wattage calculation

[altspeed]

Is the correct formula for wattage voltage squared/res= like 3.7vX3.7V=13.69/.8 Ohms=8.55W for a .8 coil on a 18350?

Also, can you just pot the probes of a multimeter on either end of a coil and fire it to check the wattage?

 

[ubergeek922]

Is the correct formula for wattage voltage squared/res= like 3.7vX3.7V=13.69/.8 Ohms=8.55W for a .8 coil on a 18350?

Also, can you just pot the probes of a multimeter on either end of a coil and fire it to check the wattage?

Yes that is the correct formula for finding wattage (power or P) when you know voltage and resistance. Below is a chart covering other formulas.

No. A regular multimeter does not measure wattage, only voltage, amperage, and resistance.

 

[altspeed]

Yes that is the correct formula for finding wattage (power or P) when you know voltage and resistance. Below is a chart covering other formulas.

No. A regular multimeter does not measure wattage, only voltage, amperage, and resistance.

View attachment 238567

but metering the wattage is immaterial because you can infer it with accurate metrics of the three permutable factors anyway I guess....duh

playing with a toy that's just plain electric as opposed to electronic is refreshing, dead basic DC theory, even polarity is fairly immaterial depending on the mod

thx ubergeek922

 

[Johnny Skillish]

Is the correct formula for wattage voltage squared/res= like 3.7vX3.7V=13.69/.8 Ohms=8.55W for a .8 coil on a 18350?

Also, can you just pot the probes of a multimeter on either end of a coil and fire it to check the wattage?

There are a couple of ways to get to your Power(Watts) number depending on which parts of the equation you already have, or are looking to have.

The short answer to your question though is that your equation is correct, but your answer IS WRONG. P = E2/R where with your numbers...3.7V X 3.7V = 13.69 / .8 = 17.11W! NOT 8.55W. (8.55 is HALF of 17.11. You must have hit divide again by accident!) you'd be pushing just over 17.11W @ 4.63A. With a fully charged 3.7V battery @ 4.2V you'd be at 22.05W @ 5.25A! You MUST also note your amp output too! making sure your setup can handle these numbers. ie. The max continuous amp output rating of your battery, the max amps of your battery spring, etc.!)

The longer version and link as follows...

ie. you'd like to vape at 14 Watts, and have a mech mod and a 3.7V batt. (4.2 fully charged) and you would need to solve for the res. of the coil you'd like to build to achieve that power. So in this case the appropriate equation is R = E2/P. Again, using the example. 4.2V X 4.2V / 14W = 17.64 / 14 = 1.26 Ohms. So you would shoot for a 1.26 wrap on your coil. (Funny, I just wrapped a 1.2 Ohm coil last night!

Ohm's Law defines the relationship between power, voltage, current, and resistance. The various possible formulas for Ohm's law are as follows...

Where...

P = power in watts
E = voltage in volts
I = current in amps
R = resistance in ohms

P = E2/R
P = I2 * R
P = E * I

E = sqrt(P * R)
E = P/I
E = I * R

I = E/R
I = P/E
I = sqrt(P/R)

R = E/I
R = E2/P
R = P/I2


These equations mean EVERYTHING in vaping! I would know them, use a calculator like the one below, and double, even triple check your answers, and setup before ever firing up any PV!

Here's a great link where you can plug in any 2 variables and get the other 2 with a quick click!

http://www.rapidtables.com/calc/electric/ohms-law-calculator.htm#dc

And no, you cannot put your multimeter on your coil to check wattage.

I hope this was helpful to you.

Vape on!
-JS

 

[altspeed]

I've been making protank coils at about 1.6-1.7 (3 looseish or 4 tight coils of of 32 kanthal on doubled 1.5 mm silica) for my ego T passthrough. I've been vaping about 6 months counting my 1st disposable ecigs, 3 1/2 months without smoking. I'm ready for my first mod and genesis setup, I really don't see getting more bang for the buck than an RSST and smoketech magneto, it looks to be an especially well made mod for the money and the rsst looks like a good entry level genny RBA, seems to be a killer setup for $75ish altogether. I thought seriously about the Ihybrid Prime or one of the new chinese hybrids, but with the magneto/RSST, I've got the protank fallback option while I'm getting the hang of the Genny

 

[Johnny Skillish]

I've been making protank coils at about 1.6-1.7 (3 looseish or 4 tight coils of of 32 kanthal on doubled 1.5 mm silica) for my ego T passthrough. I've been vaping about 6 months counting my 1st disposable ecigs, 3 1/2 months without smoking. I'm ready for my first mod and genesis setup, I really don't see getting more bang for the buck than an RSST and smoketech magneto, it looks to be an especially well made mod for the money and the rsst looks like a good entry level genny RBA, seems to be a killer setup for $75ish altogether. I thought seriously about the Ihybrid Prime or one of the new chinese hybrids, but with the magneto/RSST, I've got the protank fallback option while I'm getting the hang of the Genny

One of my setups is a Natural mod with the RSST. I've been using it for a few months now (getting a little less use since I got my Provari! and it works very well! Just built a 1.2 ohm coil on some 3/32" ss cable last night, and wicks and vapes pretty dam well! Have never had an issue with it as a true mech mod. Mine even came with "The Kick". (Although with being able to build my own coils at whatever res. I choose, I haven't needed it. Still brand new!) Although, it's funny, I'm about to post a question as to why at 14W I'm not getting as much "action" as on my Provari. But I THINK it has to do with Voltage drop? IDK yet, a bit off track here...LOL

Anyway, I also own 2 Protanks and they're FANTASTIC IMO! I'm sure you'd agree!

I've got ALL my mods in rotation right now! Provari with one of my Protanks to my left, Natural w/ RSST to my right, and a couple of others in the background! Haha!

With you already rebuilding Protank coils, you're a cinch for the genny style RBA's!

That was my first mod setup, and it was, and continues to be great fun, and great practice for me in all areas.

Good luck with that!

Vape on man!
-JS

 

[Johnny Skillish]

Yes that is the correct formula for finding wattage (power or P) when you know voltage and resistance. Below is a chart covering other formulas.

No. A regular multimeter does not measure wattage, only voltage, amperage, and resistance.

View attachment 238567

Great pie chart!

 

[altspeed]

One of my setups is a Natural mod with the RSST. I've been using it for a few months now (getting a little less use since I got my Provari! and it works very well! Just built a 1.2 ohm coil on some 3/32" ss cable last night, and wicks and vapes pretty dam well! Have never had an issue with it as a true mech mod. Mine even came with "The Kick". (Although with being able to build my own coils at whatever res. I choose, I haven't needed it. Still brand new!) Although, it's funny, I'm about to post a question as to why at 14W I'm not getting as much "action" as on my Provari. But I THINK it has to do with Voltage drop? IDK yet, a bit off track here...LOL

Anyway, I also own 2 Protanks and they're FANTASTIC IMO! I'm sure you'd agree!

I've got ALL my mods in rotation right now! Provari with one of my Protanks to my left, Natural w/ RSST to my right, and a couple of others in the background! Haha!

With you already rebuilding Protank coils, you're a cinch for the genny style RBA's!

That was my first mod setup, and it was, and continues to be great fun, and great practice for me in all areas.

Good luck with that!

Vape on man!


-JS

Thx Johnny, I'm wating to get the adjustable center pin magneto and I'm in business, getting some high drain unprotected batteries, a couple of 18650s and a couple of 18350s and a charger. I might even blow off the RSST for a few weeks. I'm hearing great stuff about 1.0s and .8s in the protank. I've got the PT 2 as well, here is a pic of a protank protector and lanyard attachment I made out of some closed cell foam pipe insulation and a piece of coathanger wire LOL, I ordered some 2mm 316 stainless like body jewelry wire to make some better looking ones.

I'm also about to experiment with lightly beadblasting some old protank parts from a broken protank 1, satiny finish on one might be cool.

BTW thanks to Nick Green for the great video on protank coils.

 

[Alexander Mundy]

Yes, please measure the voltage at your coil for the correct voltage to use in ohm's law for wattage!
Also to calculate amperage to make sure you are within a safe range for your battery.
Assuming battery voltage is incorrect and will only distort your wattage and amperage calculations above what they actually are.
Every battery has an internal resistance under load.
For instance my AW IMR18350's have .2 volt drop at 3 amp load.
Also your PV is going to have a voltage drop as well.
Mine range from .1 to .2 volts at 3 amp load.
I have two .8 ohm setups going currently with .4 volts total drop with fresh batteries.
If I assumed 4.2 volts on a fresh charge with a .8 ohm coil I would think I was vaping at 22 watts.
However in reality I am getting 3.8 volts to the coil with a fresh 4.2 volt battery so 18 watts.
Battery voltage will drop rather quickly with a .8 ohm coil to its fattest range.
When the battery drops to 3.8 volts (not under load) the coil is getting 3.45 volts under load (loss varies with load) so almost 15 watts.
Kirchhoff's law (in a simple current loop) says the amperage throughout the loop will be the same.
So with a fresh battery I am drawing 4.75 amps which is comfortably below the AW IMR18350 constant current draw limit.
Assuming 4.2 volts to the coil would be 5.2 amps still comfy but getting close to limit.

 

[ubergeek922]

Yes, please measure the voltage at your coil for the correct voltage to use in ohm's law for wattage!
Also to calculate amperage to make sure you are within a safe range for your battery.
Assuming battery voltage is incorrect and will only distort your wattage and amperage calculations above what they actually are.
Every battery has an internal resistance under load.
For instance my AW IMR18350's have .2 volt drop at 3 amp load.
Also your PV is going to have a voltage drop as well.
Mine range from .1 to .2 volts at 3 amp load.
I have two .8 ohm setups going currently with .4 volts total drop with fresh batteries.
If I assumed 4.2 volts on a fresh charge with a .8 ohm coil I would think I was vaping at 22 watts.
However in reality I am getting 3.8 volts to the coil with a fresh 4.2 volt battery so 18 watts.
Battery voltage will drop rather quickly with a .8 ohm coil to its fattest range.
When the battery drops to 3.8 volts (not under load) the coil is getting 3.45 volts under load (loss varies with load) so almost 15 watts.
Kirchhoff's law (in a simple current loop) says the amperage throughout the loop will be the same.
So with a fresh battery I am drawing 4.75 amps which is comfortably below the AW IMR18350 constant current draw limit.
Assuming 4.2 volts to the coil would be 5.2 amps still comfy but getting close to limit.

I would disagree. I would suggest always do the calculations using 4.2v regardless of actual voltage drop. Yes, it may skew your wattage and amperage calculations slightly higher than actual, but that just allows for a safety margin. If you are basing your coil or battery selection on calculations which are dependent on a couple tenths of a volt, you are asking for trouble.
You wouldn't take a 277 branch circuit and calculate your conductor size differently because they really have 270 coming from the switch gear would ya?

 

[altspeed]

I would disagree. I would suggest always do the calculations using 4.2v regardless of actual voltage drop. Yes, it may skew your wattage and amperage calculations slightly higher than actual, but that just allows for a safety margin. If you are basing your coil or battery selection on calculations which are dependent on a couple tenths of a volt, you are asking for trouble.
You wouldn't take a 277 branch circuit and calculate your conductor size differently because they really have 270 coming from the switch gear would ya?

Yeah, I was figuring if I could verify 5% voltage drop like several reviewers I run all calculations as nominal and give myself a 5% catastrophic failure cushion.

 

[MattyB1503]

Brain explodes...

Ohm's law calculators are free and readily available @ both apple and Google play stores (for those not friendly with math).

I you're dead nuts set on vaping at a particular wattage, rather than a "good or awesome vape", I would suggest a DNA20 mod; but let me pose a question. Is vaping on a one ohm single coil at given regulated V/W the same to you as vaping on a parallel dual coil reading one ohm at the same V/W?

Wattage or power rating it probably the best quantitative measure we have come up with in regards to vaping, however heat transfer is ultimately what we are after. There are quite a bit more variables that would define a theoretical Q value.

It's good to have an idea of how much power your mod is pushing but I think it's more important to practice safe rebuilding. I wouldn't get too hung up on the fine details.

 

[Alexander Mundy]

I would disagree. I would suggest always do the calculations using 4.2v regardless of actual voltage drop. Yes, it may skew your wattage and amperage calculations slightly higher than actual, but that just allows for a safety margin. If you are basing your coil or battery selection on calculations which are dependent on a couple tenths of a volt, you are asking for trouble.
You wouldn't take a 277 branch circuit and calculate your conductor size differently because they really have 270 coming from the switch gear would ya?

Agree to disagree concerning PV's.

However voltage at the switch gear is irrelevant to branch conductor size.
Apples to oranges.

 

[ubergeek922]

Agree to disagree concerning PV's.

However voltage at the switch gear is irrelevant to branch conductor size.
Apples to oranges.

I'll concede that one. In my defense, it made perfect sense in my head at the time. I wouldn't look at a nameplate and say "that's assuming 277v but we really only have 270, so our actual amperage will be less." and base conductor size on actual values. But I digress, it has no bearing on the OP.

 

[Johnny Skillish]

View attachment 238620

Thx Johnny, I'm wating to get the adjustable center pin magneto and I'm in business, getting some high drain unprotected batteries, a couple of 18650s and a couple of 18350s and a charger. I might even blow off the RSST for a few weeks. I'm hearing great stuff about 1.0s and .8s in the protank. I've got the PT 2 as well, here is a pic of a protank protector and lanyard attachment I made out of some closed cell foam pipe insulation and a piece of coathanger wire LOL, I ordered some 2mm 316 stainless like body jewelry wire to make some better looking ones.

I'm also about to experiment with lightly beadblasting some old protank parts from a broken protank 1, satiny finish on one might be cool.

BTW thanks to Nick Green for the great video on protank coils.

Sounds like you've got some great things going on!
Liking the lanyard too, and might want one! LOL
I've been focusing a bit on DIY juice right now, and coming along quite nicely as I take a vape of a RY4 mix I made....ahhhh....
Gotta check out that vid.
Always looking for new, and creative ways to do things.
Nice chatting!

-JS

 

[Johnny Skillish]

I'll concede that one. In my defense, it made perfect sense in my head at the time. I wouldn't look at a nameplate and say "that's assuming 277v but we really only have 270, so our actual amperage will be less." and base conductor size on actual values. But I digress, it has no bearing on the OP.

2 electrical gurus hard at work! LOL

Loving the intelligent discussion!

Actually posed this similar question as a thread regarding a 1.2 ohm coil I built where my vapor production is nearly nill in one mod, and roaring on my vv.

VOLTAGE DROP!

Not on a Provari though!

Vape on guys!
-JS
Great stuff guys!

 

[altspeed]

LOL...looking back at this thread it's hard to believe how many people I've met, how much gear I've been through, and how much I've learned in the just over three months since. The last post in this thread until now was five days before my first vape meet.