PWM and YOU! (V8)

[LordDavon]

So, I have received some questions about the v8 and why it hits harder than people are used to, even at it's lowest setting. Well, we have had some discussion about that in the Official DV thread, and I thought it would be good to break it out of the DV thread, since it does answer a lot of questions. So, here is the new thread, spawned from a v8 discussion, and now "PWM and YOU!"

I received my V8 today, and it is a powerhouse.


I've been using a CE4+ and an E1 Revive V2 on the provari at 4.0 Volts. Set the V8 on 4.0 Volts and promptly blew the coils on those two. I'm thinking that the V8 is putting out more than what is indicated. Dropped it down to 3.0 Volts, put a new CE4+ on it and all is well. Tons of vapor and great taste. Also changed out the innards in the E1, and it is doing great on the V8.


I have an oscilloscope (DSO Nano v2) heading this way and will take a look at the V8 output to determine the peak and average voltages at the various settings. I'll post the results here.


RodeoGeorge

Just so you know, RodeoGeorge is going to be doing a nice bit of testing with the V8 soon, so we will get some excellent info on where the voltages compare.

That is the same Oscilloscope I have. Make sure to get the latest BenF loaded on it. If you need any help getting it updated, give me a shout out on Skype. I used the dfu-util on my Mac.

If you are looking for the peak and average, I have some in my review of the V8. They may help until the DSO Nano V2 arrives. Obviously, I could only focus on a set voltage or two during the review, so a nice listing of each is really needed.

The reason the V8 blew your coils, is because it isn't a constant voltage, like your ProVari. The V8 uses Pulse Width Modulation, which means it hits the coils at about 7.2V (sometimes it peaks at 7.4V) pulses according to the DSO Nano. Even though the averages under load are lower than their intended voltage, they still produce more wattage. Here is why...

When you calculate wattage (ohms law) on a constant voltage device, you calculate the voltage squared, and divide by the ohms of resistance. This is basic ohms laws, as I know you are aware.

When you calculate wattage for a PWM device, you calculate the peak voltage squared, divide by the ohms of resistance, and then divide by the duty (percentage of pulse).

Now, taking into consideration that the PWM device is only averaging about 3.2V average (40% duty), when set to 4V, we are going to give some examples using 4V setting, with a 2 ohm cartomizer:

Constant Voltage: 4V squared = 16. Divided by 2 ohms = 8Watts
PWM: 7.2V squared = 51.84. Divided by 2 ohms = 25.92Watts. 25.92Watts divided by 40% = 10.37Watts!

Roughly, the PWM device is 25% more powerful than the constant voltage device, in this example, at the same setting. Now, these examples came from the V8. But, keep in mind that I haven't had my morning coffee, so my calculations may be off a little. Plus, the V8 does peak higher at times, so the duty would be larger at times.

LD

This explanation is pretty good, but I am having a hard time breaking this down to easier terms. This is where I could really use some help.

 

[Woody-GC]

Great idea of switching to an individual thread LD. After learning where to set our "not old yet" vv devices voltage based the ohms of the carto/atomizer now we have a new device that throws that out the window! What a learning curve! But I'm sure it will be all good in the long run. Gotta keep the brain going! 3 months of vaping and didn't know I was going to get another education. Reminds me of my old racing days! Thanks LD and lovin the reviews..

 

[LordDavon]

Thank you Woody. PWM isn't new in the world of vaping, but it was rare to see it in a fully adjustable VV. Some of the older VV devices that would go between 3,3.7, and 4 used PWM. Plus, the original Silegei Ovale V6 went 3.7, 5 and 6. But now we have the Sigelei Ovale V8, Vision VV 350 (VariStack), and Smoketech VMax. Plus, I think here are more on their way.

 

[Woody-GC]

Do all of these PWM's have a different wave or net voltage at the same set point? I'm guessing they do, but new to this so just a guess. Hopefully it won't vary within the V8 series(looking ahead) though. Love the new avatar!

 

[LordDavon]

Do all of these PWM's have a different wave or net voltage at the same set point? I'm guessing they do, but new to this so just a guess. Hopefully it won't vary within the V8 series(looking ahead) though. Love the new avatar!

No. The V8 is around 7.4V. The VariStack is around 8V. I think the V8 brings it down to make the experience more consistent, at least that is one theory.

 

[MonsterTKE]

This explanation is pretty good, but I am having a hard time breaking this down to easier terms. This is where I could really use some help.

Needs calculus, lol. Best way to think about it is calculating the wattage at its full voltage, then dividing that by the time constant aka, Duty cycle. The coil is dissipating
25.92 watts 40% of the time (as in the example formula above 7.2*2 / 2 = 25.92*.40 = 10.37)

When the coil is energized it is at the full output of the batteries, when it is not it is at zero. The PWM just gives you a nice low RMS voltage. If this device is burning out coils
I am inclined to believe was a bad ce4+ I have had 3 of them on mine at 4.5 - 5.5v (Yuk, burnt vapor).

Im of the opinion that PWM is the absolute best way to go in a stacked battery mod, there are very very little losses in this system, and practically no heat generated as the IC doesnt have to dissipate anything as heat. That being said, I tore mine apart to put it in a homemade box, and the Ic's werent labelled, so I have no idea what chip is doing the work. If I was going to build one from scratch I would probably use a PWM pin on a ATtiny to drive a power mosfet, though I would want to use the highest Frequency the chip can support.

I would love to see the scope output for this, just to see what frequency it is running at.

 

[LordDavon]

Needs calculus, lol. Best way to think about it is calculating the wattage at its full voltage, then dividing that by the time constant aka, Duty cycle. The coil is dissipating
25.92 watts 40% of the time (as in the example formula above 7.2*2 / 2 = 25.92*.40 = 10.37)

When the coil is energized it is at the full output of the batteries, when it is not it is at zero. The PWM just gives you a nice low RMS voltage. If this device is burning out coils
I am inclined to believe was a bad ce4+ I have had 3 of them on mine at 4.5 - 5.5v (Yuk, burnt vapor).

Im of the opinion that PWM is the absolute best way to go in a stacked battery mod, there are very very little losses in this system, and practically no heat generated as the IC doesnt have to dissipate anything as heat. That being said, I tore mine apart to put it in a homemade box, and the Ic's werent labelled, so I have no idea what chip is doing the work. If I was going to build one from scratch I would probably use a PWM pin on a ATtiny to drive a power mosfet, though I would want to use the highest Frequency the chip can support.

I would love to see the scope output for this, just to see what frequency it is running at.

Not sure those were easier terms, but I think I already lost everyone in the OP.

I do have the Oscilloscope up to the screen during the review, but not sure how well you can read it. Catch me on Skype on of these times, and I can get you some readings. If someone can help me best explain these things to people without getting too technical, that is great. Maybe with the two of us working together, we can work on a good explaination.

Here is one question that I can't answer, how does amperage limitation fall into place while using PWM?

 

[GoAskAl]

If this device is burning out coils I am inclined to believe was a bad ce4+ I have had 3 of them on mine at 4.5 - 5.5v (Yuk, burnt vapor).QUOTE]

I have burnt out 2 CE3s 1 Micromizer x7 and 2 3.5ml 510 Clear Clearomizers. All were working great until I hit the down volt button bring the V8 to 6v. I took my regular draw and knew right away and released the button. Lowered the voltage and tried again and nothing the coil was dead. The X7 actually sparked. I really would like to see what the V8 clocks in at 6v

 

[LordDavon]

If this device is burning out coils I am inclined to believe was a bad ce4+ I have had 3 of them on mine at 4.5 - 5.5v (Yuk, burnt vapor).QUOTE]

I have burnt out 2 CE3s 1 Micromizer x7 and 2 3.5ml 510 Clear Clearomizers. All were working great until I hit the down volt button bring the V8 to 6v. I took my regular draw and knew right away and released the button. Lowered the voltage and tried again and nothing the coil was dead. The X7 actually sparked. I really would like to see what the V8 clocks in at 6v

The Duty went between 72% and 75% Duty, with an occasional spike up higher. That's on a 2ohm carto, hitting it for just a half second, so not to blow the carto. The batteries are low, so the voltage was about 7V. That's roughly 18 Watts. I didn't give it a long test, and sometimes this thing starts lower and get higher. And, I am not sure if there is a limit to if it could get higher.

 

[MonsterTKE]

Here is one question that I can't answer, how does amperage limitation fall into place while using PWM?

Amperage is still limited by the limits of whatever IC/power mosfet they are using.

MOSFET driver IC considerations - Electronic Products

The amp limit is effectively the current that the mosfet gate can hold back during the low phase of the cycle.

 

[ckim111]

So this explains why it always seemed my ovale was firing at higher wattage than my povari. This makes my ovale unvapeable with my lr stardust

 

[JZXJ]

I am definitely looking into some 4/4.5ohm cartos or atomizers for the V8 so i can see how it does over 5v. Everything I have 2.8-3ohm works well around 3.7-4.4v, except the E1 2.4-2.8 don't work well over 3.4v for me and I generally run them at 3v.

 

[ckim111]

I am definitely looking into some 4/4.5ohm cartos or atomizers for the V8 so i can see how it does over 5v. Everything I have 2.8-3ohm works well around 3.7-4.4v, except the E1 2.4-2.8 don't work well over 3.4v for me and I generally run them at 3v.

For me even at 3.0 it gives that sour taste. Too high

 

[Blitzer]

So, I have received some questions about the V8 and why it hits harder than people are used to, even at it's lowest setting. Well, we have had some discussion about that in the Official DV thread, and I thought it would be good to break it out of the DV thread, since it does answer a lot of questions. So, here is the new thread, spawned from a V8 discussion, and now "PWM and YOU!"




Just so you know, RodeoGeorge is going to be doing a nice bit of testing with the V8 soon, so we will get some excellent info on where the voltages compare.



This explanation is pretty good, but I am having a hard time breaking this down to easier terms. This is where I could really use some help.

So you are saying a 3vdc source across a 2ohm load would be:
3 x3=9
9/2 ohms = 4.5 watts

Right?

And you are saying a 6 volt square wave across the same 2 ohm load would be:

6x6=36
36/2ohms=18
18 * .5 duty cycle= 9 watts

right?

Sorry, I am having a hard time buying this. Not saying you are wrong.

My understanding: the average voltage would be 3 volts on the square wave, with 4.5 avg watts, peaking to 9 watts during on time.

Can you point me a website that gives formulas, so I can see why you calculate like this?

 

[VapingTurtle]

Little bump seeking an answer to the previous post.

Seems to me:

Per this article (in the discussion of the derivation of the average output of PWM), "it is obvious that the average value of the signal ... is directly dependent on the duty cycle D." And the thermal time constant of the atty/carto coil is so long it would never heat to anywhere near the power (wattage) implied by the peak voltage, nor cool to the minimum anytime during the duty cycle.

Lord and MonsterTKE, your formula is calculating an average power level (watts), rather than calculating a power level based on an average energy (volts). Why?

Other PWM devices don't burn up LR attys/cartos. Why?

Is the Ovale PWM just a bad implementation that is putting out an inaccurately high voltage?

(I'm not an EE. My stupid assumptions are based on intuition.)

 

[Rocketman]

How about this example for power in a square wave (50% duty cycle):

Take a 6 volt dc source and switch it once every second between two 2 ohm loads.
The 6 volt source "sees" 2 ohms, pretty much all the time. Three amps going to one load for a second, 3 amps going to the other load for a second, then back to the first load.
The 6 volt source is supplying a total of 18 watts.
How much is consumed by the first 2 ohm load, how much by the second 2 ohm load, how much goes down the drain?




What if we left the 6 volts applied to one load for 3 seconds switched it over and left it applied to the other load for one second? A 75% duty cycle for the first load and a 25% duty cycle for the second load (both 2 ohms again).

The 6 volt source "sees" 2 ohms with 18 watts going somewhere
Would 3/4 go to the first load and 1/4 goes to the second load?

 

[LordDavon]

Little bump seeking an answer to the previous post.

Seems to me:

Per this article (in the discussion of the derivation of the average output of PWM), "it is obvious that the average value of the signal ... is directly dependent on the duty cycle D." And the thermal time constant of the atty/carto coil is so long it would never heat to anywhere near the power (wattage) implied by the peak voltage, nor cool to the minimum anytime during the duty cycle.

Lord and MonsterTKE, your formula is calculating an average power level (watts), rather than calculating a power level based on an average energy (volts). Why?

Other PWM devices don't burn up LR attys/cartos. Why?

Is the Ovale PWM just a bad implementation that is putting out an inaccurately high voltage?

(I'm not an EE. My stupid assumptions are based on intuition.)

The reason is because a PWM device pulses at a full voltage. A resistance coil reacts to this pulse, not the average duty. This is why we average the wattage, and not the voltage.

As for other PWM devices not blowing coils, some others do. The VV 350 pulses at 7.6+ volts, which is why it blows coils. The LavaTube 1.5T, on the other hand, pulses at a more reasonable 6+ volts, and tends to work better with resistance coil. But, both devices hit harder, than a constant voltage device.

My live show is at 6PM tonight, and I am bringing this up for discussion. But, I created this thread for discussion. So... discuss!

 

[VapingTurtle]

LD,

Here are two short articles for your consideration (hopefully before your show):

http://www.eznec.com/Amateur/RMS_Power.pdf

SmartGauge Electronics - RMS volts as opposed to average volts - simple explanation

 

[VapingTurtle]

So you are saying a 3vdc source across a 2ohm load would be:
3 x3=9
9/2 ohms = 4.5 watts

Right?

And you are saying a 6 volt square wave across the same 2 ohm load would be:

6x6=36
36/2ohms=18
18 * .5 duty cycle= 9 watts

right?

Sorry, I am having a hard time buying this. Not saying you are wrong.

My understanding: the average voltage would be 3 volts on the square wave, with 4.5 avg watts, peaking to 9 watts during on time.

Can you point me a website that gives formulas, so I can see why you calculate like this?

Bumping this for LD and anyone else. Unanswered question here.


Also LD, did you have an opportunity to review the docs that I linked to?

OK, I can understand that an instantaneous surge in the power could cause failure of a coil, but considering the thermal dynamics of a heating element, a higher V_max would not create a higher amount of heat dissipated for a given rms voltage. I'm still at loss as to why some PWM APVs are reputed to be so much hotter at the same setting unless the displayed settings are not consistent (i.e., one or more are in error).


LD, I missed your show. Was there a discussion of this topic?

 

[LordDavon]

Bumping this for LD and anyone else. Unanswered question here.


Also LD, did you have an opportunity to review the docs that I linked to?

OK, I can understand that an instantaneous surge in the power could cause failure of a coil, but considering the thermal dynamics of a heating element, a higher V_max would not create a higher amount of heat dissipated for a given rms voltage. I'm still at loss as to why some PWM APVs are reputed to be so much hotter at the same setting unless the displayed settings are not consistent (i.e., one or more are in error).


LD, I missed your show. Was there a discussion of this topic?

Yes, I've read them. And neither disqualify what I am saying. You are welcome to hit me up on Skype to discuss.

No, we didn't get to the topic. I was a little too content heavy, and it took up most of the show.