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I want to make a variable watt device

  1. Apr 3, 2014 #1
    i was looking at an e-cig and wondering how it regulates watts. would it be viable to make your own?

    for those of you who dont know they run off of a 18650 3.7v battery that powers a coil. the coil is in the ballpark of .3 - 3.5 ohms.

    how do i get 30 watts of regulated power and jam it though a 1ohm coil from a 3.7 volt battery. or 25watts or 50watts. just whatever wattage i want.
  2. jcsd
  3. Apr 3, 2014 #2


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    Hi hexeros. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    If your dissipating element is limited to a 1Ω resistance, then there is no way to have it dissipate 25w or 50w other than by supplying it with the applicable higher voltage. If using DC then you'll need 5v and 7.07v resp., so this means your 3.7v will need a circuit to step it up to a higher potential.
    Last edited by a moderator: May 6, 2017
  4. Apr 3, 2014 #3


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  5. Apr 3, 2014 #4
  6. Apr 3, 2014 #5
    @N O

    bear with me if you would and watch this. its lengthy but its will give you a better understanding of what i want to do.

    Last edited by a moderator: Sep 25, 2014
  7. Apr 3, 2014 #6


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    You need a switching power supply to convert the lithium battery to a higher voltage. The link I posted shows the basics, although the switching module they used doesn't work down to 3.2V (lowest lithium battery voltage) and doesn't produce a high enough output voltage for the power and elements you describe. But it shows the basic elementsa for a rudimentary device.

    Some of these devices are pretty sophisticated in terms of heating profile, etc. You will have a lot to learn about the heating elements and optimum performance profiles if you want to build a good one.

    The unit you linked to has an ARM cortex M3 microcontroller. Granted part of that is needed for the display and user interface features, but I expect there is some fancy power control too.
  8. Apr 3, 2014 #7
    thanks but the one you linked needs 4.2v min to run. run the to batteries in series giving additional voltage?
  9. Apr 3, 2014 #8


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    I would use a different switching supply. I just wanted to show you the basic idea.

    Actually, to put 50W through 3.5 ohms, you need 13 volts and 3.8 amps which will draw 15 amps from the battery when it is 3.2V. That's a reasonably beefy supply, and will require a sophisticated pcb layout.

    The supply design might look something like this: http://www.linear.com/solutions/4851 with an adjustment for output voltage. You might want to look at the data sheet and the layout reccomendations for an idea. Do you have PCB layout tools or experience?
  10. Apr 4, 2014 #9
    negative and limited. i do have a local radio shack and the time to figure this stuff out.
  11. Apr 4, 2014 #10
    seems a bit advanced for a beginner. can you link any good tutorials or videos to get me started
  12. Apr 4, 2014 #11


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    Well, if you want a compact, commercially viable efficient solution to compete with the dna30, I wouldn't know where to start. If you just want to mess around with vaps, there are lots of links (even a mod to turn a flashlight into a vap).

    The link I posted was the simplest. You could try multiple batteries, or try to find a more suitable power module. http://www.ti.com/lit/ds/slts284f/slts284f.pdf is good reading. It is the module used (PTR08100W) Hmmm -- it seems to be a step down module only. The input voltage has to be higher than the output desired.

    http://www.ti.com/lit/sg/slvt145m/slvt145m.pdf [Broken] describes lots of power solutions. I found nothing that does exactly what you want.

    You want a 3.3 V input (3.2 to 4.2V), 5V to 13V (7V?) output 50W(30W?) boost switching power module.
    Last edited by a moderator: May 6, 2017
  13. Apr 4, 2014 #12


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    Not sure this is the greatest advice, but possibly you can use a unit with lower rated output power since the use is intermittent. This would give you something to play with, anyway. For example

    You may burn it out quickly, but at least it is cheap fun.

    There are more such power modules around. Just search a bit. For example, on ebay, I used "dc power supply module step up -buck -down" for search.
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