Instructables
There is a problem with the circuit. Please see the comment from Zanderist below.

So when I wanted to quit smoking I tried an electronic cigarette. They were expensive and didn't produce enough vapor for me. I figured hey it can't be that hard and decided to look into making my own.

Approximate cost not counting batteries is about $12

I took my existing electronic cigarette and hooked it up to a voltmeter and started making notes. I found other electronic cigarette models that had variable voltages so I decided to search through several forums out there to see what range of voltages were being used.

I found that most operate off 5-8vdc with wattage being a little higher than just from the battery alone so battery voltage needs to be higher than what is being used and the amp hours need to be high.

I found that most electronic cigarette mods were using IMR 14500 3.5v Lithium Ion Batteries

Needing to control the voltage I looked at several voltage regulators and came up with the LM317 because it supports the volt range I'm working with. I also wanted to leave room for creating a desktop model.

Nicotine use in the US requires you to be 18 years of age or older but then again this project isn't about nicotine and I didn't use any when I really began to quit smoking.

Feel free to ask questions and/or make suggestions.
 
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Step 1: Application Schematics & Math

These are the general use schematics for the LM317 voltage regulator.

As far as the math goes I've done it for you so don't worry too much. I calculated the values based upon 7.5vdc but the intended use is around 6.5 to 7vdc. I left in the overhead because as the batteries get drained you can crank it up.

Step 2: My schematic and rough component layout

See image notes for more detail
Zanderist7 months ago

Don't use the LM317 IC, its rated at 1.5 amps which is too low for this application.

It would be better with the LM338t, if keeping to this design layout.

However if choosing to use the LM317t you will need to use an additional power transistor (which you can also buy at radio shack) to increase the current output.

A quick google images yeilds the following results:

https://www.google.com/search?q=lm317t+increase+current&espv=210&es_sm=122&tbm=isch&imgil=853-qQRm6avh-M%253A%253Bhttps%253A%252F%252Fencrypted-tbn2.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcQpeG2hW_Yimcj4GH0PmIpz30fgfkOMvMd-DGCpgk4ojh9p1DXRUQ%253B400%253B218%253BiEw08L4XO6s4AM%253Bhttp%25253A%25252F%25252Fwww.reuk.co.uk%25252FLM317-High-Current-Voltage-Regulator.htm&source=iu&usg=__0_BJ-c6grb9Z8IisngXh64-Crrg%3D&sa=X&ei=pKLyUvDQL-fNsQT2-4CgDw&ved=0CD0Q9QEwAg&biw=1240&bih=642#facrc=_&imgrc=853-qQRm6avh-M%253A%3BiEw08L4XO6s4AM%3Bhttp%253A%252F%252Fwww.reuk.co.uk%252FOtherImages%252Flm317t-pnp-pass-transistor-voltage-regulator.jpg%3Bhttp%253A%252F%252Fwww.reuk.co.uk%252FLM317-High-Current-Voltage-Regulator.htm%3B400%3B218

MrRedBeard (author)  Zanderist7 months ago

Wow I stand corrected! I completely over looked this when I designed it. Knowing this now I can't believe it still works after a year of heavy use. I will have to build a version 3 with the LM338t. I have already been kicking around the idea of building a variable wattage version using a micro-controller.

7.5 vdc and 2 ohms = 3.75 amps

7.5 vdc and 1.5 ohm = 5 amps

Thanks for the feedback.

From the LM317 Datasheet

Electrical Characteristics:

VI-VO = 5 V, IO = 0.5 A,

0°C ≤ TJ ≤ +125°C,

IMAX = 1.5 A,

PDMAX = 20 W, unless otherwise specified.

IO(MAX): (Maximum Output Current) :: TA = 25°C

VI - VO ≤ 15 V, PD ≤ PMAX MIN: 1.5A TYP: 2.2A

VI - VO ≤ 40 V, PD ≤ PMAX MIN: 1.5A TYP: 0.3A

Further More:

Description:

This monolithic integrated circuit is an adjustable 3-terminal

positive-voltage regulator designed to supply more

than 1.5 A of load current with an output voltage adjustable

over a 1.2 V to 37 V range. It employs internal current

limiting, thermal shutdown, and safe area

compensation.

Focus on line: "designed to supply more than 1.5 A of load current"

So, if you can keep the LM317 at 25°C (77°F)

You can supply at least 2.2A (maybe more) :: it really depens on the temperature coeffiecent

and the output current is internally limited (again accouring to the datasheet)

-- this is why it has been working for you

The texas instruments datasheet says the current range is:
MIN: 1.5A TYP: 2.2A MAX: 3.4A
@7.5 vdc
You could use: a 2 ohm - 5 ohm coil
7.5/1.5A = 5 ohms
7.5/2.2A = ~3.41 ohms
7.5/3.4A = ~2.1 ohms
7.5/3.8A = ~2 ohms

You probably would only need a mircocontroller if you wanted a display. unless your going to try a PWM style of variable wattage.

I've been trying to reverse engineer the whole variable wattage thing to sorta debunk if its just a marketing gimmick.

Something variable wattage could be done pretty simply I suppose with something called a trans-conductance amplifier .
MrRedBeard (author)  Zanderist7 months ago

Well it's not entirely a gimmick. The wattage is what drives the heat so it gives you a more consistant vape. This is done by calculating the ohm rating of the carto quickly and then delivering the amount of voltage needed to create the amount of wattage desired.

Now I'm curious about doing variable wattage without a micro-controller. I'll take a look and see what I can find too then post my findings here.

I've already blazed a trail for you to follow into then, you've cleared up the vary wattage thing then.

What you have in the following image is a noninverting op amp driving a transistor in an emitter bias configuration. Nice thing about this is it takes a very small voltage to drive the opamp. The dc voltage source you see going into the op amp could be sub'd for a potentiometer set up to be a voltage divier. What it comes down to is the gain you choose at the op amp.

VWpathfinding.jpg
MrRedBeard (author)  Zanderist7 months ago
Oh ok cool! I think I may already have the parts. I'll look tomorrow and see.
Zanderist made it!7 months ago

Just for everyone to see I have made one of my own inspired off of Redbeard.

I found a DIY tutorial that showed and explained the idea on how to make printed circuit boards.

In addition I used re purposed laptop batteries found from a dead laptop to drive the Ecig.

20140208_000447.jpg20140208_000518.jpg20140208_000604.jpg
MrRedBeard (author)  Zanderist7 months ago

That looks awesome! Great idea using the laptop battery.

hubi17 days ago

I see another problem here, the lm317 is not heatsinked, so it gets real hot and dies very quick.For this application i would use a step down switched supply.z.B. LM2596. It wastes much less power.

hsosna1 month ago

i am trying to use the lm338t adj nd on my dmm it reads that i am getting volts but when i put it on my tank it wont fire please help

MrRedBeard (author)  hsosna1 month ago

If your getting voltage out on the connector that goes to your tank then it should be good to go. Check the resistance on your carto/coil. You should get 1-3 ohms. In your dm you said you were getting 7.5vdc? That may have popped the heating element (some don't like going that high especially if they're used). If that is the case adjust the voltage down between 3-5 vdc.

Zanderist7 months ago

I also want to add if you are going to use PWM, you may need to introduce some RF shielding. The FCC may end up giving you a fine, haha.

MrRedBeard (author)  Zanderist7 months ago

Haha but that's a cool thought shaping the waveform to fit a desired freq. Thanks Zanderist now this will consume my thoughts.

levi_gatlin9 months ago
Hey if I didn't want to use the potentiometer what could I use? can you take some up close pics of the PC board sorry I'm still learning how to read circuits the only place I get parts are at radioshack and what v are the caps?
MrRedBeard (author)  levi_gatlin9 months ago
The capacitor in the list is rated for 250vdc. I built one using all radioshack parts, I will get you more info on that shortly.

As far as the variable resistor you can leave it out and have the voltage at around 7.5vdc but understand some e-liquids may not taste good.
rally51010 months ago
Thanks for the info but it seems I'm missing something. How are you getting VIN 28v from 2 3.4v Lithium batteries?
MrRedBeard (author)  rally51010 months ago
No I am getting ~6.8vdc from the 2 3.4vdc lithium batteries. The 28v is the upper tolerance of the LM317 voltage regulator.
that is some wild customization you got there!
MrRedBeard (author)  Lalalarissa1 year ago
Haha Thanks
WWC1 year ago
I am not a smoker but where do you put the magic liquid and how does it vaporize it?
MrRedBeard (author)  WWC1 year ago
It goes inside the cartomizer or atomizer which has a heating element. I used a tank on mine which fed the cartomizer through a pin size hole which kept the heating element cooler during longer operation and fed it consistently which meant I didn't have to always carry the liquid with me.