In need of some help with converting 3.7 volts down to 1.5v

Discussion in 'Power Electronics' started by zaka, Nov 21, 2014.

  1. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    Hello, I'm new to the forum so please excuse me if this is posted in the wrong forum.
    Anyways, I'm starting a project and I'm relatively new to circuits although I do have basic soldering skills. I have a personal vaporizer that is rechargeable AA powered. I also have some other vaporizers that are 18650 battery powered. Obviously I love the battery life of the 18650 over the AA.
    So I have a dummy AA battery wired up to a switch with a 18650 battery tray in an enclosure, when the switch is flipped the voltage reads around 3.85 which is correct for the battery. How can I go about limiting the 3.7 volts of the 18650 down to the 1.5v required for the vape?
    Also does resistance of the battery/device come into play when figuring all this out? What about amperage of the 18650 vs AA?
    What are some things to look for in order to control the output voltage of my "power adapter". Any advice would be greatly appreciated as I'm excited to get this project going.
    Looking to make this device as simple/cheap as possible in terms of wiring and components, my first thought was potentiometer controlled output, but I dont have enough knowledge to know if this would work. Would rather not blow anything up:)
    Thanks!
    EDIT: Let me know if theres any other specs you need about the device being used/batteries. Planning on using AW IMR 18650 with 10amp limit and 4.2v fully charged.
     
    Last edited: Nov 21, 2014
  2. Budlong

    New Member

    Nov 21, 2014
    1
    1

    I'd just try 1n4001 diodes in series (forward biased) on the positive lead, remember a diode has to forward breakover approx 0.6 volts to conduct (0.6 silicon,0.3 for germanium approx!). So start with three or four and your down close to your goal. Simple, but with a couple of issues. Such as, as the 18650 gets weak and drops its output, your 1.5 drops too. And I don't really know how much current the Vap draws but the 1n400x diodes are rated at one amp max.

    My first post friends!
    Bob
     
    cmartinez likes this.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    What current does your load draw? If this is an E-cig, there have been several threads on these forums about this...
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,554
    2,508
    Mike's question is a valid one if you want us to help you solve your problem as quickly as possible. But then again, I'm sure we'd all understand if your project is kind of confidential and you wouldn't want to give away the details.
    Anyway, there are many ways to bring a voltage down from a source... they range from simple voltage dividers and zener diodes ... all the way down to linear and buck converters. I'd suggest you study the latter if battery life is your main concern, since a buck converter (step-down) is among the most efficient way of achieving what you want.
    Check this link.
     
  5. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    Yeah its an ecig for other "uses" lol anyways it supposedly draws 15 amps at 1.5 volts. 15 amps seems rather high to me for a AA battery. But thats the load we're looking at. A buck converter seems like the best route as of now. BTW sorry for the late response, busy weekend.
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,554
    2,508
    15A @ 1.5V = 22.5 Watts!
    Yes, it is kind of high for an AA battery... I suggest you do the rest of the rest of the (rather simple) calculations and estimate the amount of time that a AA battery sourcing that kind of power would last... and then reconsider if your project is worth pursuing...
     
  7. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    When you say "the rest of the calculations" what are you referring to? Again im rather new to this whole thing lol. Just trying to figure out if it's worth it.
     
  8. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,554
    2,508
    Last edited: Nov 24, 2014
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    E-cigs tend to work out not much cheaper than smoking unless you can re-wind your own replacement coils in the atomiser head, you'd be better off looking for one you can. By far, the easiest option is to wind a coil for your vapouriser to suit the lithium battery.

    A very large proportion of E-cigs use 3.7V, and there's numerous suppliers catering for rebuilds/mods.

    There are various E-cig forums - you can probably find links to tutorials on how to wind a coil onto a wick, there are also online calculators for calculating coil resistance, wire size etc.
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,984
    3,720
    Lithium Polymer and some other lithium chemistries can put out huge current - hence the danger. Bursts of 20 amps and more are not uncommon. Check out the RC airplanes forums and suppliers for details.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    A slightly dented battery connector on my E-cig caused a short - the fault current was sufficient to spot-weld the microswitch contacts.

    That was late in the day with the battery soon due to be recharged.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,984
    3,720
    After an incident in my basement, my son now stores and charges his lipo batteries in a ceramic flower pot on the concrete floor in the garage.

    The incident included smoke, and a smoldering mess that would not extinguish with sand/baking soda. It just kept smoking. Water want going to help on lithium so we were smart enough to stay away from that.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Quite a few E-cig suppliers offer (allegedly) flame proof charging bags for charging lithium cells.

    Ceramic pots is not a bad idea, and probably not overkill for storage of charged cells as well as while charging.
     
  14. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    yes the dangers of high current is very real, I charge mine in a large bowl. I may invest in a bag. But thx for everyones input, its led me in the right direction.
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Not just lithium - size for size, NiCd hve about the same short circuit current as a car battery.

    If you have stainless steel forks - don't put fully charged NiCd cells in the cutlery drawer, the prongs of a stainless fork can glow at least dull red while shorting a cell.

    Aside from that, cadmium is extremely toxic - not something I'd risk leaking on eating utensils.
     
  16. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    I now have an intense desire to try this in a "controlled environment", thanks for sparking my curiousity. No pun intended;)
    But in all seriousness, thanks for the info. I did not know that about NiCd batteries. Always assumed lithium was much worse in terms of shorts.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Shorting a fully charged lithium is more likely to trigger thermal runaway - usually ending with the cell venting with flaming gas!
     
    zaka likes this.
  18. zaka

    Thread Starter New Member

    Nov 21, 2014
    6
    0
    yeah ive watched a few videos where people short cheap chinese 18650's, they leave quite the crater!
     
  19. RichardO

    Well-Known Member

    May 4, 2013
    1,228
    382
    I have a friend that tells this story: I was standing in the checkout lane at a store when the cashier said "Do you smell something burning?". I said "Yes! It's me!"

    He had but a battery in his pocket and it was shorted out by coins and keys in the pocket. :eek:
     
  20. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Overcharged NiCd can develop internal shorts that can suddenly give you a very hot feeling in your pocket - its best to put them in a wash basin and turn the cold tap full, it doesn't save the cells but stops them bursting if you're lucky.

    An overcharged lithium may have formed metallic lithium, which is what makes it unstable - chucking water on that will only flare up worse!!!

    The powers that be need to get their heads out from up their bottoms and re-introduce buckets of sand at fire points.
     
Loading...