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View Full Version : Why PWM may not be that hard on attys



JoeyRedShirt
11-29-2013, 09:59 AM
WARNING: JoeyRedShirt is about to have a bit of a Sheldon Cooper moment.

So I've been thinking about how coils are, you know, coiled. From an electronics point of view, this means that along with being resistors, they're also inductors. So mathematically, they can be modelled as an inductor in series with a resistor. Putting a scope on them, the voltage drop across them would look the same whether they were coiled or not, but effectively, the rising edge would actually cause their impedance to increase momentarily, making the effective resistance higher. This would mean that, in theory, because they are coiled, they wouldn't take the huge current hit that everyone thinks they take on the rising edge of the square wave, so they wouldn't be actually under any significant amount more strain than on a Provari. It would also mean that more wraps (greater inductance) should reduce rattlesnaking.

I doubt it, but do we have anyone on here that could provide any more insight into this?

Nemesis
11-29-2013, 11:46 AM
Hmmmmm .... Donuts !

JoeyRedShirt
11-29-2013, 12:20 PM
http://youtu.be/yaJTp-tfaNM

vdaedalus
11-29-2013, 01:46 PM
Haha, your OP was mostly clicks and whistles to me, but I'm curious, do you think coil spacing makes a difference? Because I swear once I started rebuilding my Protank heads with microcoils with every wrap touching its neighbour, the rattlesnaking on my VAMO practically disappeared. The number of wraps is close to the stock heads, I think; I do 7 wraps, 30AWG, and I reckon the stock heads were maybe six? But spread out, versus the micros where it's more of a ridgy cylinder.

If I put the drip tip in my mouth, leave it open (my mouth, not the drip tip), I can hear the pulses plain as day with the stock heads. With the micros, white noise.

JoeyRedShirt
11-29-2013, 01:57 PM
From what I know of how the inductive effect works (has to do with magnetic fields created by changing electric flow) it would make sense that tighter coils would make a better inductor than loose coils. The closer each individual coil is to its neighbours, the stronger the magnetic force acting on it would be. So yeah, tight coils should, in theory anyway, make for more induction and less rattlesnake.

JoeyRedShirt
11-29-2013, 02:14 PM
And to simplify my OP for anyone else who actually reads this thread: One way to smooth a PWM signal is to put an inductor in the circuit. Because an inductor is just a coil of wire, and an atomizer is just a coil of wire, that means that using an atomizer on a PWM mod smooths the signal. More coils and/or tighter coils make a better inductor, which makes a smoother signal!

The take-away from this is that you don't need to drop $200 on a Provari just because it does what a good atty does!

SCIENCE!!!

Nodnerb
11-29-2013, 03:55 PM
Inductors also resist change of current whether rising or falling.

JoeyRedShirt
11-30-2013, 06:35 AM
So, I found an online circuit simulator to demonstrate what I was saying. The circuit is a square wave source, with a peak of 6V, duty cycle of 50%, and frequency of 33.3 Hz. The resistor (bottom of circuit) is 2 Ohms, and the inductor (left side of circuit) is 50 mH (I seriously have no idea what the actual value here should be since it depends on the material used for the coil, how many wraps, how close together the wraps are, etc...but 50 mH is actually really low). The graph on the left is the current flow through the resistor (in yellow) and voltage across the resistor (green) the graph on the right is what you would see from the mod if you put it on a scope.

The current is the most important thing because Voltage = Resistance x Current

3684

Nodnerb
11-30-2013, 07:01 AM
The left graph demonstrates the inductors reluctance to change current turning the square wave into a sawtooth. The inductance is also probably the reason most coils seem to ramp up and down when firing your mod and then releasing the button.

JoeyRedShirt
11-30-2013, 07:30 AM
Inductors also resist change of current whether rising or falling.

The left graph demonstrates the inductors reluctance to change current turning the square wave into a sawtooth.
Careful! The first reply to this thread was "mmmmm....donuts!" If you're going to paraphrase, try to simplify what I said, rather than correct my sloppy simplification. You probably read real words in my OP!...lol

Redux
11-30-2013, 07:36 AM
So you say you don't have to have a provari. So let's do a drop test onto concrete and compare a evic to a provari. Provari will win everytime. I will pay for a quality mod and one a company will stand behind.


www.reduxvapers.com
Come check us out.

JoeyRedShirt
11-30-2013, 07:41 AM
So you say you don't have to have a provari. So let's do a drop test onto concrete and compare a evic to a provari. Provari will win everytime. I will pay for a quality mod and one a company will stand behind.

That's a build quality thing. That has nothing to do with the output signal. I'm attacking the idea of paying more for a smooth output. If your Provari is truly $120 worth of better built than an $80 33.3 mod, it was worth the expenditure!

Densetsu
12-01-2013, 06:12 PM
My Provaris are worth more than my 33 MHz mods to me, I have tried them side by side with the same atomizers, drippers, cartos...and yes, it's not just an annoying rattlesnake sound, there is definitely a difference in the flavour and vapour delivery.

JoeyRedShirt
12-02-2013, 06:31 AM
Okay, I'm sorry I besmirched the good name of Provari.

If your 33.3 mod is rattlesnaking, you can reduce it by using attys that have more individual coils and/or have their coils closer together. If you eliminate the rattlesnaking, you minimize the difference between PWM and flat signal. If you are a poor-a$$ student or something and can't afford/justify the expense of a $200 device, you can feel more confident in your cheap mod's performance by using coils that are better inductors instead of blowing your utilities budget on a mod!

YMMV

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