at 4.2 v or higher with a 2 amp supply is stressing the power supply, possibly into a thermal component failure if you push it hard enough.

Until these things arrived on the scene passthroughs had batteries and they have them for a reason. You are drawing your load from the battery in a passthrough when you hit the fire button, not the power supply connected to it.