18v makita lithium ion battery to run 12v bulb

Discussion in 'The Projects Forum' started by derren, Jan 11, 2013.

  1. derren

    Thread Starter New Member

    Jan 11, 2013
    Hi, can anyone help me? I want to run a 12v led bulb as a cycle helmet light as i am a keen mountain biker. i am trying to rig a 12v led bulb to my makita 18v battery as i have a lot of these batteries being a carpenter. i currently use a 12 halogen bulb which works really well but drains the battery after 30 mins and gets so hot it is starting to melt my helmet. i have been using this setup for about a year and is amazed the bulb still works. i tried to use a 12v led bulb and it was everso bright but blew after about 20 seconds. can i use a resistor or a 18v to 12 converter that wont loose any of my battery compacity. any suggestions would be much appreaciated....
  2. wayneh


    Sep 9, 2010
    You can. The resistor approach is very simple, but you'll need to calculate the heat dissipation by the resistor (I^2 * R, where I = 6v/R) and get one rated for at least twice that amount, so it lasts.

    A DC-DC buck converter would more efficient but more complicated to set up. If you have experience using ICs and building such things, it's the way to go.