Lithium Battery Monitor (Part of E-Cigarette)

Discussion in 'The Projects Forum' started by Argus McJohnsten, Apr 6, 2015.

  1. Argus McJohnsten

    Thread Starter New Member

    Apr 6, 2015
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    This is just a part of the project I'm working on, but it seems to be the biggest headache of all of it. I posted this on another forum, so some may have already seen it, I'm just wanting to get as many opinions as I can.

    It's been many years since I've done any design, so I remember just enough to hurt. I'm wanting to build a an e-cigarette "mod" basically a battery (20A capable), master toggle switch, voltage monitor, pushbutton, mosfet to allow use of smaller button, small coil (.5ohm to 2 ohm [personal preference that I haven't decided on].

    I've uploaded a screenshot of MultiSim of where I'm at now. The switch and LED1 (black box) work fine. The voltage divider, TLVH 431, Led2 works fine, but when I try combining both, that's when I get an error. Think this is just a multisim problem, or did I do something wrong?

    Provided I'm doing things halfway correct. How do I go about implementing the rest of it?

    Thanks in advance.
     
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  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,058
    3,820
    Have you read the datasheet for the shunt voltage regulator? Which page is this circuit on? What do you want to do exactly, turn the bulb on when the voltage drops to a certain level or change the brightness as it drops, ...

    Here is the datasheet...
    http://www.ti.com/lit/ds/symlink/tlvh431.pdf
     
  3. Argus McJohnsten

    Thread Starter New Member

    Apr 6, 2015
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    I want it to turn the bulb off when the voltage drops below 3.2V. I'm basing it off of one I saw referenced numerous times on here and other forums: http://www.reuk.co.uk/TL431-Battery-Voltage-Monitor.htm I changed to the TLVH431, thinking it would be better since I'm not going over 4.2V as I'm only using 1 battery.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,654
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    Yes but...the cathode of the TL431 needs to be 2.5 volts or greater, and the LED will need between 1.6 and 4 volts depending upon what kind of LED it is. The LED will be off at a higher voltage than 3.2V
     
  5. Argus McJohnsten

    Thread Starter New Member

    Apr 6, 2015
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    I got it working in multisim by adding in a couple of grounds.
    Is that 2.5V the Vref, or where are you getting that figure? I'm assuming the 1.8V is LED voltage drop. The TLVH431 is a 1.24Vref. So I assumed that meant I would need 3.04V to get the LED to turn on.
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    have you seen in the news about ecigs exploding because someone modified them? aperently they build up pressure when overf heated.
     
  7. Argus McJohnsten

    Thread Starter New Member

    Apr 6, 2015
    5
    0
    Yes I have, that's usually from not matching battery to coil, or overdrawn batteries, either cause venting in a sealed case, essentially creating a pipe bomb.

    Thank you for the heads up though.
     
  8. Argus McJohnsten

    Thread Starter New Member

    Apr 6, 2015
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    Would I be better off to use 2 cells or scrap the monitor LED?
     
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