# Just starting out on Mech Mods. Safety tips.



## oldtimerZA (17/2/16)

I just want to get all my ducks in a row before I start.
I've got my BSc(Hons) mathematics which included up to Physics Major 2 in undergrad. Part of this major we did electromagnetism and electric circuits. I also got a distinction in Electrical Technology in matric.
So I'm no stranger to electricity and circuits and all that.
But even with my knowledge I would still like to get a "that looks good" from the more experienced vapers out there.

I have the following batteries:
2x Sony VTC4 (green battery). 20A max cont current draw.
1x Samsung 25R(green battery). 20A max cont current draw
1x Samsung 30Q(pink battery). 15A max cont. current draw.

Question 0:
Am I right in assuming that these batteries top out at 4.2 V output voltage? and that their nominal voltage is 3.7V?

I'm planning on doing a dual coil build with Kanthal 24G as the wire to get a 0.5 ohm build.

Question 1:
So I'll make two coils of 1 ohm each, in parallel this should give me 0.5 ohms correct?(Kirchoffs circuit laws, I think).

Question 2:
So by my understanding , if I use ohms law:
I = V/R = 4.2V/0.5 = 8.4A

Is this well within their maximum current draws?(just double checking)

This should put out :
P = V^2 / R = +- 36 Watts of power.


I have a 510 connector ohm meter that I'll be using to verify all this.

Question 3:
In terms of heat, what should one watch out for? I understand these batteries can go into thermal runaway. So can overheating trigger this thermal runaway?(I assume it can).
In general how long can one pull for before entering dangerous overheating territory?
How to tell which hot is too hot?

Question 4:
Should the battery hit thermal runaway , what are the signs to look out for?

Thanks in advance , please add any more hints/ tips you may have.

Otherwise I'm pretty excited to get started in the world of mech mods.

Hybrid device safety(Example of a hybrid device: SMPL mech mod):
http://blog.zamplebox.com/hybrid-top-cap-devices-battery-safety

Safety Checklist :
- double check no shorting coils.
- ensure batteries are in good condition.

Reactions: Like 4 | Useful 1


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## Stevape;) (17/2/16)

I basically started vaping with a mech mod. Above said sounds in order to me. I have not experienced a thermal runaway situation so I cannot comment on that. For me it was always a case of making double sure that you dont have a coil shorting and making sure the batteries are in good condition.


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## Stosta (17/2/16)

oldtimerZA said:


> I just want to get all my ducks in a row before I start.
> I've got my BSc(Hons) mathematics which included up to Physics Major 2 in undergrad. Part of this major we did electromagnetism and electric circuits. I also got a distinction in Electrical Technology in matric.
> So I'm no stranger to electricity and circuits and all that.
> But even with my knowledge I would still like to get a "that looks good" from the more experienced vapers out there.
> ...



Nice layout of some good questions! Looking forward to seeing the responses!

Reactions: Agree 1


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## shaunnadan (17/2/16)

I have the following batteries:
2x Sony VTC4 (green battery). 20A max cont current draw.

*authentic vtc4 - 30A CDR*

1x Samsung 25R(green battery). 20A max cont current draw
1x Samsung 30Q(pink battery). 15A max cont. current draw.

Question 0:
Am I right in assuming that these batteries top out at 4.2 V output voltage? and that their nominal voltage is 3.7V?

I'm planning on doing a dual coil build with Kanthal 24G as the wire to get a 0.5 ohm build.

*correct !*

Question 1:
So I'll make two coils of 1 ohm each, in parallel this should give me 0.5 ohms correct?(Kirchoffs circuit laws, I think).

*correct !*

Question 2:
So by my understanding , if I use ohms law:
I = V/R = 4.2V/0.5 = 8.4A

*correct !*


Is this well within their maximum current draws?(just double checking)

*correct ! - your have 72% headroom*


This should put out :
P = V^2 / R = +- 36 Watts of power.

*correct !*

I have a 510 connector ohm meter that I'll be using to verify all this.

*essential tool for mechs !*

Question 3:
In terms of heat, what should one watch out for? I understand these batteries can go into thermal runaway. So can overheating trigger this thermal runaway?(I assume it can).

*most common cause is discharging batteries lower than 3.2V OR drawing too high amp limit (0.14ohm is your limit)*

In general how long can one pull for before entering dangerous overheating territory?
*
if you have built to the limit without any headroom then you fall into the general "how long is the pulse discharge rate" there is no correct answer to this question.*

How to tell which hot is too hot?
*
any heat from the battery is a sign that its too hot!*


Question 4:
Should the battery hit thermal runaway , what are the signs to look out for?
*
general chaos and anarchy !!! 

seriously its all different. ive seen batteries die without any sign , collapse gently and other times leak violently. *


Thanks in advance , please add any more hints/ tips you may have.

Post pics of your builds !!!!

Reactions: Winner 7 | Useful 1


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## oldtimerZA (17/2/16)

Excellent, thanks for all the quick responses.
Glad to know I'm on the right track. As soon as I have the build up and running I'll post pics .

Reactions: Like 2 | Winner 2


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## blujeenz (17/2/16)

oldtimerZA said:


> I just want to get all my ducks in a row before I start.
> I've got my BSc(Hons) mathematics which included up to Physics Major 2 in undergrad. Part of this major we did electromagnetism and electric circuits. I also got a distinction in Electrical Technology in matric.
> So I'm no stranger to electricity and circuits and all that.
> But even with my knowledge I would still like to get a "that looks good" from the more experienced vapers out there.
> ...



The groundwork looks good.
Q0 yes
Q1 yes
Q2 yes
Q3 assuming you're holding a metal bodied mod in your hand, *if you cant hold it its too hot*.
Q4 Im pretty sure you wont catch a runaway in time, but if you hear a loud *psssstt*, and you arent walking past any dark alleys, chances are that the mod is venting.
You may, or may not, be able to unscrew the batt end cap in time to prevent further drama.

Reactions: Funny 2


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## shaunnadan (17/2/16)

oldtimerZA said:


> Excellent, thanks for all the quick responses.
> Glad to know I'm on the right track. As soon as I have the build up and running I'll post pics .



cool stuff 

side note - Kirchhoff’s rules were specific towards the relationship of resistors in complex circuits such as junctions and loops. 

to simplify things we consider the positive post of the 510 to be the junction point.


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## shaunnadan (17/2/16)

blujeenz said:


> You may, or may not, be able to unscrew the batt end cap in time to prevent further drama.



thow it hard onto the ground! it should break something that can possibly save the situation

Reactions: Agree 1


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## blujeenz (17/2/16)

shaunnadan said:


> thow it hard onto the ground! it should break something that can possibly save the situation


I wouldnt have thought of that to be frank, but then again my SS Caravela clone is pretty damm robust, chances are good it will bounce and break a window.
Hope it doesnt ever vent while walking past the jewelers.

Reactions: Funny 1


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## oldtimerZA (17/2/16)

shaunnadan said:


> cool stuff
> 
> side note - Kirchhoff’s rules were specific towards the relationship of resistors in complex circuits such as junctions and loops.
> 
> to simplify things we consider the positive post of the 510 to be the junction point.



OK I see. Good to note.



shaunnadan said:


> thow it hard onto the ground! it should break something that can possibly save the situation


Good tip.


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## Ernest (17/2/16)

oldtimerZA said:


> I'm planning on doing a dual coil build with Kanthal 24G as the wire to get a 0.5 ohm build.


I've never used 24g on a mech, but have used 26g and did not like the ramp-up time. I now build with 28g. Maybe someone with more experience can comment on ramp-up time for 24g on a mech.


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## shaunnadan (17/2/16)

Ernest said:


> I've never used 24g on a mech, but have used 26g and did not like the ramp-up time. I now build with 28g. Maybe someone with more experience can comment on ramp-up time for 24g on a mech.



0.5ohms on 24g at a nice 3mm diameter is 11 wraps a side.... i agree the ramp time is going to be a tab bit... kinda long.

rather consider a 0.3ohm build perhaps with 6 wraps a side

Reactions: Agree 1 | Thanks 1


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## oldtimerZA (17/2/16)

I'm used to the ramp up time from my regulated mod though, so no biggy.
(unless mech mods take longer to ramp up?)


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## shaunnadan (17/2/16)

oldtimerZA said:


> I'm used to the ramp up time from my regulated mod though, so no biggy.
> (unless mech mods take longer to ramp up?)



depends on the wattage your using.

generally a regulated mod will step up the power and you can have a quicker ramp up time.

Reactions: Agree 1


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## oldtimerZA (17/2/16)

I see. That's interesting.
I have a question regarding regulated mods though.
If I have my regulated mod set to 50W and I have a 0.5 ohm coil with a single 18650 battery.
How does the mod reach the 50W?
I'm assuming that the battery can only create a potential difference of 4.2V(maximum) , which gives me a max power output of :
36 Watts. 
So how does the mod increase the voltage to reach the required wattage? or does the mod just "lie" and say its at "50W" meanwhile its only at 36W?


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## blujeenz (17/2/16)

oldtimerZA said:


> I see. That's interesting.
> I have a question regarding regulated mods though.
> If I have my regulated mod set to 50W and I have a 0.5 ohm coil with a single 18650 battery.
> How does the mod reach the 50W?
> ...


The regulated mods have boost circuitry, takes batt voltage and boosts it up to a higher voltage, ie 8.5V on my ijoy solo mini.


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## oldtimerZA (17/2/16)

But how does it work?
Surely it must drop the current in order to do so?

I see it uses a coil and diode to charge a higher voltage capacitor. But the capacitor can't have anywhere near the current draw that the battery has right?

Answered my own question :
https://en.wikipedia.org/wiki/Boost_converter

Power must be conserved, which means that when you boost the volts you drop the current.
If i understand correctly, the current is what heats the wire, not the volts.
More current flow = hotter wire.
More voltage = faster wire heat up?

So with a regulated mod you sacrifice maximum wire heat for a faster ramp up time?


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## shaunnadan (17/2/16)

Some call it magic... 

Others call it pulse width modulation


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## oldtimerZA (17/2/16)

thats fine with me as I do a "blow blow blow puffffffffffff" anyway to give the coils time to heat up


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## oldtimerZA (17/2/16)

So for my first ever mech mod build I decided to play it safe and build a single 0.7 ohm coil.
works well enough, and man is it a little bit nerve wracking vaping on a mech for the first time, but I'm sure I'll get used to it.

Also the velocity RDA posts are amazing , I tried to get the coil to behave in a Tugboat RDA, no go,I just didn't feel it was sitting right. Pulled the coil out of the tugboat , had no problems seating it nice and properly in my velocity. So I guess I'll swap the Tugboat for the velocity on my regulated mod for now.

Jammed in some home made fruity loops flavour and yum yum, vaping just fine.

Pics to follow soon.

Reactions: Like 2


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## blujeenz (17/2/16)

oldtimerZA said:


> thats fine with me as I do a "blow blow blow puffffffffffff" anyway to give the coils time to heat up


Sounds like double declutching on an DCT gearbox, not really necessary, but if it makes you think you're going faster then why not.

Reactions: Funny 1


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## oldtimerZA (17/2/16)

blujeenz said:


> Sounds like double declutching on an DCT gearbox, not really necessary, but if it makes you think you're going faster then why not.


 I mainly just do it out of habit.  I started blowing on the coil when I was test firing without the top on. Kind of just stuck with me

Reactions: Funny 1


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## DaveH (18/2/16)

oldtimerZA said:


> So with a regulated mod you sacrifice maximum wire heat for a faster ramp up time?



Not really, as @blujeenz said it can nearly double the voltage across the coil in this case (say to) 8 volts. If the voltage across the coil doubles the current through the coil doubles (Ohms Law). Now the heat produced in the coil is directly proportional to the current squared, so if the current is doubled the heat produced is quadrupled.
That is to say, current squared x resistance = Watts.

or 8squared x .5 = 32Watts.
16squared x.5 = 128Watts.

Your example 4volts x8amps = 32Watts.
now we have 8volts x16amps = 128 watts.

Clear as mud 

Dave


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## NewOobY (18/2/16)

this thread is way above my understanding of blue cable goes to bottom left post, red cable goes to bottom right post and the other cable usually green and yellow goes to the top post. And that ladies and gentlemen is how you put a plug on a cable

Reactions: Like 1 | Funny 2 | Informative 1


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## oldtimerZA (18/2/16)

DaveH said:


> Not really, as @blujeenz said it can nearly double the voltage across the coil in this case (say to) 8 volts. If the voltage across the coil doubles the current through the coil doubles (Ohms Law). Now the heat produced in the coil is directly proportional to the current squared, so if the current is doubled the heat produced is quadrupled.
> That is to say, current squared x resistance = Watts.
> 
> or 8squared x .5 = 32Watts.
> ...



Yes but the current will be limited by the circuit that's doubling the voltage.

an 18650 Battery can only put out so much power.
safe max power output of Samsung 25R eg:
20A cont current draw x 4.2V = 84 watts
doubling the voltage you halve the current draw as the power output of the battery cant be more than it's maximum.
so you can either get:
20A at 4.2V theoretical max
OR
10A at 8.4V theoretical max.

Potential difference is just that..a difference in electrical potential. We can have 100V with zero current flow ( example a charged capacitor, there is a potential difference across its legs , but the current isn't flowing anywhere).

an 18650 can never output 128Watts without failing.(unless you have some WOES cooling going on).

Dual parallel 18650s probably could , because there the current draw will be split from both batteries.
For every 1A the circuit booster (with voltage boosted to 8.4V) needs , it draws 2A from the batteries.
This limits you with a single 18650, but if you have two in parallel then the circuit booster is just drawing 1A from each battery for it's requirement. Thats why single 18650 regulated mods are limited to 50W and you require dual batteries for anything higher.

To use your own example. Yes the Power is I x I x R . so it does quadruple, but then so does the current draw from your battery. Which means on single 18650 regulated mods you are limited to certain ohm ranges ( normally >=0.3ohm) where as dual battery reg mods can go as low as 0.1 ohm coils.

So a regulated single battery mod should NEVER be able to output more watts than an unregulated single battery mod.
Which again leads to :
Either higher volts and lower current draw(or a higher resistance) for regulated. Faster heating.
vs
Higher current draw(lower resistance) and normal voltage for unregulated. higher temp.


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## blujeenz (18/2/16)

oldtimerZA said:


> Yes but the current will be limited by the circuit that's doubling the voltage.
> 
> *So a regulated single battery mod should NEVER be able to output more watts than an unregulated single battery mod.*
> Which again leads to :
> ...



So why do they?
You have overlooked PWM in your paper chase, thats probably where the golden egg is hiding.


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## oldtimerZA (18/2/16)

as far as i understand from here:
http://vapingunderground.com/threads/how-to-why-to-of-pwm-box-mods.158182/

A nice summing up: "PWM works by repeatedly turning power off & on at the desired rate so that the average power can be a specific % of the available power." - taken from above link.

Notice it can't exceed the available power , can only be a % of it.

PWM is what allows variable wattage, it doesn't actually boost the wattage. It allows you to vary the output watts from 0 - maximum watts. But you still can't exceed max watts.

How those regulated mods probably reach those watts is by taking advantage of the fact that the pulse discharge amp limit of the batteries is higher than the continuous.

So they pulse it continuously at those higher amps , turn on and off , so that the average is above the max continous watts.

Surely this will shorten your battery life and heat up the battery/circuits and mod ?

You could achieve the same effect on the mech mod by ensuring that you have a sufficiently low ohm coil and only push the button in pulses.(don't know the amount of time a pulse ise, but I've heard that it's <= 3 secs?)

So at CDR limits then the single battery reg. mod will never have higher watts than a single battery mech mod.

If anyone has an oscilloscope please could you take a picture of what the pulses look like ?

Reactions: Like 1


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## blujeenz (18/2/16)

oldtimerZA said:


> If anyone has an oscilloscope please could you take a picture of what the pulses look like



Phil Busardo usually shows a trace of the mods output waveform, SVD modulated at 33hz.
Waveform at 22:40


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## DaveH (18/2/16)

Strictly speaking we should be talking about Joules. 1 Watt = 1 Joule per second.
So a Watt is a measure of how fast we use energy (Joules), and we all can be powerful albeit for a short time.

Now the battery is supplying the energy at a constant rate, this energy is 'stored' in the inductors and capacitors in the circuit. This 'stored' energy is then directed into the load (coil) in a much shorter time period.
If we had 10 Joules of energy and we use it in 1 second we have 10 Watts, if we use it in .5 of a second we have 20 watts and in 0.1 second we have 100watts. We are not getting anything for nothing it is just the rate at which the energy is used. 

These pulsed circuits are very clever but they are not that clever we get something for nothing. By clever design of the circuit the pulses are designed so the load (the coil) thinks it is a continuous flow of current, it isn't it is pulsed.

Dave

Reactions: Like 1 | Informative 3


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## oldtimerZA (18/2/16)

DaveH said:


> Strictly speaking we should be talking about Joules. 1 Watt = 1 Joule per second.
> So a Watt is a measure of how fast we use energy (Joules), and we all can be powerful albeit for a short time.
> 
> Now the battery is supplying the energy at a constant rate, this energy is 'stored' in the inductors and capacitors in the circuit. This 'stored' energy is then directed into the load (coil) in a much shorter time period.
> ...



That's a very good point. But that raises another question I have then.

Pulsing must waste energy on the coil.
When it pulses off won't the collapsing magnetic field on the coil cause an impeding current? So our current flow through the coil will be lower than a mech mods? Because we now have (essentialy) an AC current and from what I remember coils create impedance on an AC current?

anyway a little bit of trivia for those interested in booster circuits: (I've grown quite fascinated in how all this works , it's reignited my love for electricity )
https://en.wikipedia.org/wiki/Boost_converter.

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## DaveH (18/2/16)

oldtimerZA said:


> That's a very good point. But that raises another question I have then.
> 
> Pulsing must waste energy on the coil.
> When it pulses off won't the collapsing magnetic field on the coil cause an impeding current? So our current flow through the coil will be lower than a mech mods? Because we now have (essentialy) an AC current and from what I remember coils create impedance on an AC current?



Absolutely true, although smoothing capacitors can help.




oldtimerZA said:


> (I've grown quite fascinated in how all this works , it's reignited my love for electricity )



That's good ........... just don't give it a hug!  

Dave

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## oldtimerZA (19/2/16)

Man am I excited.

I got me a coil jig and some 26g kanthal today. Going to build a ~0.5-0.6 ohm dual coil tonight. Hopefully the ramp up time will be more bearable and the coils less insanely long .


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## oldtimerZA (19/2/16)

as promised . The above is an image of a 0.6 ohm dual parallel coil build. 
Runs nicely and produces the vapour amount I like at the temp I like.

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## WARMACHINE (19/2/16)

Looking Good


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## BumbleBee (19/2/16)

oldtimerZA said:


> as promised . The above is an image of a 0.6 ohm dual parallel coil build.
> Runs nicely and produces the vapour amount I like at the temp I like.


Very neat coiling @oldtimerZA, that looks like a pretty solid build. FYI, a parallel coil is one that uses two wires for each coil, I suspect you meant "dual horizontal coils"?

This is what a parallel coil looks like...

Reactions: Like 1


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## oldtimerZA (20/2/16)

Oh didn't realise that.
I meant parallel as in "not series" .


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## WARMACHINE (22/2/16)

Here is some cool info

http://blog.zamplebox.com/hybrid-top-cap-devices-battery-safety


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## oldtimerZA (22/2/16)

Thanks for the safety tips...but I don't have a hybrid device( I have a Nemesis mech mod).I should mention that my nemesis has a top cap, with a screw in pin that connects to the atty's positive post. But it's still appreciated as someone else might find that link useful. I'll add it to the front page.


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