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Getting a led to turn on when voltage is under 3 volts on a battery

Discussion in 'Power Electronics' started by Juvoal, Nov 4, 2015.

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  1. Juvoal


    Nov 4, 2015
    I am trying to get a led to turn on when voltage drops under 3 volts. I am building a box mode for vaping and voltage is starts at 4.6. I would like a led to turn on when voltage drops under 3 volts DC.

    Can anyone help me?

    Thanks in advance
  2. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    Hello Juvoal. Have a look at a comparator. You will find lots of low voltage alarm circuits on the net.
  3. AnalogKid


    Jun 10, 2015
    What is "a box mode for vaping"?

  4. Martaine2005


    May 12, 2015
  5. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    This circuit flashes when the voltage drops to 4v. The voltage "set-point" can be adjusted by changing the 150k on the base of the first transistor.

    Arouse1973 likes this.
  6. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    It's box mod (for modification), not box mode. A fairly recent description of vaping can be found here. The box-type power units are a favorite of "cloud chasers" because they are capable of driving a very low resistance atomizer coil, usually a drip coil, to produce copious amounts of vapor.

    I use one of these box-type battery power supplies, backed up by a more traditional cylindrical battery power supply. Both have sophisticated electronics inside to safely discharge and charge high current-density lithium ion batteries. My box-mod is made by Eleaf and is called an IStick TC40W. It and the cylindrical battery power supply are used interchangeably with a Nautilus Aspire atomizer tank.

    The IStick features either power control up to 40 watts or temperature control if using nickel coils. I use it at 7.5 watts with kanthal coils. It has a blue OLED display that shows the amount of battery charge remaining, the battery voltage, the coil resistance and the power setting. After pressing a button to turn on the coil it keeps track of how long it was turned on and displays that too. It runs most of the day on one charge and re-charges overnight in about three hours.

    Unfortunately, all those features make the IStick a little pricey. So, some people prefer to "roll their own" power units. These are the same people who wind their own coils and build their own atomizers and tanks, a practice known as moding a vape. In other words you start with a commercial product and make modifications to customize it to your own taste, sort of like building a hot rod automobile in the 1960s but much less expensive. And much more dangerous since most of these moders don't know squat about the dangers associated with charging and high-current discharging lithium ion batteries.

    I may know some squat, but I prefer to purchase a manufactured product and forego the risk of a lithium ion battery blowing up in my face or melting in my hand. My battery box mod simply quits producing vapor when the voltage gets too low. That's when I know it is time to swap it out with the cylindrical battery power supply and put the box mod on the charger overnight. Even then, I charge it in a glass jar just in case an "accident" should happen.

    So, try @Colin Mitchell 's circuit or purchase a low-voltage comparator and try to roll your own. But why would you want to run the battery down any further with a blinking LED? Just turn it off, like my IStick does. The user will definitely notice when it fails to operate.

    Arouse1973 likes this.
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