Constant Load/Drain Circuit to Replace an Incandescent Bulb

Discussion in 'General Electronics Chat' started by formula08, May 9, 2010.

  1. formula08

    Thread Starter New Member

    May 9, 2010
    Hey guys! I was hoping one of you could help me out with this issue. I work at a mobile electronics shop and we install a lot of aftermarket HID headlights in new vehicles. The problem with this is the computer recognizes that the stock incandescent bulbs are no longer installed and will turn on a "light out" indicator on the dashboard. The solution to this is to install a high wattage resistor between the two headlight leads (12v and ground when the headlight switch is in the "on" position). This works great, however, the resistors always get incredibly hot.

    I was hoping to design a 12v DC circuit that could emulate the characteristics of an incandescent light bulb. More specifically, this circuit would need to allow roughly 3 amps to flow from the 12v headlight lead to the ground headlight lead to trick the computer into thinking there is a functional incandescent bulb present. Because we're dissipating 36W of energy I'm not sure if there is any way to do this without the circuit getting extremely hot but I would like to see what you experts have to say before I give up all hope. The incredibly hot resistors seem very barbaric and I hope there is a smarter solution.

    Any suggestions would be greatly appreciated and if you need any more information do not hesitate to ask.

    Thanks guys!
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    What is the current draw of the new HID lamps?

    The total draw has to be 3 amps, correct?

    So if they draw 1 amp, you need only dissipate 24 watts, and if they draw 2.5a you need only dissipate 6 watts? correct?

    What ohms are the high wattage resistors you were using?
  3. SgtWookie


    Jul 17, 2007
    Seems to me a standard headlamp dissipates about 50W on low beam, and 55W on high beam. You'd have to subtract the new from the old to get the necessary power dissipation.
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    My thoughts exactly. I was wondering if the resistor being used was sized incorrectly for the task.